320 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
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
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
Time-Resolved Photometry of Kuiper Belt Objects: Rotations, Shapes and Phase Functions
We present a systematic investigation of the rotational lightcurves of
trans-Neptunian objects based on extensive optical data from Mauna Kea. Four of
13 objects (corresponding to 31%) in our sample ((33128) 1998 BU48, 2000 GN171,
(20000) Varuna and 1999 KR16) were found to exhibit lightcurves with
peak-to-peak range > 0.15 magnitude. In a larger sample obtained by combining
our data with reliably determined lightcurves from the literature, 7 of 22
objects (32%) display significant (> 0.15 magnitude range) lightcurves. About
23% of the sampled objects have lightcurve ranges > 0.4 magnitudes. Curiously,
the objects are very large (> 250 km diameter, assuming an albedo of 0.04) and,
in the absence of rotation, should be near spherical due to self compression.
We propose that the large amplitude, short period objects are rotationally
distorted, low density rubble piles. Statistically, the trans-Neptunian objects
are less spherical than their main-belt asteroid counterparts, indicating a
higher specific angular momentum perhaps resulting from the formation epoch. In
addition to the rotational lightcurves, we measured phase darkening for 7
Kuiper Belt objects in the 0 to 2 degree phase angle range. Unlike Pluto, the
measured values show steep slopes and moderate opposition surge indicating
backscatter from low albedo porous surface materials.Comment: 22 pages, 33 figures, 12 tables, To appear in AJ sept. 200
Galaxies in Southern Bright Star Fields I. Near-infrared imaging
As a prerequisite for cosmological studies using adaptive optics techniques,
we have begun to identify and characterize faint sources in the vicinity of
bright stars at high Galactic latitudes. The initial phase of this work has
been a program of K_s imaging conducted with SOFI at the ESO NTT. From
observations of 42 southern fields evenly divided between the spring and autumn
skies, we have identified 391 additional stars and 1589 galaxies lying at
separations 60" from candidate guide stars in the magnitude range 9.0 R 12.4.
When analyzed as a "discrete deep field" with 131 arcmin^2 area, our dataset
gives galaxy number counts that agree with those derived previously over the
range 16 K_s 20.5. This consistency indicates that in the aggregate, our fields
should be suitable for future statistical studies. We provide our source
catalogue as a resource for users of large telescopes in the southern
hemisphere.Comment: 10 pages, 7 figures, accepted by A&A; Table 3 is available at
http://www.rzg.mpg.de/~ajb/data.html pending upload to CD
Testing the comet nature of main belt comets. The spectra of 133P/Elst-Pizarro and 176P/LINEAR
We present the visible spectrum of MBCs 133P/Elst-Pizarro and 176P/LINEAR, as
well as three Themis family asteroids: (62) Erato, (379), Huenna and (383)
Janina, obtained in 2007 using three telescopes at "El Roque de los Muchachos"'
Observatory, in La Palma, Spain, and the 8m Kueyen (UT2) VLT telescope at Cerro
Paranal, Chile.
The spectra of 133P and 176P resemble best those of B-type asteroid and are
very similar to those of Themis family members and are significantly different
from the spectrum of comet 162P/Siding-Spring and most of the observed cometary
nuclei. CN gas emission is not detected in the spectrum of 133P. We determine
an upper limit for the CN production rate Q(CN) = mol/s,
three orders of magnitude lower than the Q(CN) of Jupiter family comets
observed at similar heliocentric distances.
The spectra of 133P/Elst-Pizarro and 176P/LINEAR confirm that they are likely
members of the Themis family of asteroids, fragments that probably retained
volatiles, and unlikely have a cometary origin in the trans-neptunian belt or
the Oort cloud.Comment: Paper sumbmited to A&A. 7 pages and 6 figure
P/2010A2 LINEAR - I: An impact in the Asteroid Main Belt
Comet P/2010A2 LINEAR is a good candidate for membership with the Main Belt
Comet family. It was observed with several telescopes (ESO NTT, La Silla;
Gemini North, Mauna Kea; UH 2.2m, Mauna Kea) from 14 Jan. until 19 Feb. 2010 in
order to characterize and monitor it and its very unusual dust tail, which
appears almost fully detached from the nucleus; the head of the tail includes
two narrow arcs forming a cross. The immediate surroundings of the nucleus were
found dust-free, which allowed an estimate of the nucleus radius of 80-90m. A
model of the thermal evolution indicates that such a small nucleus could not
maintain any ice content for more than a few million years on its current
orbit, ruling out ice sublimation dust ejection mechanism. Rotational spin-up
and electrostatic dust levitations were also rejected, leaving an impact with a
smaller body as the favoured hypothesis, and ruling out the cometary nature of
the object.
The impact is further supported by the analysis of the tail structure.
Finston-Probstein dynamical dust modelling indicates the tail was produced by a
single burst of dust emission. More advanced models, independently indicate
that this burst populated a hollow cone with a half-opening angle alpha~40degr
and with an ejection velocity v_max ~ 0.2m/s, where the small dust grains fill
the observed tail, while the arcs are foreshortened sections of the burst cone.
The dust grains in the tail are measured to have radii between a=1-20mm, with a
differential size distribution proportional to a^(-3.44 +/- 0.08). The dust
contained in the tail is estimated to at least 8x10^8kg, which would form a
sphere of 40m radius. Analysing these results in the framework of crater
physics, we conclude that a gravity-controlled crater would have grown up to
~100m radius, i.e. comparable to the size of the body. The non-disruption of
the body suggest this was an oblique impact.Comment: 15 pages, 11 figures, in pres
- …