White dwarf

About: White dwarf is a research topic. Over the lifetime, 15004 publications have been published within this topic receiving 430597 citations. The topic is also known as: degenerate dwarf.

3D simulations of RS Ophiuchi : from accretion to nova blast

Abstract: Context. The binary star system RS Ophiuchi is a recurrent nova, with outbursts occurring about every 22 years. It consists of a red giant star (RG) and a wind accreting white dwarf close to the Chandrasekhar limit. This system is considered a prime candidate for evolving into an SNIa. For its most recent outbursts in 1985 and 2006, exquisite multiwavelength observational data are available. Aims. Deeper physical insight is needed regarding the inter-outburst accretion phase and the dynamical effects of the subsequent nova explosion in order to improve the interpretation of the observed data and to shed light on whether the system is an SNIa progenitor. Methods. We present a 3D hydrodynamic simulation of the quiescent accretion with the subsequent explosive phase. Results. The computed circumstellar mass distribution in the quiescent phase is highly structured with a mass enhancement in the orbital plane of about a factor of 2 as compared to the poleward directions. The simulated nova remnant evolves aspherically, propagating faster toward the poles. The shock velocities derived from the simulations agree with those derived from observations. For vRG = 20 km s −1 and for nearly isothermal flows, we find that 10% of the mass lost by the RG is transfered to the WD. For an RG mass

The mass of the white dwarf in the recurrent nova U Scorpii

Abstract: ABSTRA C T We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi- amplitude of the primary star was found to be KWa 93 ^ 10 km s 21 from the motion of the wings of the He II l4686-Aemission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be KRa 170 ^ 10 km s 21 . From these parameters, we obtain a mass of M1a 1:55 ^ 0:24 M( for the white dwarf primary star and a mass of M2a 0:88 ^ 0:17 M( for the secondary star. The radius of the secondary is calculated to be R2a 2:1 ^ 0: 2R (, confirming that it is evolved. The inclination of the system is calculated to be ia 828 7 ^ 28 9, consistent with the deep eclipse seen in the light- curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ,700 000 yr.

Physical properties of IP Pegasi: an eclipsing dwarf nova with an unusually cool white dwarf

Abstract: We present high speed photometric observations of the eclipsing dwarf nova IP Peg taken with the triple-beam camera ULTRACAM mounted on the William Herschel Telescope. The primary eclipse in this system was observed twice in 2004, and then a further sixteen times over a three week period in 2005. Our observations were simultaneous in the Sloan u', g' and r' bands. By phase-folding and averaging our data we make the first significant detection of the white dwarf ingress in this system and find the phase width of the white dwarf eclipse to be 0.0935 +/- 0.0003, significantly higher than the previous best value of between 0.0863 and 0.0918. The mass ratio is found to be q = M2 /M1 = 0.48 +/- 0.01, consistent with previous measurements, but we find the inclination to be 83.8 +/- 0.5 deg, significantly higher than previously reported. We find the radius of the white dwarf to be 0.0063 +/- 0.0003 solar radii, implying a white dwarf mass of 1.16 +/- 0.02 solar masses. The donor mass is 0.55 +/- 0.02 solar masses. The white dwarf temperature is more difficult to determine, since the white dwarf is seen to vary significantly in flux, even between consecutive eclipses. This is seen particularly in the u'-band, and is probably the result of absorption by disc material. Our best estimate of the temperature is 10,000 - 15,000K, which is much lower than would be expected for a CV with this period, and implies a mean accretion rate of less than 5 times 10^-11 solar masses per year, more than 40 times lower than the expected rate.

Multi-periodic pulsations of a stripped red-giant star in an eclipsing binary system

Abstract: Measurements of a precursor to a low-mass white-dwarf star reveal that such white-dwarf stars probably had a thick hydrogen envelope, which was lost by irradiation or shell flashes in the case of rapidly cooling white-dwarf stars. Before becoming low-mass white dwarfs, stripped red-giant stars evolve at nearly constant luminosity towards higher effective temperatures. The system known as J0247-25 was recently found to be a binary in which a star in this unusual evolutionary state (J0247-25B) is totally eclipsed by an apparently normal A-type star (J0247-25A). New spectroscopic and photometric observations have been used to derive precise astrophysical parameters for both stars. The data fit models in which the hotter white-dwarf precursor has a thick hydrogen envelope. This suggests that very cool low-mass white dwarfs have lost their thick hydrogen envelopes by irradiation from pulsar companions or by episodes of unstable hydrogen fusion (shell flashes). The discovery of pulsations in J0247-25B opens up new observational opportunities for the study of the structure of a low-mass white dwarf. Low-mass white-dwarf stars are the remnants of disrupted red-giant stars in binary millisecond pulsars1 and other exotic binary star systems2,3,4. Some low-mass white dwarfs cool rapidly, whereas others stay bright for millions of years because of stable fusion in thick surface hydrogen layers5. This dichotomy is not well understood, so the potential use of low-mass white dwarfs as independent clocks with which to test the spin-down ages of pulsars6,7 or as probes of the extreme environments in which low-mass white dwarfs form8,9,10 cannot fully be exploited. Here we report precise mass and radius measurements for the precursor to a low-mass white dwarf. We find that only models in which this disrupted red-giant star has a thick hydrogen envelope can match the strong constraints provided by our data. Very cool low-mass white dwarfs must therefore have lost their thick hydrogen envelopes by irradiation from pulsar companions11,12 or by episodes of unstable hydrogen fusion (shell flashes). We also find that this low-mass white-dwarf precursor is a type of pulsating star not hitherto seen. The observed pulsation frequencies are sensitive to internal processes that determine whether this star will undergo shell flashes.

Post-common envelope binaries from SDSS – XIV. The DR7 white dwarf–main-sequence binary catalogue

Abstract: We present an updated version of the spectroscopic white dwarf–main-sequence (WDMS) binary catalogue from the Sloan Digital Sky Survey (SDSS). 395 new systems are serendipitous discoveries from the spectroscopic SDSS I/II Legacy targets. As part of SDSS Extension for Galactic Understanding and Exploration (SEGUE), we have carried out a dedicated and efficient (64 per cent success rate) search for WDMS binaries with a strong contribution of the companion star, which were under-represented by all previous surveys, identifying 251 additional systems. In total, our catalogue contains 2248 WDMS binaries, and includes, where available, magnitudes from the GALEX All Sky Survey in the ultraviolet and from the United Kingdom Infrared Telescope (UKIRT) Infrared Sky Survey (UKIDSS) in the near-infrared. We also provide radial velocities of the companion stars, measured from the SDSS spectroscopy using the Na i λλ 8183.27, 8194.81 absorption doublet and/or the Hα emission. Using an updated version of our spectral decomposition/fitting technique we determine/update the white dwarf effective temperatures, surface gravities and masses, as well as the spectral type of the companion stars for the entire catalogue. Comparing the distributions of white dwarf mass, temperature and companion spectral type, we confirm that our SEGUE survey project has been successful in identifying WDMS binaries with cooler and more massive white dwarfs, as well as earlier spectral types found previously. Finally, we have developed a publicly available interactive online data base for spectroscopic SDSS WDMS binaries containing all available stellar parameters, radial velocities and magnitudes which we briefly describe.