12,856 research outputs found
Moving Objects in the Hubble Ultra Deep Field
We identify proper motion objects in the Hubble Ultra Deep Field (UDF) using
the optical data from the original UDF program in 2004 and the near-infrared
data from the 128-orbit UDF 2012 campaign. There are 12 sources brighter than
I=27 mag that display >3sigma significant proper motions. We do not find any
proper motion objects fainter than this magnitude limit. Combining optical and
near-infrared photometry, we model the spectral energy distribution of each
point-source using stellar templates and state-of-the-art white dwarf models.
For I<27 mag, we identify 23 stars with K0-M6 spectral types and two faint blue
objects that are clearly old, thick disk white dwarfs. We measure a thick disk
white dwarf space density of 0.1-1.7 E-3 per cubic parsec from these two
objects. There are no halo white dwarfs in the UDF down to I=27 mag. Combining
the Hubble Deep Field North, South, and the UDF data, we do not see any
evidence for dark matter in the form of faint halo white dwarfs, and the
observed population of white dwarfs can be explained with the standard Galactic
models.Comment: ApJ, in pres
HST and Spitzer Observations of the HD 207129 Debris Ring
A debris ring around the star HD 207129 (G0V; d = 16.0 pc) has been imaged in
scattered visible light with the ACS coronagraph on the Hubble Space Telescope
and in thermal emission using MIPS on the Spitzer Space Telescope at 70 microns
(resolved) and 160 microns (unresolved). Spitzer IRS (7-35 microns) and MIPS
(55-90 microns) spectrographs measured disk emission at >28 microns. In the HST
image the disk appears as a ~30 AU wide ring with a mean radius of ~163 AU and
is inclined by 60 degrees from pole-on. At 70 microns it appears partially
resolved and is elongated in the same direction and with nearly the same size
as seen with HST in scattered light. At 0.6 microns the ring shows no
significant brightness asymmetry, implying little or no forward scattering by
its constituent dust. With a mean surface brightness of V=23.7 mag per square
arcsec, it is the faintest disk imaged to date in scattered light.Comment: 28 pages, 8 figure
Col-OSSOS: The Colours of the Outer Solar System Origins Survey
The Colours of the Outer Solar System Origins Survey (Col-OSSOS) is acquiring
near-simultaneous , , and photometry of unprecedented precision with
the Gemini North Telescope, targeting nearly a hundred trans-Neptunian objects
(TNOs) brighter than mag discovered in the Outer Solar System
Origins Survey. Combining the optical and near-infrared photometry with the
well-characterized detection efficiency of the Col-OSSOS target sample will
provide the first flux-limited compositional dynamical map of the outer Solar
System. In this paper, we describe our observing strategy and detail the data
reduction processes we employ, including techniques to mitigate the impact of
rotational variability. We present optical and near-infrared colors for 35
TNOs. We find two taxonomic groups for the dynamically excited TNOs, the
neutral and red classes, which divide at . Based on simple
albedo and orbital distribution assumptions, we find that the neutral class
outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1.
Including in our analysis constraints from the cold classical objects, which
are known to exhibit unique albedos and colors, we find that within our
measurement uncertainty, our observations are consistent with the primordial
Solar System protoplanetesimal disk being neutral-class-dominated, with two
major compositional divisions in color space.Comment: Accepted to ApJS; on-line supplemental files will be available with
the AJS published version of the pape
A Search for Companions to Brown Dwarfs in the Taurus and Chamaeleon Star Forming Regions
We present the results of a search for companions to young brown dwarfs in
the Taurus and Chamaeleon I star forming regions (1/2-3 Myr). We have used
WFPC2 on board HST to obtain F791W and F850LP images of 47 members of these
regions that have spectral types of M6-L0 (0.01-0.1 Msun). An additional
late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with
adaptive optics at Keck Observatory. We have applied PSF subtraction to the
primaries and have searched the resulting images for objects that have colors
and magnitudes that are indicative of young low-mass objects. Through this
process, we have identified promising candidate companions to 2MASS
J04414489+2301513 (rho=0.105"/15 AU), 2MASS J04221332+1934392 (rho=0.05"/7 AU),
and ISO 217 (rho=0.03"/5 AU). We reported the discovery of the first candidate
in a previous study, showing that it has a similar proper motion as the primary
through a comparison of astrometry measured with WFPC2 and Gemini adaptive
optics. We have collected an additional epoch of data with Gemini that further
supports that result. By combining our survey with previous high-resolution
imaging in Taurus, Chamaeleon, and Upper Sco (10 Myr), we measure binary
fractions of 14/93 = 0.15+0.05/-0.03 for M4-M6 (0.1-0.3 Msun) and 4/108 =
0.04+0.03/-0.01 for >M6 (10 AU. Given the youth
and low density of these three regions, the lower binary fraction at later
types is probably primordial rather than due to dynamical interactions among
association members. The widest low-mass binaries (>100 AU) also appear to be
more common in Taurus and Chamaeleon than in the field, which suggests that the
widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or
that field brown dwarfs have been born predominantly in denser clusters where
wide systems are disrupted or inhibited from forming.Comment: Astrophysical Journal, in pres
Astrometry with the Wide-Field InfraRed Space Telescope
The Wide-Field InfraRed Space Telescope (WFIRST) will be capable of
delivering precise astrometry for faint sources over the enormous field of view
of its main camera, the Wide-Field Imager (WFI). This unprecedented combination
will be transformative for the many scientific questions that require precise
positions, distances, and velocities of stars. We describe the expectations for
the astrometric precision of the WFIRST WFI in different scenarios, illustrate
how a broad range of science cases will see significant advances with such
data, and identify aspects of WFIRST's design where small adjustments could
greatly improve its power as an astrometric instrument.Comment: version accepted to JATI
Down-Sampling coupled to Elastic Kernel Machines for Efficient Recognition of Isolated Gestures
In the field of gestural action recognition, many studies have focused on
dimensionality reduction along the spatial axis, to reduce both the variability
of gestural sequences expressed in the reduced space, and the computational
complexity of their processing. It is noticeable that very few of these methods
have explicitly addressed the dimensionality reduction along the time axis.
This is however a major issue with regard to the use of elastic distances
characterized by a quadratic complexity. To partially fill this apparent gap,
we present in this paper an approach based on temporal down-sampling associated
to elastic kernel machine learning. We experimentally show, on two data sets
that are widely referenced in the domain of human gesture recognition, and very
different in terms of quality of motion capture, that it is possible to
significantly reduce the number of skeleton frames while maintaining a good
recognition rate. The method proves to give satisfactory results at a level
currently reached by state-of-the-art methods on these data sets. The
computational complexity reduction makes this approach eligible for real-time
applications.Comment: ICPR 2014, International Conference on Pattern Recognition, Stockholm
: Sweden (2014
Deep VLT infrared observations of X-ray Dim Isolated Neutron Stars
X-ray observations have unveiled the existence of a family of radio-quiet
Isolated Neutron Stars whose X-ray emission is purely thermal, hence dubbed
X-ray Dim Isolated Neutron Stars (XDINSs). While optical observations have
allowed to relate the thermal emission to the neutron star cooling and to build
the neutron star surface thermal map, IR observations are critical to pinpoint
a spectral turnover produced by a so far unseen magnetospheric component, or by
the presence of a fallback disk. The detection of such a turnover can provide
further evidence of a link between this class of isolated neutron stars and the
magnetars, which show a distinctive spectral flattening in the IR.
Here we present the deepest IR observations ever of five XDINSs, which we use
to constrain a spectral turnover in the IR and the presence of a fallback disk.
The data are obtained using the ISAAC instrument at the VLT.
For none of our targets it was possible to identify the IR counterpart down
to limiting magnitudes H = 21.5 - 22.9. Although these limits are the deepest
ever obtained for neutron stars of this class, they are not deep enough to rule
out the existence and the nature of a possible spectral flattening in the IR.
We also derive, by using disk models, the upper limits on the mass inflow rate
in a fallback disk. We find the existence of a putative fallback disk
consistent (although not confirmed) with our observations.Comment: 6 pages, 2 figures, accepted by A&A on 26-06-200
Asteroid Distributions in the Ecliptic
We present analysis of the asteroid surface density distribution of main belt
asteroids (mean perihelion AU) in five ecliptic latitude
fields, -17 \gtsimeq \beta(\degr) \ltsimeq +15, derived from deep
\textit{Large Binocular Telescope} (LBT) band (85% completeness limit mag) and \textit{Spitzer Space Telescope} IRAC 8.0 \micron (80%
completeness limit Jy) fields enabling us to probe the 0.5--1.0
km diameter asteroid population. We discovered 58 new asteroids in the optical
survey as well as 41 new bodies in the \textit{Spitzer} fields. The derived
power law slopes of the number of asteroids per square degree are similar
within each \degr{} ecliptic latitude bin with a mean value of . For the 23 known asteroids detected in all four IRAC channels mean
albedos range from to . No low albedo asteroids
( \ltsimeq 0.1) were detected in the \textit{Spitzer} FLS fields,
whereas in the SWIRE fields they are frequent. The SWIRE data clearly samples
asteroids in the middle and outer belts providing the first estimates of these
km-sized asteroids' albedos. Our observed asteroid number densities at optical
wavelengths are generally consistent with those derived from the Standard
Asteroid Model within the ecliptic plane. However, we find an over density at
\beta \gtsimeq 5\degr{} in our optical fields, while the infrared number
densities are under dense by factors of 2 to 3 at all ecliptic latitudes.Comment: 35 pages including 5 figures, accepted to The Astronomical Journa
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