Central Bureau for Astronomical Telegrams
IAUC 3250: OBJECT IN FIELD OF 2S 1702-363
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Circular No. 3250
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
OBJECT IN FIELD OF 2S 1702-363
J. E. McClintock and C. R. Canizares, Massachusetts Institute
of Technology, report that spectroscopic observations on 1977 Aug.
1.2 UT with the 400-cm telescope at Cerro Tololo Interamerican
Observatory show that the highly variable star observed in 1978
Apr.-May by Zuiderwijk and Glass (IAUC 3221, 3226) is a late-type star,
very likely a giant (the data rule out dwarfs, and supergiants are
rare). Although it brightened by ~ 1.5 magnitudes since the epoch
of the Palomar Sky Survey (see also Mayo et al. below), such behavior
is common for late M giants. A second observation on 1978 May
26.3, using the same instrumentation, revealed no major changes in
the star's spectrum or intensity: m (6500 A) ~ 17.5, m (7000 A) ~ 16.
In both the 1977 and 1978 observations emission was not detected in
the blue: over 4200-5200 A m > 19 (cf. Zuiderwijk, IAUC 3221 and
below). Based on the measured space density of red giants in the
galactic bulge region, it is estimated that the probability of
finding a star later than M6 in a 1' diameter circle is ~ 3 percent
(B. Blanco et al. 1978, Nature 271, 638; V. Blanco, private
communication). At present there seems to be no significant evidence
linking this star to the x-ray source.
S. K. Mayo, Royal Greenwich Observatory; A. C. Fabian, J. E.
Pringle and J. A. J. Whelan, Institute of Astronomy; and W. Zealey,
U.K. Schmidt Telescope Unit, report that spectroscopic observations
on June 15.75 UT confirm that the Zuiderwijk-Glass object is a red
M star, although the data cannot determine whether it is a giant or
a dwarf or a Mira variable. Inspection of U.K. Schmidt plates
shows that on 1974 June 21 and 22 the object was below the plate
limit, i.e. that R was fainter than 20 and J fainter than 21. On
1978 May 5 the R magnitude was slightly fainter than stars 1 and 2
in the finding chart by Jernigan et al. (1978, Nature 272, 701).
According to TV magnitudes with the Anglo-Australian telescope on
June 15 B was fainter than 19 and R very similar to that of star 2.
It is thus unclear whether the object is the x-ray counterpart.
E. J. Zuiderwijk, University of Amsterdam, reports that several
deep plates were obtained with the 360-cm reflector at the European
Southern Observatory on May 16. On the blue plate (IIa-O) the
star is not visible (B > 21.5), on a red plate (IIIa-F, RG630) it
is of magnitude ~ 19 and on an infrared plate (IV-N, RG715) of
magnitude ~ 16. Given also Glass' data (IAUC 3226) it seems that the
star is a late-M giant. It is also probable that the colors
reported on IAUC 3221 are due to incorrect filter information.
1978 July 31 (3250) Brian G. Marsden
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