Multi-longitude photometry of CVs

(vsnet 1006)


We have started a two-month campaign to study the light curves of two CVs from a range of terrestrial longitudes, in order to break aliases arising from the Earth's rotation, and to study fine structure in the periodic signals.

The southern campaign star is V803 Cen, nominally varying in the range 13-17. This is an ultra-short-period binary (Porb near 27 minutes) which is now cycling between about mag 13 and 14.5 on a timescale of ~1 day. Or possibly 0.5 days. "Either way, it's a mighty soberin' thought (Pogo 1948)." We're anxious to obtain photometry around the Earth to define this period properly; single-site data have proved to be insufficient. The wave is of unknown origin, but may be the signature of the world's shortest-period dwarf nova.

So we earnestly seek your help! Photoelectric and CCD observers should probably use the comparison star 2.5 arcmin south of V803 Cen; this star has V=13.40. Differential photometry with respect to this star in any filter, or no filter, is fine. Another useful comparison is the V=13.96 star located 2.5 arcmin NE of the variable. Visual observations are plenty useful too. Care should be taken with the timing of observations.

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The northern campaign star is LX Ser, an eclipsing CV normally of magnitude 14-15. It has "permanent superhumps" in its light curve, but the power spectrum suggests waves of period slightly above and slightly below Porb. This is a challenge to unravel and demands long time- series photometry from a range of terrestrial longitudes. We have not yet established a standard comparison star, but a good choice would be the 11.5 mag star 2' NNW of the variable.

If you're interested in joining us in this enterprise, let us hear from you! I'm (JP) temporarily at You can find charts for both stars and many others in our CBA Website (, or I'll be happy to mail you printed versions. Downes and Shara (Feb 1993 PASP) also publish a chart for LX Ser, and Elvius (1975, Astr and Astrophys, 44, 117) publishes both a chart and a magnitude sequence for V803 Cen.

The 2000 positions, by the way, are:

V803 Cen: RA = 13 23 44.5            LX Ser: RA = 15 38 00.2
         DEC =-41 44 32                     DEC =+18 52 02

Joe Patterson
Jonathan Kemp
Stan Walker

                 Center for Backyard Astrophysics (CBA)

Pogo 1948, cited by Kelly, W., Universal Features Syndicate, Inc.

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