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 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 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 Looking for Trends in the Group Properties of Pulsating Subdwarf B Stars

2000 ◽  
Vol 176 ◽  
pp. 502-507
Author(s):  
M. D. Reed ◽  
S. D. Kawaler ◽  
S. J. Kleinman
Keyword(s):  
Pulsation Period ◽  
Simple Correlation ◽  
B Stars ◽  
Mode Identification ◽  
Entire Class ◽  
Subdwarf B Stars ◽  
The Future

We examine the pulsation properties for 13 members of the pulsating subdwarf B (sdBV, or EC 14026) class of stars. By looking at the pulsation structure of an entire class of stars, it may be possible to determine the various modes of pulsations (O’Brien 1998, Kleinman 1995). Unfortunately, when we examine the ensemble of pulsation periods in EC 14026 stars, we are only able to discern a simple correlation between pulsation period and gravity, and not any structure that might help with mode identification. So we can only report on the lack of structure in the pulsation periods and present some of the work underway, which we hope will identify modes in the future.

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 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 The stellar mass assembly of low-redshift, massive, central galaxies in SDSS and the TNG300 simulation

2020 ◽  
Vol 497 (4) ◽  
pp. 4262-4275
Author(s):  
Thomas M Jackson ◽  
A Pasquali ◽  
C Pacifici ◽  
C Engler ◽  
A Pillepich ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Stellar Mass ◽  
Spectral Energy ◽  
Distribution Fitting ◽  
Stellar Ages ◽  
Mass Assembly ◽  
Galaxy Assembly ◽  
The Times ◽  
Stellar Masses ◽  
Kinetic Mode

ABSTRACT The stellar mass assembly of galaxies can be affected by both secular and environmental processes. In this study, for the first time, we investigate the stellar mass assembly of $\sim 90\, 000$ low-redshift, central galaxies selected from SDSS group catalogues ($M_{\rm Stellar}\gtrsim 10^{9.5}\, \mathrm{M}_{\odot }$, $M_{\rm Halo}\gtrsim 10^{12}\, \mathrm{M}_{\odot }$) as a function of both stellar mass and halo mass. We use estimates of the times at which 10, 50, and 90 per cent of the stellar mass were assembled from photometric spectral energy distribution fitting, allowing a more complete investigation than single stellar ages alone. We consider trends in both stellar mass and halo mass simultaneously, finding dependences of all assembly times on both. We find that galaxies with higher stellar masses (at constant halo mass) have on average older lookback times, similar to previous studies of galaxy assembly. We also find that galaxies at higher halo mass (at constant stellar mass) have younger lookback times, possibly due to a larger reservoir of gas for star formation. An exception to this is a subsample with high stellar-to-halo mass ratios, which are likely massive, field spirals. We compare these observed trends to those predicted by the TNG300 simulation, finding good agreement overall as a function of either stellar mass or halo mass. However, some differences in the assembly times (of up to ∼3 Gyr) appear when considering both stellar mass and halo mass simultaneously, noticeably at intermediate stellar masses (MStellar ∼ 1011 M⊙). These discrepancies are possibly linked to the quenched fraction of galaxies and the kinetic mode active galactic nucleus feedback implemented in TNG300.

Sign in / Sign up

Export Citation Format

Share Document