Comets, centaurs and active asteroids

C/2016 R2: A Comet Rich in CO and Depleted in HCN

We report the first detection of CO emission from this comet with amounts high enough to be the primary driver of activity. The HCN production rate is significantly less than those of other comets, yet the comet does not show the typical nitrogen depletion seen in comets, which may provide important clues to its formation environment.

Volatiles in Distant Comets (Review Paper)

Womack et al. 2017, PASP, 129, 973

"This is a great contributed review. A must read for those interested in studies of volatiles of comets," Jeffrey G. Magnum, editor PASP journal.

CO in the Centaur Echeclus at 6 au

Wierzchos et al. 2017, AJ, 153, 5

We obtained a 3.6σ detection of the CO J=2-1 line that was slightly blueshifted (δv = −0.55 ± 0.10 km s−1) and narrow (ΔvFWHM = 0.53 ± 0.23 km s−1). The data are consistent with emission from a cold gas from the sunward side of the nucleus, as seen in two other comets at 6 au. Compared with the relatively unprocessed comet C/1995 O1 (Hale–Bopp), Echeclus produces significantly less CO, as do Chiron and four other Centaurs.

Key molecules in comet Hale-Bopp beyond 4 au

Mm-wavelength spectra of comet C/1995 O1 (Hale-Bopp), including the first detection of CH3OH at 5 au. Spectral line profiles show different origins for CO vs H2CO, CH3OH and HCN.

CCD Image Archive of Hale-Bopp: Dust expansion velocities

An optical archive of comet Hale-Bopp was obtained over 28 nights from June 1996 to May 1997 covering a range of heliocentric distances of r = 4.12 - 0.91. The CCD images were obtained with the 0.8-m University of Washington Manastash Ridge Observatory and the 0.25-m Pennsylvania State University at Eriemobile observatory. The reduced images clearly document the evolution of features of the coma, which were dominated by radial jetsfrom r = 4.1 - 2.3 AU, curved fan-shaped jets from r = 1.2 - 1.0 AU, and arcs or shells for 0.9 < r < 1.0 AU. We present the images and derive an average dust expansion velocity of Vdust = 0.67 ± 0.07 km s-1 from measurements of the arc features. The images in thearchive will be made available to other researchers for further study.

Hale-Bopp Visible Lightcurve from 1995-1999

We present an algorithm for reducing scatter and increasing precision in a comet light curve. As a demonstration, we processed apparent magnitudes of comet Hale-Bopp from 16 highly experienced observers (archived with the International Comet Quarterly), correcting for distance from Earth and phase angle. Different observers tend to agree on the difference in magnitudes of an object at different distances, but the magnitude reported by observer is shifted relative to that of another for an object at a fixed distance. We estimated the shifts using a self-consistent statistical approach, leading to a sharper light curve and improving the precision of the measured slopes. The final secular lightcurve for comet Hale-Bopp ranges from -7 au (pre-perihelion) to +8 au (post-perihelion) and is the best secular light curve produced to date for this “great” comet. We discuss Hale-Bopp’s lightcurve evolution and possibly related physical implications, and potential usefulness of this light curve for comparisons with other future bright comets. We also assess the appropriateness of using secular lightcurves to characterize dust production rates in Hale-Bopp and other dust-rich comets. M.W. acknowledges support from NSF grant AST-1615917.

CO in the centaur 2060 Chiron

CO emission was detected in Chiron via its J=2-1 rotational transition.


Maria Womack
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©2019 by Maria Womack