538 research outputs found
Imaging the spotty surface of Betelgeuse in the H band
This paper reports on H-band interferometric observations of Betelgeuse made
at the three-telescope interferometer IOTA. We image Betelgeuse and its
asymmetries to understand the spatial variation of the photosphere, including
its diameter, limb darkening, effective temperature, surrounding brightness,
and bright (or dark) star spots. We used different theoretical simulations of
the photosphere and dusty environment to model the visibility data. We made
images with parametric modeling and two image reconstruction algorithms: MIRA
and WISARD. We measure an average limb-darkened diameter of 44.28 +/- 0.15 mas
with linear and quadratic models and a Rosseland diameter of 45.03 +/- 0.12 mas
with a MARCS model. These measurements lead us to derive an updated effective
temperature of 3600 +/- 66 K. We detect a fully-resolved environment to which
the silicate dust shell is likely to contribute. By using two imaging
reconstruction algorithms, we unveiled two bright spots on the surface of
Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5%
of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of
the total flux. Resolved images of Betelgeuse in the H band are asymmetric at
the level of a few percent. The MOLsphere is not detected in this wavelength
range. The amount of measured limb-darkening is in good agreement with model
predictions. The two spots imaged at the surface of the star are potential
signatures of convective cells.Comment: 10 pages, 10 figures, accepted for publication in A&A, references
adde
Dynamical Masses of Young Stars in Multiple Systems
We present recent measurements of the orbital motion in the young binaries DF
Tau and ZZ Tau, and the hierarchical triple Elias 12, that were obtained with
the Fine Guidance Sensors on the HST and at the Keck Observatory using adaptive
optics. Combining these observations with previous measurements from the
literature, we compute preliminary orbital parameters for DF Tau and ZZ Tau. We
find that the orbital elements cannot yet be determined precisely because the
orbital coverage spans only about 90 degr in position angle. Nonetheless, the
range of possible values for the period and semi-major axis already defines a
useful estimate for the total mass in DF Tau and ZZ Tau, with values of
0.90{+0.85}{-0.35} M_sun and 0.81{+0.44}{-0.25} M_sun, respectively, at a
fiducial distance of 140 pc.Comment: 26 pages, 9 figures, accepted for publication in A
Temporal trends of population viral suppression in the context of Universal Test and Treat: the ANRS 12249 TasP trial in rural South Africa
A Test of Pre-Main Sequence Evolutionary Models Across the Stellar/Substellar Boundary Based on Spectra of the Young Quadruple GG Tau
We present spatially separated optical spectra of the components of the young
hierarchical quadruple GG Tau. Spectra of GG Tau Aa and Ab (separation 0".25 ~
35 AU) were obtained with the Faint Object Spectrograph aboard the Hubble Space
Telescope. Spectra of GG Tau Ba and Bb (separation 1".48 ~ 207 AU) were
obtained with both the HIRES and the LRIS spectrographs on the W. M. Keck
telescopes. The components of this mini-cluster, which span a wide range in
spectral type (K7 - M7), are used to test both evolutionary models and the
temperature scale for very young, low mass stars under the assumption of coeval
formation. Of the evolutionary models tested, those of Baraffe et al. (1998,
A&A, 337, 403) yield the most consistent ages when combined with a temperature
scale intermediate between that of dwarfs and giants. The version of the
Baraffe et al. models computed with a mixing length nearly twice the pressure
scale height is of particular interest as it predicts masses for GG Tau Aa and
Ab that are in agreement with their dynamical mass estimate.
Using this evolutionary model and a coeval (at 1.5 Myrs) temperature scale,
we find that the coldest component of the GG Tau system, GG Tau Bb, is
substellar with a mass of 0.044 +/- 0.006 Msun. This brown dwarf companion is
especially intriguing as it shows signatures of accretion, although this
accretion is not likely to alter its mass significantly. GG Tau Bb is currently
the lowest mass, spectroscopically confirmed companion to a T Tauri star, and
is one of the coldest, lowest mass T Tauri objects in the Taurus-Auriga star
forming region.Comment: 25 pages, 6 figures, accepted for publication in The Astrophysical
Journa
Observations of T-Tauri Stars using HST-GHRS: I. Far Ultraviolet Emission Lines
We have analyzed GHRS data of eight CTTS and one WTTS. The GHRS data consists
of spectral ranges 40 A wide centered on 1345, 1400, 1497, 1550, and 1900 A.
These UV spectra show strong SiIV, and CIV emission, and large quantities of
sharp (~40 km/s) H2 lines. All the H2 lines belong to the Lyman band and all
the observed lines are single peaked and optically thin. The averages of all
the H2 lines centroids for each star are negative which may indicate that they
come from an outflow. We interpret the emission in H2 as being due to
fluorescence, mostly by Ly_alpha, and identify seven excitation routes within 4
A of that line. We obtain column densities (10^12 to 10^15 cm^-2) and optical
depths (~1 or less) for each exciting transition. We conclude that the
populations are far from being in thermal equilibrium. We do not observe any
lines excited from the far blue wing of Ly_alpha, which implies that the
molecular features are excited by an absorbed profile. SiIV and CIV (corrected
for H2 emission) have widths of ~200 km/s, and an array of centroids
(blueshifted lines, centered, redshifted). These characteristics are difficult
to understand in the context of current models of the accretion shock. For DR
Tau we observe transient strong blueshifted emission, perhaps the a result of
reconnection events in the magnetosphere. We also see evidence of multiple
emission regions for the hot lines. While CIV is optically thin in most stars
in our sample, SiIV is not. However, CIV is a good predictor of SiIV and H2
emission. We conclude that most of the flux in the hot lines may be due to
accretion processes, but the line profiles can have multiple and variable
components.Comment: 67 pages, 19 figures, Accepted in Ap
VSI: the VLTI spectro-imager
The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument
of the Very Large Telescope Interferometer providing the ESO community with
spectrally-resolved, near-infrared images at angular resolutions down to 1.1
milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13
will be imaged without requiring a brighter nearby reference object. The unique
combination of high-dynamic-range imaging at high angular resolution and high
spectral resolution enables a scientific program which serves a broad user
community and at the same time provides the opportunity for breakthroughs in
many areas of astrophysic including: probing the initial conditions for planet
formation in the AU-scale environments of young stars; imaging convective cells
and other phenomena on the surfaces of stars; mapping the chemical and physical
environments of evolved stars, stellar remnants, and stellar winds; and
disentangling the central regions of active galactic nuclei and supermassive
black holes. VSI will provide these new capabilities using technologies which
have been extensively tested in the past and VSI requires little in terms of
new infrastructure on the VLTI. At the same time, VSI will be able to make
maximum use of new infrastructure as it becomes available; for example, by
combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the
measurement of up to 28 visibilities in every wavelength channel within a few
minutes. The current studies are focused on a 4-telescope version with an
upgrade to a 6-telescope one. The instrument contains its own fringe tracker
and tip-tilt control in order to reduce the constraints on the VLTI
infrastructure and maximize the scientific return.Comment: 12 pages, to be published in Proc. SPIE conference 7013 "Optical and
Infrared Interferometry", Schoeller, Danchi, and Delplancke, F. (eds.). See
also http://vsi.obs.ujf-grenoble.f
Infectious complications of targeted drugs and biotherapies in acute leukemia. Clinical practice guidelines by the European Conference on Infections in Leukemia (ECIL), a joint venture of the European Group for Blood and Marrow Transplantation (EBMT), the European Organization for Research and Treatment of Cancer (EORTC), the International Immunocompromised Host Society (ICHS) and the European Leukemia Net (ELN)
The 9th web-based European Conference on Infections in Leukemia (ECIL-9), held September 16-17, 2021, reviewed the risk of infections and febrile neutropenia associated with more recently approved immunotherapeutic agents and molecular targeted drugs for the treatment of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). Novel antibody based treatment approaches (inotuzumab ozogamicin, gemtuzumab ozogamicin, flotetuzumab), isocitrate dehydrogenases inhibitors (ivosidenib, enasidenib, olutasidenib), FLT3 kinase inhibitors (gilteritinib, midostaurin, quizartinib), a hedgehog inhibitor (glasdegib) as well as a BCL2 inhibitor (venetoclax) were reviewed with respect to their mode of action, their immunosuppressive potential, their current approval and the infectious complications and febrile neutropenia reported from clinical studies. Evidence-based recommendations for prevention and management of infectious complications and specific alerts regarding the potential for drug-drug interactions were developed and discussed in a plenary session with the panel of experts until consensus was reached. The set of recommendations was posted on the ECIL website for a month for comments from members of EBMT, EORTC, ICHS and ELN before final approval by the panelists. While a majority of these agents are not associated with a significantly increased risk when used as monotherapy, caution is required with combination therapy such as venetoclax plus hypomethylating agents, gemtuzumab ozogamicin plus cytotoxic drugs or midostaurin added to conventional AML chemotherapy
The Schrdinger-Poisson equations as the large-N limit of the Newtonian N-body system: applications to the large scale dark matter dynamics
In this paper it is argued how the dynamics of the classical Newtonian N-body
system can be described in terms of the Schrdinger-Poisson equations
in the large limit. This result is based on the stochastic quantization
introduced by Nelson, and on the Calogero conjecture. According to the Calogero
conjecture, the emerging effective Planck constant is computed in terms of the
parameters of the N-body system as , where is the gravitational constant, and are the
number and the mass of the bodies, and is their average density. The
relevance of this result in the context of large scale structure formation is
discussed. In particular, this finding gives a further argument in support of
the validity of the Schrdinger method as numerical double of the
N-body simulations of dark matter dynamics at large cosmological scales.Comment: Accepted for publication in the Euro. Phys. J.
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
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