Proposal #53

I am member of the NuSTAR Science Team and have been leading a program to search for a "second Cyg X-1" (the only persistent high mass X-ray binary containing an accreting black hole) in our Galaxy. I have undertaken a search for single-line spectroscopic binaries (SB1's) in OB associations and found a very promising candidate, HD96670, in the Carina OB association (near Eta Carina). This source is an SB1 with a well-measure orbital period (P = 5.53963 days) and semi-amplitude of its velocity of K2 = 57 km/s, yielding a mass function of f(M) = 0.104 solar masses. The optically visible star, HD96670) is an O8.5 star with uncertain luminosity class, but probably main sequence, and with magnitude values (Johnson mags) B = 7.60, V = 7.43. The mass function implies the unseen secondary in the system has mass >3Msun for any orbital inclination i > 12deg. Our NuSTAR observations (not yet published) have found the source is detectable with a hard power law spectrum that strongly suggest it is an accretion-powered source. Combined, these strongly imply the binary contains an accreting black hole.

I request/propose "precision" photometry (at the ~1% level, ideally) on this bright star over as many nights as possible over a total time duration of at least several weeks (the object is of course now only visible for ~2-3h/night) to fold at the known orbital period to search for the expected ellipsoidal modulation in brightness and color which will further constrain the orbital inclination. We request B, V, R frames with a BSM telescope (BMS-S) to do RELATIVE photometric monitoring by comparison with other similarly bright stars within ~5arcmin of HD96670. The star HD96715 is about 6arcmin to the SE at coords RA = 11:07:32.82, -59:57:48.7 and magnitude values B = 8.32, V = 8.30 and so pointings should be midway between HD96670 and HD96715, or at RA = 11:07:22, Dec = -59:55:06 (all coords J2000 of course). This assumes, of course, that the Field of View (FoV) of the BSM-S telescope/CCD is at least 15arcmin x 15arcmin to accomodate both stars. A flat field (in B,V,R) for each night would be desirable. ACCURATE UTC times for each exposure are needed. PLEASE LET ME KNOW IF THIS PROPOSAL IS ACCEPTED AND, if so, WHEN OBSERVATIONS COULD BEGIN.

Josh Grindlay
Robert Treat Paine Prof. of Astronomy
Harvard
jgrindlay@cfa.harvard.edu
617-495-7204