The demoting of VW Dra

I am setting up a programme of variables to observe, and when I searched through AAVSO:s observation planner two weeks ago for semiregular variables bright enough for my binoculars (and the very light-polluted sky where I live), one of the stars that I decided to take on board was VW Dra, with a range of 6.0-7.0 V and a period of 170 days.

Tonight I made the first observation: I found it at 6.6. As I was doing some background reading on this star, I found that the International Variable Star Index (VSX) called the star CST, a constant star.

Strange. I still have the printouts from my search using the Observation Planner, and, yes, it says 6.0-7.0, type SRD: and a period of 170 days.

But that was two weeks ago. The other day, on November 11, Sebastian Otero of AAVSO’s VSX team changed the classification of VW Dra to constant, because no variations had been found in Hipparcos data or in the Geneva database of photometry.

Checking up some previous work on this star shows few, if any, signs of variation. 50 photoelectric observations during half a year in 1977 showed a constant magnitude.1 102 photoelectric measurements in another publication found no sure signs of variations.2 The GCVS, however, lists a photoelectric variation of 0.04 mag.

The variability of the star was discovered by the English amateur astronomer T.H. Astbury. He was a school headmaster, a member of the BAA and discovered several bright variables. The discovery note, published by Oxford astronomer H.H. Turner and dated 21 January 1911, is very brief and mentions no real data on the star3 Later, the star got the designation VW Draconis, and its variation was stated as 6.3-7.0 on the photographic magnitude scale.4

Then nothing much happened with the star. The AAVSO collected a couple of thousands of observations, finding nothing, and then came the photoelectrical era that effectively demoted VW Draconis from the status of being a variable star.

I think I will drop it from my binocular programme. I want more action from my stars than this.

  1. V. P. Murnikova and S. V. Vasilyeva, “Photoelectric Observations of Vw-Draconis in 1977,” Peremennye Zvezdy Prilozhenie 3 (1979): 589. []
  2. Gregory W. Henry et al., “Photometric Variability in a Sample of 187 G and K Giants,” The Astrophysical Journal Supplement Series 130 (September 2000): 201-225. []
  3. H.H. Turner, “Neuer Veränderlicher 1.1911 Draconis”, AN vol 187 (1911), 63-64. []
  4. “Benennung von neu entdeckten veränderlichen Sternen,” Astronomische Nachrichten 212 (January 1, 1921): 353. []
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