R Dra

I’m writing a series of posts on objects I observe or find interesting for other reasons. Let’s start it off with R Dra.

This Mira with a period of 246 days varies between 6.7 and 13.2 visually. Its variability was discovered by the Norwegian astronomer Hans Geelmuyden (1844-1920) in Christiania, present-day Oslo in 1876.1

The Astronomische Gesellschaft ran a large-scale collaborative project of observing stellar positions with high-precision meridian circles. The sky was divided up into zones and the Christiania (Oslo) observatory was responsible for the zone between +65 and +70 degrees declination. Geelmuyden and C. Fearnley observed the Christiania zone. In June 1875 and June 1876 they noticed a missing star in Draco. The star had previously been observed in 1842, when Argelander observed it at magnitude 8.9; Krüger and Schönfeld had also observed it in 1858, but now it was invisible. The new variable was designated R Dra.2

R Dra is easy to find, using gamma Ursae Minoris as a starting point. It is fairly well observed, with 43 000 observations currently in the AAVSO database.

The period of R Draconis changes somewhat over the years, as this diagram of calculated versus observed maxima shows.3

Like many Miras, R Draconis is a maser source, probably situated in the circumstellar envelope around the star. Its strength varies with approximately the same period as the visual light curve.4

R Draconis is currently near its maximum; yesterday, I observed it at 7.5 in 15×70 binoculars.

  1. J. E. Isles and D. R. B. Saw, “Mira stars – III: R Dra, R Gem, S Her, T Her, U HER and R Leo,” Journal of the British Astronomical Association 99 (August 1, 1989): 165-171. []
  2. A. Winnecke, “Schreiben des Herrn Prof. Winnecke an den Herausgeber”, AN vol 89 (1877), 212; C. Fearnley, “Über den Veränderlichen R Draconis”, AN vol 90 (1877), 15. []
  3. F. Kühnlenz, “Das Periodenverhalten des Mira-Sternes R Draconis.,” Zentralinstitut fuer Astrophysik Sternwarte Sonneberg Mitteilungen ueber Veraenderliche Sterne 12 (1990): 75. []
  4. Samantha J. Osmer, Priscilla J. Benson, and Irene R. Little-Marenin, “Water Maser Emission and the Visual Light Curve of R Draconis,” Journal of the American Association of Variable Star Observers (JAAVSO) 20 (Oktober 1991): 203-207. []
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