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Pehlivan Rhodin, A., Hartman, H., Nilsson, H. & Jönsson, P. (2024). Accurate and experimentally validated transition data for Si I and Si II. Astronomy and Astrophysics, 682, Article ID A184.
Open this publication in new window or tab >>Accurate and experimentally validated transition data for Si I and Si II
2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A184Article in journal (Refereed) Published
Abstract [en]

Aims. The aim of this study is to provide radiative data for neutral and singly ionised silicon, in particular for the first experimental oscillator strengths for near-infrared Si I lines. In addition, we aim to perform atomic structure calculations both for neutral and singly ionised silicon while including lines from highly excited levels.

Methods. We performed large-scale atomic structure calculations with the relativistic multiconfiguration Dirac-Hartree-Fock method using the GRASP2K package to determine log(𝑔ƒ) values of Si I and Si II lines, taking into account valence-valence and core-valence electron correlation. In addition, we derived oscillator strengths of near-infrared Si I lines by combining the experimental branching fractions with radiative lifetimes from our calculations. The silicon plasma was obtained from a hollow cathode discharge lamp, and the intensity-calibrated high-resolution spectra between 1037 and 2655 nm were recorded by a Fourier transform spectrometer.

Results. We provide an extensive set of accurate experimental and theoretical log(𝑔ƒ) values. For the first time, we derived 17 log(𝑔ƒ) values of Si I lines in the infrared from experimental measurements. We report data for 1500 Si I lines and 500 Si II lines. The experimental uncertainties of our ƒ-values vary between 5% for the strong lines and 25% for the weak lines. The theoretical log(𝑔ƒ) values for Si I lines in the range 161 nm to 6340 nm agree very well with the experimental values of this study and complete the missing transitions involving levels up to 3s23p7s (61 970 cm−1). In addition, we provide accurate calculated log(𝑔ƒ) values of Si II lines from the levels up to 3s27f (122 483 cm−1) in the range 81 nm to 7324 nm.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
atomic data, methods: laboratory: atomic, methods: numerical, techniques: spectroscopic
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:mau:diva-66915 (URN)10.1051/0004-6361/202245686 (DOI)001178184800003 ()2-s2.0-85186144682 (Scopus ID)
Available from: 2024-04-25 Created: 2024-04-25 Last updated: 2024-04-25Bibliographically approved
Gull, T. R., Hartman, H., Teodoro, M., Hillier, D. J., Corcoran, M. F., Damineli, A., . . . Weigelt, G. (2023). Eta Carinae - The Dissipating Occulter Is an Extended Structure. Astrophysical Journal, 954(1), Article ID 104.
Open this publication in new window or tab >>Eta Carinae - The Dissipating Occulter Is an Extended Structure
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2023 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 954, no 1, article id 104Article in journal (Refereed) Published
Abstract [en]

Previous Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) longslit observations of Eta Carinae (η Car) identified numerous absorption features in both the stellar spectrum, and in the adjacent nebular spectra, along our line of sight (LOS). The absorption features became temporarily stronger when the ionizing far-ultraviolet radiation field was reduced by the periastron passage of the secondary star. Subsequently, dissipation of a dusty structure in our LOS has led to a long-term increase in the apparent brightness of η Car, an increase in the ionizing ultraviolet (UV) radiation, and the disappearance of absorption from multiple velocity-separated shells extending across the foreground Homunculus lobe. We use HST/STIS spectro-images, coupled with published infrared and radio observations, to locate this intervening dusty structure. The velocity and spatial information indicate the occulter is ≈1000 au in front of η Car. The Homunculus is a transient structure composed of dusty, partially ionized ejecta that eventually will disappear due to the relentless rain of ionizing radiation and wind from the current binary system along with dissipation and mixing with the interstellar medium. This evolving complex continues to provide an astrophysical laboratory that changes on human timescales.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2023
Keywords
Massive stars, 732, Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-62850 (URN)10.3847/1538-4357/acdcf9 (DOI)001054341100001 ()2-s2.0-85170052156 (Scopus ID)
Available from: 2023-09-27 Created: 2023-09-27 Last updated: 2023-10-10Bibliographically approved
Burheim, M., Hartman, H. & Nilsson, H. (2023). Experimental oscillator strengths of Al I lines for near-infrared astrophysical spectroscopy. Astronomy and Astrophysics, 672, Article ID A197.
Open this publication in new window or tab >>Experimental oscillator strengths of Al I lines for near-infrared astrophysical spectroscopy
2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 672, article id A197Article in journal (Refereed) Published
Abstract [en]

Context. Elemental abundances can be determined from stellar spectra, making it possible to study galactic formation and evolution. Accurate atomic data is essential for the reliable interpretation and modeling of astrophysical spectra. In this work, we perform laboratory studies on neutral aluminium. This element is found, for example, in young, massive stars and it is a key element for tracing ongoing nucleosynthesis throughout the Galaxy. The near-infrared (NIR) wavelength region is of particular importance, since extinction in this region is lower than for optical wavelengths. This makes the NIR wavelength region a better probe for highly obscured regions, such as those located close to the Galactic center.

Aims. We investigate the spectrum of neutral aluminium with the aim to provide oscillator strengths (f-values) of improved accuracy for lines in the NIR and optical regions (670–4200 nm).

Methods. Measurements of high-resolution spectra were performed using a Fourier transform spectrometer and a hollow cathode discharge lamp. The f-values were derived from experimental line intensities combined with published radiative lifetimes.

Results. We report oscillator strengths for 12 lines in the NIR and optical spectral regions, with an accuracy between 2 and 11%, as well as branching fractions for an additional 16 lines.

 

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
atomic data, methods: laboratory: atomic, techniques: spectroscopic
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-60505 (URN)10.1051/0004-6361/202245394 (DOI)000976785300010 ()2-s2.0-85156225882 (Scopus ID)
Funder
Swedish Research Council, 2016-04185
Available from: 2023-06-12 Created: 2023-06-12 Last updated: 2023-10-26Bibliographically approved
Damineli, A., Hillier, D. J., Navarete, F., Moffat, A. F. J., Weigelt, G., Corcoran, M. F., . . . Di Scala, G. (2023). The Long-term Spectral Changes of Eta Carinae: Are they Caused by a Dissipating Occulter as Indicated by CMFGEN Models?. Astrophysical Journal, 954
Open this publication in new window or tab >>The Long-term Spectral Changes of Eta Carinae: Are they Caused by a Dissipating Occulter as Indicated by CMFGEN Models?
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2023 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 954Article in journal (Refereed) Published
Abstract [en]

Eta Carinae (η Car) exhibits a unique set of P Cygni profiles with both broad and narrow components. Over many decades, the spectrum has changed-there has been an increase in observed continuum fluxes and a decrease in Fe II and H I emission-line equivalent widths. The spectrum is evolving toward that of a P Cygni star such as P Cygni itself and HDE 316285. The spectral evolution has been attributed to intrinsic variations such as a decrease in the mass-loss rate of the primary star or differential evolution in a latitudinal-dependent stellar wind. However, intrinsic wind changes conflict with three observational results: the steady long-term bolometric luminosity; the repeating X-ray light curve over the binary period; and the constancy of the dust-scattered spectrum from the Homunculus. We extend previous work that showed a secular strengthening of P Cygni absorptions by adding more orbital cycles to overcome temporary instabilities and by examining more atomic transitions. CMFGEN modeling of the primary wind shows that a time-decreasing mass-loss rate is not the best explanation for the observations. However, models with a small dissipating absorber in our line of sight can explain both the increase in brightness and changes in the emission and P Cygni absorption profiles. If the spectral evolution is caused by the dissipating circumstellar medium, and not by intrinsic changes in the binary, the dynamical timescale to recover from the Great Eruption is much less than a century, different from previous suggestions.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2023
Keywords
Stellar phenomena, Stellar mass loss, 1619, 1613, Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-62851 (URN)10.3847/1538-4357/ace596 (DOI)001106484600001 ()2-s2.0-85170544478 (Scopus ID)
Available from: 2023-09-27 Created: 2023-09-27 Last updated: 2023-12-27Bibliographically approved
Pickett, C. S., Richardson, N. D., Gull, T. R., Hillier, D. J., Hartman, H., Ibrahim, N., . . . Weigelt, G. (2022). Changes in the Na D-1 Absorption Components of eta Carinae Provide Clues on the Location of the Dissipating Central Occulter. Astrophysical Journal, 937(2), Article ID 85.
Open this publication in new window or tab >>Changes in the Na D-1 Absorption Components of eta Carinae Provide Clues on the Location of the Dissipating Central Occulter
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2022 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 937, no 2, article id 85Article in journal (Refereed) Published
Abstract [en]

The Na D absorption doublet in the spectrum of eta Carinae is complex, with multiple absorption features associated with the Great Eruption (1840s), the Lesser Eruption (1890s), and the interstellar clouds. The velocity profile is further complicated by the P Cygni profile originating in the system's stellar winds and blending with the He i lambda 5876 profile. The Na D profile contains a multitude of absorption components, including those at velocities of -145 km s(-1), -168 km s(-1), and +87 km s(-1), which we concentrate on in this analysis. Ground-based spectra recorded from 2008 to 2021 show significant variability of the -145 km s(-1) absorption throughout long-term observations. In the high-ionization phases of eta Carinae prior to the 2020 periastron passage, this feature disappeared completely but briefly reappeared across the 2020 periastron, along with a second absorption at -168 km s(-1). Over the past few decades, eta Carinae has been gradually brightening, which is shown to be caused by a dissipating occulter. The decreasing absorption of the -145 km s(-1) component, coupled with similar trends seen in absorptions of ultraviolet resonant lines, indicate that this central occulter was possibly a large clump associated with the Little Homunculus or another clump between the Little Homunculus and the star. We also report on a foreground absorption component at +87 km s(-1). Comparison of Na D absorption in the spectra of nearby systems demonstrates that this redshifted component likely originates in an extended foreground structure consistent with a previous ultraviolet spectral survey in the Carina Nebula.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2022
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-55381 (URN)10.3847/1538-4357/ac898f (DOI)000862124800001 ()2-s2.0-85139776297 (Scopus ID)
Available from: 2022-10-17 Created: 2022-10-17 Last updated: 2024-02-05Bibliographically approved
Gull, T. R., Hillier, D. J., Hartman, H., Corcoran, M. F., Damineli, A., Espinoza-Galeas, D., . . . Weigelt, G. (2022). Eta Carinae: An Evolving View of the Central Binary, Its Interacting Winds and Its Foreground Ejecta. Astrophysical Journal, 933(2), 1-28, Article ID 175.
Open this publication in new window or tab >>Eta Carinae: An Evolving View of the Central Binary, Its Interacting Winds and Its Foreground Ejecta
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2022 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 933, no 2, p. 1-28, article id 175Article in journal (Refereed) Published
Abstract [en]

FUV spectra of eta Car, recorded across two decades with HST/STIS, document multiple changes in resonant lines caused by dissipating extinction in our line of sight. The FUV flux has increased nearly tenfold, which has led to increased ionization of the multiple shells within the Homunculus and photodestruction of H-2. Comparison of observed resonant line profiles with CMFGEN model profiles allows separation of wind-wind collision and shell absorptions from the primary wind P Cygni profiles. The dissipating occulter preferentially obscured the central binary and interacting winds relative to the very extended primary wind. We are now able to monitor changes in the colliding winds with orbital phase. High-velocity transient absorptions occurred across the most recent periastron passage, indicating acceleration of the primary wind by the secondary wind, which leads to a downstream, high-velocity bow shock that is newly generated every orbital period. There is no evidence of changes in the properties of the binary winds.

Place, publisher, year, edition, pages
IOP Publishing Ltd, 2022
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-54119 (URN)10.3847/1538-4357/ac74c2 (DOI)000824070000001 ()2-s2.0-85134740173 (Scopus ID)
Available from: 2022-08-02 Created: 2022-08-02 Last updated: 2024-02-05Bibliographically approved
Gull, T. R., Navarete, F., Corcoran, M. F., Damineli, A., Espinoza, D., Hamaguchi, K., . . . Weigelt, G. (2021). Eta Carinae: A Tale of Two Periastron Passages. Astrophysical Journal, 923(1), 102-102
Open this publication in new window or tab >>Eta Carinae: A Tale of Two Periastron Passages
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2021 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 923, no 1, p. 102-102Article in journal (Refereed) Published
Abstract [en]

Since 2002, the far-ultraviolet (FUV) flux (1150–1680 Å) of Eta Carinae, monitored by the Hubble Space Telescope/Space Telescope Imaging Spectrograph, has increased by an order of magnitude. This increase is attributed to partial dissipation of a line-of-sight (LOS) occulter that blocks the central core of the system. Across the 2020 February periastron passage, changes in the FUV emission show a stronger wavelength dependence than occurred across the 2003 July periastron passage. Across both periastron passages, most of the FUV spectrum dropped in flux then recovered a few months later. The 2020 periastron passage included enhancements of FUV flux in narrow spectral intervals near periastron followed by a transient absorption and recovery to pre-periastron flux levels. The drop in flux is due to increased absorption by singly ionized species as the secondary star plunges deep into the wind of the primary star, which blocks the companion's ionizing radiation. The enhanced FUV emission is caused by the companion's wind-blown cavity briefly opening a window to deeper layers of the primary star. This is the first time transient brightening has been seen in the FUV comparable to transients previously seen at longer wavelengths. Changes in resonance line-velocity profiles hint that the dissipating occulter is associated with material in LOS moving at −100 to −300 km s−1, similar in velocity of structures previously associated with the 1890s lesser eruption

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2021
Keywords
Space and Planetary Science, Astronomy and Astrophysics
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-47504 (URN)10.3847/1538-4357/ac22a6 (DOI)000729981800001 ()2-s2.0-85122897490 (Scopus ID)
Available from: 2021-12-14 Created: 2021-12-14 Last updated: 2023-10-02Bibliographically approved
Hartman, H., Burheim, M., Nilsson, H., Li, W. & Jönsson, P. (2021). Laboratory Atomic Astrophysics for near-infrared Stellar Spectroscopy. In: : . Paper presented at The 20.5th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (CS20.5).
Open this publication in new window or tab >>Laboratory Atomic Astrophysics for near-infrared Stellar Spectroscopy
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2021 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Astronomical infrared observations are of increasing importance for stellar spectroscopy. The analysis of element abundance relies on high-quality observations, stellar models, and ultimately on accurate atomic data. With the growing number of near-IR astronomical observations and surveys, the absence of highaccuracy data is becoming apparent and a severe limiting factor.We run a program to take up the task to provide evaluated, high-accuracy atomic data for important transitions in the near-infrared spectral region, mainly 1-5 microns. A combinations of both experimental and theoretical techniques is used, to provide complete sets of data with a low uncertainty. FTS measurements of a discharge are combined with laser induced fluorescence techniques, and GRASP2k and ATSP2k atomic structure calculations for the theoretical values.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-47283 (URN)10.5281/zenodo.4564259 (DOI)
Conference
The 20.5th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (CS20.5)
Projects
https://mau.se/forskning/projekt/experimental-and-computational-atomic-astrophysics/
Funder
Swedish Research Council, 2016-04185
Available from: 2021-12-07 Created: 2021-12-07 Last updated: 2023-10-26Bibliographically approved
Weigelt, G., Hofmann, K.-H. -., Schertl, D., Lopez, B., Petrov, R. G., Lagarde, S., . . . Leinert, C. (2021). VLTI-MATISSE chromatic aperture-synthesis imaging of eta Carinae's stellar wind across the Br alpha line Periastron passage observations in February 2020. Astronomy and Astrophysics, 652, Article ID A140.
Open this publication in new window or tab >>VLTI-MATISSE chromatic aperture-synthesis imaging of eta Carinae's stellar wind across the Br alpha line Periastron passage observations in February 2020
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2021 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 652, article id A140Article in journal (Refereed) Published
Abstract [en]

Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis similar to 15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, eta Car A, is a luminous blue variable (LBV); the secondary, eta Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV eta Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of eta Car's WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Br alpha imaging of eta Car's distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of eta Car A's stellar windin several spectral channels distributed across the Br alpha 4.052 mu m line (spectral resolving power R similar to 960). Our observations were performed close to periastron passage in February 2020 (orbital phase similar to 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (similar to 14 au). The radius of the faintest outer wind regions is similar to 26 mas (similar to 60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 +/- 0.06 mas (6.54 +/- 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.

Place, publisher, year, edition, pages
EDP Sciences, 2021
Keywords
stars: winds, outflows, stars: individual: eta Carinae, stars: massive, stars: mass-loss, binaries: general, techniques: interferometric
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-62917 (URN)10.1051/0004-6361/202141240 (DOI)000688233900004 ()2-s2.0-85114009207 (Scopus ID)
Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2023-10-06Bibliographically approved
Li, W., Rynkun, P., Radziute, L., Gaigalas, G., Atalay, B., Papoulia, A., . . . Jönsson, P. (2020). Multiconfiguration Dirac-Hartree-Fock calculations of Lande g-factors for ions of astrophysical interest: B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II. Astronomy and Astrophysics, 639, Article ID A25.
Open this publication in new window or tab >>Multiconfiguration Dirac-Hartree-Fock calculations of Lande g-factors for ions of astrophysical interest: B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II
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2020 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 639, article id A25Article in journal (Refereed) Published
Abstract [en]

Aims. The Lande g-factor is an important parameter in astrophysical spectropolarimetry, used to characterize the response of a line to a given value of the magnetic field. The purpose of this paper is to present accurate Lande g-factors for states in B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II.Methods. The multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, which are implemented in the general-purpose relativistic atomic structure package GRASP2K, are employed in the present work to compute the Lande g-factors for states in B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II. The accuracy of the wave functions for the states, and thus the accuracy of the resulting Lande g-factors, is evaluated by comparing the computed excitation energies and energy separations with the National Institute of Standards and Technology (NIST) recommended data.Results. All excitation energies are in very good agreement with the NIST values except for Ti II, which has an average difference of 1.06%. The average uncertainty of the energy separations is well below 1% except for the even states of Al I; odd states of Si I, Ca I, Ti II, Zr III; and even states of Sn II for which the relative differences range between 1% and 2%. Comparisons of the computed Lande g-factors are made with available NIST data and experimental values. Analysing the LS-composition of the wave functions, we quantify the departures from LS-coupling and summarize the states for which there is a difference of more than 10% between the computed Lande g-factor and the Lande g-factor in pure LS-coupling. Finally, we compare the computed Lande g-factors with values from the Kurucz database.

Place, publisher, year, edition, pages
EDP Sciences, 2020
Keywords
atomic data, magnetic fields
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:mau:diva-17912 (URN)10.1051/0004-6361/202037794 (DOI)000550006800001 ()2-s2.0-85088087578 (Scopus ID)
Available from: 2020-08-13 Created: 2020-08-13 Last updated: 2024-02-05Bibliographically approved
Projects
External interactions and Nuclear Effects in Atoms for Plasma Diagnostics and Fundamental Physics; Malmö UniversityExperimental and computational atomic astrophysics; Malmö University; Publications
Burheim, M., Hartman, H. & Nilsson, H. (2023). Experimental oscillator strengths of Al I lines for near-infrared astrophysical spectroscopy. Astronomy and Astrophysics, 672, Article ID A197.
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9853-2555

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