Bright outburst of V585 Lyr (= TK4) in September 2003

V585 Lyr (= TK4) was discovered as an UG type dwarf nova by T. V. Kryachko of Sternberg Astronomical Institute (Russia) on Moscow archive plates (see IBVS 5058) taken with the 40-cm astrograph. The object was reported to be in a bright outburst on 2003, Sep 14.1076 UT by Mark Simonsen, who visually observed it at mag 13.9 [vsnet-outburst 5857].

The UG subclassification of V585 Lyr has not yet been firmly established, although a number of parameters seem to point to an SU UMa type dwarf nova. Given the brightness of the September 2003 outburst, I decided to start an unfiltered CCD photometry session at CBA Belgium Observatory on Sep 14th, at 18h58m UT. The session lasted for 2.7 hours, and was conducted under very clear skies. I used the 0.35-m f/6.3 telescope of CBA Belgium Observatory and an ST-7 CCD.

The image at left unambiguously identifies the outbursting object. Compare this image with an earlier negative identification. 

Outburst image of V585 Lyr, obtained at CBA Belgium Observatory on 2003, Sep 14.847 UT, using an unfiltered ST-7 CCD on a 0.35-m f/6.3 SCT telescope. Exposure time was 50 sec. North is up.

The resulting light curve is depicted below. It shows a rather constant object, indicating that the present outburst either is a normal outburst, or that superhumps have yet to develop. 

The night of September 15/16, 2003 was not very well suited for CCD photometry, due to the presence of thin clouds. I nevertheless decided to launch another observing session on V585 Lyr, lasting for nearly 3 hours. I made CCD exposures of 50 sec each, using the same equipment as described above. To increase the photon count, I decided to perform image stacking, grouping each time 3 exposures. The resulting light curve is shown below. Although there is somewhat more low-amplitude variation in the curve, it seems that superhumps have not (yet) developed at this stage of the outburst. 

It was clear again on September 16/17, 2003, with much better sky conditions than yesterday. Using the 0.35-m f/6.3 telescope and ST-7 CCD, I could follow V585 Lyr for 3.8 hours (unfiltered photometry). Similar to the nights before, the light curve (see figure below) is not showing modulations with an amplitude > 0.1 mag. I used the PDM technique to look for periodicities in the above (and combined) light curves, but no significant signal could be detected.

Due to a business trip, I had to skip the next couple of nights. Exactly then, superhumps started to develop, and V585 Lyr was identified as a new UGSU type variable with a (short) superhump period of 0.0603 d [vsnet-campaign-dn 3939]. 

My next opportunity to observe V585 Lyr came on September 19/20, 2003, when the sky was again very clear. Superhumps were very well developed by that time, and are easy to recognize in the light curve below. 

I continued to observe V585 Lyr on several follow-up nights, and all observation light curves are shown below.










Copyright © 2003 - Tonny Vanmunster.