P/2008 CL94 (Lemmon) and P/2011 S1 (Gibbs): comet-like activity at large heliocentric distances

Based on spectroscopic and photometric observations we analyzed the dust environment of two minor distant objects, P/2008 CL94 (Lemmon) and P/2011 S1 (Gibbs). Both targets demonstrated the comet-like activity beyond the “zone of water-ice sublimation”. Meanwhile the spectrum of P/2008 CL94 (Lemmon) did not reveal molecular emission features above reflected continuum in a spectral region of 4100-6800Å. Reddening of the continuum is linear along the dispersion with the mean normalized reflectivity gradient equals to 2.0% ± 0.4%. The normalized reflectivity of P/2011 S1 (Gibbs) derived from the V−R and R−I color indices equals 11% ± 9% and 26% ± 6% respectively. Both objects have likely small nuclei (about 2 and 4 km in the radii for P/2008 CL94 and P/2011 S1 respectively), which are consistent with nucleus sizes of 'Jupiter-family' comets. The level of physical activity of P/2008 CL94 and S/2011 S1 is characterized by R-Afρ quantity of 106 ± 3 cm and 76 ± 8 cm respectively. The Afρ values are resulted in dust production rates of about 1-2 kg/s, assuming the average geometric albedo of grains of 0.1 and the dust outflow velocities between 1 and 10 m/s.