112 research outputs found
High-resolution spectroscopy of extremely metal-poor stars in the least evolved galaxies: Bootes II
We present high-resolution Magellan/MIKE spectra of the four brightest
confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II).
These stars all inhabit the metal-poor tail of the Boo II metallicity
distribution function. The chemical abundance pattern of all detectable
elements in these stars is consistent with that of the Galactic halo. However,
all four stars have undetectable amounts of neutron-capture elements Sr and Ba,
with upper limits comparable to the lowest ever detected in the halo or in
other dwarf galaxies. One star exhibits significant radial velocity variations
over time, suggesting it to be in a binary system. Its variable velocity has
likely increased past determinations of the Boo II velocity dispersion. Our
four stars span a limited metallicity range, but their enhanced
{\alpha}-abundances and low neutron-capture abundances are consistent with the
interpretation that Boo II has been enriched by very few generations of stars.
The chemical abundance pattern in Boo II confirms the emerging trend that the
faintest dwarf galaxies have neutron-capture abundances distinct from the halo,
suggesting the dominant source of neutron-capture elements in halo stars may be
different than in ultra-faint dwarfs.Comment: 10 pages, 5 figures, 4 tables. Updated to match ApJ accepted versio
X-ray Properties of Optically Variable Low-mass AGN Candidates
We present an X-ray analysis of fourteen nearby (z < 0.044) AGN in low mass
galaxies (M_* <= 5*10^9 Msun) selected based on their optical variability
(Baldassare et al. 2020). Comparing and contrasting different AGN selection
techniques in low-mass galaxies is essential for obtaining an accurate estimate
of the active fraction in this regime. We use both new and archival
observations from the Chandra X-ray Observatory to search for X-ray point
sources consistent with AGN. Four objects have detected nuclear X-ray emission
with luminosities ranging from L_0.5-7 ~ 3*10^40 to 9*10^42 erg s^-1 with two
more marginal detections. All of the detected galaxies have luminosities
exceeding those anticipated from X-ray binaries, and all sources are nuclear,
suggesting the X-ray emission in most sources is due to an AGN. These
observations demonstrate the success of variability at identifying AGN in
low-mass galaxies. We also explore emission line diagnostics and discuss the
differences in the results of these methods for AGN selection, in particular
regarding low-mass and low-metallicity systems
WIP Regulates Signaling via the High Affinity Receptor for Immunoglobulin E in Mast Cells
Wiskott-Aldrich syndrome proteinâinteracting protein (WIP) stabilizes actin filaments and is important for immunoreceptor-mediated signal transduction leading to actin cytoskeleton rearrangement in T and B cells. Here we report a role for WIP in signaling pathways downstream of the high affinity receptor for immunoglobulin (Ig)E (FcΔRI) in mast cells. WIP-deficient bone marrowâderived mast cells (BMMCs) were impaired in their capacity to degranulate and secrete interleukin 6 after FcΔRI ligation. Calcium mobilization, phosphorylation of Syk, phospholipase C-g2, and c-Jun NH2-terminal kinase were markedly decreased in WIP-deficient BMMCs. WIP was found to associate with Syk after FcΔRI ligation and to inhibit Syk degradation as evidenced by markedly diminished Syk levels in WIP-deficient BMMCs. WIP-deficient BMMCs exhibited no apparent defect in their subcortical actin network and were normal in their ability to form protrusions when exposed to an IgE-coated surface. However, the kinetics of actin changes and the cell shape changes that follow FcΔRI signaling were altered in WIP-deficient BMMCs. These results suggest that WIP regulates FcΔRI-mediated mast cell activation by regulating Syk levels and actin cytoskeleton rearrangement
Spectroscopic follow-up of variability-selected active galactic nuclei in the Chandra Deep Field South
Luminous AGNs are usually selected by their non-stellar colours or their
X-ray emission. Colour selection cannot be used to select low-luminosity AGNs,
since their emission is dominated by the host galaxy. Objects with low X-ray to
optical ratio escape even the deepest X-ray surveys performed so far. In a
previous study we presented a sample of candidates selected through optical
variability in the Chandra Deep Field South, where repeated optical
observations were performed for the STRESS supernova survey. We obtained new
optical spectroscopy for a sample of variability selected candidates with the
ESO NTT telescope. We analysed the new spectra, together with those existing in
the literature and studied the distribution of the objects in U-B and B-V
colours, optical and X-ray luminosity, and variability amplitude. A large
fraction (17/27) of the observed candidates are broad-line luminous AGNs,
confirming the efficiency of variability in detecting quasars. We detect: i)
extended objects which would have escaped the colour selection and ii) objects
of very low X-ray to optical ratio. Several objects resulted to be
narrow-emission line galaxies where variability indicates nuclear activity,
while no emission lines were detected in others. Some of these galaxies have
variability and X-ray to optical ratio close to active galactic nuclei, while
others have much lower variability and X-ray to optical ratio. This result can
be explained by the dilution of the nuclear light due to the host galaxy. Our
results demonstrate the effectiveness of supernova search programmes to detect
large samples of low-luminosity AGNs. A sizable fraction of the AGN in our
variability sample had escaped X-ray detection (5/47) and/or colour selection
(9/48). Spectroscopic follow-up to fainter flux limits is strongly encouraged.Comment: 14 pages, 11 figures, to appear in A&
Complex regional pain syndrome : The matter of white matter?
Introduction: Many central pathophysiological aspects of complex regional pain syndrome (CRPS) are still unknown. Although brain-imaging studies are increasingly supporting the contribution of the central nervous system to the generation and maintenance of the CRPS pain, the brain's white-matter alterations are seldom investigated. Methods: In this study, we used diffusion tensor imaging to explore white-matter changes in twelve CRPS-type-1 female patients suffering from chronic right upper-limb pain compared with twelve healthy control subjects. Results: Tract-based spatial-statistics analysis revealed significantly higher mean diffusivity, axial diffusivity, and radial diffusivity in the CRPS patients, suggesting that the structural connectivity is altered in CRPS. All these measures were altered in the genu, body, and splenium of corpus callosum, as well as in the left anterior and posterior and the right superior parts of the corona radiata. Axial diffusivity was significantly correlated with clinical motor symptoms at whole-brain level, supporting the physiological significance of the observed white-matter abnormalities. Conclusions: Altogether, our findings further corroborate the involvement of the central nervous system in CRPS.Peer reviewe
Photometric Reverberation Mapping of the Broad Emission Line Region in Quasars
A method is proposed for measuring the size of the broad emission line region
(BLR) in quasars using broadband photometric data. A feasibility study, based
on numerical simulations, points to the advantages and pitfalls associated with
this approach. The method is applied to a subset of the Palomar-Green quasar
sample for which independent BLR size measurements are available. An agreement
is found between the results of the photometric method and the spectroscopic
reverberation mapping technique. Implications for the measurement of BLR sizes
and black hole masses for numerous quasars in the era of large surveys are
discussed.Comment: 19 pages, 17 figures; published versio
The southern stellar stream spectroscopic survey (S (5)): Overview, target selection, data reduction, validation, and early science
We introduce the southern stellar stream spectroscopy survey (S5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9âm Anglo-Australian Telescopeâs 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S5 has mapped nine DES streams and three streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the S5 program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction, and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on S5, including future public data releases, can be found at http://s5collab.github.io
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
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