Stars, Planets, and ISM Seminar

AM CVn systems are a type of compact binary that features mass transfer between a helium-rich white dwarf accretor and a degenerate or semi-degenerate donor. These systems have orbital periods of roughly 5–65 minutes and serve as a platform for studying stellar evolution, accretion disk physics, and gravitational waves. In optical observations, the light is primarily from the accreting white dwarf or its disk, leaving the donor star unobserved. Given the donor star’s expected cool temperature, its emission is mainly in the far-infrared bands. For this project, we combined multi-wavelength data from ultraviolet to far-infrared with the objective of detecting an infrared excess from the donor star for the first time. Using photometric data along with distance and reddening parameters, we determined the temperature and radius of both the accretor and the donor by fitting a double blackbody model: wavelengths below 20,000 angstroms represented the white dwarf, while wavelengths above represented the donor star. Our work led to the discovery of a reliable infrared excess in 10 systems, marking the first detection of the donor star in AM CVn systems.
 

Malia Kao, The University of Texas at Austin

Navigating the Sea of White Dwarfs in Gaia with UMAP

Before the Gaia space telescope survey, about 30,000 white dwarfs were known. Since Gaia launched in 2011, it has increased this number by an order of magnitude, and in its most recent data release in 2022, low-resolution (R~70) spectra were released for about 100,000 white dwarfs. We utilized an unsupervised machine learning algorithm called UMAP to organize these 100,000 white dwarfs into a 2D map where different regions are correlated to different spectral features. A few of the unique groups we've identified are white dwarfs that exhibit metal pollution from active or recent planetary accretion, white dwarfs in binary systems, pulsating white dwarfs, and very cool temperature carbon-atmosphere white dwarfs, among many others. By exploring the different regions of the UMAP, we can probe different questions regarding stellar and planetary evolution.