Central Bureau for Astronomical Telegrams
IAUC 5125: Sgr A*
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Circular No. 5125
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
SAGITTARIUS A*
M. R. Rosa, European Southern Observatory (ESO), Garching; H.
Zinnecker, Institute for Astronomy and Astrophysics, University of
Wurzburg; and A. Moneti, ESO, La Silla, report: "We have discovered
two new unresolved optical sources very close to the compact,
nonthermal radio source Sgr A* in the Galactic Center (GC). The new
sources were found on CCD images, taken through a Gunn z filter at
the ESO New Technology Telescope in 1".0 seeing (image scale
0".3/pixel) on July 24. They are hidden behind the seeing disk of
the mag 17.6 source IRR1/CCD2 (Henry et al. 1984, Ap.J. 285, L27).
The co-added image of five 40-min exposures was deconvolved using
the Lucy algorithm, providing a final resolution of 0".4 FWHM. The
two new sources were revealed unambiguously after subtracting a
scaled image of the nearby point source IRR2/CCD1 (ibid.) from the
elongated, deconvolved image of IRR1/CCD2. The two sources, named
GZ-A and GZ-B, are separated by 0".7 with a position angle
perpendicular to the galactic plane to within a few degrees. GZ-A and
GZ-B together are fainter than IRR2/CCD1 by about 2 mag, and GZ-B
appears to be the brighter of the two. Furthermore, we have
identified optically, for the first time, at least a dozen previously
known 2-micron sources in our CCD image, including IRS7. A 30-min
exposure, taken by J. Melnick (ESO, La Silla) under 0".54 seeing
(image scale 0".15/pixel) with the ESO NTT, confirms the brighter
point source identifications and also shows an elongated image of
IRR1. Using the positions (Tollestrup et al. 1990, A.J. 98, 204) of
the optically identified infrared sources, we derive the following
positions (equinox 1950.0; r.m.s. +/- 0".2): GZ-A, R.A. =
17h42m29s.35, Decl. = -29 59'18".5; GZ-B, R.A. = 17h42m29s.31, Decl.
= -29 59'18".1. These are in the system of IRS7 (R.A. =
17h42m29s.32, Decl. = -29 59'12".7), whose recent detection at the
VLA (Yusuf-Zadeh et al. 1989, IAU Symp. 136, p. 443) enables us to
relate our two new sources to the VLA position of Sgr A* (R.A. =
17h42m29s.324, Decl. = -29 59'18".51). Thus Sgr A* coincides with
GZ-A to within 0".3 and with GZ-B to within 0".5. While GZ-B is
likely to be identical with IRS16NW (Forrest et al. 1986, Ap.J. 301,
L49), there is no known infrared counterpart of GZ-A. Therefore
GZ-A, the source closest to Sgr A*, seems to be an intrinsically
very blue object. Because of the close proximity to Sgr A*, we
suggest that the two new sources are indeed in the GC."
1990 October 30 (5125) Daniel W. E. Green
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