Central Bureau for Astronomical Telegrams
IAUC 2910: 1975n; GX 1+4
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Circular No. 2910
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK
Western Union: RAPID SATELLITE CAMBMASS
COMET WEST (1975n)
Further precise positions have been reported as follows:
1975/76 UT R. A. (1950) Decl. m2 Observer
Dec. 6.40324 20 34 18.46 -38 12 40.3 13.5 Gilmore
6.41156 20 34 18.76 -38 12 36.9 "
Jan. 1.45451 21 09 09.36 -35 03 36.0 Herald
25.44167 21 58 38.20 -30 26 40.8 "
27.43090 22 03 40.23 -29 53 40.5 "
A. C. Gilmore (Carter Observatory). Measurer: P. M. Kilmartin.
D. Herald (Kambah, near Canberra).
Further total visual magnitude estimates: 1975 Dec. 23.42 UT,
10.1 (B. Nikolau, Palmerston North, New Zealand, 20-cm reflector);
26.43, 9.0 (Nikolau); 1976 Jan. 20.36, 6.5 (Nikolau; stubby tail 2'
long in p.a. 90o); Feb. 1.37, 6.8 (A. C. Gilmore, Wellington, New
Zealand, 15-cm refractor); 4.37, 5.7 (Gilmore, 10 x 50 binoculars).
E. P. Ney and K. M. Merrill, O'Brien Observatory, University
of Minnesota, report the following infrared magnitudes, obtained on
Feb. 2.8 UT with a diaphragm of 20": 1.6 um, 6.2; 2.2 um, 5.8; 3.5 um,
3.6; 4.8 um, 1.4; 8.5 um, -1.7; 10.6 um, -2.5; 12.5 um, -2.7; 18 um,
-3.7. They suggest that comet 1975n is very similar to comet 1973
XII (Kohoutek) before perihelion, comet 1975n being intrinsically
perhaps 0.2 magnitude the fainter; both comets show the 10-um silicate
features at about the same strength and have similar albedos.
Although comet 1975n seems to have been running 1-2 magnitudes
brighter than predicted (IAUC 2871) during December and much of January,
this trend will not necessarily be maintained through perihelion
passage. The predicted positions should not be in error by
more than 1'. Application of the ub quantity calculated by E.
Everhart, University of Denver, to a new orbit determined by the
undersigned from 28 observations 1975 Aug. 10 to 1976 Jan. 27 gives
(l/a)orig = +0.001671 +/- 0.000075 AU**-1; it appears that, unlike 1973
XII (IAUC 2684), comet 1975n cannot be a "new" comet a la Oort.
GX 1+4
J. Doty, SAS-3 Group, Massachusetts Institute of Technology,
reports that during 1975 Dec. 25-27 the source GX 1+4 (3U 1728-24)
was varying with a mean period of 122s.607 +/- 0s.006 (cf. IAUC 2870).
1976 February 5 (2910) Brian G. Marsden
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