856 research outputs found
A Case Study of Implementing Collaborative Student Support Teams to Support Students on the Path to High School Graduation
This research explores who is at risk of dropping out of high school and how collaborative Student Support Teams can contribute to students staying on track to graduate high school. The issue of student success is important because graduation is positively correlated with important life outcomes and ability to earn an adequate income in the labor market. For this paper, âat-risk studentsâ is defined as students considered in danger of not graduating, not being promoted, or not meeting other education-related goals. The research looks at high school dropout indicators and how the Collaborative Response Model contributes to student success in school. The results will inform the ways in which society, particularly education system support teams, can positively support youth who are at risk of early school leaving
Embedded Clusters and the IMF
Despite valiant efforts over nearly five decades, attempts to determine the
IMF over a complete mass range for galactic field stars and in open clusters
have proved difficult. Infrared imaging observations of extremely young
embedded clusters coupled with Monte Carlo modeling of their luminosity
functions are improving this situation and providing important new
contributions to our fundamental knowledge of the IMF and its universality in
both space and time.Comment: 6 pages, 2 figures to appear in "The IMF@50", Kluwer Academic Press,
eds. C. Corbelli, F. Palla, & Hans Zinnecke
Molecular basis for resistance of acanthamoeba tubulins to all major classes of antitubulin compounds
Tubulin is essential to eukaryotic cells and is targeted by several antineoplastics, herbicides, and antimicrobials. We demonstrate that Acanthamoeba spp. are resistant to five antimicrotubule compounds, unlike any other eukaryote studied so far. Resistance correlates with critical amino acid differences within the inhibitor binding sites of the tubulin heterodimers
The Star Formation Region NGC 6530: distance, ages and Initial Mass Function
We present astrometry and photometry, down to , of the very
young open cluster NGC6530, obtained from observations taken with the Wide
Field Imager camera at the MPG/ESO 2.2 m Telescope. Both the vs. and
the vs. color-magnitude diagrams (CMD) show the upper main sequence
dominated by very bright cluster stars, while, due to the high obscuration of
the giant molecular cloud surrounding the cluster, the blue envelopes of the
diagrams at are limited to the main sequence stars at the
distance of NGC6530. This particular structure of the NGC6530 CMD allows us to
conclude that its distance is about pc, significantly lower
than the previous determination of d=1800 pc. We have positionally matched our
optical catalog with the list of X-ray sources found in a Chandra-ACIS
observation, finding a total of 828 common stars, 90% of which are pre-main
sequence stars in NGC6530. Using evolutionary tracks of Siess et al. (2000)},
mass and age values are inferred for these stars. The median age of the cluster
is about 2.3 Myr; in the mass range (0.6--4.0), the Initial Mass
Function (IMF) shows a power law index , consistent with both
the Salpeter index (1.35), and with the index derived for other young clusters
; towards smaller masses the IMF shows a peak and then it starts to decrease.Comment: 32 pages, 13 ps figures, in press in Astronomy and Astrophysic
A Constraint on brown dwarf formation via ejection: radial variation of the stellar and substellar mass function of the young open cluster IC2391
Using the Wide Field Imager (WFI) at the ESO 2.2m telescope at La Silla and
the CPAPIR camera at the CTIO 1.5m telescope at Cerro Tololo, we have performed
an extensive, multiband photometric survey of the open cluster IC2391 (D~146pc,
age~50Myr, solar metallicity). Here we present the results from our photometric
survey and from a spectroscopic follow-up of the central part of the survey.Comment: 4 pages, 3 figures, to appear in the proceedings of the Cool Stars 15
conferenc
A multiwavelength study of embedded clusters in W5-east, NGC 7538, S235, S252 and S254-S258
articleWe present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538. Spitzer data is combined with NIR observations to identify and classify the young population while 12CO and 13CO observations are used to examine the parental molecular cloud. We detect in total 3021 young stellar objects (YSOs). Of those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material. We identify in total 41 embedded clusters containing between 52 and 73 perâcent of the YSOs. Clusters are in general non-virialized, turbulent and have star formation efficiencies between 5 and 50 perâcent. We compare the physical properties of embedded clusters harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc.This work is based in part on observations made with the Spitzer
Space Telescope, which is operated by the Jet Propulsion Laboratory,
Caltech, under a contract with NASA. Support for this work
was provided by NASA through a contract issued by JPL/Caltech.
We also thank NOAO for their student thesis support. The Five College
Radio Astronomy Observatory was supported by NSF grant
AST 0540852. CB is supported by an RCUK Fellowship at the University
of Exeter, UK. This work is based in part on the IRAC postBCD
processing software âIRACPROCâ developed by Mike Schuster,
Massimo Marengo and Brian Patten at the Smithsonian Astrophysical
Observatory. This research used the facilities of the Canadian
Astronomy Data Centre operated by the National Research Council
of Canada with the support of the Canadian Space Agency. This research
has made use of the NASA/ IPAC Infrared Science Archive,
which is operated by the Jet Propulsion Laboratory, California Institute
of Technology, under contract with the National Aeronautics
and Space Administration. We thank the Spanish MINECO
for funding support from grants CSD2009-00038, AYA2009-07304
and AYA2012-32032
The Initial Mass Function as given by the fragmentation
The dichotomy between a universal mass function (IMF) and a variable IMF
which depends on local physical parameters characterises observational and
theoretical stellar astronomy. In this contribution the available distributions
of probability are briefly reviewed. The physical nature of two of them, gamma
variate and lognormal, is then explained once the framework of the
fragmentation is introduced. Interpolating techniques are then applied to the
sample of the first 10 pc and to the open cluster NGC6649: in both cases
lognormal distribution produces the best fit. The three power law function has
also been investigated and visual comparison with an artificially generated
sample of 100000 stars suggests that the variations in the spectral index are
simply due to the small number of stars available in the observational sample.
In order to derive the sample of masses, a new formula that allows us to
express the mass as a function of the absolute magnitude and (B-V) for MAIN V,
GIANTS III and SUPERGIANTS I is derived.Comment: 6 pages 9 figure
The Initial Mass Function of the Orion Nebula Cluster across the H-burning limit
We present a new census of the Orion Nebula Cluster (ONC) over a large field
of view (>30'x30'), significantly increasing the known population of stellar
and substellar cluster members with precisely determined properties. We develop
and exploit a technique to determine stellar effective temperatures from
optical colors, nearly doubling the previously available number of objects with
effective temperature determinations in this benchmark cluster. Our technique
utilizes colors from deep photometry in the I-band and in two medium-band
filters at lambda~753 and 770nm, which accurately measure the depth of a
molecular feature present in the spectra of cool stars. From these colors we
can derive effective temperatures with a precision corresponding to better than
one-half spectral subtype, and importantly this precision is independent of the
extinction to the individual stars. Also, because this technique utilizes only
photometry redward of 750nm, the results are only mildly sensitive to optical
veiling produced by accretion. Completing our census with previously available
data, we place some 1750 sources in the Hertzsprung-Russel diagram and assign
masses and ages down to 0.02 solar masses. At faint luminosities, we detect a
large population of background sources which is easily separated in our
photometry from the bona fide cluster members. The resulting initial mass
function of the cluster has good completeness well into the substellar mass
range, and we find that it declines steeply with decreasing mass. This suggests
a deficiency of newly formed brown dwarfs in the cluster compared to the
Galactic disk population.Comment: 16 pages, 18 figures. Accepted for publication in The Astrophysical
Journa
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