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IAUC 8708: 73P

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                                                  Circular No. 8708
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)

     L. Lara, P. Rodrigues, R. Rodrigo, H. Boehnhardt, T. Bonev,
and G. Borisov write that R-band images of component 'B' taken on
May 7.9 UT with the Calar Alto 2.2-m telescope (+ CAFOS) showed a
much brighter coma than on May 2; image processing revealed two
short (2000 km) pairs of arclets at p.a. about 100/300 deg and
about 180/270 deg.  R- and B-band images of component 'B' on May
9.0 UT taken with the 2-m telescope (+ focal reducer) of the
Bulgarian National Astronomical Observatory, Rozhen, showed that a
10" aperture centered on the coma was 3.5 mag brighter than similar
images taken on May 5.0.  CN-filter images taken on May 8.9 with
the same instrumentation revealed a pair of prominent coma arclets
extending about 5000 km on either side of the sun-comet line.
     D. E. Harker, University of California, San Diego; C. E.
Woodward, University of Minnesota; M. L. Sitko, Space Science
Institute and University of Cincinnati; D. H. Wooden, NASA Ames
Research Center; and D. K. Lynch and R. W. Russell, The Aerospace
Corporation, report on observations made of comet 73P's component
'B' using the Gemini-N telescope (+ Michelle) on Apr. 29.5 UT.
Images of fragment 'B' obtained at 11.7 and 18.5 microns show a
dust tail at p.a. 25 deg, extending > 16" from the nuclear
condensation.  The coma appears "detached" from the nucleus with a
maximum in the surface brightness 3".0 from the peak nuclear
isophote.  A silicate emission feature is observed in the 10-micron
region, both on and offsetted from the nuclear condensation.  The
continuum flux (measured at 8.0 and 12.5 microns) observed on the
nuclear condensation is fitted with a blackbody temperature of 310
+/- 10 K -- a color temperature 15 percent higher than that of a
blackbody at an equivalent heliocentric distance (1.11 AU).  The
feature-to-continuum ratio at 10.5 microns is 1.15.  The offset
spectrum towards the detached region of the coma 3".0 to the
southwest has a derived blackbody continuum temperature of 280 +/-
10 K (a color temperature 6 percent higher than that of an
equivalent blackbody), with an observed 10.5-micron silicate-
feature-to-continuum ratio of 1.25.  No distinct emission peaks
arising from crystalline silicates were observed in either spectra,
and the observed spectral-energy distribution can be modelled by an
admixture of amorphous olivine and amorphous pyroxene grains.
Spectra from 17 to 23 microns are featureless in both the central
and offset positions.  The measured fluxes in the 0".6 x 1".0
spectral extraction box centered on the nuclear condensation are as
follows:  11.7 microns, 0.68 +/- 0.03 Jy; 18.5 microns, 0.85 +/-
0.03 Jy.  At the offset of 3".0, the fluxes are as follows:  11.7
microns, 0.36 +/- 0.02 Jy; 18.5 microns = 0.47 +/- 0.02 Jy.

                      (C) Copyright 2006 CBAT
2006 May 10                    (8708)            Daniel W. E. Green

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