A Search for Main‐Sequence Companions to Subdwarf B Stars Using the Two Micron All Sky Survey

2004 ◽  
Vol 116 (820) ◽  
pp. 506-515 ◽  
Author(s):  
M. D. Reed ◽  
Rae Stiening
Keyword(s):  
Main Sequence ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Sky Survey

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 Hot subdwarf B stars with neutron star components

2020 ◽  
Vol 634 ◽  
pp. A126 ◽  
Author(s):  
You Wu ◽  
Xuefei Chen ◽  
Hailiang Chen ◽  
Zhenwei Li ◽  
Zhanwen Han
Keyword(s):  
Mass Transfer ◽  
Neutron Star ◽  
Main Sequence ◽  
Galactic Disk ◽  
B Stars ◽  
Common Envelope ◽  
Subdwarf B Stars ◽  
Linear Formula ◽  
The Galaxy ◽  
The Common

Context. Subdwarf B stars (sdBs) play a crucial role in stellar evolution, asteroseismology, and far-UV radiation of early-type galaxies, and have been intensively studied with observation and theory. It has theoretically been predicted that sdBs with neutron star (NS) companions exist in the Galaxy, but none have been discovered yet. This remains a puzzle in this field. In a previous study (hereafter Paper I), we have studied the formation channels of sdB+NS binaries from main-sequence (MS) stars plus NS binaries by establishing a model grid, but it is still unclear how these binaries consisting of MS stars and NS binaries came to be in the first place. Aims. We systematically study the formation of sdB+NS binaries from their original zero-age main-sequence progenitors. We bridge the gap left by our previous study in this way. We obtain the statistical population properties of sdB+NS binaries and provide some guidance for observational efforts. Methods. We first used Hurley’s rapid binary evolution code BSE to evolve 107 primordial binaries to the point where the companions of NS+MS, NS+Hertzsprung gap star, and NS+Giant Branch star binaries have just filled their Roche lobes. Next, we injected these binaries into the model grid we developed in Paper I to obtain the properties of the sdB+NS populations. We adopted two prescriptions of NS natal kicks: the classical Maxwellian distribution with a dispersion of σ = 265 km s−1, and a linear formula that assumes that the kick velocity is associated with the ratio of ejected to remnant mass. Different values of αCE, where αCE is the common-envelope ejection efficiency, were chosen to examine the effect of common-envelope evolution on the results. Results. In the Galaxy, the birthrate of sdB+NS binaries is about 10−4 yr−1 and there are ∼7000 − 21 000 such binaries. This contributes 0.3−0.5% of all sdB binaries in the most favorable case. Most Galactic sdB+NS binaries (≳60%) arise from the channel of stable mass transfer. The value of αCE has little effect on the results, but when we use the linear formula prescription of NS natal kick, the number and birthrate doubles in comparison to the results we obtained with the Maxwellian distribution. The orbital periods of sdB+NS binaries from different formation channels differ significantly, as expected. This results in two peaks in the radial velocity (RV) semi-amplitude distribution: 100 − 150 km s−1 for stable mass transfer, and 400 − 600 km s−1 for common-envelope ejection. However, the two sdB+NS binary populations exhibit similar delay-time distributions, which both peak at about 0.2 Gyr. This indicates that Galactic sdB+NS binaries are born in very young populations, probably in the Galactic disk. The sdB+NS binaries produced from the common-envelope ejection channel are potential sources of strong gravitational wave radiation (GWR), and about ∼100 − 300 could be detected by the Laser Interferometer Space Antenna (LISA) with a signal-to-noise ratio of 1. Conclusions. Most sdB+NS binaries are located in the Galactic disk with small RV semi-amplitudes. SdB+NS binaries with large RV semi-amplitudes are expected to be strong GWR sources, some of which could be detected by LISA in the future.

scholarly journals Are sdAs helium core stars?

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Ingrid Pelisoli ◽  
S. O. Kepler ◽  
Detlev Koester
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Physical Nature ◽  
Sloan Digital Sky Survey ◽  
Distance Modulus ◽  
Main Sequence Stars ◽  
Sky Survey ◽  
Balmer Lines ◽  
Low Mass ◽  
Binary Evolution

AbstractEvolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

scholarly journals Constraints on pre-main-sequence evolution from stellar pulsations

2013 ◽  
Vol 9 (S301) ◽  
pp. 137-144
Author(s):  
M. P. Casey ◽  
K. Zwintz ◽  
D. B. Guenther
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Sequence Evolution ◽  
B Stars ◽  
Stellar Pulsations ◽  
Pms Stars

AbstractPulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus – δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis.A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\break constraints — or lack thereof — that these results can put on PMS stellar evolution.

scholarly journals First Kepler results on compact pulsators - III. Subdwarf B stars with V1093 Her and hybrid (DW Lyn) type pulsations

2010 ◽  
Vol 409 (4) ◽  
pp. 1496-1508 ◽  
Author(s):  
M. D. Reed ◽  
S. D. Kawaler ◽  
R. H. Østensen ◽  
S. Bloemen ◽  
A. Baran ◽  
...  
Keyword(s):  
B Stars ◽  
Subdwarf B Stars

scholarly journals Resolving the pulsations of subdwarf B stars: PG 0154+182, HS 1824+5745 and HS 2151+0857

2006 ◽  
Vol 369 (3) ◽  
pp. 1529-1536 ◽  
Author(s):  
M. D. Reed ◽  
J. R. Eggen ◽  
A.- Y. Zhou ◽  
D. M. Terndrup ◽  
S. L. Harms ◽  
...  
Keyword(s):  
B Stars ◽  
Subdwarf B Stars

scholarly journals The Status of the Absolute Calibration of Stellar Fluxes Between 912 and 1200 Å

1985 ◽  
Vol 111 ◽  
pp. 479-483
Author(s):  
R. S. Polidan ◽  
J. B. Holberg
Keyword(s):  
Planetary Nebula ◽  
White Dwarfs ◽  
Main Sequence ◽  
Absolute Calibration ◽  
Energy Distributions ◽  
B Stars ◽  
The Status ◽  
The Absolute ◽  
Flux Calibration

Recent results have shed new light on the status of the calibration of absolute stellar fluxes between 912 and 1200 Å. Observations of hot white dwarfs, subdwarfs and planetary nebula nuclei with the Voyager ultraviolet spectrometers provide evidence that the current calibration agrees very well with extrapolations of IUE energy distributions shortwards of 1200 Å. Voyager observations of main sequence B-stars used as flux calibration sources have revealed that many are variable in brightness in the 912–1200 Å region. We conclude there is no current observational motivation for any revision of the 912 to 1200 Å calibration described by Holberg et al. (1982).

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