The timing of cod spawning on the Scotian Shelf

We used results from the Scotian Shelf Ichtyoplankton Programme to describe the spatial and temporal distributions of cod eggs and larvae off the coast of Nova Scotia. Summer spawning is restricted to the waters along the Laurentian Channel. Eggs and/or larvae are found in the spring in all areas where spawning activities are detected. Late fall - early winter spawning takes place over several banks and along the southern coast of Nova Scotia. A match between the seasonal blooms and the time of spawning does not appear to be essential, although it might exist in the spring. Larval drift from spawning grounds to nursery grounds is apparently rare on the Scotlan Shelf. These findings are discussed with reference to the match-mismatch hypothesis of Cushing

The timing of cod spawning on the Scotian Shelf

We used results from the Scotian Shelf Ichtyoplankton Programme to describe the spatial and temporal distributions of cod eggs and larvae off the coast of Nova Scotia. Summer spawning is restricted to the waters along the Laurentian Channel. Eggs and/or larvae are found in the spring in all areas where spawning activities are detected. Late fall - early winter spawning takes place over several banks and along the southern coast of Nova Scotia. A match between the seasonal blooms and the time of spawning does not appear to be essential, although it might exist in the spring. Larval drift from spawning grounds to nursery grounds is apparently rare on the Scotlan Shelf. These findings are discussed with reference to the match-mismatch hypothesis of Cushing

Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions

Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion

In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions

A nearby young M dwarf with a wide, possibly planetary-mass companion

We present the identification of two previously known young objects in the solar neighbourhood as a likely very wide binary. TYC 9486-927-1, an active, rapidly rotating early-M dwarf, and 2MASS J21265040-8140293, a low-gravity L3 dwarf previously identified as candidate members of the $\sim$45 Myr old Tucana Horologium association (TucHor). An updated proper motion measurement of the L3 secondary, and a detailed analysis of the pair's kinematics in the context of known nearby, young stars, reveals that they share common proper motion and are likely bound. New observations and analyses reveal the primary exhibits Li 6708~\AA~absorption consistent with M dwarfs younger than TucHor but older than the $\sim$10 Myr TW Hydra association yielding an age range of 10-45 Myr. A revised kinematic analysis suggests the space motions and positions of the pair are closer to, but not entirely in agreement with, the $\sim$24 Myr old $\beta$ Pictoris moving group. This revised 10-45 Myr age range yields a mass range of 11.6--15 M$_J$ for the secondary. It is thus likely 2MASS J21265040-8140293short is the widest orbit planetary mass object known ($>$4500AU) and its estimated mass, age, spectral type, and $T_{eff}$ are similar to the well-studied planet $\beta$ Pictoris b. Because of their extreme separation and youth, this low-mass pair provide an interesting case study for very wide binary formation and evolution.Peer reviewedFinal Accepted Versio

Global X-ray properties of the O and B stars in Carina

The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the Lx/Lbol ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(Lx/Lbol) is -7.26 for single objects, with a dispersion of only 0.21dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the Lx/Lbol ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the Lx/Lbol ratio in the medium (1.0--2.5keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared to "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest amongst these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.Comment: 30 pages, 9 figures. Accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special Issue papers are available at http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at leas

Évolution de la dynamique moléculaire chez des enzymes d’une même famille

Problématique : L’utilisation d’enzymes en industrie et en pharmaceutique gagne en popularité comme alternative plus verte et efficace aux catalyseurs fonctionnant en solvants organiques. L’ingénierie de nouvelles réactions enzymatiques demeure difficile et inefficace dû à la difficulté de prédire les conséquences de l’ingénierie sur la structure, la fonction et la dynamique des protéines. Selon des articles récents, des mouvements moléculaires concertés favoriseraient la catalyse chez plusieurs enzymes, mais les mécanismes sous-jacents à cette flexibilité atomique restent nébuleux. Nous ignorons toujours si la séquence, la structure et/ou la fonction d’une protéine sont reliées à sa dynamique. La compréhension des phénomènes sous-jacents à la dynamique moléculaire pourrait faciliter l’ingénierie des protéines. Hypothèse : La dynamique d’une protéine est encodée par sa structure tertiaire et influence sa fonction. Des protéines ayant une structure et une fonction similaires devraient donc avoir une dynamique similaire. Méthodologie : Nous avons utilisé la RMN pour caractériser la dynamique moléculaire à l’échelle de la micro/milliseconde de protéines homologues appartenant à la même sous-famille de la superfamille des ribonucléases A, soit les RNases 3 des grands singes Pongo pygmaeus, Macaca fascicularis et l’humain. Résultats et conclusions : La dynamique moléculaire en l’absence de ligand des RNases 3 de P. pygmaeus et de M. fascicularis est très similaire à celle de l’humain. Ceci va dans le sens de notre hypothèse et nous laisse entrevoir l’effet de la séquence et de la distance phylogénique sur la dynamique. Des expériences supplémentaires seront nécessaires pour déterminer la fonction biologique exacte des protéines étudiées.</p