1,524 research outputs found
Update on the Nature of Virgo Overdensity
We use the Eighth Data Release of Sloan Digital Sky Survey (SDSS DR8) catalog
with its additional sky coverage of the southern Galactic hemisphere, to
measure the extent and study the nature of the Virgo Overdensity (VOD; Juric et
al. 2008). The data show that the VOD extends over no less than 2000 deg^2,
with its true extent likely closer to 3000 deg^2. We test whether the VOD can
be attributed to a tilt in the stellar halo ellipsoid with respect to the plane
of the Galactic disk and find that the observed symmetry of the north-south
Galactic hemisphere star counts excludes this possibility. We argue that the
Virgo Overdensity, in spite of its wide area and cloud-like appearance, is
still best explained by a minor merger. Its appearance and position is
qualitatively similar to a near perigalacticon merger event and, assuming that
the VOD and the Virgo Stellar Stream share the same progenitor, consistent with
the VSS orbit determined by Casetti-Dinescu et al. (2009).Comment: 9 pages,6 figures; accepted for publication in A
Tracing Sagittarius Structure with SDSS and SEGUE Imaging and Spectroscopy
We show that the Sagittarius dwarf tidal stream can be traced with very red
K/M-giant stars selected from SDSS photometry. A subset of these stars are
spectroscopically confirmed with SEGUE and SDSS spectra, and the distance scale
of 2MASS and SDSS M giants is calibrated to the RR Lyrae distance scale. The
absolute g band magnitude of the K/M-giant stars at the tip of the giant branch
is M_g=-1.0. The line-of-sight velocities of the M giant and BHB stars that are
spatially coincident with the Sgr dwarf tidal stream are consistent with those
of previous authors, reinforcing the need for new models that can explain all
of the Sgr tidal debris stream observations. We estimate stellar densities
along the tidal tails that can be used to help constrain future models. The
K/M-giant, BHB, and F-turnoff stars in the lower surface brightness tidal
stream that is adjacent to the main leading Sgr dwarf tidal tail have
velocities and metallicities that are similar to those of the stars in the
leading tidal tail. The ratio of K/M giants to BHBs and BHBs to F-turnoff stars
are also similar for both branches of the leading tidal tail. We show that
there is an additional low-metallicity tidal stream near the Sgr trailing tidal
tail.Comment: 19 figures, accepted for publication in ApJ, references update
Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. I. Crowded Field Photometry and Cluster Fiducial Sequences in ugriz
We present photometry for globular and open cluster stars observed with the
Sloan Digital Sky Survey (SDSS). In order to exploit over 100 million stellar
objects with r < 22.5 mag observed by SDSS, we need to understand the
characteristics of stars in the SDSS ugriz filters. While star clusters provide
important calibration samples for stellar colors, the regions close to globular
clusters, where the fraction of field stars is smallest, are too crowded for
the standard SDSS photometric pipeline to process. To complement the SDSS
imaging survey, we reduce the SDSS imaging data for crowded cluster fields
using the DAOPHOT/ALLFRAME suite of programs and present photometry for 17
globular clusters and 3 open clusters in a SDSS value-added catalog. Our
photometry and cluster fiducial sequences are on the native SDSS 2.5-meter
ugriz photometric system, and the fiducial sequences can be directly applied to
the SDSS photometry without relying upon any transformations. Model photometry
for red giant branch and main-sequence stars obtained by Girardi et al. cannot
be matched simultaneously to fiducial sequences; their colors differ by
~0.02-0.05 mag. Good agreement (< ~0.02 mag in colors) is found with Clem et
al. empirical fiducial sequences in u'g'r'i'z' when using the transformation
equations in Tucker et al.Comment: 30 pages, 25 figures. Accepted for publication in ApJS. Version with
high resolution figures available at
http://www.astronomy.ohio-state.edu/~deokkeun/AnJohnson.pd
New Peptides Isolated from Lyngbya Species: A Review
Cyanobacteria of the genus Lyngbya have proven to be prodigious producers of secondary metabolites. Many of these compounds are bioactive and show potential for therapeutic use. This review covers peptides and hybrid polyketide-non-ribosomal peptides isolated from Lyngbya species. The structures and bioactivities of 50 Lyngbya peptides which were reported since 2007 are presented
Serotonin tranporter methylation and response to cognitive behaviour therapy in children with anxiety disorders
Anxiety disorders that are the most commonly occurring psychiatric disorders in childhood, are associated with a range of social and educational impairments and often continue into adulthood. Cognitive behaviour therapy (CBT) is an effective treatment option for the majority of cases, although up to 35-45% of children do not achieve remission. Recent research suggests that some genetic variants may be associated with a more beneficial response to psychological therapy. Epigenetic mechanisms such as DNA methylation work at the interface between genetic and environmental influences. Furthermore, epigenetic alterations at the serotonin transporter (SERT) promoter region have been associated with environmental influences such as stressful life experiences. In this study, we measured DNA methylation upstream of SERT in 116 children with an anxiety disorder, before and after receiving CBT. Change during treatment in percentage DNA methylation was significantly different in treatment responders vs nonresponders. This effect was driven by one CpG site in particular, at which responders increased in methylation, whereas nonresponders showed a decrease in DNA methylation. This is the first study to demonstrate differences in SERT methylation change in association with response to a purely psychological therapy. These findings confirm that biological changes occur alongside changes in symptomatology following a psychological therapy such as CBT
H-alpha Equivalent Width Variations across the Face of a Microlensed K Giant in the Galactic Bulge
We present VLT FORS1 spectroscopy that temporally resolves the second caustic
crossing of the Bulge K giant source of microlensing event EROS 2000-BLG-5, the
first time this has been accomplished for several phases of a caustic transit.
The ~1 angstrom H-alpha equivalent width of the source star increases slightly
as the center of the star egresses the caustic and then plummets by 30% during
the final limb crossing. These changes are not seen in contemporaneous spectra
of control stars in the FORS1 slit, but are qualitatively consistent with
expectations from stellar atmosphere models as the caustic differentially
magnifies different portions of the stellar face of the target. Observations
such as these in a variety of stellar lines are equivalent to atmospheric
tomography and are expected to provide a direct test of stellar models.Comment: 15 pages, including 1 table and 4 figures. As accepted by ApJ
Letters, vol 55
Insight Into the Formation of the Milky Way Through Cold Halo Substructure. I. The ECHOS of Milky Way Formation
We identify ten -- seven for the first time -- elements of cold halo
substructure (ECHOS) in the volume within 17.5 kpc of the Sun in the inner halo
of the Milky Way. Our result is based on the observed spatial and radial
velocity distribution of metal-poor main sequence turnoff (MPMSTO) stars in 137
Sloan Extension for Galactic Understanding and Exploration (SEGUE) lines of
sight. We point out that the observed radial velocity distribution is
consistent with a smooth stellar component of the Milky Way's inner halo
overall, but disagrees significantly at the radial velocities that correspond
to our detections. We show that all of our detections are statistically
significant and that we expect no false positives. We also use our detections
and completeness estimates to infer a formal upper limit of 0.34 +/- 0.02 on
the fraction of the MPMSTO population in the inner halo that belong to ECHOS.
Our detections and completeness calculations suggest that there is a
significant population of low fractional overdensity ECHOS in the inner halo,
and we predict that 1/3 of the inner halo (by volume) harbors ECHOS with MPMSTO
star number densities n ~ 15 kpc^-3. ECHOS are likely older than known surface
brightness substructure, so our detections provide us with a direct measure of
the accretion history of the Milky Way in a region and time interval that has
yet to be fully explored. In concert with previous studies, our result suggests
that the level of merger activity has been roughly constant over the past few
Gyr and that there has been no accretion of single stellar systems more massive
than a few percent of a Milky Way mass in that interval. (abridged)Comment: 47 pages, 23 figures, and 6 tables in emulaetapj format; accepted for
publication in Ap
Decreased startle modulation during anticipation in the postpartum period in comparison to late pregnancy
Knowledge about healthy women’s psychophysiological adaptations during the large neuroendocrine changes of pregnancy and childbirth is essential in order to understand why these events have the potential to disrupt mental health in vulnerable individuals. This study aimed to compare startle response modulation, an objective psychophysiological measure demonstrated to be influenced by anxiety and depression, longitudinally across late pregnancy and the postpartum period. The acoustic startle response modulation was assessed during anticipation of affective images and during image viewing in 31 healthy women during gestational weeks 36–39 and again at 4 to 6 weeks postpartum. No startle modulation by affective images was observed at either time point. Significant modulation during anticipation stimuli was found at pregnancy assessment but was reduced in the postpartum period. The women rated the unpleasant images more negative and more arousing and the pleasant images more positive at the postpartum assessment. Self-reported anxiety and depressive symptoms did not change between assessments. The observed postpartum decrease in modulation of startle by anticipation suggests a relatively deactivated defense system in the postpartum period
Aurora kinase A drives the evolution of resistance to third-generation EGFR inhibitors in lung cancer.
Although targeted therapies often elicit profound initial patient responses, these effects are transient due to residual disease leading to acquired resistance. How tumors transition between drug responsiveness, tolerance and resistance, especially in the absence of preexisting subclones, remains unclear. In epidermal growth factor receptor (EGFR)-mutant lung adenocarcinoma cells, we demonstrate that residual disease and acquired resistance in response to EGFR inhibitors requires Aurora kinase A (AURKA) activity. Nongenetic resistance through the activation of AURKA by its coactivator TPX2 emerges in response to chronic EGFR inhibition where it mitigates drug-induced apoptosis. Aurora kinase inhibitors suppress this adaptive survival program, increasing the magnitude and duration of EGFR inhibitor response in preclinical models. Treatment-induced activation of AURKA is associated with resistance to EGFR inhibitors in vitro, in vivo and in most individuals with EGFR-mutant lung adenocarcinoma. These findings delineate a molecular path whereby drug resistance emerges from drug-tolerant cells and unveils a synthetic lethal strategy for enhancing responses to EGFR inhibitors by suppressing AURKA-driven residual disease and acquired resistance
Diophantine approximation in Kleinian groups : singular, extremal, and bad limit points
The overall aim of this note is to initiate a ‘manifold’ theory for metric Diophantine approximation on the limit sets of Kleinian groups. We investigate the notions of singular and extremal limit points within the geometrically finite Kleinian group framework. Also, we consider the natural analogue of Davenport's problem regarding badly approximable limit points in a given subset of the limit set. Beyond extremality, we discuss potential Khintchine-type statements for subsets of the limit set. These can be interpreted as the conjectural ‘manifold’ strengthening of Sullivan's logarithmic law for geodesics
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