The nature of cometary grains from remote sensing

Physical property data of cometary grains are derived primarily from thermal emission measurement and optical scattering. Results consistent with the properties of micrometeorites collected in the stratosphere are described

Quantification of UV stimulated ice chemistry: CO and CO2

Recent laboratory experiments are presented that show that during photolysis of the pure ices there is evidence of the interconversion of CO to CO2 and CO2 to CO using Lyman alpha (1216A) radiation. In addition, there is a substantial amount of another substance being produced. This substance is evident by its infrared absorption peak at 2235 cm(-1). It is believed that this new peak is due to carbon suboxide, C3O2. CO and CO2 have already been detected in comets, and C3O2 has been suggested as a cometary from radiation of CO. Comparisons are made between our results at 1215A and proton radiation experiments and radiation at other wavelengths. The suggestion is that the processing of ices is energy dependent, i.e., dependent on the type of radiation. Several difficult problems have to be solved before these radiation conversions can be quantified. The steps that we are taking to quantify the kinetics are discussed

Cometary dust composition

The earth based measurements and in situ sampling of Comet Halley have provided new data about the chemical composition of cometary grains. Recent progress in laboratory studies of interplanetary dust particles (IDPs) complement the comet data, allowing inferences about the mineralogy and physical structure of the comet dust to be drawn from the observed elemental composition and infrared spectra. The in situ dust composition measurements at Halley, the composition of IDPs and their relation to comet dust, and the origin of the 3.4 micron hydrocarbon feature is discussed. Related discussion is also presented on aromatic components in comets and the 3.4 micron feature. These topics are briefly summarized

3 - 14 Micron Spectroscopy of Comets C/2002 O4 (Honig), C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 Y1 (Juels-Holvorcem), 69P/Taylor, and the Relationships among Grain Temperature, Silicate Band Strength and Structure among Comet Families

We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002 and February 2003: C/2002 O4 (Honig) on August 1, 2002, C/2002 V1 (NEAT) on Jan. 9 and 10, 2003, C/2002 X5 (Kudo-Fujikawa) on Jan. 9 and 10, 2003, and C/2002 Y1 (Juels-Holvorcem) on Feb. 20, 2003. In addition, we include data obtained much earlier on 69P/Taylor (February 9, 1998) but not previously published. For Comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate emission band was detected, being approximately 23%, 12%, 15%, and 10%, respectively, above the continuum. The data for Comet Juels-Holvorcem were of insufficient quality to detect the presence of a silicate band of comparable strength to the other three objects, and we place an upper limit of 24% on this feature. The silicate features in both NEAT and Kudo-Fujikawa contained structure indicating the presence of crystalline material. Combining these data with those of other comets, we confirm the correlation between silicate band strength and grain temperature of Gehrz & Ney (1992) and Williams et al. (1997) for dynamically new and long period comets, but the majority of Jupiter family objects may deviate from this relation. The limited data available on Jupiter family objects suggest that they may have silicate bands that are slightly different from the former objects. Finally, when compared to the silicate emission bands observed in pre-main sequence stars, the dynamically new and long period comets most closely resemble the more evolved stellar systems, while the limited data (in quantity and quality) on Jupiter family objects seem to suggest that these have spectra more like the less-evolved stars.Comment: 45 pages, 12 figure

A Spitzer Study of Comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT)

We present infrared images and spectra of comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger program to observe comets inside of 5 AU from the sun with the Spitzer Space Telescope. The nucleus of comet 2P/Encke was observed at two vastly different phase angles (20 degrees and 63 degrees). Model fits to the spectral energy distributions of the nucleus suggest comet Encke's infrared beaming parameter derived from the near-Earth asteroid thermal model may have a phase angle dependence. The observed emission from comet Encke's dust coma is best-modeled using predominately amorphous carbon grains with a grain size distribution that peaks near 0.4 microns, and the silicate contribution by mass to the sub-micron dust coma is constrained to 31%. Comet 67P/Churyumov-Gerasimenko was observed with distinct coma emission in excess of a model nucleus at a heliocentric distance of 5.0 AU. The coma detection suggests that sublimation processes are still active or grains from recent activity remain near the nucleus. Comet C/2001 HT50 (LINEAR-NEAT) showed evidence for crystalline silicates in the spectrum obtained at 3.2 AU and we derive a silicate-to-carbon dust ratio of 0.6. The ratio is an order of magnitude lower than that derived for comets 9P/Tempel 1 during the Deep Impact encounter and C/1995 O1 (Hale-Bopp).Comment: Accepted for publication in the Astrophysical Journal 48 pages, 15 figures, 10 table

Solar System Objects in the ISOPHOT 170 micron Serendipity Survey

The ISOPHOT Serendipity Survey (ISOSS) covered approximately 15 % of the sky at a wavelength of 170 micron while the ISO satellite was slewing from one target to the next. By chance ISOSS slews went over many solar system objects (SSOs). We identified the comets, asteroids and planets in the slews through a fast and effective search procedure based on N-body ephemeris and flux estimates. The detections were analysed from a calibration and scientific point of view. Through the measurements of the well-known asteroids Ceres, Pallas, Juno and Vesta and the planets Uranus and Neptune it was possible to improve the photometric calibration of ISOSS and to extend it to higher flux regimes. We were also able to establish calibration schemes for the important slew end data. For the other asteroids we derived radiometric diameters and albedos through a recent thermophysical model. The scientific results are discussed in the context of our current knowledge of size, shape and albedos, derived from IRAS observations, occultation measurements and lightcurve inversion techniques. In all cases where IRAS observations were available we confirm the derived diameters and albedos. For the five asteroids without IRAS detections only one was clearly detected and the radiometric results agreed with sizes given by occultation and HST observations. Four different comets have clearly been detected at 170 micron and two have marginal detections. The observational results are presented to be used by thermal comet models in the future. The nine ISOSS slews over Hale-Bopp revealed extended and asymmetric structures related to the dust tail. We attribute the enhanced emission in post-perihelion observations to large particles around the nucleus. The signal patterns are indicative of a concentration of the particles in trail direction.Comment: 15 pages, 6 figures, 6 tables; Accepted for publication in Astronomy and Astrophysic

Cometary Dust in the Debris Disks of HD 31648 and HD 163296: Two ``Baby'' beta Pics

The debris disks surrounding the pre-main sequence stars HD 31648 and HD 163296 were observed spectroscopically between 3 and 14 microns. Both possess a silicate emission feature at 10 microns which resembles that of the star beta Pictoris and those observed in solar system comets. The structure of the band is consistent with a mixture of olivine and pyroxene material, plus an underlying continuum of unspecified origin. The similarity in both size and structure of the silicate band suggests that the material in these systems had a processing history similar to that in our own solar system prior to the time that the grains were incorporated into comets.Comment: 17 pages, AASTeX, 5 eps figures, accepted for publication in Ap.

The Stardust – a successful encounter with the remarkable comet Wild 2

On January 2, 2004 the Stardust spacecraft completed a close flyby of comet Wild2 (P81). Flying at a relative speed of 6.1 km/s within 237km of the 5 km nucleus, the spacecraft took 72 close-in images, measured the flux of impacting particles and did TOF mass spectrometry

The Embedded Super Star Cluster of SBS0335-052

We analyze the infrared (6-100 micron) spectral energy distribution of the blue compact dwarf and metal-poor (Z=Z_solar/41) galaxy SBS0335-052. With the help of DUSTY (Ivezic et al. 1999), a program that solves the radiation transfer equations in a spherical environment, we evaluate that the infrared (IR) emission of SBS0335-052 is produced by an embedded super-star cluster (SSC) hidden under 10^5 M_solar of dust, causing 30 mag of visual extinction. This implies that one cannot detect any stellar emission from the 2x10^6 M_solar stellar cluster even at near-infrared (NIR) wavelengths. The derived grain size distribution departs markedly from the widely accepted size distribution inferred for dust in our galaxy (the so-called MRN distribution, Mathis et al. 1977), but resembles what is seen around AGNs, namely an absence of PAH and smaller grains, and grains that grow to larger sizes (around 1 micron). The fact that a significant amount of dust is present in such a low-metallicity galaxy, hiding from UV and optical view most of the star formation activity in the galaxy, and that the dust size distribution cannot be reproduced by a standard galactic law, should be borne in mind when interpreting the spectrum of primeval galaxies.Comment: 32 pages, 3 figures,accepted for publication in A

SN 2007od: A Type IIP SN with Circumstellar Interaction

SN 2007od exhibits characteristics that have rarely been seen in a Type IIP supernova (SN). Optical V band photometry reveals a very steep brightness decline between the plateau and nebular phases of ~4.5 mag, likely due to SN 2007od containing a low mass of 56Ni. The optical spectra show an evolution from normal Type IIP with broad Halpha emission, to a complex, four component Halpha emission profile exhibiting asymmetries caused by dust extinction after day 232. This is similar to the spectral evolution of the Type IIn SN 1998S, although no early-time narrow (~200 km s-1) Halpha component was present in SN 2007od. In both SNe, the intermediate-width Halpha emission components are thought to arise in the interaction between the ejecta and its circumstellar medium (CSM). SN 2007od also shows a mid-IR excess due to new dust. The evolution of the Halpha profile and the presence of the mid-IR excess provide strong evidence that SN 2007od formed new dust before day 232. Late-time observations reveal a flattening of the visible lightcurve. This flattening is a strong indication of the presence of a light echo, which likely accounts for much of the broad, underlying Halpha component seen at late-times. We believe the multi-peaked Halpha emission is consistent with the interaction of the ejecta with a circumstellar ring or torus (for the inner components at \pm1500 km s-1), and a single blob or cloud of circumstellar material out of the plane of the CSM ring (for the outer component at -5000 km s-1). The most probable location for the formation of new dust is in the cool dense shell created by the interaction between the expanding ejecta and its CSM. Monte Carlo radiative transfer modeling of the dust emission from SN 2007od implies that up to 4x 10-4Msun of new dust has formed. This is similar to the amounts of dust formed in other CCSNe such as SNe 1999em, 2004et, and 2006jc.Comment: 35 pages, 6 figures. Accepted for publication in Ap