14 research outputs found
Limb-Darkened Radiation-Driven Winds from Massive Stars
We calculated the influence of the limb-darkened finite disk correction
factor in the theory of radiation-driven winds from massive stars. We solved
the 1-D m-CAK hydrodynamical equation of rotating radiation-driven winds for
all three known solutions, i.e., fast, \Omega-slow and \delta-slow. We found
that for the fast solution, the mass loss rate is increased by a factor \sim
10%, while the terminal velocity is reduced about 10%, when compared with the
solution using a finite disk correction factor from a uniformly bright star.
For the other two slow solutions the changes are almost negligible. Although,
we found that the limb darkening has no effects on the wind momentum luminosity
relationship, it would affect the calculation of synthetic line profiles and
the derivation of accurate wind parameters.Comment: Accepted for publication in ApJ. 19 pages, 6 figure
A method to deconvolve stellar rotational velocities
Rotational speed is an important physical parameter of stars and knowing the
distribution of stellar rotational velocities is essential for the
understanding stellar evolution. However, it cannot be measured directly but
the convolution of the rotational speed and the sine of the inclination angle,
. We developed a method to deconvolve this inverse problem and obtain
the cumulative distribution function (CDF) for stellar rotational velocities
extending the work of Chandrasekhar & M\"unch (1950). This method is applied a)
to theoretical synthetic data recovering the original velocity distribution
with very small error; b) to a sample of about 12.000 field main--sequence
stars, corroborating that the velocity distribution function is
non--Maxwellian, but is better described by distributions based on the concept
of maximum entropy, such as Tsallis or Kaniadakis distribution functions. This
is a very robust and novel method that deconvolve the rotational velocity
cumulative distribution function from a sample of data in just one
single step without needing any convergence criteria.Comment: Accepted in A&
Genomic investigations of unexplained acute hepatitis in children
Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children
A method to deconvolve stellar rotational velocities II
Aims. Knowing the distribution of stellar rotational velocities is essential for understanding stellar evolution. Because we measure the projected rotational speed v sin i, we need to solve an ill-posed problem given by a Fredholm integral of the first kind to recover the “true” rotational velocity distribution.
Methods. After discretization of the Fredholm integral we apply the Tikhonov regularization method to obtain directly the probability distribution function for stellar rotational velocities. We propose a simple and straightforward procedure to determine the Tikhonov parameter. We applied Monte Carlo simulations to prove that the Tikhonov method is a consistent estimator and asymptotically unbiased.
Results. This method is applied to a sample of cluster stars. We obtain confidence intervals using a bootstrap method. Our results are in close agreement with those obtained using the Lucy method for recovering the probability density distribution of rotational velocities. Furthermore, Lucy estimation lies inside our confidence interval.
Conclusions. Tikhonov regularization is a highly robust method that deconvolves the rotational velocity probability density function from a sample of v sin i data directly without the need for any convergence criteria
A method to deconvolve mass ratio distribution of binary stars
Aims. It is important to know the binary mass-ratio distribution to better understand the evolution of stars in binary systems and to constrain their formation. However, in most cases, that is, for single-lined spectroscopic binaries, the mass ratio cannot be measured directly, but can only be derived as the convolution of a function that depends on the mass ratio and on the unknown inclination angle of the orbit on the plane of the sky.
Methods. We extend our previous method for deconvolving this inverse problem by obtaining the cumulative distribution function (CDF) for the mass-ratio distribution as an integral.
Results. After a suitable transformation of variables, this problem becomes the same as the problem of rotational velocities vsini, allowing a close analytic formulation for the CDF. We here apply our method to two real datasets: a sample of Am star binary systems, and a sample of massive spectroscopic binaries in the Cyg OB2 association.
Conclusions. We are able to reproduce previous results for the sample of Am stars. In addition, the mass-ratio distribution of massive stars shows an excess of systems with a low mass ratio, in contrast to what was claimed elsewhere. Our method proves to be very reliable and deconvolves the distribution from a sample in one single step