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Piskunov, Nikolai, professorORCID iD iconorcid.org/0000-0001-5742-7767
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Publications (10 of 167) Show all publications
Yan, F., Nortmann, L., Reiners, A., Piskunov, N., Hatzes, A., Seemann, U., . . . Stempels, H. C. (2023). CRIRES+ detection of CO emissions lines and temperature inversions on the dayside of WASP-18b and WASP-76b. Astronomy and Astrophysics, 672, Article ID A107.
Open this publication in new window or tab >>CRIRES+ detection of CO emissions lines and temperature inversions on the dayside of WASP-18b and WASP-76b
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 672, article id A107Article in journal (Refereed) Published
Abstract [en]

The dayside atmospheres of ultra-hot Jupiters (UHJs) are predicted to possess temperature inversion layers with extremely high temperatures at high altitudes. We observed the dayside thermal emission spectra of WASP-18b and WASP-76b with the new CRIRES+ high-resolution spectrograph at near-infrared wavelengths. Using the cross-correlation technique, we detected strong CO emission lines in both planets, which confirms the existence of temperature inversions on their dayside hemispheres. The two planets are the first UHJs orbiting F-type stars with CO emission lines detected; previous detections were mostly for UHJs orbiting A-type stars. Evidence of weak H2O emission signals is also found for both planets. We further applied forward-model retrievals on the detected CO lines and retrieved the temperature-pressure profiles along with the CO volume mixing ratios. The retrieved logarithmic CO mixing ratio of WASP-18b (-2.2(-1.5)(+1.4)) is slightly higher than the value predicted by the self-consistent model assuming solar abundance. For WASP-76b, the retrieved CO mixing ratio (-3.6(-1.6)(+1.8)) is broadly consistent with the value of solar abundance. In addition, we included the equatorial rotation velocity (upsilon(eq)) in the retrieval when analyzing the line profile broadening. The obtained upsilon(eq) is 7.0 +/- 2.9 km s(-1) for WASP-18b and 5.2(-3.0)(+2.5) km s(-1) for WASP-76b, which are consistent with the tidally locked rotational velocities.

Place, publisher, year, edition, pages
EDP SciencesEDP SCIENCES S A, 2023
Keywords
planets and satellites, atmospheres, techniques, spectroscopic, individual, WASP-18b, WASP-76b
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-501983 (URN)10.1051/0004-6361/202245371 (DOI)000964933400002 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2023-05-22 Created: 2023-05-22 Last updated: 2024-01-15Bibliographically approved
Dorn, R. J., Bristow, P., Smoker, J. V., Rodler, F., Lavail, A., Accardo, M., . . . Wehrhahn, A. (2023). CRIRES+ on sky at the ESO Very Large Telescope: Observing the Universe at infrared wavelengths and high spectral resolution. Astronomy and Astrophysics, 671, Article ID A24.
Open this publication in new window or tab >>CRIRES+ on sky at the ESO Very Large Telescope: Observing the Universe at infrared wavelengths and high spectral resolution
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, article id A24Article in journal (Refereed) Published
Abstract [en]

The CRyogenic InfraRed Echelle Spectrograph (CRIRES) Upgrade project CRIRES+ extended the capabilities of CRIRES. It transformed this VLT instrument into a cross-dispersed spectrograph to increase the wavelength range that is covered simultaneously by up to a factor of ten. In addition, a new detector focal plane array of three Hawaii 2RG detectors with a 5.3 mu m cutoff wavelength replaced the existing detectors. Amongst many other improvements, a new spectropolarimetric unit was added and the calibration system has been enhanced. The instrument was installed at the VLT on Unit Telescope 3 at the beginning of 2020 and successfully commissioned and verified for science operations during 2021, partly remotely from Europe due to the COVID-19 pandemic. The instrument was subsequently offered to the community from October 2021 onwards. This article describes the performance and capabilities of the upgraded instrument and presents on sky results.

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
instrumentation, spectrographs, techniques, radial velocities, polarimeters, spectroscopic, adaptive optics
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-507485 (URN)10.1051/0004-6361/202245217 (DOI)000975275100001 ()
Available from: 2023-07-07 Created: 2023-07-07 Last updated: 2023-07-07Bibliographically approved
Hahlin, A., Kochukhov, O., Rains, A., Lavail, A., Hatzes, A., Piskunov, N., . . . Stempels, H. C. (2023). Determination of small-scale magnetic fields on Sun-like stars in the near-infrared using CRIRES+. Astronomy and Astrophysics, 675, Article ID A91.
Open this publication in new window or tab >>Determination of small-scale magnetic fields on Sun-like stars in the near-infrared using CRIRES+
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 675, article id A91Article in journal (Refereed) Published
Abstract [en]

Aims: We aim to characterise the small-scale magnetic fields of a sample of 16 Sun-like stars and investigate the capabilities of the newly upgraded near-infrared (NIR) instrument CRIRES+ at the Very Large Telescope in the context of small-scale magnetic field studies. Our targets also had their magnetic fields studied with optical spectra, which allowed us to compare magnetic field properties at different spatial scales on the stellar surface and to contrast small-scale magnetic field measurements at different wavelengths.

Methods: We analysed the Zeeman broadening signature for six magnetically sensitive and insensitive Fe I lines in the H-band to measure small-scale magnetic fields on the stellar surfaces of our sample. We used polarised radiative transfer modelling and non-local thermodynamic equilibrium departure coefficients in combination with Markov chain Monte Carlo sampling to determine magnetic field characteristics and non-magnetic stellar parameters. We used two different approaches to describe the small-scale magnetic fields. The first is a two-component model with a single magnetic region and a free magnetic field strength. The second model contains multiple magnetic components with fixed magnetic field strengths.

Results: We found average magnetic field strengths ranging from & SIM;0.4 kG down to < 0.1 kG. The results align closely with other results from high-resolution NIR spectrographs, such as SPIRou. It appears that the typical magnetic field strength in the magnetic region is slightly stronger than 1.3 kG, and for most stars in our sample, this strength is between 1 and 2 kG. We also found that the small-scale fields correlate with the large-scale fields and that the small-scale fields are at least ten times stronger than the large-scale fields inferred with Zeeman Doppler imaging. The two- and multi-component models produce systematically different results, as the strong fields from the multi-component model increase the obtained mean magnetic field strength. When comparing our results with the optical measurements of small-scale fields, we found a systematic offset two to three times stronger than fields in the optical results. This discrepancy cannot be explained by uncertainties in stellar parameters. Care should therefore be taken when comparing results obtained at different wavelengths until a clear cause can be established.

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
stars, magnetic field, solar-type, techniques, spectroscopic
National Category
Astronomy, Astrophysics and Cosmology Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-509279 (URN)10.1051/0004-6361/202346314 (DOI)001023434900010 ()
Funder
Swedish Research Council, 2019-03548Knut and Alice Wallenberg Foundation
Available from: 2023-08-23 Created: 2023-08-23 Last updated: 2023-08-23Bibliographically approved
Potravnov, I., Ryabchikova, T., Piskunov, N., Pakhomov, Y. & Kniazev, A. (2023). Doppler imaging of a southern ApSi star HD 152564. Monthly notices of the Royal Astronomical Society, 527(4), 10376-10387
Open this publication in new window or tab >>Doppler imaging of a southern ApSi star HD 152564
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2023 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 527, no 4, p. 10376-10387Article in journal (Refereed) Published
Abstract [en]

We present the results of the spectroscopic study of a chemically peculiar star HD 152564. Using medium-resolution (R = 37 000) observations obtained with the high-resolution fibre échelle spectrograph mounted on the South African Large Telescope, we determined atmospheric parameters Teff = 11 950 ± 200 K and log g = 3.6 ± 0.2 dex. Abundance analysis revealed mild deficiency of the light elements and an overabundance of up to ∼2 dex of metals, with the greatest excess for silicon. With these characteristics, HD 152564 is a typical member of the silicon subgroup of Ap stars. The rotational modulation of the light curve and line profiles of HD 152564 are typical for the inhomogeneous surface distribution of elements in its atmosphere. We performed multi-element Doppler imaging of the surface of HD 152564. Abundance maps constructed for He, O, Mg, Si, and Fe revealed the concentration of these elements in a sequence of equatorial spots as well as in the circumpolar rings. The photometric maximum of the light curve coincided with the visibility of two most overabundant silicon spots. Abundances determined from the different ionization stages of Fe and Si show clear evidence for vertical stratification of these elements in the atmosphere of HD 152564. Meanwhile, the horizontal distribution of silicon reconstructed from the lines of different ionization stages and excitation energies appears to be identical with increasing average abundance deeper in atmosphere.

Place, publisher, year, edition, pages
Oxford University Press, 2023
Keywords
stars: abundances, stars: chemically peculiar, stars: fundamental parameters, stars: imaging, stars: individual: HD 152564, starspots
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-524324 (URN)10.1093/mnras/stad3893 (DOI)001134499800013 ()
Available from: 2024-03-06 Created: 2024-03-06 Last updated: 2024-03-06Bibliographically approved
Wehrhahn, A., Piskunov, N. & Ryabchikova, T. (2023). PySME: Spectroscopy Made Easier. Astronomy and Astrophysics, 671, Article ID A171.
Open this publication in new window or tab >>PySME: Spectroscopy Made Easier
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 671, article id A171Article in journal (Refereed) Published
Abstract [en]

Context: The characterization of exoplanets requires the reliable determination of the fundamental parameters of their host stars. Spectral fitting plays an important role in this process. For the majority of stellar parameters, matching synthetic spectra to the observations provides a robust and unique solution for the fundamental parameters, such as effective temperature, surface gravity, abundances, radial and rotational velocities, among others.

Aims: Here, we present a new software package for fitting high-resolution stellar spectra that is easy to use, available for common platforms, and free from commercial licenses. We call it PySME. It is based on the proven Spectroscopy Made Easy package, later referred to as IDL SME or "original" SME.

Methods: The IDL (Interactive Data Language) part of the original SME code has been rewritten in Python, but we kept the efficient C++ and FORTRAN code responsible for molecular-ionization equilibrium, opacities, and spectral synthesis. In the process we updated some components of the optimization procedure to offer more flexibility and better analysis of the convergence. The result is a more modern package with the same functionality as the original SME.

Results: We applied PySME to a few stars of different spectral types and compared the derived fundamental parameters with the results from IDL SME and other techniques. We show that PySME works at least as well as the original SME.

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
Solar and Stellar Astrophysics (astro-ph.SR), Earth and Planetary Astrophysics (astro-ph.EP), Instrumentation and Methods for Astrophysics (astro-ph.IM), FOS: Physical sciences, FOS: Physical sciences
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-489813 (URN)10.1051/0004-6361/202244482 (DOI)000957946000003 ()
Available from: 2022-12-05 Created: 2022-12-05 Last updated: 2023-05-04Bibliographically approved
Lesjak, F., Nortmann, L., Yan, F., Cont, D., Reiners, A., Piskunov, N., . . . Shulyak, D. (2023). Retrieval of the dayside atmosphere of WASP-43b with CRIRES+. Astronomy and Astrophysics, 678, Article ID A23.
Open this publication in new window or tab >>Retrieval of the dayside atmosphere of WASP-43b with CRIRES+
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 678, article id A23Article in journal (Refereed) Published
Abstract [en]

Accurately estimating the C/O ratio of hot Jupiter atmospheres is a promising pathway towards understanding planet formation and migration, as well as the formation of clouds and the overall atmospheric composition. The atmosphere of the hot Jupiter WASP-43b has been extensively analysed using low-resolution observations with HST and Spitzer, but these previous observations did not cover the K band, which hosts prominent spectral features of major carbon-bearing species such as CO and CH4. As a result, the ability to establish precise constraints on the C/O ratio was limited. Moreover, the planet has not been studied at high spectral resolution, which can provide insights into the atmospheric dynamics. In this study, we present the first high-resolution dayside spectra of WASP-43b with the new CRIRES+ spectrograph. By observing the planet in the K band, we successfully detected the presence of CO and provide evidence for the existence of H2O using the cross-correlation method. This discovery represents the first direct detection of CO in the atmosphere of WASP-43b. Furthermore, we retrieved the temperature-pressure profile, abundances of CO and H2O, and a super-solar C/O ratio of 0.78 by applying a Bayesian retrieval framework to the data. Our findings also shed light on the atmospheric characteristics of WASP-43b. We found no evidence for a cloud deck on the dayside, and recovered a line broadening indicative of an equatorial super-rotation corresponding to a jet with a wind speed of similar to 5kms(-1), matching the results of previous forward models and low-resolution atmospheric retrievals for this planet.

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
planets and satellites: atmospheres, techniques: spectroscopic, planets and satellites: individual: WASP-43b
National Category
Astronomy, Astrophysics and Cosmology Aerospace Engineering
Identifiers
urn:nbn:se:uu:diva-518365 (URN)10.1051/0004-6361/202347151 (DOI)001083944300006 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2023-12-18 Created: 2023-12-18 Last updated: 2023-12-18Bibliographically approved
Bristow, P., Baruffolo, A., Smoker, J., Rodler, F., Dorn, R. J., Cumani, C., . . . Valenzuela, J. J. (2022). CRIRES+: Characterisation and preparation during the pandemic. In: Evans, CJ Bryant, JJ Motohara, K (Ed.), Ground-based and Airborne Instrumentation for Astronomy IX: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy IX, JUL 17-22, 2022, Montreal, CANADA. SPIE - International Society for Optical Engineering, Article ID 121845X.
Open this publication in new window or tab >>CRIRES+: Characterisation and preparation during the pandemic
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2022 (English)In: Ground-based and Airborne Instrumentation for Astronomy IX / [ed] Evans, CJ Bryant, JJ Motohara, K, SPIE - International Society for Optical Engineering, 2022, article id 121845XConference paper, Published paper (Refereed)
Abstract [en]

In early 2020 the upgraded(1) CRIRES2 instrument, was installed at the VLT, however the onset of the global pandemic prevented the completion of some aspects of the installation while characterisation and commissioning had to be conducted with a remote connection from Europe. This resulted in a somewhat experimental, ad-hoc, approach to characterisation that required tight co-ordination between Paranal scientists and the instrument team in Europe. Moreover, with the observatory operating at minimal staffing, we had to find workarounds for some unfinished parts of the installation and adapt our characterisation, calibration and operations strategies accordingly. In particular, we discuss the adaptation made to the metrology strategy that illustrates well the pragmatic and ultimately successful approach adopted for getting CRIRES+ ready for operations.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2022
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X ; 12184
Keywords
Instrument installation, remote testing, remote characterisation, Near infra-red spectrograph, high resolution spectrograh
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-488357 (URN)10.1117/12.2630207 (DOI)000860684700157 ()978-1-5106-5350-4 (ISBN)978-1-5106-5349-8 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy IX, JUL 17-22, 2022, Montreal, CANADA
Available from: 2022-11-15 Created: 2022-11-15 Last updated: 2022-11-15Bibliographically approved
Wehrhahn, A., Boldt-Christmas, L., Rains, A. D., Piskunov, N., Nortmann, L., Lesjak, F., . . . Seeman, U. (2022). CRIRES+ detection of H2O and CO in the transmission spectra of WASP-107 b.
Open this publication in new window or tab >>CRIRES+ detection of H2O and CO in the transmission spectra of WASP-107 b
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2022 (English)Manuscript (preprint) (Other academic)
Abstract [en]

WASP-107 b is a warm super-Neptune with a large extended atmosphere orbiting a bright K dwarf of solar composition. The planet's size and the brightness of its stellar host make it highly amenable to atmospheric characterisation, with previous detections of both He and H2O. We observe it here for the first time in high-resolution spectroscopy in the K-band. To obtain a transmission spectrum of the exoplanet atmosphere, we observe a transit event of WASP-107 b for a total of 5.4 hours (2.7 hours in transit) in the K-band with an average SNR = 64 for each exposure using the high-resolution infrared CRIRES+ spectrograph on the Very Large Telescope on Cerro Paranal, Chile. We aim to demonstrate the capabilities of this new instrument for exoplanet characterisation by searching for the presence of molecular features of key chemical species in the atmosphere with spectral lines detectable in this band, such as CO, CO2, H2O, and CH4. The search for particular chemical species is conducted by using the cross-correlation method on the observed spectra. The transit spectroscopy observations are first cleaned from the stellar and telluric features using the SYSREM algorithm, and the remaining spectral information is then compared to a model transmission spectrum. The model transmission spectrum is obtained using the petitRADTRANS code based on expectations for a warm Neptune-class planet and the observed orbital parameters. We report the detection of H2O in the atmosphere of WASP-107 b with 4.71 sigma significance, as well as a detection of CO at 3.46 sigma. The velocities of these detections show signs of atmospheric weather patterns, such as day-to-night-side temperature gradients. We do not detect the presence of CO2 or CH4. Our results confirm the chemical composition of the WASP-107 b's atmosphere and pave the way for efficient atmospheric studies of other planets of the same class. They show that the newly upgraded high-resolution spectrograph CRIRES+ is suitable for exoplanet transit observations. All detections and non-detections are in agreement with previous transmission studies of WASP-107 b based on low-resolution spectroscopy.

Publisher
p. 9
Keywords
planets and satellites: atmospheres, techniques: spectroscopic, planets and satellites: individuals: WASP-107b
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-489820 (URN)
Available from: 2022-12-06 Created: 2022-12-06 Last updated: 2022-12-09Bibliographically approved
Dorn, R. J., Bristow, P., Smoker, J., Rodler, F., Accardo, M., Van den Ancker, M., . . . Vernet, J. (2022). CRIRES+ on sky: High spectral resolution at infrared wavelength enabling better science at the ESO VLT. In: Evans, CJ, Bryant, JJ, Motohara, K (Ed.), Ground-Based And Airborne Instrumentation For Astronomy IX: . Paper presented at Conference on Ground-Based and Airborne Instrumentation for Astronomy IX, JUL 17-22, 2022, Montreal, Canada. SPIE - International Society for Optical Engineering, 12184, Article ID 121841F.
Open this publication in new window or tab >>CRIRES+ on sky: High spectral resolution at infrared wavelength enabling better science at the ESO VLT
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2022 (English)In: Ground-Based And Airborne Instrumentation For Astronomy IX / [ed] Evans, CJ, Bryant, JJ, Motohara, K, SPIE - International Society for Optical Engineering, 2022, Vol. 12184, article id 121841FConference paper, Published paper (Refereed)
Abstract [en]

CRIRES+ extended the capabilities of CRIRES, the CRyogenic InfraRed Echelle Spectrograph. It transformed this VLT instrument into a cross-dispersed spectrograph to increase the wavelength range that is covered simultaneously by a factor of ten. In addition, a new detector focal plane array of three Hawaii 2RG detectors with a 5.3 mu m cut-off wavelength replaced the existing detectors. Amongst many other improvements a new spectropolarimetric unit was added and the calibration system has been enhanced. The instrument was installed at the VLT on Unit Telescope 3 beginning of 2020 and successfully commissioned and verified for science operations during 2021, partly remote from Europe due to the pandemic. The instrument was subsequently offered to the community from October 2021 onwards. This article describes the performance and capabilities of this development and presents on sky results.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2022
Series
Proceedings of SPIE, ISSN 0277-786X, E-ISSN 1996-756X
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-488311 (URN)10.1117/12.2629969 (DOI)000860684700037 ()978-1-5106-5350-4 (ISBN)978-1-5106-5349-8 (ISBN)
Conference
Conference on Ground-Based and Airborne Instrumentation for Astronomy IX, JUL 17-22, 2022, Montreal, Canada
Available from: 2022-12-05 Created: 2022-12-05 Last updated: 2022-12-05Bibliographically approved
Ryabchikova, T., Piskunov, N. & Pakhomov, Y. (2022). Using Molecular Lines to Determine Carbon and Nitrogen Abundances in the Atmospheres of Cool Stars. Atoms, 10(4), Article ID 103.
Open this publication in new window or tab >>Using Molecular Lines to Determine Carbon and Nitrogen Abundances in the Atmospheres of Cool Stars
2022 (English)In: Atoms, E-ISSN 2218-2004, Vol. 10, no 4, article id 103Article in journal (Refereed) Published
Abstract [en]

Simultaneous analysis of the C2 and CN molecular bands in the 5100–5200 and 7930–8100 Å spectral regions is a promising alternative for the accurate determination of the carbon (C) and nitrogen (N) abundance in the atmospheres of the solar-like stars. Practical implementation of this new method became possible after recent improvements of the molecular constants for both molecules. The new molecular data predicted the correct line strength and line positions; therefore, they were included in the Vienna Atomic Line Database (VALD), which is widely used by astronomers and spectroscopists. In this paper, we demonstrate that the molecular data analysis provides C and, in particular, N abundances consistent with those derived from the atomic lines. We illustrate this by performing the analysis for three stars. Our results provide strong arguments for using the combination of C2 and CN molecular lines for accurate nitrogen abundance determination keeping in mind the difficulties of using the N i lines in the observed spectra of the solar-like stars.

Place, publisher, year, edition, pages
MDPI, 2022
Keywords
stellar spectra, atomic and molecular data, databases
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-493331 (URN)10.3390/atoms10040103 (DOI)000902217500001 ()
Available from: 2023-01-18 Created: 2023-01-18 Last updated: 2023-01-18Bibliographically approved
Projects
Ansökan om konferensbidrag: Inbjudan av talare till konferensen A Stellar Journey A symposium in celebration of Bengt Gustafsson´s 65th birthday, Uppsala, 23-27 juni 2008 [2008-01243_VR]; Uppsala UniversityWorkshop: Precision wavelength calibrations [2009-02823_VR]; Uppsala UniversityStars and Planets: Discovery and characterization [2010-04094_VR]; Uppsala UniversityVALD - an atomic and molecular database for spectroscopic applications [2010-05987_VR]; Uppsala University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5742-7767

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