An Ultramassive, Fast-Spinning White Dwarf in a Peculiar Binary System

Mereghetti, S.; Tiengo, A.; Esposito, P.; Palombara, N. La; Israel, G. L.; Stella, L.

doi:10.1126/science.1176252

Cited by 107 publications

(139 citation statements)

References 26 publications

(35 reference statements)

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“…These two stars lie very close in the L X -L BOL plane. The same is true for the spectroscopic binary HD 49798, which is in a 1.55 day orbit with a neutron star or white dwarf companion (Mereghetti et al 2009(Mereghetti et al , 2013. For this star we plot in Fig.…”

Section: Discussionmentioning

confidence: 88%

The lack of X-ray pulsations in the extreme helium star BD+37°442 and its possible stellar wind X-ray emission

Mereghetti

Palombara

Tiengo

et al. 2016

Mon. Not. R. Astron. Soc.

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We report the results of a new XMM-Newton observation of the helium-rich hot subdwarf BD +37 • 442 carried out in February 2016. The possible periodicity at 19 s seen in a 2011 shorter observation is not confirmed, thus dismissing the evidence for a binary nature. This implies that the observed soft X-ray emission, with a luminosity of a few 10 31 erg s −1 , originates in BD +37 • 442 itself, rather than in an accreting neutron star companion. The X-ray spectrum is well fit by thermal plasma emission with a temperature of 0.22 keV and nonsolar element abundances. Besides the overabundance of He, C and N already known from optical/UV studies, the X-ray spectra indicate also a significant excess of Ne. The soft X-ray spectrum and the ratio of X-ray to bolometric luminosity, L X /L BOL ∼ 2 × 10 −7 , are similar to those observed in massive early type stars. This indicates that the mechanisms responsible for plasma shock-heating can work also in the weak stellar winds (mass loss ratesṀ W 10 −8 M yr −1 ) of low-mass hot stars.

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Section: Discussionmentioning

confidence: 88%

The lack of X-ray pulsations in the extreme helium star BD+37°442 and its possible stellar wind X-ray emission

Mereghetti

Palombara

Tiengo

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The system HD 49798/RXJ 0648.0-418 is confirmation of the existence of a rapidly rotating massive WD + He star system. Based on data from the XMM − Newton satellite, the masses of the hot subdwarf HD 49798 and the WD are constrained to be 1.50±0.05 M and 1.28±0.05 M , respectively (Mereghetti et al 2009). Wang & Han (2010c) suggested that the hot subdwarf HD 49798 and its X-ray pulsating companion could evolve into an SN Ia in the future.…”

Section: Discussion and Summarymentioning

confidence: 99%

Helium-star evolutionary channel to super-Chandrasekhar mass type Ia supernovae

Liu

Chen

Wang

et al. 2010

A&A

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The recent discovery of several overluminous type Ia supernovae (SNe Ia) indicates that the explosive masses of white dwarfs may significantly exceed the canonical Chandrasekhar-mass limit. Rapid differential rotation may support these massive white dwarfs (WDs). Based on the single-degenerate scenario and assuming that the WDs would differentially rotate when the accretion ratė M > 3 × 10 −7 M yr −1 , we performed the numerical calculations for ∼1000 binary systems consisting of a He star and a CO WD with Eggleton's stellar evolution code. We present the initial parameters in the orbital period − helium star-mass plane (for WD masses of 1.0 M and 1.2 M , respectively), which lead to super-Chandrasekhar mass SNe Ia. Our results indicate that for an initially massive WD of 1.2 M , a large number of SNe Ia may result from super-Chandrasekhar mass WDs. The highest mass of the WD at the moment of the SNe Ia explosion is 1.81 M , but very massive (>1.85 M ) WDs cannot be formed. However, when the initial mass of WDs is 1.0 M , the explosive masses of SNe Ia are nearly uniform, which is consistent with the rareness of super-Chandrasekhar mass SNe Ia in observations.

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“…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. The predicted amount of accreted material is sufficient for the WD to reach the Chandrasekhar limit.…”

Section: Introductionmentioning

confidence: 99%

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

Geier

Hirsch

Tillich

et al. 2011

A&A

102

109

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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.

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An Ultramassive, Fast-Spinning White Dwarf in a Peculiar Binary System

Cited by 107 publications

References 26 publications

The lack of X-ray pulsations in the extreme helium star BD+37°442 and its possible stellar wind X-ray emission

The lack of X-ray pulsations in the extreme helium star BD+37°442 and its possible stellar wind X-ray emission

Helium-star evolutionary channel to super-Chandrasekhar mass type Ia supernovae

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

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