Cochran et al. 2012 presented observations of four comets (7P/Pons-Winnecke, 96P/Machholz 1, 108P/Ciffreo, and 125P/Spacewatch), which were shown to have no significant gas emission. All four comets were observed at heliocentric distances of <1.75 AU (in 1989, 2007, 1985, and 1996 respectively). Bauer et al. 2021 (in preparation) presented NEOWISE observations of the same four comets, the majority of which showed emission at ~2AU that was dominated by CO2/CO. This result suggests that CO2/CO may drive dust production for these objects. In March 2021, 7P was observed at ~1.5 AU in five HB filters (RC, BC, C2, CN, and OH) using the Large Monolithic Imager (LMI) at Lowell Observatory. The comet was visible in all gas filters except OH. Average AfRho values of 28.62 cm and 19.34 cm (RC and BC respectively) were found. Constraining gas production for “dry” comets like 7P will help explore the various drivers of cometary activity including in these comets for which water may play only a minor role.
Cochran, A. L., Barker, E. S., & Grey, C. L. 2012, Icarus, 218, 144, doi: 10.1016/j.icarus.2011.12.010
Bauer, J. M., Gicquel, A., Kramer, E., et al. 2021, (in preparation)