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Piskunov, Nikolai
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Publications (10 of 133) Show all publications
Piskunov, N. & Valenti, J. A. (2017). Spectroscopy Made Easy: Evolution. Astronomy and Astrophysics, 597, Article ID A16.
Open this publication in new window or tab >>Spectroscopy Made Easy: Evolution
2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 597, article id A16Article in journal (Refereed) Published
Abstract [en]

Context. The Spectroscopy Made Easy (SME) package has become a popular tool for analyzing stellar spectra, often in connection with large surveys or exoplanet research. SME has evolved significantly since it was first described in 1996, but many of the original caveats and potholes still haunt users. The main drivers for this paper are complexity of the modeling task, the large user community, and the massive effort that has gone into SME.

Aims. We do not intend to give a comprehensive introduction to stellar atmospheres, but will describe changes to key components of SME: the equation of state, opacities, and radiative transfer. We will describe the analysis and fitting procedure and investigate various error sources that affect inferred parameters.

Methods. We review the current status of SME, emphasizing new algorithms and methods. We describe some best practices for using the package, based on lessons learned over two decades of SME usage. We present a new way to assess uncertainties in derived stellar parameters.

Results. Improvements made to SME, better line data, and new model atmospheres yield more realistic stellar spectra, but in many cases systematic errors still dominate over measurement uncertainty. Future enhancements are outlined.

Keyword
stars: abundances, radiative transfer, stars: fundamental parameters, stars: atmospheres, techniques: spectroscopic
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-317615 (URN)10.1051/0004-6361/201629124 (DOI)000392392900084 ()
Available from: 2017-03-16 Created: 2017-03-16 Last updated: 2017-11-29Bibliographically approved
de Jong, R. S., Barden, S. C., Bellido-Tirado, O., Brynnel, J. G., Frey, S., Giannone, D., . . . Starkenburg, E. (2016). 4MOST: the 4-metre Multi-Object Spectroscopic Telescope project at preliminary design review. In: Christopher J Evans (Ed.), GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND. , 9908, Article ID UNSP 99081O.
Open this publication in new window or tab >>4MOST: the 4-metre Multi-Object Spectroscopic Telescope project at preliminary design review
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2016 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI / [ed] Christopher J Evans, 2016, Vol. 9908, article id UNSP 99081OConference paper, Published 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.

Series
Proceedings of SPIE, ISSN 0277-786X ; 9908
Keyword
Wide-field multi-object spectrograph facility, VISTA telescope, tilting-spine fibre postioner, wide field corrector, facility simulator, fibre-fed spectrographs, science operations, Gaia, eROSITA, Euclid, PLATO
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-316358 (URN)10.1117/12.2232832 (DOI)000391509100044 ()978-1-5106-0196-3 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND
Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-03-06Bibliographically approved
Ryabchikova, T., Piskunov, N., Pakhomov, Y., Tsymbal, V., Titarenko, A., Sitnova, T., . . . Mashonkina, L. (2016). Accuracy of atmospheric parameters of FGK dwarfs determined by spectrum fitting. Monthly notices of the Royal Astronomical Society, 456(2), 1221-1234.
Open this publication in new window or tab >>Accuracy of atmospheric parameters of FGK dwarfs determined by spectrum fitting
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2016 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 456, no 2, p. 1221-1234Article in journal (Refereed) Published
Abstract [en]

We performed extensive tests of the accuracy of atmospheric parameter determination for FGK stars based on the spectrum fitting procedure SpectroscopyMade Easy (SME). Our stellar sample consists of 13 objects, including the Sun, in the temperature range 5000-6600K and metallicity range -1.4-+0.4. The analysed stars have the advantage of having parameters derived by interferometry. For each star, we use spectra obtained with different spectrographs and different signal-to-noise ratios (S/N). For the fitting, we adopted three different sets of constraints and test how the derived parameters depend upon the spectral regions (masks) used in SME. We developed and implemented in SME a new method for estimating uncertainties in the resulting parameters based on fitting residuals, partial derivatives, and data uncertainties. For stars in the 5700-6600K range, the best agreement with the effective temperatures derived by interferometry is achieved when spectrum fitting includes the Ha and H beta lines, while for cooler stars the choice of the mask does not affect the results. The derived atmospheric parameters do not strongly depend on spectral resolution and S/N of the observations, while the uncertainties in temperature and surface gravity increase with increasing effective temperature, with minima at 50K in T-eff and 0.1 dex in log g, for spectra with S/N=150-200. A non-local thermodynamic equilibrium (NLTE) analysis of the Ti I/Ti II and Fe I/Fe II ionization equilibria and abundances determined from the atomic CI (NLTE) and molecular CH species supports the parameters we derived with SME by fitting the observed spectra including the hydrogen lines.

Keyword
methods: data analysis, methods: observational, stars: abundances, stars: fundamental parameters
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-294589 (URN)10.1093/mnras/stv2725 (DOI)000372264200006 ()
Available from: 2016-05-26 Created: 2016-05-25 Last updated: 2017-11-30Bibliographically approved
Follert, R., Taubert, D., Hollandt, J., Monte, C., Oliva, E., Seemann, U., . . . Tordo, S. (2016). Characterizing the cross dispersion reflection gratings of CRIRES. In: Advances In Optical And Mechanical Technologies For Telescopes And Instrumentation Ii: . Paper presented at Conference on Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, JUN 26-JUL 01, 2016, Edinburgh, ENGLAND. , Article ID UNSP 99122B.
Open this publication in new window or tab >>Characterizing the cross dispersion reflection gratings of CRIRES
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2016 (English)In: Advances In Optical And Mechanical Technologies For Telescopes And Instrumentation Ii, 2016, article id UNSP 99122BConference paper, Published 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.

Series
Proceedings of SPIE, ISSN 0277-786X ; 9912
Keyword
CRIRES+, echelle spectrograph, infrared instrumentation, VLT, diffraction efficiency
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-311408 (URN)10.1117/12.2232569 (DOI)000387747900072 ()9781510602038; 9781510602045 (ISBN)
Conference
Conference on Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, JUN 26-JUL 01, 2016, Edinburgh, ENGLAND
Available from: 2016-12-27 Created: 2016-12-27 Last updated: 2016-12-27Bibliographically approved
Marconi, A., Di Marcantonio, P., D'Odorico, V., Cristiani, S., Maiolino, R., Oliva, E., . . . Zackrisson, E. (2016). EELT-HIRES the high-resolution spectrograph for the E-ELT. In: Christopher J Evans (Ed.), GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND. , 9908, Article ID UNSP 990823.
Open this publication in new window or tab >>EELT-HIRES the high-resolution spectrograph for the E-ELT
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2016 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI / [ed] Christopher J Evans, 2016, Vol. 9908, article id UNSP 990823Conference paper, Published paper (Refereed)
Abstract [en]

The first generation of E-ELT instruments will include an optical infrared High Resolution Spectrograph, conventionally indicated as EELT-HIRES, which will be capable of providing unique breakthroughs in the fields of exoplanets, star and planet formation, physics and evolution of stars and galaxies, cosmology and fundamental physics. A 2-year long phase A study for EELT-HIRES has just started and will be performed by a consortium composed of institutes and organisations from Brazil, Chile, Denmark, France, Germany, Italy, Poland, Portugal, Spain, Sweden, Switzerland and United Kingdom. In this paper we describe the science goals and the preliminary technical concept for EELT-HIRES which will be developed during the phase A, as well as its planned development and consortium organisation during the study.

Series
Proceedings of SPIE, ISSN 0277-786X ; 9908
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-316360 (URN)10.1117/12.2231653 (DOI)000391509100058 ()978-1-5106-0196-3 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND
Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-03-06Bibliographically approved
Thompson, S. J., Queloz, D., Baraffe, I., Brake, M., Dolgopolov, A., Fisher, M., . . . Young, J. (2016). HARS3 for a Roboticized Isaac Newton Telescope. In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND. , 9908, Article ID UNSP 99086F.
Open this publication in new window or tab >>HARS3 for a Roboticized Isaac Newton Telescope
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2016 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI, 2016, Vol. 9908, article id UNSP 99086FConference paper, Published paper (Refereed)
Abstract [en]

We present a description of a new instrument development, HARPS3, planned to be installed on an upgraded and roboticized Isaac Newton Telescope by end-2018. HARPS3 will be a high resolution (R similar or equal to 115,000) echelle spectrograph with a wavelength range from 380-690 nm. It is being built as part of the Terra Hunting Experiment {a future 10 year radial velocity measurement programme to discover Earth-like exoplanets. The instrument design is based on the successful HARPS spectrograph on the 3.6m ESO telescope and HARPS-N on the TNG telescope. The main changes to the design in HARPS3 will be: a customised fibre adapter at the Cassegrain focus providing a stabilised beam feed and on-sky fibre diameter approximate to 1.4 arcsec, the implementation of a new continuous flow cryostat to keep the CCD temperature very stable, detailed characterisation of the HARPS3 CCD to map the effective pixel positions and thus provide an improved accuracy wavelength solution, an optimised integrated polarimeter and the instrument integrated into a robotic operation. The robotic operation will optimise our programme which requires our target stars to be measured on a nightly basis. We present an overview of the entire project, including a description of our anticipated robotic operation.

Series
Proceedings of SPIE, ISSN 0277-786X ; 9908
Keyword
High resolution spectroscopy, robotic operations, RV measurements, exoplanets
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-316361 (URN)10.1117/12.2232111 (DOI)000391509100184 ()978-1-5106-0196-3 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND
Available from: 2017-03-02 Created: 2017-03-02 Last updated: 2017-03-02Bibliographically approved
Boyarchuk, A. A., Shustov, B. M., Savanov, I. S., Sachkov, M. E., Bisikalo, D. V., Mashonkina, L. I., . . . Kil'pio, E. Y. (2016). Scientific problems addressed by the Spektr-UV space project (world space Observatory-Ultraviolet). Astronomy reports (Print), 60(1), 1-42.
Open this publication in new window or tab >>Scientific problems addressed by the Spektr-UV space project (world space Observatory-Ultraviolet)
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2016 (English)In: Astronomy reports (Print), ISSN 1063-7729, E-ISSN 1562-6881, Vol. 60, no 1, p. 1-42Article in journal (Refereed) Published
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.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-277797 (URN)10.1134/S1063772916010017 (DOI)000368685900001 ()
Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2017-11-30Bibliographically approved
Dorn, R. J., Follert, R., Bristow, P., Cumani, C., Eschbaumer, S., Grunhut, J., . . . Tordo, S. (2016). The " plus " for CRIRES: enabling better science at infrared wavelength and high spectral resolution at the ESO VLT. In: Christopher J Evans (Ed.), GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND. , 9908, Article ID 99080I.
Open this publication in new window or tab >>The " plus " for CRIRES: enabling better science at infrared wavelength and high spectral resolution at the ESO VLT
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2016 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VI / [ed] Christopher J Evans, 2016, Vol. 9908, article id 99080IConference paper, Published 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.

Series
Proceedings of SPIE, ISSN 0277-786X ; 9908
Keyword
astronomical instrumentation, infrared spectrographs, high spectral resolution, upgrade of existing VLT instruments, infrared spectrometers, wavelength calibration, radial-velocities, extra-solar planets
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-316359 (URN)10.1117/12.2232837 (DOI)000391509100013 ()978-1-5106-0196-3 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VI, JUN 26-30, 2016, Edinburgh, SCOTLAND
Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-03-06Bibliographically approved
Dubernet, M. L., Antony, B. K., Ba, Y. A., Babikov, Y. L., Bartschat, K., Boudon, V., . . . Zwoelf, C. M. (2016). The virtual atomic and molecular data centre (VAMDC) consortium. Journal of Physics B: Atomic, Molecular and Optical Physics, 49(7), Article ID 074003.
Open this publication in new window or tab >>The virtual atomic and molecular data centre (VAMDC) consortium
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2016 (English)In: 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) Published
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.

Keyword
databases, atoms, molecules, spectroscopy, kinetic data, astrophysics
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-292996 (URN)10.1088/0953-4075/49/7/074003 (DOI)000372911000003 ()
Available from: 2016-05-18 Created: 2016-05-11 Last updated: 2017-11-30Bibliographically approved
Ryabchikova, T., Piskunov, N., Kurucz, R. L., Stempels, E. H. C., Heiter, U., Pakhomov, Y. & Barklem, P. S. (2015). A major upgrade of the VALD database. Physica Scripta, 90(5), Article ID 054005.
Open this publication in new window or tab >>A major upgrade of the VALD database
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2015 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 90, no 5, article id 054005Article in journal (Refereed) Published
Abstract [en]

Vienna atomic line database (VALD) is a collection of critically evaluated laboratory parameters for individual atomic transitions, complemented by theoretical calculations. VALD is actively used by astronomers for stellar spectroscopic studies-model atmosphere calculations, atmospheric parameter determinations, abundance analysis etc. The two first VALD releases contained parameters for atomic transitions only. In a major upgrade of VALD-VALD3, publically available from spring 2014, atomic data was complemented with parameters of molecular lines. The diatomic molecules C-2, CH, CN, CO, OH, MgH, SiH, TiO are now included. For each transition VALD provides species name, wavelength, energy, quantum number J and Lande-factor of the lower and upper levels, radiative, Stark and van der Waals damping factors and a full description of electronic configurarion and term information of both levels. Compared to the previous versions we have revised and verify all of the existing data and added new measurements and calculations for transitions in the range between 20 angstrom and 200 microns. All transitions were complemented with term designations in a consistent way and electron configurations when available. All data were checked for consistency: listed wavelength versus Ritz, selection rules etc. A new bibliographic system keeps track of literature references for each parameter in a given transition throughout the merging process so that every selected data entry can be traced to the original source. The query language and the extraction tools can now handle various units, vacuum and air wavelengths. In the upgrade process we had an intensive interaction with data producers, which was very helpful for improving the quality of the VALD content.

Keyword
data bases, atomic and molecular data, astrophysics
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-259165 (URN)10.1088/0031-8949/90/5/054005 (DOI)000356498700006 ()
Available from: 2015-07-29 Created: 2015-07-29 Last updated: 2017-12-04Bibliographically approved
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