A study of the distant activity of comet C/2006 W3 (Christensen) withHerscheland ground-based radio telescopes

Abstract

Comet C/2006 W3 (Christensen) was observed in November 2009 at 3.3 AU from the Sun with Herschel.The PACS instrument acquired images of the dust coma in 70-μm and 160-μm filters and spectra covering several H 2 O rotational lines. Spectra in the range 450-1550 GHz were acquired with SPIRE. The comet emission continuum from 70 to 672 μm was measured, but no lines were detected. The spectral energy distribution indicates thermal emission from large particles and provides a measure of the size distribution index and dust production rate. The upper limit to the water production rate is compared to the production rates of other species (CO, CH 3 OH, HCN, H 2 S, OH) measured with the IRAM 30-m and Nançay telescopes. The coma is found to be strongly enriched in species more volatile than water, in comparison to comets observed closer to the Sun. The CO to H 2 O production rate ratio exceeds 220%. The dust-to-gas production rate ratio is on the order of 1.

Forbidden oxygen lines in Comets C/2006 W3 Christensen and C/2007 Q3 Siding Spring at large heliocentric distance: Implications for the sublimation of volatile ices

“…We can rule out CO as a dominant parent of O I by the following argument. The inferred CO production rate in Siding Spring is comparable to that for Christensen as measured by Bockelée-Morvan et al (2010) and Ootsubo et al (2011). To evaluate whether this is realistic, we employ our continuum flux to get a rough estimate of the quantity Afq, which serves as a model independent measure of the dust production rate, for Siding Spring.…”

Activity of Comet C/2006 W3 Christensen

“…For this purpose we compared calculated outgassing rates of the model nuclei of different compositions and structures, orbiting like the considered comet to the data derived from observations (Bockelée-Morvan et al, 2010;de Val-Borro et al, 2014;Ootsubo et al, 2012). The number of data is very small, only eight values of the production rates.…”

“…At $5 AU the H 2 O production rate was about 2:0 Â 10 27 s À1 (de Val-Borro et al, 2014). The dust-to-gas production rate ratio was: about one close to perihelion (Bockelée-Morvan et al, 2010), and 0.3-0.4 from 3.35 AU to 4.96 AU (de Val-Borro et al, 2014). In this work we attempted to find constrains for the composition and structure of the cometary nucleus moving in the long-period orbit with a far perihelion distance.…”

“…Composition of the model nucleus is described by model d (high abundance of the CO ice, v CO ¼ 0:2). The data were derived from observations performed using Herschel Space telescope, the IRAM millimeter telescope, the Nancay radio telescope and the AKARI infrared satellite (see (Bockelée-Morvan et al, 2010;de Val-Borro et al, 2014;Ootsubo et al, 2012)). The active region is located at the pole and its area S corresponding to the curves is 2.5 km 2 .…”

“…Its activity was monitored by various spectroscopic instruments from 3.66 AU before perihelion till 5 AU after perihelion. Close to perihelion the fluxes of CO and H 2 O seemed to be comparable, $2-4 Â 10 28 s À1 (Bockelée- Morvan et al, 2010;Ootsubo et al, 2012). At $5 AU the H 2 O production rate was about 2:0 Â 10 27 s À1 (de Val-Borro et al, 2014).…”