4U 0115+63
Abstract
M. Johns, McGraw-Hill Observatory; A. Koski, University of Michigan; and C. Canizares and J. McClintock, Massachusetts Institute of Technology, report observations of the brightest star in the combined SAS-3 and HEAO-1 error boxes for 4U 0115+63 (cf. IAUC 3163). The observations were performed with the McGraw-Hill Observatory's 130-cm telescope on Kitt Peak. Photoelectric photometry gives the values V = 15.64, B-V = +1.44, U-B = +0.31 (all +/- 0.05) for Feb. 3.2 UT. A spectrogram obtained with the Mark II photon-counting spectrometer on Feb. 4.2 shows strong emission at H-alpha and possible emission at H-beta but no other distinct stellar features. These characteristics make it nearly certain that the star is the optical counterpart of the x-ray source. The colors are consistent with those of an ~ B-type star with Av >~ 5 magnitudes. S. Rappaport, G. Clark, L. Cominsky and F. Li, Massachusetts Institute of Technology, report that SAS-3 observations of the x-ray Doppler curve for the transient source 4U 0115+63 (cf. IAUC 3161) have revealed its binary nature. The orbit of the x-ray star is moderately eccentric and has a period of 24 days. The measured mass function of 5 Msol requires that the companion have a mass > 5 Msol. The high optical luminosity likely to be associated with such a star makes the object with mv ~ 16 in the SAS-3 and HEAO-1 error boxes (IAUC 3163) the most promising candidate for the optical counterpart; see also the note by Johns et al. above. Observers are urged to search for optical variability of this candidate during x-ray decline and for the binary period.
- Publication:
-
International Astronomical Union Circular
- Pub Date:
- February 1978
- Bibcode:
- 1978IAUC.3171....1J