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IAUC 6601: SAX J1750.8-2900; NOVALIKE Var IN Sgr; 81P

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                                                  Circular No. 6601
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SAX J1750.8-2900
     J. Marti, I. F. Mirabel and S. Chaty, Service d'Astrophysique,
Centre d'Etudes de Saclay; and L. F. Rodriguez, Instituto de Astronomia,
Universidad Nacional Autonoma de Mexico, report: "We tentatively
identify the radio counterpart of the galactic center x-ray transient
SAX J1750.8-2900 with a variable VLA radio source, NVSS J175050-290311,
the second of the three candidates listed on IAUC 6597.  The 20-cm flux
density of this object (which has positional uncertainty 10") was reported
in the NRAO/VLA Sky Survey (NVSS) database to be 3.5 mJy (a measurement in
1993), whereas Helfand et al. (1992, Ap. J. Suppl. 80, 211) give a 20-cm flux
density of 34 mJy (a measurement in 1989) for what is evidently the same radio
source, 0.491-1.042, located at R.A. = 17h50m51s.47, Decl. = -29d03'13".6
(equinox 2000.0, uncertainty 1")."

     F. Kerber and H. Gratl, University of Innsbruck; and M. Roth,
Las Campanas Observatory, report: "We have found dramatic changes in
the spectrum of the novalike object reported by Y. Sakurai in Feb. 1996
(cf. IAUC 6322, 6323) at R.A. = 17h52m32s.69, Decl. = -17d41'07".7
(equinox 2000.0), compared to our observations from one year ago.
The object was suspected to be undergoing a late He-flash (IAUC 6325, 6328),
and our group has been monitoring the object's evolution since discovery.
Spectra obtained on 1997 Mar. 23.33 UT at the 2.5-m du Pont telescope
show very prominent lines in the C2 Swan bands (bandheads 473, 516 and 558 nm)
not seen before.  In addition, the H Balmer lines seem to have weakened
considerably compared to a year ago.  The object was expected to change
quickly in astronomical terms, but the observed change is certainly much
faster and much more massive than expected."

     Further to the report concerning comet C/1995 O1 on IAUC 6600,
J. Sarmecanic, D. J. Osip, M. Fomenkova and B. Jones report
that mid-infrared imaging of comet 81P with the 1.5-m reflector at
Mt. Lemmon during Mar. 5.27-5.33 UT yields the following photometric
magnitudes (10-arcsec circular aperture, uncertainties 0.2 mag):
[8.7 microns] = 4.3, [10.3 microns] = 3.2, [11.7 microns] = 2.4 and
[12.5 microns] = 2.1.  The resulting color temperature is
200 +/- 20 K, consistent with the equilibrium blackbody
temperature of 213 K at r = 1.7 AU.  There is no evidence for
excess silicate emission.

                      (C) Copyright 1997 CBAT
1997 March 24                  (6601)              Brian G. Marsden

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