Comet C/2011 W3 (Lovejoy): Orbit Determination, Outbursts, Disintegration of Nucleus, Dust-Tail Morphology, and Relationship to New Cluster of Bright Sungrazers

We describe the physical and orbital properties of C/2011 W3. After surviving perihelion, the comet underwent major changes (permanent loss of nuclear condensation, formation of spine tail). The process of disintegration culminated with an outburst on December 17.6 (T+1.6 d) and this delayed response is inconsistent with the rubble pile model. Probable cause was thermal stress from the heat pulse into the nucleus after perihelion, which could also produce fragmentation of sungrazers far from the Sun. The spine tail was a synchronic feature, made up of dust released at <30 m/s. Since the nucleus would have been located on the synchrone, we computed the astrometric positions of the missing nucleus as the coordinates of the points of intersection of the spine tail's axis with lines of forced orbital-period variation, derived from orbital solutions based on preperihelion astrometry from the ground. The resulting osculating orbital period was 698+/-2 years, which proves that C/2011 W3 is the first major member of the predicted new, 21st-century cluster of bright Kreutz-system sungrazers. The spine tail's tip contained dust 1-2 mm in diameter. The bizarre appearance of the dust tail in images taken hours after perihelion with coronagraphs on SOHO and STEREO is readily understood. The disconnection of the comet's head from the preperihelion tail and the apparent activity attenuation near perihelion are both caused by sublimation of all dust at heliocentric distances smaller than ~1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. The longest-imaged grains had a radiation-pressure parameter beta ~ 0.6, probably submicron-sized silicate grains. The place of C/2011 W3 within the hierarchy of the Kreutz system and its genealogy via a 14th century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1.Comment: Submitted to Astrophysical Journal; 35 pages, 18 figures, 8 table

Tidal interactions - crude body model in dynamical investigations

The paper presents results of investigations of small bodies dynamics in a vicinity of giant planets. We used the most simple body model: gravitationally bounded, rotating contact binary affected by the tidal force acting from a planet. Spin variations of such binaries were extensively studied during planetary close encounters. Two main types of dynamical behaviour were observed: (i) huge but interim fluctuations of the angular velocity and (ii) permanent changes of a rotation during a close approach. The first type is observed mainly for fast rotators, while the second one was encountered in a population of slowly spinning objects with periods longer than 12 hours. Conclusions on usability of such crude physical body models in dynamical investigations and a comparison to previous results were attached. The results allow us to formulate a thesis explaining the phenomenon of creation of the extremely slow rotators and an observational excess of such type of objects

Temporal Correlation Between Outbursts and Fragmentation Events of Comet 168P/Hergenrother

Outbursts are known to begin with a sudden appearance and steep brightening of a "stellar nucleus" --- an unresolved image of a plume of material on its way from the comet's surface and an initial stage of an expanding halo of ejecta. Since the brightness of this feature is routinely reported, together with astrometry, by most comet observers as the "nuclear magnitude," it is straightforward to determine the onset time, a fundamental parameter of any outburst, by inspecting the chronological lists of such observations for a major jump in the nuclear brightness. Although it is inadmissible to mix nuclear magnitudes by different observers without first carefully examining their compatibility, the time constraints obtained from data sets reported by different observers can readily be combined. The intersection of these sets provides the tightest possible constraint on the outburst's onset time. Applied to comet 168P/Hergenrother during its 2012 return to perihelion, three outbursts were detected and their timing determined with good to excellent accuracy. Six fragmentation events experienced by the comet are shown to have occurred in the same period of time as the outbursts. Three companions are likely to have broken off from the primary in the first outburst, two companions in the second outburst, and one companion in the last outburst. All companions were short-lived, belonging to the class of excessively brittle fragments. Yet, the results suggest that most of the mass lost in the first outburst remained relatively intact during the liftoff, while the opposite was the case in the last outburst.Comment: 24 pages, 12 tables, 3 figures; to appear in the International Comet Quarterl

Sublimation rates of carbon monoxide and carbon dioxide from comets at large heliocentric distances

Using a simple model for outgassing from a small flat surface area, the sublimation rates of carbon monoxide and carbon dioxide, two species more volatile than water ice that are known to be present in comets, are calculated for a suddenly activated discrete source on the rotating nucleus. The instantaneous sublimation rate depends upon the comet's heliocentric distance and the Sun's zenith angle at the location of the source. The values are derived for the constants of CO and CO2 in an expression that yields the local rotation-averaged sublimation rate as a function of the comet's spin parameters and the source's cometocentric latitude

Dynamical and photometric investigation of cometary type 2 tails

Photographic observations of the antitail of Comet Kohoutek (1973f) are photometrically studied and the results compared with the working model of an antitail. The applied technique of photometric reduction is described and the radial and transverse profiles of the antitail, corrected for the effects of the variable intensity of the sky background, are derived. The most important result reached so far is a quantitative confirmation of the previously suggested hypothesis, arguing that dust particles in the antitail suffered a significant loss in radius due to evaporation near the perihelion passage. Only particles initially larger than 0.1 to 0.15 mm in diameter survived. Numerically, however, this result is still tentative, because the dynamical effect exerted by particle evaporation remains to be accounted for