VARIABLE STAR OF THE MONTH:

HL CANIS MAJORIS

This one is a dwarf nova and again, one does not need photometer eyeballs in order to make good observations. Reporting its presence or absence will be useful but magnitude estimates will be even more useful.

The history of its discovery is interesting. Dr Chris Mauche of JPL says that an X-ray survey failed to show Sirius but did show an object near the position of Sirius. This object turned out to be a dwarf nova, outshining Sirius in X-rays although the latter is about 40 000 times brighter in visible light. It has a couple of outbursts a month, each lasting several days, so new observers should not become frustrated at its lack of activity.

Being only about 9 arc minutes from Sirius, HL should be easy to find. It sits near the centre of the elongated parallelogram formed by the stars 87, 104, 85 and 92. The problem is the glare of Sirius’s light, scattered by contaminated optics or the atmosphere. Observing HL is like other activities one can name where size is not everything. In good conditions, a good 8cm refractor will show the star better than my 32cm Cassegrain, because of my dirty optics and atmosphere.

If you can see the 118 star and not see HL then the star is not in outburst and you are justified in reporting it as such. If you are fortunate enough to have clean optics and a non-scattering atmosphere, you should be able to see the 130 star and you can report is as being rainter than 13.0. At outburst, HL sometimes reaches mag 11.4 and at other times only mag 11.8 or so. Enjoy you variable star observing.

Danie