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

**Authors:** Sarah Gebruers, Andrew Tkachenko, Dominic M. Bowman, Timothy Van Reeth, Siemen Burssens, Luc IJspeert, Laurent Mahy, Ilya Straumit, Maosheng Xiang, Hans-Walter Rix, Conny Aerts  
**arXiv:** [2206.11280](https://arxiv.org/abs/2206.11280)  
**Date:** 2022-06-22  
**Summary page:** https://www.summarizepaper.com/en/paper/2206.11280v1/

## Key points

- Study analyzes high-resolution FEROS spectroscopy for a sample of 166 B-type stars assembled from TESS photometry
- Spectroscopic data are necessary to break degeneracies in asteroseismic modelling of the interior structure in high- and intermediate-mass stars
- Precise photospheric stellar parameters derived for detailed asteroseismic studies through a homogeneous spectroscopic analysis
- Variability types of these stars are classified based on all currently available TESS sectors, almost all targets have at least one sector of TESS data available
- 26 spectroscopic double-lined binaries were identified, while the remainder of the sample includes 42 supergiants in the Large Magellanic Cloud (LMC) galaxy and 98 Galactic stars
- The spectra of the Galactic stars are analyzed with zeta-Payne, a machine learning-based spectrum analysis algorithm
- Five main surface parameters with average formal precisions: 70 K (Teff), 0.03 dex (logg), 0.07 dex ([M/H]), 8 km/s (vsini), and 0.7 km/s (vmicro)
- Average internal uncertainties found for FEROS spectra with their spectrum analysis method presented: 430 K (Teff), 0.12 dex (logg), 0.13 dex ([M/H]), 12 km/s (vsini), and 2 km/s (vmicro)
- Eight out of the 98 Galactic targets are fast rotating g-mode pulsators occurring between slowly pulsating B (SPB) stars and delta Scuti instability strips; their g-mode frequencies shifted to relatively high frequency values due to their rotation can be explained by gravity darkening effect as well as their apparently too low Teff relative to SPB instability region.
- Thirteen new HgMn stars were discovered among which only one is found in a binary system resulting in an unreliable low binary rate of 8%
- Sample selection and observations along with improvements made to the spectrum reduction pipeline are discussed in Sects 2 & 3 respectively
- Photometric & spectroscopic results are given in Sect 5; while internal uncertainties & peculiar stars discussed in Sect 6 along with obtained results placed into context of Hertzsprung Russell diagram by Langer & Kudritzki 2014
- Study provides valuable insights into asteroseismic modeling through precise photospheric stellar parameters derived from high resolution FEROS spectroscopy aiding future studies on interior structure modeling for these

## Summary

This study focuses on the analysis of high-resolution FEROS spectroscopy for a sample of 166 B-type stars assembled from TESS photometry. Spectroscopic data are necessary to break degeneracies in asteroseismic modelling of the interior structure in high- and intermediate-mass stars, and this work derives precise photospheric stellar parameters suitable for detailed asteroseismic studies through a homogeneous spectroscopic analysis. The variability types of these stars are classified based on all currently available TESS sectors, and almost all targets currently have at least one sector of TESS data available. The obtained high-resolution spectra for all 166 targets with the FEROS spectrograph in the context of a large program are analyzed using the Least-Squares Deconvolution method to investigate spectral line profile variability and detect binary systems. The results show that 26 spectroscopic double-lined binaries were identified, while the remainder of the sample includes 42 supergiants in the Large Magellanic Cloud (LMC) galaxy and 98 Galactic stars. The spectra of the Galactic stars are analyzed with zeta-Payne, a machine learning-based spectrum analysis algorithm. The study determines five main surface parameters with average formal precisions: 70 K (Teff), 0.03 dex (logg), 0.07 dex ([M/H]), 8 km/s (vsini), and 0.7 km/s (vmicro). The average internal uncertainties found for FEROS spectra with their spectrum analysis method are also presented: 430 K (Teff), 0.12 dex (logg), 0.13 dex ([M/H]), 12 km/s (vsini), and 2 km/s (vmicro). Furthermore, this work finds spectroscopic evidence that eight out of the 98 Galactic targets are fast rotating g-mode pulsators occurring between slowly pulsating B (SPB) stars and delta Scuti instability strips; their g-mode frequencies shifted to relatively high frequency values due to their rotation can be explained by gravity darkening effect as well as their apparently too low Teff relative to SPB instability region. Additionally, 13 new HgMn stars were discovered among which only one is found in a binary system resulting in an unreliable low binary rate of 8%. The sample selection and observations along with improvements made to the spectrum reduction pipeline are discussed in Sects 2 & 3 respectively; while Sect 4 presents classification results along with summary of zeta Payne framework & tests for specific set up used here. In Sect 5 both photometric & spectroscopic results are given; while internal uncertainties & peculiar stars discussed in Sect 6 along with obtained results placed into context of Hertzsprung Russell diagram by Langer & Kudritzki 2014 . Lastly Sect 7 concludes this study which provides valuable insights into asteroseismic modeling through precise photospheric stellar parameters derived from high resolution FEROS spectroscopy aiding future studies on interior structure modeling for these types of stars . To complement these data within this work , available TESS photometry was reanalyzed using simple aperture photometry(SAP) & pre data search conditioning(PDC SAP) light curves output from NASA SPOC pipeline downloaded from MAST2 . In most cases PDC SAP light curves were sufficient for variability classification ; however correcting instrumental effects to derive reliable lists of pulsation frequencies is subject to future work .