Central Bureau for Astronomical Telegrams
IAUC 4047: EXO 0748-676; CENTRAL STAR IN NGC 2346
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Circular No. 4047
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 617-495-7244/7440/7444
EXO 0748-676
H. Pedersen, S. Cristiani and S. d'Odorico, European Southern
Observatory; and B. Thomsen, Aarhus University, telex: "Spectra
covering the range 380-680 nm were obtained on Mar. 17.037 and
18.144 UT using the ESO faint-object spectrograph and camera attached
to the 3.6-m telescope at La Silla. The spectra show a blue
continuum with emission lines of H and He II 468.6 nm, as is
characteristic of optical counterparts of low-mass x-ray binaries.
Continued CCD photometry (IAUC 4039) shows a slow decline in
brightness, and on Mar. 16 the maximum brightness was V = 17.3.
The lightcurve varies erratically from orbit to orbit. Using data
provided by P. Angebault the object's position has been determined
as R.A. = 7h48m24s90 +/- 0s20, Decl. = -67deg37'32"3 +/- 1"0 (equinox
1950.0). The source is contained in the error box of the G-ray burst
source GB 811016 (Katoh et al. 1984, AIP Proc. 115, 390), which may be
repetitive (Schaefer and Cline 1985, Ap.J. 289, 490). A correspondence
of an x-ray transient with a G-ray burst source would be
the first of its kind, although the possibility of a chance
coincidence cannot be excluded."
CENTRAL STAR IN NGC 2346
B. E. Schaefer, Goddard Space Flight Center, writes: "
Photoelectric V magnitude observations with the No. 2 0.9-m reflector
at Kitt Peak gave: 1984 Oct. 17.45 UT, 16.55; 1985 Feb. 11.12,
15.6; 12.17, 14.3; 13.22, 12.5:; 14.28, 12.09; 15.28, 11.78;
16.35, 11.61; 17.26, 11.54. Infrared photometry with the 1.3-m
telescope on Feb. 11.30 gave J = 12.20, H = 10.56, K = 9.08, L =
7.4. The comparison star b of Kohoutek (IBVS 2113) is a variable
with a range between V = 10.9 and 11.4. Visual estimates for when
the central star is fainter than V ~ 13 must be used with great
caution because of interference by the nebula. The V magnitudes
by Acker and Jasniewicz (1985, A. Ap. 143, L1) used an incorrect
nebular correction because of a typographical error in the note by
Kohoutek (1983, MNRAS 204, 93p)."
Visual magnitude estimates: Jan. 30.06 UT, 12.2 (J. Bortle,
Stormville, NY); Feb. 6.7, [13.7 (M. Verdenet, Bourbon-Lancy,
France); 10.7, 14.6 (Verdenet); 18.7, 11.8 (Verdenet); 19.7, 12.0
(Verdenet); 21.14, 13.0 (Bortle); 22.7, 15.0 (Verdenet); 24.7,
15.2 (Verdenet); 26.7, 13.6 (Verdenet); 27.7, 13.3 (Verdenet).
1985 March 21 (4047) Brian G. Marsden
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