Galin B. Borisov

Rotation-stimulated structures in the CN and C3 comae of comet 103P/Hartley 2 close to the EPOXI encounter ,

In late 2010 a Jupiter Family comet 103P/Hartley 2 was a subject of an intensive world-wide investigation. On UT October 20.7 the comet approached the Earth within only 0.12 AU, and on UT November 4.6 it was visited by NASAs EPOXI spacecraft. We joined this international effort and organized an observing campaign. The images of the comet were obtained through narrowband filters using the 2-m telescope of the Rozhen National Astronomical Observatory. They were taken during 4 nights around the moment of the EPOXI encounter. Image processing methods and periodicity analysis techniques were used to reveal transient coma structures and investigate their repeatability and kinematics. We observe shells, arc-, jet- and spiral-like patterns, very similar for the CN and C3 comae. The CN features expanded outwards with the sky-plane projected velocities between 0.1 to 0.3 km/s. A corkscrew structure, observed on November 6, evolved with a much higher velocity of 0.66 km/s. Photometry of the inner coma of CN shows variability with a period of 18.32+/-0.30 h (valid for the middle moment of our run, UT 2010 Nov. 5.0835), which we attribute to the nucleus rotation. This result is fully consistent with independent determinations around the same time by other teams. The pattern of repeatability is, however, not perfect, which is understendable given the suggested excitation of the rotation state, and the variability detected in CN correlates well with the cyclic changes in HCN, but only in the active phases. The revealed coma structures, along with the snapshot of the nucleus orientation obtained by EPOXI, let us estimate the spin axis orientation. We obtained RA=122 deg, Dec=+16 deg (epoch J2000.0), neglecting at this point the rotational excitation.

Broadband imaging and narrowband polarimetry of comet 73P/Schwassmann-Wachmann 3, components B and C, on 3, 4, 8, and 9 May 2006

Context. The Jupiter family comet 73P/Schwassmann-Wachmann 3 (SW3) split into several pieces in 1995. Some of the original fragments were observed during the next apparition of the comet in 1999−2001. The last return of the comet in 2005−2006 was accompanied by tremendous further splitting of some SW3 components – in particular component B – into a large number of subfragments. Aims. We present observations of components B and C during their closest approach to Earth in the first half of May 2006. These results aim at characterizing the properties of dust particles released from the fragments of comet SW3 and at identifying dusty and gaseous structures in the comae and tail regions of components B and C, which could be useful for conclusions about the presence of active regions and break-up events of the components. Methods. We used narrowband imaging polarimetry and an analysis of the broadband surface brightness for the characterization of the dust comae of the SW3 components. Coma and tail structures in components B and C were enhanced by numerical methods. Results. The degree of linear polarization of components B and C follows the empirical phase-angle dependence as derived from other comets. Fragment B was found in outburst on May 8. The brightness outburst was accompanied by changes in the shape of the coma. During the outburst, the spatial distribution of the linear polarization showed some peculiarities that had disappeared again on May 9. Arc-like signatures of a temporary nature, typical of fragmentation events, are seen in broadband filter images of component B on 3, 8, and 9 May 2006. The secondary dust tail, seen in component B on 3 and 4 May 2006, marks the synchrone of an earlier splitting event around 25 April 2006. Fan-like coma structures are found in the sunward coma hemisphere of components B and C that might be related to localized enhanced activity on the rotating nuclei.

Broadband linear polarization of Jupiter Trojans

Trojan asteroids orbit in the Lagrange points of the system Sun-planet-asteroid. Their dynamical stability make their physical properties important proxies for the early evolution of our solar system. To study their origin, we want to characterize the surfaces of Jupiter Trojan asteroids and check possible similarities with objects of the main belt and of the Kuiper Belt. We have obtained high-accuracy broad-band linear polarization measurements of six Jupiter Trojans of the L4 population and tried to estimate the main features of their polarimetric behaviour. We have compared the polarimetric properties of our targets among themselves, and with those of other atmosphere-less bodies of our solar system. Our sample show approximately homogeneous polarimetric behaviour, although some distinct features are found between them. In general, the polarimetric properties of Trojan asteroids are similar to those of D- and P-type main-belt asteroids. No sign of coma activity is detected in any of the observed objects. An extended polarimetric survey may help to further investigate the origin and the surface evolution of Jupiter Trojans.

Rotational variation of the linear polarization of the asteroid (3200) Phaethon as evidence for inhomogeneity in its surface properties

This work was supported via a grant (ST/M000834/1) from the UK Science and Technology Facilities Council. We gratefully acknowledge observing grant support from the Institute of Astronomy and Rozhen National Astronomical Observatory, Bulgarian Academy of Sciences. The Calern Asteroid Polarimetric Survey (CAPS), carried out at Calern in the framework of C2PU, is a collaboration between INAF –Torino Astrophysical Observatory and the Observatoire de la cote d’Azur. The GOTO Observatory is a collaboration between the University of Warwick and Monash University (as the Monash–Warwick Alliance), Armagh Observatory & Planetarium, the University of Sheffield, the University of Leicester, the National Astronomical Research Institute of Thailand (NARIT), the Instituto de Astrofsica de Canarias (IAC), the University of Turku, and Rene Breton (University of Manchester). TB acknowledges financial support by contract DN 18/13-12.12.2017 with the Bulgarian NSF. This research was made possible through the use of the AAVSO Photometric All-Sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen’s University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation.