Observation of the Oort-cloud comet C/2009 P1 (Garradd) at the 6-m SAO RAS telescope
Currently, attempts are underway to establish a taxonomy of comets on
the basis of their composition and to link it to the place of their
origin. A comparison of physical characteristics of short-period comets
with those with long-period and new comets may elucidate which properties
of comets are primordial and which are the product of subsequent evolution.
Study of polarization properties of different comets may also provide
classification of comets and understanding the main processes of dust
formation in the protosolar nebula. In addition, polarimetric
characteristics of comets may indicate differences in the properties
of dust on the surface and inside of the nuclei through observations
of jets and different fragments of comets. For these purposes, we
conduct systematic polarimetric observations of comets that are available
for our instruments. Comet Garradd was unusually dust-rich, and its
activity was complex and changed significantly over time. The comet
produced lots of dust and gas long before it reached the snow line.
This means that its activity was caused by something other than water
ice, for example, by sublimation of more volatile components CO or CO2.
The water production rate in comet Garradd was highly asymmetric around
perihelion. Our post-perihelion observations of the comet Garradd were
performed at the 6-m telescope BTA of the Special Astrophysical
Observatory (Russia) with the SCORPIO-2 multi-mode focal reducer.
Observations of the comet were obtained, when its heliocentric distance
increased from 1.65 to 2.23 au. Analysis of photometrical data of the
comet allow to isolate two features (dust and gas tails) in cometary
coma oriented in the solar and antisolar directions. We estimated the
shift of structures with time in cometary coma during our observations
we determined the period of rotation of the nucleus as
11.1±0.8 hours. Analysis of spectral observations of the comet
allows us to identify the emission bands of neutral molecules such as
C2, C3, CN, CH, and NH2
as well as CO+ and H2O+ ions (Fig.2).
Fig.1. Image of the comet C/2009 P1 (Garradd) with isophotes obtained in the Ç-SDSS filter on February 2, 2012 (left-hand panel) and processed with digital filters (right-hand panel) in order to distinguish low-contrast structures in the comet come
Fig.2. Spectrum of the comet obtained on February 2, 2012. Sky background and continuum (the reflected sunlight by cometary dust particles) were subtracted. Separately in the box, the observed (a solid line) and model (a dashed line) spectra of the emission line C2 (Δν = + 1) are shown for comparison