108 research outputs found
Rotation-stimulated structures in the CN and C3 comae of comet 103P/Hartley 2 around 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 NASA's
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.Comment: 9 pages, 10 figures, submitted to Astron. Astrophy
The Sources of HCN and CH3OH and the Rotational Temperature in Comet 103P/Hartley 2 from Time-Resolved Millimeter Spectroscopy
One of the least understood properties of comets is the compositional
structure of their nuclei, which can either be homogeneous or heterogeneous.
The nucleus structure can be conveniently studied at millimeter wavelengths,
using velocity-resolved spectral time series of the emission lines, obtained
simultaneously for multiple molecules as the body rotates. Using this
technique, we investigated the sources of CH3OH and HCN in comet 103P/Hartley
2, the target of NASA's EPOXI mission, which had an exceptionally favorable
apparition in late 2010. Our monitoring with the IRAM 30 m telescope shows
short-term variability of the spectral lines caused by nucleus rotation. The
varying production rates generate changes in brightness by a factor of 4 for
HCN and by a factor of 2 for CH3OH, and they are remarkably well correlated in
time. With the addition of the velocity information from the line profiles, we
identify the main sources of outgassing: two jets, oppositely directed in a
radial sense, and icy grains, injected into the coma primarily through one of
the jets. The mixing ratio of CH3OH and HCN is dramatically different in the
two jets, which evidently shows large-scale chemical heterogeneity of the
nucleus. We propose a network of identities linking the two jets with
morphological features reported elsewhere, and postulate that the chemical
heterogeneity may result from thermal evolution. The model-dependent average
production rates are 3.5x10**26 molec/s for CH3OH and 1.25x10**25 molec/s for
HCN, and their ratio of 28 is rather high but not abnormal. The rotational
temperature from CH3OH varied strongly, presumably due to nucleus rotation,
with the average value being 47 K.Comment: Published in ApJ 756, 80 (2012). Supplementary materials available at
http://www.its.caltech.edu/~mdrahus/103p_paperII.htm
Rotation State of Comet 103P/Hartley 2 from Radio Spectroscopy at 1 mm
The nuclei of active comets emit molecules anisotropically from discrete
vents. As the nucleus rotates, we expect to observe periodic variability in the
molecular emission line profiles, which can be studied through mm/submm
spectroscopy. Using this technique we investigated the HCN atmosphere of comet
103P/Hartley 2, the target of NASA's EPOXI mission, which had an exceptionally
favorable apparition in late 2010. We detected short-term evolution of the
spectral line profile, which was stimulated by the nucleus rotation, and which
provides evidence for rapid deceleration and excitation of the rotation state.
The measured rate of change in the rotation period is +1.00 \pm 0.15 min per
day and the period itself is 18.32 \pm 0.03 hr, both applicable at the epoch of
the EPOXI encounter. Surprisingly, the spin-down efficiency is lower by two
orders of magnitude than the measurement in comet 9P/Tempel 1 and the best
theoretical prediction. This secures rotational stability of the comet's
nucleus during the next few returns, although we anticipate a catastrophic
disruption from spin-up as its ultimate fate.Comment: Accepted for publication in ApJ Letter
Fast Rotation and Trailing Fragments of the Active Asteroid P/2012 F5 (Gibbs)
While having a comet-like appearance, P/2012 F5 (Gibbs) has an orbit native
to the Main Asteroid Belt, and physically is a km-sized asteroid which recently
(mid 2011) experienced an impulsive mass ejection event. Here we report new
observations of this object obtained with the Keck II telescope on UT 2014
August 26. The data show previously undetected 200-m scale fragments of the
main nucleus, and reveal a rapid nucleus spin with a rotation period of 3.24
0.01 hr. The existence of large fragments and the fast nucleus spin are
both consistent with rotational instability and partial disruption of the
object. To date, many fast rotators have been identified among the minor
bodies, which, however, do not eject detectable fragments at the present-day
epoch, and also fragmentation events have been observed, but with no rotation
period measured. P/2012 F5 is unique in that for the first time we detected
fragments and quantified the rotation rate of one and the same object. The
rapid spin rate of P/2012 F5 is very close to the spin rates of two other
active asteroids in the Main Belt, 133P/Elst-Pizarro and (62412), confirming
the existence of a population of fast rotators among these objects. But while
P/2012 F5 shows impulsive ejection of dust and fragments, the mass loss from
133P is prolonged and recurrent. We believe that these two types of activity
observed in the rapidly rotating active asteroids have a common origin in the
rotational instability of the nucleus.Comment: To appear in the 2015 March 20 issue of ApJ Letter
A photometric and spectroscopic study of WW And - an Algol-type, long period binary system with an accretion disc
We have analyzed the available spectra of WW And and for the first time
obtained a reasonably well defined radial velocity curve of the primary star.
Combined with the available radial velocity curve of the secondary component,
these data led to the first determination of the spectroscopic mass ratio of
the system at q-spec = 0.16 +/- 0.03. We also determined the radius of the
accretion disc from analysis of the double-peaked H-alpha emission lines. Our
new, high-precision, Johnson VRI and the previously available Stromgren vby
light curves were modelled with stellar and accretion disc models. A consistent
model for WW And - a semidetached system harbouring an accretion disc which is
optically thick in its inner region, but optically thin in the outer parts -
agrees well with both spectroscopic and photometric data.Comment: Accepted by New Astronom
CN Morphology Studies of Comet 103P/Hartley 2
We report on narrowband CN imaging of Comet 103P/Hartley 2 obtained at Lowell
Observatory on 39 nights from 2010 July until 2011 January. We observed two
features, one generally to the north and the other generally to the south. The
CN morphology varied during the apparition: no morphology was seen in July; in
August and September the northern feature dominated and appeared as a mostly
face-on spiral; in October, November, and December the northern and southern
features were roughly equal in brightness and looked like more side-on
corkscrews; in January the southern feature was dominant but the morphology was
indistinct due to very low signal. The morphology changed smoothly during each
night and similar morphology was seen from night to night. However, the
morphology did not exactly repeat each rotation cycle, suggesting that there is
a small non-principal axis rotation. Based on the repetition of the morphology,
we find evidence that the fundamental rotation period was increasing: 16.7 hr
from August 13-17, 17.2 hr from September 10-13, 18.2 hr from October 12-19,
and 18.7 hr from October 31-November 7. We conducted Monte Carlo jet modeling
to constrain the pole orientation and locations of the active regions based on
the observed morphology. Our preliminary, self-consistent pole solution has an
obliquity of 10 deg relative to the comet's orbital plane (i.e., it is centered
near RA = 257 deg and Dec=+67 deg with an uncertainty around this position of
about 15 deg) and has two mid-latitude sources, one in each hemisphere.Comment: Accepted by The Astronomical Journal; 23 pages of text, 2 tables, 8
figure
Rotation of the nucleus, gas kinematics and emission pattern of comet 8P/Tuttle : preliminary results from optical imaging of the CN coma
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