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Classic LBV in M31 -- AF And in Eruption

ATel #10752; R. M. Humphreys, C. E. Woodward (Univ. Minnesota), R. Mark Wagner (LBTO and Ohio State Univ.), J. C. Martin (Univ. Illinois, Springfield)
on 15 Sep 2017; 14:23 UT
Credential Certification: Roberta Humphreys (roberta@umn.edu)

Subjects: Optical, Star, Transient, Variables

A recent spectrum of the classic Luminous Blue Variable (LBV) AF And (J004333.08+411210.3 = Var 19) in M31 confirms that it has undergone a significant spectroscopic transition since 2015 October (see ATEL 10502). A moderate resolution spectrum was obtained on 28 Aug 2017 UT at the MMT on Mt. Hopkins, Arizona using the Blue Channel Spectrograph with the 500 line/mm grating. The spectrum reveals strong, narrow Hydrogen emission lines with prominent P Cygni absorption profiles and broad wings. Emission lines of Fe II with P Cygni profiles are present. The He I lines and Mg II 4481 are in absorption. Previous spectra observed in 2010 (see Fig. 5 in Humphreys et al. ApJ, 790, 48), 2013 and 2015 resembled an Of/late WN star with N III emission and strong He I emission. Its spectrum is now similar to that of a late B-type supergiant. These spectral changes correspond to a shift in its energy distribution to cooler temperatures likely due to enhanced mass loss and the formation of a cooler dense wind similar to other LBV/S Dor variables as first suggested by the visual brightening and redder color of AF And reported in ATEL 10383. The current spectrum and the spectra from 2010, 2013, and 2015 are at http://etacar.umn.edu/LuminousStars/M31M33/M31stars.html . AF And slowly increased in apparent brightness from 2014 but since May 2017 it has shown very little change in magnitude or color. On Aug 23 it was V = 16.2 with B-V = 0.15. See https://go.uis.edu/m31m33photcat .