## 3. Results## 3.1. OB supergiants4U0900-40/HD77581, 4U1700-37/HD153919, Cyg XR-1/HDE226868, and
HD152667 are all binary systems with an OB supergiant primary (Dolan
& Tapia 1988; 1984; 1989). No member of this group has a
measurable parallax (Table 1). If each of these systems is at a
distance consistent with its spectroscopic parallax, then 4U0900-40,
4U1700-37 and Cyg XR-1 have peculiar tangential velocities t
km s If we locate 4U0900-40 at its spectroscopic-parallax distance, then
the peculiar tangential velocity we derive from its proper motion as
measured by Hipparcos (40
km s ## 3.2. Be/X-ray sourcesThree of the sources in our sample, X Per, A0535 +26/HDE245770, and 4U1145-619(= Cen X-5)/HD102567, are X-ray binary systems with Be star primaries. In each case, a compact secondary is the X-ray source (Dolan et al. 1998). 4U1145-619 has a measured parallax that is significant at the 2 level (Table 1). Only a lower limit to the distance to X Per and A0535+26 can be obtained from the Hipparcos observations. Chevalier & Ilovaisky (1998, hereafter CI) included all three sources in a survey of 13 Be/X-ray binary systems. CI found a distance of 830 (+2870, -330) pc to X Per, 330 (+450, -120) pc to A0535+26, and 500 (+500, -200) pc to 4U1145-619. These distances are consistent with the distance we find for 4U1145-619 and the lower limits we find for X Per and A0535+26. CI interpret the Hipparcos results for A0535+26 and X Per as measurements of their parallax because they apparently selected a significance criterion C . (The Hipparcos parallax measurements for these two sources have R = 1.3 and 1.7, respectively.) The distances CI derive for several Be/X-ray binary systems are
significantly smaller than the previously accepted
spectroscopic-parallax distances for these systems. CI concluded that
Be/X-ray binaries are relatively nearby, low-velocity systems (d
kpc, t
km s The 90% (1.6) confidence interval on the Hipparcos parallax measurement of 4U1145-619 extends to 0.43 arcsec, which corresponds to a distance of 2.3 kpc. (The best estimate of its distance given in Table 1 is 510 pc. The uncertainty on the best estimate means that if the measurement were repeated many times using the same technique, the distribution of the values obtained for the best estimate would lie in the range 120 pc to 900 pc 90% of the time.) Neguerela (1998) gives an estimate of 3.1 kpc (no uncertainty stated) for the spectroscopic-parallax distance of 4U1145-619. The distance ranges corresponding to the 90% confidence intervals on the spectroscopic and astrometric parallaxes of 4U1145-619 probably overlap. ## 3.3. HZ43The hot DA white dwarf HZ43 (Margon et al. 1976), a soft X- ray
source and high proper motion spectroscopic binary, was included in
the trigonometric parallax program of the U. S. Naval Observatory.
Dahn et al. (1982) found the system's parallax to be 15.5
mas and its proper motion 176
mas
toward 235.8 © European Southern Observatory (ESO) 1999 Online publication: October 14, 1999 |