DNe update Sep 2000

Eclipsing Dwarf Novae update September 2000

Bill Worraker

PROGRAMME CHANGES

Stars Dropped:
On advice from Prof. Fred Ringwald that enough photometric observations of V503 Cyg are available to show that it is non-eclipsing, this star has now been dropped from the programme.
Photometric data from Lasse Jensen (CBA, Denmark) on T Leo and AY Lyr in outburst in previous years, together with IBVS 4059 (on AY Lyr) have shown superhumps in both stars but no sign of eclipses. These stars are therefore also dropped from the programme as non-eclipsers.
A high-quality 7.6-hour photometric dataset from Tonny Vanmunster (CBA, Belgium) on RZ LMi shows clear superhumps (a full 5 cycles!), but no sign of eclipses. Tonny also advises that several detailed photometric studies have revealed no sign of eclipses. RZ LMi is therefore also dropped from the programme as a non-eclipser.

Stars Added:
Added this month (September 2000) are AR And, CY Lyr and LL Lyr; see the latest programme list for details. AR And reaches 11th magnitude at maximum, while CY Lyr and LL Lyr reach 13th magnitude, so all three should be relatively easy to reach when in outburst.

THE 2000 JULY SUPEROUTBURST OF V844 HER

On July 17 the SU UMa star V844 Her went into outburst at magnitude 12.2. This was its first detected outburst since 1999 September 29 when it was seen by Hazel McGee [see the article by Gary Poyner, VSSC 102, p.5 (1999 December)]. V844 Her has a very short orbital period of 1.32 hours (estimated from its superhump period), which places it amongst the dwarf novae with the shortest known periods. Several such stars (e.g. WZ Sge, HV Vir, LL And) have very long outburst intervals (measured in years to decades) and only appear to undergo superoutbursts. Thus far V844 Her has similarly been observed only to undergo superoutbursts, but its outburst cycle of 260 days is much shorter. It is thus perhaps a unique system.

Photometry with a view to detecting possible eclipse behaviour during the 2000 July outburst was received for 3 nights, July 19/20, 20/21 and 21/22. Superhumps of about 0.2 mag amplitude were clearly visible on the second and third nights. The most interesting light curves obtained were for July 21/22, when both Graham Salmon and David Boyd were taking unfiltered CCD measurements. There was considerable overlap between their data sets, allowing confirmation of a superhump trough at July 21.960UT and a peak at 21.981UT. Combining Graham Salmon's light curves for the second and third nights allows the superhump period (assumed stable for at least the intervening 24 hours) to be estimated as 1.415 hours or 0.059 days, rather longer than the figure quoted in Gary Poyner's article. The superhumps are of fairly typical shape, the 'rising' portions of the curves occupying about half the time taken by the 'falling' portions. See light curve below.

As for eclipse behaviour, none is evident in these light curves. Although V844 Her will remain on the EDNe programme since we do not yet have coverage of three complete orbits, it appears unlikely that it is an eclipsing system.

Photometric Results on V844 Her for 2000 July 21/22:

Graham Salmon:
LX200 10" f10 + Norman Walker filter box + SXL8 CCD (unfiltered). Exposures 60 sec with 15 sec dead time Data reduction: Average of results from cf with stars 2, 6 and 7 of TA seq. David Boyd:
0.102m refractor + HX15 CCD (unfiltered). Exposures: 60 sec Note: Results based on linear fit with corrected magnitudes for reference stars.

Photometric Results on V844 Her for 2000 July 21/22:
Graham Salmon: LX200 10" f10 + Norman Walker filter box + SXL8 CCD (unfiltered). Exposures 60 sec with 15 sec dead time Data reduction: Average of results from cf with stars 2, 6 and 7 of TA seq.	David Boyd: 0.102m refractor + HX15 CCD (unfiltered). Exposures: 60 sec Note: Results based on linear fit with corrected magnitudes for reference stars.

THE 2000 AUGUST SUPEROUTBURST OF GX CAS

On August 21 Gary Poyner reported the SU UMa-type dwarf nova GX Cas to be in outburst at visual magnitude 13.7. Nick James obtained a continuous 5.5-hour photometric dataset on the night of August 23/24 (pretty well as long a run as possible at this time of year!). The resulting light curve is on The Astronomer web pages
This light curve shows beautiful superhumps of about 0.3 mag crest-to-trough amplitude, but no sign of eclipses. Once again, although there is insufficient data to make a final decision on this star, it appears very unlikely that it is an eclipsing system.