3,615 research outputs found
Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri
Short-exposure Planetary Camera images of T Tauri have been obtained using broadband filters spanning the wavelength range 0.55-0.80 μm. The optically visible star lies very close to an arc of reflection nebulosity. The arc's northern arm extends approximately 5" from the star, while its southwestern arm appears brighter and extends only 2". The arc shows an approximate symmetry along an axis toward the west-northwest, the direction of Hind's Nebula and the blueshifted molecular outflow. The morphology of the reflected light is similar to models of scattered light within an illuminated, axisymmetric outflow cavity in a circumbinary envelope, viewed ≈ 45° from the outflow axis. However, our model images do not successfully account for the amount of limb brightening that is seen. No optical counterpart to the infrared companion is seen to a limiting magnitude of V = 19.6, which suggests A_V > 7 mag toward this source. There is no evidence for an optical tertiary, to a limiting ΔV = 5.1 mag fainter than the primary, at the position where such an object has been previously reported
Hubble Space Telescope Observations of the Draco Dwarf Spheroidal
We present an F606W-F814W color-magnitude diagram for the Draco dwarf
spheroidal galaxy based on Hubble Space Telescope WFPC2 images. The luminosity
function is well-sampled to 3 magnitudes below the turn-off. We see no evidence
for multiple turnoffs and conclude that, at least over the field of the view of
the WFPC2, star formation was primarily single-epoch. If the observed number of
blue stragglers is due to extended star formation, then roughly 6% (upper
limit) of the stars could be half as old as the bulk of the galaxy. The color
difference between the red giant branch and the turnoff is consistent with an
old population and is very similar to that observed in the old, metal-poor
Galactic globular clusters M68 and M92. Despite its red horizontal branch,
Draco appears to be older than M68 and M92 by 1.6 +/- 2.5 Gyrs, lending support
to the argument that the ``second parameter'' which governs horizontal branch
morphology must be something other than age. Draco's observed luminosity
function is very similar to that of M68, and the derived initial mass function
is consistent with that of the solar neighborhood.Comment: 16 pages, AASTeX, 9 postscript figures, figures 1 and 2 available at
ftp://bb3.jpl.nasa.gov/pub/draco/. Accepted for publication in the
Astronomical Journa
Observations and Implications of the Star Formation History of the LMC
We present derivations of star formation histories based on color-magnitude
diagrams of three fields in the LMC from HST/WFPC2 observations. A significant
component of stars older than 4 Gyr is required to match the observed
color-magnitude diagrams. Models with a dispersion-free age-metallicity
relation are unable to reproduce the width of the observed main sequence;
models with a range of metallicity at a given age provide a much better fit.
Such models allow us to construct complete ``population boxes'' for the LMC
based entirely on color-magnitude diagrams; remarkably, these qualitatively
reproduce the age-metallicity relation observed in LMC clusters. We discuss
some of the uncertainties in deriving star formation histories. We find,
independently of the models, that the LMC bar field has a larger relative
component of older stars than the outer fields. The main implications suggested
by this study are: 1) the star formation history of field stars appears to
differ from the age distribution of clusters, 2) there is no obvious evidence
for bursty star formation, but our ability to measure bursts shorter in
duration than 25% of any given age is limited by the statistics of the
observed number of stars, 3) there may be some correlation of the star
formation rate with the last close passage of the LMC/SMC/Milky Way, but there
is no dramatic effect, and 4) the derived star formation history is probably
consistent with observed abundances, based on recent chemical evolution models.Comment: Accepted by AJ, 36 pages including 12 figure
Stellar Populations in Three Outer Fields of the LMC
We present HST photometry for three fields in the outer disk of the LMC
extending approximately four magnitudes below the faintest main sequence
turnoff. We cannot detect any strongly significant differences in the stellar
populations of the three fields based on the morphologies of the
color-magnitude diagrams, the luminosity functions, and the relative numbers of
stars in different evolutionary stages. Our observations therefore suggest
similar star formation histories in these regions, although some variations are
certainly allowed. The fields are located in two regions of the LMC: one is in
the north-east field and two are located in the north-west. Under the
assumption of a common star formation history, we combine the three fields with
ground-based data at the same location as one of the fields to improve
statistics for the brightest stars. We compare this stellar population with
those predicted from several simple star formation histories suggested in the
literature, using a combination of the R-method of Bertelli et al (1992) and
comparisons with the observed luminosity function. The only model which we
consider that is not rejected by the observations is one in which the star
formation rate is roughly constant for most of the LMC's history and then
increases by a factor of three about 2 Gyr ago. Such a model has roughly equal
numbers of stars older and younger than 4 Gyr, and thus is not dominated by
young stars. This star formation history, combined with a closed box chemical
evolution model, is consistent with observations that the metallicity of the
LMC has doubled in the past 2 Gyr.Comment: 30 pages, includes 10 postscript figures. Figure 1 avaiable at
ftp://charon.nmsu.edu/pub/mgeha/LMC. Accepted for publication in Astronomical
Journa
WFPC2 Observations of the Cooling Flow Elliptical in Abell 1795
We present WFPC2 images of the core of the cooling flow cD galaxy in Abell
1795. An irregular, asymmetric dust lane extends 7 \h75 kpc in projection to
the north-northwest. The dust shares the morphology observed in the H
and excess UV emission. We see both diffuse and knotty blue emission around the
dust lane, especially at the ends. The dust and emission features lie on the
edge of the radio lobes, suggesting star formation induced by the radio source
or the deflection of the radio jets off of pre-existing dust and gas. We
measure an apparent R significantly less than 3.1, implying that the
extinction law is not Galactic in the dust lane, or the presence of line
emission which is proportional to the extinction. The dust mass is at least
2 M\solar\ and is more likely to be 6.5 M\solar.Comment: 14 pages, LaTeX, Figure 4 included, Postscript Figs. 1-3 available at
ftp://astro.nmsu.edu/pub/JASON/A1795/, accepted for publication in ApJ
Letter
Broad clinical phenotypes associated with TAR-DNA binding protein (TARDBP) mutations in amyotrophic lateral sclerosis
The finding of TDP-43 as a major component of ubiquitinated protein inclusions in amyotrophic lateral sclerosis (ALS) has led to the identification of 30 mutations in the transactive response-DNA binding protein (TARDBP) gene, encoding TDP-43. All but one are in exon 6, which encodes the glycine-rich domain. The aim of this study was to determine the frequency of TARDBP mutations in a large cohort of motor neurone disease patients from Northern England (42 non-superoxide dismutase 1 (SOD1) familial ALS (FALS), nine ALS-frontotemporal dementia, 474 sporadic ALS (SALS), 45 progressive muscular atrophy cases). We identified four mutations, two of which were novel, in two familial (FALS) and two sporadic (SALS) cases, giving a frequency of TARDBP mutations in non-SOD1 FALS of 5% and SALS of 0.4%. Analysis of clinical data identified that patients had typical ALS, with limb or bulbar onset, and showed considerable variation in age of onset and rapidity of disease course. However, all cases had an absence of clinically overt cognitive dysfunction
The Effectiveness of Alcohol Screening and Brief Intervention in Emergency Departments: A Multicentre Pragmatic Cluster Randomized Controlled Trial
BACKGROUND:
Alcohol misuse is common in people attending emergency departments (EDs) and there is some evidence of efficacy of alcohol screening and brief interventions (SBI). This study investigated the effectiveness of SBI approaches of different intensities delivered by ED staff in nine typical EDs in England: the SIPS ED trial.
METHODS AND FINDINGS:
Pragmatic multicentre cluster randomized controlled trial of SBI for hazardous and harmful drinkers presenting to ED. Nine EDs were randomized to three conditions: a patient information leaflet (PIL), 5 minutes of brief advice (BA), and referral to an alcohol health worker who provided 20 minutes of brief lifestyle counseling (BLC). The primary outcome measure was the Alcohol Use Disorders Identification Test (AUDIT) status at 6 months. Of 5899 patients aged 18 or more presenting to EDs, 3737 (63·3%) were eligible to participate and 1497 (40·1%) screened positive for hazardous or harmful drinking, of whom 1204 (80·4%) gave consent to participate in the trial. Follow up rates were 72% (n?=?863) at six, and 67% (n?=?810) at 12 months. There was no evidence of any differences between intervention conditions for AUDIT status or any other outcome measures at months 6 or 12 in an intention to treat analysis. At month 6, compared to the PIL group, the odds ratio of being AUDIT negative for brief advice was 1·103 (95% CI 0·328 to 3·715). The odds ratio comparing BLC to PIL was 1·247 (95% CI 0·315 to 4·939). A per protocol analysis confirmed these findings.
CONCLUSIONS:
SBI is difficult to implement in typical EDs. The results do not support widespread implementation of alcohol SBI in ED beyond screening followed by simple clinical feedback and alcohol information, which is likely to be easier and less expensive to implement than more complex interventions
Hubble Space Telescope WFPC2 Imaging of FS Tauri and Haro 6-5B
We have observed the field of FS Tauri (Haro 6-5) with the Wide Field Planetary Camera 2 on the Hubble Space Telescope. Centered on Haro 6-5B and adjacent to the nebulous binary system of FS Tauri A there is an extended complex of reflection nebulosity that includes a diffuse, hourglass-shaped structure. H6-5B, the source of a bipolar jet, is not directly visible but appears to illuminate a compact, bipolar nebula which we assume to be a protostellar disk similar to HH 30. The bipolar jet appears twisted, which explains the unusually broad width measured in ground-based images. We present the first resolved photometry of the FS Tau A components at visual wavelengths. The fluxes of the fainter, eastern component are well matched by a 3360 K blackbody with an extinction of A_V = 8. For the western star, however, any reasonable, reddened blackbody energy distribution underestimates the K-band photometry by over 2 mag. This may indicate errors in the infrared photometry or errors in our visible measurements due to bright reflection nebulosity very close to the star. The binary was separated by 0."239 ± 0."005 at a position angle of 84° ± 1."5 on 1996 January 25. There is no nebulosity around FS Tau A at the orientation suggested for a disk based on previous, ground-based polarization measurements
Hubble Space Telescope WFPC2 Images of Emission Nebulosity near XZ Tauri
XZ Tauri is a M3 V T Tauri star with a pre-main-sequence binary companion detected by infrared speckle interferometry at a projected separation of 0".3 (about 40 AU). Previous ground-based observations of the system have shown bipolar emission nebulosity, including a possible jet knot. Images obtained with the Wide Field and Planetary Camera 2 on the Hubble Space Telescope show an elongated, filled bubble of emission nebulosity extending over 4" to the north of the system which contains two or three compact knots. The source of the nebulosity is undetermined. For the first time, the components are separated in visible light, and the southern component (XZ Tau S) dominates the integrated light of the system. The reverse has been found to be true in the near-infrared. Thus we confirm that XZ Tauri belongs to the small class of young binaries with cool infrared companions
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