CBA Belgium Website

CW Mon - a grazing eclipser in outburst during November 2002

CW Mon is an UGSS-type dwarf nova, located at RA 06h36m54.53s, Dec +00°02'16.3'' (J2000.0), with a magnitude range given in the online "Catalog and Atlas of Cataclysmic Variables" of 11.9-16.3. The object was detected in outburst on 2002, Oct 29.4 UT by Dan Taylor at mag 14.4. In the following days it further brightened (see vsnet for details).

In an email message of Nov 5th, 2002 (vsnet-campaign-dn 2971), Taichi Kato announced the probable detection of grazing eclipses by Kiyota (Tsukuba, Japan) , recorded in CCD observations obtained on Nov 3, 2002 :

"An eclipse-like fading (depth 0.2 mag in V, duration ~40 min) was clearly recorded in Nov. 3 long observation. Although the feature became less sharp, a similar fading was observed on Nov. 4. These observations, together with the suggested large inclination (Szkody and Mateo 1986, AJ, 92, 483), suggest that these fadings correspond to grazing eclipses as seen in U Gem. Since the orbital period has not been yet exactly established to make an ephemeris (the period by Szkody and Mateo was derived from a single-night IR observation), long (preferably 4 hours until dawn) nightly observations are strongly encourged to unambiguously identify the (probable) eclipses."

I realised a CCD observing session on CW Mon on November 5/6, 2002 at CBA Belgium, during 4.3 hours. Unfortunately, atmospheric conditions were very poor, with several cloud fields passing by. The light curve, reproduced below, shows some small amplitude (about 0.1 mag) irregularities, but no obvious indication of an eclipse.

Apparently, the "grazing eclipse" nature of CW Mon was already known before. In a private email message from Joe Patterson, Columbia University, NY, received on Nov 7th, 2002, Joe states :

"CW Mon is a grazing eclipser which is very much like U Gem in Porb and orbital waveform. In quiescence. I've observed full orbits a few times over the years, and Rich Stover has observed many... he showed me his quite beautiful results, but I think never published them apart from an AAS abstract [Stover & Allen 1987, BAAS, 19, 1058], which contains most of the relevant info I think."