4U 1630-47

J. Grindlay, Center for Astrophysics, reports that his photometry and spectroscopy at Cerro Tololo Interamerican Observatory of stars in the ~ 30" error circle given by Wilson et al. (1977, Astrophys. J. 215, L111) for the x-ray source 4U 1630-47 has revealed an emission-line object, possibly variable. Image-tube spectrograms (range 3900-7100 A, dispersion 120 A/mm) obtained on Aug. 20 with the 100-cm telescope with an east-west (3" x 10") slit centered on the brightest star in or near the error circle (R. A. = 16h30m14s.5, Decl. = -47o16'18", equinox 1950.0, uncertainty +/- 3") showed strong H-alpha, H-beta, N II and possibly broad He II 4686 A in emission. An observation on Aug. 22 showed strong Ha, N II, O III and possibly broad 4650 A and 4686 A emission; H-beta was not detected, so variability is suggested. On Aug. 22 the H-alpha and N II emission lines appeared to have P-Cyg profiles. Photometry of this star with a 12".5 diaphragm on Aug. 19 yielded V ~ 15.5, B-V ~ +0.9, U-B ~ +0.7 and V-R ~ +0.2 (uncertainty +/- 0.2 magnitude); significant H-alpha emission was detected with a 16-A interference filter at a flux level of about 1.7 x 10**-14 erg cm**-2 s**-1. A 60-min IV-N exposure with the 400-cm telescope on Aug. 24 shows that a star of red magnitude ~ 22 located ~ 3" to the southwest would also have been included in the slit, but no nebulosity is obvious in the immediate field. Further photometry and spectroscopy of the candidate star and surrounding field are urgent since the x-ray source, a recurrent transient with period ~ 615 days (Jones et al. 1976, Astrophys. J. 210, L9), is expected to turn on during the next week or so. Kaluzienski and Holt report that the x-ray source remains (through Sept. 5) below the Ariel 5 detection threshold for this source of ~ 0.2 times the Crab (at 3-6 keV). Previous observations indicate an expected peak intensity of about 0.37 times the Crab.