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.

Infrared Signatures of Disrupted Minor Planets at White Dwarfs

Abstract: Spitzer Space Observatory IRAC and MIPS photometric observations are presented for 20 white dwarfs with T eff 20, 000 K and metal-contaminated photospheres. A warm circumstellar disk is detected at GD 16 and likely at PG 1457?086, while the remaining targets fail to reveal mid-infrared excess typical of dust disks, including a number of heavily polluted stars. Extending previous studies, over 50% of all single white dwarfs with implied metal-accretion rates dM/dt 3 ? 108 g s?1 display a warm infrared excess from orbiting dust; the likely result of a tidally destroyed minor planet. This benchmark accretion rate lies between the dust production rates of 106 g s?1 in the solar system zodiacal cloud and 1010 g s?1 often inferred for debris disks at main-sequence A-type stars. It is estimated that between 1% and 3% of all single white dwarfs with cooling ages less than around 0.5 Gyr possess circumstellar dust, signifying an underlying population of minor planets.

Links between dwarf and classical novae, and implications for the space densities and evolution of cataclysmic binaries

Abstract: The effects of mass and angular momentum losses during a nova eruption are investigated by simulation in the context of a new nova evolution model. It is argued that surveys for cataclysmic variables (CVs) are very incomplete and that the local space density of CVs could well be 0.0001/cu pc. It is shown that the competing effets of mass and angular momentum loss usually increase the separation of a red and white dwarf during a nova eruption. The reasons why old novae remain bright for about a century after eruption and why they reduce the mass transfer rate (MTR) and eventually go into a state of hibernation for a thousand to a million years, eventually reviving as dwarf novae or novalike variables, are discussed. The results of these simulations are used to demonstrate the consistency of variable MTR in resolving the MTR discrepancy. 43 references.

The White Dwarf Initial–Final Mass Relation for Progenitor Stars from 0.85 to 7.5 M ⊙ *

Abstract: We present the initial–final mass relation (IFMR) based on the self-consistent analysis of Sirius B and 79 white dwarfs from 13 star clusters. We have also acquired additional signal on eight white dwarfs previously analyzed in the NGC 2099 cluster field, four of which are consistent with membership. These re-observed white dwarfs have masses ranging from 0.72 to 0.97 M ⊙, with initial masses from 3.0 to 3.65 M ⊙, where the IFMR has an important change in slope that these new data help to observationally confirm. In total, this directly measured IFMR has small scatter (σ = 0.06 M ⊙) and spans from progenitors of 0.85 to 7.5 M ⊙. Applying two different stellar evolutionary models to infer two different sets of white dwarf progenitor masses shows that, when the same model is also used to derive the cluster ages, the resulting IFMR has weak sensitivity to the adopted model at all but the highest initial masses (>5.5 M ⊙). The nonlinearity of the IFMR is also clearly observed with moderate slopes at lower masses (0.08 M final/M initial) and higher masses (0.11 M final/M initial) that are broken up by a steep slope (0.19 M final/M initial) between progenitors from 2.85 to 3.6 M ⊙. This IFMR shows total stellar mass loss ranges from 33% of M initial at 0.83 M ⊙ to 83% of M initial at 7.5 M ⊙. Testing this total mass loss for dependence on progenitor metallicity, however, finds no detectable sensitivity across the moderate range of −0.15 < [Fe/H] < +0.15.

Infrared Spectra of the Subluminous Type Ia Supernova SN 1999by

Abstract: Near-infrared (NIR) spectra of the subluminous Type Ia supernova SN 1999by are presented that cover the time evolution from about 4 days before to 2 weeks after maximum light. Analysis of these data was accomplished through the construction of an extended set of delayed detonation (DD) models covering the entire range of normal to subluminous SNe Ia. The explosion, light curves, and time evolution of the synthetic spectra were calculated self-consistently for each model, with the only free parameters being the initial structure of the white dwarf and the description of the nuclear burning front during the explosion. From these, one model was selected for SN 1999by by matching the synthetic and observed optical light curves, principally the rapid brightness decline. DD models require a minimum amount of burning during the deflagration phase, which implies a lower limit for the 56Ni mass of about 0.1 M☉ and consequently a lower limit for the SN brightness. The models that best match the optical light curve of SN 1999by were those with a 56Ni production close to this theoretical minimum. The data are consistent with little or no interstellar reddening [E(B-V) ≤ 0.12 mag], and we derive a distance of 11 ± 2.5 Mpc for SN 1999by, in agreement with other estimates. Without any modification, the synthetic spectra from this subluminous model match reasonably well the observed IR spectra taken on 1999 May 6, 10, 16, and 24. These dates correspond roughly to -4, 0, 6, and 14 days after maximum light. Prior to maximum, the NIR spectra of SN 1999by are dominated by products of explosive carbon burning (O, Mg) and Si. Spectra taken after maximum light are dominated by products of incomplete Si burning. Unlike the behavior of normal Type Ia SNe, lines from iron-group elements begin to show up only in our last spectrum taken about 2 weeks after maximum light. The implied distribution of elements in velocity space agrees well with the DD model predictions for a subluminous SN Ia. Regardless of the explosion model, the long duration of the phases dominated by layers of explosive carbon and oxygen burning argues that SN 1999by was the explosion of a white dwarf at or near the Chandrasekhar mass. The good agreement between the observations and the models without fine-tuning a large number of free parameters suggests that DD models are a good description of at least subluminous Type Ia SNe. Pure deflagration scenarios or mergers are unlikely, and helium-triggered explosions can be ruled out. However, problems for DD models still remain, since the data seem to be at odds with recent three-dimensional models of the deflagration phase that predict significant mixing of the inner layers of the white dwarf prior to detonation. Possible solutions include the effects of rapid rotation on the propagation of nuclear flames during the explosive phase of burning or extensive burning of carbon just prior to the runaway.

3D deflagration simulations leaving bound remnants: a model for 2002cx-like Type Ia supernovae

Abstract: cx-like supernovae are a sub-class of sub-luminous Type Ia supernovae. Their light curves and spectra are characterized by distinct features that indicate strong mixing of the explosion ejecta. Pure turbulent deagrations have been shown to produce such mixed ejecta. Here, we present hydrodynamics, nucleosynthesis and radiative transfer calculations for a 3D full-star deagration of a Chandrasekhar-mass white dwarf. Our model is able to reproduce the characteristic observational features of SN 2005hk (a proto-typical 2002cx-like supernova), not only in the optical, but also in the near- infrared. For that purpose we present, for the rst time, ve near-infrared spectra of SN 2005hk from 0:2 to 26:6 days with respect to B-band maximum. Since our model burns only small parts of the initial white dwarf, it fails to completely unbind the white dwarf and leaves behind a bound remnant of 1.03 M { consisting mainly of unburned carbon and oxygen, but also enriched by some amount of intermediate-mass and iron-group elements from the explosion products that fall back on the remnant. We discuss possibilities for detecting this bound remnant and how it might inuence the late-time observables of 2002cx-like SNe.