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CO-activity in comet C/2016 R2 (PANSTARRS)

ATel #11254; M. de Val-Borro (NASA GSFC, CUA), S. N. Milam (NASA GSFC), M. A. Cordiner (NASA GSFC, CUA), S. B. Charnley (NASA GSFC), G. L. Villanueva (NASA GSFC), Y.-J. Kuan (Taiwan Normal University)
on 4 Feb 2018; 19:49 UT
Credential Certification: Miguel de Val-Borro (miguel.devalborro@nasa.gov)

Subjects: Millimeter, Comet, Solar System Object

We report observations of the CO (2-1) rotational line at 230 GHz in comet C/2016 R2 (PANSTARRS) with the Arizona Radio Observatory's Submillimeter Telescope between Jan 9.99-16.23 UT. This object is known to be in outburst since December 2017 (CBET #4464). Mapping of the CO distribution shows that the line emission is detected up to 1' from the nucleus with the signal peaking close to the nucleus position. The beam size of SMT is 32" at this frequency. The line intensity ranges from 0.34-0.50 K km/s during the observing period, with a line width between 1.0-1.3 km/s and a velocity shift around 1 km/s. A preliminary analysis of the data shows that the CO production rates span from 1.02e29 to 1.44e29 molec/s , assuming a gas kinetic temperature of 30 K. Other molecular lines (CH3OH, HCN, CS, H2CO, HCO+) were not detected in the SMT observations indicating the coma is strongly depleted in these species compared with CO. As the comet reaches higher temperatures during its perihelion passage on May 9 at a heliocentric distance of 2.6 au, it is expected that other species will be detectable and further multi-frequency monitoring of this object is desirable.

In the table below we list the observing dates, line areas in the main-beam brightness temperature scale and derived CO production rates with statistical errors.

Date rh Δ Intensity FWHM Shift Q(CO)
(UT) (au) (au) (K km/s) (km/s) (km/s) (molec/s)
2018-01-10.02 2.89 2.11 0.34 ± 0.02 1.07 ± 0.13 0.99 ± 0.04 (1.02 ± 0.08)×1029
2018-01-13.91 2.87 2.14 0.47 ± 0.03 1.28 ± 0.52 1.01 ± 0.16 (1.44 ± 0.12)×1029
2018-01-16.16 2.86 2.15 0.37 ± 0.01 1.05 ± 0.05 0.99 ± 0.02 (1.14 ± 0.03)×1029