Central Bureau for Astronomical Telegrams

IAUC 6902: 1998bu; SAX J1808.4-3658 = XTE J1808-369

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                                                 Circular No. 6902
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
Phone 617-495-7244/7440/7444 (for emergency use only)


SUPERNOVA 1998bu IN NGC 3368
     U. Munari, R. Barbon, L. Tomasella, and M. Rejkuba, Asiago
Astrophysical Observatory, communicate:  "Echelle CCD spectra of SN
1998bu obtained with the Asiago 1.82-m telescope during May 11.81-
11.90 UT reveal strong interstellar Na I D absorption.  The Na I
absorption from M96 is seen at heliocentric radial velocity +744.8
+/- 0.3 km/s, with an equivalent width for the Na I D_1 of 0.035
nm, which corresponds to E(B-V) = 0.15 according to the Munari and
Zwitter (1997, A.Ap. 318, 269) calibration.  The Na I absorption
arising inside our Galaxy is seen at heliocentric radial velocity
-6 +/- 1.5 km/s, with a Na I D_1 equivalent width of 0.019 nm and
corresponding E(B-V) = 0.06."
     R. Evans and W. Wild, University of Chicago, report the
following photometric magnitudes obtained with the Yerkes 1-m
reflector during May 11.13-11.15 UT:  B = 13.1, V = 12.7, R = 12.3,
I = 12.2 (comparison star HR 1433).
     L. Boschini, Bergamo, Italy, reports the following position
for SN 1998bu (cf. IAUC 6899) from an unfiltered CCD image obtained
on May 10.84 UT with a 0.25-m telescope:  R.A. = 10h46m46s.01,
Decl. = +11o50'07".5 (equinox 2000.0), mag 12.6.  Identical
positions have been measured by D. Hanzl, Brno, Czech Republic, and
by G. Masi, Ceccano, Italy; Masi's unfiltered CCD image, obtained
on May 10.821, yields mag 12.6.
     Visual magnitude estimates:  May 11.83 UT, 11.9 (A. Baransky,
Kiev, Ukraine); 11.88, 12.0 (K. Hornoch, Lelekovice, Czech
Republic); 12.72, 12.2 (B. Monard, Pretoria, South Africa); 12.8,
12.2 (L. Kiss, Szeged, Hungary); 12.82, 12.0 (Baransky).


SAX J1808.4-3658 = XTE J1808-369
     W. Percival, P. Charles, E. Kuulkers, L. Miller, and T.
Shahbaz, University of Oxford; and R. McLure and J. Dunlop,
University of Edinburgh, report:  "We performed infrared
observations of the proposed optical counterpart (IAUC 6885) of
this object (IAUC 6876, 6877, 6878) with the U.K. Infrared
Telescope on May 2.6 and 4.6 UT.  We find K = 17.17 and 17.33 (+/-
0.04), respectively, indicating that the source has faded by about
3.5 mag compared to its discovery magnitude.  This dramatic fading
in the infrared, together with the near-simultaneous abrupt decline
in x-rays (IAUC 6897), strengthens its identification as the
optical counterpart."

                      (C) Copyright 1998 CBAT
1998 May 13                    (6902)            Daniel W. E. Green

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