190 research outputs found
The Multiple Origin of Blue Straggler Stars: Theory vs. Observations
In this chapter we review the various suggested channels for the formation
and evolution of blue straggler stars (BSSs) in different environments and
their observational predictions. These include mass transfer during binary
stellar evolution - case A/B/C and D (wind Roche-lobe overflow) mass transfer,
stellar collisions during single and binary encounters in dense stellar
cluster, and coupled dynamical and stellar evolution of triple systems. We also
explore the importance of the BSS and binary dynamics in stellar clusters. We
review the various observed properties of BSSs in different environments (halo
and bulge BSSs, BSSs in globular clusters and BSSs in old open clusters), and
compare the current observations with the theoretical predictions for BSS
formation. We try to constrain the likely progenitors and processes that play a
role in the formation of BSSs and their evolution. We find that multiple
channels of BSS formation are likely to take part in producing the observed
BSSs, and we point out the strengths and weaknesses of each the formation
channel in respect to the observational constraints. Finally we point out
directions to further explore the origin of BSS, and highlight eclipsing binary
BSSs as important observational tool.Comment: Chapter 11, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
A phase 1 study of mTORC1/2 inhibitor BI 860585 as a single agent or with exemestane or paclitaxel in patients with advanced solid tumors
This phase 1 trial (NCT01938846) determined the maximum tolerated dose (MTD) of the mTOR serine/threonine kinase inhibitor, BI 860585, as monotherapy and with exemestane or paclitaxel in patients with advanced solid tumors. This 3+3 dose-escalation study assessed BI 860585 monotherapy (5â300 mg/day; Arm A), BI 860585 (40â220 mg/day; Arm B) with 25 mg/day exemestane, and BI 860585 (80â220 mg/day; Arm C) with 60â80 mg/m2 /week paclitaxel, in 28-day cycles. Primary endpoints were the number of patients with dose-limiting toxicities (DLTs) in cycle 1 and the MTD. Forty-one, 25, and 24 patients were treated (Arms A, B, and C). DLTs were observed in four (rash (n = 2), elevated alanine aminotransferase/aspartate aminotransferase, diarrhea), four (rash (n = 3), stomatitis, and increased gamma-glutamyl transferase), and two (diarrhea, increased blood creatine phosphokinase) patients in cycle 1. The BI 860585 MTD was 220 mg/day (Arm A) and 160 mg/day (Arms B and C). Nine patients achieved an objective response (Arm B: Four partial responses (PRs); Arm C: Four PRs; one complete response). The disease control rate was 20%, 28%, and 58% (Arms A, B, and C). The most frequent treatment-related adverse events (AEs) were hyperglycemia (54%) and diarrhea (39%) (Arm A); diarrhea (40%) and stomatitis (40%) (Arm B); fatigue (58%) and diarrhea (58%) (Arm C). The MTD was determined in all arms. Antitumor activity was observed with BI 860585 monotherapy and in combination with exemestane or paclitaxel
Mass Transfer by Stellar Wind
I review the process of mass transfer in a binary system through a stellar
wind, with an emphasis on systems containing a red giant. I show how wind
accretion in a binary system is different from the usually assumed Bondi-Hoyle
approximation, first as far as the flow's structure is concerned, but most
importantly, also for the mass accretion and specific angular momentum loss.
This has important implications on the evolution of the orbital parameters. I
also discuss the impact of wind accretion, on the chemical pollution and change
in spin of the accreting star. The last section deals with observations and
covers systems that most likely went through wind mass transfer: barium and
related stars, symbiotic stars and central stars of planetary nebulae (CSPN).
The most recent observations of cool CSPN progenitors of barium stars, as well
as of carbon-rich post-common envelope systems, are providing unique
constraints on the mass transfer processes.Comment: Chapter 7, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
The Leishmania donovani Lipophosphoglycan Excludes the Vesicular Proton-ATPase from Phagosomes by Impairing the Recruitment of Synaptotagmin V
We recently showed that the exocytosis regulator Synaptotagmin (Syt) V is recruited to the nascent phagosome and remains associated throughout the maturation process. In this study, we investigated the possibility that Syt V plays a role in regulating interactions between the phagosome and the endocytic organelles. Silencing of Syt V by RNA interference revealed that Syt V contributes to phagolysosome biogenesis by regulating the acquisition of cathepsin D and the vesicular proton-ATPase. In contrast, recruitment of cathepsin B, the early endosomal marker EEA1 and the lysosomal marker LAMP1 to phagosomes was normal in the absence of Syt V. As Leishmania donovani promastigotes inhibit phagosome maturation, we investigated their potential impact on the phagosomal association of Syt V. This inhibition of phagolysosome biogenesis is mediated by the virulence glycolipid lipophosphoglycan, a polymer of the repeating GalÎČ1,4Manα1-PO4 units attached to the promastigote surface via an unusual glycosylphosphatidylinositol anchor. Our results showed that insertion of lipophosphoglycan into ganglioside GM1-containing microdomains excluded or caused dissociation of Syt V from phagosome membranes. As a consequence, L. donovani promatigotes established infection in a phagosome from which the vesicular proton-ATPase was excluded and which failed to acidify. Collectively, these results reveal a novel function for Syt V in phagolysosome biogenesis and provide novel insight into the mechanism of vesicular proton-ATPase recruitment to maturing phagosomes. We also provide novel findings into the mechanism of Leishmania pathogenesis, whereby targeting of Syt V is part of the strategy used by L. donovani promastigotes to prevent phagosome acidification
A Non-Cytosolic Protein of Trypanosoma evansi Induces CD45-Dependent Lymphocyte Death
In a recent study dealing with a mouse model of Trypanosoma evansi-associated disease, a remarkable synchrony between the parasitaemia peak and the white-blood-cell count nadir was noticed. The present study was designed to establish whether there is a direct causal link between the parasite load during its exponential phase of growth and the disappearance of peripheral blood leukocytes. In vitro experiments performed with trypanosomes and purified peripheral blood mononucleated cells revealed the existence of a lymphotoxin embedded in the T. evansi membrane: a protein sensitive to serine proteases, with a molecular mass of less than 30 kDa. Lymphocytes death induced by this protein was found to depend on the intervention of a lymphocytic protein tyrosine phosphatase. When lymphocytes were exposed to increasing quantities of a monoclonal antibody raised against the extracellular portion of CD45, a transmembrane protein tyrosine phosphatase covering over 10% of the lymphocyte surface, T. evansi membrane extracts showed a dose-dependent decrease in cytotoxicity. As the regulatory functions of CD45 concern not only the fate of lymphocytes but also the activation threshold of the TCR-dependent signal and the amplitude and nature of cytokinic effects, this demonstration of its involvement in T. evansi-dependent lymphotoxicity suggests that T. evansi might manipulate, via CD45, the host's cytokinic and adaptive responses
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
Discovery of Halpha satellite emission in a low state of the SW Sextantis star BB Doradus
BB Dor was observed during its low state state in 2009. Signatures of both
binary components are revealed in the average optical spectrum; no signature of
accretion is observed. Narrow emission lines of Halpha, HeI and Na-D, as well
as TiO absorption troughs trace the motion of the irradiated secondary star. We
detect two additional components in the Halpha emission line that share many
characteristics of similar "satellite" lines observed in the low state of
magnetic cataclysmic variables of AM Her type. It is the first time such
emission components are detected for an SW Sex star.Comment: 7 pages, 8 figures, accepted by MNRA
An incisive look at the symbiotic star SS Leporis -- Milli-arcsecond imaging with PIONIER/VLTI
Context. Determining the mass transfer in a close binary system is of prime
importance for understanding its evolution. SS Leporis, a symbiotic star
showing the Algol paradox and presenting clear evidence of ongoing mass
transfer, in which the donor has been thought to fill its Roche lobe, is a
target particularly suited to this kind of study. Aims. Since previous
spectroscopic and interferometric observations have not been able to fully
constrain the system morphology and characteristics, we go one step further to
determine its orbital parameters, for which we need new interferometric
observations directly probing the inner parts of the system with a much higher
number of spatial frequencies. Methods. We use data obtained at eight different
epochs with the VLTI instruments AMBER and PIONIER in the H- and K-bands. We
performed aperture synthesis imaging to obtain the first model-independent view
of this system. We then modelled it as a binary (whose giant is spatially
resolved) that is surrounded by a circumbinary disc. Results. Combining these
interferometric measurements with previous radial velocities, we fully
constrain the orbit of the system. We then determine the mass of each star and
significantly revise the mass ratio. The M giant also appears to be almost
twice smaller than previously thought. Additionally, the low spectral
resolution of the data allows the flux of both stars and of the dusty disc to
be determined along the H and K bands, and thereby extracting their
temperatures. Conclusions. We find that the M giant actually does not stricto
sensus fill its Roche lobe. The mass transfer is more likely to occur through
the accretion of an important part of the giant wind. We finally rise the
possibility for an enhanced mass loss from the giant, and we show that an
accretion disc should have formed around the A star.Comment: 11 pages, 5 figures, published in A&A Appendix presenting reduced
data and extracted parameters Reduced data can be found on the CD
Evolutionary constraints on the long-period subdwarf B binary PG1018-047
We have revisited the sdB+K-star long-period binary PGâ1018â047 based on 20 new high-resolution Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectra that provided regular coverage over a period of more than 26â m. We refine the period and establish that the orbit is significantly eccentric (Pâ=â751.6 ± 1.9âd and eâ=â0.049 ± 0.008). A simultaneous fit derived from the narrow metal lines visible in the spectrum of the sdB star and the metal lines in the red part of the spectrum that originate from the companion provides the mass ratio, MMS/MsdB = 1.52 ± 0.04, for the system. From an NLTE model atmosphere analysis of the combined spectra, we find Teffâ=â29900 ± 330âK, logâgâ= 5.65 ± 0.06âdex and log(nHe/nH)â=ââ3.98 ± 0.16âdex for the primary, consistent with a B-type hot subdwarf star. The spectral contribution of the companion is consistent with a K5V-type star. With the companion having a mass of only ⌠0.7âMâ, this system lies close to the boundary below which stable Roche lobe overflow (RLOF) cannot be supported. To model the evolution of such a system, we have extended earlier MESA models towards lower companion masses. We find that both phase-dependent mass loss during RLOF, when 30 to 40âperâcent of the available mass is lost through the outer Lagrange point and phase-dependent mass loss during RLOF in combination with a circumbinary disc of maximum MCB = 0.001âMâ could have formed the PGâ1018â047 binary system
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