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IAUC 6406: 1996ac; GRO J1655-40

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                                                  Circular No. 6406
Central Bureau for Astronomical Telegrams
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)
Phone 617-495-7244/7440/7444 (for emergency use only)

     R. H. McNaught reports his discovery of an apparent supernova
on a U film taken on May 21.4 UT by K. S. Russell with the U.K.
Schmidt Telescope, at which time SN 1996ac was fainter by about 1
mag than on May 9.5, when its magnitude was about 16.5 on a similar
exposure taken by M. J. Drinkwater.  SN 1996ac is located at R.A. =
12h24m11s.24, Decl. = +1o24'14".7 (equinox 2000.0), which is 2".2
west and 3".2 north of the galaxy's center.  A nearby star (mag
about 17.5) has position end figures 13s.78, 23'46".6.  No star
appears at the position of SN 1996ac on an I survey plate taken on
1991 Apr. 6, nor is anything present on a Palomar Sky Survey B film
taken on 1992 Apr. 7.
     L. Wang and J. C. Wheeler, University of Texas, report:  "A
low-resolution (FWHM 1.2 nm) spectrogram of SN 1996ac was obtained
on May 23 UT using the 2.1-m telescope at McDonald Observatory.
The spectrum confirms that this is a type-Ia supernova about a
month past optical maximum."

GRO J1655-40
     K. Horne, E. T. Harlaftis, and R. Baptista, University of St.
Andrews; C. Hellier and A. Allan, Keele University; H. Johnston,
Anglo-Australian Observatory; J. Patterson and J. Kemp, Columbia
University; C. Haswell, University of Sussex and Columbia
University; and W. Chen, Goddard Space Flight Center, report on the
optical/ultraviolet brightening of GRO J1655-40 during the recent
x-ray outburst (IAUC 6393):  "Cerro Tololo photometry on May 10.41
UT gave Johnson magnitudes U = 17.0, B = 16.8, V = 15.4, R = 14.4,
I = 13.4, which fit a power-law spectrum with slope 1/3, reddened
by E(B-V) = 1.5 mag.  Anglo-Australian Telescope spectra obtained
on May 10.48, 11.57, and 12.57 confirm the red continuum slope,
with emission from He II at 468.6 nm and CIII/NIII at 464.0 nm
(FWHM = 2 nm, EW = 0.2 nm), and broad absorption filled in by
multi-component emission at H-beta and H-alpha.  Simultaneous
HST/XTE data on May 13.9-14.3 show 5- to 10-percent variations on
timescales of 2 s-10 min.  Deep 220-nm absorption in the HST
spectrum suggests E(B-V) = 1.3 mag.  HST/XTE observations were
planned for May 20.59-20.80, 27.8-28.1, June 8.53, and two
additional times in June."

                      (C) Copyright 1996 CBAT
1996 May 24                    (6406)            Daniel W. E. Green

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