64,251 research outputs found
Full-depth Coadds of the WISE and First-year NEOWISE-Reactivation Images
The Near Earth Object Wide-field Infrared Survey Explorer (NEOWISE)
Reactivation mission released data from its first full year of observations in
2015. This data set includes ~2.5 million exposures in each of W1 and W2,
effectively doubling the amount of WISE imaging available at 3.4 and 4.6
microns relative to the AllWISE release. We have created the first ever
full-sky set of coadds combining all publicly available W1 and W2 exposures
from both the AllWISE and NEOWISE-Reactivation (NEOWISER) mission phases. We
employ an adaptation of the unWISE image coaddition framework (Lang 2014),
which preserves the native WISE angular resolution and is optimized for forced
photometry. By incorporating two additional scans of the entire sky, we not
only improve the W1/W2 depths, but also largely eliminate time-dependent
artifacts such as off-axis scattered moonlight. We anticipate that our new
coadds will have a broad range of applications, including target selection for
upcoming spectroscopic cosmology surveys, identification of distant/massive
galaxy clusters, and discovery of high-redshift quasars. In particular, our
full-depth AllWISE+NEOWISER coadds will be an important input for the Dark
Energy Spectroscopic Instrument (DESI) selection of luminous red galaxy and
quasar targets. Our full-depth W1/W2 coadds are already in use within the DECam
Legacy Survey (DECaLS) and Mayall z-band Legacy Survey (MzLS) reduction
pipelines. Much more work still remains in order to fully leverage NEOWISER
imaging for astrophysical applications beyond the solar system.Comment: coadds available at http://unwise.me, zoomable full-sky rendering at
http://legacysurvey.org/viewe
Phenomenological Models for the Gap Anisotropy of Bi-2212 as Measured by ARPES
Recently, high resolution angle-resolved photoemission spectroscopy has been
used to determine the detailed momentum dependence of the superconducting gap
in the high temperature superconductor Bi-2212. In this paper, we first
describe tight binding fits to the normal state dispersion and superlattice
modulation effects. We then discuss various theoretical models in light of the
gap measurements. We find that the simplest model which fits the data is the
anisotropic s-wave gap , which within a one-band BCS frame-
work suggests the importance of next near neighbor Cu-Cu interactions. Various
alternative interpretations of the observed gap are also discussed, along with
the implications for microscopic theories of high temperature superconductors.Comment: 14 pages, revtex, 9 uuencoded postscript figure
Additional Evidence Supporting a Model of Shallow, High-Speed Supergranulation
Recently, Duvall and Hanasoge ({\it Solar Phys.} {\bf 287}, 71-83, 2013)
found that large distance separation travel-time differences from a
center to an annulus implied a model of the average
supergranular cell that has a peak upflow of at a depth of
and a corresponding peak outward horizontal flow of
at a depth of . In the present work, this effect
is further studied by measuring and modeling center-to-quadrant travel-time
differences , which roughly agree with this model.
Simulations are analyzed that show that such a model flow would lead to the
expected travel-time differences. As a check for possible systematic errors,
the center-to-annulus travel-time differences are found
not to vary with heliocentric angle. A consistency check finds an increase of
with the temporal frequency by a factor of two,
which is not predicted by the ray theory
Evolution of the Population of Very Strong MgII Absorbers
We present a study of the evolution of several classes of MgII absorbers, and
their corresponding FeII absorption, over a large fraction of cosmic history:
2.3 to 8.7 Gyrs from the Big Bang. Our sample consists of 87 strong
(Wr(MgII)>0.3 A) MgII absorbers, with redshifts 0.2<z<2.5, measured in 81
quasar spectra obtained from the Very Large Telescope(VLT)/Ultraviolet and
Visual Echelle Spectrograph(UVES) archives of high-resolution spectra (R \sim
45,000). No evolutionary trend in Wr(FeII)/Wr(MgII) is found for moderately
strong MgII absorbers (0.3<Wr(MgII)<1.0 A). However, at lower z we find an
absence of very strong MgII absorbers (those with Wr(MgII)>1 A) with small
ratios of equivalent widths of FeII to MgII. At high z, very strong MgII
absorbers with both small and large Wr(FeII)/Wr(MgII) values are present. We
compare our findings to a sample of 100 weak MgII absorbers (Wr(MgII)<0.3 A)
found in the same quasar spectra by Narayanan et al. (2007).
The main effect driving the evolution of very strong MgII systems is the
difference between the kinematic profiles at low and high redshifts. At high z,
we observe that, among the very strong MgII absorbers, all of the systems with
small ratios of Wr(FeII)/Wr(MgII) have relatively large velocity spreads,
resulting in less saturated profiles. At low z, such kinematically spread
systems are absent, and both FeII and MgII are saturated, leading to
Wr(FeII)/Wr(MgII) values that are all close to 1. The high redshift, small
Wr(FeII)/Wr(MgII) systems could correspond to sub-DLA systems, many of which
have large velocity spreads and are possibly linked to superwinds in star
forming galaxies. In addition to the change in saturation due to kinematic
evolution, the smaller Wr(FeII)/Wr(MgII) values could be due to a lower
abundance of Fe at high z, which would indicate relatively early stages of star
formation in those environments.Comment: 20 pages, 14 figures (figure 1 is a set of 87 figures, which is
available on the online version), accepted for publication in the MNRA
- …