6,005 research outputs found
The volumetric rate of calcium-rich transients in the local universe
We present a measurement of the volumetric rate of `calcium-rich' optical
transients in the local universe, using a sample of three events from the
Palomar Transient Factory (PTF). This measurement builds on a detailed study of
the PTF transient detection efficiencies, and uses a Monte Carlo simulation of
the PTF survey. We measure the volumetric rate of calcium-rich transients to be
higher than previous estimates: events
yr Mpc. This is equivalent to 33-94% of the local volumetric type
Ia supernova rate. This calcium-rich transient rate is sufficient to reproduce
the observed calcium abundances in galaxy clusters, assuming an asymptotic
calcium yield per calcium-rich event of ~0.05. We also
study the PTF detection efficiency of these transients as a function of
position within their candidate host galaxies. We confirm as a real physical
effect previous results that suggest calcium-rich transients prefer large
physical offsets from their host galaxies.Comment: Accepted for publication in ApJ. 9 pages, 5 figure
Asteroid family identification using the Hierarchical Clustering Method and WISE/NEOWISE physical properties
Using albedos from WISE/NEOWISE to separate distinct albedo groups within the
Main Belt asteroids, we apply the Hierarchical Clustering Method to these
subpopulations and identify dynamically associated clusters of asteroids. While
this survey is limited to the ~35% of known Main Belt asteroids that were
detected by NEOWISE, we present the families linked from these objects as
higher confidence associations than can be obtained from dynamical linking
alone. We find that over one-third of the observed population of the Main Belt
is represented in the high-confidence cores of dynamical families. The albedo
distribution of family members differs significantly from the albedo
distribution of background objects in the same region of the Main Belt, however
interpretation of this effect is complicated by the incomplete identification
of lower-confidence family members. In total we link 38,298 asteroids into 76
distinct families. This work represents a critical step necessary to debias the
albedo and size distributions of asteroids in the Main Belt and understand the
formation and history of small bodies in our Solar system.Comment: Accepted to ApJ. Full version of Table 3 to be published
electronically in Ap
Synthetic Spectra for Type Ia Supernovae at Early Epochs
We present the current status of our construction of synthetic spectra for
type Ia supernovae. These properly take into account the effects of NLTE and an
adequate representation of line blocking and blanketing. The models are based
on a sophisticated atomic database. We show that the synthetic spectrum
reproduces the observed spectrum of 'normal' SN-Ia near maximum light from the
UV to the near-IR. However, further improvements are necessary before truly
quantitative analyses of observed SN-Ia spectra can be performed. In
particular, the inner boundary condition has to be fundamentally modified. This
is due to the dominance of electron scattering over true absorption processes
coupled with the flat density structure in these objectsComment: To appear in "Proceedings of the IAU Colloquium 192 - Supernovae (10
Years of SN1993J)", eds. J.M. Marcaide and K.W. Weile
Main Belt Asteroids with WISE/NEOWISE: Near-Infrared Albedos
We present revised near-infrared albedo fits of 2835 Main Belt asteroids
observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010.
These fits are derived from reflected-light near-infrared images taken
simultaneously with thermal emission measurements, allowing for more accurate
measurements of the near-infrared albedos than is possible for visible albedo
measurements. As our sample requires reflected light measurements, it
undersamples small, low albedo asteroids, as well as those with blue spectral
slopes across the wavelengths investigated. We find that the Main Belt
separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 um.
Conversely, the 4.6 um albedo distribution spans the full range of possible
values with no clear grouping. Asteroid families show a narrow distribution of
3.4 um albedos within each family that map to one of the three observed
groupings, with the (221) Eos family being the sole family associated with the
16% reflectance 3.4 um albedo group. We show that near-infrared albedos derived
from simultaneous thermal emission and reflected light measurements are an
important indicator of asteroid taxonomy and can identify interesting targets
for spectroscopic followup.Comment: Accepted for publication in ApJ; full version of Table1 to be
published electronically in the journa
NEOWISE: Observations of the Irregular Satellites of Jupiter and Saturn
We present thermal model fits for 11 Jovian and 3 Saturnian irregular
satellites based on measurements from the WISE/NEOWISE dataset. Our fits
confirm spacecraft-measured diameters for the objects with in situ observations
(Himalia and Phoebe) and provide diameters and albedo for 12 previously
unmeasured objects, 10 Jovian and 2 Saturnian irregular satellites. The
best-fit thermal model beaming parameters are comparable to what is observed
for other small bodies in the outer Solar System, while the visible, W1, and W2
albedos trace the taxonomic classifications previously established in the
literature. Reflectance properties for the irregular satellites measured are
similar to the Jovian Trojan and Hilda Populations, implying common origins.Comment: 17 pages, 3 figures, accepted for publication in Astrophysical
Journa
NEOWISE Reactivation Mission Year Three: Asteroid Diameters and Albedos
The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE)
reactivation mission has completed its third year of surveying the sky in the
thermal infrared for near-Earth asteroids and comets. NEOWISE collects
simultaneous observations at 3.4 um and 4.6 um of solar system objects passing
through its field of regard. These data allow for the determination of total
thermal emission from bodies in the inner solar system, and thus the sizes of
these objects. In this paper we present thermal model fits of asteroid
diameters for 170 NEOs and 6110 MBAs detected during the third year of the
survey, as well as the associated optical geometric albedos. We compare our
results with previous thermal model results from NEOWISE for overlapping sample
sets, as well as diameters determined through other independent methods, and
find that our diameter measurements for NEOs agree to within 26% (1-sigma) of
previously measured values. Diameters for the MBAs are within 17% (1-sigma).
This brings the total number of unique near-Earth objects characterized by the
NEOWISE survey to 541, surpassing the number observed during the fully
cryogenic mission in 2010.Comment: Accepted for publication in A
A spectroscopically confirmed z=1.327 galaxy-scale deflector magnifying a z~8 Lyman-Break galaxy in the Brightest of Reionizing Galaxies survey
We present a detailed analysis of an individual case of gravitational lensing
of a Lyman-Break galaxy (LBG) in a blank field, identified in Hubble
Space Telescope imaging obtained as part of the Brightest of Reionizing
Galaxies survey. To investigate the close proximity of the bright
() -dropout to a small group of foreground galaxies, we
obtained deep spectroscopy of the dropout and two foreground galaxies using
VLT/X-Shooter. We detect H-, H-, [OIII] and [OII] emission in
the brightest two foreground galaxies (unresolved at the natural seeing of
arcsec), placing the pair at . We can rule out emission lines
contributing all of the observed broadband flux in band at
, allowing us to exclude the candidate as a low redshift
interloper with broadband photometry dominated by strong emission lines. The
foreground galaxy pair lies at the peak of the luminosity, redshift and
separation distributions for deflectors of strongly lensed objects,
and we make a marginal detection of a demagnified secondary image in the
deepest () filter. We show that the configuration can be accurately
modelled by a singular isothermal ellipsoidal deflector and a S\'{e}rsic source
magnified by a factor of . The reconstructed source in the
best-fitting model is consistent with luminosities and morphologies of
LBGs in the literature. The lens model yields a group mass of
and a stellar mass-to-light ratio for the
brightest deflector galaxy of within its effective radius. The foreground galaxies'
redshifts would make this one of the few strong lensing deflectors discovered
at .Comment: Accepted for publication in MNRAS. 16 pages, 11 figures, 3 table
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