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Start Over Subject b stars Publisher CDS Content Level Research
1. Analysis of the B3IV star HD 43317
ID:
ivo://CDS.VizieR/J/A+A/542/A55
Title:
Analysis of the B3IV star HD 43317
Short Name:
J/A+A/542/A55
Date:
21 Oct 2021
Publisher:
CDS
Description:
OB stars are important building blocks of the Universe, but we have only a limited sample of them well understood enough from an asteroseismological point of view to provide feedback on the current evolutionary models. Our study adds one special case to this sample, with more observational constraints than for most of these stars. Our goal is to analyse and interpret the pulsational behaviour of the B3 IV star HD 43317 using the CoRoT light curve along with the ground-based spectroscopy gathered by the Harps instrument. This way we continue our efforts to map the Beta Cep and SPB instability strips. We used different techniques to reveal the abundances and fundamental stellar parameters from the newly-obtained high-resolution spectra. We used various time-series analysis tools to explore the nature of variations present in the light curve. We calculated the moments and used the pixel-by-pixel method to look for line profile variations in the high- resolution spectra. We find that HD 43317 is a single fast rotator (v_rot_~50%v_crit_) and hybrid SPB/Beta Cep-type pulsator with Solar metal abundances. We interpret the variations in photometry and spectroscopy as a result of rotational modulation connected to surface inhomogeneities, combined with the presence of both g and p mode pulsations. We detect a series of ten consecutive frequencies with an almost constant period spacing of 6339s as well as a second shorter sequence consisting of seven frequencies with a spacing of 6380s. The dominant frequencies fall in the regime of gravito- inertial modes.
2. APOGEE2-N NIR spectra of B-type stars
ID:
ivo://CDS.VizieR/J/ApJ/894/5
Title:
APOGEE2-N NIR spectra of B-type stars
Short Name:
J/ApJ/894/5
Date:
19 Jan 2022 00:59:33
Publisher:
CDS
Description:
We present a semi-empirical spectral classification scheme for normal B-type stars using near-infrared (NIR) spectra (1.5-1.7{mu}m) from the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment (APOGEE2)-N data release 14 (DR14) database. The main motivation for working with B-type stars is their importance in the evolution of young stellar clusters; however, we also take advantage of having a numerous sample (316 stars) of B-type star candidates in APOGEE2-N, for which we also have optical (3600-9100{AA}) counterparts from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey. By first obtaining an accurate spectral classification of the sources using the LAMOST DR3 spectra and the canonical spectral classification scheme, we found a linear relation between optical spectral types and the equivalent widths of the hydrogen lines of the Brackett series in the APOGEE2-N NIR spectra. This relation extends smoothly from a similar relation for O and early B stars found by Roman-Lopes+ (2018, J/ApJ/855/68). This way, we obtain a catalog of B-type sources with features in both the optical and NIR and a classification scheme refined down to one spectral subclass.
3. AS 78 & MWC 657 spectroscopy
ID:
ivo://CDS.VizieR/J/A+AS/147/5
Title:
AS 78 & MWC 657 spectroscopy
Short Name:
J/A+AS/147/5
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of low- and high-resolution spectroscopic and multicolour photometric observations of two early-type emission-line stars, AS 78 and MWC 657. They were identified by Dong & Hu (1991ChA&A..15..275D) with the IRAS sources 03549+5602 and 22407+6008, respectively, among many other sources displaying a very strong infrared excess, V-[25]>=8mag. AS 78 is recognized as a photometric variable for the first time. A large near-IR excess radiation is detected in AS 78 and confirmed by new, higher-quality, data for MWC 657. Significant variations in the Balmer line profiles are detected for both objects. Modelling of the Balmer line profiles of AS 78 obtained in 1994 yields the following parameters of the star and its wind: T_eff_~17000K, logL_bol_/L_{sun}_~4.0, dM/dt~10^-6^M_{sun}_/yr. The photometric and new spectroscopic data indicate that the star's T_eff_ increases with time, while the stellar wind changes its structure. Distances towards both objects are estimated on the basis of their radial velocities and the galactic rotation curve. Consideration of different options about the nature and evolutionary state of both objects leads us to suggest that they are binary systems containing a B-type intermediate-luminosity star and a gaseous disk around the less luminous component.
4. A spectroscopic orbit for Regulus
ID:
ivo://CDS.VizieR/J/ApJ/682/L117
Title:
A spectroscopic orbit for Regulus
Short Name:
J/ApJ/682/L117
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a radial velocity study of the rapidly rotating B star Regulus that indicates the star is a single-lined spectroscopic binary. The orbital period (40.11 days) and probable semimajor axis (0.35AU) are large enough that the system is not interacting at present. However, the mass function suggests that the secondary has a low mass (M_2_>0.30M_{sun}_), and we argue that the companion may be a white dwarf. Such a star would be the remnant of a former mass donor that was the source of the large spin angular momentum of Regulus itself.
5. A stellar rotation census of B stars
ID:
ivo://CDS.VizieR/J/ApJ/722/605
Title:
A stellar rotation census of B stars
Short Name:
J/ApJ/722/605
Date:
21 Oct 2021
Publisher:
CDS
Description:
Two recent observing campaigns provide us with moderate dispersion spectra of more than 230 cluster and 370 field B stars. Combining them and the spectra of the B stars from our previous investigations (~430 cluster and ~100 field B stars) yields a large, homogeneous sample for studying the rotational properties of B stars. We derive the projected rotational velocity vsini, effective temperature, gravity, mass, and critical rotation speed V_crit_ for each star. We compare the evolutionary trends of rotation (measured according to the polar gravity of the star) with recent models that treat internal mixing.
6. Asteroseismology of KIC 10526294
ID:
ivo://CDS.VizieR/J/A+A/580/A27
Title:
Asteroseismology of KIC 10526294
Short Name:
J/A+A/580/A27
Date:
21 Oct 2021
Publisher:
CDS
Description:
KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra diffusive mixing. We find a tight mass, metallicity relation within the ranges M~3.13 to 3.25M_{sun}_ and Z~0.014 to 0.028. We deduce that an exponentially decaying diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of f_ov between 0.017 and 0.018. Moreover, the inclusion of extra diffusive mixing with a value of log D_mix between 1.75 and 2.00dex (with Dmix in cm^2^/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra mixing is considered, irrespective of the (M,Z) combination within the allowed seismic range. The inclusion of diffusive mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
7. Bayesian statistics for massive stars
ID:
ivo://CDS.VizieR/J/MNRAS/454/28
Title:
Bayesian statistics for massive stars
Short Name:
J/MNRAS/454/28
Date:
21 Oct 2021
Publisher:
CDS
Description:
Spectral analysis is a powerful tool to investigate stellar properties and it has been widely used for decades now. However, the methods considered to perform this kind of analysis are mostly based on iteration among a few diagnostic lines to determine the stellar parameters. While these methods are often simple and fast, they can lead to errors and large uncertainties due to the required assumptions. Here, we present a method based on Bayesian statistics to find simultaneously the best combination of effective temperature, surface gravity, projected rotational velocity, and microturbulence velocity, using all the available spectral lines. Different tests are discussed to demonstrate the strength of our method, which we apply to 54 mid-resolution spectra of field and cluster B stars obtained at the Observatoire du Mont-Megantic. We compare our results with those found in the literature. Differences are seen which are well explained by the different methods used. We conclude that the B-star microturbulence velocities are often underestimated. We also confirm the trend that B stars in clusters are on average faster rotators than field B stars.
8. B6-B9.5 stars abundance analysis
ID:
ivo://CDS.VizieR/J/A+A/506/213
Title:
B6-B9.5 stars abundance analysis
Short Name:
J/A+A/506/213
Date:
21 Oct 2021
Publisher:
CDS
Description:
The CoRoT satellite is collecting precise time-resolved photometry for tens of asteroseismology targets. To ensure a correct interpretation of the CoRoT data, the atmospheric parameters, chemical compositions, and rotational velocities of the stars must be determined. The main goal of the ground-based seismology support program for the CoRoT mission was to obtain photometric and spectroscopic data for stars in the fields monitored by the satellite. These ground-based observations were collected in the GAUDI archive. High-resolution spectra of more than 200 B-type stars are available in this database, and about 45% of them is analysed here. To derive the effective temperature of the stars, we used photometric indices. Surface gravities were obtained by comparing observed and theoretical Balmer line profiles. To determine the chemical abundances and rotational velocities, we used a spectrum synthesis method, which consisted of comparing the observed spectrum with theoretical ones based on the assumption of LTE. Atmospheric parameters, chemical abundances, and rotational velocities were determined for 89 late-B stars. The dominant species in their spectra are iron-peak elements. The average Fe abundance is 7.24+/-0.45dex. The average rotational velocity is 126km/s, but there are 13 and 20 stars with low and moderate Vsini values, respectively. The analysis of this sample of 89 late B-type stars reveals many chemically peculiar (CP) stars. Some of them were previously known, but at least 9 new CP candidates, among which at least two HgMn stars, are identified in our study. These CP stars as a group exhibit Vsini values lower than the stars with normal surface chemical composition.
9. BEAST sample properties
ID:
ivo://CDS.VizieR/J/A+A/646/A164
Title:
BEAST sample properties
Short Name:
J/A+A/646/A164
Date:
21 Oct 2021
Publisher:
CDS
Description:
While the occurrence rate of wide giant planets appears to increase with stellar mass at least up through the A-type regime, B-type stars have so far not been systematically studied in large scale surveys. It therefore remains unclear up to what stellar mass this occurrence trend continues. The B-star Exoplanet Abundance Study (BEAST) is a direct imaging survey with the Extreme Adaptive Optics instrument SPHERE, targeting 85 B-type stars in the young Scorpius-Centaurus (Sco-Cen) region with the aim of detecting giant planets at wide separations and constraining their occurrence rate and physical properties. The statistical outcome of the survey will help determining if and where an upper stellar mass limit for planet formation occurs. Here, we describe the selection and characterization of the BEAST target sample.
10. Binary red supergiants. II. B-type companions
ID:
ivo://CDS.VizieR/J/ApJ/875/124
Title:
Binary red supergiants. II. B-type companions
Short Name:
J/ApJ/875/124
Date:
20 Jan 2022 11:13:46
Publisher:
CDS
Description:
The percentage of massive main-sequence OB stars in binary systems is thought to be as high as 100%. However, very few Galactic binary red supergiants (RSGs) have been identified, despite the fact that these stars are the evolved descendants of OB stars. As shown in our recent paper, binary RSGs will likely have B-type companions, as dictated by stellar evolution considerations. Such a system will have a very unique photometric signature due to the shape of the spectral energy distribution. Using photometric cutoffs, it should therefore be possible to detect candidate RSG+B star binary systems. Here we present our spectroscopic follow-up observations of such candidates. Out of our initial list of 280 candidates in M31 and M33, we observed 149 and confirmed 63 as newly discovered RSG+B star binary systems. Additional spectra of four candidate systems in the Small Magellanic Cloud confirmed all of them as new RSG+B star binaries including the first known RSG+Be star system. By fitting BSTAR06 and MARCS model atmospheres to the newly obtained spectra, we place estimates on the temperatures and subtypes of both the B stars and RSGs. Overall, we have found 87 new RSG+B star binary systems in M31, M33 and the Small and Large Magellanic Clouds. Our future studies are aimed at determining the binary fraction of RSGs.

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