115 research outputs found
Constraints on the Stellar/Sub-stellar Mass Function in the Inner Orion Nebula Cluster
We present the results of a 0.5-0.9" FWHM imaging survey at K (2.2 micron)
and H (1.6 micron) covering 5.1' x 5.1' centered on Theta 1C Ori, the most
massive star in the Orion Nebula Cluster (ONC). At the age and distance of this
cluster, and in the absence of extinction, the hydrogen burning limit (0.08 Mo)
occurs at K~13.5 mag while an object of mass 0.02 Mo has K~16.2 mag. Our
photometry is complete for source detection at the 7 sigma level to K~17.5 mag
and thus is sensitive to objects as low-mass as 0.02 Mo seen through visual
extinction values as high as 10 magnitudes. We use the observed magnitudes,
colors, and star counts to constrain the shape of the inner ONC stellar mass
function across the hydrogen burning limit. After determining the stellar age
and near-infrared excess properties of the optically visible stars in this same
inner ONC region, we present a new technique that incorporates these
distributions when extracting the mass function from the observed density of
stars in the K-(H-K) diagram. We find that our data are inconsistent with a
mass function that rises across the stellar/sub-stellar boundary. Instead, we
find that the most likely form of the inner ONC mass function is one that rises
to a peak around 0.15 Mo, and then declines across the hydrogen-burning limit
with slope N(log M) ~ M^(0.57+/-0.05). We emphasize that our conclusions apply
to the inner 0.71 pc x 0.71 pc of the ONC only; they may not apply to the ONC
as a whole where some evidence for general mass segregation has been found.Comment: Accepted for publication in the Astrophysical Journal.
Preprints/tables also available at http://phobos.caltech.edu/~jmc/papers/onc
Improving access to emergency contraception pills through strengthening service delivery and demand generation: A systematic review of current evidence in low and middle-income countries
© 2014 Dawson et al. Objectives: Emergency contraception pills (ECP) are among the 13 essential commodities in the framework for action established by the UN Commission on Life-Saving Commodities for Women and Children. Despite having been on the market for nearly 20 years, a number of barriers still limit women's access to ECP in low- and middle-income countries (LMIC) including limited consumer knowledge and poor availability. This paper reports the results of a review to synthesise the current evidence on service delivery strategies to improve access to ECP.Methods: A narrative synthesis methodology was used to examine peer reviewed research literature (2003 to 2013) from diverse methodological traditions to provide critical insights into strategies to improve access from a service delivery perspective. The studies were appraised using established scoring systems and the findings of included papers thematically analysed and patterns mapped across all findings using concept mapping.Findings: Ten papers were included in the review. Despite limited research of adequate quality, promising strategies to improve access were identified including: advance provision of ECP; task shifting and sharing; intersectoral collaboration for sexual assault; m-health for information provision; and scale up through national family planning programs.Conclusion: There are a number of gaps in the research concerning service delivery and ECP in LMIC. These include a lack of knowledge concerning private/commercial sector contributions to improving access, the needs of vulnerable groups of women, approaches to enhancing intersectoral collaboration, evidence for social marketing models and investment cases for ECP
Workforce interventions to improve access to emergency contraception pills: A systematic review of current evidence in low- and middle-income countries and recommendations for improving performance Health systems and services in low and middle income settings
© 2015 Dawson et al.; licensee BioMed Central. Background: Emergency contraceptive pills (ECP) are one of the 13 essential commodities addressed by the UN Commission on Life-Saving Commodities for Women and Children. Although ECP have been available for 20 years, a number of barriers still limit women's access ECP in low and middle-income countries (LMIC). The workforce who prescribe or dispense ECP are diverse reflecting the varied contexts where ECP are available across the health, commercial and justice sectors and in the community. No reviews currently exist that examine the roles and experiences of the workforce that provide ECP in LMIC. Method: We present a narrative synthesis of research to: identify provider factors that facilitate and constraint access to ECP; assess the effectiveness of associated interventions and; explore associated health system issues in LMIC. A search of bibliographic databases, meta-indexes and websites was undertaken to retrieve peer reviewed and grey literature. Literature was screened and identified documents examined to appraise quality. Results: Thirty-seven documents were included in the review. Studies focused on formal health workers revealing knowledge gaps concerning the role of private sector and non-health providers who increasingly provide ECP. Data from the findings section in the documents were coded under 4 themes: provider knowledge; provider attitudes and beliefs; provider practice and provider training. The analysis revealed provider knowledge gaps, less than favourable attitudes and practice issues. The findings provide limited insight into products prescribed and/or dispensed, the frequency of provision, and information and advice offered to consumers. Pre and in-service training needs were noted. Conclusion: As the provision of ECPs shifts from the clinic-based health sector to increasing provision by the private sector, the limited understanding of provider performance and the practice gaps revealed in this review highlight the need to further examine provider performance to inform the development of appropriate workforce interventions. A standardized approach to assessing performance using agreed outcomes measures may serve to ensure a systematic way forward that is inclusive of the diverse workforce that deliver ECP. Recommendations are outlined to enhance the performance of providers to improve access to ECP. A framework is offered to help guide this process with indicators
First Detection of Millimeter Dust Emission from Brown Dwarf Disks
We report results from the first deep millimeter continuum survey targeting
Brown Dwarfs (BDs). The survey led to the first detection of cold dust in the
disks around two young BDs (CFHT-BD-Tau 4 and IC348 613), with deep JCMT and
IRAM observations reaching flux levels of a few mJy. The dust masses are
estimated to be a few Earth masses assuming the same dust opacities as usually
applied to TTauri stars.Comment: 5 pages, accepted for ApJ
An HST/WFPC2 Survey for Brown Dwarf Binaries in the alpha Per and the Pleiades Open Clusters
We present the results of a high-resolution imaging survey for brown dwarf
(BD) binaries in two open clusters. The observations were carried out with
WFPC2 onboard HST. Our sample consists of 8 BD candidates in the alpha Per
cluster and 25 BD candidates in the Pleiades. We have resolved 4 binaries in
the Pleiades with separations in the range 0".094--0".058, corresponding to
projected separations between 11.7~AU and 7.2~AU. No binaries were found among
the alpha Per targets. Three of the binaries have proper motions consistent
with cluster membership in the Pleiades cluster, and for one of them we report
the detection of Halpha in emission and LiI absorption obtained from
Keck~II/ESI spectroscopy. One of the binaries does not have a proper motion
consistent with Pleiades membership. We estimate that BD binaries wider than
12~AU are less frequent than 9% in the alphaPer and Pleiades clusters. This is
consistent with an extension to substellar masses of a trend observed among
stellar binaries: the maximum semimajor axis of binary systems decreases with
decreasing primary mass. We find a binary frequency of 2 binaries over 13 BDs
with confirmed proper motion membership in the Pleiades, corresponding to a
binary fraction of 15%(1 sigma error bar +15%/-5%). These binaries are limited
to the separation range 7-12~AU and their mass ratios are larger than 0.7. The
relatively high binary frequency (>10%), the bias to separations smaller than
about 15 AU and the trend to high mass ratios (q>0.7) are fundamental
properties of BDs. Current theories of BD formation do not appear to provide a
good description of all these properties.Comment: Accepted by ApJ (scheduled publication in volume 594, September 1,
2003
The Discovery of a Companion to the Very Cool Dwarf Gl~569~B with the Keck Adaptive Optics Facility
We report observations obtained with the Keck adaptive optics facility of the
nearby (d=9.8 pc) binary Gl~569. The system was known to be composed of a cool
primary (dM2) and a very cool secondary (dM8.5) with a separation of 5" (49
Astronomical Units). We have found that Gl~569~B is itself double with a
separation of only 0".1010".002 (1 Astronomical Unit). This detection
demonstrates the superb spatial resolution that can be achieved with adaptive
optics at Keck. The difference in brightness between Gl~569~B and the companion
is 0.5 magnitudes in the J, H and K' bands. Thus, both objects have
similarly red colors and very likely constitute a very low-mass binary system.
For reasonable assumptions about the age (0.12~Gyr--1.0~Gyr) and total mass of
the system (0.09~M--0.15~M), we estimate that the orbital
period is 3 years. Follow-up observations will allow us to obtain an
astrometric orbit solution and will yield direct dynamical masses that can
constrain evolutionary models of very low-mass stars and brown dwarfs
Optical Spectroscopy of the Surface Population of the rho Ophiuchi Molecular Cloud: The First Wave of Star Formation
We present the results of optical spectroscopy of 139 stars obtained with the
Hydra multi-object spectrograph. The objects extend over a 1.3 square degree
area surrounding the main cloud of the rho Oph complex. The objects were
selected from narrowband images to have H alpha in emission. Using the presence
of strong H alpha emission, lithium absorption, location in the
Hertzsprung-Russell diagram, or previously reported x-ray emission, we were
able to identify 88 objects as young stars associated with the cloud. Strong H
alpha emission was confirmed in 39 objects with line widths consistent with
their origin in magnetospheric accretion columns. Two of the strongest
emission-line objects are young, x-ray emitting brown dwarf candidates with M8
spectral types. Comparisons of the bolometric luminosities and effective
temperatures with theoretical models suggest a medianage for this population of
2.1 Myr which is signifcantly older than the ages derived for objects in the
cloud core. It appears that these stars formed contemporaneously with low mass
stars in the Upper Scorpius subgroup, likely triggered by massive stars in the
Upper-Centaurus subgroup.Comment: 35 pages of postscript which includes seven figures (some of which
are multi-panel) and four postscript tables. Astronomical Journal (in press
The orbit of the brown dwarf binary Gl 569B
We present photometric, astrometric and spectroscopic observations of the
nearby (9.8 pc) low-mass binary Gl 569Bab (in turn being a companion to the
early-M star Gl 569A), made with the Keck adaptive optics facility. Having
observed Gl 569Bab since August 1999, we are able to see orbital motion and to
determine the orbital parameters of the pair. We find the orbital period to be
892 +/- 25 days, the semi-major axis to be 0.90 +/- 0.02 AU, the eccentricity
to be 0.32 +/- 0.02 and the inclination of the system to be 34+/- 3 degrees
(1-sigma). The total mass is found to be 0.123 (-0.022/+0.027) Msun (3-sigma).
In addition, we have obtained low resolution (R=1500-1700) near-infrared
spectra of each of the components in the J- and K-bands. We determine the
spectral types of the objects to be M8.5V (Gl 569Ba) and M9V (Gl 569Bb) with an
uncertainty of half a subclass. We also present new J- and K-band photometry
which allows us to accurately place the objects in the HR diagram. Most likely
the binary system is comprised of two brown dwarfs with a mass ratio of 0.89
and with an age of approximately 300 Myr.Comment: Accepted for publication in ApJ, 28 pages, figures include
Membership and Multiplicity among Very Low-Mass Stars and Brown Dwarfs in the Pleiades Cluster
We present near-infrared photometry and optical spectroscopy of very low-mass
stars and brown dwarf candidates in the Pleiades open cluster. The membership
status of these objects is assessed. Eight objects out of 45 appear to be
non-members. A search for companions among 34 very low-mass Pleiades members
(M0.09 M) in high-spatial resolution images obtained with the
Hubble Space Telescope and the adaptive optics system of the
Canada-France-Hawaii telescope produced no resolved binaries with separations
larger than 0.2 arcsec (a ~ 27 AU; P ~ 444 years). Nevertheless, we find
evidence for a binary sequence in the color-magnitude diagrams, in agreement
with the results of Steele & Jameson (1995) for higher mass stars. We compare
the multiplicity statistics of the Pleiades very low-mass stars and brown
dwarfs with that of G and K-type main sequence stars in the solar neighborhood
(Duquennoy & Mayor 1991). We find that there is some evidence for a deficiency
of wide binary systems (separation >27 AU) among the Pleiades very low-mass
members. We briefly discuss how this result can fit with current scenarios of
brown dwarf formation. We correct the Pleiades substellar mass function for the
contamination of cluster non-members found in this work. We find a
contamination level of 33% among the brown dwarf candidates identified by
Bouvier et al. (1998). Assuming a power law IMF across the substellar boundary,
we find a slope dN/dM ~ M^{-0.53}, implying that the number of objects per mass
bin is still rising but the contribution to the total mass of the cluster is
declining in the brown dwarf regime.Comment: to be published in The Astrophysical Journa
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