461 research outputs found
The Second Galex Ultraviolet Variability (GUVV-2) Catalog
We present the second Galaxy Evolution Explorer (GALEX) Ultraviolet
Variability (GUVV-2) Catalog that contains information on 410 newly discovered
time-variable sources gained through simultaneous near (NUV 1750-2750A) and far
(FUV 1350-1750A) ultraviolet photometric observations. Source variability was
determined by comparing the NUV and/or FUV fluxes derived from orbital
exposures recorded during a series of multiple observational visits to 169
GALEX fields on the sky. These sources, which were contained within a sky-area
of 161 square deg, varied on average by amplitudes of NUV = 0.6 mag and FUV =
0.9 mag during these observations. Of the 114 variable sources in the catalog
with previously known identifications, 67 can be categorized as being active
galaxies (QSO's, Seyfert 1 or BL Lac objects). The next largest groups of UV
variables are RR Lyrae stars, X-ray sources and novae.
By using a combination of UV and visible color-color plots we have been able
to tentatively identify 36 possible RR Lyrae and/or Delta Scuti type stars, as
well as 35 probable AGN's, many of which may be previously unidentified QSO's
or blazars. Finally, we show data for 3 particular variable objects: the
contact binary system of SDSS J141818.97+525006.7, the eclipsing dwarf nova
system of IY UMa and the highly variable unidentified source SDSS
J104325.06+563258.1.Comment: Astronomical Journal accepte
A photospheric metal line profile analysis of hot DA white dwarfs with circumstellar material
Some hot DA white dwarfs have circumstellar high ion absorption features in
their spectra, in addition to those originating in the photosphere. In many
cases, the line profiles of these absorbing components are unresolved. Given
the importance of the atmospheric composition of white dwarfs to studies of
stellar evolution, extra-solar planetary systems and the interstellar medium,
we examine the effect of including circumstellar line profiles in the abundance
estimates of photospheric metals in six DA stars. The photospheric C and Si
abundances are reduced in five cases where the circumstellar contamination is
strong, though the relative weakness of the circumstellar Si IV absorption
introduces minimal contamination, resulting in a small change in abundance. The
inability of previous, approximate models to reproduce the photospheric line
profiles here demonstrates the need for a technique that accounts for the
physical line profiles of both the circumstellar and photospheric lines when
modelling these blended absorption features.Comment: 7 pages, 5 figues, 3 tables, accepted for publication in MNRA
New 3-D gas density maps of NaI and CaII interstellar absorption within 300pc
We present new high resolution (R>50,000) absorption measurements of the NaI
doublet (5889 - 5895A) along 482 nearby sight-lines, in addition to 807 new
measurements of the CaII K (3933A) absorption line. We have combined these new
data with previously reported measurements to produce a catalog of absorptions
towards a total of 1857 early-type stars located within 800pc of the Sun. Using
these data we have determined the approximate 3-dimensional spatial
distribution of neutral and partly ionized interstellar gasdensity within a
distance-cube of 300pc from the Sun. All newly recorded spectra were analyzed
by means of a multi-component line profile-fitting program, in most cases using
simultaneous fits to the line doublets. Normalized absorption profiles were
fitted by varying the velocity, doppler width and column density for all
intervening interstellar clouds. The resulting total column densities were then
used in conjunction with the Hipparcos distances of the target stars to
construct inversion maps of the 3-D spatial density distribution of the NaI and
CaII bearing gas. A plot of the equivalent width of NaI versus distance reveals
a wall of neutral gas at ~80pc that can be associated with the boundary wall to
the central rarefied Local Cavity region. In contrast, a similar plot for the
equivalent width of CaII shows no sharply increasing absorption at 80pc, but
instead we observe a slowly increasing value of CaII equivalent width with
increasing sight-line distance sampled.Comment: A&A accepte
Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk
We present Hubble Space Telescope STIS far-UV spectra of the edge-on disk
around 49 Ceti, one of the very few debris disks showing sub-mm CO emission.
Many atomic absorption lines are present in the spectra, most of which arise
from circumstellar gas lying along the line-of-sight to the central star. We
determined the line-of-sight CI column density, estimated the total carbon
column density, and set limits on the OI column density. Surprisingly, no
line-of-sight CO absorption was seen. We discuss possible explanations for this
non-detection, and present preliminary estimates of the carbon abundances in
the line-of-sight gas. The C/Fe ratio is much greater than the solar value,
suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of Beta
Pictoris.Comment: Accepted for publication in ApJ Letters. 5 pages, 4 figure
Life Stress and Inhibitory Control Deficits: Teaching BrainWise as a Neurocognitive Intervention in Vulnerable Populations
The chapter describes inhibitory control in the context of broader and related constructs, executive function and self-regulation. We discuss the adaptive functions of inhibitory control, as well as evidence that life stress, such as poverty, maltreatment, homelessness, and mental illness, negatively impacts individuals’ inhibitory control and overall self-regulation skills. Moreover, these stressors are known to disrupt the development and functioning of crucial brain systems underlying inhibitory control. Following this review, we discuss a critical thinking skills intervention, BrainWise, which is designed to teach inhibitory and self-regulation skills to children, youth and adults. We describe the implementation of the program, and review evidence for its effectiveness with various populations, including our recent study that demonstrated the success of BrainWise in teaching these skills to homeless men living in transitional housing. Finally, we describe our proposed future applications of this intervention to veterans suffering serious mental health challenges. Our overarching goals are to highlight the importance of inhibitory control and overall self-regulation, the vulnerability of these important skills to life stress, and the promise held by one neurocognitive intervention for improving inhibitory control in high-risk populations
GALEX observations of quasar variability in the ultraviolet
Using archival observations recorded over a 5+ year timeframe with the NASA
Galaxy Evolution Explorer (GALEX) satellite, we present a study of the
ultraviolet (UV) variability of 4360 quasars of redshifts up to z=2.5 that have
optical counterparts in the Sloan Digital Sky Survey DR5 spectroscopic catalog.
The observed changes in both the far UV (FUV: 1350-1785A) and near UV (NUV:
1770-2830A) AB magnitudes as a function of time may help differentiate between
models of the emission mechanisms thought to operate in these active galaxies.
A list of NUV and FUV variable quasars was derived from the UV light-curves of
sources with 5 or more observational visits by GALEX that spanned a time-frame
greater than 3 months. By measuring the error in the derived mean UV magnitude
from the series of GALEX observations for each source, quasars whose UV
variability was greater than the 3-sigma variance from the mean observed value
were deemed to be (intrinsically) UV variable. This conservative selection
criterion (which was applied to both FUV and NUV observations) resulted in
identifying 550 NUV and 371 FUV quasars as being statistically significant UV
variable objects.Comment: A&A Accepted, spelling of author's name corrected (Neill
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