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Variable C in M33 in Eruption

ATel #5362; R. M. Humphreys (Institute for Astrophysics, University of Minnesota), K . Weis, B. Burggraf, D. Bomans (Astronomisches Institut, Ruhr-Universitaet, Bochum), J. C. Martin (University of Illinois, Springfield), H. Meusinger (Tautenburg Observatory)
on 4 Sep 2013; 20:56 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Roberta Humphreys (roberta@umn.edu)

Subjects: Optical, Star, Variables

Referred to by ATel #: 5403, 5538

The classical or normal LBV/S Doradus variable, Var C in M33 (Hubble & Sandage 1953) has entered an LBV-type eruption or high mass loss phase during which it increases in visual brightness and forms an optically thick wind at maximum light. In the past century Var C has experienced two long duration maxima (1940 - 1953, 1982 - 1993:) plus at least two briefer brightenings. The most recent was in 2001-2005. See Burggraf et al. 2013 (to be submitted) for the historic light curve and new observations up to 2012. The current eruption apparently began in late 2010 or early 2011. Our spectrum from 03 Oct. 2010 shows hydrogen emission with P Cygni profiles, Fe II emission plus absorption lines of He I, N II and Si IV, resembling an early B-type supergiant. It was thus still in its quiescent or hot stage at that time. See also Clark et al. 2012. Photometry, from the Tautenburg Obs., from its minimum in 2009 - 2010 to the present show that it brightened from V of 17.5 mag in Feb 2010 to 16.2 mag a year later in Feb 2011. The most recent photometry from the Barber Obs. Springfield. Il., on 01 Sep 2013, yields V of 15.6 mag.and B of 15.9 mag. Current spectra are now needed during its maximum light.