Detection of a new sample of Galactic White Dwarfs in the direction of the Small Magellanic Cloud

TL;DR

This study demonstrates UVIT's effectiveness in discovering and characterizing white dwarfs in the Milky Way, identifying new candidates, and estimating their properties and space density, highlighting UVIT's potential for future white dwarf surveys.

Contribution

First use of UVIT data combined with Gaia DR3 to identify and analyze white dwarfs and low-mass candidates in the Milky Way.

Findings

Identified 43 WDs, 37 new; 13 WD+MS candidates; 161 UV bright MS stars.

WD masses range from 0.2 to 1.3 M$_{ ext{sun}}$, temperatures 10,000-15,000 K.

Estimated WD space density within 1 kpc as 1.3×10$^{-3}$ pc$^{-3}$.

Abstract

In this study, we demonstrate the efficacy of the Ultraviolet Imaging Telescope (UVIT) in identifying and characterizing white dwarfs (WDs) within the Milky Way Galaxy. Leveraging the UVIT point source catalogue towards SMC and crossmatching with Gaia DR3 data, we identified 43 single WDs (37 new detections), 13 new WD+main sequence (MS) candidates and 161 UV bright MS stars by analysing their Spectral Energy Distributions (SED). Using the WD evolutionary models, we determine the masses, effective temperatures, and cooling ages of these identified WDs. Masses of these WDs range from 0.2 to 1.3 M$_{\odot}$ and effective temperatures (T$_{eff}$) between 10000 K to 15000 K, with cooling ages spanning 0.1 to 2 Gyr. Notably, we detect hotter WDs compared to literature values, which is attributed to the sensitivity of UVIT. Furthermore, we report the detection of 20 new extremely low-mass (ELM) candidates from our analysis. Future spectroscopic studies of the ELM candidates will help us understand the formation scenarios of these exotic objects. Despite limitations in Gaia DR3 distance measurements for optically faint WDs, we provide a crude estimate of the WD space density within 1kpc as 1.3 $\times$ 10$^{-3}$ pc$^{-3}$, which is higher than previous estimates in the literature. Our results underscore the instrumental capabilities of UVIT and anticipate the forthcoming UV missions like INSIST for systematic WD discovery. Our methodology sets a precedent for future analyses in other UVIT fields to find more WDs and perform spectroscopic studies to verify their candidacy.