Central Bureau for Astronomical Telegrams
IAUC 7146: eta Car; NO SN IN UGC 11093
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Circular No. 7146
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)
eta CARINAE
K. Davidson, R. M. Humphreys, and K. Ishibashi, University of
Minnesota; T. R. Gull, Goddard Space Flight Center, NASA; M. Hamuy,
University of Arizona; and L. Berdnikov and P. Whitelock, South
African Astronomical Observatory (SAAO), write: "Hubble Space
Telescope STIS observations show that eta Car unexpectedly
increased in brightness by a factor of about 2 (0.6 to 0.8 mag)
between Dec. 1997 and Feb. 1999 at wavelengths around 800 nm. STIS
acquisition images, 'peakup' countrates (see the STIS instrument
handbook), and slit spectra all showed the trend progressively in
data obtained on 1997 Dec. 31, 1998 Mar. 19, Nov. 25, and 1999 Feb.
21. These data refer specifically to the central star at spatial
resolution about 0".1. The images and slit spectra also show
similar brightening in at least the inner parts of the surrounding
Homunculus nebula, composed of ejecta from the giant eruption seen
150 yr ago. Photometry done at Cerro Tololo and SAAO on 1999 Apr.
17 agree that the Homunculus nebula now has V about 5.25 within a
diameter of 20", indicating a 0.45-mag difference since the end of
1997 (cf. van Genderen et al. 1999, A.Ap. 343, 847). This is the
largest and most rapid brightening of eta Car in the past 50 yr,
and the object is now brighter than at any time in the past 130 yr.
Light-travel-time effects may explain the difference in brightening
rates between the star and its surrounding nebula. The phenomenon
may continue. Additional photometry and spectroscopy are needed."
T. S. Metcalfe, University of Texas, Austin; and R. M.
Humphreys, University of Minnesota, report: "UBV differential
photometry of eta Car on Apr. 18 with the 1.5-m reflector (+ Texas
3-channel photometer + 20" aperture) at Cerro Tololo Interamerican
Observatory gave V = 5.2, B = 5.9, and U = 5.4 (confirming the
0.5-mag rise since Jan. 1998). The aperture included the entire
Homunculus nebula."
NO SUPERNOVA IN UGC 11093
P. Garnavich, S. Jha, P. Challis, and R. Kirshner, Center for
Astrophysics, report that a high-quality spectrum of SN 1999bs was
obtained by P. Berlind with the 1.5-m Tillinghast telescope on Apr.
18.5 UT, which indicates that this is not a supernova, as reported
on IAUC 7143, but a dwarf nova in outburst. The spectrum now shows
rather narrow (1000 km/s half-width) Balmer absorption lines from
H-beta to H-zeta at their rest wavelengths. The low Galactic
latitude (+14o) and large separation (nearly 3') from UGC 11093 is
consistent with this object being a Galactic variable.
(C) Copyright 1999 CBAT
1999 April 19 (7146) Daniel W. E. Green
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