502 research outputs found
Exploring the dimming event of RW Aur A through multi-epoch VLT/X-Shooter spectroscopy
RW Aur A is a CTTS that has suddenly undergone three major dimming events
since 2010. We aim to understand the dimming properties, examine accretion
variability, and derive the physical properties of the inner disc traced by the
CO ro-vibrational emission at NIR wavelengths (2.3 mic).
We compared two epochs of X-Shooter observations, during and after the
dimming. We modelled the rarely detected CO bandhead emission in both epochs to
examine whether the inner disc properties had changed. The SED was used to
derive the extinction properties of the dimmed spectrum and compare the
infrared excess between the two epochs. Lines tracing accretion were used to
derive the mass accretion rate in both states. The CO originates from a region
with physical properties of T=3000 K, N=1x10 cm and
vsini=113 km/s. The extinction properties of the dimming layer were derived
with the effective optical depth ranging from teff 2.5-1.5 from the UV to the
NIR. The inferred mass accretion rate Macc is Msun/yr and Msun/yr after and during the dimming respectively. By fitting the
SED, additional emission is observed in the IR during the dimming event from
dust grains with temperatures of 500-700K. The physical conditions traced by
the CO are similar for both epochs, indicating that the inner gaseous disc
properties do not change during the dimming events. The extinction curve is
flatter than that of the ISM, and large grains of a few hundred microns are
thus required. When we correct for the observed extinction, Macc is constant in
the two epochs, suggesting that the accretion is stable and therefore does not
cause the dimming. The additional hot emission in the NIR is located at about
0.5 au from the star. The dimming events could be due to a dust-laden wind, a
severe puffing-up of the inner rim, or a perturbation caused by the recent
star-disc encounter.Comment: Accepted by Astronomy & Astrophysic
A comprehensive thermodynamic study of the U-Am-O ternary system: multiple experimental investigations and Calphad modelling
International audienc
Young Suns Exoplanet Survey: Detection of a wide-orbit planetary-mass companion to a solar-type Sco-Cen member
The Young Suns Exoplanet Survey consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of 15 ± 3 Myr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211–6456207) that is located at a distance of 94.6 ± 0.3 pc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to 1.00±0.02M⊙ and an age of 16.7±1.4 Myr. The companion TYC 8998-760-1 b is detected at a projected separation of 1.71″, which implies a projected physical separation of 162 au. Photometric measurements ranging from Y to M band provide a mass estimate of 14±3 M_(jup) by comparison to BT-Settl and AMES-dusty isochrones, corresponding to a mass ratio of q = 0.013 ± 0.003 with respect to the primary. We rule out additional companions to TYC 8998-760-1 that are more massive than 12 M_(jup) and farther than 12 au away from the host. Future polarimetric and spectroscopic observations of this system with ground and space based observatories will facilitate testing of formation and evolution scenarios shaping the architecture of the circumstellar environment around this ‘young Sun’
An Investigation into the Mutagenic Effect of Urban Dust under Its Chronic Action on Laboratory Animals
This article examines the action of soil dust in the city of Balkhash in an experiment on laboratory animals. In the city of Balkhash, 35 % of its territory is characterized by a dangerous, to various extents, level of soil pollution. The rest of the city’s territory has demonstrated increased (supra-background) concentrations of toxic elements. The findings obtained in the course of the study attest to the adverse effect of the chemical composition of soil dust in ecogenetic disturbances of the chromosome apparatus of the marrow cells of mice. The general experiment involved 210 animals
The impact on disability of initial treatment with methotrexate in patients with rheumatoid arthritis: results from the MARI study
The study aimed to assess in a population of subjects with rheumatoid arthritis (RA) treated with methotrexate (MTX) how the initial approach to the treatment influenced subsequent disability. We performed a cross-sectional analysis of data collected during the baseline visit of the MARI study, a multicenter observational study on patients with RA on treatment with MTX for at least 12 months. Subjects who fulfilled the Health Assessment Questionnaire (HAQ) were included in the evaluation. For every patient we retrospectively evaluated the disease duration, the duration of symptoms before the diagnosis, the time elapsed before first MTX treatment, the initial MTX dose, and the concomitant medications in the first six months of therapy. Disability was defined as a DI-HAQ score ≥1. The study population included 1015 subjects. Patients with a DI-HAQ score ≥1 had a longer duration of symptoms before diagnosis, a higher delay in treatment initiation, a lower initial dose of MTX and a more frequent co-treatment with symptomatic drugs. Disability was found less frequently in subjects treated with other concomitant disease modifying anti-rheumatic drugs (DMARDs) but not with biological agents. Logistic regression analysis identified as significant predictors of disability: older age, female sex, a longer time to complete diagnosis, a delay in starting MTX treatment higher than 6 months, and a concomitant treatment with symptomatic drugs, while a combination therapy with other DMARDs was associated with a lower risk of disability. A late diagnosis and a delay in starting a treatment with MTX are associated with poorer functional outcomes in patients with RA
Investigating the highest melting temperature materials : a laser melting study of the TaC-HfC system
TaC, HfC and their solid solutions are promising candidate materials for thermal protection structures in hypersonic vehicles because of their very high melting temperatures (\u3e4000 K) among other properties. The melting temperatures of slightly hypostoichiometric TaC, HfC and three solid solution compositions (Ta1−xHfxC, with x = 0.8, 0.5 and 0.2) have long been identified as the highest known. In the current research, they were reassessed, for the first time in the last fifty years, using a laser heating technique. They were found to melt in the range of 4041–4232 K, with HfC having the highest and TaC the lowest. Spectral radiance of the hot samples was measured in situ, showing that the optical emissivity of these compounds plays a fundamental role in their heat balance. Independently, the results show that the melting point for HfC0.98, (4232 ± 84) K, is the highest recorded for any compound studied until now
The Young Suns Exoplanet Survey: Detection of a wide orbit planetary mass companion to a solar-type Sco-Cen member
The Young Suns Exoplanet Survey (YSES) consists of a homogeneous sample of 70
young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the
Scorpius-Centaurus association with an average age of Myr. We report
the detection of a co-moving companion around the K3IV star TYC 8998-760-1
(2MASSJ13251211-6456207) that is located at a distance of pc
using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER
constrain the mass of the star to and an age of
Myr. The companion TYC 8998-760-1 b is detected at a projected
separation of 1.71'', which implies a projected physical separation of
au. Photometric measurements ranging from to band provide a mass
estimate of by comparison to BT-Settl and AMES-dusty
isochrones, corresponding to a mass ratio of with respect to
the primary. We rule out additional companions to TYC 8998-760-1 that are more
massive than and farther than au away from the host.
Future polarimetric and spectroscopic observations of this system with ground
and space based observatories will facilitate testing of formation and
evolution scenarios shaping the architecture of the circumstellar environment
around this 'young Sun'.Comment: Accepted for publication in MNRAS (15 pages, 9 figures
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