Behaviour of Comet 21P/Giacobini-Zinner during the 1998 perihelion

Abstract

Abstract. Comet 21P/Giacobini-Zinner was observed from Nov. 8 to Dec. 10, 1998. Pre-and post-perihelion CCD images of the gas (CN, C 2 ) and dust (green and red continua) coma were obtained with the 82 cm IAC-80 telescope at Teide Observatory (Canary Islands, Spain). For v p = 0.85r −0.5 H and v d = 1.19 km s −1 (i.e. characteristic of HCN being the CN parent species), the CN column density profiles are best reproduced with parent and daughter lifetimes of the order of 19 300 and 256 000 s. An equally good reproduction of the observed profiles is achieved by considering that a mixture of nitrogen compounds expanding at v p = 1 km s −1 and with a lifetime of 19 000 s produces CN with an ejection velocity of v d = 2.5 km s −1 and a lifetime of 174 000 s. Fitting the observed CN profiles with variable velocities and lifetimes, the results indicate that the nature of the CN precursor in comet 21P/Giacobini-Zinner is still unclear, ruling out HCN as the only precursor and favouring a mixture of nitrogen compounds. Regarding C 2 , the derived lifetimes are 35 000 and 62 000 s, if the parent and daughter velocities are fixed at ∼1 km s −1 . Gas production rates derived by means of the Vectorial modeling with the mentioned above lifetimes and velocities indicate that (i) the comet activity decreases with decreasing r H (i.e. peak activity is not reached at the perihelion), and (ii) as already known, the comet is typically depleted in C 2 with a log Q C 2 Q CN ≈ −0.4. The azimuthally averaged surface brightness profiles of the continuum images are well fitted with m ≥ 1 in a log B − log ρ representation at projected radial distances (ρ) larger than 1000 km. The continuum light scattered from the dust in the coma of comet Giacobini-Zinner is redder than the Sun light on every date from Nov. 8 to 24, regardless the cometocentric distance. On Nov. 25, there is a sudden change in the dust color, being considerably bluer than the Sun, whereas on Dec. 7 and 8, the dust became much redder than it was before. These color variations do not seem to be related to sudden variations (relative minimum or maximum) in the cometary activity. The gas-to-dust mass ratio is ∼1, but affected by a large uncertainty (about a factor of 2) since the comet was not simultaneously imaged in the OH band, and the H 2 O production rate has been considered from other measurements taken some weeks before ours.

The dust coma of the active Centaur P/2004 A1 (LONEOS): a CO-driven environment?

“…Our results for this Centaur indicate a significant dust production rate: values found at a heliocentric distance of 5.5 AU are of the same order of those found for several active comets at much lower heliocentric distances: 19P/Borrelly, 400-500 cm at 1.4 AU (Schleicher et al 2003); 81P/Wild 2, ∼350 cm at 2.1 AU (Schulz et al 2003); 21P/Giacobini-Zinner, 300-400 cm at 1 AU (Lara et al 2003); 67P/Churyumov-Gerasimenko, ∼400 cm at (Bauer et al 2003a). …”

Thermal modeling of the active Centaur P/2004 A1 (LONEOS)

“…the sky-plane radius) range from 288 to 334 cm. These results indicate a significant dust production rate: values found at a heliocentric distance of 5.5 AU are nearly the same as those found for several active comets at much lower heliocentric distances: 19P/Borrelly, 400-500 cm at 1.4 AU (Schleicher et al 2003); 81P/Wild 2, ∼350 cm at 2.1 AU (Schulz et al 2003); 21P/Giacobini-Zinner, 300-400 cm at 1 AU (Lara et al 2003); 67P/Churyumov-Gerasimenko, ∼400 cm at 1.2 AU (Weiler et al 2004). The unusually high (as compared to other minor bodies at the same heliocentric distance) level of activity for the Centaur P/2004 A1 (LONEOS) is also confirmed by the results of the application of the same inverse dust tail model applied to other active Centaurs and several short-period comets.…”

Isotopic abundance of nitrogen and carbon in distant comets

“…Following the same lead, Bonev & Komitov (2000) find that C 2 N 2 is indeed to be preferred over HCN as a single parent of CN. A recent analysis of the CN profile in comet 21P/Giacobini-Zinner by Lara et al (2003) showed that HCN should be ruled out as the sole parent of CN. On the other hand, several analyses present HCN as the major or sole source of CN (e.g., Korsun & Jockers 2002;Lara et al 2004).…”