33 research outputs found
Pulsation of the Lambda Bootis star HD 210111
CONTEXT. The Lambda Bootis stars are a small spectroscopic subgroup of
Population I A-type stars and show significant underabundances of metals. Many
are Delta Scuti pulsators.
AIMS. HD 210111 was selected for a detailed multisite pulsation study to
determine whether its pulsation properties differ from those of normal A stars.
METHODS. 262 hours of high-precision photometry were obtained at the SAAO and
SSO observatories.
RESULTS. 13 statistically significant pulsation frequencies were detected
with very small photometric amplitudes from 1 to 7 millimag in the visual. A
comparison with earlier 1994 measurements indicates a small increase in
amplitude. As a byproduct, one of the comparison stars, HD 210571, was
discovered to be a millimag variable with a frequency of 1.235 c/d and is
probably a new Gamma Doradus variable. The observed wide range of excited
frequencies from 12 to 30 c/d in HD 210111 can be explained with both the
single- and double-star hypothesis. HD 210111 is in a similar evolutionary
status to FG Vir, which also shows a wide range of excited frequencies with a
similar frequency spacing near 4 c/d. This is interpreted as successive radial
orders of the excited nonradial modes. In the double-star hypothesis previously
evoked for HD 210111, the low and the high frequencies originate in different
stars: here HD 210111 would resemble Theta^2 Tau.
CONCLUSIONS. The pulsation of the Lambda Bootis star HD 210111 does not
differ from that of normal Delta Scuti stars.Comment: 6 pages, 2 figures, 2 tables, submitted to A&
Towards ensemble asteroseismology of the young open clusters Chi Persei and NGC 6910
As a result of the variability survey in Chi Persei and NGC6910, the number
of Beta Cep stars that are members of these two open clusters is increased to
twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational
properties, in particular the frequency spectra, of Beta Cep stars in both
clusters and explain the differences in terms of the global parameters of the
clusters. We also indicate that the more complicated pattern of the variability
among B type stars in Chi Persei is very likely caused by higher rotational
velocities of stars in this cluster. We conclude that the sample of pulsating
stars in the two open clusters constitutes a very good starting point for the
ensemble asteroseismology of Beta Cep-type stars and maybe also for other
B-type pulsators.Comment: 4 pages, Astronomische Nachrichten, HELAS IV Conference, Arecife,
Lanzarote, Feb 2010, submitte
A photometric study of the southern Blazhko star SS For Unambiguous detection of quintuplet components
We present our analysis of photometric data in the Johnson B and V filter of
the southern Blazhko star SS For. In parallel, we analyzed the V observations
obtained with the ASAS-3 photometry of the star gathered between 2000 and 2008.
In the frequency spectra resulting from a Fourier analysis of our data, the
triplet structure is detectable up to high order, both in the B and V data.
Moreover, we find evidence for quintuplet components. We confirm from our data
that the modulation components decrease less steeply than the harmonics of the
main frequency. We derived the variations of the Fourier parameters quantifying
the light curve shape over the Blazhko cycle. There is good agreement between
the spectroscopic abundance and the metallicity determined from the Fourier
parameters of the average light curve. SS For is peculiar as a Blazhko star
because of its strong variations around minimum light.Comment: 15 pages, 14 figures, accepted for publication in MNRA
Photometric multi-site campaign on the open cluster NGC 884 I. Detection of the variable stars
CONTEXT: Recent progress in the seismic interpretation of field beta Cep
stars has resulted in improvements of the physics in the stellar structure and
evolution models of massive stars. Further asteroseismic constraints can be
obtained from studying ensembles of stars in a young open cluster, which all
have similar age, distance and chemical composition.
AIMS: To improve our comprehension of the beta Cep stars, we studied the
young open cluster NGC 884 to discover new B-type pulsators, besides the two
known beta Cep stars, and other variable stars.
METHODS: An extensive multi-site campaign was set up to gather accurate CCD
photometry time series in four filters (U, B, V, I) of a field of NGC884.
Fifteen different instruments collected almost 77500 CCD images in 1286 hours.
The images were calibrated and reduced to transform the CCD frames into
interpretable differential light curves. Various variability indicators and
frequency analyses were applied to detect variable stars in the field. Absolute
photometry was taken to deduce some general cluster and stellar properties.
RESULTS: We achieved an accuracy for the brightest stars of 5.7 mmag in V,
6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in the
amplitude spectra is 50 micromag in the V band. Our campaign confirms the
previously known pulsators, and we report more than one hundred new multi- and
mono-periodic B-, A- and F-type stars. Their interpretation in terms of
classical instability domains is not straightforward, pointing to imperfections
in theoretical instability computations. In addition, we have discovered six
new eclipsing binaries and four candidates as well as other irregular variable
stars in the observed field.Comment: Accepted for publication in Astronomy and Astrophysics, 21 pages, 14
figures, 4 tables. The full appendix is available at
http://www.ster.kuleuven.be/~sophies/Appendix.pdf (74 MB, 169 pages, 343
figures, 1 table
Evolution of pathogenicity and sexual reproduction in eight Candida genomes
Candida species are the most common cause of opportunistic fungal infection worldwide. Here we report the genome sequences of six Candida species and compare these and related pathogens and non-pathogens. There are significant expansions of cell wall, secreted and transporter gene families in pathogenic species, suggesting adaptations associated with virulence. Large genomic tracts are homozygous in three diploid species, possibly resulting from recent recombination events. Surprisingly, key components of the mating and meiosis pathways are missing from several species. These include major differences at the mating-type loci (MTL); Lodderomyces elongisporus lacks MTL, and components of the a1/2 cell identity determinant were lost in other species, raising questions about how mating and cell types are controlled. Analysis of the CUG leucine-to-serine genetic-code change reveals that 99% of ancestral CUG codons were erased and new ones arose elsewhere. Lastly, we revise the Candida albicans gene catalogue, identifying many new genes.publishe
The kinetochore receptor for the cohesin loading complex
Summary The ring-shaped cohesin complex brings together distant DNA domains to maintain, express, and segregate the genome. Establishing specific chromosomal linkages depends on cohesin recruitment to defined loci. One such locus is the budding yeast centromere, which is a paradigm for targeted cohesin loading. The kinetochore, a multiprotein complex that connects centromeres to microtubules, drives the recruitment of high levels of cohesin to link sister chromatids together. We have exploited this system to determine the mechanism of specific cohesin recruitment. We show that phosphorylation of the Ctf19 kinetochore protein by a conserved kinase, DDK, provides a binding site for the Scc2/4 cohesin loading complex, thereby directing cohesin loading to centromeres. A similar mechanism targets cohesin to chromosomes in vertebrates. These findings represent a complete molecular description of targeted cohesin loading, a phenomenon with wide-ranging importance in chromosome segregation and, in multicellular organisms, transcription regulation
European agricultural landscapes, common agricultural policy and ecosystem services: a review
Since the 1950s, intensification and scale enlargement of agriculture have changed agricultural landscapes across Europe. The intensification and scale enlargement of farming was initially driven by the large-scale application of synthetic fertilizers, mechanization and subsidies of the European Common Agricultural Policy (CAP). Then, after the 1990s, a further intensification and scale enlargement, and land abandonment in less favored areas was caused by globalization of commodity markets and CAP reforms. The landscape changes during the past six decades have changed the flows and values of ecosystem services. Here, we have reviewed the literature on agricultural policies and management, landscape structure and composition, and the contribution of ecosystem services to regional competitiveness. The objective was to define an analytical framework to determine and assess ecosystem services at the landscape scale. In contrast to natural ecosystems, ecosystem service flows and values in agricultural landscapes are often a result of interactions between agricultural management and ecological structures. We describe how land management by farmers and other land managers relates to landscape structure and composition. We also examine the influence of commodity markets and policies on the behavior of land managers. Additionally, we studied the influence of consumer demand on flows and values of the ecosystem services that originate from the agricultural landscape
A photometric study of the southern Blazhko star SS For: unambiguous detection of quintuplet components
We present our analysis of photometric data in the Johnson B and V filter of the southern Blazhko star SS For. In parallel, we analysed the V observations obtained with the All Sky Automated Survey-3 photometry of the star gathered between 2000 and 2008
Structure of Escherichia coli aspartate α-decarboxylase Asn72Ala: probing the role of Asn72 in pyruvoyl cofactor formation
The crystal structure of the Asn72Ala site-directed mutant of Escherichia coli aspartate α-decarboxylase (ADC) has been determined at 1.7 Å resolution. The refined structure is consistent with the presence of a hydrolysis product serine in the active site in place of the pyruvoyl group required for catalysis, which suggests that the role of Asn72 is to protect the ester formed during ADC activation from hydrolysis. In previously determined structures of activated ADC, including the wild type and other site-directed mutants, the C-terminal region of the protein is disordered, but in the Asn72Ala mutant these residues are ordered owing to an interaction with the active site of the neighbouring symmetry-related multimer