701 research outputs found
The Stellar Populations of the Carina Dwarf Spheroidal Galaxy: I. a New Color-Magnitude Diagram for the Giant and Horizontal Branches
We report on the first in a series of studies of the Carina dwarf spheroidal
galaxy, a nearby satellite of our Galaxy. Our two major results are: 1) precise
BI photometry (\sigma_{B-I} \simlt 0.05 for V \simlt 22) for 11,489 stars
in the Carina field, and 2) the detection of two, morphologically distinct,
horizontal branches, which confirms that star formation in Carina occurred in
two well-separated episodes. The old horizontal branch and RR Lyrae instability
strip belong to a > 10 Gyr stellar population, while the populous red-clump
horizontal branch belongs to an approximately 6 Gyr stellar population. We
derive a distance modulus for Carina from the apparent
magnitudes of the old horizontal branch and the tip of the red giant branch,
and discuss modifications to the previously estimated distance, total
magnitude, and stellar ages. Using the color of the red giant branch, we
estimate the metallicities of the younger and older populations to be [Fe/H] =
-2.0 and -2.2, respectively.Comment: 18 pages, 9 figures, uses AAS LaTex macros, PostScript figures
available through anonymous ftp, accepted for publication in the Astronomical
Journal, DAO-tsh94-
The Effects of Age on Red Giant Metallicities Derived from the Near-Infrared Ca II Triplet
We have obtained spectra with resolution 2.5 Angstroms in the region
7500-9500 Angstroms for 116 red giants in 5 Galactic globular clusters and 6
old open clusters (5 with published metallicities, and one previously
unmeasured). The signal-to-noise ranges from 20 to 85. We measure the
equivalent widths of the infrared Ca II triplet absorption lines in each stars
and compare to cluster metallicities taken from the literature. With globular
cluster abundances on the Carretta & Gratton scale, and open cluster abundances
taken from the compilation of Friel and collaborators, we find a linear
relation between [Fe/H] and Ca II line strength spanning the range -2 < [Fe/H]
< -0.2 and ages from 2.5 - 13 Gyr. No evidence for an age effect on the
metallicity calibration is observed. Using this calibration, we find the
metallicity of the old open cluster Trumpler 5 to be [Fe/H] = -0.56 +/-0.11.
Considering the 10 clusters of known metallicity shifted to a common distance
and reddening, we find that the additional metallicity error introduced by the
variation of horizontal branch/red clump magnitude with metallicity and age is
of order +/-0.05 dex, which can be neglected in comparison to the intrinsic
scatter in our method. The results are discussed in the context of abundance
determinations for red giants in Local Group galaxies.Comment: Accepted by MNRAS; 21 pages in LaTeX MNRAS style, 6 tables, 6 figure
Deep proteogenomics; high throughput gene validation by multidimensional liquid chromatography and mass spectrometry of proteins from the fungal wheat pathogen Stagonospora nodorum
BACKGROUND: Stagonospora nodorum, a fungal ascomycete in the class dothideomycetes, is a
damaging pathogen of wheat. It is a model for necrotrophic fungi that cause necrotic symptoms via
the interaction of multiple effector proteins with cultivar-specific receptors. A draft genome
sequence and annotation was published in 2007. A second-pass gene prediction using a training set
of 795 fully EST-supported genes predicted a total of 10762 version 2 nuclear-encoded genes, with
an additional 5354 less reliable version 1 genes also retained.
RESULTS: In this study, we subjected soluble mycelial proteins to proteolysis followed by 2D LC
MALDI-MS/MS. Comparison of the detected peptides with the gene models validated 2134 genes.
62% of these genes (1324) were not supported by prior EST evidence. Of the 2134 validated genes,
all but 188 were version 2 annotations. Statistical analysis of the validated gene models revealed a
preponderance of cytoplasmic and nuclear localised proteins, and proteins with intracellularassociated
GO terms. These statistical associations are consistent with the source of the peptides
used in the study. Comparison with a 6-frame translation of the S. nodorum genome assembly
confirmed 905 existing gene annotations (including 119 not previously confirmed) and provided
evidence supporting 144 genes with coding exon frameshift modifications, 604 genes with
extensions of coding exons into annotated introns or untranslated regions (UTRs), 3 new gene
annotations which were supported by tblastn to NR, and 44 potential new genes residing within
un-assembled regions of the genome.
CONCLUSION: We conclude that 2D LC MALDI-MS/MS is a powerful, rapid and economical tool to
aid in the annotation of fungal genomic assemblies
A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies
The Wisconsin H Alpha Mapper has been used to set the first deep upper limits
on the intensity of diffuse H alpha emission from warm ionized gas in the Local
Group dwarf spheroidal galaxies (dSphs) Draco and Ursa Minor. Assuming a
velocity dispersion of 15 km/s for the ionized gas, we set limits for the H
alpha intensity of less or equal to 0.024 Rayleighs and less or equal to 0.021
Rayleighs for the Draco and Ursa Minor dSphs, respectively, averaged over our 1
degree circular beam. Adopting a simple model for the ionized interstellar
medium, these limits translate to upper bounds on the mass of ionized gas of
approximately less than 10% of the stellar mass, or approximately 10 times the
upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa
Minor dSphs could contain substantial amounts of interstellar gas, equivalent
to all of the gas injected by dying stars since the end of their main star
forming episodes more than 8 Gyr in the past, without violating these limits on
the mass of ionized gas.Comment: 10 pages, 2 figures, AASTeX two-column format. Accepted for
publication in The Astrophysical Journa
The genome sequence of the biocontrol fungus Metarhizium anisopliae and comparative genomics of Metarhizium species.
Background: Metarhizium anisopliae is an important fungal biocontrol agent of insect pests of agricultural crops. Genomics can aid the successful commercialization of biopesticides by identification of key genes differentiating closely related species, selection of virulent microbial isolates which are amenable to industrial scale production and formulation and through the reduction of phenotypic variability. The genome of Metarhizium isolate ARSEF23 was recently published as a model for M. anisopliae, however phylogenetic analysis has since re-classified this isolate as M. robertsii. We present a new annotated genome sequence of M. anisopliae (isolate Ma69) and whole genome comparison to M. robertsii (ARSEF23) and M. acridum (CQMa 102).Results: Whole genome analysis of M. anisopliae indicates significant macrosynteny with M. robertsii but with some large genomic inversions. In comparison to M. acridum, the genome of M. anisopliae shares lower sequence homology. While alignments overall are co-linear, the genome of M. acridum is not contiguous enough to conclusively observe macrosynteny. Mating type gene analysis revealed both MAT1-1 and MAT1-2 genes present in M. anisopliae suggesting putative homothallism, despite having no known teleomorph, in contrast with the putatively heterothallic M. acridum isolate CQMa 102 (MAT1-2) and M. robertsii isolate ARSEF23 (altered MAT1-1). Repetitive DNA and RIP analysis revealed M. acridum to have twice the repetitive content of the other two species and M. anisopliae to be five times more RIP affected than M. robertsii. We also present an initial bioinformatic survey of candidate pathogenicity genes in M. anisopliae.Conclusions: The annotated genome of M. anisopliae is an important resource for the identification of virulence genes specific to M. anisopliae and development of species- and strain- specific assays. New insight into the possibility of homothallism and RIP affectedness has important implications for the development of M. anisopliae as a biopesticide as it may indicate the potential for greater inherent diversity in this species than the other species. This could present opportunities to select isolates with unique combinations of pathogenicity factors, or it may point to instability in the species, a negative attribute in a biopesticide
A novel mode of chromosomal evolution peculiar to filamentous Ascomycete fungi
Background: Gene loss, inversions, translocations, and other chromosomal rearrangements vary among species, resulting in different rates of structural genome evolution. Major chromosomal rearrangements are rare in most eukaryotes, giving large regions with the same genes in the same order and orientation across species. These regions of macrosynteny have been very useful for locating homologous genes in different species and to guide the assembly of genome sequences. Previous analyses in the fungi have indicated that macrosynteny is rare; instead, comparisons across species show no synteny or only microsyntenic regions encompassing usually five or fewer genes. To test the hypothesis that chromosomal evolution is different in the fungi compared to other eukaryotes, synteny was compared between species of the major fungal taxa. Results: These analyses identified a novel form of evolution in which genes are conserved within homologous chromosomes, but with randomized orders and orientations. This mode of evolution is designated mesosynteny, to differentiate it from micro-and macrosynteny seen in other organisms. Mesosynteny is an alternative evolutionary pathway very different from macrosyntenic conservation. Surprisingly, mesosynteny was not found in all fungal groups. Instead, mesosynteny appears to be restricted to filamentous Ascomycetes and was most striking between species in the Dothideomycetes. Conclusions: The existence of mesosynteny between relatively distantly related Ascomycetes could be explained by a high frequency of chromosomal inversions, but translocations must be extremely rare. The mechanism for this phenomenon is not known, but presumably involves generation of frequent inversions during meiosis
Dwarf Cepheids in the Carina Dwarf Spheroidal Galaxy
We have discovered 20 dwarf Cepheids (DC) in the Carina dSph galaxy from the
analysis of individual CCD images obtained for a deep photometric study of the
system. These short-period pulsating variable stars are by far the most distant
(~100 kpc) and faintest (V ~ 23.0) DCs known. The Carina DCs obey a
well-defined period-luminosity relation, allowing us to readily distinguish
between overtone and fundamental pulsators in nearly every case. Unlike RR Lyr
stars, the pulsation mode turns out to be uncorrelated with light-curve shape,
nor do the overtone pulsators tend towards shorter periods compared to the
fundamental pulsators. Using the period-luminosity (PL) relations from Nemec et
al. (1994 AJ, 108, 222) and McNamara (1995, AJ, 109, 1751), we derive (m-M)_0 =
20.06 +/- 0.12, for E(B-V) = 0.025 and [Fe/H] = -2.0, in good agreement with
recent, independent estimates of the distance/reddening of Carina. The error
reflects the uncertainties in the DC distance scale, and in the metallicity and
reddening of Carina. The frequency of DCs among upper main sequence stars in
Carina is approximately 3%. The ratio of dwarf Cepheids to RR Lyr stars in
Carina is 0.13 +/- 0.10, though this result is highly sensitive to the
star-formation history of Carina and the evolution of the Horizontal Branch. We
discuss how DCs may be useful to search effectively for substructure in the
Galactic halo out to Galactocentric distances of ~100 kpc.Comment: 20 pages of text, 7 figure
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