Interferometric mapping of the 3.3-mm continuum emission of comet 17P/Holmes after its 2007 outburst

Abstract

Context. Comet 17P/Holmes underwent a dramatic outburst in October 2007, caused by the sudden fragmentation of its nucleus and the production of a large quantity of grains scattering sunlight. Aims. We report on 90 GHz continuum observations carried out with the IRAM Plateau de Bure interferometer on 27.1 and 28.2 October 2007 UT, i.e., 4−5 days after the outburst. These observations probed the thermal radiation of large dust particles, and therefore provide the best constraints on the mass in the ejecta debris. Methods. The thermal emission of the debris was modelled and coupled to a time-dependent description of their expansion after the outburst. The analysis was performed in the Fourier plane. Visibilities were computed for the two observing dates and compared to the data to measure their velocity and mass. Optical data and 250-GHz continuum measurements published in the literature were used to further constrain the dust kinematics and size distribution. Results. Two distinct dust components in terms of kinematic properties are identified in the data. The large-velocity component, with typical velocities V 0 of 50−100 m s −1 for 1 mm particles, displays a steep size distribution with a size index estimated to q = −3.7 (±0.1), assuming a minimum grain size of 0.1 μm. It corresponds to the fast expanding shell observed in optical images. The slowlymoving "core" component (V 0 = 7−9 m s −1 ) detected near the nucleus has a size index |q| < 3.4 and contains a higher proportion of large particles than the shell. The dust mass in the core is in the range 0.1−1 that of the shell. Using optical constants pertaining to porous grains (50% porosity) made of astronomical silicates mixed with water ice (48% in mass), the total dust mass M dust injected by the outburst is estimated to 4−14 × 10 11 kg, corresponding to 3−9% the nucleus mass.

Comet 17p/Holmes: Contrast in Activity Between Before and After the 2007 Outburst

“…It is found that the infrared spectrum of the diffuse emission can be explained by a mixture of amorphous and crystalline silicate materials as observed in most comets (Watanabe et al 2009;Reach et al 2010). Total ejecta mass was estimated to be 10 10 -10 13 kg (Montalto et al 2008;Altenhoff et al 2009;Reach et al 2010;Ishiguro et al 2010;Boissier et al 2012). More than a 2-m-thick surface layer could be blown off by the initial event although this is strongly dependent on the size distribution and maximum size of the dust par-ticles .…”

Catastrophic Disruption of Comet Ison

“…Epifani et al (2001) showed millimeter-sized dust in the coma of 2P/Encke typically had velocities of <10 m s −1 but reached velocities >30 m s −1 approximately two weeks before perihelion. On the other hand, Boissier et al (2012) found a population of millimeter-sized grains in the coma of 17P/ Holmes with velocities of 50-100 m s −1 after a fragmentation event. Sekanina & Chodas (2012) determined that as C/2013 W3 (Lovejoy) was disrupted shortly after perihelion, the millimeter-sized dust was released at velocities of up to 30 m s −1 .…”

“…Boissier et al 2012). Though sample opacities for millimeter-sized grains of varying porosity, ice/silicate mixture, and size distribution have been published (Jewitt & Luu 1990;Boissier et al 2012), the nature of the millimeter grains cannot be determined with these observations. Dust masses could be significantly higher if the millimeter-sized dust grains are very porous, containing little ice.…”

“…(Sub)Millimeter-wavelength observations are most sensitive to the thermal radiation emitted by millimeter-sized dust particles and have been shown to directly probe the grain mass contained within larger particles (Jewitt & Luu 1990;Altenhoff et al 1999;Jewitt & Matthews 1999;Bockelée-Morvan et al 2010;Boissier et al 2012). In this paper, we present single-dish Submillimeter Common-User Bolometer Array 2 (SCUBA-2) observations at 850 μm of the dust continuum of comet ISON acquired over six days prior to perihelion on 2013 November 28.…”

Millimetre continuum observations of comet C/2009 P1 (Garradd)

“…We used the model of dust thermal emission presented by Boissier et al (2012). Absorption cross-sections were calculated with the Mie theory, taking a refractive index ((n, k) = (2.05, 0.007) at 1.91 mm) corresponding to porous grains (P = 0.5) composed of a 50:50 mixture of crystalline (Fabian et al 2001) and amorphous silicates (Draine 1985).…”