The bright phase of Variable C in M33

ATel #5403; R. Viotti (INAF-IAPS, Roma) C. Rossi, F. Montagni (Phys. Dep., La Sapienza University, Roma) and R. Gualandi (Loiano Station, INAF-Osservatorio Astronomico di Bologna)
on 20 Sep 2013; 13:03 UT
Credential Certification: Francesco Verrecchia (francesco.verrecchia@asdc.asi.it)

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Following ATel #5362 notifying that the luminous S Doradus star Var C in M33 has entered in a luminous stage, we report that the preliminary analysis of Greve Observatory archive images of the galaxy shows that the star’s V magnitude varied from 17.06 on 9 Dec 2009 to 16.13 on 26 Feb 2011 and to 15.94 on 22 Sep same year.

Our highest luminosity record was of 15.60 on 22 Feb 2012. At present V=16.00. A similar trend was displayed in the Cousin r filter during 2011-2013 with V-r about +0.4. Our observations indicate that the brightening had mostly taken place during the year 2010. Shorter timescale oscillations, also typical of S Dor variables, are probably present and might alter the overall aspect of the long term light curve.

Only H emissions are clearly seen in a noisy lowres spectrum obtained at Loiano Obs. on 18 Sep confirming the low excitation state of the star.