236 research outputs found
A MiMeS analysis of the magnetic field and circumstellar environment of the weak-wind O9 sub-giant star HD 57682
I will review our recent analysis of the magnetic properties of the O9IV star
HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the
Canada-France-Hawaii telescope within the context of the Magnetism in Massive
Stars (MiMeS) Large Program. I discuss our most recent determination of the
rotational period from longitudinal magnetic field measurements and Halpha
variability - the latter obtained from over a decade's worth of professional
and amateur spectroscopic observations. Lastly, I will report on our
investigation of the magnetic field geometry and the effects of the field on
the circumstellar environment.Comment: 2 pages, 2 figures, IAUS272 - Active OB Stars: Structure, Evolution,
Mass Loss and Critical Limit
Of?p stars: a class of slowly rotating magnetic massive stars
Only 5 Of?p stars have been identified in the Galaxy. Of these, 3 have been
studied in detail, and within the past 5 years magnetic fields have been
detected in each of them. The observed magnetic and spectral characteristics
are indicative of organised magnetic fields, likely of fossil origin, confining
their supersonic stellar winds into dense, structured magnetospheres. The
systematic detection of magnetic fields in these stars strongly suggests that
the Of?p stars represent a general class of magnetic O-type stars.Comment: Proceedings of IAUS 272: Active OB star
Gene expression networks and cis-elements combinatorial models in soybean: circadian clock and drought responses.
The MiMeS Survey of Magnetism in Massive Stars: CNO surface abundances of Galactic O stars
The evolution of massive stars is still partly unconstrained. Mass,
metallicity, mass loss and rotation are the main drivers of stellar evolution.
Binarity and magnetic field may also significantly affect the fate of massive
stars. Our goal is to investigate the evolution of single O stars in the
Galaxy. For that, we use a sample of 74 objects comprising all luminosity
classes and spectral types from O4 to O9.7. We rely on optical spectroscopy
obtained in the context of the MiMeS survey of massive stars. We perform
spectral modelling with the code CMFGEN. We determine the surface properties of
the sample stars, with special emphasis on abundances of carbon, nitrogen and
oxygen. Most of our sample stars have initial masses in the range 20 to 50
Msun. We show that nitrogen is more enriched and carbon/oxygen more depleted in
supergiants than in dwarfs, with giants showing intermediate degrees of mixing.
CNO abundances are observed in the range of values predicted by nucleosynthesis
through the CNO cycle. More massive stars, within a given luminosity class,
appear to be more chemically enriched than lower mass stars. We compare our
results with predictions of three types of evolutionary models and show that,
for two sets of models, 80% of our sample can be explained by stellar evolution
including rotation. The effect of magnetism on surface abundances is
unconstrained. Our study indicates that, in the 20-50 Msun mass range, the
surface chemical abundances of most single O stars in the Galaxy are fairly
well accounted for by stellar evolution of rotating stars.Comment: 15 pages, 12 figures. Accepted in Astronomy & Astrophysic
Expression patterns of GmAP2/EREB-Like transcription factors involved in soybean responses to water deficit.
Soybean farming has faced several losses in productivity due to drought events in the last few decades. However, plants have molecular mechanisms to prevent and protect against water deficit injuries, and transcription factors play an important role in triggering different defense mechanisms. Understanding the expression patterns of transcription factors in response to water deficit and to environmental diurnal changes is very important for unveiling water deficit stress tolerance mechanisms. Here, we analyzed the expression patterns of ten APETALA2/Ethylene Responsive Element Binding-like (AP2/ EREB-like) transcription factors in two soybean genotypes (BR16: drought-sensitive; and Embrapa 48: drought-tolerant). According to phylogenetic and domain analyses, these genes can be included in the DREB and ERF subfamilies. We also analyzed a GmDRIP-like gene that encodes a DREB negative regulator. We detected the up-regulation of 9 GmAP2/EREB-like genes and identified transcriptional differences that were dependent on the levels of the stress applied and the tissue type analyzed (the expression of the GmDREB1F-like gene, for example, was four times higher in roots than in leaves). The GmDRIP-like gene was not induced by water deficit in BR16 during the longest periods of stress, but was significantly induced in Embrapa 48; this suggests a possible genetic/molecular difference between the responses of these cultivars to water deficit stress. Additionally, RNAseq gene expression analysis over a 24-h time course indicates that the expression patterns of several GmDREB-like genes are subject to oscillation over the course of the day, indicating a possible circadian regulation
Floração, frutificação e maturação de frutos de Arachis pintoi cv. BRS Mandobi em ambiente controlado.
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