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IAUC 7594: V4643 Sgr; C/2000 W1; C/1999 T1

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IAUC number

                                                  Circular No. 7594
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)

     M. Della Valle, Arcetri Astrophysical Observatory, Florence;
L. Da Silva, Observatorio Nacional, Rio de Janeiro; E. Pompei,
European Southern Observatory; and R. Williams, Space Telescope
Science Institute, report:  "Preliminary analysis of a spectrum
(range 390-900 nm, resolution 48000) of V4643 Sgr (Nova Sgr 2001),
obtained on Feb. 26.35 UT at La Silla with the 1.5-m telescope (+
Fiber-fed Extended Range Optical Spectrograph), shows a nova close
to maximum light that has a heavily absorbed continuum.  The
spectrum is dominated by broad emission lines of the Balmer series,
split into two asymmetric components and flanked by P-Cyg profiles.
Also prominent are emission lines due to Na I (mult. 1), He I
(mult. 11), N II (mult. 3, 21), He II (1), and O I (4).  The lack
of Fe II lines and the large expansion velocities (the FWZI
measured for H-alpha yields about 10000 km/s) suggest that this
nova belongs to the He/N spectroscopic class (see Williams 1992,
A.J. 104, 725)."

     Further to the report on IAUC 7586, A. C. Gilmore reports that
3-min unfiltered CCD images taken on Mar. 3.61 UT with the
University of Canterbury's Mount John Observatory 1-m f/7.7
telescope showed only a diffuse parabolic glow at the comet's
expected position.  The glow was brighter and about 1' across at
the 'head' end.  The 'tail', in p.a. 80 deg, was at least 10' long
and widened to about 2' across at the frame's edge.  No stellar
central condensation was found, though anything brighter than red
mag 20 should have been detected.

     C. E. Woodward, J. E. Lyke, and R. D. Gehrz, University of
Minnesota (UM), report 7- to 23-micron photometry of this comet on
Feb. 21.51 UT at the Mt. Lemmon Observing Facility 1.52-m telescope
(+ UM bolometer + IRTF narrowband 'silicate' filters).  No evidence
for strong silicate emission (cf. IAUC 7582) was observed at 11
microns; a blackbody fit to the observed spectral energy
distribution yields a color temperature of 270 +/- 20 K.  Observed
magnitudes:  [7.9 microns] = 3.19 +/- 0.25, [8.8 microns] = 3.24
+/- 0.22, [9.8 microns] = 2.93 +/- 0.27, [10.3 microns] = 2.91 +/-
0.12, [11.7 microns] = 1.68 +/- 0.12, [12.5 microns] = 2.05 +/-
0.22, [18.3 microns] = 0.42 +/- 0.23, and [23.0 microns] = 0.62 +/-

                      (C) Copyright 2001 CBAT
2001 March 6                   (7594)            Daniel W. E. Green

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