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  • 1.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    O'Mara, B. J.
    Stempels, H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Hydrogen Line Formation in Cool Stars2001In: 11th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun / [ed] Garcia Lopez, Ramon J.; Rebolo, Rafael; Zapaterio Osorio, Mario Rosa, San Francisco: Astronomical Society of the Pacific , 2001, p. 766-Conference paper (Other academic)
  • 2.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Hydrogen Balmer Lines as Probes of Stellar Atmospheres2003In: IAUS 210, Modelling of stellar atmospheres, 2003, p. E28-Conference paper (Other scientific)
  • 3.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    A list of data for the broadening of metallic lines by neutral hydrogen collisions2000In: ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES, ISSN 0365-0138, Vol. 142, no 3, p. 467-473Article in journal (Refereed)
  • 4.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    Self broadening of hydrogen lines: initial results2000In: ASTRONOMY AND ASTROPHYSICS, ISSN 0004-6361, Vol. 355, no 1, p. L5-L8Article in journal (Refereed)
  • 5.
    Barklem, Paul
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    O'Mara, BJ
    Self-broadening in Balmer line wing formation in stellar atmospheres2000In: ASTRONOMY AND ASTROPHYSICS, ISSN 0004-6361, Vol. 363, no 3, p. 1091-1105Article in journal (Refereed)
  • 6.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Stempels, H.C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Allende Prieto, C.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    O'Mara, B.J.
    Detailed analysis of Balmer lines in cool dwarf stars2002In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 385, p. 951-Article in journal (Refereed)
  • 7.
    Barklem, Paul
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Stempels, H.C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, Observational Astronomy.
    O'Mara, J.B.
    Balmer lines and effective temperatures in cool stars2003In: 12th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, 2003, p. 1103-Conference paper (Other academic)
  • 8.
    Boyarchuk, A. A.
    et al.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Shustov, B. M.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Savanov, I. S.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Sachkov, M. E.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Bisikalo, D. V.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Mashonkina, L. I.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Wiebe, D. Z.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Shematovich, V. I.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Shchekinov, Yu. A.
    Southern Fed Univ, Rostov Na Donu 344006, Russia..
    Ryabchikova, T. A.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Chugai, N. N.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Ivanov, P. B.
    Russian Acad Sci, Lebedev Phys Inst, Ctr Astro Space, Moscow, Russia..
    Voshchinnikov, N. V.
    St Petersburg State Univ, St Petersburg 199034, Russia..
    Gomez de Castro, A. I.
    Univ Complutense Madrid, Plaza Ciencias 3, E-28040 Madrid, Spain..
    Lamzin, S. A.
    Moscow MV Lomonosov State Univ, Sternberg Astron Inst, Moscow 119992, Russia..
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ayres, T.
    Univ Colorado, Boulder, CO 80309 USA..
    Strassmeier, K. G.
    Leibniz Inst Astrophys Potsdam, Sternwarte 16, D-14482 Potsdam, Germany..
    Jeffrey, S.
    Armagh Observ, Coll Hill, Armagh BT61 9DG, North Ireland..
    Zwintz, S. K.
    Univ Innsbruck, Tech Str 25-8, A-6020 Innsbruck, Austria..
    Shulyak, D.
    Univ Gottingen, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Gerard, J. -C
    Hubert, B.
    Univ Liege, LPAP, Liege, Belgium..
    Fossati, L.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Lammer, H.
    Austrian Acad Sci, Space Res Inst, Schmiedlstr 6, A-8042 Graz, Austria..
    Werner, K.
    Univ Tubingen, Tubingen, Germany..
    Zhilkin, A. G.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Kaigorodov, P. V.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Sichevskii, S. G.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Ustamuich, S.
    Univ Complutense Madrid, Plaza Ciencias 3, E-28040 Madrid, Spain..
    Kanev, E. N.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Kil'pio, E. Yu.
    Russian Acad Sci, Inst Astron, Ul Pyatnitskaya 48, Moscow 119017, Russia..
    Scientific problems addressed by the Spektr-UV space project (world space Observatory-Ultraviolet)2016In: Astronomy reports (Print), ISSN 1063-7729, E-ISSN 1562-6881, Vol. 60, no 1, p. 1-42Article in journal (Refereed)
    Abstract [en]

    The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory-Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115-310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems.

  • 9. Brewer, John M.
    et al.
    Fischer, Debra A.
    Basu, Sarbani
    Valenti, Jeff A.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Accurate Gravities of F, G, and K Stars from High Resolution Spectra Without External Constraints2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 805, no 2, article id 126Article in journal (Refereed)
    Abstract [en]

    We demonstrate a new procedure to derive accurate and precise surface gravities from high resolution spectra without the use of external constraints. Our analysis utilizes Spectroscopy Made Easy with robust spectral line constraints and uses an iterative process to mitigate degeneracies in the fitting process. We adopt an updated radiative transfer code, a new treatment for neutral perturber broadening, a line list with multiple gravity constraints and separate fitting for global stellar properties and abundance determinations. To investigate the sources of temperature dependent trends in determining log g noted in previous studies, we obtained Keck HIRES spectra of 42 Kepler asteroseismic stars. In comparison to asteroseismically determined log g our spectroscopic analysis has a constant offset of 0.01 dex with a rms scatter of 0.05 dex. We also analyzed 30 spectra which had published surface gravities determined using the a/R-* technique from planetary transits and found a constant offset of 0.06 dex and rms scatter of 0.07 dex. The two samples covered effective temperatures between 5000 and 6700 K with log g between 3.7 and 4.6.

  • 10. Briquet, M.
    et al.
    Aerts, C.
    Lüftinger, T.
    De Cat, P.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Scuflaire, R.
    He and Si surface inhomogeneities of four Bp variable stars2004In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 413, p. 273-Article in journal (Other scientific)
  • 11. Brown, A.
    et al.
    Korhonen, H.
    Berdyugina, S.
    Tofany, B.
    Ayres, T. R.
    Kowalski, A.
    Hawley, S.
    Harper, G.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Starspot variability and evolution from modeling Kepler photometry of active late-type stars2011In: IAU Symposium 273 (The Physics of Sun and Star Spots), 2011, Vol. 273, p. 78-82Conference paper (Refereed)
    Abstract [en]

    The Kepler satellite provides a unique opportunity to study the detailed optical photometric variability of late-type stars with unprecedentedly long (several year) continuous monitoring and sensitivity to very small-scale variations. We are studying a sample of over two hundred cool (mid-A - late-K spectral type) stars using Kepler long-cadence (30 minute sampling) observations. These stars show a remarkable range of photometric variability, but in this paper we concentrate on rotational modulation due to starspots and flaring. Modulation at the 0.1% level is readily discernable. We highlight the rapid timescales of starspot evolution seen on solar-like stars with rotational periods between 2 and 7 days.

  • 12. Brown, A.
    et al.
    Korhonen, H.
    Berdyugina, S.
    Walkowicz, L.
    Kowalski, A.
    Hawley, S.
    Neff, J.
    Ramsey, L.
    Redman, S.
    Saar, S.
    Furesz, G.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Harper, G.
    Ayres, T.
    Tofany, B.
    Kepler Observations of Starspot Evolution, Differential Rotation, and Flares on Late-Type Stars2011In: American Astronomical Society Meeting Abstracts #218, 2011Conference paper (Refereed)
    Abstract [en]

    The Kepler satellite is providing spectacular optical photometric light-curves of unprecedented precision and duration that routinely allow detailed studies of stellar magnetic activity on late-type stars that were difficult, if not impossible, to attempt previously. Rotational modulation due to starspots is commonly seen in the Kepler light-curves of late-type stars, allowing detailed study of the surface distribution of their photospheric magnetic activity. Kepler is providing multi-year duration light-curves that allow us to investigate how activity phenomena – such as the growth, migration, and decay of starspots, differential rotation, activity cycles, and flaring – operate on single and binary stars with a wide range of mass and convection zone depth. We present the first results from detailed starspot modeling using newly-developed light-curve inversion codes for a range of GALEX-selected stars with typical rotation periods of a few days, that we have observed as part of our 200 target Kepler Cycle 1/2 Guest Observer programs. The physical properties of the stars have been measured using high resolution optical spectroscopy, which allows the Kepler results to be placed within the existing framework of knowledge regarding stellar magnetic activity. These results demonstrate the powerful diagnostic capability provided by tracking starspot evolution essentially continuously for more than 16 months. The starspots are clearly sampling the stellar rotation rate at different latitudes, enabling us to measure the differential rotation and starspot lifetimes. As would be expected, stars with few day rotation show frequent flaring that is easily seen as ”white-light” flares in Kepler light-curves. We compare the observed flare rates and occurrence with the starspot properties. This work contains results obtained using the NASA Kepler satellite and from the Apache Point Observatory, the MMT (using NOAO community access time), and the Hobby-Eberly Telescope. Funding is provided by NASA Kepler grants NNX10AC51G and NNX11AC79G.

  • 13. Brown, Alexander
    et al.
    Neff, James E.
    Ayres, Thomas R.
    Kowalski, Adam
    Hawley, Suzanne
    Berdyugina, Svetlana
    Harper, Graham M.
    Korhonen, Heidi
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Saar, Steven
    Walkowicz, Lucianne
    Wells, Mark A.
    Serendipitous Discovery of a Dwarf Nova in the Kepler Field Near the G Dwarf Kic 54388452015In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 149, no 2, article id 67Article in journal (Refereed)
    Abstract [en]

    The Kepler satellite provides a unique window into stellar temporal variability by observing a wide variety of stars with multi-year, near-continuous, high precision, optical photometric time series. While most Kepler targets are faint stars with poorly known physical properties, many unexpected discoveries should result from a long photometric survey of such a large area of sky. During our Kepler Guest Observer programs that monitored late-type stars for starspot and flaring variability, we discovered a previously unknown dwarf nova that lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This dwarf nova underwent nine outbursts over a 4 year time span. The two largest outbursts lasted similar to 17-18 days and show strong modulations with a 110.8 minute period and a declining amplitude during the outburst decay phase. These properties are characteristic of an SU UMa-type cataclysmic variable. By analogy with other dwarf nova light curves, we associate the 110.8 minute (1.847 hr) period with the superhump period, close to but slightly longer than the orbital period of the binary. No precursor outbursts are seen before the super-outbursts and the overall super-outburst morphology corresponds to Osaki & Meyer "Case B" outbursts, which are initiated when the outer edge of the disk reaches the tidal truncation radius. "Case B" outbursts are rare within the Kepler light curves of dwarf novae. The dwarf nova is undergoing relatively slow mass transfer, as evidenced by the long intervals between outbursts, but the mass transfer rate appears to be steady, because the smaller "normal" outbursts show a strong correlation between the integrated outburst energy and the elapsed time since the previous outburst. At super-outburst maximum the system was at V similar to 18, but in quiescence it is fainter than V similar to 22, which will make any detailed quiescent follow-up of this system difficult.

  • 14.
    Cole, E. M.
    et al.
    Univ Helsinki, Dept Phys, FIN-00014 Helsinki, Finland..
    Hackman, T.
    Univ Helsinki, Dept Phys, FIN-00014 Helsinki, Finland.;Univ Turku, Finnish Ctr Astron ESO, Piikkio 21500, Finland..
    Kapyka, M. J.
    Aalto Univ, Dept Comp Sci, ReSoLVE Ctr Excellence, Espoo 00076, Finland..
    Ilyin, I.
    Leibniz Inst Astrophys Potsdam, D-14882 Potsdam, Germany..
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Doppler imaging of LQ Hydrae for 1998-20022015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 581, article id A69Article in journal (Refereed)
    Abstract [en]

    Aims. We study the spot distribution on the surface of LQ Hya during the observing seasons October 1998-November 2002. We look for persistent active longitudes, trends in the level of spot activity and compare to photometric data. Methods. We apply the Doppler imaging technique on photospheric spectral lines using an inversion code to retrieve images of the surface temperature. Results. We present new temperature maps using multiple spectral lines for a total of 7 seasons. Conclusions. We find no evidence for active longitudes persisting over multiple observing seasons. The spot activity appears to be concentrated to two latitude regions. Using the currently accepted rotation period, we find spot structures to show a trend in the phase-time plot, indicative of a need for a longer period. We conclude that the long-term activity of LQ Hya is more chaotic than that of some magnetically active binary stars analyzed with similar methods, but still with clear indications of an activity cycle from the photometry.

  • 15. Cowley, C.R.
    et al.
    Hubrig, S.
    Ryabchikova, T.A.
    Mathys, G.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Mittermayer, P.
    The core-wing anomaly of cool Ap stars - Abnormal Balmer profiles2001In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 367, no 3, p. 939-942Article in journal (Refereed)
  • 16.
    de Jong, Roelof S.
    et al.
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Barden, Samuel C.
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Bellido-Tirado, Olga
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Brynnel, Joar G.
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Frey, Steffen
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Giannone, Domenico
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Haynes, Roger
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany.;InnoFSPEC, Potsdam, Germany..
    Johl, Diana
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Phillips, Daniel
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Schnurr, Olivier
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Walcher, Jakob C.
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Winkler, Roland
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Ansorge, Wolfgang R.
    RAMS CON Management Consultants, Assling, Germany..
    Feltzing, Sofia
    Lund Observ, Lund, Sweden..
    McMahon, Richard G.
    Univ Cambridge, Cambridge CB2 1TN, England..
    Baker, Gabriella
    Australian Astron Observ, Sydney, NSW, Australia..
    Caillier, Patrick
    Ctr Rech Astrophys Lyon, Lyon, France..
    Dwelly, Tom
    Max Planck Inst Extraterr Phys, Munich, Germany..
    Gaessler, Wolfgang
    Max Planck Inst Astron, Heidelberg, Germany..
    Iwer, Olaf
    European Southern Observ, Garching, Germany..
    Mandel, Holger G.
    Heidelberg Univ, Zentrum Astron, Heidelberg, Germany..
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Pragt, Johan H.
    NOVA ASTRON, Dwingeloo, Netherlands..
    Walton, Nicholas A.
    Univ Cambridge, Cambridge CB2 1TN, England..
    Bensby, Thomas
    Lund Observ, Lund, Sweden..
    Bergemann, Maria
    Max Planck Inst Astron, Heidelberg, Germany..
    Chiappini, Cristina
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Christlieb, Norbert
    Heidelberg Univ, Zentrum Astron, Heidelberg, Germany..
    Cioni, Maria-Rosa L.
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Driver, Simon
    Univ Western Australia, Perth, WA, Australia..
    Finoguenov, Alexis
    Max Planck Inst Extraterr Phys, Munich, Germany..
    Helmi, Amina
    Kapteyn Astron Inst, Groningen, Netherlands..
    Irwin, Michael J.
    Univ Cambridge, Cambridge CB2 1TN, England..
    Kitaur, Francisco-Shu
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Kneib, Jean-Paul
    Ecole Polytech Fed Lausanne, CH-1015 Lausanne, Switzerland..
    Liske, Jochen
    Univ Hamburg, Hamburg, Germany. Univ Potsdam, Potsdam, Germany. Univ Hertfordshire, Hatfield AL10 9AB, Herts, England..
    Merloni, Andrea
    Max Planck Inst Extraterr Phys, Munich, Germany..
    Minchev, Ivan
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    Richard, Johan
    Ctr Rech Astrophys Lyon, Lyon, France..
    Starkenburg, Else
    Leibniz Inst Astrophys Potsdam AIP, An Sternwarte 16, D-14482 Potsdam, Germany..
    4MOST: the 4-metre Multi-Object Spectroscopic Telescope project at preliminary design review2016In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI / [ed] Christopher J Evans, 2016, Vol. 9908, article id UNSP 99081OConference paper (Refereed)
    Abstract [en]

    We present an overview of the 4MOST project at the Preliminary Design Review. 4MOST is a major new wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of ESO. 4MOST has a broad range of science goals ranging from Galactic Archaeology and stellar physics to the high-energy physics, galaxy evolution, and cosmology. Starting in 2021, 4MOST will deploy 2436 fibres in a 4.1 square degree field-of-view using a positioner based on the tilting spine principle. The fibres will feed one high-resolution (R similar to 20,000) and two medium-resolution (R similar to 5000) spectrographs with fixed 3-channel designs and identical 6k x 6k CCD detectors. 4MOST will have a unique operations concept in which 5-year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept, showing that we can expect to observe more than 25 million objects in each 5-year survey period and will eventually be used to plan and conduct the actual survey.

  • 17.
    Dorn, Reinhold J.
    et al.
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Follert, Roman
    Thuringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany..
    Bristow, Paul
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Cumani, Claudio
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Eschbaumer, Siegfried
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Grunhut, Jason
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Haimerl, Andreas
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Hatzes, Artie
    Thuringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany..
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Hinterschuster, Renate
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Ives, Derek J.
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Jung, Yves
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Kerber, Florian
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Klein, Barbara
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Lavail, Alexis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy. European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Lizon, Jean Louis
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Loewinger, Tom
    Thuringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany..
    Molina-Conde, Ignacio
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Nicholson, Belinda
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Marquart, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Oliva, Ernesto
    INAF Arcetri Osservatorio, Largo E Fermi 5, I-50125 Florence, Italy..
    Origlia, Livia
    INAF Bologna Observ, Via Ranzani 1, I-40127 Bologna, Italy..
    Pasquini, Luca
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Paufique, Jerome
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Reiners, Ansgar
    Univ Gottingen, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Seemann, Ulf
    Univ Gottingen, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Stegmeier, Jorg
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Stempels, Eric
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Tordo, Sebastien
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    The " plus " for CRIRES: enabling better science at infrared wavelength and high spectral resolution at the ESO VLT2016In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI / [ed] Christopher J Evans, 2016, Vol. 9908, article id 99080IConference paper (Refereed)
    Abstract [en]

    The adaptive optics (AO) assisted CRIRES instrument was a IR (0.92 - 5.2 mu m) high-resolution spectrograph in operation from 2006 to 2014 at the Very Large Telescope (VLT) observatory. CRIRES was a unique instrument, accessing a parameter space (wavelength range and spectral resolution) up to now largely uncharted. It consisted of a single-order spectrograph providing long-slit (40 arcsecond) spectroscopy with a resolving power up to R=100 000. However the setup was limited to a narrow, single-shot, spectral range of about 1/70 of the central wavelength, resulting in low observing efficiency for many scientific programmes requiring a broad spectral coverage. The CRIRES upgrade project, CRIRES, transfouns this VLT instrument into a cross-dispersed spectrograph to increase the simultaneously covered wavelength range by a factor of ten. A new and larger detector focal plane array of three Hawaii 2RG detectors with 5.3 mu m cut-off wavelength will replace the existing detectors. For advanced wavelength calibration, custom-made absorption gas cells and an etalon system will be added. A spectro-polarimetric unit will allow the recording of circular and linear polarized spectra. This upgrade will be supported by dedicated data reduction software allowing the community to take full advantage of the new capabilities. CRIRES has now entered its assembly and integration phase and will return with all new capabilities by the beginning of 2018 to the Very Large Telescope in Chile. This article will provide the reader with an update of the current status of the instrument as well as the remaining steps until final installation at the Paranal Observatory.

  • 18.
    Dubernet, M. L.
    et al.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Antony, B. K.
    Indian Sch Mines, Dept Appl Phys, Dhanbad 826004, Bihar, India..
    Ba, Y. A.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Babikov, Yu L.
    Russian Acad Sci, Inst Atmospher Opt, Zuev Sq 1, Tomsk 634021, Russia.;Tomsk State Univ, Tomsk 634050, Russia..
    Bartschat, K.
    Drake Univ, Dept Phys & Astron, Des Moines, IA 50311 USA..
    Boudon, V.
    Univ Bourgogne Franche Comte, CNRS, UMR 6303, Lab Interdisciplinaire Carnot Bourgogne, 9 Ave Alain Savary,BP 47 870, F-21078 Dijon, France..
    Braams, B. J.
    IAEA, Vienna Int Ctr, Div Phys & Chem Sci, Nucl Data Sect, A-1400 Vienna, Austria..
    Chung, H-K
    IAEA, Vienna Int Ctr, Div Phys & Chem Sci, Nucl Data Sect, A-1400 Vienna, Austria..
    Daniel, F.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France..
    Delahaye, F.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Del Zanna, G.
    Ctr Math Sci, DAMTP, Wilberforce Rd, Cambridge CB3 0WA, England..
    de Urquijo, J.
    Univ Nacl Autonoma Mexico, Inst Ciencias Fis, POB 48-3, Cuernavaca 62251, Morelos, Mexico..
    Dimitrijevic, M. S.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France.;Astron Observ, Volgina 7, Belgrade 11060, Serbia..
    Domaracka, A.
    UCN, ENSICAEN, CNRS, CIMAP,UMR 6252,CEA, Bd Henri Becquerel,BP 5133, F-14070 Caen 5, France..
    Doronin, M.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Drouin, B. J.
    CALTECH, Jet Prop Lab, 4800 Oak Grove Dr, Pasadena, CA 91109 USA..
    Endres, C. P.
    Max Planck Inst Extraterr Phys, Giessenbachstr, D-85748 Garching, Germany..
    Fazliev, A. Z.
    Russian Acad Sci, Inst Atmospher Opt, Zuev Sq 1, Tomsk 634021, Russia..
    Gagarin, S. V.
    Russian Fed Nucl Ctr All Russian Inst Tech Phys R, Snezhinsk, Russia..
    Gordon, I. E.
    Harvard Smithsonian Ctr Astrophys, Atom & Mol Phys Div, MS50,60 Garden St, Cambridge, MA 02138 USA..
    Gratier, P.
    Univ Bordeaux, LAB, UMR 5804, F-33270 Florac, France.;CNRS, LAB, UMR 5804, F-33270 Florac, France..
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Hill, C.
    UCL, Dept Phys & Astron, Mortimer St, London WC1E 6BT, England..
    Jevremovic, D.
    Astron Observ, Volgina 7, Belgrade 11060, Serbia..
    Joblin, C.
    Univ Toulouse, UPS OMP, CNRS, Inst Rech Astrophys & Planetol, 9 Av Colonel Roche, F-31028 Toulouse 4, France..
    Kasprzak, A.
    Observ Paris, SRCV, 61 Av Denfert Rochereau, F-75014 Paris, France..
    Krishnakumar, E.
    Tata Inst Fundamental Res, Dept Nucl & Atom Phys, Homi Bhabha Rd, Bombay 400005, Maharashtra, India..
    Leto, G.
    INAF Osservatorio Astrofis Catania, Via S Sofia 78, I-95123 Catania, Italy..
    Loboda, P. A.
    Russian Fed Nucl Ctr All Russian Inst Tech Phys R, Snezhinsk, Russia.;Natl Res Nucl Univ, Moscow Engn Phys Inst MEPhI, Moscow, Russia..
    Louge, T.
    Univ Toulouse, UPS OMP, CNRS, Inst Rech Astrophys & Planetol, 9 Av Colonel Roche, F-31028 Toulouse 4, France..
    Maclot, S.
    UCN, ENSICAEN, CNRS, CIMAP,UMR 6252,CEA, Bd Henri Becquerel,BP 5133, F-14070 Caen 5, France.;Univ Caen Normandie, Esplanade Paix, CS 14032, F-14032 Caen 5, France..
    Marinkovic, B. P.
    Univ Belgrade, Inst Phys Belgrade, POB 57, Belgrade 11001, Serbia..
    Markwick, A.
    Univ Manchester, Sch Phys & Astron, Jodrell Bank Ctr Astrophys, Oxford Rd, Manchester M13 9PL, Lancs, England..
    Marquart, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Mason, H. E.
    Ctr Math Sci, DAMTP, Wilberforce Rd, Cambridge CB3 0WA, England..
    Mason, N. J.
    Open Univ, Dept Phys Sci, Walton Hall, Milton Keynes MK7 6AA, Bucks, England..
    Mendoza, C.
    IVIC, Ctr Fis, POB 20632, Caracas 1020A, Venezuela..
    Mihajlov, A. A.
    Univ Belgrade, Inst Phys Belgrade, POB 57, Belgrade 11001, Serbia..
    Millar, T. J.
    Queens Univ Belfast, Sch Math & Phys, Univ Rd, Belfast BT7 1NN, Antrim, North Ireland..
    Moreau, N.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Mulas, G.
    Univ Toulouse, UPS OMP, CNRS, Inst Rech Astrophys & Planetol, 9 Av Colonel Roche, F-31028 Toulouse 4, France.;Osservatorio Astron Cagliari, Ist Nazl AstroFis, Via Sci 5, I-09047 Selargius, CA, Italy..
    Pakhomov, Yu
    RAS, Inst Astron, Pyatnitskaya 48, Moscow 119017, Russia..
    Palmeri, P.
    Univ Mons, Phys Atom & Astrophys, B-7000 Mons, Belgium..
    Pancheshnyi, S.
    ABB Corp Res, Segelhofstr 1K, CH-5405 Baden, Switzerland..
    Perevalov, V. I.
    Russian Acad Sci, Inst Atmospher Opt, Zuev Sq 1, Tomsk 634021, Russia..
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Postler, J.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25-3, A-6020 Innsbruck, Austria..
    Quinet, P.
    Univ Mons, Phys Atom & Astrophys, B-7000 Mons, Belgium.;Univ Liege, IPNAS, B-4000 Liege, Belgium..
    Quintas-Sanchez, E.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Ralchenko, Yu
    NIST, Atom Spect Grp, Gaithersburg, MD 20899 USA..
    Rhee, Y-J
    Korea Atom Energy Res Inst, Nucl Data Ctr, Taejon 305353, South Korea..
    Rixon, G.
    Univ Cambridge, Inst Astron, Madingley Rd, Cambridge CB3 0HA, England..
    Rothman, L. S.
    Harvard Smithsonian Ctr Astrophys, Atom & Mol Phys Div, MS50,60 Garden St, Cambridge, MA 02138 USA..
    Roueff, E.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Ryabchikova, T.
    RAS, Inst Astron, Pyatnitskaya 48, Moscow 119017, Russia..
    Sahal-Brechot, S.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Scheier, P.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, Technikerstr 25-3, A-6020 Innsbruck, Austria..
    Schlemmer, S.
    Univ Cologne, Inst Phys 1, zulpicher Str 77, D-50937 Kln, Germany..
    Schmitt, B.
    Univ Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France..
    Stempels, Eric H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Tashkun, S.
    Russian Acad Sci, Inst Atmospher Opt, Zuev Sq 1, Tomsk 634021, Russia..
    Tennyson, J.
    UCL, Dept Phys & Astron, Mortimer St, London WC1E 6BT, England..
    Tyuterev, Vl G.
    Univ Reims, GSMA, UMR CNRS 7331, Reims, France..
    Vujcic, V.
    Astron Observ, Volgina 7, Belgrade 11060, Serbia.;Univ Belgrade, Fac Org Sci, Jove Ilica 33, Belgrade 11000, Serbia..
    Wakelam, V.
    Univ Bordeaux, LAB, UMR 5804, F-33270 Florac, France.;CNRS, LAB, UMR 5804, F-33270 Florac, France..
    Walton, N. A.
    Univ Cambridge, Inst Astron, Madingley Rd, Cambridge CB3 0HA, England..
    Zatsarinny, O.
    Drake Univ, Dept Phys & Astron, Des Moines, IA 50311 USA..
    Zeippen, C. J.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    Zwoelf, C. M.
    Univ Paris 06, Univ Sorbonne, CNRS, LERMA,Observ Paris,PSL Res Univ, 5 Pl Janssen, F-92190 Meudon, France..
    The virtual atomic and molecular data centre (VAMDC) consortium2016In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 49, no 7, article id 074003Article in journal (Refereed)
    Abstract [en]

    The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

  • 19. Fischer, Debra A.
    et al.
    Gaidos, Eric
    Howard, Andrew W.
    Giguere, Matthew J.
    Johnson, John A.
    Marcy, Geoffrey W.
    Wright, Jason T.
    Valenti, Jeff A.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Clubb, Kelsey I.
    Isaacson, Howard
    Apps, Kevin
    Lepine, Sebastien
    Mann, Andrew
    Moriarty, John
    Brewer, John
    Spronck, Julien F. P.
    Schwab, Christian
    Szymkowiak, Andrew
    M2K. II. A Triple-Planet System Orbiting Hip 572742012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 745, no 1, p. 21-Article in journal (Refereed)
    Abstract [en]

    Doppler observations from Keck Observatory have revealed a triple-planet system orbiting the nearby K4V star, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with M sin i = 11.6 M-circle plus (0.036 M-Jup), an orbital period of 8.135 +/- 0.004 days, and slightly eccentric orbit e = 0.19 +/- 0.1. We calculate a transit probability of 6.5% for the inner planet. The second planet has M sin i = 0.4 M-Jup with an orbital period of 32.0 +/- 0.02 days in a nearly circular orbit (e = 0.05 +/- 0.03). The third planet has M sin i = 0.53 M-Jup with an orbital period of 432 +/- 8 days (1.18 years) and an eccentricity e = 0.23 +/- 0.03. This discovery adds to the number of super-Earth mass planets with M sin i < 12 M-circle plus that have been detected with Doppler surveys. We find that 56% +/- 18% of super-Earths are members of multi-planet systems. This is certainly a lower limit because of observational detectability limits, yet significantly higher than the fraction of Jupiter mass exoplanets, 20% +/- 8%, that are members of Doppler-detected, multi-planet systems.

  • 20. Follert, R.
    et al.
    Dorn, R. J.
    Oliva, E.
    Lizon, J. L.
    Hatzes, A.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Reiners, A.
    Seemann, U.
    Stempels, Eric
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Marquart, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Lockhart, Matthew
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Anglada-Escude, G.
    Loewinger, T.
    Baade, D.
    Grunhut, J.
    Bristow, P.
    Klein, B.
    Jung, Y.
    Ives, D. J.
    Kerber, F.
    Pozna, E.
    Paufique, J.
    Kaeufl, H. U.
    Origlia, L.
    Valenti, E.
    Gojak, D.
    Hilker, M.
    Pasquini, L.
    Smette, A.
    Smoker, J.
    CRIRES plus: a cross-dispersed high-resolution infrared spectrograph for the ESO VLT2014In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY V, 2014, Vol. 9147, article id 914719Conference paper (Refereed)
    Abstract [en]

    High-resolution infrared spectroscopy plays an important role in astrophysics from the search for exoplanets to cosmology. Yet, many existing infrared spectrographs are limited by a rather small simultaneous wavelength coverage. The AO assisted CRIRES instrument, installed at the ESO VLT on Paranal, is one of the few IR (0.92-5.2 mu m) high-resolution spectrographs in operation since 2006. However it has a limitation that hampers its efficient use: the wavelength range covered in a single exposure is limited to similar to 15 nanometers. The CRIRES Upgrade project (CRIRES+) will transform CRIRES into a cross-dispersed spectrograph and will also add new capabilities. By introducing cross-dispersion elements the simultaneously covered wavelength range will be increased by at least a factor of 10 with respect to the present configuration, while the operational wavelength range will be preserved. For advanced wavelength calibration, new custom made absorption gas cells and etalons will be added. A spectro-polarimetric unit will allow one for the first time to record circularly polarized spectra at the highest spectral resolution. This will be all supported by a new data reduction software which will allow the community to take full advantage of the new capabilities of CRIRES+.

  • 21.
    Follert, Roman
    et al.
    Thuringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany..
    Taubert, Dieter
    Phys Tech Bundesanstalt, Fachbereich Detektorradiometrie & Strahlungstherm, Abbestr 2-12, D-10587 Berlin, Germany..
    Hollandt, Joerg
    Phys Tech Bundesanstalt, Fachbereich Detektorradiometrie & Strahlungstherm, Abbestr 2-12, D-10587 Berlin, Germany..
    Monte, Christian
    Phys Tech Bundesanstalt, Fachbereich Detektorradiometrie & Strahlungstherm, Abbestr 2-12, D-10587 Berlin, Germany..
    Oliva, Ernesto
    INAF Osservatori Arcetri, Largo E Fermi 5, I-50125 Florence, Italy..
    Seemann, Ulf
    Georg August Univ Gottingen, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Loewinger, Tom
    Thuringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany..
    Anwand-Heerwart, Heiko
    Georg August Univ Gottingen, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Schmidt, Christof
    Georg August Univ Gottingen, Zent Werkstatt Fak Phys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Dorn, Reinhold J.
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Bristow, Paul
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Hatzes, Artie
    Thuringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany..
    Reiners, Ansgar
    Georg August Univ Gottingen, Inst Astrophys, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Stempels, Eric
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Marquart, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Lavail, Alexis
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Cumani, Claudio
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Grunhut, Jason
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Haimerl, Andreas
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Hinterschuster, Renate
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Ives, Derek J.
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Jung, Yves
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Kerber, Florian
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Klein, Barbara
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Lizon, Jean Louis
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Molina-Conde, Ignacio
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Nicholson, Belinda
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Origlia, Livia
    INAF Osservatorio Bologna, Via Ranzani 1, I-40127 Bologna, Italy..
    Pasquini, Luca
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Paufique, Jerome
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Stegmeier, Joerg
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Tordo, Sebastien
    European Org Astron Res Southern Hemisphere, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
    Characterizing the cross dispersion reflection gratings of CRIRES2016In: Advances In Optical And Mechanical Technologies For Telescopes And Instrumentation Ii, 2016, article id UNSP 99122BConference paper (Refereed)
    Abstract [en]

    The CRIRES+ project attempts to upgrade the CRIRES instrument into a cross dispersed echelle spectrograph with a simultaneous recording of 8-10 diffraction orders. In order to transform the CRIRES spectrograph into a cross-dispersing instrument, a set of six reflection gratings, each one optimized for one of the wavelength bands CRIRES+ will operate in (YJHKLM), will be used as cross dispersion elements in CRIRES+. Due to the upgrade nature of the project, the choice of gratings depends on the fixed geometry of the instrument. Thus, custom made gratings would be required to achieve the ambitious design goals. Custom made gratings have the disadvantage, though, that they come at an extraordinary price and with lead times of more than 12 months. To mitigate this, a set of off-the-shelf gratings was obtained which had grating parameters very close to the ones being identified as optimal. To ensure that the rigorous specifications for CRIRES+ will be fulfilled, the CRIRES+ team started a collaboration with the Physikalisch-Technische Bundesanstalt Berlin (PTB) to characterize gratings under conditions similar to the operating conditions in CRIRES+ (angle of incidence, wavelength range). The respective test setup was designed in collaboration between PTB and the CRIRES+ consortium. The PTB provided optical radiation sources and calibrated detectors for each wavelength range. With this setup, it is possible to measure the absolute efficiency of the gratings both wavelength dependent and polarization state dependent in a wavelength range from 0.9 mu m to 6 mu m.

  • 22. Hackman, T.
    et al.
    Mantere, M. J.
    Jetsu, L.
    Ilyin, I.
    Kajatkari, P.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Lehtinen, J.
    Lindborg, M.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Tuominen, I.
    Spot activity of II Peg2011In: Astronomical Notes - Astronomische Nachrichten, ISSN 0004-6337, E-ISSN 1521-3994, Vol. 332, no 9-10, p. 859-865Article in journal (Refereed)
    Abstract [en]

    We have studied the long-term spot activity of the RS CVn star II Peg by means of Doppler imaging based on spectroscopy and time series analysis of photometry. We present 28 Doppler imaging temperature maps spanning the years 1994-2010, of which 14 were calculated for the present study. The longitudinal spot distribution, derived from the surface temperature maps, is compared with epochs of the light curve minima, derived from photometric observations. We detect a longitudinal drift in the major spot structure during 1995-2003. After this there is a clear decrease in the activity level and no clear drift can be seen. We conclude that the variations could be caused by a cyclic behaviour of the underlying magnetic dynamo.

  • 23. Hackman, T.
    et al.
    Mantere, M. J.
    Lindborg, M.
    Ilyin, I.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Tuominen, I.
    Doppler images of II Pegasi for 2004-20102012In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 538, p. A126-Article in journal (Refereed)
    Abstract [en]

    Aims. We study the spot activity of II Peg during the years 2004-2010 to determine long- and short-term changes in the magnetic activity. In a previous study, we detected a persistent active longitude, as well as major changes in the spot configuration occurring on a timescale of shorter than a year. The main objective of this study is to determine whether the same phenomena persist in the star during these six years of spectroscopic monitoring. Methods. The observations were collected with the high-resolution SOFIN spectrograph at the Nordic Optical Telescope. The temperature maps were calculated using a Doppler imaging code based on Tikhonov regularization. Results. We present 12 new temperature maps that show spots distributed mainly over high and intermediate latitudes. In each image, 1-3 main active regions can be identified. The activity level of the star is clearly lower than during our previous study for the years 1994-2002. In contrast to the previous observations, we detect no clear drift of the active regions with respect to the rotation of the star. Conclusions. Having shown a systematic longitudinal drift of the spot-generating mechanism during 1994-2002, the star has clearly switched to a low-activity state for 2004-2010, during which the spot locations appear more random over phase space. It could be that the star is near to a minimum of its activity cycle.

  • 24.
    Heiter, Ulrike
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Barklem, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
    Fossati, L.
    Kildiyarova, R.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Kupka, F.
    Obbrugger, M.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Plez, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ryabchikova, T.
    Stempels, H. C.
    Stütz, C.
    Weiss, W. W.
    VALD — an atomic and molecular database for astrophysics2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 130, p. 012011-Article in journal (Refereed)
    Abstract [en]

    The VALD database of atomic and molecular data aims to ensure a robust and consistent analysis of astrophysical spectra. We offer a convenient e-mail and web-based user interface to a vast collection of spectral line parameters for all chemical elements and in the future also for molecules. An international team is working on the following tasks: collecting line parameters from relevant theoretical and experimental publications, computing line parameters, evaluating the data quality by comparison of similar data from different sources and by comparison with astrophysical observations, and incorporating the data into VALD. A unique feature of VALD is its capability to provide the most comprehensive spectral line lists for specific astrophysical plasma conditions defined by the user.

  • 25.
    Heiter, Ulrike
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Gustafsson, Bengt
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy. Theoretical Astrophysics.
    Jordi, C.
    Carrasco, J. M.
    Cool stars in the Gaia photometric system2005In: 13th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, 2005, p. 635-Conference paper (Other scientific)
  • 26. Howard, Andrew W.
    et al.
    Johnson, John Asher
    Marcy, Geoffrey W.
    Fischer, Debra A.
    Wright, Jason T.
    Henry, Gregory W.
    Isaacson, Howard
    Valenti, Jeff A.
    Anderson, Jay
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    The NASA-UC Eia-earth program. II. a planet orbiting HD 156668 with a minimum mass of four earth masses2011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 726, no 2, p. 73-Article in journal (Refereed)
    Abstract [en]

    We report the discovery of HD 156668 b, an extrasolar planet with a minimum mass of M-P sin i = 4.15 M-circle plus. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 days. The Doppler semi-amplitude of this planet, K = 1.89 m s(-1), is among the lowest ever detected, on par with the detection of GJ 581 e using HARPS. A longer period (P approximate to 2.3 years), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of similar to 3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.

  • 27. Howard, Andrew W.
    et al.
    Johnson, John Asher
    Marcy, Geoffrey W.
    Fischer, Debra A.
    Wright, Jason T.
    Henry, Gregory W.
    Isaacson, Howard
    Valenti, Jeff A.
    Anderson, Jay
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    THE NASA-UC ETA-EARTH PROGRAM. III. A SUPER-EARTH ORBITING HD 97658 AND A NEPTUNE-MASS PLANET ORBITING G1 7852011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 730, no 1, p. 10-Article in journal (Refereed)
    Abstract [en]

    We report the discovery of planets orbiting two bright, nearby early K dwarf stars, HD 97658 and G1 785. These planets were detected by Keplerian modeling of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth with minimum mass M sin i = 8.2 +/- 1.2 M-circle plus, orbital period P = 9.494 +/- 0.005 days, and an orbit that is consistent with circular. G1 785 b is a Neptune-mass planet with M sin i = 21.6 +/- 2.0 M-circle plus, P = 74.39 +/- 0.12 days, and orbital eccentricity e = 0.30 +/- 0.09. Photometric observations with the T12 0.8 m automatic photometric telescope at Fairborn Observatory show that HD 97658 is photometrically constant at the radial velocity period to 0.09 mmag, supporting the existence of the planet.

  • 28. Johns-Krull, Christopher M.
    et al.
    Chen, Wei
    Valenti, Jeff A.
    Jeffers, Sandra V.
    Piskunov, Nikolai E.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Makaganiuk, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Stempels, Eric
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Snik, Frans
    Keller, Christoph
    Rodenhuis, M.
    Magnetically Controlled Accretion on the Classical T Tauri Stars GQ Lupi and TW Hydrae2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 765, no 1, p. 11-Article in journal (Refereed)
    Abstract [en]

    We present high spectral resolution (R approximate to 108,000) Stokes V polarimetry of the classical T Tauri stars (CTTSs) GQ Lup and TW Hya obtained with the polarimetric upgrade to the HARPS spectrometer on the ESO 3.6 m telescope. We present data on both photospheric lines and emission lines, concentrating our discussion on the polarization properties of the He I emission lines at 5876 angstrom and 6678 angstrom. The He I lines in these CTTSs contain both narrow emission cores, believed to come from near the accretion shock region on these stars, and broad emission components which may come from either a wind or the large-scale magnetospheric accretion flow. We detect strong polarization in the narrow component of the two He I emission lines in both stars. We observe a maximum implied field strength of 6.05 +/- 0.24 kG in the 5876 angstrom line of GQ Lup, making it the star with the highest field strength measured in this line for a CTTS. We find field strengths in the two He I lines that are consistent with each other, in contrast to what has been reported in the literature on at least one star. We do not detect any polarization in the broad component of the He I lines on these stars, strengthening the conclusion that they form over a substantially different volume relative to the formation region of the narrow component of the He I lines.

  • 29. Johns-Krull, C.M.
    et al.
    Valenti, J.A.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Saar, S.
    Hatzes, A.
    New Measurements of T Tauri Magnetic Fields: Testing Magnetospheric Accretion2001In: Magnetic Fields Across the Hertzsprung-Russell Diagram, ASP Conf. Ser., vol. 248, 2001, p. 527-Conference paper (Other scientific)
  • 30. Joshi, S.
    et al.
    Ryabchikova, T.
    Kochukhov, Oleg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Sachkov, M.
    Tiwari, S. K.
    Chakradhari, N. K.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Time-resolved photometric and spectroscopic analysis of the luminous Ap star HD 1034982010In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 401, no 2, p. 1299-1307Article in journal (Refereed)
    Abstract [en]

    We present the results of the photometric and spectroscopic monitoring of the luminous Ap star HD 103498. The time-series photometric observations were carried out on 17 nights using a three-channel fast photometer attached to the 1.04-m optical telescope at the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. The photometric data from five nights in 2007 show a clear signature of 15-min periodicity. However, the follow-up observations during 2007-2009 did not reproduce any such periodicity. To confirm the photometric light variations, time-series spectroscopic observations were carried out with the 2.56-m Nordic Optical Telescope (NOT) at La Palma on 2009 February 2. No radial velocity variations were present in this data set, which is in full agreement with the photometric observations taken around the same date. Model atmosphere and abundance analysis of HD 103498 show that the star is evolved from the main sequence and its atmospheric abundances are similar to those of two other evolved Ap stars, HD 133792 and HD 204411: large overabundances of Si, Cr and Fe and moderate overabundances of the rare-earth elements. These chemical properties and a higher effective temperature distinguish HD 103498 from any known roAp star.

  • 31. Knoglinger, P.
    et al.
    Nesvacil, N.
    Kupka, F.
    Mittermayer, P.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Weiss, W.W.
    Bruntt, H.
    Tools and Methods for Abundance Analysis2003In: IAUS 210, Modelling of stellar atmospheres, 2003, p. E66-Conference paper (Other scientific)
  • 32.
    Kochukhov, O
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Department of Physics and Astronomy, Observational Astronomy.
    Ilyin, I.
    Ilyina, S.
    Tuominen, I.
    Magnetic Doppler Imaging of alpha2 CVn2001In: Magnetic Fields Across the Hertzsprung-Russell Diagram, Conference Proceedings, 2001, p. 321-Conference paper (Other scientific)
  • 33.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Adelman, S.J.
    Gulliver, A.F.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Weather in stellar atmosphere revealed by the dynamics of mercury clouds in alpha Andromedae2007In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 3, no 8, p. 526-529Article in journal (Refereed)
    Abstract [en]

    The formation of long-lasting structures at the surfaces of stars is commonly ascribed to the action of strong magnetic fields. This paradigm is supported by observations of evolving cool spots in the Sun and active late-type stars, and stationary chemical spots in the early-type magnetic stars. However, results of our seven-year monitoring of mercury spots in non-magnetic early-type star αAndromedae show that the picture of magnetically driven structure formation is fundamentally incomplete. Using an indirect stellar-surface mapping technique, we construct a series of two-dimensional images of starspots and discover a secular evolution of the mercury cloud cover in this star. This remarkable structure-formation process, observed for the first time in any star, is plausibly attributed to a non-equilibrium, dynamical evolution of the heavy-element clouds created by atomic diffusion, and may have the same underlying physics as the weather patterns on terrestrial and giant planets.

  • 34.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Bagnulo, S.
    Wade, G. A.
    Sangalli, L.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Landstreet, J. D.
    Petit, P.
    Sigut, T. A. A.
    Magnetic Doppler imaging of 53 Camelopardalis in all four Stokes parameters2004In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 414, p. 613-Article in journal (Refereed)
  • 35.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Drake, N.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    de la Reza, R.
    Multi-element abundance Doppler imaging of the rapidly oscillating Ap star HR 38312004In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 424, p. 935-Article in journal (Refereed)
  • 36.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Freytag, Bernd
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Steffen, M.
    3-D Hydrodynamic Simulation of Convection in A Stars2006In: IAUS 239, Convection in Astrophysics, 2006, p. 169-Conference paper (Other scientific)
  • 37.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Ryde, N.
    Gustafsson, B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Bagnulo, S.
    Plez, B.
    Magnetic fields in M dwarf stars from high-resolution infrared spectra2009In: COOL STARS, STELLAR SYSTEMS AND THE SUN: Proceedings of the 15th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun, 2009, Vol. 1094, p. 124-129Conference paper (Refereed)
    Abstract [en]

    Magnetic fields play a central role in the atmospheric properties and variability of active M dwarfs. Information on the strength and structure of magnetic fields in these objects is vital for understanding dynamo mechanisms and magnetically-driven activity of low-mass stars, and for constraining theories of star formation and evolution. We have initiated the first systematic high-resolution survey of magnetically sensitive infrared spectral lines in M dwarf stars using the CRIRES instrument at the ESO VLT. We have completed observations for a sample of 35 active and inactive M dwarfs. Here we report first results of our project, demonstrating a clear detection of magnetic splitting of lines in the spectra of several M dwarfs. We assess diagnostic potential of different Zeeman-sensitive lines in the observed spectral region and apply spectrum synthesis modelling to infer magnetic field properties of selected M dwarfs.

  • 38.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Makaganiuk, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Least-squares deconvolution of the stellar intensity and polarization spectra2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 524, no 1, p. A5-Article in journal (Refereed)
    Abstract [en]

    Context. Least-squares deconvolution (LSD) is a powerful method of extracting high-precision average line profiles from the stellar intensity and polarization spectra. This technique is widely used for detection, characterization, and detailed mapping of the temperature, magnetic, and chemical abundance structures on the surfaces of stars. Aims. Despite its common usage, the LSD method is poorly documented and has never been tested with realistic synthetic spectra. In this study we revisit the key assumptions of the LSD technique, clarify its numerical implementation, discuss possible improvements and give recommendations of how to make LSD results understandable and reproducible. We also address the problem of interpretation of the moments and shapes of the LSD profiles in terms of physical parameters. Methods. We have developed an improved, multiprofile version of LSD (iLSD) and have extended the deconvolution procedure to linear polarization analysis taking into account anomalous Zeeman splitting of spectral lines. The iLSD method is applied to the theoretical Stokes parameter spectra computed for a wide wavelength interval containing all relevant spectral lines. We test various methods of interpreting the mean profiles, investigating how coarse approximations of the multiline technique translate into errors of the derived parameters. Results. We find that, generally, the Stokes parameter LSD profiles do not behave as a real spectral line with respect to the variation of magnetic field and elemental abundance. This problem is especially prominent for the Stokes I (intensity) variation with abundance and Stokes Q (linear polarization) variation with magnetic field. At the same time, the Stokes V (circular polarization) LSD spectra closely resemble the profile of a properly chosen synthetic line for the magnetic field strength up to 1 kG. The longitudinal field estimated from the Stokes V LSD profile is accurate to within 10% for the field strength below 5 kG and to within a few percent for the fields weaker than 1 kG. Our iLSD technique offers clear advantages over the standard LSD method in the individual analysis of different chemical elements. Conclusions. We conclude that the usual method of interpreting the LSD profiles by assuming that they are equivalent to a real spectral line gives satisfactory results only in a limited parameter range and thus should be applied with caution. A more trustworthy approach is to abandon the single-line approximation of the average profiles and apply LSD consistently to observations and synthetic spectra.

  • 39.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Makaganiuk, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Jeffers, S. V.
    Johns-Krull, C. M.
    Keller, C. U.
    Rodenhuis, M.
    Snik, F.
    Stempels, H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Valenti, J. A.
    Are there tangled magnetic fields on HgMn stars?2013In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 554, p. A61-Article in journal (Refereed)
    Abstract [en]

    Context. Several recent spectrophotometric studies failed to detect significant global magnetic fields in late-B HgMn chemically peculiar stars, but some investigations have suggested the presence of strong unstructured or tangled fields in these objects. Aims. We used detailed spectrum synthesis analysis to search for evidence of tangled magnetic fields in high-quality observed spectra of eight slowly rotating HgMn stars and one normal late-B star. We also evaluated recent sporadic detections of weak longitudinal magnetic fields in HgMn stars based on the moment technique. Methods. Our spectrum synthesis code calculated the Zeeman broadening of metal lines in HARPS spectra, assuming an unstructured, turbulent magnetic field. A simple line formation model with a homogeneous radial field distribution was applied to assess compatibility between previous longitudinal field measurements and the observed mean circular polarization signatures. Results. Our analysis of the Zeeman broadening of magnetically sensitive spectral lines reveals no evidence of tangled magnetic fields in any of the studied HgMn or normal stars. We infer upper limits of 200-700 G for the mean magnetic field modulus - much smaller than the field strengths implied by studies based on differential magnetic line intensification and quadratic field diagnostics. The new HARPSpol longitudinal field measurements for the extreme HgMn star HD65949 and the normal late-B star 21 Peg are consistent with zero at a precision of 3-6 G. Re-analysis of our Stokes V spectra of the spotted HgMn star HD11753 shows that the recent moment technique measurements retrieved from the same data are incompatible with the lack of circular polarization signatures in the spectrum of this star. Conclusions. We conclude that there is no evidence for substantial tangled magnetic fields on the surfaces of studied HgMn stars. We cannot independently confirm the presence of very strong quadratic or marginal longitudinal fields for these stars, so results from the moment technique are likely to be spurious.

  • 40.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Makaganiuk, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Jeffers, S. V.
    Johns-Krull, C. M.
    Keller, C. U.
    Rodenhuis, M.
    Snik, F.
    Stempels, Henricus C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Valenti, J. A.
    No magnetic field in the spotted HgMn star mu Leporis2011In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 534, p. L13-Article in journal (Refereed)
    Abstract [en]

    Context. Chemically peculiar stars of the mercury-manganese (HgMn) type represent a new class of spotted late-B stars, in which evolving surface chemical inhomogeneities are apparently unrelated to the presence of strong magnetic fields but are produced by some hitherto unknown astrophysical mechanism.

    Aims. The goal of this study is to perform a detailed line profile variability analysis and carry out a sensitive magnetic field search for one of the brightest HgMn stars -mu Lep.

    Methods. We acquired a set of very high-quality intensity and polarization spectra of mu Lep with the HARPSpol polarimeter. These data were analyzed with the multiline technique of least-squares deconvolution in order to extract information on the magnetic field and line profile variability.

    Results. Our spectra show very weak but definite variability in the lines of Sc, all Fe-peak elements represented in the spectrum of mu Lep, as well as Y, Sr, and Hg. Variability might also be present in the lines of Si and Mg. Anomalous profile shapes of Ti II and YII lines suggest a dominant axisymmetric distribution of these elements. At the same time, we found no evidence of the magnetic field in mu Lep, with the 3 sigma upper limit of only 3 G for the mean longitudinal magnetic field. This is the most stringent upper limit on the possible magnetic field derived for a spotted HgMn star.

    Conclusions. The very weak variability detected for many elements in the spectrum mu Lep suggests that low-contrast chemical inhomogeneities may be common in HgMn stars and that they have not been recognized until now due to the limited precision of previous spectroscopic observations and a lack of time-series data. The null result of the magnetic field search reinforces the conclusion that formation of chemical spots in HgMn stars is not magnetically driven.

  • 41.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Makaganiuk, Vitalii
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Snik, F.
    Jeffers, S. V.
    Johns-Krull, C. M.
    Keller, C. U.
    Rodenhuis, M.
    Valenti, J. A.
    First detection of linear polarization in the line profiles of active cool stars2011In: Astrophysical Journal Letters, ISSN 2041-8205, Vol. 732, no 2, p. L19-Article in journal (Refereed)
    Abstract [en]

    The application of high-resolution spectropolarimetry has led to major progress in understanding the magnetism and activity of late-type stars. During the last decade, magnetic fields have been discovered and mapped for many types of active cool stars using spectropolarimetric data. However, these observations and modeling attempts are fundamentally incomplete since they are based on the interpretation of the circular polarization alone. Taking advantage of the newly built HARPS polarimeter, we have obtained the first systematic observations of several cool active stars in all four Stokes parameters. Here we report the detection of magnetically induced linear polarization for the primary component of the very active RS CVn binary HR 1099 and for the moderately active K dwarf epsilon Eri. For both stars the amplitude of linear polarization signatures is measured to be similar to 10(-4) of the unpolarized continuum, which is approximately a factor of 10 lower than for circular polarization. This is the first detection of the linear polarization in line profiles of cool active stars. Our observations of the inactive solar-like star alpha Cen A show neither circular nor linear polarization above the level of similar to 10(-5), indicating the absence of a net longitudinal magnetic field stronger than 0.2 G.

  • 42.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Doppler Imaging of stellar magnetic fields. II. Numerical experiments2002In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 388, p. 868-888Article in journal (Refereed)
  • 43.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Magnetic Doppler Imaging of Active Stars2006In: Solar and Stellar Activity Cycles, 26th meeting of the IAU, Joint Discussion 8, 2006Conference paper (Other scientific)
  • 44.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Bagnulo, S.
    Landstreet, J.D.
    Sigut, T.A.A.
    Petit, P.
    Wade, G.A.
    Magnetic Doppler Imaging of Chemically Peculiar Stars2003In: The 3rd Solar Polarization Workshop, ASP conf. Ser., vol. 307, 2003, p. 549-Conference paper (Other scientific)
  • 45.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ilyin, I.
    Ilyina, S.
    Tuominen, I.
    Doppler Imaging of stellar magnetic fields. III. Abundance distribution and magnetic field geometry of alpha 2 CVn2002In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 389, p. 420-438Article in journal (Refereed)
  • 46.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Sachkov, M.
    Kudryavtsev, D.
    Inhomogeneous distribution of mercury on the surfaces of rapidly rotating HgMn stars2005In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 439, p. 1093-Article in journal (Refereed)
  • 47.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Valenti, J.
    Johns-Krull, C.
    The Search and Modelling of Magnetic Fields on M Dwarfs2001In: Magnetic Fields Across the Hertzsprung-Russell Diagram, Conference Proceedings, 2001, p. 219-Conference paper (Other scientific)
  • 48.
    Kochukhov, Oleg
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Rusomarov, Naum
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Valenti, J. A.
    Stempels, H. C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Snik, F.
    Rodenhuis, M.
    Piskunov, Nikolai
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Makaganiuk, V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Keller, C. U.
    Johns-Krull, C. M.
    Magnetic field topology and chemical spot distributions in the extreme Ap star HD 750492015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 574, article id A79Article in journal (Refereed)
    Abstract [en]

    Context. Intermediate-mass, magnetic chemically peculiar (Ap) stars provide a unique opportunity to study the topology of stellar magnetic fields in detail and to investigate magnetically driven processes of spot formation. Aims. Here we aim to derive the surface magnetic field geometry and chemical abundance distributions for the extraordinary Ap star HD 75049. This object hosts a surface field of similar to 30 kG, one of the strongest known for any non-degenerate star. Methods. We used time-series of high-resolution HARPS intensity and circular polarisation observations. These data were interpreted with the help of magnetic Doppler imaging and model atmospheres incorporating effects of a non-solar chemical composition and a strong magnetic field. Results. Based on high-precision measurements of the mean magnetic field modulus, we refined the rotational period of HD 75049 to P-rot = 4.048267 +/- 0.000036 d. We also derived basic stellar parameters, T-eff = 10 250 +/- 250 K and log g = 4.3 +/- 0.1. Magnetic Doppler imaging revealed that the field topology of HD 75049 is poloidal and dominated by a dipolar contribution with a peak surface field strength of 39 kG. At the same time, deviations from the classical axisymmetric oblique dipolar configuration are significant. Chemical surface maps of Si, Cr, Fe, and Nd show abundance contrasts of 0.5-1.4 dex, which is low compared with many other Ap stars. Of the chemical elements, Nd is found to be enhanced close to the magnetic pole, whereas Si and Cr are concentrated predominantly at the magnetic equator. The iron distribution shows low-contrast features both at the magnetic equator and the pole. Conclusions. The morphology of the magnetic field and the properties of chemical spots in HD 75049 are qualitatively similar to those of Ap stars with weaker fields. Consequently, whatever mechanism forms and sustains global magnetic fields in intermediate-mass main-sequence stars, it operates in the same way over the entire observed range of magnetic field strengths.

  • 49.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ryabchikova, T.
    Piskunov, Nikolai
    Department of Physics and Astronomy, Observational Astronomy.
    No magnetic field variation with pulsation phase in the roAp star gamma Equulei2004In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 415, p. 13-Article in journal (Refereed)
  • 50.
    Kochukhov, Oleg
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Ryabchikova, T.
    Piskunov, Nikolai
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics. Department of Physics and Astronomy, Observational Astronomy.
    Time-Resolved Spectroscopy of the roAp Star gamma Equ2001In: Magnetic Fields Across the Hertzsprung-Russell Diagram, Conference Proceedings, 2001, p. 341-Conference paper (Other scientific)
123 1 - 50 of 137
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