241 research outputs found
Post-AGB stars with hot circumstellar dust: binarity of the low-amplitude pulsators
While the first binary post-AGB stars were serendipitously discovered, the
distinct characteristics of their Spectral Energy Distribution (SED) allowed us
to launch a more systematic search for binaries. We selected post-AGB objects
which show a broad dust excess often starting already at H or K, pointing to
the presence of a gravitationally bound dusty disc in the system. We started a
very extensive multi-wavelength study of those systems and here we report on
our radial velocity and photometric monitoring results for six stars of early F
type, which are pulsators of small amplitude. To determine the radial velocity
of low signal-to-noise time-series, we constructed dedicated auto-correlation
masks. The radial velocity variations were subjected to detailed analysis to
differentiate between pulsational variability and variability due to orbital
motion. Finally orbital minimalisation was performed to constrain the orbital
elements. All of the six objects are binaries, with orbital periods ranging
from 120 to 1800 days. Five systems have non-circular orbits. The mass
functions range from 0.004 to 0.57 solar mass and the companions are likely
unevolved objects of (very) low initial mass. We argue that these binaries must
have been subject to severe binary interaction when the primary was a cool
supergiant. Although the origin of the circumstellar disc is not well
understood, the disc is generally believed to be formed during this strong
interaction phase. The eccentric orbits of these highly evolved objects remain
poorly understood. With the measured orbits and mass functions we conclude that
the circumbinary discs seem to have a major impact on the evolution of a
significant fraction of binary systems.Comment: 13 pages, 15 figures, accepted for Astronomy and Astrophysic
Detailed abundance study of four s-process enriched post-AGB stars in the Large Magellanic Cloud
AGB nucleosynthesis in the Large Magellanic Cloud. Detailed abundance analysis of the RV Tauri star MACHO47.2496.8
Context. Abundance analysis of post-AGB objects as probes of AGB
nucleosynthesis. Aims. A detailed photospheric abundance study is performed on
the carbon-rich post-AGB candidate MACHO47.2496.8 in the LMC. Methods.
High-resolution, high signal-to-noise ESO VLT-UVES spectra of MACHO47.2496.8
are analysed by performing detailed spectrum synthesis modelling using
state-of-the-art carbon-rich MARCS atmosphere models. Results. The spectrum of
MACHO47.2496.8 is not only dominated by bands of carbon bearing molecules, but
also by lines of atomic transitions of s-process elements. The metallicity of
[Fe/H]=-1.4 is surprisingly low for a field LMC star. The C/O ratio, however
difficult to quantify, is greater than 2, and the s-process enrichment is
large: the light s-process elements are enhanced by 1.2 dex compared to iron
([ls/Fe]=+1.2), while for the heavy s-process elements an even stronger
enrichment is measured: [hs/Fe]=+2.1. The lead abundance is comparable to the
[hs/Fe]. With its low intrinsic metallicity and its luminosity at the low end
of the carbon star luminosity function, the star represents likely the final
stage of a low initial mass star. Conclusions. The LMC RV Tauri star
MACHO47.2496.8 is highly carbon and s-process enriched, and is most probable a
genuine post-C(N-type) AGB star. This is the first detailed abundance analysis
of an extragalactic post-AGB star to date.Comment: 12 pages, 6 figures, accepted by A&
Alternative splicing in the fragile X gene <i>FMR1</i>
Human Molecular Genetics 2 pp. 399-404 (1993)The authors wish to note a mistake which was incorporated in figure 3 where both Asp and Asn were given the letter code N. A correct version of the figure and its legend is printed below.</p
Alternative splicing in the fragile X gene <i>FMR1</i>
Human Molecular Genetics 2 pp. 399-404 (1993)The authors wish to note a mistake which was incorporated in figure 3 where both Asp and Asn were given the letter code N. A correct version of the figure and its legend is printed below.</p
An Eco RI RFLP in the 5′ region of the human NF1 gene
Von Recklinghausen neurofibromatosis or type l neurofibromatosis (NF1), is one of the most common autosomal dominant disorders. NF1 is characterized by neurofibromas, café-au-lait spots and Lisch nodules of the iris. The NF1 gene is located in 17q11.2. The restriction fragment length polymorphism reported here will be useful in linkage analysis in NF1 families.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47634/1/439_2004_Article_BF00420953.pd
Choosing event-driven and daily HIV pre-exposure prophylaxis - data from two European PrEP demonstration projects among men who have sex with men
The puzzling dredge-up pattern in NGC 1978
Low-mass stars are element factories that efficiently release their products
in the final stages of their evolution by means of stellar winds. Since they
are large in number, they contribute significantly to the cosmic matter cycle.
To assess this contribution quantitatively, it is crucial to obtain a detailed
picture of the stellar interior, particularly with regard to nucleosynthesis
and mixing mechanisms. We seek to benchmark stellar evolutionary models of
low-mass stars. In particular, we measure the surface abundance of ^{12}C in
thermally pulsing AGB stars with well-known mass and metallicity, which can be
used to infer information about the onset and efficiency of the third
dredge-up. We recorded high-resolution near-infrared spectra of AGB stars in
the LMC cluster NGC 1978. The sample comprised both oxygen-rich and carbon-rich
stars, and is well-constrained in terms of the stellar mass, metallicity, and
age. We derived the C/O and ^{12}C/^{13}C ratio from the target spectra by a
comparison to synthetic spectra. Then, we compared the outcomes of stellar
evolutionary models with our measurements. The M stars in NGC 1978 show values
of C/O and ^{12}C/^{13}C that can best be explained with moderate extra-mixing
on the RGB coupled to a moderate oxygen enhancement in the chemical
composition. These oxygen-rich stars do not seem to have undergone third
dredge-up episodes (yet). The C stars show carbon-to-oxygen and carbon isotopic
ratios consistent with the occurrence of the third dredge-up. We did not find S
stars in this cluster. None of the theoretical schemes that we considered was
able to reproduce the observations appropriately. Instead, we discuss some
non-standard scenarios to explain the puzzling abundance pattern in NGC 1978.Comment: 16 pages, 9 figures, 4 tables, accepted for publication in A&A,
language revise
FRA2A is a CGG repeat expansion associated with silencing of AFF3
Folate-sensitive fragile sites (FSFS) are a rare cytogenetically visible subset of dynamic mutations. Of the eight molecularly characterized FSFS, four are associated with intellectual disability (ID). Cytogenetic expression results from CGG tri-nucleotide-repeat expansion mutation associated with local CpG hypermethylation and transcriptional silencing. The best studied is the FRAXA site in the FMR1 gene, where large expansions cause fragile X syndrome, the most common inherited ID syndrome. Here we studied three families with FRA2A expression at 2q11 associated with a wide spectrum of neurodevelopmental phenotypes. We identified a polymorphic CGG repeat in a conserved, brain-active alternative promoter of the AFF3 gene, an autosomal homolog of the X-linked AFF2/FMR2 gene: Expansion of the AFF2 CGG repeat causes FRAXE ID. We found that FRA2A-expressing individuals have mosaic expansions of the AFF3 CGG repeat in the range of several hundred repeat units. Moreover, bisulfite sequencing and pyrosequencing both suggest AFF3 promoter hypermethylation. cSNP-analysis demonstrates monoallelic expression of the AFF3 gene in FRA2A carriers thus predicting that FRA2A expression results in functional haploinsufficiency for AFF3 at least in a subset of tissues. By whole-mount in situ hybridization the mouse AFF3 ortholog shows strong regional expression in the developing brain, somites and limb buds in 9.5-12.5dpc mouse embryos. Our data suggest that there may be an association between FRA2A and a delay in the acquisition of motor and language skills in the families studied here. However, additional cases are required to firmly establish a causal relationship
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