57 research outputs found
Models for Pop I stars: implications for age determinations
Starting from a few topical astrophysical questions which require the
knowledge of the age of Pop I stars, we discuss the needed precision on the age
in order to make progresses in these areas of research. Then we review the
effects of various inputs of the stellar models on the age determination and
try to identify those affecting the most the lifetimes of stars.Comment: 10 pages, 6 figures, 2 tables, IAU Symp. 258, D. Soderblom et al. ed
The Effects of Stellar Rotation. I. Impact on the Ionizing Spectra and Integrated Properties of Stellar Populations
We present a sample of synthetic massive stellar populations created using
the Starburst99 evolutionary synthesis code and new sets of stellar
evolutionary tracks, including one set that adopts a detailed treatment of
rotation. Using the outputs of the Starburst99 code, we compare the
populations' integrated properties, including ionizing radiation fields,
bolometric luminosities, and colors. With these comparisons we are able to
probe the specific effects of rotation on the properties of a stellar
population. We find that a population of rotating stars produces a much harder
ionizing radiation field and a higher bolometric luminosity, changes that are
primarily attributable to the effects of rotational mixing on the lifetimes,
luminosities, effective temperatures, and mass loss rates of massive stars. We
consider the implications of the profound effects that rotation can have on a
stellar population, and discuss the importance of refining stellar evolutionary
models for future work in the study of extragalactic, and particularly
high-redshift, stellar populations.Comment: 13 pages, 8 figures; accepted for publication in the Astrophysical
Journa
Red Supergiants in the Andromeda Galaxy (M31)
Red supergiants are a short-lived stage in the evolution of moderately
massive stars (10-25Mo), and as such their location in the H-R diagram provides
an exacting test of stellar evolutionary models. Since massive star evolution
is strongly affected by the amount of mass-loss a star suffers, and since the
mass-loss rates depend upon metallicity, it is highly desirable to study the
physical properties of these stars in galaxies of various metallicities. Here
we identify a sample of red supergiants in M31 (the most metal-rich of the
Local Group galaxies) and derive their physical properties by fitting MARCS
atmosphere models to moderate resolution optical spectroscopy, and from V-K
photometry.Comment: Accepted for publication in the Astrophysical Journa
Models for Massive Stellar Populations with Rotation
We present and discuss evolutionary synthesis models for massive stellar
populations generated with the Starburst99 code in combination with a new set
of stellar evolution models accounting for rotation. The new stellar evolution
models were compiled from several data releases of the Geneva group and cover
heavy-element abundances ranging from twice solar to one fifth solar. The
evolution models were computed for rotation velocities on the zero-age
main-sequence of 0 and 300 km/s and with the latest revision of stellar
mass-loss rates. Since the mass coverage is incomplete, in particular at
non-solar chemical composition, our parameter study is still preliminary and
must be viewed as exploratory. Stellar population properties computed with
Starburst99 and the new evolution models show some marked differences in
comparison with models obtained using earlier tracks. Since individual stars
now tend to be more luminous and bluer when on the blue side of the
Hertzsprung-Russell diagram, the populations mirror this trend. For instance,
increases by factors of two or more are found for the light-to-mass ratios at
ultraviolet to near-infrared wavelengths, as well as for the output of hydrogen
ionizing photons. If these results are confirmed once the evolution models have
matured, recalibrations of certain star-formation and initial mass function
indicators will be required.Comment: Accepted for publication in Ap
Targeted Proteomics Allows Quantification of Ethylene Receptors and Reveals SlETR3 Accumulation in Never-Ripe Tomatoes
Ethylene regulates fruit ripening and several plant functions (germination, plant growth, plant-microbe interactions). Protein quantification of ethylene receptors (ETRs) is essential to study their functions, but is impaired by low resolution tools such as antibodies that are mostly nonspecific, or the lack of sensitivity of shotgun proteomic approaches. We developed a targeted proteomic method, to quantify low-abundance proteins such as ETRs, and coupled this to mRNAs analyses, in two tomato lines: Wild Type (WT) and Never-Ripe (NR) which is insensitive to ethylene because of a gain-of-function mutation in ETR3. We obtained mRNA and protein abundance profiles for each ETR over the fruit development period. Despite a limiting number of replicates, we propose Pearson correlations between mRNA and protein profiles as interesting indicators to discriminate the two genotypes: such correlations are mostly positive in the WT and are affected by the NR mutation. The influence of putative post-transcriptional and post-translational changes are discussed. In NR fruits, the observed accumulation of the mutated ETR3 protein between ripening stages (Mature Green and Breaker + 8 days) may be a cause of NR tomatoes to stay orange. The label-free quantitative proteomics analysis of membrane proteins, concomitant to Parallel Reaction Monitoring analysis, may be a resource to study changes over tomato fruit development. These results could lead to studies about ETR subfunctions and interconnections over fruit development. Variations of RNA-protein correlations may open new fields of research in ETR regulation. Finally, similar approaches may be developed to study ETRs in whole plant development and plant-microorganism interactions
The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCS
stellar atmosphere models to determine the effective temperatures of 74
Galactic red supergiants. From these we find a new effective temperature scale
that is significantly warmer than those in the literature. We show that this
temperature scale, along with the newly derived bolometric corrections, gives
much better agreement between our red supergiants and stellar evolutionary
tracks. This agreement provides an independent verification of our new
temperature scale. The combination of effective temperature and bolometric
luminosities allows us to calculate stellar radii; the coolest and most
luminous stars have radii of roughly 1500 solar radii (7 AU), in excellent
accordance with the largest stellar radii predicted from current evolutionary
theory. We find that similar results are obtained for the effective
temperatures and bolometric luminosities using only the de-reddened V-K colors,
providing a powerful demonstration of the self-consistency of the MARCS models.Comment: 32 pages, 16 figures; Accepted by the Astrophysical Journa
Can hippocampal neurites and growth cones climb over obstacles?
Guidance molecules, such as Sema3A or Netrin-1, can induce growth cone (GC) repulsion or attraction in the presence of a flat surface, but very little is known of the action of guidance molecules in the presence of obstacles. Therefore we combined chemical and mechanical cues by applying a steady Netrin-1 stream to the GCs of dissociated hippocampal neurons plated on polydimethylsiloxane (PDMS) surfaces patterned with lines 2 \ub5m wide, with 4 \ub5m period and with a height varying from 100 to 600 nm. GC turning experiments performed 24 hours after plating showed that filopodia crawl over these lines within minutes. These filopodia do not show staining for the adhesion marker Paxillin. GCs and neurites crawl over lines 100 nm high, but less frequently and on a longer time scale over lines higher than 300 nm; neurites never crawl over lines 600 nm high. When neurons are grown for 3 days over patterned surfaces, also neurites can cross lines 300 nm and 600 nm high, grow parallel to and on top of these lines and express Paxillin. Axons - selectively stained with SMI 312 - do not differ from dendrites in their ability to cross these lines. Our results show that highly motile structures such as filopodia climb over high obstacle in response to chemical cues, but larger neuronal structures are less prompt and require hours or days to climb similar obstacles
Le mérycisme ou rumination humaine, une entité rare chez l'adulte : diagnostic et nosologie
Vergleich von 968 Patienten mit intrakraniellen Aneurysmen und polyzystischer Nierenerkrankung aus der @neurIST Datenbank, der Kuopio Kohorte und einem Review der Literatur zu PKD-Patienten
- …