325 research outputs found
Optical investigation of Comet Halley
The physical properties of Comet P/Halley are being monitored from the ground using state of the art optical detectors. The long time base (1982-present) of the observations provides a unique record of the development of activity in a single comet. In addition, physical properties of other comets are measured to provide a reference against which Comet Halley may be compared. Results for the past year include: (1) publication of the first results on the surface brightness profiles of dust comets; (2) charge coupled device measurements of Comet Bowell show that the activity of comets can persist at least to heliocentric distances R = 13.6 AU; (3) a study of the back-scattering phase angle dependences of 5 comets (including Halley) shows evidence for small linear phase coefficients in each case; (4) temporal monitoring of P/Halley continues
Extinction in the Coma of Comet 17P/Holmes
On 2007 October 29 the outbursting comet 17P/Holmes passed within 0.79 arcsec
of a background star. We recorded the event using optical, narrowband
photometry and detect a 3% to 4% dip in stellar brightness bracketing the time
of closest approach to the comet nucleus. The detected dimming implies an
optical depth tau~0.04 at 1.5 arcsec from the nucleus and an optical depth
towards the nucleus center tau_n<13.3. At the time of our observations, the
coma was optically thick only within rho<~0.01 arcsec from the nucleus. By
combining the measured extinction and the scattered light from the coma we
estimate a dust red geometric albedo p_d=0.006+/-0.002 at 16 deg phase angle.
Our measurements place the most stringent constraints on the extinction optical
depth of any cometary coma.Comment: 5 pages, 3 figures, 2 table. Accepted for publication in ApJ
Dynamics of Large Fragments in the Tail of Active Asteroid P/2010 A2
We examine the motions of large fragments at the head of the dust tail of
active asteroid P/2010 A2. In previous work we showed that these fragments were
ejected from the primary nucleus in early 2009, either following a
hypervelocity impact or by rotationally induced break-up. Here, we follow their
positions through a series of Hubble Space Telescope images taken during the
first half of 2010. The orbital evolution of each fragment allows us to
constrain its velocity relative to the main nucleus after leaving its sphere of
gravitational influence. We find that the fragments constituting a prominent
X-shaped tail feature were emitted in a direction opposite to the motion of the
asteroid and towards the south of its orbital plane. Derived emission
velocities of these primary fragments range between 0.02 and 0.3 m/s,
comparable to the ~0.08 m/s gravitational escape speed from the nucleus. Their
sizes are on the order of decimeters or larger. We obtain the best fits to our
data with ejection velocity vectors lying in a plane that includes the nucleus.
This may suggest that the cause of the disruption of P/2010 A2 is rotational
break-up.Comment: 30 pages, 8 figures, accepted for publication by The Astrophysical
Journa
Large Particles in Active Asteroid P/2010 A2
Previously unknown asteroid P/2010 A2 rose to prominence in 2010 by forming a
transient, comet-like tail consisting of ejected dust. The observed dust
production was interpreted as either the result of a hypervelocity impact with
a smaller body or of a rotational disruption. We have re-observed this object,
finding that large particles remain a full orbital period after the initial
outburst. In the intervening years, particles smaller than ~3 mm in radius have
been dispersed by radiation pressure, leaving only larger particles in the
trail. Since the total mass is dominated by the largest particles, the
radiation pressure filtering allows us to obtain a more reliable estimate of
the debris mass than was previously possible. We find that the mass contained
in the debris is ~5x10^8 kg (assumed density 3000 kg m^-3), the ratio of the
total debris mass to the nucleus mass is ~0.1 and that events like P/2010 A2
contribute <3% to the Zodiacal dust production rate. Physical properties of the
nucleus and debris are also determined.Comment: 16 pages, 4 figures; ApJLett, in Pres
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