Central Bureau for Astronomical Telegrams
IAUC 6356: GRO J1744-28
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Circular No. 6356
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
D. M. Cole, D. E. Vanden Berk, R. C. Nichol, J. M. Quashnock,
S. A. Severson, M. C. Miller, D. Q. Lamb, University of Chicago,
report: "We have determined the HST Guide Star reference frame
positions of seven bright stars encircling the position of the
variable radio source (IAUC 6307, 6323) lying within the XTE error
box (IAUC 6291) for GRO J1744-28, using the STScI Digitized Sky
Survey scans and the IRAF/STSDAS GASP package. Using these stars
(finding charts of which are available from us upon request), we
have calculated the rms positions and errors of two stars in the
optical and five stars in the infrared near the position of the
variable radio source on images obtained with the help of R.
Rutledge (the coordinates are end figures for R.A. = 17h44m and
Decl. = -28o45'; equinox 2000.0): star 'a', 36s.844 +/- 0s.004,
38".16 +/- 0".08; star 'b', 36s.655 +/- 0s.010, 36".93 +/- 0".10;
star 'A', 37s.035 +/- 0s.004, 37".59 +/- 0".08; star 'B', 37s.068
+/- 0s.004, 35".91 +/- 0".07; star 'C', 36s.844 +/- 0s.005, 38".28
+/- 0".08; star 'D', 36s.998 +/- 0s.004, 34".26 +/- 0".07; star
'E', 36s.640 +/- 0s.005, 37".98 +/- 0".08. The astrometry was
performed on images obtained from IAUC 6310, 6314, and 6326; and
private communication from Augusteijn and Van de Steene; Fletcher,
Cooray, and Burke; Blanco, Lidman, and Glazebrook; and Keane. The
detections of star 'a' in the UKST Bj (IAUC 6314) and the ESO NTT
V (IAUC 6326) images are marginal, so we did not use those images
in our calculation of the position of this star. Star 'b' is the
second star in the I and R reported by Augusteijn et al. (IAUC
6326), and star 'E' is the star immediately west of 'C' in the
near-infrared images. We note that there are no other objects
visible in the vicinity of the variable radio source that are
brighter than approximately 22 in R (IAUC 6326) and 22 in J
(Keane, private comm.). Although our relative astrometry is
excellent, our absolute astrometry is limited by systematic offsets
between the HST Guide Star and radio coordinate systems. In order
to estimate the offset for this field, we have compared the 17 PPM
stars within 0.7 degrees of the radio source with their positions
in the HST Guide Star Catalogue. We find R.A.(PPM-HST) = -0".333
+/- 0".295, Decl.(PPM-HST) = -0".024 +/- 0".285. Star 'a' and 'C'
are almost certainly the same star, but our position for this star
is 0".9 away from the position of the variable radio source. It
is not clear that the systematic offset between the HST Guide Star
and radio coordinate systems is sufficient to reconcile the two
positions. All other stars visible in the optical or infrared lie
more than 2" from the radio source."
(C) Copyright 1996 CBAT
1996 March 27 (6356) Daniel W. E. Green
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