Hubble Space Telescope STIS Spectroscopy of Long Period Dwarf Novae in Quiescence

TL;DR

This study analyzes HST STIS spectra of five long period dwarf novae in quiescence to determine white dwarf properties and compare their temperatures with those below the period gap, revealing greater temperature dispersion above the gap.

Contribution

First detailed spectral analysis of long period dwarf novae's white dwarfs during quiescence, providing insights into their properties and evolutionary implications.

Findings

White dwarfs are partially exposed in all five systems.

Surface temperatures above the period gap show greater dispersion than below.

White dwarf temperatures above the gap are more varied than previously thought.

Abstract

We present the results of a synthetic spectral analysis of HST STIS spectra of five long period dwarf novae obtained during their quiescence to determine the properties of their white dwarfs which are little known for systems above the CV period gap. The five systems, TU Men, BD Pav, SS Aur, TT Crt, and V442 Cen were observed as part of an HST Snapshot project. The spectra are described and fitted with combinations of white dwarf photospheres and accretion disks. We provide evidence that the white dwarfs in all five systems are at least partially exposed. We discuss the evolutionary implications of our model fitting results and compare these dwarf novae to previously analyzed FUV spectra of other dwarf novae above the period gap. The dispersion in CV WD temperatures above the period gap is substantially greater than one finds below the period gap where there is a surprisingly narrow dispersion in temperatures around 15,000K. There appears to be a larger spread of surface temperatures in dwarf novae above the period than is seen below the gap.