421 research outputs found
P/2010 A2 LINEAR II: dynamical dust modelling
P/2010 A2 is an object on an asteroidal orbit that was observed to have an
extended tail or debris trail in January 2010. In this work, we fit the
outburst of P/2010 A2 with a conical burst model, and verify previous
suspicions that this was a one--time collisional event rather than an sustained
cometary outburst, implying that P/2010 A2 is not a new Main Belt Comet driven
by ice sublimation. We find that the best--fit cone opening angle is about 40
to 50 degrees, in agreement with numerical and laboratory simulations of
cratering events. Mapping debris orbits to sky positions suggests that the
distinctive arc features in the debris correspond to the same debris cone
inferred from the extended dust. From the velocity of the debris, and from the
presence of a velocity maximum at around 15 cm/s, we infer that the surface of
A2 probably has a very low strength (<1 kPa), comparable to lunar regolith.Comment: 14 pages, 25 figures; accepted by Astronomy and Astrophysic
The Calibration of the HST Kuiper Belt Object Search: Setting the Record Straight
The limiting magnitude of the HST data set used by Cochran et al. (1995) to
detect small objects in the Kuiper belt is reevaluated, and the methods used
are described in detail. It is shown, by implanting artificial objects in the
original HST images, and re-reducing the images using our original algorithm,
that the limiting magnitude of our images (as defined by the 50% detectability
limit) is . This value is statistically the same as the value found in
the original analysis. We find that of the moving Kuiper belt objects
with are detected when trailing losses are included. In the same data
in which these faint objects are detected, we find that the number of false
detections brighter than is less than one per WFPC2 image. We show
that, primarily due to a zero-point calibration error, but partly due to
inadequacies in modeling the HST'S data noise characteristics and Cochran et
al.'s reduction techniques, Brown et al. 1997 underestimate the SNR of objects
in the HST dataset by over a factor of 2, and their conclusions are therefore
invalid.Comment: Accepted to ApJ Letters; 10 pages plus 3 figures, LaTe
The nucleus of 103P/Hartley 2, target of the EPOXI mission
103P/Hartley 2 was selected as the target comet for the Deep Impact extended
mission, EPOXI, in October 2007. There have been no direct optical observations
of the nucleus of this comet, as it has always been highly active when
previously observed. We aimed to recover the comet near to aphelion, to a)
confirm that it had not broken up and was in the predicted position, b) to
provide astrometry and brightness information for mission planning, and c) to
continue the characterisation of the nucleus. We observed the comet at
heliocentric distances between 5.7 and 5.5 AU, using FORS2 at the VLT, at 4
epochs between May and July 2008. We performed VRI photometry on deep stacked
images to look for activity and measure the absolute magnitude and therefore
estimate the size of the nucleus. We recovered the comet near the expected
position, with a magnitude of m_R = 23.74 \pm 0.06 at the first epoch. The
comet had no visible coma, although comparison of the profile with a stellar
one showed that there was faint activity, or possibly a contribution to the
flux from the dust trail from previous activity. This activity appears to fade
at further epochs, implying that this is a continuation of activity past
aphelion from the previous apparition rather than an early start to activity
before the next perihelion. Our data imply a nucleus radius of \le 1 km for an
assumed 4% albedo; we estimate a ~6% albedo. We measure a colour of (V-R) = 0.
26 \pm 0.09.Comment: 5 pages, 4 figures, accepted for publication in A&
Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2
The first detected interstellar object 'Oumuamua that passed within 0.25au of
the Sun on 2017 September 9 was presumably ejected from a stellar system. We
use its newly determined non-Keplerian trajectory together with the
reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past
close encounters. Such an "encounter" could reveal the home system from which
'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90%
confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity
of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower
encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249,
3.8Myr ago. Two more stars have encounter distances and velocities intermediate
to these. The encounter parameters are similar across six different
non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by
scattering from a giant planet in one of the systems is plausible, but requires
a rather unlikely configuration to achieve the high velocities found. A binary
star system is more likely to produce the observed velocities. None of the four
home candidates have published exoplanets or are known to be binaries. Given
that the 7 million stars in Gaia DR2 with 6D phase space information is just a
small fraction of all stars for which we can eventually reconstruct orbits, it
is a priori unlikely that our current search would find 'Oumuamua's home star
system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown
dwarfs every Myr, the plausibility of a home system depends also on an
appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa
Characterisation of candidate members of (136108) Haumea's family
Ragozzine & Brown [2007] presented a list of candidate members of the first
collisional family to be found among the trans-Neptunian Objects (TNOs), the
one associated with (136108) Haumea (2003 EL61). We aim to identify which of
the candidate members of the Haumea collisional family are true members, by
searching for water ice on their surfaces. We also attempt to test the theory
that the family members are made of almost pure water ice by using optical
light-curves to constrain their densities. We use optical and near-infrared
photometry to identify water ice, in particular using the (J - H_S) colour as a
sensitive measure of the absorption feature at 1.6 micron. We use the CH_4
filter of the new Hawk-I instrument at the VLT as a short H-band (H_S) for this
as it is more sensitive to the water ice feature than the usual H filter. We
report colours for 22 candidate family members, including NIR colours for 15.
We confirm that 2003 SQ317 and 2005 CB79 are family members, bringing the total
number of confirmed family members to 10. We reject 8 candidates as having no
water ice absorption based on our Hawk-I measurements, and 5 more based on
their optical colours. The combination of the large proportion of rejected
candidates and time lost to weather prevent us from putting strong constraints
on the density of the family members based on the light-curves obtained so far;
we can still say that none of the family members (except Haumea) require a
large density to explain their light-curve.Comment: 9 pages, 5 figures, accepted for publication in A&
Analysis of the rotational properties of Kuiper belt objects
We use optical data on 10 Kuiper Belt objects (KBOs) to investigate their
rotational properties. Of the 10, three (30%) exhibit light variations with
amplitude delta_m >= 0.15 mag, and 1 out of 10 (10%) has delta_m >= 0.40 mag,
which is in good agreement with previous surveys. These data, in combination
with the existing database, are used to discuss the rotational periods, shapes,
and densities of Kuiper Belt objects. We find that, in the sampled size range,
Kuiper Belt objects have a higher fraction of low amplitude lightcurves and
rotate slower than main belt asteroids. The data also show that the rotational
properties and the shapes of KBOs depend on size. If we split the database of
KBO rotational properties into two size ranges with diameter larger and smaller
than 400 km, we find that: (1) the mean lightcurve amplitudes of the two groups
are different with 98.5% confidence, (2) the corresponding power-law shape
distributions seem to be different, although the existing data are too sparse
to render this difference significant, and (3) the two groups occupy different
regions on a spin period vs. lightcurve amplitude diagram. These differences
are interpreted in the context of KBO collisional evolution.Comment: 15 pages, 14 figures, LaTeX. Astronomical Journal in pres
Characterisation of candidate members of (136108) Haumea's family: II. Follow-up observations
From a dynamical analysis of the orbital elements of transneptunian objects
(TNOs), Ragozzine & Brown reported a list of candidate members of the first
collisional family found among this population, associated with (136108) Haumea
(a.k.a. 2003 EL61). We aim to distinguish the true members of the Haumea
collisional family from interlopers. We search for water ice on their surfaces,
which is a common characteristic of the known family members. The properties of
the confirmed family are used to constrain the formation mechanism of Haumea,
its satellites, and its family. Optical and near-infrared photometry is used to
identify water ice. We use in particular the CH4 filter of the Hawk-I
instrument at the European Southern Observatory Very Large Telescope as a short
H-band (Hs), the (J-Hs) colour being a sensitive measure of the water ice
absorption band at 1.6 {\mu}m. Continuing our previous study headed by
Snodgrass, we report colours for 8 candidate family members, including
near-infrared colours for 5. We confirm one object as a genuine member of the
collisional family (2003 UZ117), and reject 5 others. The lack of infrared data
for the two remaining objects prevent any conclusion from being drawn. The
total number of rejected members is therefore 17. The 11 confirmed members
represent only a third of the 36 candidates. The origin of Haumea's family is
likely to be related to an impact event. However, a scenario explaining all the
peculiarities of Haumea itself and its family remains elusive.Comment: 8 pages, 4 figures, accepted for publication in A&
Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact
On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission
crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material
ejected by the impact expanded into the normal coma, produced by ordinary
cometary activity.
The characteristics of the non-impact coma and cloud produced by the impact
were studied by observations in the visible wavelengths and in the near-IR. The
scattering characteristics of the "normal" coma of solid particles were studied
by comparing images in various spectral regions, from the UV to the near-IR.
For the non-impact coma, a proxy of the dust production has been measured in
various spectral regions. The presence of sublimating grains has been detected.
Their lifetime was found to be about 11 hours. Regarding the cloud produced by
the impact, the total geometric cross section multiplied by the albedo was
measured as a function of the color and time. The projected velocity appeared
to obey a Gaussian distribution with the average velocity of the order of 115
m/s. By comparing the observations taken about 3 hours after the impact, we
have found a strong decrease in the cross section in J filter, while that in Ks
remained almost constant. This is interpreted as the result of sublimation of
grains dominated by particles of sizes of the order of some microns.Comment: Accepted by A&
Lightcurves of 20--100 kilometer Kuiper Belt Objects using the Hubble Space Telescope
We report high precision photometry of three small and one larger Kuiper Belt
Objects (KBOs) obtained with the Advanced Camera for Surveys onboard the Hubble
Space Telescope (ACS/HST). The three small bodies are the smallest KBOs for
which lightcurve measurements are available. 2003 BF91 has a diameter of 20
kilometers (assuming 10% albedo) and a 1.09 magnitude, 9.1-hour lightcurve that
is feasibly explained by the rotation of an elongated, coherent body that is
supported by material strength and best imagined as an icy outer Solar System
analog to asteroid (243) Ida. Two other small KBOs, 2003 BG91 and 2003 BH91
(diameters 31 and 18 km, with albedo 10%), exhibit an unremarkable lightcurve
and no detectable photometric variation, respectively. For the larger KBO 2000
FV53 (116 km diameter, assuming 10% albedo) we strongly detect a non-sinusoidal
periodic (7.5 hours) brightness variation with a very small amplitude (0.07
mag). This KBO may be nearly spherical, a result that might not be unusual in
the Kuiper Belt but would be remarkable among outer Solar System satellites of
similar size. We carry out a study of possible physical states and bulk
densities under the assumptions of both fluid equilibrium and finite, non-zero
internal friction. The densities for the these KBOs are likely to be in the
range 1--2 g/cm3, and a plausible solution for 2000 FV53 is a rubble pile of
this density that is held slightly out of the minimum-energy shape by internal
friction among constituent blocks that are relatively small. Our interpretation
of 2000 FV53 as a pulverized but essentially primordial object and 2003 BF91 as
a collisional fragment is consistent with models of collisional timescales in
the outer Solar System. We compile all published KBO lightcurve data and
compare our results to the larger population. [abridged]Comment: AJ, in press. Tables 1-4 will be electronic only in published version
but appear here in full. Figures 1,3,5 in colo
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