Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf

We have used 605 days of photometric data from the Kepler spacecraft to study KIC 6614501, a close binary system with an orbital period of 0.15749747(25) days (3.779939 h), that consists of a low-mass subdwarf B (sdB) star and a white dwarf (WD). As seen in many other similar systems, the gravitatio...

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Detalles Bibliográficos
Autor principal: Althaus, Leandro Gabriel
Formato: Articulo
Lenguaje:Inglés
Publicado: 2012
Materias:
Ciencias Astronómicas
Binaries: close
Stars: individual: KIC 6614501
Subdwarfs
White dwarfs
Acceso en línea:http://sedici.unlp.edu.ar/handle/10915/84638
Aporte de:
SEDICI (UNLP) de Universidad Nacional de La Plata
id I19-R120-10915-84638
record_format dspace
institution Universidad Nacional de La Plata
institution_str I-19
repository_str R-120
collection SEDICI (UNLP)
language Inglés
topic Ciencias Astronómicas
Binaries: close
Stars: individual: KIC 6614501
Subdwarfs
White dwarfs
spellingShingle Ciencias Astronómicas
Binaries: close
Stars: individual: KIC 6614501
Subdwarfs
White dwarfs
Althaus, Leandro Gabriel
Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf
topic_facet Ciencias Astronómicas
Binaries: close
Stars: individual: KIC 6614501
Subdwarfs
White dwarfs
description We have used 605 days of photometric data from the Kepler spacecraft to study KIC 6614501, a close binary system with an orbital period of 0.15749747(25) days (3.779939 h), that consists of a low-mass subdwarf B (sdB) star and a white dwarf (WD). As seen in many other similar systems, the gravitational field of the WD produces an ellipsoidal deformation of the sdB which appears in the light curve as a modulation at two times the orbital frequency. The ellipsoidal deformation of the sdB implies that the system has a maximum inclination of ~40°, with i ≈ 20° being the most likely. The orbital radial velocity (RV) of the sdB star is high enough to produce a Doppler beaming effect with an amplitude of 432 ± 5 ppm, clearly visible in the folded light curve. The photometric amplitude that we obtain, K 1 = 85.8kms -1, is ~12 per cent less than the spectroscopic RV amplitude of 97.2 ± 2.0kms -1. The discrepancy is due to the photometric contamination from a close object at about 5arcsec north-west of KIC 6614501, which is difficult to remove. The atmospheric parameters of the sdB star, T eff = 23700 ± 500K and logg = 5.70 ± 0.10, imply that it is a rare object below the extreme horizontal branch (EHB), similar to HD 188112. The comparison with different evolutionary tracks suggests a mass between ~0.18 and ~0.25 M ⊙, too low to sustain core helium burning. If the mass was close to 0.18-0.19 M ⊙, the star could be already on the final He-core WD cooling track. A higher mass, up to ~0.25M ⊙, would be compatible with a He-core WD progenitor undergoing a cooling phase in a H-shell flash loop. A third possibility, with a mass between ~0.32 and ~0.40 M ⊙, cannot be excluded and would imply that the sdB is a 'normal' (but with an unusually low mass) EHB star burning He in its core. In all these different scenarios, the system is expected to merge in less than 3.1 Gyr due to gravitational wave radiation.
format Articulo
Articulo
author Althaus, Leandro Gabriel
author_facet Althaus, Leandro Gabriel
author_sort Althaus, Leandro Gabriel
title Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf
title_short Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf
title_full Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf
title_fullStr Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf
title_full_unstemmed Orbital properties of an unusually low-mass sdB star in a close binary system with a white dwarf
title_sort orbital properties of an unusually low-mass sdb star in a close binary system with a white dwarf
publishDate 2012
url http://sedici.unlp.edu.ar/handle/10915/84638
work_keys_str_mv AT althausleandrogabriel orbitalpropertiesofanunusuallylowmasssdbstarinaclosebinarysystemwithawhitedwarf
bdutipo_str Repositorios
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