scholarly journals Progress in the study of pulsating subdwarf B stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 589-595
Author(s):  
M. D Reed
Keyword(s):  
Differential Rotation ◽  
Observational Constraints ◽  
Interior Structure ◽  
Horizontal Branch ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Rotation Periods ◽  
Horizontal Branch Stars ◽  
Short Period

AbstractDuring Kepler's main mission, nearly 20 pulsating subdwarf B (sdB: extreme horizontal branch stars) were discovered. Many of these stars were observed for three years, accumulating over 1.5 million observations. Only through these extended observations have we been able to identify pulsation modes, applying constraints for structure models. Discoveries include nearly-evenly-spaced asymptotic period overtones which represent the interior structure and rotationally-induced frequency multiplets from which we have learned that rotation periods are long, even when in short-period binaries. This paper reviews progress on observational constraints and highlights some of our discoveries including radially differential rotation, conflicting stratification indicators and mode lifetimes.

scholarly journals Some Blue Stars of Peculiar Type in the Region of the South Galactic Pole

1973 ◽  
Vol 50 ◽  
pp. 245-250
Author(s):  
J. A. Graham ◽  
A. Slettebak
Keyword(s):  
Classification Criteria ◽  
Type Star ◽  
Horizontal Branch ◽  
The South ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Horizontal Branch Stars ◽  
Photometric Observations ◽  
Late Type Star ◽  
Objective Prism

uvby photometric observations have been used in conjunction with slit spectra to classify 90 stars which were noted as peculiar by Slettebak and Brundage in a recent objective prism survey of the South Galactic Pole region. In this paper, we review the photometric classification criteria and identify in the Slettebak-Brundage list, 8 subdwarf O stars, 10 subdwarf B stars, 10 horizontal branch stars, 1 white dwarf star and 26 late subdwarf stars. Three stars with outstanding peculiarities are SB (Slettebak-Brundage) 58 which is a helium subdwarf O star, SB 319 (CD–38°245), a late type star with extremely weak metal lines and SB 845 (BD–13°6465), an A type star with a very small Balmer discontinuity.

scholarly journals K2 observations of the pulsating subdwarf B stars UY Sex and V1405 Ori

2020 ◽  
Vol 492 (4) ◽  
pp. 5202-5217
Author(s):  
M D Reed ◽  
M Yeager ◽  
J Vos ◽  
J H Telting ◽  
R H Østensen ◽  
...  
Keyword(s):  
Rotation Period ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Fundamental Properties ◽  
The Core ◽  
Rotation Periods ◽  
Short Period ◽  
Marginal Detection

ABSTRACT We processed and analysed K2 observations of the pulsating subdwarf-B (sdBV) stars UY Sex and V1405 Ori. We detect 97 p-mode pulsations in UY Sex while we discover V1405 Ori to be a rare rich hybrid pulsator with over 100 p-mode pulsations and 19 g-mode pulsations. We detect frequency multiplets, which we use to identify pulsation modes as well as determine rotation periods. For UY Sex, we find a rotation period of the envelope of 24.6 ± 3.5 d and for V1405 Ori, we find a rotation period of 0.555 ± 0.029 d for the p modes and a marginal detection of 4.2 ± 0.4 d for the g modes. We discover that V1405 Ori is unique among sdBV stars observed to date. It is a rich hybrid pulsator, allowing us to simultaneously probe the envelope and interior; its frequency multiplets indicate V1405 Ori to be rotating differentially with the core rotating more slowly than the envelope, and it is also in a short-period binary (0.398 d) with an envelope that is nearly but not quite tidally locked. For both stars, we have obtained spectroscopic follow-up observations and examine combining them with Gaia parallaxes and archival photometry to determine fundamental properties. Our derived masses are inconsistent with spectroscopy and previous determinations and indicate problems with the methodology.

scholarly journals Why do hot subdwarf stars pulsate?

2015 ◽  
Vol 11 (A29B) ◽  
pp. 521-524
Author(s):  
Stephan Geier
Keyword(s):  
Red Giants ◽  
Horizontal Branch ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Long Period ◽  
Sdb Stars ◽  
Short Period ◽  
Instability Regions

AbstractHot subdwarf B stars (sdBs) are the stripped cores of red giants located at the bluest extension of the horizontal branch. Several different kinds of pulsators are found among those stars. The mechanism that drives those pulsations is well known and the theoretically predicted instability regions for both the short-period p-mode and the long-period g-mode pulsators match the observed distributions fairly well. However, it remains unclear why only a fraction of the sdB stars pulsate, while stars with otherwise very similar parameters do not show pulsations. From an observers perspective I review possible candidates for the missing parameter that makes sdB stars pulsate or not.

scholarly journals TESS observations of pulsating subdwarf B stars: extraordinarily short-period gravity modes in CD−28° 1974

2020 ◽  
Vol 493 (4) ◽  
pp. 5162-5169 ◽  
Author(s):  
M D Reed ◽  
K A Shoaf ◽  
P Németh ◽  
J Vos ◽  
M Uzundag ◽  
...  
Keyword(s):  
Main Sequence ◽  
Orbital Motion ◽  
Proper Motions ◽  
Reflection Effect ◽  
Echelle Spectrograph ◽  
Single Star ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Short Period ◽  
Typical Period

ABSTRACT Transiting Exoplanet Survey Satellite (TESS) observations show CD−28° 1974 to be a gravity(g)-mode-dominated hybrid pulsating subdwarf B (sdBV) star. It shows 13 secure periods that form an ℓ = 1 asymptotic sequence near the typical period spacing. Extraordinarily, these periods lie between 1500 and 3300 s, whereas typical $\ell = 1\, g$ modes in sdBV stars occur between 3300 and 10 000 s. This indicates a structure somewhat different from typical sdBV stars. CD−28° 1974 has a visually close F/G main-sequence companion 1.33 arcsec away, which may be a physical companion. Gaia proper motions indicate a comoving pair with the same distance. A reanalysis of Ultraviolet and Visual Echelle Spectrograph (UVES) spectra failed to detect any orbital motion and the light curve shows no reflection effect or ellipsoidal variability, making an unseen close companion unlikely. The implication is that CD−28° 1974 has become a hot subdwarf via single star or post-merger evolution.

scholarly journals Differential rotation in convective envelopes: constraints from eclipsing binaries

2019 ◽  
Vol 491 (1) ◽  
pp. 690-707 ◽  
Author(s):  
Adam S Jermyn ◽  
Jamie Tayar ◽  
Jim Fuller
Keyword(s):  
Differential Rotation ◽  
Orbital Period ◽  
Binary Systems ◽  
Rotation Period ◽  
Eclipsing Binaries ◽  
Rotation Periods ◽  
Short Period ◽  
Orbital Periods ◽  
The Difference ◽  
Surface Convection

ABSTRACT Over time, tides synchronize the rotation periods of stars in a binary system to the orbital period. However, if the star exhibits differential rotation, then only a portion of it can rotate at the orbital period, so the rotation period at the surface may not match the orbital period. The difference between the rotation and orbital periods can therefore be used to infer the extent of the differential rotation. We use a simple parametrization of differential rotation in stars with convective envelopes in circular orbits to predict the difference between the surface rotation period and the orbital period. Comparing this parametrization to observed eclipsing binary systems, we find that in the surface convection zones of stars in short-period binaries there is very little radial differential rotation, with |r∂rln Ω| < 0.02. This holds even for longer orbital periods, though it is harder to say which systems are synchronized at long periods, and larger differential rotation is degenerate with asynchronous rotation.

scholarly journals First Kepler results on compact pulsators - V. Slowly pulsating subdwarf B stars in short-period binaries

2010 ◽  
Vol 409 (4) ◽  
pp. 1509-1517 ◽  
Author(s):  
S. D. Kawaler ◽  
M. D. Reed ◽  
R. H. Østensen ◽  
S. Bloemen ◽  
D. W. Kurtz ◽  
...  
Keyword(s):  
B Stars ◽  
Subdwarf B Stars ◽  
Short Period

scholarly journals The EC14026 Stars - Pulsating Hot Subdwarfs

1998 ◽  
Vol 185 ◽  
pp. 361-366
Author(s):  
C. Koen ◽  
D. O'Donoghue ◽  
D. Kilkenny ◽  
R.S. Stobie
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Plane ◽  
Cataclysmic Variables ◽  
Galactic Nuclei ◽  
Horizontal Branch ◽  
Stellar Objects ◽  
B Stars ◽  
Horizontal Branch Stars ◽  
Blue Object ◽  
Hot Subdwarfs

The Edinburgh-Cape Blue Object Survey (Stobie et al. 1997a) is a southern hemisphere survey to discover hot, blue stellar objects brighter than B=18 at galactic latitudes more than 30° from the galactic plane. The main categories of object detected are hot subdwarfs, white dwarfs, blue horizontal branch stars, apparently normal B stars, cataclysmic variables and (stellar-like) active galactic nuclei. Over 50% of the EC Survey comprises hot subdwarfs.

scholarly journals Mode identification in three pulsating hot subdwarfs observed with TESS satellite

2020 ◽  
Vol 495 (3) ◽  
pp. 2844-2857
Author(s):  
S K Sahoo ◽  
A S Baran ◽  
U Heber ◽  
J Ostrowski ◽  
S Sanjayan ◽  
...  
Keyword(s):  
Spectral Energy ◽  
Data Sets ◽  
B Stars ◽  
Mode Identification ◽  
Subdwarf B Stars ◽  
Stellar Oscillations ◽  
Horizontal Branch Stars ◽  
Trigonometric Parallaxes ◽  
Hot Subdwarfs ◽  
Stellar Masses

ABSTRACT We report on the detection of pulsations of three pulsating subdwarf B stars observed by the Transiting Exoplanet Survey Satellite (TESS) satellite and our results of mode identification in these stars based on an asymptotic period relation. SB 459 (TIC 067584818), SB 815 (TIC 169285097), and PG 0342 + 026 (TIC 457168745) have been monitored during single sectors resulting in 27 d coverage. These data sets allowed for detecting, in each star, a few tens of frequencies that we interpreted as stellar oscillations. We found no multiplets, though we partially constrained mode geometry by means of period spacing, which recently became a key tool in analyses of pulsating subdwarf B stars. Standard routine that we have used allowed us to select candidates for trapped modes that surely bear signatures of non-uniform chemical profile inside the stars. We have also done statistical analysis using collected spectroscopic and asteroseismic data of previously known subdwarf B stars along with our three stars. Making use of high precision trigonometric parallaxes from the Gaia mission and spectral energy distributions we converted atmospheric parameters to stellar ones. Radii, masses, and luminosities are close to their canonical values for extreme horizontal branch stars. In particular, the stellar masses are close to the canonical one of 0.47 M⊙ for all three stars but uncertainties on the mass are large. The results of the analyses presented here will provide important constrains for asteroseismic modelling.

Asteroseismology of tidally distorted sdB stars

2019 ◽  
Vol 489 (3) ◽  
pp. 3066-3072 ◽  
Author(s):  
Holly P Preece ◽  
C Simon Jeffery ◽  
Christopher A Tout
Keyword(s):  
Normal Modes ◽  
Frequency Shifts ◽  
B Stars ◽  
Tidal Distortion ◽  
Common Envelope ◽  
Subdwarf B Stars ◽  
Sdb Stars ◽  
Short Period ◽  
Split Mode ◽  
Orbital Periods

ABSTRACT Most subdwarf B stars are located in post-common envelope binaries. Many are in short-period systems subject to tidal influence, and many show pulsations useful for asteroseismic inference. In combination, one must quantify when and how tidal distortion affects the normal modes. We present a method for computing tidal distortion and associated frequency shifts. Validation is by application to polytropes and comparison with previous work. For typical sdB stars, a tidal distortion to the radius of between $0.2\,$ and $2\,$ per cent is generated for orbital periods of 0.1 d. Application to numerical helium core-burning stars identifies the period and mass-ratio domain where tidal frequency shifts become significant and quantifies those shifts in terms of binary properties and pulsation modes. Tidal shifts disrupt the symmetric form of rotationally split multiplets by introducing an asymmetric offset to modes. Tides do not affect the total spread of a rotationally split mode unless the stars are rotating sufficiently slowly that the rotational splitting is smaller than the tidal splitting.

scholarly journals The Scale Height of Blue Halo subdwarf B Stars

1995 ◽  
Vol 164 ◽  
pp. 403-403
Author(s):  
K.S. De Boer ◽  
A. Theissen ◽  
U. Heber ◽  
S. Moehler
Keyword(s):  
Spatial Distribution ◽  
Scale Height ◽  
Horizontal Branch ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Sdb Stars ◽  
The Past ◽  
Halo Stars ◽  
Red Giant ◽  
Branch Type

Numerous blue halo stars have been discovered during the past decade (e.g. the Palomar-Green Survey). Many are horizontal branch type, being HBA, HBB, sdB, or sdO star. The sdB stars (Teff between ≈ 18 000 and ≈ 30 000 K) are the endproducts of evolution in the red-giant phase. This means that the spatial distribution of the sdB stars can be used to get insight in the population nature and in their spatial origin.

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