# Spectroscopic Observations of the Intermediate Polar EX Hydrae in Quiescence

## TL;DR

This study presents spectroscopic observations of the intermediate polar EX Hya in quiescence, revealing spin-modulated radial velocities, accretion curtain emissions, and disc overflow, confirming theoretical models of accretion processes.

## Contribution

First detection of spin-modulated radial velocities from the outer disc in an intermediate polar, supporting accretion curtain models and disc overflow during quiescence.

## Key findings

- Spin-modulated radial velocities consistent with outer disc origin.
- Evidence of accretion curtain extending near Roche lobe radius.
- Confirmation of disc overflow during quiescence.

## Abstract

Results from spectroscopic observations of the Intermediate Polar (IP) EX Hya in quiescence during 1991 and 2001 are presented. Spin-modulated radial velocities consistent with an outer disc origin were detected for the first time in an IP. The spin pulsation was modulated with velocities near ~500-600 km/s. These velocities are consistent with those of material circulating at the outer edge of the accretion disc, suggesting corotation of the accretion curtain with material near the Roche lobe radius. Furthermore, spin Doppler tomograms have revealed evidence of the accretion curtain emission extending from velocities of ~500 km/s to ~1000 km/s. These findings have confirmed the theoretical model predictions of King & Wynn (1999), Belle et al. (2002) and Norton et al. (2004) for EX Hya, which predict large accretion curtains that extend to a distance close to the Roche lobe radius in this system. Evidence for overflow stream of material falling onto the magnetosphere was observed, confirming the result of Belle et al. (2005) that disc overflow in EX Hya is present during quiescence as well as outburst. It appears that the hbeta and hgamma spin radial velocities originated from the rotation of the funnel at the outer disc edge, while those of halpha were produced due to the flow of material along the field lines far from the white dwarf (narrow component) and close to the white dwarf (broad-base component), in agreement with the accretion curtain model.