TY  - JOUR
A1  - Raddi, Roberto
A1  - Hollands, M. A.
A1  - Koester, D.
A1  - Hermes, J. J.
A1  - Gansicke, B. T.
A1  - Heber, Ulrich
A1  - Shen, Ken J.
A1  - Townsley, D. M.
A1  - Pala, Anna Francesca
A1  - Reding, J. S.
A1  - Toloza, O. F.
A1  - Pelisoli, Ingrid Domingos
A1  - Geier, Stephan Alfred
A1  - Fusillo, Nicola Pietro Gentile
A1  - Munari, Ullisse
A1  - Strader, J.
T1  - Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae
JF  - Monthly notices of the Royal Astronomical Society
N2  - We report the discovery of three stars that, along with the prototype LP 40-365, form a distinct class of chemically peculiar runaway stars that are the survivors of thermonuclear explosions. Spectroscopy of the four confirmed LP 40-365 stars finds ONe-dominated atmospheres enriched with remarkably similar amounts of nuclear ashes of partial O- and Si-burning. Kinematic evidence is consistent with ejection from a binary supernova progenitor; at least two stars have rest-frame velocities indicating they are unbound to the Galaxy. With masses and radii ranging between 0.20 and 0.28M(circle dot) and between 0.16 and 0.60 R-circle dot, respectively, we speculate these inflated white dwarfs are the partly burnt remnants of either peculiar Type Iax or electron-capture supernovae. Adopting supernova rates from the literature, we estimate that similar to 20 LP 40-365 stars brighter than 19 mag should be detectable within 2 kpc from the Sun at the end of the Gaia mission. We suggest that as they cool, these stars will evolve in their spectroscopic appearance, and eventually become peculiar O-rich white dwarfs. Finally, we stress that the discovery of new LP 40-365 stars will be useful to further constrain their evolution, supplying key boundary conditions to the modelling of explosion mechanisms, supernova rates, and nucleosynthetic yields of peculiar thermonuclear explosions.
KW  - stars: individual: LP 40-365
KW  - subdwarfs
KW  - supernovae: general
KW  - white dwarfs
KW  - Galaxy: kinematics and dynamics
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz1618
SN  - 0035-8711
SN  - 1365-2966
VL  - 489
IS  - 2
SP  - 1489
EP  - 1508
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Smith, Bryce A.
A1  - Barlow, Brad N.
A1  - Rosenthal, Benjamin
A1  - Hermes, J. J.
A1  - Schaffenroth, Veronika
T1  - Pulse Timing Discovery of a Three-day Companion to the Hot Subdwarf BPM 36430
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Hot subdwarf B stars are core-helium-burning objects that have undergone envelope stripping, likely by a binary companion. Using high-speed photometry from the Transiting Exoplanet Survey Satellite, we have discovered the hot subdwarf BPM 36430 is a hybrid sdBV(rs) pulsator exhibiting several low-amplitude g-modes and a strong p-mode pulsation. The latter shows a clear, periodic variation in its pulse arrival times. Fits to this phase oscillation imply BPM 36430 orbits a barycenter approximately 10 light-seconds away once every 3.1 days. Using the CHIRON echelle spectrograph on the CTIO 1.5 m telescope, we confirm the reflex motion by detecting a radial-velocity variation with semiamplitude, period, and phase in agreement with the pulse timings. We conclude that a white dwarf companion with minimum mass of approximate to 0.42 M (circle dot) orbits BPM 36430. Our study represents only the second time a companion orbiting a pulsating hot subdwarf or white dwarf has been detected from pulse timings and confirmed with radial velocities.
Y1  - 2022
U6  - https://doi.org/10.3847/1538-4357/ac9384
SN  - 0004-637X
SN  - 1538-4357
VL  - 939
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Charpinet, Stéphane
A1  - Brassard, P.
A1  - Fontaine, G.
A1  - Van Grootel, Valerie
A1  - Zong, Weika
A1  - Giammichele, N.
A1  - Heber, Ulrich
A1  - Bognár, Zsófia
A1  - Geier, Stephan Alfred
A1  - Green, Elizabeth M.
A1  - Hermes, J. J.
A1  - Kilkenny, D.
A1  - Ostensen, R. H.
A1  - Pelisoli, Ingrid Domingos
A1  - Silvotti, R.
A1  - Telting, J. H.
A1  - Vuckovic, Maja
A1  - Worters, H. L.
A1  - Baran, Andrzej S.
A1  - Bell, Keaton J.
A1  - Bradley, Paul A.
A1  - Debes, J. H.
A1  - Kawaler, S. D.
A1  - Kolaczek-Szymanski, P.
A1  - Murphy, S. J.
A1  - Pigulski, A.
A1  - Sodor, A.
A1  - Uzundag, Murat
A1  - Handberg, R.
A1  - Kjeldsen, H.
A1  - Ricker, G. R.
A1  - Vanderspek, R. K.
T1  - TESS first look at evolved compact pulsators Discovery and asteroseismic probing of the g-mode hot B subdwarf pulsator EC 21494-7018
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494-7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494-7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 +/- 0.009x2006;M-circle dot) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (greater than or similar to 2;M-circle dot) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 +/- 0.0010;M-circle dot), radius (0.1694 +/- 0.0081;R-circle dot), and luminosity (8.2 +/- 1.1;L-circle dot). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494-7018 has burnt similar to 43% (in mass) of its central helium and possesses a relatively large mixed core (M-core;=;0.198 +/- 0.010;M-circle dot), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)(core) = 0.16(-0.05)(+0.13)X(O)core=0.16-0.05+0.13$ X(mathrm{O})_{mathrm{core}}=0.16_{-0.05}<^>{+0.13} $) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain C-12(alpha,;gamma)O-16 nuclear reaction rate.
KW  - asteroseismology
KW  - stars
KW  - interiors
KW  - oscillations
KW  - horizontal-branch
KW  - individual
KW  - TIC 278659026
KW  - subdwarfs
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201935395
SN  - 0004-6361
SN  - 1432-0746
VL  - 632
PB  - EDP Sciences
CY  - Les Ulis
ER  -