19 research outputs found
Comparison of Convective Overshooting Models and Their Impact on Abundances from Integrated Light Spectroscopy of Young ( 3 Gyr) Star Clusters
As part of an ongoing program to measure detailed chemical abundances in
nearby galaxies, we use a sample of young to intermediate age clusters in the
Large Magellanic Cloud with ages of 10 Myr to 2 Gyr to evaluate the effect of
isochrone parameters, specifically core convective overshooting, on Fe
abundance results from high resolution, integrated light spectroscopy. In this
work we also obtain fiducial Fe abundances from high resolution spectroscopy of
the cluster individual member stars. We compare the Fe abundance results for
the individual stars to the results from isochrones and integrated light
spectroscopy to determine whether isochrones with convective overshooting
should be used in our integrated light analysis of young to intermediate age
(10 Myr -3 Gyr) star clusters. We find that when using the isochrones from the
Teramo group, we obtain more accurate results for young and intermediate age
clusters over the entire age range when using isochrones without convective
overshooting. While convective overshooting is not the only uncertain aspect of
stellar evolution, it is one of the most readily parametrized ingredients in
stellar evolution models, and thus important to evaluate for the specific
models used in our integrated light analysis. This work demonstrates that our
method for integrated light spectroscopy of star clusters can provide unique
tests for future constraints on stellar evolution models of young and
intermediate age clusters.Comment: 16 pages, accepted for publication in Ap
Detailed Chemical Abundances of Extragalactic Globular Clusters using High Resolution, Integrated Light Spectra.
Globular clusters (GCs) are luminous, observationally accessible objects that are
good tracers of the total star formation and evolutionary history of galaxies. We
present the first detailed chemical abundances for GCs in M31 using a new abundance analysis technique designed for high resolution, integrated light (IL) spectra
of GCs. This technique has recently been developed using a training set of old GCs
in the Milky Way (MW), and makes possible detailed chemical evolution studies of
distant galaxies, where high resolution abundance analysis of individual stars are not
obtainable. For the 5 M31 GCs presented here, we measure abundances of 14 elements: Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, and Ba. We find the M31 GCs have ages (>10 Gyr) and chemical properties similar to MW GCs, including an
enhancement in the α-elements Ca, Ti and Si of [α/Fe]∼+0.4.
In this thesis, we also further develop this IL abundance analysis method to include
GCs of ages 10 Myr-12 Gyrs using GCs in the Large Magellanic Cloud (LMC),
which contains the necessary sample of clusters over this wide age range. This work
demonstrates for the first time that this IL abundance analysis method can be used on clusters of all ages, and that ages can be constrained to within 1−2 Gyr for clusters with ages of ∼2 Gyr and within a few 100 Myr for clusters with ages <1 Gyr. We find that we can measure [Fe/H] in clusters with ages <12 Gyrs with similar or
only slightly larger uncertainties (0.1-0.25 dex) than those obtained for old GCs; the
slightly larger uncertainties are due to the rapid evolution in stellar populations at
these ages.
Using the LMC clusters, we also investigate the effects of statistical fluctuations
in the theoretical cluster stellar populations used in our analysis. We also develop
strategies to allow for statistical variations in these stellar populations, and find
that the stability of the Fe line abundance solution can provide tight constraints on
the appropriate theoretical stellar populations. Detailed chemical abundances of 22
elements are reported for six LMC clusters.Ph.D.Astronomy and AstrophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75989/1/jcolucci_1.pd
Globular Cluster Abundances from High-Resolution, Integrated-Light Spectroscopy. III. The Large Magellanic Cloud: Fe and Ages
In this paper we refine our method for the abundance analysis of high
resolution spectroscopy of the integrated light of unresolved globular clusters
(GCs). This method was previously demonstrated for the analysis of old (10
Gyr) Milky Way GCs. Here we extend the technique to young clusters using a
training set of 9 GCs in the Large Magellanic Cloud (LMC). Depending on the
signal-to-noise ratio of the data, we use 20-100 Fe lines per cluster to
successfully constrain the ages of old clusters to within a 5 Gyr range,
the ages of 2 Gyr clusters to a 1-2 Gyr range, and the ages of the
youngest clusters (0.05-1 Gyr) to a 200 Myr range. We also demonstrate
that we can measure [Fe/H] in clusters with any age less than 12 Gyrs with
similar or only slightly larger uncertainties (0.1-0.25 dex) than those
obtained for old Milky Way GCs (0.1 dex); the slightly larger uncertainties are
due to the rapid evolution in stellar populations at these ages. In this paper,
we present only Fe abundances and ages. In the next paper in this series, we
present our complete analysis of the elements for which we are able
to measure abundances. For several of the clusters in this sample, there are no
high resolution abundances in the literature from individual member stars; our
results are the first detailed chemical abundances available. The spectra used
in this paper were obtained at Las Campanas with the echelle on the du Pont
Telescope and with the MIKE spectrograph on the Magellan Clay Telescope.Comment: 34 pages, accepted for publication in Ap
Globular Cluster Abundances from High-Resolution, Integrated-Light Spectroscopy. IV. The Large Magellanic Cloud: , Fe-peak, Light, and Heavy Elements
We present detailed chemical abundances in 8 clusters in the Large Magellanic
Cloud (LMC). We measure abundances of 22 elements for clusters spanning a range
in age of 0.05 to 12 Gyr, providing a comprehensive picture of the chemical
enrichment and star formation history of the LMC. The abundances were obtained
from individual absorption lines using a new method for analysis of high
resolution (25,000) integrated light spectra of star clusters. This
method was developed and presented in Papers I, II, and III of this series. In
this paper, we develop an additional integrated light -minimization
spectral synthesis technique to facilitate measurement of weak (15 m\AA)
spectral lines and abundances in low signal-to-noise ratio data (S/N30).
Additionally, we supplement the integrated light abundance measurements with
detailed abundances that we measure for individual stars in the youngest
clusters (Age2 Gyr) in our sample. In both the integrated light and stellar
abundances we find evolution of [/Fe] with [Fe/H] and age. Fe-peak
abundance ratios are similar to those in the Milky Way, with the exception of
[Cu/Fe] and [Mn/Fe], which are sub-solar at high metallicities. The heavy
elements Ba, La, Nd, Sm, and Eu are significantly enhanced in the youngest
clusters. Also, the heavy to light s-process ratio is elevated relative to the
Milky Way ([Ba/Y]) and increases with decreasing age, indicating a
strong contribution of low-metallicity AGB star ejecta to the interstellar
medium throughout the later history of the LMC. We also find a correlation of
integrated light Na and Al abundances with cluster mass, in the sense that more
massive, older clusters are enriched in the light elements Na and Al with
respect to Fe, which implies that these clusters harbor star-to-star abundance
variations as is common in the Milky Way.Comment: 38 pages, Accepted for publication in the Astrophysical Journa
Discovery of Precursor LBV Outbursts in Two Recent Optical Transients: The Fitfully Variable Missing Links UGC 2773-OT and SN 2009ip
We present progenitor-star detections, light curves, and optical spectra of
SN2009ip and the 2009 optical transient in UGC2773 (U2773-OT), which were not
genuine SNe. Precursor variability in the decade before outburst indicates that
both of the progenitor stars were LBVs. Their pre-outburst light curves
resemble the S Doradus phases that preceded giant eruptions of eta Carinae and
SN1954J (V12 in NGC2403), with intermediate progenitor luminosities. HST
detections a decade before discovery indicate that the SN2009ip and U2773-OT
progenitors were supergiants with likely initial masses of 50-80 Msun and
\ga20 Msun, respectively. Both outbursts had spectra befitting known LBVs,
although in different physical states. SN 2009ip exhibited a hot LBV spectrum
with characteristic speeds of 550 km/s, plus faster material up to 5000 km/s,
resembling the slow Homunculus and fast blast wave of eta Carinae. U2773-OT
shows a forest of narrow absorption and emission lines comparable to that of S
Dor in its cool state, plus [CaII] emission and an IR excess indicative of
dust, similar to SN2008S and N300-OT. [CaII] emission is probably tied to a
dusty pre-outburst environment, and not the outburst mechanism. SN2009ip and
U2773-OT may provide a critical link between historical LBV eruptions, while
U2773-OT may provide a link between LBVs and SN2008S and N300-OT. Future
searches will uncover more examples of precursor LBV variability of this kind,
providing key clues that may help unravel the instability driving LBVs.Comment: 18 pages, 13 Figures, accepted AJ. added significant material while
revising after referee repor
Genome-wide association studies of autoimmune vitiligo identify 23 new risk loci and highlight key pathways and regulatory variants
Vitiligo is an autoimmune disease in which depigmented skin results from the destruction of melanocytes1, with epidemiological association with other autoimmune diseases2. In previous linkage and genome-wide association studies (GWAS1 and GWAS2), we identified 27 vitiligo susceptibility loci in patients of European ancestry. We carried out a third GWAS (GWAS3) in European-ancestry subjects, with augmented GWAS1 and GWAS2 controls, genome-wide imputation, and meta-analysis of all three GWAS, followed by an independent replication. The combined analyses, with 4,680 cases and 39,586 controls, identified 23 new significantly associated loci and 7 suggestive loci. Most encode immune and apoptotic regulators, with some also associated with other autoimmune diseases, as well as several melanocyte regulators. Bioinformatic analyses indicate a predominance of causal regulatory variation, some of which corresponds to expression quantitative trait loci (eQTLs) at these loci. Together, the identified genes provide a framework for the genetic architecture and pathobiology of vitiligo, highlight relationships with other autoimmune diseases and melanoma, and offer potential targets for treatment