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Piskunov, Nikolai, professor
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Publications (10 of 145) Show all publications
Piskunov, N., Stempels, E., Lavail, A., Escuti, M., Snik, F., Dolgopolov, A., . . . Valenti, E. (2018). A unique infrared spectropolarimetric unit for CRIRES+. In: Evans, CJ Simard, L Takami, H (Ed.), GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, USA. SPIE-INT SOC OPTICAL ENGINEERING, Article ID 1070234.
Open this publication in new window or tab >>A unique infrared spectropolarimetric unit for CRIRES+
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2018 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII / [ed] Evans, CJ Simard, L Takami, H, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 1070234Conference paper, Published paper (Refereed)
Abstract [en]

High-resolution infrared spectropolarimetry has many science applications in astrophysics. One of them is measuring weak magnetic fields using the Zeeman effect. Infrared domain is particularly advantageous as Zeeman splitting of spectral lines is proportional to the square of the wavelength while the intrinsic width of the line cores increases only linearly. Important science cases include detection and monitoring of global magnetic fields on solar-type stars, study of the magnetic field evolution from stellar formation to the final stages of the stellar life with massive stellar winds, and the dynamo mechanism operation across the boundary between fully-and partially-convective stars. CRIRES+ (the CRIRES upgrade project) includes a novel spectropolarimetric unit (SPU) based on polarization gratings. The novel design allows to perform beam-splitting very early in the optical path, directly after the tertiary mirror of the telescope (the ESO Very Large Telescope, VLT), minimizing instrumental polarization. The new SPU performs polarization beam-splitting in the near-infrared while keeping the telescope beam mostly unchanged in the optical domain, making it compatible with the adaptive optics system of the CRIRES+ instrument. The SPU consists of four beam-splitters optimized for measuring circular and linear polarization of spectral lines in YJ and HK bands. The SPU can perform beam switching allowing to correct for throughput in each beam and for variations in detector pixel sensitivity. Other new features of CRIRES+, such as substantially increased wavelength coverage, stability and advanced data reduction pipeline will further enhance the sensitivity of the polarimetric mode. The combination of the SPU, CRIRES+ and the VLT is a unique facility for making major progress in understanding stellar activity. In this article we present the design of the SPU, laboratory measurements of individual components and of the whole unit as well as the performance prediction for the operation at the VLT.

Place, publisher, year, edition, pages
SPIE-INT SOC OPTICAL ENGINEERING, 2018
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 10702
Keywords
Spectroscopy, Spectropolarimetry, Polarisation gratings, Stokes parameters
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-373550 (URN)10.1117/12.2313512 (DOI)000452664300275 ()978-1-5106-1958-6 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, USA
Funder
Knut and Alice Wallenberg Foundation
Available from: 2019-01-17 Created: 2019-01-17 Last updated: 2019-01-17Bibliographically approved
Dorval, P., Snik, F., Piskunov, N., Navarro, R., Kragt, J., ter Horst, R., . . . Thompson, S. (2018). Analysis of the polarimetric performance of the HARPS3 Cassegrain adaptor unit. In: Evans, CJ Simard, L Takami, H (Ed.), Ground-Based And Airborne Instrumentation For Astronomy VII: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX. , Article ID UNSP 107026B.
Open this publication in new window or tab >>Analysis of the polarimetric performance of the HARPS3 Cassegrain adaptor unit
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2018 (English)In: Ground-Based And Airborne Instrumentation For Astronomy VII / [ed] Evans, CJ Simard, L Takami, H, 2018, article id UNSP 107026BConference paper, Published paper (Refereed)
Abstract [en]

The third version of the High Accuracy Radial velocity Planet Searcher (HARPS3) instrument is built for a ten-year programme aimed at achieving 10 cm/sec radial velocity precision on nearby stars to search for Earth-like planets. HARPS3 will be commissioned on the to-be-roboticized 2.54-m Isaac Newton Telescope at La Palma in 2021. One of the main changes compared to its predecessors is the novel dual-beam Cassegrain focus, featuring a stabilised beam feed into the HARPS3 spectrograph and an insertable polarimetric sub-unit. This polarimetric sub-unit enables HARPS3 to directly measure stellar activity signatures, which can be useful for correcting activity-induced radial velocity jitter in the search for Earth-like planets. The sub-unit consists of superachromatic polymer quarter- and half-wave retarders for circular and linear polarizations respectively, designed to suppress polarized fringing, and a novel polarimetric beam splitter based on a wire-grid design, separating the two polarimetric beams by 30 mm and feeding two separate science fibers. The dual-beam exchange implementation in combination with the extreme stability of the HARPS3 spectrograph enables a polarimetric sensitivity of 10(-5) on bright stars. One of the main challenges of such a system is in the characterization of instrumental polarization effects which limit the polarimetric accuracy of the polarimetric observing mode. By design and characterization of this subsystem and by pre-emptively mitigating possible noise sources, we can minimize the noise characteristics of the polarization sub-unit to allow for precise observations. In this paper we report on the design, realization, assembly, alignment, and testing of the polarimetric unit to be installed in the Cassegrain Adaptor Unit of the HARPS3 spectrograph.

Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 10702
Keywords
polarization, instrumentation: spectrographs
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-373094 (URN)10.1117/12.2312535 (DOI)000452664300155 ()978-1-5106-1958-6 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX
Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically approved
Marconi, A., Prieto, C. A., Amado, P. J., Amate, M., Augusto, S. R., Becerril, S., . . . Zackrisson, E. (2018). ELT-HIRES, the high resolution spectrograph for the ELT: results from the Phase A study. In: Evans, CJ Simard, L Takami, H (Ed.), GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX, USA. SPIE-INT SOC OPTICAL ENGINEERING, Article ID 107021Y.
Open this publication in new window or tab >>ELT-HIRES, the high resolution spectrograph for the ELT: results from the Phase A study
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2018 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII / [ed] Evans, CJ Simard, L Takami, H, SPIE-INT SOC OPTICAL ENGINEERING , 2018, article id 107021YConference paper, Published paper (Refereed)
Abstract [en]

We present the results from the phase A study of ELT-HIRES, an optical-infrared High Resolution Spectrograph for ELT, which has just been completed by a consortium of 30 institutes from 12 countries forming a team of about 200 scientists and engineers. The top science cases of ELT-HIRES will be the detection of life signatures from exoplanet atmospheres, tests on the stability of Nature's fundamental couplings, the direct detection of the cosmic acceleration. However, the science requirements of these science cases enable many other groundbreaking science cases. The baseline design, which allows to fulfil the top science cases, consists in a modular fiber fed cross-dispersed echelle spectrograph with two ultra-stable spectral arms providing a simultaneous spectral range of 0.4-1.8 pm at a spectral resolution of 100, 000. The fiber-feeding allows ELT-HIRES to have several, interchangeable observing modes including a SCAO module and a small diffraction-limited IFU.

Place, publisher, year, edition, pages
SPIE-INT SOC OPTICAL ENGINEERING, 2018
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 10702
Keywords
EXTREMELY LARGE TELESCOPES, HIGH RESOLUTION SPECTROSCOPY, EXOPLANETS, STARS AND PLANETS FORMATION, PHYSICS AND EVOLUTION OF STARS, PHYSICS AND EVOLUTION OF GALAXIES, COSMOLOGY, FUNDAMENTAL PHYSICS
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-373548 (URN)10.1117/12.2311664 (DOI)000452664300043 ()978-1-5106-1958-6 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX, USA
Available from: 2019-01-17 Created: 2019-01-17 Last updated: 2019-01-17Bibliographically approved
Brucalassi, A., Dorn, R. J., Follert, R., Hatzes, A., Bristow, P., Seemann, U., . . . Umlauf, T. (2018). Full System Test and early Preliminary Acceptance Europe results for CRIRES. In: Evans, CJ, Simard, L, Takami, H (Ed.), Ground-Based And Airborne Instrumentation For Astronomy VII: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX. , Article ID UNSP 1070239.
Open this publication in new window or tab >>Full System Test and early Preliminary Acceptance Europe results for CRIRES
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2018 (English)In: Ground-Based And Airborne Instrumentation For Astronomy VII / [ed] Evans, CJ, Simard, L, Takami, H, 2018, article id UNSP 1070239Conference paper, Published paper (Refereed)
Abstract [en]

CRIRES+ is the new high-resolution NIR echelle spectrograph intended to be operated at the platform B of VLT Unit telescope UT3. It will cover from Y to M bands (0.95-5.3um) with a spectral resolution of R = 50000 or R = 100000. The main scientific goals are the search of super-Earths in the habitable zone of low-mass stars, the characterisation of transiting planets atmosphere and the study of the origin and evolution of stellar magnetic fields. Based on the heritage of the old adaptive optics (AO) assisted VLT instrument CRIRES, the new spectrograph will present improved optical layout, a new detector system and a new calibration unit providing optimal performances in terms of simultaneous wavelength coverage and radial velocity accuracy (a few m/s). The total observing efficiency will be enhanced by a factor of 10 with respect to CRIRES. An innovative spectro-polarimetry mode will be also offered and a new metrology system will ensure very high system stability and repeatability. Fiinally, the CRIRES+ project will also provide the community with a new data reduction software (DRS) package. CRIRES+ is currently at the initial phase of its Preliminary Acceptance in Europe (PAE) and it will be commissioned early in 2019 at VLT. This work outlines the main results obtained during the initial phase of the full system test at ESO HQ Garching.

Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 10702
Keywords
CRIRES, VLT, high resolution spectroscopy, echelle spectrograph, infrared instrumentation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-373093 (URN)10.1117/12.2313743 (DOI)000452664300080 ()978-1-5106-1958-6 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy VII, JUN 10-14, 2018, Austin, TX
Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-11Bibliographically approved
Regandell, S., Marquart, T. & Piskunov, N. (2018). Inside a VAMDC data node-putting standards into practical software. Physica Scripta, 93(3), Article ID 035001.
Open this publication in new window or tab >>Inside a VAMDC data node-putting standards into practical software
2018 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 93, no 3, article id 035001Article in journal (Refereed) Published
Abstract [en]

Access to molecular and atomic data is critical for many forms of remote sensing analysis across different fields. Many atomic and molecular databases are however highly specialised for their intended application, complicating querying and combination data between sources. The Virtual Atomic and Molecular Data Centre, VAMDC, is an electronic infrastructure that allows each database to register as a 'node'. Through services such as VAMDC's portal website, users can then access and query all nodes in a homogenised way. Today all major Atomic and Molecular databases are attached to VAMDC This article describes the software tools we developed to help data providers create and manage a VAMDC node. It gives an overview of the VAMDC infrastructure and of the various standards it uses. The article then discusses the development choices made and how the standards are implemented in practice. It concludes with a full example of implementing a VAMDC node using a real-life case as well as future plans for the node software.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
databases, atomic and molecular physics, stellar atmospheres, data analysis, science infrastructure
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-348835 (URN)10.1088/1402-4896/aaa268 (DOI)000425690300001 ()
Available from: 2018-04-25 Created: 2018-04-25 Last updated: 2018-04-25Bibliographically approved
Aronson, E. & Piskunov, N. (2018). Model-independent Exoplanet Transit Spectroscopy. Astronomical Journal, 155(5), Article ID 208.
Open this publication in new window or tab >>Model-independent Exoplanet Transit Spectroscopy
2018 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 155, no 5, article id 208Article in journal (Refereed) Published
Abstract [en]

We propose a new data analysis method for obtaining transmission spectra of exoplanet atmospheres and brightness variation across the stellar disk from transit observations. The new method is capable of recovering exoplanet atmosphere absorption spectra and stellar specific intensities without relying on theoretical models of stars and planets. We simultaneously fit both stellar specific intensity and planetary radius directly to transit light curves. This allows stellar models to be removed from the data analysis. Furthermore, we use a data quality weighted filtering technique to achieve an optimal trade-off between spectral resolution and reconstruction fidelity homogenizing the signal-to-noise ratio across the wavelength range. Such an approach is more efficient than conventional data binning onto a low-resolution wavelength grid. We demonstrate that our analysis is capable of reproducing results achieved by using an explicit quadratic limb-darkening equation and that the filtering technique helps eliminate spurious spectral features in regions with strong telluric absorption. The method is applied to the VLT FORS2 observations of the exoplanets GJ 1214 b and WASP-49 b, and our results are in agreement with previous studies. Comparisons between obtained stellar specific intensity and numerical models indicates that the method is capable of accurately reconstructing the specific intensity. The proposed method enables more robust characterization of exoplanetary atmospheres by separating derivation of planetary transmission and stellar specific intensity spectra (that is model-independent) from chemical and physical interpretation.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
methods: data analysis, planets and satellites: atmospheres, techniques: spectroscopic
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-356193 (URN)10.3847/1538-3881/aaa3fe (DOI)000430925000001 ()
Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-07-30Bibliographically approved
Ryabchikova, T., Pakhomov, Y. & Piskunov, N. (2018). VALD: The Meeting Point of Data Producers and Data Users. Galaxies, 6(3), Article ID 93.
Open this publication in new window or tab >>VALD: The Meeting Point of Data Producers and Data Users
2018 (English)In: Galaxies, E-ISSN 2075-4434, Vol. 6, no 3, article id 93Article in journal (Refereed) Published
Abstract [en]

Vienna Atomic Line Database (VALD) contains data on atomic and molecular energy levels and parameters of spectral lines required for stellar spectra analysis. Hundreds of millions of lines for fine spectral synthesis and for opacity calculations are collected in the present version of VALD (VALD3). Critical evaluation of the data and the diversity of extraction tools support the high popularity of VALD among users. The data model of VALD3 incorporates obligatory links to the bibliography making our database more attractive as a publishing platform for data producers. The VALD data quality and completeness are constantly improving allowing better reproduction of stellar spectra. To illustrate continuous evolution of the data content we present a comparative analysis of the recent experimental and theoretical atomic data for Fe-group elements, which will be included in the next VALD release. This release will also include a possibility for extracting the line data with full isotopic and hyperfine structures.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
stellar spectra, atomic and molecular data, databases
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-369523 (URN)10.3390/galaxies6030093 (DOI)000448333500028 ()
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Piskunov, N. (2017). Main High-Resolution Near-IR Spectrometer for the VLT. In: Balega, YY Kudryavtsev, DO Romanyuk, II Yakunin, IA (Ed.), Stars: From Collapse To Collapse. Paper presented at Conference on Stars: From Collapse to Collapse. Special Astrophys Observ, Nizhny Arkhyz, RUSSIA, OCT 03-07, 2016 (pp. 514-517). , 510
Open this publication in new window or tab >>Main High-Resolution Near-IR Spectrometer for the VLT
2017 (English)In: Stars: From Collapse To Collapse / [ed] Balega, YY Kudryavtsev, DO Romanyuk, II Yakunin, IA, 2017, Vol. 510, p. 514-517Conference paper, Published paper (Refereed)
Abstract [en]

We present the ongoing CRISES+ project on the development of a cross dispersed high resolution near-infrared spectrometer for the ESO Very Large Telescope. The presentation highlights the relation between science objectives, technical solutions, and the structure of the project. We also share some of the insights on the implementation and management of the project that are crucial for keeping the tight time-line through efficient interaction between consortium members.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-347315 (URN)000411770200129 ()978-1-58381-904-3 (ISBN)
Conference
Conference on Stars: From Collapse to Collapse. Special Astrophys Observ, Nizhny Arkhyz, RUSSIA, OCT 03-07, 2016
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2018-03-29Bibliographically approved
Piskunov, N., Ryabchikova, T., Pakhomov, Y., Sitnova, T., Alekseeva, S., Mashonkina, L. & Nordlander, T. (2017). Program Package for the Analysis of High Resolution High Signal-To-Noise Stellar Spectra. In: Balega, YY Kudryavtsev, DO Romanyuk, II Yakunin, IA (Ed.), Stars: From Collapse To Collapse. Paper presented at Conference on Stars: From Collapse to Collapse. Special Astrophys Observ, Nizhny Arkhyz, RUSSIA, OCT 03-07, 2016 (pp. 509-513). , 510
Open this publication in new window or tab >>Program Package for the Analysis of High Resolution High Signal-To-Noise Stellar Spectra
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2017 (English)In: Stars: From Collapse To Collapse / [ed] Balega, YY Kudryavtsev, DO Romanyuk, II Yakunin, IA, 2017, Vol. 510, p. 509-513Conference paper, Published paper (Refereed)
Abstract [en]

The program package SME (Spectroscopy Made Easy), designed to perform an analysis of stellar spectra using spectral fitting techniques, was updated due to adding new functions (isotopic and hyperfine splittins) in VALD and including grids of NLTE calculations for energy levels of few chemical elements. SME allows to derive automatically stellar atmospheric parameters: effective temperature, surface gravity, chemical abundances, radial and rotational velocities, turbulent velocities, taking into account all the effects defining spectral line formation. SME package uses the best grids of stellar atmospheres that allows us to perform spectral analysis with the similar accuracy in wide range of stellar parameters and metallicities from dwarfs to giants of BAFGK spectral classes.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-347314 (URN)000411770200128 ()978-1-58381-904-3 (ISBN)
Conference
Conference on Stars: From Collapse to Collapse. Special Astrophys Observ, Nizhny Arkhyz, RUSSIA, OCT 03-07, 2016
Available from: 2018-03-29 Created: 2018-03-29 Last updated: 2018-03-29Bibliographically approved
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.

Keywords
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
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