332 research outputs found
Persistent Transport Barrier on the West Florida Shelf
Analysis of drifter trajectories in the Gulf of Mexico has revealed the
existence of a region on the southern portion of the West Florida Shelf (WFS)
that is not visited by drifters that are released outside of the region. This
so-called ``forbidden zone'' (FZ) suggests the existence of a persistent
cross-shelf transport barrier on the southern portion of the WFS. In this
letter a year-long record of surface currents produced by a Hybrid-Coordinate
Ocean Model simulation of the WFS is used to identify Lagrangian coherent
structures (LCSs), which reveal the presence of a robust and persistent
cross-shelf transport barrier in approximately the same location as the
boundary of the FZ. The location of the cross-shelf transport barrier undergoes
a seasonal oscillation, being closer to the coast in the summer than in the
winter. A month-long record of surface currents inferred from high-frequency
(HF) radar measurements in a roughly 60 km 80 km region on the WFS off
Tampa Bay is also used to identify LCSs, which reveal the presence of robust
transient transport barriers. While the HF-radar-derived transport barriers
cannot be unambiguously linked to the boundary of the FZ, this analysis does
demonstrate the feasibility of monitoring transport barriers on the WFS using a
HF-radar-based measurement system. The implications of a persistent cross-shelf
transport barrier on the WFS for the development of harmful algal blooms on the
shoreward side of the barrier are considered.Comment: Submitted to Geophysical Research Letter
Displaying the Heterogeneity of the SN 2002cx-like Subclass of Type Ia Supernovae with Observations of the Pan-STARRS-1 Discovered SN2009ku
SN2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SNIa), and a
member of the distinct SN2002cx-like class of SNeIa. Its light curves are
similar to the prototypical SN2002cx, but are slightly broader and have a later
rise to maximum in g. SN2009ku is brighter (~0.6 mag) than other SN2002cx-like
objects, peaking at M_V = -18.4 mag - which is still significantly fainter than
typical SNeIa. SN2009ku, which had an ejecta velocity of ~2000 kms^-1 at 18
days after maximum brightness is spectroscopically most similar to SN2008ha,
which also had extremely low-velocity ejecta. However, SN2008ha had an
exceedingly low luminosity, peaking at M_V = -14.2 mag, ~4 mag fainter than
SN2009ku. The contrast of high luminosity and low ejecta velocity for SN2009ku
is contrary to an emerging trend seen for the SN2002cx class. SN2009ku is a
counter-example of a previously held belief that the class was more homogeneous
than typical SNeIa, indicating that the class has a diverse progenitor
population and/or complicated explosion physics. As the first example of a
member of this class of objects from the new generation of transient surveys,
SN2009ku is an indication of the potential for these surveys to find rare and
interesting objects.Comment: 7 pages, 3 figure
Zooming In on the Progenitors of Superluminous Supernovae With the HST
We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the
host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including
11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the
superb angular resolution of HST, we characterize the galaxies' morphological
properties, sizes and star formation rate (SFR) densities. We determine the
supernova (SN) locations within the host galaxies through precise astrometric
matching, and measure physical and host-normalized offsets, as well as the SN
positions within the cumulative distribution of UV light pixel brightness. We
find that the host galaxies of H-poor SLSNe are irregular, compact dwarf
galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR
densities are high ( ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe
form in overdense environments. Their locations trace the UV light of their
host galaxies, with a distribution intermediate between that of long-duration
gamma-ray bursts (LGRBs) (which are strongly clustered on the brightest regions
of their hosts) and a uniform distribution (characteristic of normal
core-collapse SNe), though cannot be statistically distinguished from either
with the current sample size. Taken together, this strengthens the picture that
SLSN progenitors require different conditions than those of ordinary
core-collapse SNe to form, and that they explode in broadly similar galaxies as
do LGRBs. If the tendency for SLSNe to be less clustered on the brightest
regions than are LGRBs is confirmed by a larger sample, this would indicate a
different, potentially lower-mass progenitor for SLSNe than LRGBs.Comment: ApJ in press; matches published version. Minor changes following
referee's comments; conclusions unchange
The Foundation Supernova Survey: Measuring Cosmological Parameters with Supernovae from a Single Telescope
Measurements of the dark energy equation-of-state parameter, , have been
limited by uncertainty in the selection effects and photometric calibration of
Type Ia supernovae (SNe Ia). The Foundation Supernova Survey is
designed to lower these uncertainties by creating a new sample of SNe
Ia observed on the Pan-STARRS system. Here, we combine the Foundation sample
with SNe from the Pan-STARRS Medium Deep Survey and measure cosmological
parameters with 1,338 SNe from a single telescope and a single, well-calibrated
photometric system. For the first time, both the low- and high- data are
predominantly discovered by surveys that do not target pre-selected galaxies,
reducing selection bias uncertainties. The data include 875 SNe without
spectroscopic classifications and we show that we can robustly marginalize over
CC SN contamination. We measure Foundation Hubble residuals to be fainter than
the pre-existing low- Hubble residuals by mag (stat+sys).
By combining the SN Ia data with cosmic microwave background constraints, we
find , consistent with CDM. With 463
spectroscopically classified SNe Ia alone, we measure . Using
the more homogeneous and better-characterized Foundation sample gives a 55%
reduction in the systematic uncertainty attributed to SN Ia sample selection
biases. Although use of just a single photometric system at low and high
redshift increases the impact of photometric calibration uncertainties in this
analysis, previous low- samples may have correlated calibration
uncertainties that were neglected in past studies. The full Foundation sample
will observe up to 800 SNe to anchor the LSST and WFIRST Hubble diagrams.Comment: 30 pages, 17 figures, accepted by Ap
Hydrogen-Poor Superluminous Supernovae and Long-Duration Gamma-Ray Bursts Have Similar Host Galaxies
We present optical spectroscopy and optical/near-IR photometry of 31 host
galaxies of hydrogen-poor superluminous supernovae (SLSNe), including 15 events
from the Pan-STARRS1 Medium Deep Survey. Our sample spans the redshift range
0.1 < z < 1.6 and is the first comprehensive host galaxy study of this specific
subclass of cosmic explosions. Combining the multi-band photometry and
emission-line measurements, we determine the luminosities, stellar masses, star
formation rates and metallicities. We find that as a whole, the hosts of SLSNe
are a low-luminosity ( ~ -17.3 mag), low stellar mass ( ~ 2 x 10^8
M_sun) population, with a high median specific star formation rate ( ~ 2
Gyr^-1). The median metallicity of our spectroscopic sample is low, 12 +
log(O/H}) ~ 8.35 ~ 0.45 Z_sun, although at least one host galaxy has solar
metallicity. The host galaxies of H-poor SLSNe are statistically distinct from
the hosts of GOODS core-collapse SNe (which cover a similar redshift range),
but resemble the host galaxies of long-duration gamma-ray bursts (LGRBs) in
terms of stellar mass, SFR, sSFR and metallicity. This result indicates that
the environmental causes leading to massive stars forming either SLSNe or LGRBs
are similar, and in particular that SLSNe are more effectively formed in low
metallicity environments. We speculate that the key ingredient is large core
angular momentum, leading to a rapidly-spinning magnetar in SLSNe and an
accreting black hole in LGRBs.Comment: ApJ in press; updated to match accepted version. Some additional data
added, discussion of selection effects expanded; conclusions unchanged. 22
pages in emulateapj forma
The Time-Domain Spectroscopic Survey: Understanding the Optically Variable Sky with SEQUELS in SDSS-III
The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject
primarily aimed at obtaining identification spectra of ~220,000
optically-variable objects systematically selected from SDSS/Pan-STARRS1
multi-epoch imaging. We present a preview of the science enabled by TDSS, based
on TDSS spectra taken over ~320 deg^2 of sky as part of the SEQUELS survey in
SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the
15,746 TDSS-selected single-epoch spectra of photometrically variable objects
in SEQUELS, we determine the demographics of our variability-selected sample,
and investigate the unique spectral characteristics inherent in samples
selected by variability. We show that variability-based selection of quasars
complements color-based selection by selecting additional redder quasars, and
mitigates redshift biases to produce a smooth quasar redshift distribution over
a wide range of redshifts. The resulting quasar sample contains systematically
higher fractions of blazars and broad absorption line quasars than from
color-selected samples. Similarly, we show that M-dwarfs in the TDSS-selected
stellar sample have systematically higher chromospheric active fractions than
the underlying M-dwarf population, based on their H-alpha emission. TDSS also
contains a large number of RR Lyrae and eclipsing binary stars with
main-sequence colors, including a few composite-spectrum binaries. Finally, our
visual inspection of TDSS spectra uncovers a significant number of peculiar
spectra, and we highlight a few cases of these interesting objects. With a
factor of ~15 more spectra, the main TDSS survey in SDSS-IV will leverage the
lessons learned from these early results for a variety of time-domain science
applications.Comment: 17 pages, 14 figures, submitted to Ap
GALEX Detection of Shock Breakout in Type II-P Supernova PS1-13arp: Implications for the Progenitor Star Wind
We present the GALEX detection of a UV burst at the time of explosion of an
optically normal Type II-P supernova (PS1-13arp) from the Pan-STARRS1 survey at
z=0.1665. The temperature and luminosity of the UV burst match the theoretical
predictions for shock breakout in a red supergiant, but with a duration a
factor of ~50 longer than expected. We compare the light curve of
PS1-13arp to previous GALEX detections of Type IIP SNe, and find clear
distinctions that indicate that the UV emission is powered by shock breakout,
and not by the subsequent cooling envelope emission previously detected in
these systems. We interpret the ~ 1 d duration of the UV signal with a shock
breakout in the wind of a red supergiant with a pre-explosion mass-loss rate of
~ 10^-3 Msun yr^-1. This mass-loss rate is enough to prolong the duration of
the shock breakout signal, but not enough to produce an excess in the optical
plateau light curve or narrow emission lines powered by circumstellar
interaction. This detection of non-standard, potentially episodic high
mass-loss in a RSG SN progenitor has favorable consequences for the prospects
of future wide-field UV surveys to detect shock breakout directly in these
systems, and provide a sensitive probe of the pre-explosion conditions of SN
progenitors.Comment: Accepted for Publication in Ap
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