Central Bureau for Astronomical Telegrams
IAUC 6326: GRO J1744-28
The following International Astronomical Union Circular may be linked-to from your own Web pages, but must not otherwise be redistributed (see these notes on the conditions under which circulars are made available on our WWW site).
Read IAUC 6327
.dvi or
.ps format.
Circular No. 6326
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
GRO J1744-28
T. Augusteijn and G. Van de Steene, European Southern
Observatory (ESO); F. van der Hooft, University of Amsterdam; J.
van Paradijs, University of Amsterdam and University of Alabama at
Huntsville; C. Kouveliotou, Universities Space Research Association
and Marshall Space Flight Center (MSFC), NASA; G. J. Fishman, MSFC;
and W. H. G. Lewin and R. Rutledge, Massachusetts Institute of
Technology, report: "Using the ESO New Technology Telescope (NTT)
and Danish 1.5-m telescope (D1.5), we have made V, R, and I images
of the region around the Zytkow-Irwin star (IAUC 6314), for which
we find R = 19.3 +/- 0.1 (NTT, Feb. 9.323 UT), R = 19.2 +/- 0.1
(D1.5, Feb. 18.362), I = 17.7 +/- 0.1 (D1.5, Feb. 18.369). In a 2-
min V image taken at the NTT on Jan. 21.360, we see the source just
above the background, at V about 21.5. In the images taken with
the D1.5, we notice the presence of a second star, fainter by about
2.5 mag in both R and I, offset by about 2".1 to the west and about
1".2 to the north. We have obtained spectra (range 550-1000 nm,
resolution 2.9 nm) of the Zytkow-Irwin star, using the NTT on Feb.
9.332 and 9.347 (exposure times 15 min each). We do not find any
strong spectral features in the average spectrum, with an upper
limit of about 0.4 nm to an emission line at H-alpha. From a
visual comparison between the Gunn z image and the ESO K' image
(IAUC 6321), we find a good match where the Zytkow-Irwin star
coincides with 'star C'. The corresponding optical and K-band
magnitudes are consistent with a source having intrinsic colors
similar to those of a low-mass x-ray binary reddened by E(B-V)
about 3; with V about 21.5 and an assumed distance of 7 kpc, the
corresponding absolute visual magnitude MV about -2, in agreement
with the value expected for its x-ray luminosity and orbital period
(van Paradijs and McClintock, 1994, A.Ap. 290, 133). However,
since the Zytkow-Irwin star was about equally bright in R several
years ago, and transient low-mass x-ray binaries in outburst are
expected to brighten by several magnitudes in R, it still seems
possible that this source is not the true counterpart of the x-ray
source. If the variable radio source (IAUC 6307) coincides with
the x-ray source, we suspect that the interstellar reddening of GRO
J1744-28 may substantially exceed the above value, and that its
optical counterpart remains to be detected."
(C) Copyright 1996 CBAT
1996 February 26 (6326) Daniel W. E. Green
Read IAUC 6327
.dvi or
.ps format.
Our Web policy. Index to the CBAT/MPC/ICQ pages.
