CHEMICAL COMPOSITION OF COMET C/2007 N3 (LULIN): ANOTHER ''ATYPICAL'' COMET

We measured the volatile chemical composition of comet C/2007 N3 (Lulin) on three dates from 2009 January 30 to February 1 using NIRSPEC, the high-resolution (λ/Δλ ≈ 25,000), long-slit echelle spectrograph at Keck 2. We sampled nine primary (parent) volatile species (H2O, C2H6, CH3OH, H2CO, CH4, HCN, C2H2, NH3, CO) and two product species (OH* and NH2). We also report upper limits for HDO and CH3D. C/2007 N3 (Lulin) displayed an unusual composition when compared to other comets. Based on comets measured to date, CH4 and C2H6 exhibited 'normal' abundances relative to water, CO and HCN were only moderately depleted, C2H2 and H2CO were more severely depleted, and CH3OH was significantly enriched. Comet C/2007 N3 (Lulin) is another important and unusual addition to the growing population of comets with measured parent volatile compositions, illustrating that these studies have not yet reached the level where new observations simply add another sample to a population with well-established statistics.