Special Notice #205: Rapid fading in the luminous blue variable S Doradus

April 15, 2010: Noel D. Richardson and Douglas R. Gies (Georgia State University) announced on 2010 April 14 (Astronomer's Telegram #2560) that S Doradus is currently fading in optical brightness, while its hydrogen Balmer line (H-alpha) brightness is increasing. The V-band magnitude of S Dor (as measured by ASAS-3; Pojmanski, G., 2002, AcA 52, 397) has been declining for more than a thousand days. The star began a more rapid decline earlier this year, and is now fainter than V=9.5. BVRI photometry by G. Di Scala (Sydney, NSW, Australia) shows that the star was at V=9.83 on 2010 March 08.4535 (JD 2455263.9535), and the most recent visual observation (A. Plummer, Linden, NSW, Australia) put the star at m(vis)=9.9 on April 08.4215 (JD 2455294.9215). Observations of S Dor are encouraged to follow this current event.
S Dor is the class prototype for the luminous blue variables, supermassive stars that exhibit irregular photometric variability, and are experiencing substantial mass loss. All observations of S Dor -- both visual estimates and CCD photometry -- will be important for studying the current event. Intensive CCD time-series observations are not critically needed, but nightly photometry will be very useful.
S Dor is located in the Large Magellanic Cloud, at the following (J2000) coordinates: RA: 05 18 14.35 , Dec: -69 15 01.1
Charts for S Dor may be plotted using AAVSO VSP (http://www.aavso.org/vsp).
Please promptly report all observations to the AAVSO using the name "S DOR".
This AAVSO Special Notice was prepared by Dr. Matthew Templeton. ---------------------------------------------------
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