Stellar labels for hot stars from low-resolution spectra

Xiang, Maosheng; Rix, Hans─Walter; Ting, Yuan-Sen; Kudritzki, Rolf‐Peter; Conroy, Charlie; Zari, E.; Shi, Jianrong; Przybilla, N.; Ramírez-Tannus, M. C.; Tkachenko, A.; Gebruers, Sarah; Liu, Xiaowei

doi:10.1051/0004-6361/202141570

Cited by 60 publications

(50 citation statements)

References 130 publications

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“…The importance of B-type supergiants in this context lies in their large luminosities, so that sight lines to very distant parts of the Milky Way may become traceable in the era of large spectroscopic surveys (e.g. Xiang et al 2022). A comparison with stellar evolution models then also allows the fundamental parameters to be determined.…”

Section: Discussionmentioning

confidence: 99%

Quantitative spectroscopy of B-type supergiants

Weßmayer

Przybilla

Butler

2022

A&A

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Context. B-type supergiants are versatile tools to address a number of highly-relevant astrophysical topics, ranging from stellar atmospheres over stellar and galactic evolution to the characterisation of interstellar sightlines and to the cosmic distance scale. Aims. A hybrid non-LTE (local thermodynamic equilibrium) approach -involving line-blanketed model atmospheres computed under the assumption of LTE in combination with line formation calculations that account for deviations from LTE -is tested for quantitative analyses of B-type supergiants of mass up to about 30 M , characterising a sample of 14 Galactic objects in a comprehensive way. Methods. Hydrostatic plane-parallel atmospheric structures and synthetic spectra computed with Kurucz's Atlas12 code together with the non-LTE line-formation codes Detail/Surface are compared to results from full non-LTE calculations with Tlusty, and the effects of turbulent pressure on the models are investigated. High-resolution spectra at signal-to-noise ratio > 130 are analysed for atmospheric parameters, using Stark-broadened hydrogen lines and multiple metal ionisation equilibria, and for elemental abundances. Fundamental stellar parameters are derived by considering stellar evolution tracks and Gaia early data release 3 (EDR3) parallaxes. Interstellar reddening and the reddening law along the sight lines towards the target stars are determined by matching model spectral energy distributions to observed ones. Results. Our hybrid non-LTE approach turns out to be equivalent to hydrostatic full non-LTE modelling for the deeper photospheric layers of the B-type supergiants under consideration, where most lines of the optical spectrum are formed. Turbulent pressure can become relevant for microturbulent velocities larger than 10 km s −1 . The changes in the atmospheric density structure affect many diagnostic lines, implying systematic changes in atmospheric parameters, for instance an increase in surface gravities by up to 0.05 dex. A high precision and accuracy is achieved for all derived parameters by bringing multiple indicators to agreement simultaneously. Effective temperatures are determined to 2-3% uncertainty, surface gravities to better than 0.07 dex, masses to about 5%, radii to about 10%, luminosities to better than 25%, and spectroscopic distances to 10% uncertainty typically. Abundances for chemical species that are accessible from the optical spectra (He, C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe) are derived with uncertainties of 0.05 to 0.10 dex (1σ standard deviations). The observed spectra are reproduced well by the model spectra. The derived N/C versus N/O ratios tightly follow the predictions from Geneva stellar evolution models that account for rotation, and spectroscopic and Gaia EDR3 distances are closely matched. Finally, the methodology is tested for analyses of intermediate-resolution spectra of extragalactic B-type supergiants.

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Section: Discussionmentioning

confidence: 99%

Quantitative spectroscopy of B-type supergiants

Weßmayer

Przybilla

Butler

2022

A&A

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“…Recently, Hawkins (2022) mapped azimuthal variations in the Galactic disc, using both Gaia DR3 data and sample OBAFtype stars from the LAMOST survey published by Xiang et al (2022). Using the LAMOST sample, the author found an azimuthal structure on top of the radial gradient, which does not necessarily follow the spiral arms.…”

Section: Discussionmentioning

confidence: 99%

The chemical signature of the Galactic spiral arms revealed by Gaia DR3

Poggio

Recio–Blanco

Palicio

et al. 2022

A&A

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Taking advantage of the recent Gaia Data Release 3 (DR3), we mapped chemical inhomogeneities in the Milky Way's disc out to a distance of ∼ 4 kpc from the Sun, using different samples of bright giant stars. The samples were selected using effective temperatures and surface gravities from the GSP-Spec module, and they are expected to trace stellar populations of a different typical age. The cool (old) giants exhibit a relatively smooth radial metallicity gradient with an azimuthal dependence. Binning in Galactic azimuth ϕ, the slope gradually varies from d[M/H]/dR ∼ −0.054 dex kpc −1 at ϕ ∼ −20 • to ∼ −0.036 dex kpc −1 at ϕ ∼ 20 • . On the other hand, the relatively hotter (and younger) stars present remarkable inhomogeneities, which are apparent as three (possibly four) metal-rich elongated features in correspondence with the spiral arms' locations in the Galactic disc. When projected onto the Galactic radius, those features manifest themselves as statistically significant bumps on top of the observed radial metallicity gradients with amplitudes up to ∼ 0.05−0.1 dex, making the assumption of a linear radial decrease not applicable for this sample. The strong correlation between the spiral structure of the Galaxy and the observed chemical pattern in the young sample indicates that the spiral arms might be at the origin of the detected chemical inhomogeneities. In this scenario, the spiral arms would leave a strong signature in the younger stars which progressively disappears when cooler (and older) giants are considered.

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“…8). In their recent study of OBA-type stars in the LAMOST survey, Xiang et al (2022) demonstrated that the impact of NLTE effects on the spectroscopically inferred T eff values is negligible for stars cooler than 25 000 K. In particular, the authors showed an overall good consistency between the Kurucz LTE and Potsdam Wolf-Rayet (PoWR; Hainich et al 2019) NLTE models at T eff 25 000 K (their Figs. C.1 and C.2), and reported a good agreement between the parameters obtained with the LTE and NLTE models for stars below that same T eff cut-off value (their Fig.…”

Section: Spectrum Analysis With Zeta-paynementioning

confidence: 96%

Analysis of high-resolution FEROS spectroscopy for a sample of variable B-type stars assembled from TESS photometry,

Gebruers

Tkachenko

Bowman

et al. 2022

A&A

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Context. Spectroscopic data are necessary to break degeneracies in the asteroseismic modelling of the interior structure in high-and intermediate-mass stars. With the TESS mission, the number of bright intermediate-mass B-type stars with long photometric light curves that are suitable for detailed asteroseismic studies has increased substantially compared to the pre-TESS era. Aims. We derive precise photospheric stellar parameters for a sample of 166 B-type stars with TESS light curves through a homogeneous spectroscopic analysis. The variability types of these sample stars are also classified based on all currently available TESS sectors, and they are ultimately prioritised according to their astrophysical potential. Methods. We obtained high-resolution spectra for all 166 targets with the FEROS spectrograph in the context of a large program. The spectra were reduced with the CERES pipeline, which we adapted to improve the quality of the reduced spectra. These spectra were subsequently analysed with zeta-Payne, a machine-learning-based spectrum analysis algorithm, to infer precise stellar labels for all stars in the sample. Furthermore, the least-squares deconvolution (LSD) method was employed to investigate spectral line profile variability (LPV) and isolate binary systems from presumably single stars. Results. The LSD profile analysis identified 26 spectroscopic double-lined binaries; the remainder of the sample are 42 supergiants in the Large Magellanic Cloud galaxy and 98 Galactic stars, both with and without apparent LPV. For the Galactic single stars and singlelined spectroscopic binaries, we determine their five main surface parameters: effective temperature (T eff ), surface gravity (log g), global metallicity ([M/H]), projected rotational velocity (v sin i), and microturbulent velocity (ξ) with average formal precisions of 70 K, 0.03 dex, 0.07 dex, 8 km s −1 , and 0.7 km s −1 , respectively. The average internal uncertainties we find for FEROS spectra with our spectrum analysis method are 430 K (T eff ), 0.12 dex (log g), 0.13 dex ([M/H]), 12 km s −1 (v sin i), and 2 km s −1 (ξ). Conclusions. We find spectroscopic evidence that 8 of the 98 galactic single or SB1 variables are fast-rotating gravity-mode pulsators occurring in between the slowly pulsating B (SPB) stars and δ Scuti instability strips. The g-mode frequencies of these pulsators are shifted to relatively high frequency values due to their rotation, and their apparently too low T eff relative to the SPB instability region can in most cases be explained by the gravity darkening effect. We also discover 13 new HgMn stars in the Galactic sample of which only one is found in a spectroscopic binary, resulting in a biased and therefore unreliable low binary rate of only 8%.

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Stellar labels for hot stars from low-resolution spectra

Cited by 60 publications

References 130 publications

Quantitative spectroscopy of B-type supergiants

Quantitative spectroscopy of B-type supergiants

The chemical signature of the Galactic spiral arms revealed by Gaia DR3

Analysis of high-resolution FEROS spectroscopy for a sample of variable B-type stars assembled from TESS photometry,

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