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                                                  Circular No. 8717
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. L. Sitko, University of Cincinnati and Space Science
Institute; R. W. Russell, D. K. Lynch, R. Ford, and K. Crawford,
The Aerospace Corporation; E. F. Polomski, University of Minnesota;
and W. Golisch, D. Griep, and P. Sears, Infrared Telescope Facility
(IRTF), NASA, report on observations made of comet 73P's components
'B' and 'C' using the IRTF (+ BASS) on May 18 and 19 UT.  Both
components exhibited a smooth continuum between 3 and 13 microns,
on top of which a silicate emission band from 8.5 to 12.2 microns
was observed.  For component 'C', an underlying blackbody,
normalized to the continuum fluxes at 7.8 and 12.5 microns, yielded
grain temperatures of 295 K on May 18.73, 295 K on May 19.65, and
300 K on May 19.75, with an estimated uncertainty of +/- 5 K.  For
'B', the temperatures were 285 K on May 18.66 and 300 K on May
19.70.  These derived temperatures were between 2 and 7 percent
higher than that of an equivalent blackbody at the heliocentric
distance of the comet.  The feature-to-continuum ratios in the
silicate band for 'C' were 1.25 on May 18.73, 1.25 on May 19.65,
and 1.23 on May 19.75.  For 'B', the ratio was 1.18 for both nights.
These values are consistent with those previously reported for 'B'
observed on Apr. 29.5 (IAUC 8708), but the silicate band in 'C' was
slightly weaker than on Mar. 17.05 (IAUC 8701).  On both nights in
May, the spectrum of 'B' showed the possible presence of the 3.4-
micron organic emission band.  The feature was undetected in 'C'.
The measured flux between 10.5 and 11.0 microns, using the 3".4
circular entrance aperture of BASS, was 28.7 +/- 0.3 Jy (equivalent
magnitude m_N = 0.37 +/- 0.01) on May 18.73.  On May 19.76, the
flux had dropped to 9.0 +/- 0.2 Jy (m_N = 1.62 +/- 0.02), but
brightened to 15.0 +/- 0.2 Jy (m_N = 1.07 +/- 0.01) only 2 hr later.
For 'B', the flux was 7.7 +/- 0.1 Jy (m_N = 1.79 +/- 0.01) on May
18.66 and 5.5 +/- 0.02 Jy (m_N = 2.16 +/- 0.01) on May 19.70.

COMETS C/2006 G3 AND C/2006 H2 (SOHO)
     Additional Kreutz sungrazing comets have been found on SOHO
website images (cf. IAUC 8714).  C/2006 G3 was elongated and
diffuse, reaching mag 7.5 at 7.1 solar radii on Apr. 14.563 UT,
when it had an 84" tail.  C/2006 H2 was tiny but slightly elongated
and too faint for photometry.

 Comet        2006 UT       R.A.(2000)Decl.   Inst.  F    MPEC
 C/2006 G3    Apr. 14.526   1 38.8   + 8 38   C2     HS   2006-K29
 C/2006 H2    Apr. 17.493   1 49.0   + 9 40   C2     HS   2006-K29

                      (C) Copyright 2006 CBAT
2006 June 3                    (8717)            Daniel W. E. Green

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