191 research outputs found
Looking for Distributed Star Formation in L1630: A Near-infrared (J, H, K) Survey
We have carried out a simultaneous, multi-band (J, H, K) survey over an area
of 1320 arcmin^2 in the L1630 region, concentrating on the region away from the
dense molecular cores and with modest visual extinctions (\leq 10 mag).
Previous studies found that star formation in L1630 occurs mainly in four
localized clusters, which in turn are associated with the four most massive
molecular cores (Lada et al. 1991; Lada 1992). The goal of this study is to
look for a distributed population of pre-main-sequence stars in the outlying
areas outside the known star-forming cores. More than 60% of the
pre-main-sequence stars in the active star forming regions of NGC 2024 and NGC
2023 show a near-infrared excess in the color-color diagram. In the outlying
areas of L1630, excluding the known star forming regions, we found that among
510 infrared sources with the near-infrared colors ((J-H) and (H-K)) determined
and photometric uncertainty at K better than 0.10 mag, the fraction of the
sources with a near-infrared excess is 3%--8%; the surface density of the
sources with a near-infrared excess is less than half of that found in the
distributed population in L1641, and 1/20 of that in the young cluster NGC
2023. This extremely low fraction and low surface density of sources with a
near-infrared excess strongly indicates that recent star formation activity has
been very low in the outlying region of L1630. The sources without a
near-infrared excess could be either background/foreground field stars, or
associated with the cloud, but formed a long time ago (more than 2 Myrs). Our
results are consistent with McKee's model of photoionization-regulated star
formation.Comment: 30 pages, 10 figures To appear in ApJ Oct 1997, Vol 48
Maladaptive schemas as a potential mechanism through which irrational beliefs relate to psychological distress in athletes
© 2019 Elsevier Ltd Objectives: The psychological wellbeing of athletes, in particular the concept of psychological distress, is receiving growing research attention. Irrational beliefs as proposed in Rational Emotive Behaviour Therapy (REBT) have been shown to be positively related to the psychological distress of athletes, but the mechanisms by which irrational beliefs predict psychological distress remain unclear. The role of maladaptive schemas, as proposed in Schema Therapy (ST), in the relationship between irrational beliefs and psychological distress has not yet been studied, despite the conceptual similarities between REBT and ST. Design and method: Participants were self-selected triathletes (n = 124), duathletes (n = 9), swimmers (n = 7), cyclists (n = 17) and runners (n = 57). A single timepoint cross-sectional study design was used to investigate simple mediation models using the PROCESS macro. Results: Results revealed that maladaptive schemas fully mediated the positive relationship between irrational beliefs and symptoms of anxiety, and depression (psychological distress). Conclusions: These findings suggest that maladaptive schemas are a potential mechanism through which irrational beliefs predict psychological distress. Results may help practitioners begin to understand how REBT and ST may be applied in tandem for the benefit of greater athlete psychological wellbeing
First occurrence of Xanthomonas campestris pv. raphanion wallflower (Erysimum cheiri) in the United Kingdom
In a study of diseases caused by Xanthomonas campestris on UK nursery-grown wallflowers (Erysimum cheiri), one isolate (P764) obtained in 1990 from Sussex differed from the others. The affected plants (cv. Bedder Mixed), showed distorted growth with chlorotic and necrotic spots, but no sectored V-shaped wilting, the most common symptom associated with xanthomonads in wallflowers. Other X. campestris isolates (including P763), were obtained from wallflowers with typical wilting. Infected plant material was comminuted in sterile 0.1% peptone solution and loopfuls streaked onto yeast dextrose chalk agar and nutrient dextrose agar (Lelliott & Stead, 1987). Plates were incubated for up to 72 hours at 28°C. Xanthomonas-like colonies were purified by re-streaking and isolates were maintained at -80°C (Protect System, UK)
2MASS Observations of the Perseus, Orion A, Orion B, and Monoceros R2 Molecular Clouds
We use the 2MASS Second Incremental Release Point Source Catalog to
investigate the spatial distribution of young stars in the Perseus, Orion A,
Orion B, and MonR2 molecular clouds. After subtracting a semi-empirical model
of the field star contamination from the observed star counts, stellar surface
density maps are used to identify compact clusters and any stellar population
found more uniformly distributed over the molecular cloud. Each cloud contains
between 2 to 7 clusters, with at least half of the cluster population found in
a single, rich cluster. In addition, a distributed stellar population is
inferred in the Orion A and MonR2 molecular clouds within the uncertainties of
the field star subtraction with a surface density between 0.013 - 0.083
arcmin**-2. The fraction of the total stellar population contained in clusters
for the nominal extinction model ranges from ~50-100% if the distributed
population is relatively young (< 10 Myr), to ~25%-70% if it is relatively old
(~100 Myr). The relatively high fraction of stars contained in clusters
regardless of the age of the distributed population, in conjunction with the
young ages generally inferred for embedded clusters in nearby molecular clouds,
indicates that a substantial fraction of the total stellar population in these
regions has formed within the past few million years in dense clusters. This
suggests that either the star formation rate in each these clouds has recently
peaked if one assumes clouds have ages > 10 Myr, or molecular clouds are
younger than typically thought if one assumes that the star formation rate has
been approximately constant in time.Comment: to appear in AJ, December 2000; see also
http://astro.caltech.edu/~jmc/papers/2mass_cloud
An equatorial wind from the massive young stellar object S140 IRS 1
The discovery of the second equatorial ionized stellar wind from a massive
young stellar object is reported. High resolution radio continuum maps of S140
IRS 1 reveal a highly elongated source that is perpendicular to the larger
scale bipolar molecular outflow. This picture is confirmed by location of a
small scale monopolar near-IR reflection nebula at the base of the blueshifted
lobe. A second epoch of observations over a five year baseline show little
ordered outward proper motion of clumps as would have been expected for a jet.
A third epoch, taken only 50 days after the second, did show significant
changes in the radio morphology. These radio properties can all be understood
in the context of an equatorial wind driven by radiation pressure from the
central star and inner disc acting on the gas in the surface layers of the disc
as proposed by Drew et al. (1998). This equatorial wind system is briefly
compared with the one in S106IR, and contrasted with other massive young
stellar objects that drive ionized jets.Comment: 19 pages, 5 figures, accepted by ApJ, minor changes in light of
referees repor
Spitzer Observations of NGC 1333: A Study of Structure and Evolution in a Nearby Embedded Cluster
We present a comprehensive analysis of structure in the young, embedded
cluster, NGC 1333 using members identified with Spitzer and 2MASS photometry
based on their IR-excess emission. In total, 137 members are identified in this
way, composed of 39 protostars and 98 more evolved pre-main sequence stars with
disks. Of the latter class, four are transition/debris disk candidates. The
fraction of exposed pre-main sequence stars with disks is 83% +/- 11%, showing
that there is a measurable diskless pre-main sequence population. The sources
in each of the Class I and Class II evolutionary states are shown to have very
different spatial distributions relative to the distribution of the dense gas
in their natal cloud. However, the distribution of nearest neighbor spacings
among these two groups of sources are found to be quite similar, with a strong
peak at spacings of 0.045 pc. Radial and azimuthal density profiles and surface
density maps computed from the identified YSOs show that NGC 1333 is elongated
and not strongly centrally concentrated, confirming previous claims in the
literature. We interpret these new results as signs of a low velocity
dispersion, extremely young cluster that is not in virial equilibrium.Comment: 59 pages, 20 figures, accepted to ApJ, verion with full resolution
figures available at
http://www.cfa.harvard.edu/~rgutermuth/preprints/gutermuth_ngc1333.pdf .
Updated to fix astro-ph figure garblin
Turbulence driven by outflow-blown cavities in the molecular cloud of NGC 1333
Outflows from young stellar objects have been identified as a possible source
of turbulence in molecular clouds. To investigate the relationship between
outflows, cloud dynamics and turbulence, we compare the kinematics of the
molecular gas associated with NGC 1333, traced in 13CO(1-0), with the
distribution of young stellar objects (YSOs) within. We find a velocity
dispersion of ~ 1-1.6 km/s in 13CO that does not significantly vary across the
cloud, and is uncorrelated with the number of nearby young stellar outflows
identified from optical and submillimeter observations. However, from velocity
channel maps we identify about 20 cavities or depressions in the 13CO intensity
of scales > 0.1-0.2 pc and velocity widths 1-3 km/s. The cavities exhibit limb
brightened rims in both individual velocity channel maps and position velocity
diagrams, suggesting that they are slowly expanding. We interpret these
cavities to be remnants of past YSO outflow activity: If these cavities are
presently empty, they would fill in on time scales of a million years. This can
exceed the lifetime of a YSO outflow phase, or the transit time of the central
star through the cavity, explaining the the absence of any clear correlation
between the cavities and YSO outflows. We find that the momentum and energy
deposition associated with the expansion of the cavities is sufficient to power
the turbulence in the cloud. In this way we conclude that the cavities are an
important intermediary step between the conversion of YSO outflow energy and
momentum into cloud turbulent motions.Comment: Accepted for publication in ApJ. Check out
http://astro.pas.rochester.edu/~aquillen/coolpics.html for channel map and
PosVel movies of N133
CSO Bolocam 1.1 mm continuum mapping of the Braid Nebula star formation region in Cygnus OB7
We present a 1.1 mm map of the Braid Nebula star formation region in Cygnus OB7 taken using Bolocam on the Caltech Submillimeter Observatory. Within the 1 deg2 covered by the map, we have detected 55 cold dust clumps all of which are new detections. A number of these clumps are coincident with IRAS point sources although the majority are not. Some of the previously studied optical/near-IR sources are detected at 1.1 mm. We estimate total dust/gas masses for the 55 clumps together with peak visual extinctions. We conclude that over the whole region, approximately 20% of the clumps are associated with IRAS sources suggesting that these are protostellar objects. The remaining 80% are classed as starless clumps. In addition, both FU Orionis (FUor) like objects in the field, the Braid Star and HH 381 IRS, are associated with strong millimeter emission. This implies that FUor eruptions can occur at very early stages of pre-main-sequence life. Finally, we determine that the cumulative clump mass function for the region is very similar to that found in both the Perseus and Ï? Ophiuchus star-forming regions. © 2011. The American Astronomical Society. All rights reserved
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An observational study of cometary globules near the Rosette nebula
Molecular line observations are reported of two regions containing small cometary globules at the edge of the Rosette Nebula. Observations of the CO, 13CO and 18CO J = 2 - 1,and CO J = 4 -3 molecular lines towards Globule 1, the most prominent of the group, show it has a well-developed head-tail structure, with a head diameter ~0.4pc, and a tail extending ~ 1.3 pc behind it. The major axis of the system points about 45 degrees away from the direction to the centre of the Rosette Nebula (which contains the presumed illuminating stars), and 20 degrees out of the plane of the sky, along a projected line towards the luminous (924 L⊙) infrared source IRAS 06314+0427. The CO lines have a complex velocity structure; with a pronounced broadening at the front of the head (as viewed from IRAS 06314+0427); a velocity gradient ~1.4 km s-1 along the tail, and material at the front of the head is blue-shifted by ~0.5 km s-1 compared to surrounding gas. The CO J = 2 - 1 line intensity peaks towards the front of the head, and along the edges of the tail. The 13CO J =2 - 1 antenna temperatures in the head are very similar to those of CO, suggesting very high opacities or column densities, or that there is significant CO self-absorption. There is a narrow rim of CO J = 4 - 3 emission around the front of the head over a limited velocity range, which correlates with the position of a faint optical rim, and a narrow ridge of 2 μm H2 emission. These data give strong support to the Radiation Driven Implosion (RDI) model of Lefloch and Lazareff (1994 - hereafter LL94), which was developed to explain the physical structure of cometary globules. Using an RDI simulation, a remarkably good fit to the data has been obtained, allowing the CO, 13CO and C18O spatial structures and velocity field to be modelled. This simulation suggests that Globule 1 is ~400,000 years old, and has a mass ~ 50 M⊙. Additional observations towards the region close to IRAS 06314+0427 show that it is associated with an intense molecular concentration lying at the northern end of a ~ 5 pc long molecular ridge, with a mass ~ 330 M⊙, and lies close to the centre of a shell-like condensation
Polarimetric variations of binary stars. V. Pre-main-sequence spectroscopic binaries located in Ophiuchus and Scorpius
We present polarimetric observations of 7 pre-main-sequence (PMS)
spectroscopic binaries located in the rho Oph and Upper Sco star forming
regions (SFRs). The average observed polarizations at 7660A are between 0.5%
and 3.5%. After estimates of the interstellar polarization are removed, all
binaries have an intrinsic polarization above 0.4%. Two binaries,
NTTS162814-2427 and NTTS162819-2423S, present high levels of intrinsic
polarization between 1.5% and 2.1%. All 7 PMS binaries have a statistically
variable or possibly variable polarization. Combining these results with our
previous sample of binaries located in the Tau, Aur and Ori SFRs, 68% of the
binaries have an intrinsic polarization above 0.5%, and 90% of the binaries are
polarimetrically variable or possibly variable. NTTS160814-1857,
NTTS162814-2427, and NTTS162819-2423S are clearly polarimetrically variable.
The first two also exhibit phase-locked variations over ~10 and ~40 orbits
respectively. NTTS160905-1859 shows periodic variations that are not
phased-locked and only present for short intervals of time. The amplitudes of
the variations reach a few tenths of a percent. The high-eccentricity system
NTTS162814-2427 shows single-periodic variations, in agreement with our
previous numerical simulations. Non-periodic events introduce stochastic noise
that partially masks the periodic variations and prevents the Brown, McLean, &
Emslie (1978) formalism from finding a reasonable estimate of the inclination.Comment: 63 pages, including 21 figures and 18 tables, accepted by A
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