Another 17.5m faint stellar-like object discovered by the LINEAR team on Dec. 20, 1999, close to the Camelopardalis/Cassiopeia border aroused suspicion because of its unusual orbit. Detailed observations of comet C/1999 Y1 (LINEAR) showed a faint, 12" small coma and a short tail of 20" at PA=70° between Dec. 21 and Dec. 27 (IAUC 7338). According to the orbital elements it passes perihelion in March 2001.
Although not a bright comet, no less than 45 observations by 7 members of the German comet section were received until January 2002. Taking into account additional 145 international observations quite reliable statements can be made. The brightness evolution can be simulated by the formula
thereby ignoring the brightness estimates during spring 2000 made by few observers which are known to give systematically too bright estimates. Thus, this comet reached two maxima of magnitude 12.5m: in November 2000 and in August 2001. The apparent coma diameter was in the order of 1' in August 2000, increased steadily to 1.7' until November 2000, thereafter declining to 1.3' in January 2001; in August 2001 it measured 1' again. The absolute coma diameter increased during 2000 from 190.000 km to 210.000 km, but measured only 110.000 km in August 2001. The degree of condensation was DC 3-4 in August 2000, increased to a maximum of DC 4-5 until November, therafter decreasing to DC 3-4 in January 2001. During summer 2001 the reported estimates give DC 4-5, in accordance with the significantly smaller coma.
Infrared observations at the National Astronomical Observatory of Japan showed an anti-tail of 2' in PA=30° on Sep. 21 and 26. It seemed to originate from a jet-like structure at PA=140°, but the central condensation was not on the line connecting both features.
Total Brightness and Coma diameter
Andreas Kammerer
