The Detection of CN in Interstellar Comet 3I/ATLAS
ATel #17352; David Schleicher (Lowell Observatory)
on 22 Aug 2025; 17:02 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Theodore Kareta (theodore.kareta@villanova.edu)
I obtained 3 sets of narrowband photoelectric photometry for Interstellar
Comet 3I/ATLAS (2025 N1) on 2025 August 19 (r=2.91 AU) using the Hall
42-inch (1.1-m) telescope at Lowell Observatory. A clear signal from CN
emission was measured, but other gas species (OH, NH, C2, and C3) were only
marginally detected within our standard 97 arcsec aperture. The 3 observational
sets for CN, possibly the first measurements of this species in Comet 3I,
yielded logarithmic production rates of 24.95+/-0.25, 24.84+/-0.11, and
24.86+/-0.10, for an unweighted log mean value of 24.89 mol/s. The poorly
constrained values for C2 and C3 (individual measurements following sky and
continuum subtraction having uncertainties >100%) are consistent with these
two carbon-chain species being depleted with respect to CN, based on our
Lowell database of comet compositions (Schleicher and Bair 2016; AAS/DPS
Meeting #48, paper #308.04). The data for OH and NH were even more uncertain,
and are not considered to be useful. Unexpectedly, the well-known dust coma
was also difficult to detect, yielding a log Afrho value of about 1.9 cm.
