4,145 research outputs found
Oxygen and Sodium Abundances in M13 (NGC 6205) Giants: Linking Globular Cluster Formation Scenarios, Deep Mixing, and Post-RGB Evolution
We present O, Na, and Fe abundances, as well as radial velocities, for 113
red giant branch (RGB) and asymptotic giant branch (AGB) stars in the globular
cluster M13. The abundances and velocities are based on spectra obtained with
the WIYN-Hydra spectrograph, and the observations range in luminosity from the
horizontal branch (HB) to RGB-tip. The results are examined in the context of
recent globular cluster formation scenarios. We find that M13 exhibits many key
characteristics that suggest its formation and chemical enrichment are
well-described by current models. Some of these observations include: the
central concentration of O-poor stars, the notable decrease in [O/Fe] (but
small increase in [Na/Fe]) with increasing luminosity that affects primarily
the "extreme" population, the small fraction of stars with halo-like
composition, and the paucity of O-poor AGB stars. In agreement with recent
work, we conclude that the most O-poor M13 giants are likely He-enriched and
that most (all?) O-poor RGB stars evolve to become extreme HB and AGB-manqu\'e
stars. In contrast, the "primordial" and "intermediate" population stars appear
to experience standard HB and AGB evolution.Comment: Accepted for publication in The Astrophysical Journal Letters. 18
pages; 3 figures; 1 tabl
Detailed Abundances for a Large Sample of Giant Stars in the Globular Cluster 47 Tucanae (NGC 104)
47 Tuc is an ideal target to study chemical evolution and GC formation in
massive more metal-rich GCs since is the closest, massive GC. We present
chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu in 164 red
giant branch (RGB) stars in the massive globular cluster 47 Tuc using spectra
obtained with both the Hydra multi-fiber spectrograph at the Blanco 4-m
telescope and the FLAMES multi-object spectrograph at the Very Large Telescope.
We find an average [Fe/H]=--0.790.09 dex, consistent with literature
values, as well as over-abundances of alpha-elements
([\alpha/\mbox{Fe}]\sim0.3 dex). The n-capture process elements indicate that
47 Tuc is r-process dominated ([Eu/La]=+0.24), and the light elements O, Na,
and Al exhibit star-to-star variations. The Na-O anti-correlation, a signature
typically seen in Galactic globular clusters, is present in 47 Tuc, and extends
to include a small number of stars with [O/Fe] \,--0.5. Additionally, the
[O/Na] ratios of our sample reveal that the cluster stars can be separated into
three distinct populations. A KS-test demonstrates that the O-poor/Na-rich
stars are more centrally concentrated than the O-rich/Na-poor stars. The
observed number and radial distribution of 47 Tuc's stellar populations, as
distinguished by their light element composition, agrees closely with the
results obtained from photometric data. We do not find evidence supporting a
strong Na-Al correlation in 47 Tuc, which is consistent with current models of
AGB nucleosynthesis yields.Comment: Accepted for publication in The Astrophysical Journa
NGC 7789: An Open Cluster Case Study
We have obtained high-resolution spectra of 32 giants in the open cluster NGC
7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore
differences in atmospheric parameters and elemental abundances caused by the
use of the linelist developed for the Gaia-ESO Survey (GES) compared to one
based on Arcturus used in our previous work. [Fe/H] values decrease when using
the GES linelist instead of the Arcturus-based linelist; these differences are
probably driven by systematically lower (~ -0.1 dex) GES surface gravities.
Using the GES linelist we determine abundances for 10 elements - Fe, Mg, Si,
Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity
[Fe/H] = 0.03 +/- 0.07 dex, in good agreement with literature values, and a
lower [Mg/Fe] abundance than has been reported before for this cluster (0.11
+/- 0.05 dex). We also find the neutron-capture element barium to be highly
enhanced - [Ba/Fe] = +0.48 +/- 0.08 - and disparate from cluster measurements
of neutron-capture elements La and Zr (-0.08 +/- 0.05 and 0.08 +/- 0.08,
respectively). This is in accordance with recent discoveries of supersolar Ba
enhancement in young clusters along with more modest enhancement of other
neutron-capture elements formed in similar environments.Comment: 15 pages, 9 figures, Table 1 typo fixe
Metallicity Distribution Functions, Radial Velocities, and Alpha Element Abundances in Three Off-Axis Bulge Fields
We present radial velocities and chemical abundance ratios of [Fe/H], [O/Fe],
[Si/Fe], and [Ca/Fe] for 264 red giant branch (RGB) stars in three Galactic
bulge off-axis fields located near (l,b)=(-5.5,-7), (-4,-9), and (+8.5,+9). The
results are based on equivalent width and spectrum synthesis analyses of
moderate resolution (R~18,000), high signal-to-noise ratio (S/N~75-300) spectra
obtained with the Hydra spectrographs on the Blanco 4m and WIYN 3.5m
telescopes. The targets were selected from the blue side of the giant branch to
avoid cool stars that would be strongly affected by CN and TiO; however, a
comparison of the color-metallicity distribution in literature samples suggests
our selection of bluer targets should not present a significant bias against
metal-rich stars. We find a full range in metallicity that spans
[Fe/H]\approx-1.5 to +0.5, and that, in accordance with the previously observed
minor-axis vertical metallicity gradient, the median [Fe/H] also declines with
increasing Galactic latitude in off-axis fields. The off-axis vertical [Fe/H]
gradient in the southern bulge is estimated to be ~0.4 dex/kpc. The (+8.5,+9)
field exhibits a higher than expected metallicity, with a median [Fe/H]=-0.23,
that might be related to a stronger presence of the X--shaped bulge structure
along that line-of-sight. All fields exhibit an identical, strong decrease in
velocity dispersion with increasing metallicity that is consistent with
observations in similar minor-axis outer bulge fields. Additionally, the
[O/Fe], [Si/Fe], and [Ca/Fe] versus [Fe/H] trends are identical among our three
fields, and are in good agreement with past bulge studies. [abridged]Comment: Accepted for Publication in the Astrophysical Journal; 120 pages
(main text ends on page 24); 22 figures (figures end on page 46); 6 tables;
electronic versions of the tables can be made available upon request to
author C. Johnso
Verification of Successful Kainic Acid Injections in a Temporal Lobe Epilepsy Mouse Model
Temporal lobe epilepsy (TLE) is the most prominent form of partial epilepsy in adults. Reproductive endocrine comorbidities appear in patients with TLE at significantly higher rates than in the general population. These comorbidities include polycystic ovary syndrome, hypothalamic amenorrhea, hyperandrogenism, irregular menstrual cycle, lower testosterone levels, hypogonadism, erectile dysfunction, and decreased semen motility. It is believed that gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus play an important role in the development of these comorbidities. The kainic acid (KA) mouse model is used to study epilepsy-associated changes in GnRH neurophysiology. Our lab recently observed that the activity of GnRH neurons is altered in KA-injected mice (Li et al., eNeuro 2018). To ensure validity of the data, we must verify the success of all KA injections as indicated by the presence of sclerosis and/or gliosis in the hippocampus. Nissl (Cresyl violet) staining is used to visually verify the presence of sclerosis. This research seeks to determine if all KA injections effectively trigger seizures and later development of hippocampal damage and to identify effectiveness of the different methods of verification
AGB Sodium Abundances in the Globular Cluster 47 Tucanae (NGC 104)
A recent analysis comparing the [Na/Fe] distributions of red giant branch
(RGB) and asymptotic giant branch (AGB) stars in the Galactic globular cluster
NGC 6752 found that the ratio of Na-poor to Na-rich stars changes from 30:70 on
the RGB to 100:0 on the AGB. The surprising paucity of Na-rich stars on the AGB
in NGC 6752 warrants additional investigations to determine if the failure of a
significant fraction of stars to ascend the AGB is an attribute common to all
globular clusters. Therefore, we present radial velocities, [Fe/H], and [Na/Fe]
abundances for 35 AGB stars in the Galactic globular cluster 47 Tucanae (47
Tuc; NGC 104), and compare the AGB [Na/Fe] distribution with a similar RGB
sample published previously. The abundances and velocities were derived from
high resolution spectra obtained with the Michigan/Magellan Fiber System (M2FS)
and MSpec spectrograph on the Magellan-Clay 6.5m telescope. We find the average
heliocentric radial velocity and [Fe/H] values to be =-18.56 km s^-1
(sigma=10.21 km s^-1) and =-0.68 (sigma=0.08), respectively, in
agreement with previous literature estimates. The average [Na/Fe] abundance is
0.12 dex lower in the 47 Tuc AGB sample compared to the RGB sample, and the
ratio of Na-poor to Na-rich stars is 63:37 on the AGB and 45:55 on the RGB.
However, in contrast to NGC 6752, the two 47 Tuc populations have nearly
identical [Na/Fe] dispersion and interquartile range values. The data presented
here suggest that only a small fraction <20% of Na-rich stars in 47 Tuc may
fail to ascend the AGB. Regardless of the cause for the lower average [Na/Fe]
abundance in AGB stars, we find that Na-poor stars and at least some Na-rich
stars in 47 Tuc evolve through the early AGB phase. [abridged]Comment: Accepted for publication in the Astronomical Journal; 15 pages; 8
figures; 4 table
Caryoscope: An Open Source Java application for viewing microarray data in a genomic context
BACKGROUND: Microarray-based comparative genome hybridization experiments generate data that can be mapped onto the genome. These data are interpreted more easily when represented graphically in a genomic context. RESULTS: We have developed Caryoscope, which is an open source Java application for visualizing microarray data from array comparative genome hybridization experiments in a genomic context. Caryoscope can read General Feature Format files (GFF files), as well as comma- and tab-delimited files, that define the genomic positions of the microarray reporters for which data are obtained. The microarray data can be browsed using an interactive, zoomable interface, which helps users identify regions of chromosomal deletion or amplification. The graphical representation of the data can be exported in a number of graphic formats, including publication-quality formats such as PostScript. CONCLUSION: Caryoscope is a useful tool that can aid in the visualization, exploration and interpretation of microarray data in a genomic context
A closer look at parameter identifiability, model selection and handling of censored data with Bayesian Inference in mathematical models of tumour growth
Mathematical models (MMs) are a powerful tool to help us understand and
predict the dynamics of tumour growth under various conditions. In this work,
we use 5 MMs with an increasing number of parameters to explore how certain
(often overlooked) decisions in estimating parameters from data of experimental
tumour growth affect the outcome of the analysis. In particular, we propose a
framework for including tumour volume measurements that fall outside the upper
and lower limits of detection, which are normally discarded. We demonstrate how
excluding censored data results in an overestimation of the initial tumour
volume and the MM-predicted tumour volumes prior to the first measurements, and
an underestimation of the carrying capacity and the MM-predicted tumour volumes
beyond the latest measurable time points. We show in which way the choice of
prior for the MM parameters can impact the posterior distributions, and
illustrate that reporting the highest-likelihood parameters and their 95%
credible interval can lead to confusing or misleading interpretations. We hope
this work will encourage others to carefully consider choices made in parameter
estimation and to adopt the approaches we put forward herein.Comment: 15 pages, 7 figure
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