The X-ray transient Swift J063933.6+054918 is a M-dwarf flare star
ATel #4642; N. Masetti, M. Dadina (INAF/IASF, Bologna), R. Gualandi and I. Bruni (INAF/Astron. Obs. of Bologna)
on 12 Dec 2012; 09:06 UT
Credential Certification: Nicola Masetti (masetti@iasfbo.inaf.it)
Subjects: Optical, X-ray, Star, Transient, Variables
In order to investigate the nature of the optical counterpart (ATels #4634, #4635) of the recently-discovered X-ray transient Swift J063933.6+054918 (ATel #4631), starting at 22:07 UT of December 10, 2012, we collected two 20-min optical spectra with the BFOSC instrument mounted on the 1.5m "G.D. Cassini" telescope of the Astronomical Observatory of Bologna in Loiano (Italy).
The overall appearance of the optical spectral continuum is indeed that of a M-type dwarf, with several evident TiO molecular absorption bands, thus confirming the classification of Rau et al. (ATel #4634) and of Evans et al. (ATel #4635) obtained photometrically.
We also detect an H-alpha emission line at a wavelength consistent with the restframe value and with equivalent width 4.8+-0.5 Angstroms. Besides, further emission lines (H-beta and HeII at 4686 and 5411 Angstroms) are possibly detected.
We thus spectroscopically confirm the previous suggestion reported in ATels #4634 and #4635 that this object is a M-dwarf flare star.
