552 research outputs found
Difficulties Associated with Stepparenting as Predictors of Remarital Satisfaction and Adjustment
As a result of high divorce and remarriage rates, stepfamilies have become commonplace in society. Researchers and clinicians have suggested that stepchildren can positively and negatively affect remarriage quality. Despite the increasing literature on stepfamilies, few studies have comparatively researched specific stepparenting difficulties as they affect marital satisfaction. Utilizing a sample of newlyweds, this study examines fourteen stepparenting related issues, as measured by the stepparenting subscale of the Questionnaire for Couples in Stepfamilies, and their relationship to marital satisfaction and adjustment
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The ACS Survey Of Galactic Globular Clusters. VI. NGC 6366: A Heavily Stripped Galactic Globular Cluster
We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic globular clusters (GCs) to construct a color-magnitude diagram for the bulge cluster, NGC 6366. The luminosity function derived from those data extends to M(F606W) similar to 9, or masses of similar to 0.3 M(circle dot). Unlike most GCs, the mass function peaks near the main-sequence turnoff with significantly fewer low-mass stars even after correction for completeness and mass segregation. Using a multimass King model, we extrapolate the global cluster behavior and find the global mass function to be poorly matched by a power law, with a particular deficit of stars with masses between 0.5 and 0.7 M(circle dot). We briefly discuss this interesting anomaly within the context of tidal stripping.NASA GO-10775, 5-26555Space Telescope Science InstituteInstituto de Astrofisica de Canarias P3-94Ministry of Education and Science of the Kingdom of Spain AYA-2008-67913Astronom
The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy
We present new Hubble Space Telescope photometry of the massive globular
cluster M54 (NGC 6715) and the superposed core of the tidally disrupted
Sagittarius (Sgr) dSph galaxy as part of the ACS Survey of Galactic Globular
Clusters. Our deep (F606W~26.5), high-precision photometry yields an
unprecedentedly detailed color-magnitude diagram showing the extended blue
horizontal branch and multiple main sequences of the M54+Sgr system. The
distance and reddening to M54 are revised usingboth isochrone and main-sequence
fitting to (m-M)_0=17.27 and E(B-V)=0.15. Preliminary assessment finds the
M54+Sgr field to be dominated by the old metal-poor populations of Sgr and the
globular cluster. Multiple turnoffs indicate the presence of at least two
intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H]=-0.4
to -0.6. We also clearly show, for the first time, a prominent, 2.3 Gyr old Sgr
population of near-solar abundance. A trace population of even younger (0.1-0.8
Gyr old), more metal-rich ([Fe/H]\sim0.6) stars is also indicated. The Sgr
age-metallicity relation is consistent with a closed-box model and multiple
(4-5) star formation bursts over the entire life of the satellite, including
the time since Sgr began disrupting.Comment: Accepted to ApJ Letter; 11 pages, 2 figures; figure 1 uploaded as
jpg; paper in ApJ format with full-resolution figures available at:
http://www.astro.ufl.edu/~ata/public_hstgc/paperIV/paperIV.p
Brain charts for the human lifespan
Over the past few decades, neuroimaging has become a ubiquitous tool in basic
research and clinical studies of the human brain. However, no reference standards
currently exist to quantify individual diferences in neuroimaging metrics over time,
in contrast to growth charts for anthropometric traits such as height and weight1
.
Here we assemble an interactive open resource to benchmark brain morphology
derived from any current or future sample of MRI data (http://www.brainchart.io/).
With the goal of basing these reference charts on the largest and most inclusive
dataset available, acknowledging limitations due to known biases of MRI studies
relative to the diversity of the global population, we aggregated 123,984 MRI scans,
across more than 100 primary studies, from 101,457 human participants between 115
days post-conception to 100 years of age. MRI metrics were quantifed by centile
scores, relative to non-linear trajectories2
of brain structural changes, and rates of
change, over the lifespan. Brain charts identifed previously unreported neurodevelo pmental milestones3
, showed high stability of individuals across longitudinal
assessments, and demonstrated robustness to technical and methodological
diferences between primary studies. Centile scores showed increased heritability
compared with non-centiled MRI phenotypes, and provided a standardized measure
of atypical brain structure that revealed patterns of neuroanatomical variation across
neurological and psychiatric disorders. In summary, brain charts are an essential step
towards robust quantifcation of individual variation benchmarked to normative
trajectories in multiple, commonly used neuroimaging phenotypes
The ACS Survey of Galactic Globular Clusters. IX. Horizontal Branch Morphology and the Second Parameter Phenomenon
The horizontal branch (HB) morphology of globular clusters (GCs) is most
strongly influenced by metallicity. The second parameter phenomenon
acknowledges that metallicity alone is not enough to describe the HB morphology
of all GCs. In particular, the outer Galactic halo contains GCs with redder HBs
at a given metallicity than are found inside the Solar circle. Thus, at least a
second parameter is required to characterize HB morphology. Here we analyze the
median color difference between the HB and the red giant branch (RGB), d(V-I),
measured from HST ACS photometry of 60 GCs within ~20 kpc of the Galactic
Center. Analysis of this homogeneous data set reveals that, after the influence
of metallicity has been removed, the correlation between d(V-I) and age is
stronger than that of any other parameter considered. Expanding the sample to
include HST photometry of the 6 most distant Galactic GCs lends additional
support to the correlation between d(V-I) and age. This result is robust with
respect to the adopted metallicity scale and the method of age determination,
but must bear the caveat that high quality, detailed abundance information is
not available for a significant fraction of the sample. When a subset of GCs
with similar metallicities and ages are considered, a correlation between
d(V-I) and central luminosity density is exposed. With respect to the existence
of GCs with anomalously red HBs at a given metallicity, we conclude that age is
the second parameter and central density is most likely the third. Important
problems related to HB morphology in GCs, notably multi-modal distributions and
faint blue tails, remain to be explained. (Abridged)Comment: Accepted for publication in ApJ; 49 pages, 19 figure
The ACS Survey of Galactic Globular Clusters. II. Stellar Evolution Tracks, Isochrones, Luminosity Functions, and Synthetic Horizontal-Branch Models
The ACS Survey of Galactic Globular Clusters, an HST Treasury Project, will
deliver high quality, homogeneous photometry of 65 globular clusters. This
paper introduces a new collection of stellar evolution tracks and isochrones
suitable for analyzing the ACS Survey data. Stellar evolution models were
computed at [Fe/H]= -2.5, -2.0, -1.5, -1.0, -0.5, and 0; [alpha/Fe]= -0.2, 0,
0.2, 0.4, 0.6, and 0.8; and three initial He abundances for masses from 0.1 to
1.8 Msun and ages from 2 to 15 Gyr. Each isochrone spans a wide range in
luminosity from Mv~14 up to the tip of the red giant branch. These are
complemented by a set of He-burning tracks that extend from the zero age
horizontal branch to the onset of thermal pulsations on the asymptotic giant
branch. In addition, a set of computer programs are provided that make it
possible to interpolate the isochrones in [Fe/H], generate luminosity functions
from the isochrones, and create synthetic horizontal branch models. The tracks
and isochrones have been converted to the observational plane with two
different color-Teff transformations, one synthetic and one semi-empirical, in
ground-based B, V, and I, and F606W and F814W for both ACS-WFC and WFPC2
systems. All models and programs presented in this paper are available from
http://stellar.dartmouth.edu/~models/Comment: 46 pages, 12 figures, AJ in press; figures 11 and 12 are reduced in
siz
The ACS Survey of Galactic Globular Clusters XI: The Three-Dimensional Orientation of the Sagittarius Dwarf Spheroidal Galaxy and its Globular Clusters
We use observations from the ACS study of Galactic globular clusters to
investigate the spatial distribution of the inner regions of the disrupting
Sagittarius dwarf spheroidal galaxy (Sgr). We combine previously published
analyses of four Sgr member clusters located near or in the Sgr core (M54, Arp
2, Terzan 7 and Terzan 8) with a new analysis of diffuse Sgr material
identified in the background of five low-latitude Galactic bulge clusters (NGC
6624, 6637, 6652, 6681 and 6809) observed as part of the ACS survey. By
comparing the bulge cluster CMDs to our previous analysis of the M54/Sgr core,
we estimate distances to these background features. The combined data from four
Sgr member clusters and five Sgr background features provides nine independent
measures of the Sgr distance and, as a group, provide uniformly measured and
calibrated probes of different parts of the inner regions of Sgr spanning
twenty degrees over the face of the disrupting dwarf. This allows us, for the
first time, to constrain the three dimensional orientation of Sgr's disrupting
core and globular cluster system and compare that orientation to the
predictions of an N-body model of tidal disruption. The density and distance of
Sgr debris is consistent with models that favor a relatively high Sgr core mass
and a slightly greater distance (28-30 kpc, with a mean of 29.4 kpc). Our
analysis also suggests that M54 is in the foreground of Sgr by ~2 kpc,
projected on the center of the Sgr dSph. While this would imply a remarkable
alignment of the cluster and the Sgr nucleus along the line of sight, we can
not identify any systematic effect in our analysis that would falsely create
the measured 2 kpc separation. Finally, we find that the cluster Terzan 7 has
the most discrepant distance (25 kpc) among the four Sgr core clusters, which
may suggest a different dynamical history than the other Sgr core clusters.Comment: 41 pages, 16 figures, accepted to Ap
The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters without PreviousHubble Space Telescope Photometry
We present the first results of a large Advanced Camera for Surveys (ACS) survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N (signal-to-noise ratio) 10 for main-sequence stars with masses 0.2 M⊙ in a sample of globulars using the ACS Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, NGC 6779, NGC 5053, NGC 6144, Palomar 2, E3, Lyngå 7, Palomar 1, and NGC 6366. Our color-magnitude diagrams (CMDs) extend reliably from the horizontal branch to as much as 7 mag fainter than the main-sequence turnoff and represent the deepest CMDs published to date for these clusters. Using fiducial sequences for three standard clusters (M92, NGC 6752, and 47 Tuc) with well-known metallicities and distances, we perform main-sequence fitting on the target clusters in order to obtain estimates of their distances and reddenings. These comparisons, along with fitting the cluster main sequences to theoretical isochrones, yield ages for the target clusters. We find that the majority of the clusters have ages that are consistent with the standard clusters at their metallicities. The exceptions are E3, which appears ~2 Gyr younger than 47 Tuc, and Pal 1, which could be as much as 8 Gyr younger than 47 Tuc
Expression and trans-specific polymorphism of self-incompatibility RNases in Coffea (Rubiaceae)
Self-incompatibility (SI) is widespread in the angiosperms, but identifying the biochemical components of SI mechanisms has proven to be difficult in most lineages. Coffea (coffee; Rubiaceae) is a genus of old-world tropical understory trees in which the vast majority of diploid species utilize a mechanism of gametophytic self-incompatibility (GSI). The S-RNase GSI system was one of the first SI mechanisms to be biochemically characterized, and likely represents the ancestral Eudicot condition as evidenced by its functional characterization in both asterid (Solanaceae, Plantaginaceae) and rosid (Rosaceae) lineages. The S-RNase GSI mechanism employs the activity of class III RNase T2 proteins to terminate the growth of "self" pollen tubes. Here, we investigate the mechanism of Coffea GSI and specifically examine the potential for homology to S-RNase GSI by sequencing class III RNase T2 genes in populations of 14 African and Madagascan Coffea species and the closely related self-compatible species Psilanthus ebracteolatus. Phylogenetic analyses of these sequences aligned to a diverse sample of plant RNase T2 genes show that the Coffea genome contains at least three class III RNase T2 genes. Patterns of tissue-specific gene expression identify one of these RNase T2 genes as the putative Coffea S-RNase gene. We show that populations of SI Coffea are remarkably polymorphic for putative S-RNase alleles, and exhibit a persistent pattern of trans-specific polymorphism characteristic of all S-RNase genes previously isolated from GSI Eudicot lineages. We thus conclude that Coffea GSI is most likely homologous to the classic Eudicot S-RNase system, which was retained since the divergence of the Rubiaceae lineage from an ancient SI Eudicot ancestor, nearly 90 million years ago.United States National Science Foundation [0849186]; Society of Systematic Biologists; American Society of Plant Taxonomists; Duke University Graduate Schoolinfo:eu-repo/semantics/publishedVersio
The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
We present the first results of a large ACS Survey of Galactic globular
clusters. This Hubble Space Telescope (HST) Treasury project is designed to
obtain photometry with S/N > ~10 for main sequence stars with masses > ~0.2Msun
in a sample of globulars using the Advanced Camera for Surveys (ACS) Wide Field
Channel. Here we focus on clusters without previous HST imaging data. These
include NGC 5466, 6779, 5053, 6144, Palomar 2, E 3, Lynga 7, Palomar 1, and NGC
6366. Our CMDs extend reliably from the horizontal branch to as much as seven
magnitudes fainter than the main sequence turnoff and represent the deepest
CMDs published to-date for these clusters. Using fiducial sequences for three
standard clusters (M92, NGC 6752, and 47 Tuc) with well-known metallicities and
distances, we perform main sequence fitting on the target clusters in order to
obtain estimates of their distances and reddenings. These comparisons along
with fitting the cluster main sequences to theoretical isochrones yield ages
for the target clusters. We find that the majority of the clusters have ages
that are consistent with the standard clusters at their metallicities. The
exceptions are E 3 which appears ~2 Gyr younger than 47 Tuc, and Pal 1, which
could be as much as 8 Gyr younger than 47 Tuc.Comment: 22 pages, 29 figures, accepted for publication in The Astronomical
Journal, April 2007. High resolution version available at
http://www.astro.ufl.edu/~ata/GC_Treasury/Web_Page/publications.htm
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