Subdwarfs and white dwarfs from the 2MASS, Tycho-2, XPM and UCAC3 catalogues

TL;DR

This study utilizes multi-catalog photometry and proper motions to identify and analyze all-sky samples of white dwarfs and subdwarfs, revealing their distribution, kinematics, and metallicity relations, with implications for galactic structure.

Contribution

The paper presents a new method combining multi-catalog data and Monte-Carlo simulations to select and analyze subdwarfs and white dwarfs, providing insights into their distribution and properties.

Findings

Most subdwarfs are part of the galactic halo.

Evolved subdwarfs mainly belong to the thick disk.

Subdwarfs show concentration towards the galactic center hemisphere.

Abstract

The photometry from 2MASS, UCAC3 and SuperCosmos catalogues together with the proper motions from the Tycho-2, XPM and UCAC3 catalogues are used to select the all-sky samples of 34 white dwarfs, 1996 evolved and 7769 unevolved subdwarfs candidates for R from 9 to 17 magnitude. The samples are separated from the main sequence with admixture less than 10% owing to the detailed analysis of the distribution of the stars in the different color index (CI) vs. reduced proper motion (RPM) diagrams for various latitudes with special attention to the estimation of admixtures in the samples and with Monte-Carlo simulation. It is shown that the XPM and UCAC3 have the same level of proper motion accuracy. Most of the selected stars has at least 6-band photometry with accuracy is proved to be better than 0.2. The multi-color photometry allows us to eliminate some admixtures and reveal some binaries. The empirical calibrations of absolute magnitude versus CI and RPM for Hipparcos stars give us photometric distances and 3D distribution for all the stars. Although the selection method and uneven distribution of the XPM and UCAC3 data provide noticeable biases the preliminary conclusions are made. The subdwarfs show some concentration to the galactic centre hemisphere with voids because of extinction in the Gould belt and galactic plane. Some yet unexplained overdensities of the evolved subdwarfs are seen in several parts of the sky. For 183 stars with radial velocities 3D motion and galactic orbits are calculated. For 56 stars with Fe/H collected from various sources we find the relations of the metallicity with CI, asymmetric drift velocity and orbital eccentricity. It is shown that most unevolved subdwarfs belong to the halo with the scale height of $8\pm1$ kpc and local mass density of halo subdwarfs of $2\cdot10^{-5} M\sun pc^{-3}$. Most evolved subdwarfs belong to the thick disk with the scale height of $1.25\pm0.1$ kpc. Main parameters of the selected stars are compiled into new SDWD catalogue for future investigations. Special attention should be paid to spectroscopic observations of these stars because 53% of the selected white dwarfs, 94% of evolved and 98% of unevolved subdwarfs are now classified for the first time whereas the existed spectral classification is wrong in many cases.