# Fuse and IUE Spectroscopy of the Prototype Dwarf Nova ER Ursa Majoris During Quiescence

## TL;DR

This study analyzes FUV spectra of the dwarf nova ER UMa during quiescence, revealing a hot white dwarf and quantifying accretion rates, providing insights into its accretion processes and spectral characteristics.

## Contribution

First detailed FUV spectral analysis of ER UMa during quiescence using FUSE and IUE data, estimating accretion rates and white dwarf temperature.

## Key findings

- White dwarf temperature is 32,000 K, hotter than typical dwarf novae.
- Accretion rate during quiescence is approximately 7.3 x 10^-11 M_sun/yr.
- White dwarf contributes 55% of FUV flux, disk 45%.

## Abstract

ER Ursae Majoris is the prototype for a subset of SU UMa-type dwarf novae characterized by short cycle times between outburst, high outburst frequency, and ``negative'' superhumps. It suffers superoutbursts every 43 days, lasting 20 days, normal outbursts every 4 days and has an outburst amplitude of 3 magnitudes. We have carried out a far ultraviolet (FUV) spectral analysis of ER UMa in quiescence, by fitting Far Ultraviolet Spectroscopic Explorer (FUSE) and International Ultraviolet Explorer (IUE) spectra with model accretion disks and high gravity photosphere models. Using the Gaia parallax distance and an orbital inclination of $50^{\circ}$, we find that during the brief quiescence of only four days, the accretion rate is $7.3 \times 10^{-11}M_{\odot}$/yr, with the ER UMa white dwarf contributing 55% of the FUV flux and the accretion disk contributing the remaining 45\% of the flux. The white dwarf in ER UMa is markedly hotter (32,000~K) than the other white dwarfs in dwarf novae below the CV period gap which have typical temperatures $\sim$15,000~K. For a higher inclinations of 60 to 75 degrees, the accretion rates that we derive are roughly an order of magnitude higher $1 - 3 \times 10^{-10}M_{\odot}$/yr.