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Optical spectroscopy of MWC 148 (HESS J0632+057) around the time of enhanced Tev and X-ray emission

ATel #11233; K. A. Stoyanov, R. K. Zamanov, I. Kh. Iliev (Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, Bulgaria)
on 26 Jan 2018; 16:33 UT
Credential Certification: Kiril Stoyanov (kstoyanov@astro.bas.bg)

Subjects: Optical, Binary, Black Hole, Neutron Star

Referred to by ATel #: 11257

According to ATel#11223, the gamma-ray binary MWC 148 (HESS J0632+057) is in high X-ray and TeV state. We performed optical spectroscopy of this object on the night of 2018 Jan 25 and compare the results with our previous spectral observations. All observations are obtained with the ESpeRo spectrograph (Bonev et al. 2017, BlgAJ, 26, 67) at the 2m RCC telescope at Rozhen NAO, Bulgaria. Here are the dates of the observations and the equivalent width of the H-alpha emission line in angstroms:

2015 Dec 27 EW=-42.21
2016 Jan 30 EW=-41.87
2017 Dec 30 EW=-44.10
2018 Jan 25 EW=-44.50

On the base on our latest observations, we can confirm that the radius of the circumstellar disc around the B0pe donor star is greater compared to the data presented in Zamanov et al. (2016, A&A, 593, 97). On the Fig. 1 is a comparison of the H-alpha and H-beta emission lines, obtained on 2014 Jan 13 and 2018 Jan 25(four years apart). It is visible that the H-alpha emission is increased, while there are no significant changes in the H-beta line. This is a clear evidence for structural changes in the outer parts of the circumstellar disc, where the H-alpha emission is formed.

Fig. 1 Comparison between the H-alpha and H-beta lines obtained in 2014 and 2018