215 research outputs found
Outcomes For Street Children and Youth Under Multidisciplinary Care in a Drop-In Centre in Tegucigalpa, Honduras
BACKGROUND: There is little evidence to describe the feasibility and outcomes of services for the care of street children and youth in low-income countries. AIMS: To describe the outcomes of a multidisciplinary case management approach delivered in a drop-in centre for street children and youth. METHODS: A longitudinal study of street children and youth followed in an urban drop-in centre. Four hundred (400) street children and youth received a multidisciplinary case management therapeutic package based on the community reinforcement approach. The main outcomes were changes in psychological distress, substance abuse and social situation scores. RESULTS: The median follow-up time for the cohort was 18 months. There were reductions in the levels of psychological distress (p = 0.0001) and substance abuse (p ≤ 0.0001) in the cohort as well as an improvement in the social situation of street children and youth (p = 0.0001). There was a main effect of gender (p < 0.001) and a significant interaction of gender over time (p < 0.001) on improvements in levels of psychological distress. Survival analysis showed that the probability of remaining on substances at 12 months was 0.76 (95% CI: 0.69-0.81) and 0.51 (95% CI: 0.42-0.59) at 24 months. At 12 months, fewer female patients remained using substances compared to male (p < 0.01). CONCLUSION: To be most effective, programmes and strategies for children and youth in street situations in developing countries should target both their health and social needs
Service engagement in interventions for street-connected children and young people: a summary of evidence supplementing a recent Cochrane–Campbell review
Abstract
Background This paper builds on a Cochrane–Campbell systematic review of interventions that reduce harms and promote reintegration in street-connected children and young people focusing on intervention outcomes. The aim of the present analysis is to explore questions raised in the systematic review over the potential role of service engagement in mediating outcomes of relevant interventions.
Objective The paper summarises engagement-related findings from quantitative intervention evaluations with street-connected populations of children and young people, as reported by study authors. It seeks to contribute to theoretical and methodological understandings of service engagement with street-connected youth populations and to highlight gaps in current knowledge.
Methods Drawing on the original search for the Cochrane–Campbell review, we rescreened search results in our database and included quantitative findings if relevant to our current research questions, regardless of study design. Additionally, we sought new study publications from authors whose work was included in the original systematic review. The discussion explores relevant data from five studies included in the original systematic review, ten studies excluded from the review, and two studies published after the completion of the review.
Results The measures of service engagement in the included studies focused on treatment attendance, ‘level of engagement’, and service satisfaction. Evidence on the impact of service engagement on other outcomes in interventions for street-connected children and young people was limited. Available data on the predictors and impact of service engagement were mixed and appear not to provide robust support for common hypotheses in the relevant context
The Initial Mass Function and Disk Frequency of the Rho Ophiuchi Cloud: An Extinction-Limited Sample
We have completed an optical spectroscopic survey of an unbiased,
extinction-limited sample of candidate young stars covering 1.3 square degrees
of the Rho Ophiuchi star forming region. While infrared, X-ray, and optical
surveys of the cloud have identified many young stellar objects (YSOs), these
surveys are biased towards particular stages of stellar evolution and are not
optimal for studies of the disk frequency and initial mass function.We have
obtained over 300 optical spectra to help identify 135 association members
based on the presence of H-alpha in emission, lithium absorption, X-ray
emission, a mid-infrared excess, a common proper motion, reflection nebulosity,
and/or extinction considerations. Spectral types along with R and I band
photometry were used to derive effective temperatures and bolometric
luminosities for association members to compare with theoretical tracks and
isochrones for pre-main-sequence stars. An average age of 3.1 Myr is derived
for this population which is intermediate between that of objects embedded in
the cloud core of Rho Ophiuchi and low mass stars in the Upper Scorpius
subgroup. Consistent with this age we find a circumstellar disk frequency of
27% plus or minus 5%. We also constructed an initial mass function for an
extinction-limited sample of 123 YSOs (A_v less than or equal to 8 mag), which
is consistent with the field star initial mass function for YSOs with masses >
0.2 M_sun. There may be a deficit of brown dwarfs but this result relies on
completeness corrections and requires confirmation.Comment: 46 pages, 7 figures, 4 table
Oph 1622-2405: Not a Planetary-Mass Binary
We present an analysis of the mass and age of the young low-mass binary Oph
1622-2405. Using resolved optical spectroscopy of the binary, we measure
spectral types of M7.25+/-0.25 and M8.75+/-0.25 for the A and B components,
respectively. We show that our spectra are inconsistent with the spectral types
of M9 and M9.5-L0 from Jayawardhana & Ivanov and M9+/-0.5 and M9.5+/-0.5 from
Close and coworkers. Based on our spectral types and the theoretical
evolutionary models of Chabrier and Baraffe, we estimate masses of 0.055 and
0.019 Msun for Oph 1622-2405A and B, which are significantly higher than the
values of 0.013 and 0.007 Msun derived by Jayawardhana & Ivanov and above the
range of masses observed for extrasolar planets (M<=0.015 Msun). Planet-like
mass estimates are further contradicted by our demonstration that Oph
1622-2405A is only slightly later (by 0.5 subclass) than the composite of the
young eclipsing binary brown dwarf 2M 0535-0546, whose components have
dynamical masses of 0.034 and 0.054 Msun. To constrain the age of Oph
1622-2405, we compare the strengths of gravity-sensitive absorption lines in
optical and near-infrared spectra of the primary to lines in field dwarfs (>1
Gyr) and members of Taurus (~1 Myr) and Upper Scorpius (~5 Myr). The line
strengths for Oph 1622-2405A are inconsistent with membership in Ophiuchus (<1
Myr) and instead indicate an age similar to that of Upper Sco, which is
agreement with a similar analysis performed by Close and coworkers. We conclude
that Oph 1622-2405 is part of an older population in Sco-Cen, perhaps Upper Sco
itself.Comment: The Astrophysical Journal, in pres
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
A Distributed Population of Low Mass Pre-Main Sequence Stars near the Taurus Molecular Clouds
We present a drift scan survey covering a ~5 deg by 50 deg region toward the
southern portion of the Taurus-Auriga molecular cloud. Data taken in the B,R,I
filters with the Quest-2 camera on the Palomar 48-inch telescope were combined
with 2MASS near-infrared photometry to select candidate young stars. Follow-up
optical spectroscopy of 190 candidates led to identification of 42 new low mass
pre-main sequence stars with spectral types M4-M8, of which approximately half
exhibit surface gravity signatures similar to known Taurus stars while the
other half exhibit surface gravity signatures similar to members of the
somewhat older Upper Sco, TW Hya and Beta Pic associations. The pre-main
sequence stars are spread over ~35 deg, and many are located well outside of
previously explored regions. From assessment of the spatial and proper motion
distributions, we argue that the new pre-main sequence stars identified far
from the clouds cannot have originated from the vicinity of the 1-2 Myr-old
subclusters which contain the bulk of the identified Taurus members, but
instead represent a newly-identified area of recent star-formation near the
clouds.Comment: Accepted for publication in AJ. 13 pages including 9 figures (2 in
color) and 1 table. A separate file tabA1.ps contains a hard copy of a second
table which will be published in electronic form onl
Are There Age Spreads in Star Forming Regions?
A luminosity spread at a given effective temperature is ubiquitously seen in
the Hertzsprung-Russell (HR) diagrams of young star forming regions and often
interpreted in terms of a prolonged period (>=10 Myr) of star formation. I
review the evidence that the observed luminosity spreads are genuine and not
caused by astrophysical sources of scatter. I then address whether the
luminosity spreads necessarily imply large age spreads, by comparing HR diagram
ages with ages from independent clocks such as stellar rotation rate, the
presence of circumstellar material and lithium depletion. I argue that whilst
there probably is a true luminosity dispersion, there is little evidence to
support age spreads larger than a few Myr. This paradox could be resolved by
brief periods of rapid accretion during the class I pre main-sequence phase.Comment: To appear in the proceedings of JENAM10: Star Clusters in the Era of
Large Surveys, 8 page
The low-mass Initial Mass Function in the Orion Nebula cluster based on HST/NICMOS III imaging
We present deep HST/NICMOS Camera 3 F110W and F160W imaging of a 26'x33',
corresponding to 3.1pcx3.8pc, non-contiguous field towards the Orion Nebula
Cluster (ONC). The main aim is to determine the ratio of low--mass stars to
brown dwarfs for the cluster as a function of radius out to a radial distance
of 1.5pc. The sensitivity of the data outside the nebulous central region is
F160W=21.0 mag, significantly deeper than previous studies of the region over a
comparable area. We create an extinction limited sample and determine the ratio
of low-mass stars (0.08-1Msun) to brown dwarfs (0.02-0.08Msun and
0.03-0.08Msun) for the cluster as a whole and for several annuli. The ratio
found for the cluster within a radius of 1.5pc is
R(02)=N(0.08-1Msun)/N(0.02-0.08Msun)=1.7+-0.2, and
R(03)=N(0.08-1Msun)/N(0.03-0.08Msun)=2.4+-0.2, after correcting for field
stars. The ratio for the central 0.3pcx0.3pc region down to 0.03Msun was
previously found to be R(03)=3.3+0.8-0.7, suggesting the low-mass content of
the cluster is mass segregated. We discuss the implications of a gradient in
the ratio of stars to brown dwarfs in the ONC in the context of previous
measurements of the cluster and for other nearby star forming regions. We
further discuss the current evidence for variations in the low-mass IMF and
primordial mass segregation.Comment: Accepted to A&
Multi-fibre optical spectroscopy of low-mass stars and brown dwarfs in Upper Sco
We have obtained multi-fibre intermediate-resolution optical spectroscopy of
94 photometric and proper motion selected low-mass star and brown dwarf
candidates in Upper Sco with AAT/AAOmega. We have estimated the spectral types
and measured the equivalent widths of youth and gravity diagnostic features to
confirm the spectroscopic membership of about 95% of the candidates extracted
from 6.5 square degrees in Upper Sco. We also detect lithium in the spectra
with the highest signal-to-noise, consolidating our conclusions about their
youth. Furthermore, we derive an estimate of our selections using spectroscopic
data obtained for a large number of stars falling into the instrument's
field-of-view. We have estimated the effective temperatures and masses for each
new spectroscopic member using the latest evolutionary models available for
low-mass stars and brown dwarfs. Combining the current optical spectroscopy
presented here with near-infrared spectroscopy obtained for the faintest
photometric candidates, we confirm the shape and slope of our earlier
photometric mass function. The luminosity function drawn from the spectroscopic
sample of 113 USco members peaks at around M6 and is flat at later spectral
type. We may detect the presence of the M7/M8 gap in the luminosity function as
a result of the dust properties in substellar atmospheres. The mass function
may peak at 0.2 Msun and is quite flat in the substellar regime. We observe a
possible excess of cool low-mass brown dwarfs compared to IC 348 and the
extrapolation of the field mass functions, supporting the original hypothesis
that Upper Sco may possess an excess of brown dwarfs. This result shows that
the selection of photometric candidates based on five band photometry available
from the UKIDSS GCS and complemented partially by proper motions can lead to a
good representation of the spectroscopic mass function (abridged).Comment: Accepted by A&A: 18 pages with 9 figures and 3 tables in main, 2
figures and 4 tables in Appendices. Some tables in electronic forma
Population analysis of open clusters: radii and mass segregation
Aims: Based on our well-determined sample of open clusters in the all-sky
catalogue ASCC-2.5 we derive new linear sizes of some 600 clusters, and
investigate the effect of mass segregation of stars in open clusters. Methods:
Using statistical methods, we study the distribution of linear sizes as a
function of spatial position and cluster age. We also examine statistically the
distribution of stars of different masses within clusters as a function of the
cluster age. Results: No significant dependence of the cluster size on location
in the Galaxy is detected for younger clusters (< 200 Myr), whereas older
clusters inside the solar orbit turned out to be, on average, smaller than
outside. Also, small old clusters are preferentially found close to the
Galactic plane, whereas larger ones more frequently live farther away from the
plane and at larger Galactocentric distances. For clusters with (V - M_V) <
10.5, a clear dependence of the apparent radius on age has been detected: the
cluster radii decrease by a factor of about 2 from an age of 10 Myr to an age
of 1 Gyr. A detailed analysis shows that this observed effect can be explained
by mass segregation and does not necessarily reflect a real decrease of cluster
radii. We found evidence for the latter for the majority of clusters older than
30 Myr. Among the youngest clusters (between 5 and 30 Myr), there are some
clusters with a significant grade of mass segregation, whereas some others show
no segregation at all. At a cluster age between 50 and 100 Myrs, the
distribution of stars of different masses becomes more regular over cluster
area. In older clusters the evolution of the massive stars is the most
prominent effect we observe.Comment: 14 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
- …