[Vsnet-alert 8418] GY Hya, a probable DN with a long period

[Berto Monard]

GY Hya, described in the online CV atlas as ug:, has been observed at CBA Pretoria since March 2002 and found to be a probable DN with a period of 0.347237d (+/- 0.000001d).

The star field around GY Hya was measured by A Henden in June 1999. As a note to his sequence table, B Sumner comments that with B-V=1.05, GY Hya looks as if it were perhaps wrongly classified as a CV. Later additions to the Henden Sumner sequence file mention the outbursting GY Hya to have a B-V= 0.50, which definitely confirmed the blue colour of the outbursting object. 

Early unfiltered CCD observations (March-May 2002) at CBA Pretoria hinted at a long period CV with a light curve dominated by the secondary star.   

After an outburst notification by Rod Stubbings, an all night run timeseries photometry was dedicated to GY Hya on 13 May 2004. The timing was exactly right and two eclipses were caught, separated by more than 8 hours. 
Further short observations on 14, 15 and 18 May and another long one on 22 May, allowed to determine the Porb as 0.34725d (8.3338 h) over a baseline of more than 9d. 

Occasional observations since then and a re-visit to the 2002 data allowed to derive a more accurate period and the following eclipse ephemeris:  JD 2453139.215 + n (0.347237).

An interesting observation of this system is that at the time of eclipse the brightness during outburst is the same as during quiescense, something not unexpected for such a system. The overall brightness outside eclipse was measured to be only 0.7CR brighter during the outburst stage. Observations in V and B can be expected to show much larger changes.


Berto Monard
Bronberg Observatory / CBA Pretoria