A $Gaia$ Data Release 2 catalogue of white dwarfs and a comparison with SDSS (1807.03315v3)

Abstract: We present a catalogue of white dwarf candidates selected from the second data release of $Gaia$ (DR2). We used a sample of spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey (SDSS) to map the entire space spanned by these objects in the $Gaia$ Hertzsprung-Russell diagram. We then defined a set of cuts in absolute magnitude, colour, and a number of $Gaia$ quality flags to remove the majority of contaminating objects. Finally, we adopt a method analogous to the one presented in our earlier SDSS photometric catalogues to calculate a probability of being a white dwarf ($P_{\mathrm{WD}}$) for all $Gaia$ sources which passed the initial selection. The final catalogue is composed of $486\,641$ stars with calculated $P_{\mathrm{WD}}$ from which it is possible to select a sample of $\simeq 260\,000$ high-confidence white dwarf candidates in the magnitude range $8<G\<21$. By comparing this catalogue with a sample of SDSS white dwarf candidates we estimate an upper limit in completeness of $85$ per cent for white dwarfs with $G \leq 20$ mag and $T_{\mathrm{eff}} > 7000$ K, at high Galactic latitudes ($|b|>20^{\circ}$). However, the completeness drops at low Galactic latitudes, and the magnitude limit of the catalogue varies significantly across the sky as a function of $Gaia$'s scanning law. We also provide the list of objects within our sample with available SDSS spectroscopy. We use this spectroscopic sample to characterise the observed structure of the white dwarf distribution in the H-R diagram.

• The paper presents a comprehensive Gaia DR2 catalogue of around 260,000 high-confidence white dwarfs, validated against SDSS spectroscopic data.
• It employs stringent criteria on absolute magnitude, color, and quality flags to effectively minimize contamination from non-white dwarf objects.
• The study estimates up to 85% completeness for white dwarfs brighter than G=20, offering a robust dataset for future Galactic evolution research.

Analysis of the Gaia DR2 Catalogue of White Dwarfs

The paper conducted by Gentile Fusillo et al. provides an extensive catalogue of white dwarf candidates derived from the second data release of Gaia (DR2), meticulously compared to the Sloan Digital Sky Survey (SDSS). This paper represents a significant effort in the astronomical community to utilize Gaia’s precise capabilities for a comprehensive identification and classification of white dwarfs across the sky.

Methodology

The authors employed the spectral data from the SDSS as a foundation to map the position of spectroscopically confirmed white dwarfs in the Gaia Hertzsprung-Russell (H-R) diagram. Utilizing this reference, they defined stringent criteria for absolute magnitude, color, and quality flags from Gaia to minimize the contamination by non-white dwarf objects. The result is a catalog consisting of approximately 486 stars, focusing on high-confidence candidates within a magnitude range of 8 < G < 21.

The catalogue utilized data from Gaia DR2, which includes stellar positions, parallaxes, and photometric information in the G, BP, and RP bands. These crucial parameters were employed to create a wide-ranging map of potential white dwarfs and to calculate a probability of any given Gaia source being a white dwarf. Notably, this approach provides a dataset of approximately 260,000 high-confidence white dwarfs, marking a substantial increase in sample size compared to prior compilations.

Results and Robustness

Through comparisons with a specially curated sample of SDSS candidates, the paper estimates an upper limit in completeness of 85% for white dwarfs brighter than G = 20 mag and with effective temperatures exceeding 7000 K. However, it is observed that completeness diminishes at lower galactic latitudes. A significant contribution of this work lies in its ability to characteristically profile the white dwarf distribution on the H-R diagram using available spectroscopy data from SDSS, identifying features such as bifurcations in cooling sequences which correlate with different atmospheric compositions.

The research provides critical insights into the size and distribution of white dwarfs, influencing our understanding of the Galactic stellar population. It effectively leverages Gaia's improvements in astrometric precision to overcome historical challenges in assembling large, homogenous samples of these dense stellar remnants.

Implications and Future Observations

Implications of this comprehensive catalogue extend to refining models of Galactic evolution by using white dwarfs as tracers. The completeness and rigorous criteria applied mean this dataset serves as a robust tool for future studies in stellar evolution, atmospheric analysis, and Galactic archaeology.

While the catalogue adheres strictly to the data available in DR2, further enhancements can be anticipated with subsequent Gaia releases. Future work could focus on integrating spectroscopic follow-up campaigns to enhance the accuracy of atmospheric parameters and validate candidates further. The increasing availability of large telescopic arrays could eventually lead to an unprecedented characterization of the astrophysical properties and distribution of white dwarfs throughout the Milky Way, refining our broad understanding with high fidelity.

In conclusion, the work presented by Gentile Fusillo et al. sets a strong foundation for expanding the landscape of white dwarf research, providing a pivotal resource for ongoing and future astronomical investigations into stellar remnants and Galactic dynamics.