scholarly journals K2 observations of the sdBV + dM/bd binaries PHL 457 and EQ Psc

2019 ◽  
Vol 489 (2) ◽  
pp. 1556-1571 ◽  
Author(s):  
A S Baran ◽  
J H Telting ◽  
C S Jeffery ◽  
R H Østensen ◽  
J Vos ◽  
...  
Keyword(s):  
Broad Band ◽  
Spectral Energy ◽  
B Stars ◽  
Subdwarf B Stars ◽  
Amplitude Spectra ◽  
Orbital Phase ◽  
Hot Subdwarfs ◽  
Orbital Periods ◽  
Core Rotation ◽  
Calculated Amplitude

ABSTRACT We present an analysis of two pulsating subdwarf B stars PHL 457 and EQ Psc observed during the K2 mission. The K2 light curves of both stars show variation consistent with irradiation of a cooler companion by the hot subdwarf. They also show higher frequency oscillations consistent with pulsation. Using new spectroscopic data, we measured the radial velocity, effective temperature, surface gravity, and helium abundance of both hot subdwarfs as a function of orbital phase. We confirm the previously published spectroscopic orbit of PHL 457, and present the first spectroscopic orbit of EQ Psc. The orbital periods are 0.313 and 0.801 d, respectively. For EQ Psc, we find a strong correlation between Teff and orbital phase, due to contribution of light from the irradiated companion. We calculated amplitude spectra, identified significant pulsation frequencies, and searched for multiplets and asymptotic period spacings. By means of multiplets and period spacing, we identified the degrees of several pulsation modes in each star. The g-mode multiplets indicate subsynchronous core rotation with periods of 4.6 d (PHL 457) and 9.4 d (EQ Psc). We made spectral energy disctribution (SED) fits of PHL 457 and EQ Psc using available broad-band photometry and Gaia data. While the SED of PHL 457 shows no evidence of a cool companion, the SED for EQ Psc clearly shows an infrared (IR) access consistent with a secondary with a temperature of about 6800 K and a radius of 0.23 R⊙. This is the first detection of an IR access in any sdB + dM binary.

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.

scholarly journals A search for variable subdwarf B stars in TESS full frame images – I. Variable objects in the southern ecliptic hemisphere

2020 ◽  
Vol 499 (4) ◽  
pp. 5508-5526
Author(s):  
S K Sahoo ◽  
A S Baran ◽  
S Sanjayan ◽  
J Ostrowski
Keyword(s):  
Preliminary Analysis ◽  
Variable Stars ◽  
Eclipsing Binaries ◽  
Spectral Classification ◽  
B Stars ◽  
Mode Identification ◽  
Pulsating Stars ◽  
Subdwarf B Stars ◽  
Amplitude Spectra

ABSTRACT We report the results of our search for pulsating subdwarf B stars in full frame images, sampled at 30 min cadence and collected during Year 1 of the TESS mission. Year 1 covers most of the southern ecliptic hemisphere. The sample of objects we checked for pulsations was selected from a subdwarf B stars data base available to public. Only two positive detections have been achieved, however, as a by-product of our search we found 1807 variable objects, most of them not classified, hence their specific variability class cannot be confirmed at this stage. Our preliminary discoveries include: 2 new subdwarf B (sdB) pulsators, 26 variables with known sdB spectra, 83 non-classified pulsating stars, 83 eclipsing binaries (detached and semidetached), a mix of 1535 pulsators and non-eclipsing binaries, two novae, and 77 variables with known (non-sdB) spectral classification. Among eclipsing binaries we identified two known HW Vir systems and four new candidates. The amplitude spectra of the two sdB pulsators are not rich in modes, but we derive estimates of the modal degree for one of them. In addition, we selected five sdBV candidates for mode identification among 83 pulsators and describe our results based on this preliminary analysis. Further progress will require spectral classification of the newly discovered variable stars, which hopefully include more subdwarf B stars.

scholarly journals Orbital periods of 22 subdwarf B stars

2003 ◽  
Vol 338 (3) ◽  
pp. 752-764 ◽  
Author(s):  
L. Morales-Rueda ◽  
P. F. L. Maxted ◽  
T. R. Marsh ◽  
R. C. North ◽  
U. Heber
Keyword(s):  
B Stars ◽  
Subdwarf B Stars ◽  
Orbital Periods

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 challenging SED of AP Librae

2011 ◽  
Vol 7 (S284) ◽  
pp. 411-413 ◽  
Author(s):  
David Sanchez ◽  
Berrie Giebels ◽  
Pascal Fortin ◽  
Keyword(s):  
Spectral Energy Distribution ◽  
Broad Band ◽  
Low Frequency ◽  
Theoretical Models ◽  
Intermediate Frequency ◽  
High Energy ◽  
Spectral Energy ◽  
Broad Band Emission ◽  
Band Emission ◽  
Bl Lac

AbstractMatching the broad-band emission of active galaxies with the predictions of theoretical models can be used to derive constraints on the properties of the emitting region and to probe the physical processes involved. AP Librae is the third low frequency peaked BL Lac (LBL) detected at very high energy (VHE, E>100GeV) by an Atmospheric Cherenkov Telescope; most VHE BL Lacs (34 out of 39) belong to the high-frequency and intermediate-frequency BL Lac classes (HBL and IBL). LBL objects tend to have a higher luminosity with lower peak frequencies than HBLs or IBLs. The characterization of their time-averaged spectral energy distribution is challenging for emission models such as synchrotron self-Compton (SSC) models.

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 From rest-frame luminosity functions to observer-frame colour distributions: tackling the next challenge in cosmological simulations

2020 ◽  
Vol 497 (3) ◽  
pp. 3026-3046 ◽  
Author(s):  
Matías Bravo ◽  
Claudia del P Lagos ◽  
Aaron S G Robotham ◽  
Sabine Bellstedt ◽  
Danail Obreschkow
Keyword(s):  
Survey Design ◽  
Target Selection ◽  
Broad Band ◽  
Complex Mixture ◽  
Far Infrared ◽  
Bimodal Distribution ◽  
Spectral Energy ◽  
Recent Success ◽  
Luminosity Functions ◽  
Radiation Output

ABSTRACT Galaxy spectral energy distributions (SEDs) remain among the most challenging yet informative quantities to reproduce in simulations due to the large and complex mixture of physical processes that shape the radiation output of a galaxy. With the increasing number of surveys utilizing broad-band colours as part of their target selection criteria, the production of realistic SEDs in simulations is necessary for assisting in survey design and interpretation of observations. The recent success in reproducing the observed luminosity functions (LFs) from far-ultraviolet (UV) to far-infrared (IR), using the state-of-the-art semi-analytic model shark and the SED generator ProSpect, represents a critical step towards better galaxy colour predictions. We show that with shark and ProSpect we can closely reproduce the optical colour distributions observed in the panchromatic Galaxy And Mass Assembly (GAMA) survey. The treatment of feedback, star formation, central–satellite interactions, and radiation reprocessing by dust are critical for this achievement. The first three processes create a bimodal distribution, while dust attenuation defines the location and shape of the blue and red populations. While a naive comparison between observation and simulations displays the known issue of overquenching of satellite galaxies, the introduction of empirically motivated observational errors and classification from the same group finder used in GAMA greatly reduces this tension. The introduction of random reassignment of ${\sim} 15{{\ \rm per\ cent}}$ of centrals/satellites as satellites/centrals on the simulation classification closely resembles the outcome of the group finder, providing a computationally less intensive method to compare simulations with observations.

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