Central Bureau for Astronomical Telegrams
IAUC 4970: (2060); 1989c1
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Read IAUC 4971
Circular No. 4970
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN or GREEN@CFA.BITNET MARSDEN or GREEN@CFAPS2.SPAN
(2060) CHIRON
R. M. West, European Southern Observatory, communicates:
"CCD photometry, mostly in 1".2 seeing, of (2060) Chiron and its
coma (cf. IAUC 4770, 4947), now at r = 11.2 AU, has been performed
with the Danish 1.54-m reflector at La Silla during four
consecutive nights commencing on Feb. 21.05 UT. From offset guided
exposures totalling 170 min, preliminary, mean standard magnitudes
in a 10" circular aperture are B = 17.17, V = 16.54. The diffuse
coma extends to at least 16" (projected 130 000 km) from the image
center in the southeast quadrant with main axis at p.a. 143 deg;
the sky-subtracted coma surface brightness at 7" in this direction
is 25.2 and 24.6 mag/arcsec2 in B and V, respectively. Thus, the
B-V colors of Chiron and its coma are both similar to the solar
value. No obvious night-to-night morphological changes were seen
in the coma."
COMET AUSTIN (1989c1)
West also communicates: "On a blue (IIa-O + GG385 filter;
6-min exposure) offset-guided ESO Schmidt plate, obtained by H.-E.
Schuster and G. Pizarro at low altitude in evening twilight on Feb.
25.03 UT, a weak and complex ion tail at least 2.2 deg long
(extending beyond the plate edge) is seen at p.a. 108 deg. It has
two narrow, main components shaped like a helix with crossovers at
13'.5 and 33'.0 from the center; further out, the very faint
structure appears to be more chaotic. A 20' stubby dust tail
extends toward p.a. 157 deg. A seemingly-featureless, symmetrical
coma surrounds the diffuse central condensation. A 12-min exposure
on Feb. 26.03 shows the tail with less structure, about 1 deg long
in p.a. 114 deg; there are two faint subtails north and one faint
subtail south of the main ion tail, within 10 deg on either side,
lengths about 20'. The stubby dust tail is 18' long in p.a. 153
deg. Since the Feb. 26 plate is deeper, the structures are
definitely fainter than on Feb. 25."
Total visual magnitude estimates (cf. IAUC 4965): Feb. 15.45
UT, 7.0 (T. Lovejoy, Melbourne, Vic., 15x80 binoculars); 16.10, 7.7
(A. Hale, Las Cruces, NM, 10x50 binoculars); 18.53, 7.4 (A. Pearce,
Scarborough, W.A., 20x80 binoculars); 19.39, 7.3 (P. M. Kilmartin,
Lake Tekapo, New Zealand, 10x50 binoculars); 21.01, 6.9 (G. R.
Chester, Rixeyville, VA, 0.37-m reflector; faint extension of coma
about 5' long in p.a. 90 deg); 21.38, 7.8 (A. F. Jones, Nelson, New
Zealand, 11x80 binoculars); 22.53, 7.3 (Pearce); 24.43, 7.7
(Kilmartin); 24.52, 6.9 (Pearce).
1990 February 26 (4970) Daniel W. E. Green
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