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.

The CFHT Open Star Cluster Survey. IV. Two Rich, Young Open Star Clusters: NGC 2168 (M35) and NGC 2323 (M50)

Abstract: We continue our study of rich Galactic clusters by presenting deep CCD observations of both NGC 2168 (M35) and NGC 2323 (M50). Both clusters are found to be rich (NGC 2168 contains at least 1000 stars brighter than V = 22, and NGC 2323 contains ~2100 stars brighter than our photometric limit of V ~ 23) and young (NGC 2168 age = 180 Myr and for NGC 2323 age = 130 Myr). The color-magnitude diagrams for the clusters exhibit clear main sequences stretching over 14 mag in the (V, B-V)-plane. Comparing these long main sequences with those of earlier clusters in the survey, as well as with the Hyades, has allowed for accurate distances to be established for each cluster (for NGC 2168 d = 912 pc and for NGC 2323 d = 1000 pc). Analysis of the luminosity and mass functions suggests that, despite their young ages, both clusters are somewhat dynamically relaxed, exhibiting signs of mass segregation. This is especially interesting in the case of NGC 2323, which has an age of only 1.3 times the dynamical relaxation time. The present photometry is also deep enough to detect all of the white dwarfs in both clusters. We discuss some interesting candidates that may be the remnants of quite massive (M ≥ 5 M⊙) progenitor stars. The white dwarf cooling age of NGC 2168 is found to be in good agreement with the main-sequence turnoff age. These objects are potentially very important for setting constraints on the white dwarf initial-final mass relationship and the upper mass limit for white dwarf production.

Spin-Up/Spin-Down models for Type Ia Supernovae

Abstract: In the single degenerate scenario for Type Ia supernova (SNeIa), a white dwarf (WD) must gain a significant amount of matter from a companion star. Because the accreted mass carries angular momentum, the WD is likely to achieve fast spin periods, which can increase the critical mass, $M_{crit}$, needed for explosion. When $M_{crit}$ is higher than the maximum mass achieved by the WD, the WD must spin down before it can explode. This introduces a delay between the time at which the WD has completed its epoch of mass gain and the time of the explosion. Matter ejected from the binary during mass transfer therefore has a chance to become diffuse, and the explosion occurs in a medium with a density similar to that of typical regions of the interstellar medium. Also, either by the end of the WD's mass increase or else by the time of explosion, the donor may exhaust its stellar envelope and become a WD. This alters, generally diminishing, explosion signatures related to the donor star. Nevertheless, the spin-up/spin-down model is highly predictive. Prior to explosion, progenitors can be super-$M_{Ch}$ WDs in either wide binaries with WD companions, or else in cataclysmic variables. These systems can be discovered and studied through wide-field surveys. Post explosion, the spin-up/spin-down model predicts a population of fast-moving WDs, low-mass stars, and even brown dwarfs. In addition, the spin-up/spin-down model provides a paradigm which may be able to explain both the similarities and the diversity observed among SNeIa.

Thirty-Five New Pulsating Da White Dwarf Stars

Abstract: We present 35 new pulsating DA (hydrogen atmosphere) white dwarf stars discovered from the Sloan Digital Sky Survey (SDSS) and the Hamburg Quasar Survey (HQS). We have acquired high-speed time series photometry of preselected DA white dwarfs with a prime focus CCD photometer on the 2.1 m telescope at McDonald Observatory over 15 months. We selected these stars on the basis of prior photometric and spectroscopic observations by the SDSS and HQS. For the homogeneous SDSS sample, we achieve a success rate of 80% for finding new variables at a detection threshold of 0.1%-0.3%. With 35 newly discovered DA variable white dwarfs, we almost double the current sample of 39.

Transit surveys for earths in the habitable zones of white dwarfs

Abstract: To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs and show that it extends from ≈0.005 to 0.02 AU for white dwarfs with masses from 0.4 to 0.9 M ☉, temperatures less than ≈104 K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be deeply eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favor detection of planets similar to Earth: similar size, temperature, and rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.

CONSTRAINING TYPE Ia SUPERNOVAE PROGENITORS FROM THREE YEARS OF SUPERNOVA LEGACY SURVEY DATA

Abstract: While it is generally accepted that Type Ia supernovae are the result of the explosion of a carbon-oxygen white dwarf accreting mass in a binary system, the details of their genesis still elude us, and the nature of the binary companion is uncertain. Kasen points out that the presence of a non-degenerate companion in the progenitor system could leave an observable trace: a flux excess in the early rise portion of the light curve caused by the ejecta impact with the companion itself. This excess would be observable only under favorable viewing angles, and its intensity depends on the nature of the companion. We searched for the signature of a non-degenerate companion in three years of Supernova Legacy Survey data by generating synthetic light curves accounting for the effects of shocking and comparing true and synthetic time series with Kolmogorov-Smirnov tests. Our most constraining result comes from noting that the shocking effect is more prominent in the rest-frame B than V band: we rule out a contribution from white dwarf-red giant binary systems to Type Ia supernova explosions greater than 10% at the 2{sigma}, and greater than 20% at the 3{sigma} level.