3,478 research outputs found
The Power of Axisymmetric Pulsar
Stationary force-free magnetosphere of an axisymmetric pulsar is shown to
have a separatrix inclination angle of 77.3. The electromagnetic field
has an singularity inside the separatrix near the light cylinder. A
numerical simulation of the magnetosphere which crudely reproduces these
properties is presented. The numerical results are used to estimate the power
of an axisymmetric pulsar: . A need for a better
numerical simulation is pointed out.Comment: 9 page
Spectroscopy of Candidate Members of the Eta Cha and MBM12 Young Associations
We present an analysis of candidate members of the Eta Cha and MBM 12A young
associations. For an area of 0.7 deg^2 toward Eta Cha, we have performed a
search for members of the association by combining JHK_s photometry from 2MASS
and i photometry from DENIS with followup optical spectroscopy at Magellan
Observatory. We report the discovery of three new members with spectral types
of M5.25-M5.75, corresponding to masses of 0.13-0.08 M_sun by theoretical
evolutionary models. Two and three of these members were found independently by
Lyo and coworkers and Song and coworkers, respectively. Meanwhile, no brown
dwarfs were detected in Eta Cha down to the completeness limit of 0.015 M_sun.
For MBM 12A, we have obtained spectra of three of the remaining candidate
members that lacked spectroscopy at the end of the survey by Luhman, all of
which are found to be field M dwarfs. Ogura and coworkers have recently
presented four "probable" members of MBM 12A. However, two of these objects
were previously classified as field dwarfs by the spectroscopy of Luhman. In
this work, we find that the other two objects are field dwarfs as well.Comment: to be published in The Astrophysical Journal, 19 pages, 7 figure
Testing the Attractiveness and Efficacy of Baits for the Monitoring and Control of the Thief Ant, Solenopsis papuana
Solenopsis papuana is one of the few introduced ant species that have widely infiltrated undisturbed mesic and wet forests in Hawaii. This may be problematic since many endemic Hawaiian insects are limited to mountain forests, and methods for monitoring and controlling S. papuana would be useful. Four non-toxic monitoring baits (corn syrup, SPAM®, peanut butter, and tuna/ corn syrup blend) and five ant pesticide baits (Advion® Fire Ant BaitTM, Amdro® Ant Block®, ExtinguishTM Plus, MaxForce® Complete Brand Granular Insect Bait, and SiestaTM) were tested for attractiveness to S. papuana in choice tests at Lyon Arboretum and Pahole Natural Area Reserve (NAR) on the island of Oahu. Amdro® Ant Block® and SiestaTM were also tested for efficacy against S. papuana in field plots at Pahole NAR. SPAM® and peanut butter were the most attractive monitoring baits at both locations. There were few significant differences in at- tractiveness among the five ant pesticides, but Amdro® Ant Block® attracted the highest or second highest number of ants at both sites, while rankings among the other baits were inconsistent. Amdro® Ant Block® presented in bait stations 2.5 m apart greatly reduced the number of ants at monitoring cards in field plots, by an average of 96% from pre-treatment levels over the course of the 246-day trial. Ant numbers also declined in the SiestaTM plots (by 77%), but more closely mir- rored fluctuations in the untreated control plots. These methods were effective for monitoring and suppressing S. papuana populations in localized natural areas in the Waianae Mountain Range
The Diverse Stellar Populations of the W3 Star Forming Complex
An 800 sq-arcmin mosaic image of the W3 star forming complex obtained with
the Chandra X-ray Observatory gives a valuable new view of the spatial
structure of its young stellar populations. The Chandra image reveals about
1300 faint X-ray sources, most of which are PMS stars in the cloud. Some, but
not all, of the high-mass stars producing hypercompact and ultracompact H II
(UCHII) regions are also seen, as reported in a previous study.
The Chandra images reveal three dramatically different embedded stellar
populations. The W3 Main cluster extends over 7 pc with about 900 X-ray stars
in a nearly-spherical distribution centered on the well-studied UCHII regions
and high-mass protostars. The cluster surrounding the prototypical UCHII region
W3(OH) shows a much smaller (<0.6 pc), asymmetrical, and clumpy distribution of
about 50 PMS stars. The massive star ionizing the W3 North H II region is
completely isolated without any accompanying PMS stars. In W3 Main, the
inferred ages of the widely distributed PMS stars are significantly older than
the inferred ages of the central OB stars illuminating the UCHIIs. We suggest
that different formation mechanisms are necessary to explain the diversity of
the W3 stellar populations: cluster-wide gravitational collapse with delayed OB
star formation in W3 Main, collect-and-collapse triggering by shock fronts in
W3(OH), and a runaway O star or isolated massive star formation in W3 North.Comment: To appear in the Astrophysical Journal. 21 pages, 5 figures. A
version with high-quality figures is available at
http://www.astro.psu.edu/users/edf/W3_Chandra.pd
Neural Dynamics in Parkinsonian Brain:The Boundary Between Synchronized and Nonsynchronized Dynamics
Synchronous oscillatory dynamics is frequently observed in the human brain.
We analyze the fine temporal structure of phase-locking in a realistic network
model and match it with the experimental data from parkinsonian patients. We
show that the experimentally observed intermittent synchrony can be generated
just by moderately increased coupling strength in the basal ganglia circuits
due to the lack of dopamine. Comparison of the experimental and modeling data
suggest that brain activity in Parkinson's disease resides in the large
boundary region between synchronized and nonsynchronized dynamics. Being on the
edge of synchrony may allow for easy formation of transient neuronal
assemblies
Young Stellar Population of the Bright-Rimmed Clouds BRC 5, BRC 7 and BRC 39
Bright-rimmed clouds (BRCs), illuminated and shaped by nearby OB stars, are
potential sites of recent/ongoing star formation. Here we present an optical
and infrared photometric study of three BRCs: BRC 5, BRC 7 and BRC 39 to obtain
a census of the young stellar population, thereby inferring the star formation
scenario, in these regions. In each BRC, the Class I sources are found to be
located mostly near the bright rim or inside the cloud, whereas the Class II
sources are preferentially outside, with younger sources closer to the rim.
This provides strong support to sequential star formation triggered by
radiation driven implosion due to the UV radiation. Moreover, each BRC contains
a small group of young stars being revealed at its head, as the next-generation
stars. In particular, the young stars at the heads of BRC 5 and BRC 7 are found
to be intermediate/high mass stars, which, under proper conditions, may
themselves trigger further star birth, thereby propagating star formation out
to long distances.Comment: 30 pages, 7 Figures, 6 Tables, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Young stellar population and ongoing star formation in the HII complex Sh2-252
In this paper an extensive survey of the star forming complex Sh2-252 has
been undertaken with an aim to explore its hidden young stellar population as
well as to understand the structure and star formation history. This complex is
composed of five embedded clusters associated with the sub-regions A, C, E, NGC
2175s and Teu 136. Using 2MASS-NIR and Spitzer-IRAC, MIPS photometry we
identified 577 young stellar objects (YSOs), of which, 163 are Class I, 400 are
Class II and 14 are transition disk YSOs. Spatial distribution of the candidate
YSOs shows that they are mostly clustered around the sub-regions in the western
half of the complex, suggesting enhanced star formation activity towards its
west. Using the spectral energy distribution and optical colour-magnitude
diagram based age analyses, we derived probable evolutionary status of the
sub-regions of Sh2-252. Our analysis shows that the region A is the youngest (~
0.5 Myr), the regions B, C and E are of similar evolutionary stage (~ 1-2 Myr)
and the clusters NGC 2175s and Teu 136 are slightly evolved (~ 2-3 Myr).
Morphology of the region in the 1.1 mm map shows a semi-circular shaped
molecular shell composed of several clumps and YSOs bordering the western
ionization front of Sh2-252. Our analyses suggest that next generation star
formation is currently under way along this border and that possibly
fragmentation of the matter collected during the expansion of the HII region as
one of the major processes responsible for such stars. We observed the densest
concentration of YSOs (mostly Class I, ~ 0.5 Myr) at the western outskirts of
the complex, within a molecular clump associated with water and methanol masers
and we suggest that it is indeed a site of cluster formation at a very early
evolutionary stage, sandwiched between the two relatively evolved CHII regions
A and B.Comment: 19 pages, 13 figures, Accepted for publication in MNRA
Multiwavelength Study of NGC 281 Region
We present a multiwavelength study of the NGC 281 complex which contains the
young cluster IC 1590 at the center, using deep wide-field optical UBVI_c
photometry, slitless spectroscopy along with archival data sets in the
near-infrared (NIR) and X-ray. The extent of IC 1590 is estimated to be ~6.5
pc. The cluster region shows a relatively small amount of differential
reddening. The majority of the identified young stellar objects (YSOs) are low
mass PMS stars having age <1-2 Myr and mass 0.5-3.5 M_\odot. The slope (\Gamma)
of the mass function for IC 1590, in the mass range 2 < M/M_\odot \le 54, is
found to be -1.11+-0.15. The slope of the K-band luminosity function
(0.37+-0.07) is similar to the average value (~0.4) reported for young
clusters. The distribution of gas and dust obtained from the IRAS, CO and radio
maps indicates clumpy structures around the central cluster. The radial
distribution of the young stellar objects, their ages, \Delta(H-K) NIR-excess,
and the fraction of classical T Tauri stars suggest triggered star formation at
the periphery of the cluster region. However, deeper optical, NIR and MIR
observations are needed to have a conclusive view of star formation scenario in
the region. The properties of the Class 0/I and Class II sources detected by
using the Spitzer mid-infrared observations indicate that a majority of the
Class II sources are X-ray emitting stars, whereas X-ray emission is absent
from the Class 0/I sources. The spatial distribution of Class 0/I and Class II
sources reveals the presence of three sub-clusters in the NGC 281 West region.Comment: 29 pages, 21 figures and 11 tables, Accepted for the publication in
PAS
Low-mass young stellar population and star formation history of the cluster IC 1805 in the W4 H{\sc ii} region
W4 is a giant H{\sc ii} region ionized by the OB stars of the cluster
IC~1805. The H{\sc ii} region/cluster complex has been a subject of numerous
investigations as it is an excellent laboratory for studying the feedback
effect of massive stars on the surrounding region. However, the low-mass
stellar content of the cluster IC~1805 remains poorly studied till now. With
the aim to unravel the low-mass stellar population of the cluster, we present
the results of a multiwavelength study based on deep optical data obtained with
the Canada-France-Hawaii Telescope, infrared data from 2MASS, Space
Telescope and X-ray data from Space Telescope. The present optical
dataset is complete enough to detect stars down to 0.2~M, which is the
deepest optical observations so far for the cluster. We identified 384
candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within
the cluster using various colour-colour and colour-magnitude diagrams. We
inferred the mean age of the identified YSOs to be 2.5 Myr and mass in
the range 0.3 - 2.5 M. The mass function of our YSO sample has a power
law index of -1.23 0.23, close to the Salpeter value (-1.35), and
consistent with those of other star-forming complexes. We explored the disk
evolution of the cluster members and found that the diskless sources are
relatively older compared to the disk bearing YSO candidates. We examined the
effect of high-mass stars on the circumstellar disks and found that within
uncertainties, the influence of massive stars on the disk fraction seems to be
insignificant. We also studied the spatial correlation of the YSOs with the
distribution of gas and dust of the complex to conclude that IC 1805 would have
formed in a large filamentary cloud.Comment: Accepted for publication in MNRAS; 34 pages, 10 figure
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