The hot subdwarf B + white dwarf binary KPD 1930+2752

Geier, S.; Nesslinger, S.; Heber, U.; Przybilla, N.; Napiwotzki, R.; Kudritzki, R. P.

doi:10.1051/0004-6361:20066098

Cited by 135 publications

(192 citation statements)

References 43 publications

Supporting

Mentioning

181

Contrasting

Order By: Relevance

“…The synthetic spectra are convolved at a resolution of 1.0 Å. a practical recipe for computing some sort of saturated metallicity in model atmospheres, namely multipling the solar abundances of metals by a factor 10, for example. This is the same as the suggestion previously made by O'Toole & Heber (2006), Geier et al (2007), and Gianninas et al (2010), but with the added justification of the saturation effect. Figure 3 furthermore reveals that the saturation effect is verified over the full range of parameters displayed in the plot.…”

Section: Exploring Metallicity Effects On Spectral Linessupporting

confidence: 82%

A non-LTE analysis of the hot subdwarf O star BD+28°4211

Latour

Fontaine

Green

et al. 2015

A&A

View full text Add to dashboard Cite

We present the second part of our detailed analysis of the hot subdwarf O (sdO) and spectroscopic standard star BD+28 • 4211, in which we focus on the optical spectrum. This target was selected to revisit the more general question of how reliably the atmospheric parameters of a very hot star can be inferred from optical spectroscopy alone. Given its status as a spectrophotometric standard, spectral data of exceptional quality are available for BD+28 • 4211. In the first part of our study, we determined the abundances of some 11 metals detected in the atmosphere of BD+28 • 4211 using UV and far-UV spectra of the star and corroborated the fundamental parameters estimated in past studies (T eff ∼ 82 000 K, log g ∼ 6.2, and solar N(He)/N(H)). In this work, we aim at rederiving these secured parameters on the sole basis of high-quality optical spectra. A first grid of non-LTE line-blanketed model atmospheres, including C, N, O, Mg, Si, S, Fe, and Ni with the abundances derived from the UV spectrum, does not give satisfactory results when we apply a standard simultaneous fitting procedure to the observed H and He lines of our optical spectra. The line profiles are not finely reproduced and the resulting effective temperatures, in particular, are too low by ∼10 000 K. We next investigate the probable cause of this failure, that is, the importance of missing opacity sources on the atmospheric stratification. We thus compare line profiles computed from models with artificially boosted metallicities, from solar abundances to 15× these values. We find that the structural effects saturate for a metallicity of ∼10× solar, and use this to compute a second full grid of models and synthetic spectra. This metal-enriched grid allows us to achieve significantly improved spectral fits with models having the expected parameters. As an a posteriori test, we compared the detailed profiles of several model spectral lines with high-resolution spectra culled from archived HIRES observations. The agreement between our synthetic lines and the observed lines is very convincing. Our test case thus reveals that there is still a need for models with enhanced metallicity for better estimating the atmospheric parameters of objects such as hot subdwarfs and hot white dwarfs if only optical spectra are available.

show abstract

Section: Exploring Metallicity Effects On Spectral Linessupporting

confidence: 82%

A non-LTE analysis of the hot subdwarf O star BD+28°4211

Latour

Fontaine

Green

et al. 2015

A&A

View full text Add to dashboard Cite

show abstract

“…Spectral lines of hydrogen and helium were fitted by means of chi-squared minimization using SPAS, and statistical errors were calculated with a bootstrapping algorithm. Minimum errors reflecting systematic shifts when using different model grids (ΔT eff = 500 K; Δ log g = 0.05; Δ log y = 0.1, for a discussion see Geier et al 2007) have been adopted in cases where the statistical errors were lower. Example fits for a typical sdB, an sdOB and a He-sdO star are shown in Fig.…”

Section: Final Target Samplementioning

confidence: 99%

“…Transfer of mass or the subsequent merger of the system may cause the WD to approach the Chandrasekhar limit, ignite carbon under degenerate conditions, and explode as a SN Ia (Webbink 1984;Iben & Tutukov 1984). One of the best-known candidate systems for this double degenerate merger scenario is the sdB+WD binary KPD 1930+2752 (Maxted et al 2000a;Geier et al 2007). Mereghetti et al (2009) showed that in the X-ray binary HD 49798 a massive (>1.2 M ) white dwarf accretes matter from a closely orbiting subdwarf O companion.…”

Section: Introductionmentioning

confidence: 99%

The MUCHFUSS project – searching for hot subdwarf binaries with massive unseen companions

Geier

Hirsch

Tillich

et al. 2011

A&A

Self Cite

104

109

View full text Add to dashboard Cite

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding sdBs with compact companions like supermassive white dwarfs (M > 1.0 M ), neutron stars or black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they are likely to exist in our Galaxy. A determination of the orbital parameters is sufficient to put a lower limit on the companion mass by calculating the binary mass function. If this lower limit exceeds the Chandrasekhar mass and no sign of a companion is visible in the spectra, the existence of a massive compact companion is proven without the need for any additional assumptions. We identified about 1100 hot subdwarf stars from the SDSS by colour selection and visual inspection of their spectra. Stars with high velocities have been reobserved and individual SDSS spectra have been analysed. In total 127 radial velocity variable subdwarfs have been discovered. Binaries with high RV shifts and binaries with moderate shifts within short timespans have the highest probability of hosting massive compact companions. Atmospheric parameters of 69 hot subdwarfs in these binary systems have been determined by means of a quantitative spectral analysis. The atmospheric parameter distribution of the selected sample does not differ from previously studied samples of hot subdwarfs. The systems are considered the best candidates to search for massive compact companions by follow-up time resolved spectroscopy.

show abstract

“…This is the case for the sdB+WD binary KPD 1930+2752, which is the best known DD progenitor candidate for SN Ia (Maxted et al 2000;Geier et al 2007).…”

Section: Introductionmentioning

confidence: 99%

“…The discovery of the sdB+WD binary KPD 1930+2752, however, has highlighted the importance of such systems as SN Ia progenitor candidates (Billères et al 2000;Maxted et al 2000;Geier et al 2007). Hot subdwarf stars (sdBs) are core helium-burning stars situated at the hot end of the horizontal branch with masses around 0.5 M (Heber 1986).…”

Section: Introductionmentioning

confidence: 99%

Binaries discovered by the SPY project

Geier¹,

Heber²,

Kupfer³

et al. 2010

A&A

Self Cite

View full text Add to dashboard Cite

Aims. The ESO SN Ia Progenitor Survey (SPY) aims at finding merging double degenerate binaries as candidates for supernova type Ia (SN Ia) explosions. A white dwarf merger has also been suggested to explain the formation of rare types of stars like R CrB, extreme helium or He sdO stars. Here we present the hot subdwarf B binary GD 687, which will merge in less than a Hubble time.Methods. The orbital parameters of the close binary have been determined from time resolved spectroscopy. Since GD 687 is a singlelined binary, the spectra contain only information about the subdwarf primary and its orbit. From high resolution spectra the projected rotational velocity was derived. Assuming orbital synchronisation, the inclination of the system and the mass of the unseen companion were constrained. Results. The derived inclination is i = 39.3 +6.2 −5.6• . The mass M 2 = 0.71 +0.22 −0.21 M indicates that the companion must be a white dwarf, most likely of C/O composition. This is only the fourth case that an sdB companion has been proven to be a white dwarf unambiguously. Its mass is somewhat larger than the average white dwarf mass, but may be as high as 0.93 M in which case the total mass of the system comes close to the Chandrasekhar limit. Conclusions. GD 687 will evolve into a double degenerate system and merge to form a rare supermassive white dwarf with a mass in excess of solar. A death in a sub-Chandrasekhar supernova is also conceivable.

show abstract

The hot subdwarf B + white dwarf binary KPD 1930+2752

Cited by 135 publications

References 43 publications

A non-LTE analysis of the hot subdwarf O star BD+28°4211

A non-LTE analysis of the hot subdwarf O star BD+28°4211

The MUCHFUSS project – searching for hot subdwarf binaries with massive unseen companions

Binaries discovered by the SPY project

Contact Info

Product

Resources

About