ﻻ يوجد ملخص باللغة العربية
We use 156 044 white dwarf candidates with $geq5sigma$ significant parallax measurements from the Gaia mission to measure the velocity dispersion of the Galactic disc; $(sigma_U,sigma_V,sigma_W) = (30.8, 23.9, 20.0)$ km s$^{-1}$. We identify 142 objects that are inconsistent with disc membership at the $>5sigma$ level. This is the largest sample of field halo white dwarfs identified to date. We perform a detailed model atmosphere analysis using optical and near-infrared photometry and parallaxes to constrain the mass and cooling age of each white dwarf. The white dwarf cooling ages of our targets range from 7 Myr for J1657+2056 to 10.3 Gyr for J1049-7400. The latter provides a firm lower limit of 10.3 Gyr for the age of the inner halo based on the well-understood physics of white dwarfs. Including the pre-white dwarf evolutionary lifetimes, and limiting our sample to the recently formed white dwarfs with cooling ages of $<500$ Myr, we estimate an age of $10.9 pm 0.4$ Gyr (internal errors only) for the Galactic inner halo. The coolest white dwarfs in our sample also give similar results. For example, J1049-7400 has a total age of 10.9-11.1 Gyr. Our age measurements are consistent with other measurements of the age of the inner halo, including the white dwarf based measurements of the globular clusters M4, NGC 6397, and 47 Tuc.
The contribution of white dwarfs of the different Galactic populations to the stellar content of our Galaxy is only poorly known. Some authors claim a vast population of halo white dwarfs, which would be in accordance with some investigations of the
We analyzed the velocity space of the thin and thick-disk Gaia white dwarf population within 100 pc looking for signatures of the Hercules stellar stream. We aimed to identify those objects belonging to the Hercules stream and, by taking advantage of
Gaia will identify several 1e5 white dwarfs, most of which will be in the solar neighborhood at distances of a few hundred parsecs. Ground-based optical follow-up spectroscopy of this sample of stellar remnants is essential to unlock the enormous sci
We present a detailed analysis of the white dwarf luminosity functions derived from the local 40 pc sample and the deep proper motion catalog of Munn et al (2014, 2017). Many of the previous studies ignored the contribution of thick disk white dwarfs
We analyse the 100pc Gaia white dwarf volume-limited sample by means of VOSA (Virtual Observatory SED Analyser) with the aim of identifying candidates for displaying infrared excesses. Our search focuses on the study of the spectral energy distributi