395 research outputs found
On the origin of variable structures in the winds of hot luminous stars
Examination of the temporal variability properties of several strong optical
recombination lines in a large sample of Galactic Wolf-Rayet (WR) stars reveals
possible trends, especially in the more homogeneous WC than the diverse WN
subtypes, of increasing wind variability with cooler subtypes. This could imply
that a serious contender for the driver of the variations is stochastic,
magnetic subsurface convection associated with the 170 kK partial-ionization
zone of iron, which should occupy a deeper and larger zone of greater mass in
cooler WR subtypes. This empirical evidence suggests that the heretofore
proposed ubiquitous driver of wind variability, radiative instabilities, may
not be the only mechanism playing a role in the stochastic multiple
small-scaled structures seen in the winds of hot luminous stars. In addition to
small-scale stochastic behaviour, subsurface convection guided by a global
magnetic field with localized emerging loops may also be at the origin of the
large-scale corotating interaction regions as seen frequently in O stars and
occasionally in the winds of their descendant WR stars.Comment: 8 pages, 2 figures and 2 tables. Monthly Notices of the Royal
Astronomical Society 201
P18-11. DALIA: dendritic cell and lipopeptide-induced immunity against AIDS: a phase I trial
International audiencen.
Modeling Variable Linear Polarization Produced by Co-Rotating Interaction Regions (CIRs) Across Optical Recombination Lines of Wolf-Rayet Stars
Massive star winds are structured both stochastically ("clumps") and often
coherently (Co-rotation Interaction Regions, or CIRs). Evidence for CIRs
threading the winds of Wolf-Rayet (WR) stars arises from multiple diagnostics
including linear polarimetry. Some observations indicate changes in
polarization position angle across optical recombination emission lines from a
WR star wind but limited to blueshifted Doppler velocities. We explore a model
involving a spherical wind with a single conical CIR stemming from a rotating
star as qualitative proof-of-concept. To obtain a realistic distribution of
limb polarization and limb darkening across the pseudo-photosphere formed in
the optically thick wind of a WR star, we used Monte Carlo radiative transfer
(MCRT). Results are shown for a parameter study. For line properties similar to
WR 6 (EZ CMa; HD 50896), the combination of the MCRT results, a simple model
for the CIR, and the Sobolev approximation for the line formation, we were able
to reproduce variations in both polarization amplitude and position angle
commensurate with observations. Characterizing CIRs in WR~winds has added
importance for providing stellar rotation periods since the v sin i values are
unobtainable because the pseudo-photosphere forms in the wind itself.Comment: This is a pre-copyedited, author-produced PDF of an article accepted
for publication in MNRAS following peer revie
Metallicity variations in the Type II globular cluster NGC6934
The Hubble Space Telescope photometric survey of Galactic globular clusters
(GCs) has revealed a peculiar "chromosome map" for NGC6934. Besides a typical
sequence, similar to that observed in Type I GCs, NGC 6934 displays additional
stars on the red side, analogous to the anomalous, Type II GCs, as defined in
our previous work. We present a chemical abundance analysis of four red giants
in this GC. Two stars are located on the chromosome map sequence common to all
GCs, and another two on the additional sequence. We find: (i) star-to-star Fe
variations, with the two anomalous stars being enriched by ~0.2 dex. Due to our
small-size sample, this difference is at the ~2.5 sigma level; (ii) no evidence
for variations in the slow neutron-capture abundances over Fe, at odds with
what is often observed in anomalous Type II GCs, e.g. M 22 and Omega Centauri;
(iii) no large variations in light elements C, O and Na, compatible with the
targets location on the lower part of the chromosome map where such variations
are not expected. Since the analyzed stars are homogeneous in light elements,
the only way to reproduce the photometric splits on the sub-giant (SGB) and the
red-giant (RGB) branches is to assume that red-RGB/faint-SGB stars are enhanced
in [Fe/H] by ~0.2. This fact corroborates the spectroscopic evidence of a
metallicity variation in NGC6934. The observed chemical pattern resembles only
partially the other Type II GCs, suggesting that NGC6934 might belong either to
a third class of GCs, or be a link between normal Type I and anomalous Type II
GCs.Comment: 26 pages, 9 figures, accepted for publication in Ap
A massive helium star with a sufficiently strong magnetic field to form a magnetar
Magnetars are highly magnetized neutron stars; their formation mechanism is
unknown. Hot helium-rich stars with spectra dominated by emission lines are
known as Wolf-Rayet stars. We observe the binary system HD 45166 using
spectropolarimetry, finding that it contains a Wolf-Rayet star with a mass of 2
solar masses and a magnetic field of 43 kilogauss. Stellar evolution
calculations indicate that this component will explode as a type Ib or IIb
supernova, and the strong magnetic field favors a magnetar remnant. We propose
that the magnatized Wolf-Rayet star formed by the merger of two lower mass
helium stars.Comment: Published in Science on the 18 August 2023. Radial velocities,
spectra, and software available in: https://zenodo.org/record/8042656 ESO
press release: www.eso.org/public/news/eso231
CD4 cell count and the risk of AIDS or death in HIV-Infected adults on combination antiretroviral therapy with a suppressed viral load: a longitudinal cohort study from COHERE.
BACKGROUND: Most adults infected with HIV achieve viral suppression within a year of starting combination antiretroviral therapy (cART). It is important to understand the risk of AIDS events or death for patients with a suppressed viral load.
METHODS AND FINDINGS: Using data from the Collaboration of Observational HIV Epidemiological Research Europe (2010 merger), we assessed the risk of a new AIDS-defining event or death in successfully treated patients. We accumulated episodes of viral suppression for each patient while on cART, each episode beginning with the second of two consecutive plasma viral load measurements 500 copies/µl, the first of two consecutive measurements between 50-500 copies/µl, cART interruption or administrative censoring. We used stratified multivariate Cox models to estimate the association between time updated CD4 cell count and a new AIDS event or death or death alone. 75,336 patients contributed 104,265 suppression episodes and were suppressed while on cART for a median 2.7 years. The mortality rate was 4.8 per 1,000 years of viral suppression. A higher CD4 cell count was always associated with a reduced risk of a new AIDS event or death; with a hazard ratio per 100 cells/µl (95% CI) of: 0.35 (0.30-0.40) for counts <200 cells/µl, 0.81 (0.71-0.92) for counts 200 to <350 cells/µl, 0.74 (0.66-0.83) for counts 350 to <500 cells/µl, and 0.96 (0.92-0.99) for counts ≥500 cells/µl. A higher CD4 cell count became even more beneficial over time for patients with CD4 cell counts <200 cells/µl.
CONCLUSIONS: Despite the low mortality rate, the risk of a new AIDS event or death follows a CD4 cell count gradient in patients with viral suppression. A higher CD4 cell count was associated with the greatest benefit for patients with a CD4 cell count <200 cells/µl but still some slight benefit for those with a CD4 cell count ≥500 cells/µl
LSD1 cooperates with CTIP2 to promote HIV-1 transcriptional silencing
Microglial cells are the main HIV-1 targets in the central nervous system (CNS) and constitute an important reservoir of latently infected cells. Establishment and persistence of these reservoirs rely on the chromatin structure of the integrated proviruses. We have previously demonstrated that the cellular cofactor CTIP2 forces heterochromatin formation and HIV-1 gene silencing by recruiting HDAC and HMT activities at the integrated viral promoter. In the present work, we report that the histone demethylase LSD1 represses HIV-1 transcription and viral expression in a synergistic manner with CTIP2. We show that recruitment of LSD1 at the HIV-1 proximal promoter is associated with both H3K4me3 and H3K9me3 epigenetic marks. Finally, our data suggest that LSD1-induced H3K4 trimethylation is linked to hSET1 recruitment at the integrated provirus
Clear cell carcinoma arising in previous episiotomy scar: a case report and review of the literature
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