14 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
Triple F - a comet nucleus sample return mission
The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three sample cores of the upper 50cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS. © The Author(s) 2008
Image restoration by simple adaptive deconvolution
A new version of an iterative scheme of deconvolution originally introduced by
Richardson (1972) and [ Lucy (1974) is presented. This algorithm is based on the
Maximum Likelihood principle and imposes additional constraints on the solution
of the inverse problem. The main idea of the newly presented method is to link
the number of iterations with the local difference between the
object profile in the input image and the noisy background. If this difference
is of the order of the noise level, only very few iterations are performed,
whereas if this difference is much greater than this level, the number of
iterations attains its maximum assigned value. Thus, the number of iterations
is used as a regularizer for the restoration. Due to this adaptive approach,
the background noise is highly suppressed and the probability of restoration
artefacts is seriously diminished. What is more, the quality of restored images
(described by the Kullback-Leibler distance between deconvolved and original
profile) for the adaptive iterative scheme increases in comparison with the
original approach, whereas the mean number of iterations per one pixel is
substantially reduced. Some examples of the deconvolution of one- and
two-dimensional profiles presenting advantages of the new algorithm are
described. Photometric fidelity of both methods is also compared and the
predominance of the adaptive approach is confirmed
Spiral structures and temperature distribution in the quiescent accretion disc of the cataclysmic binary V2051 Ophiuchi
We present the capabilities of our new code for obtaining Doppler maps
implementing the maximum likelihood approach. As test data, we used
observations of the dwarf nova V2051 Ophiuchi. The system was observed in
quiescence at least 16 d before the onset of the next outburst. Using Doppler
maps obtained for ten emission lines covering three orbital cycles, we detected
spiral structures in the accretion disc of V2051 Oph. However, these structures
could be biased as our data sampled the orbital period of the binary at only
eight different orbital phases. Our Doppler maps show evolution from a one-arm
wave structure in H to two-armed waves in the other lines. The location
of the two-arm structures agrees with simulations showing tidally driven spiral
waves in the accretion disc. During consecutive cycles, the qualitative
characteristics of the detected structures remained similar but the central
absorption increased. For the first time, using the Doppler tomography method,
we obtained temperature maps of the accretion disc. However, taking into
account all the assumptions involved when using our method to retrieve them,
the result should be treated with caution. Our maps present a relatively flat
distribution of the temperature over the disc, showing no temperature increase
at the location of the spiral arms. Using `ring masking', we have revealed an
ionized region located close to the expected location of stream--disc
interactions. We found the average temperature of the accretion disc to be 5600
K, which is below the critical limit deduced from the disc instability model.Comment: Accepted for publication in MNRA
The excited spin state of 1I/2017 U1 ‘Oumuamua
We show that `Oumuamua's excited spin could be in a high energy LAM state,
which implies that its shape could be far from the highly elongated shape found
in previous studies. CLEAN and ANOVA algorithms are used to analyze `Oumuamua's
lightcurve using 818 observations over 29.3~days. Two fundamental periodicities
are found at frequencies (2.770.11) and (6.420.18)~cycles/day,
corresponding to (8.670.34)~h and (3.740.11)~h, respectively. The
phased data show that the lightcurve does not repeat in a simple manner, but
approximately shows a double minimum at 2.77~cycles/day and a single minimum at
6.42~cycles/day. This is characteristic of an excited spin state. `Oumuamua
could be spinning in either the long (LAM) or short (SAM) axis mode. For both,
the long axis precesses around the total angular momentum vector with an
average period of (8.670.34)~h. For the three LAMs we have found, the
possible rotation periods around the long axis are 6.58, 13.15, or 54.48~h,
with 54.48~h being the most likely. `Oumuamua may also be nutating with
respective periods of half of these values. We have also found two possible SAM
states where `Oumuamua oscillates around the long axis with possible periods at
13.15 and 54.48~h, the latter as the most likely. In this case any nutation
will occur with the same periods. Determination of the spin state, the
amplitude of the nutation, the direction of the TAMV, and the average total
spin period may be possible with a direct model fit to the lightcurve. We find
that `Oumuamua is "cigar-shaped"', if close to its lowest rotational energy,
and an extremely oblate spheroid if close to its highest energy state for its
total angular momentum.Comment: 8 pages, 3 figure
Rotation of the Nucleus, Gas Kinematics and Emission Pattern of Comet 8P/Tuttle: Preliminary Results from Optical Imaging of the CN Coma
Preliminary photometric results for the 2003 eclipse of EE Cep
We report multicolour photometric observations of the 2003 eclipse of the long-period (5.6 yr) eclipsing binary EE Cep. Measurements were obtained with ten telescopes at eight observatories in four countries. In most cases, UBV(RI)C broad band filters have been used. The light curve shape shows that the obscuring body is an almost dark disk around a low-luminosity central object. However, variations of the colour indices during the eclipse indicate that the obscuring body emits a considerable amount of radiation in the near infrared. © Springer 2005