2,520 research outputs found
The stellar content of the infalling molecular clump G286.21+0.17
The early evolution during massive star cluster formation is still uncertain.
Observing embedded clusters at their earliest stages of formation can provide
insight into the spatial and temporal distribution of the stars and thus probe
different star cluster formation models. We present near-infrared imaging of an
8'*13'(5.4pc*8.7pc) region around the massive infalling clump G286.21+0.17(also
known as BYF73). The stellar content across the field is determined and
photometry is derived in order to { obtain} stellar parameters for the cluster
members. We find evidence for some sub-structure (on scales less than a pc
diameter) within the region with apparently at least three different
sub-clusters associated with the molecular clump based on differences in
extinction and disk fractions. At the center of the clump we identify a deeply
embedded sub-cluster. Near-infrared excess is detected for 39-44% in the two
sub-clusters associated with molecular material and 27% for the exposed
cluster. Using the disk excess as a proxy for age this suggests the clusters
are very young. The current total stellar mass is estimated to be at least 200
Msun. The molecular core hosts a rich population of pre-main sequence stars.
There is evidence for multiple events of star formation both in terms of the
spatial distribution within the star forming region and possibly from the disk
frequency.Comment: Submitted to A
The M31 Globular Cluster Luminosity Function
We combine our compilation of photometry of M31 globular cluster and probable
cluster candidates with new near-infrared photometry for 30 objects. Using
these data we determine the globular cluster luminosity function (GCLF) in
multiple filters for the M31 halo clusters. We find a GCLF peak and dispersion
of V_0^0=16.84 +/-0.11, sigma_t=0.93 +/- 0.13 (Gaussian sigma = 1.20 +/- 0.14),
consistent with previous results. The halo GCLF peak colors (e.g., B^0_0 -
V^0_0) are consistent with the average cluster colors. We also measure V-band
GCLF parameters for several other subsamples of the M31 globular cluster
population. The inner third of the clusters have a GCLF peak significantly
brigher than that of the outer clusters (delta V =~ 0.5mag). Dividing the
sample by both galacticentric distance and metallicity, we find that the GCLF
also varies with metallicity, as the metal-poor clusters are on average 0.36
mag fainter than the metal-rich clusters. Our modeling of the catalog selection
effects suggests that they are not the cause of the measured differences, but a
more complete, less-contaminated M31 cluster catalog is required for
confirmation. Our results imply that dynamical destruction is not the only
factor causing variation in the M31 GCLF: metallicity, age, and cluster initial
mass function may also be important.Comment: AJ, in press. 36 pages, including 7 figure
Refractory and super-refractory status epilepticus in adults: a 9-year cohort study.
While status epilepticus (SE) persisting after two antiseizure agents is called refractory (RSE), super-refractory status epilepticus (SRSE) defines SE continuing after general anaesthesia. Its prevalence and related clinical profiles have received limited attention, and most studies were restricted to intensive care facilities. We therefore aimed at describing RSE and SRSE frequencies and identifying associated clinical variables.
Between 2006 and 2015, consecutive adult SE episodes were prospectively recorded in a registry. Occurrence of RSE and SRSE and their relationship to clinical variables of interest, including outcome, were analysed.
Of 804 SE episodes, 268 (33.3%) were RSE and 33 (4%) SRSE. Coma induction for SE treatment occurred in 79 (9.8%) episodes. Severe consciousness impairment (OR 1.67; 95% CI 1.24-2.46; P = 0.001), increasing age (OR 1.01, 95% CI 1.01-1.02), and lack of remote symptomatic SE aetiology (OR 0.48; 95% CI 0.32-0.72) were independently associated with RSE, while severe consciousness impairment (OR 4.26; 95% CI 1.44-12.60) and younger age (OR 0.96; 95% CI 0.95-0.99) correlated with SRSE; however, most SRSE episodes were not predicted by these variables. Mortality was 15.5% overall, higher in RSE (24.5%) and SRSE (37.9%) than in non-refractory SE (9.8%) (P < 0.001).
Super-refractory status epilepticus appears clearly less prevalent in this cohort than previously reported, probably as it is not restricted to intensive care unit. SRSE emerges in younger patients with marked consciousness impairment, pointing to the underlying severe clinical background, but these variables do not predict most SRSE developments. There is currently a knowledge gap for prediction of SRSE occurrence that needs to be filled
WIYN Open Cluster Study 1: Deep Photometry of NGC 188
We have employed precise V and I photometry of NGC 188 at WIYN to explore the
cluster luminosity function (LF) and study the cluster white dwarfs (WDs). Our
photometry is offset by V = 0.052 (fainter) from Sandage (1962) and Eggen &
Sandage (1969). All published photometry for the past three decades have been
based on these two calibrations, which are in error by 0.05 +- 0.01. We employ
the Pinsonneault etal (1998) fiducial main sequence to derive a cluster
distance modulus of 11.43 +- 0.08. We report observations that are >= 50%
complete to V = 24.6 and find that the cluster central-field LF peaks at M_I ~
3 to 4. This is unlike the solar neighborhood LF and unlike the LFs of
dynamically unevolved portions of open and globular clusters, which rise
continuously until M_I ~ 9.5. Although we find that >= 50% of the unresolved
cluster objects are multiple systems, their presence cannot account for the
shape of the NGC 188 LF. For theoretical reasons (Terlevich 1987; Vesperini &
Heggie 1997) having to do with the survivability of NGC 188 we believe the
cluster is highly dynamically evolved and that the missing low luminosity stars
are either in the cluster outskirts or have left the cluster altogether. We
identify nine candidate WDs, of which we expect three to six are bona fide
cluster WDs. The luminosities of the faintest likely WD indicates an age
(Bergeron, Wesemael, & Beauchamp 1995) of 1.14 +- 0.09 Gyrs. This is a lower
limit to the cluster age and observations probing to V = 27 or 28 will be
necessary to find the faintest cluster WDs and independently determine the
cluster age. While our age limit is not surprising for this ~6 Gyr old cluster,
our result demonstrates the value of the WD age technique with its very low
internal errors. (abridged)Comment: 26 pages, uuencoded gunzip'ed latex + 16 postscrip figures, to be
published in A
Treating the Gibbs phenomenon in barycentric rational interpolation and approximation via the S-Gibbs algorithm
In this work, we extend the so-called mapped bases or fake nodes approach to the barycentric rational interpolation of Floater-Hormann and to AAA approximants. More precisely, we focus on the reconstruction of discontinuous functions by the S-Gibbs algorithm introduced in [12]. Numerical tests show that it yields an accurate approximation of discontinuous functions
Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. II. Optical and Near Infrared Star Formation History of the Starburst Cluster NGC 2070 in 30 Doradus
We present a study of the recent star formation of 30 Doradus in the Large
Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula
Treasury Project (HTTP). In this paper we focus on the stars within 20 pc of
the center of the massive ionizing cluster of 30 Doradus, NGC 2070. We
recovered the star formation history by comparing deep optical and NIR
color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated
with the latest PARSEC models, which include all stellar phases from pre-main
sequence to post- main sequence. For the first time in this region we are able
to measure the star formation using intermediate and low mass stars
simultaneously. Our results suggest that NGC2070 experienced a prolonged
activity. In particular, we find that the star formation in the region: i)
exceeded the average LMC rate ~ 20 Myr ago; ii) accelerated dramatically ~ 7
Myr ago; and iii) reached a peak value 1-3 Myr ago. We did not find significant
deviations from a Kroupa initial mass function down to 0.5 Msun. The average
internal reddening E(B-V) is found to be between 0.3 and 0.4 mag.Comment: Submitted to Ap
Recent advances on IMF research
Here I discuss recent work on brown dwarfs, massive stars and the IMF in
general. The stellar IMF can be well described by an invariant two-part power
law in present-day star-formation events within the Local Group of galaxies. It
is nearly identical in shape to the pre-stellar core mass function. The
majority of brown dwarfs follow a separate IMF. Evidence from globular clusters
and ultra-compact dwarf galaxies has emerged that IMFs may have been top heavy
depending on the star-formation rate density. The IGIMF then ranges from bottom
heavy at low galaxy-wide star formation rates to being top-heavy in
galaxy-scale star bursts.Comment: 6 pages, LaTeX, to appear in The Labyrinth of Star Formation, 18-22
June 2012, Crete, (eds.) D. Stamatellos, S. Goodwin, and D. Ward-Thompson,
Springer, in press; replaced version: very minor corrections plus the
addition of reference Smith & Lucey (2013) on the bottom-heavy IMF in
elliptical galaxie
The Evolution of Globular Clusters in the Galaxy
We investigate the evolution of globular clusters using N-body calculations
and anisotropic Fokker-Planck (FP) calculations. The models include a mass
spectrum, mass loss due to stellar evolution, and the tidal field of the parent
galaxy. Recent N-body calculations have revealed a serious discrepancy between
the results of N-body calculations and isotropic FP calculations. The main
reason for the discrepancy is an oversimplified treatment of the tidal field
employed in the isotropic FP models. In this paper we perform a series of
calculations with anisotropic FP models with a better treatment of the tidal
boundary and compare these with N-body calculations. The new tidal boundary
condition in our FP model includes one free parameter. We find that a single
value of this parameter gives satisfactory agreement between the N-body and FP
models over a wide range of initial conditions.
Using the improved FP model, we carry out an extensive survey of the
evolution of globular clusters over a wide range of initial conditions varying
the slope of the mass function, the central concentration, and the relaxation
time. The evolution of clusters is followed up to the moment of core collapse
or the disruption of the clusters in the tidal field of the parent galaxy. In
general, our model clusters, calculated with the anisotropic FP model with the
improved treatment for the tidal boundary, live longer than isotropic models.
The difference in the lifetime between the isotropic and anisotropic models is
particularly large when the effect of mass loss via stellar evolution is rather
significant. On the other hand the difference is small for relaxation-
dominated clusters which initially have steep mass functions and high central
concentrations.Comment: 36 pages, 11 figures, LaTeX; added figures and tables; accepted by
Ap
DDO Photometry of M71: Carbon and Nitrogen Patterns Among Evolving Giants
We present V, B-V, and DDO C(41-42) and C(42-45) photometry for a sample of
75 red giants down to M_V = +2 in the relatively metal-rich Galactic globular
cluster M71. The C(41-42) colors reveal a bimodal distribution of CN band
strengths generally anticorrelated with CH band strength as measured by the
C(42-45) color. Both DDO colors agree well with those found in 47 Tucanae -- a
nearby globular cluster of similar metallicity -- and suggest nearly identical
C and N abundance patterns among the giants of both clusters. A comparison with
synthetic DDO colors demonstrates that little change in surface C or N
abundance is required to match the colors of the M71 giants over the entire
luminosity range observed. Apparently like 47 Tuc (a cluster of much greater
mass and central concentration), M71 exhibits an abundance pattern which cannot
be solely the result of internal mixing.Comment: To appear in the Astronomical Journal, November 2001. 17 Pages, 5
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