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IAUC 5263: 1991aa; 1991X

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                                                  Circular No. 5263
Central Bureau for Astronomical Telegrams
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

     R. H. McNaught, Anglo-Australian Observatory, reports his
discovery of an apparent supernova (mag about 16) on an R plate taken
by S. M. Hughes with the 1.2-m U.K. Schmidt Telescope on May 7.50
UT.  The supernova is located at R.A. = 12h42m34s.70, Decl. =
-6 02'38".3 (equinox 1950.0), being offset from the galaxy nucleus
by 13".2 east, 5".0 south, and situated at the end of the bar and at
the start of a spiral arm.  No star appears at this position on the
SERC J or first Palomar surveys.  A nearby star of mag about 17 is
located at R.A. = 12h42m28s.91, Decl. = -6 03'28".9.
     M. Della Valle, European Southern Observatory, and H.
Rottgering, Leiden Observatory, communicate:  "A spectrogram (range
360-700 nm, resolution about 2 nm; relative-flux-calibrated)
obtained under non-photometric conditions on May 10.1 UT at La Silla
with the 3.6-m telescope (+ EFOSC) shows broad absorption lines due
to Si II (635.5 nm) and Ca II (H, K).  Other absorptions are observed
at 496.7 (Fe II), 444.5, and 430.9 nm.  The unusual weakness
of the Si II line and the simultaneous absence of He I (587.6 nm)
suggests that this may be a type-Ib (He-poor) supernova like SN
1987M (Filippenko et al. 1990, A.J. 100, 1575) around maximum.
However, the available data do not exclude the case of a type-Ia object
such as SN 1984A (Barbon et al. 1989, A.Ap. 220, 83) at an early
evolutionary stage."

     K. Krisciunas, Joint Astronomy Centre, Hilo, reports photometry
obtained by W. Gear and J. Aycock with the U.K. Infrared Telescope
(+ single-channel near-infrared photometer UKT9), using HD 106965 as
the comparison star.  The following magnitudes were obtained with a
19".6 aperture centered on SN 1991X:  May 7.438, J = 12.643 +/-
0.013; 7.440, H = 12.033 +/- 0.015; 7.442, K = 11.793 +/- 0.017.
The remaining magnitudes were obtained with a 12".4 aperture:
centered on the supernova, May 7.445, J = 13.262 +/- 0.009; 7.447, H =
12.785 +/- 0.023; 7.449, K = 12.529 +/- 0.022; centered on the galaxy
nucleus, May 7.453, J = 11.402 +/- 0.007; 7.454, H = 10.694 +/-
0.006; 7.455, K = 10.413 +/- 0.007.
     Magnitude estimates (cf. IAUC 5258), visual unless otherwise
noted:  May 5.53 UT, 13.8: (T. Cragg, Coonabarabran, N.S.W;
correction to IAUC 5258); 5.9, 14: (J. E. Arud, Notodden, Norway;
CCD); 6.0, 13.8: (T. Sandvik, Sofiemyr, Norway; T-Max 400 film);
6.97, 14.0 (H. Dahle, Oslo, Norway); 10.00, 13.0 (D. Rodriguez,
Madrid, Spain).

1991 May 10                    (5263)             Daniel W. E. Green

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