MBCAA Observatory

EX Hya

Observed: 9 Feb 2011

Michel Bonnardeau
13 Feb 2011

Abstract

A light curve for this cataclysmic star, classified as both IP and NL, is presented and compared with the ephemeris, after its May 2010 outburst.

Introduction

EX Hya is a cataclysmic star, that is a binary system with an accreting white dwarf. The orbital period is 1.63 hour. The white dwarf is magnetic and this modulates the accretion with the spin period of 1.12 hour (almost equal to the orbital period). The system also has outbursts, such as the one in May 2010. It is then classified as both an Intermediate Polar and a Nova Like.

The ephemeris for the orbital motion (the eclipse) is given by Hellier and Sproats (1992); the one for the maxima of the spin modulation is given by Mauche et al (2009).

Observations

The observations were carried out with a 203 mm f/6.3 SC telescope, a Rc filter and a SBIG ST7-E camera (KAF401E CCD). 116 usable images were obtained, each with an exposure duration of 60 seconds.

The comparison star is GSC 6709-0321 (AAVSO 000-BBT-327) with a Rc magnitude of 10.886, computed from the CMC14 r' magnitude, the 2MASS J, H, Ks magnitudes and using the transformation formulas of Bilir et al (2007).

The check star is GSC 6709-0006 (AAVSO 000-BBT-331). It is observed with the magnitude 11.855 +/- 0.014 +/- 0.017 where the first +/- is the average 1-sigma statistical uncertainty, and the second +/- is the standard deviation.

The air mass was very high (>3). However the sky was clear, an Rc filter was used to minimize the atmospheric effect, and EX Hya is fairly bright, so the data should be trustworthy.

The light curves:

Red: EX Hya, Blue: the check star shifted by 2.0mag. The error bars are +/- the 1-sigma statistical uncertainties. The eclipses, as predicted by the ephemeris of Hellier and Sproats (1992) are shown as to1 and to2.

The extra losses during the session.