Engineering topics
Publications and source records attributed to Thorstensen, J..
An improved position is presented for the X-ray source H2252-033 using the Ariel V Sky Survey Instrument, and precise positioning using the Scanning Modulation Collimator on HEAO-1. The source is identified optically with a 13th magnitude emission-line object, which is probably a white dwarf binary with a well formed accretion disk, with similarities to the dwarf novae (e.g., SS Cyg) at minimum.
A precise (20 arcsec) position and an optical counterpart are presented for the weak X-ray source 4U 2129+47. The optical counterpart shows weak but distinct He II 4686-A and C III-N III 4640-4650-A emission. Both H-beta and Ca II H and K are sometimes visible in absorption. Numerous plates and spectrophotometric observations from the 1978 observing season show that the blue magnitude varies from 16.7 to 18.0 in a period of 5.2382 hours. The light curve is sinusoidal in appearance, but with sharply defined V-shaped minima. It is proposed that most of the optical emission from this system originates at the X-ray heated face of the normal star and hence that this system is analogous to HZ Her/Her X-1. This is one of the few intrinsically faint optical counterparts of X-ray sources that show clear evidence of binary nature. The observations suggest a distance of 1.2-1.6 kpc for the source, and a consequent X-ray luminosity of approximately 10 to the 34.8 ergs/s.
The weak hard X-ray source 2A 0526-328 is identified with a previously unknown cataclysmic variable on the basis of its optical emission-line spectrum and a precise X-ray location. This star has a V magnitude of about 11 and spectral properties similar to dwarf novae at minimum light and AM Her, but shows no polarization. It is likely to be a Z Camelopardalis-type system in a very extended standstill (i.e., 'novalike' or UX Ursae Majoris-type) or a recurrent nova that has not erupted in recent times.
We have discovered a highly variable star very close to the center of the SAS 3 error circle for the flaring X-ray source Aquila X-1 (3U 1908+00). Photographic photometry over the last 4 years shows covariability; the optical counterpart brightens from B greater than 20 to B approximately 17 mag during times of X-ray outburst, thus establishing the identification. Spectrophotometry of this star during its quiescent state shows spectral features of a K0 star with no obvious peculiarities; its distance must be at least 1.7 kpc.