Formaldehyde in Comets C/1995 O1 (Hale‐Bopp), C/2002 T7 (LINEAR), and C/2001 Q4 (NEAT): Investigating the Cometary Origin of H2CO

Stefanie N. Milam, Anthony J. Remijan, Maria Womack, Leif Abrell, L. M. Ziurys, Susan Wyckoff, A. J. Apponi, D. N. Friedel, L. E. Snyder, J. M. Veal, Patrick Palmer, L. M. Woodney (+6 others)
2006 Astrophysical Journal  
Observations of formaldehyde (H 2 CO) have been conducted toward comets C/1995 O1 ( Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) using the Arizona Radio Observatory (ARO) 12 m telescope at 1.2 and 2 mm. Aperture synthesis maps of H 2 CO at 3 mm were made using the Berkeley-Illinois-Maryland Association ( BIMA) interferometer toward comet Hale-Bopp. These data indicate that the production rate of H 2 CO is $3:7 ; 10 28 s À1 at $1 AU in comet Hale-Bopp, using a simple Monte Carlo model,
more » ... a nuclear origin for the molecule is assumed. However, maps of H 2 CO in Hale-Bopp, in comparison with CO, show an extended distribution (r s $ 15,000 km) with small-scale structure oriented roughly along the comet-Sun direction. This result suggests a source of H 2 CO other than the comet nucleus. The extended source of formaldehyde is probably grains composed of a mixture of silicates and organic material. The production rate for H 2 CO increases to Q $ 1:4 ; 10 29 s À1 assuming such an extended grain source. This value implies a Q/Q(H 2 O) $ 1:4%, which is similar to the production rate ratio of Q/Q(H 2 O) $ 4% derived from in situ measurements of H 2 CO in comet Halley. Production rates for H 2 CO toward comets C/2002 T7 (LINEAR) and C/2001 Q4 ( NEAT) are 1:4 ; 10 27 and 5:6 ; 10 26 s À1 , respectively, modeled using the extended grain source. The spectra of H 2 CO measured toward comet C/2002 T7 ( LINEAR) show evidence for a second velocity component, most likely arising from comet fragmentation. Subject headingg s: astrobiology -comets: individual ( Hale-Bopp (C/1995 O1), NEAT (C/2001 Q4), LINEAR (C/2002 T7)) -radio lines: solar system -techniques: interferometric
doi:10.1086/506501 fatcat:e37ptspob5b27pko5txpj7wao4