207 research outputs found
Molecular Emission Line Formation in Prestellar Cores
We investigate general aspects of molecular line formation under conditions
which are typical of prestellar cores. Focusing on simple linear molecules, we
study formation of their rotational lines by radiative transfer simulations. We
present a thermalization diagram to show the effects of collisions and
radiation on the level excitation. We construct a detailed scheme (contribution
chart) to illustrate the formation of emission line profiles. This chart can be
used as an efficient tool to identify which parts of the cloud contribute to a
specific line profile. We show how molecular line characteristics for uniform
model clouds depend on hydrogen density, molecular column density, and kinetic
temperature. The results are presented in a 2D plane to illustrate cooperative
effects of the physical factors. We also use a core model with a non-uniform
density distribution and chemical stratification to study the effects of cloud
contraction and rotation on spectral line maps. We discuss the main issues that
should be taken into account when dealing with interpretation and simulation of
observed molecular lines.Comment: Accepted for publication in Ap
Polarization of AGN in UV Spectral Range
We present the review of some new problems in cosmology and physics of stars
in connection with future launching of WSO. We discuss three problems. UV
observations of distant z > 6 quasars allow to obtain information on the soft <
1 KeV X-ray radiation of the accretion disk around a supermassive black hole
because of its cosmological redshift. Really the region of X-ray radiation is
insufficiently investigated because of high galactic absorption. In a result
one will get important information on the reionization zone of the Universe.
Astronomers from ESO revealed the effect of alignment of electric vectors of
polarized QSOs. One of the probable mechanism of such alignment is the
conversion of QSO radiation into low mass pseudoscalar particles (axions) in
the extragalactic magnetic field. These boson like particles have been
predicted by new SUSY particle physics theory. Since the probability of such
conversion is increasing namely in UV spectral range one can expect the strong
correlation between UV spectral energy distribution of QSO radiation and
polarimetric data in the optical range. In the stellar physics one of the
interesting problems is the origin of the X-ray sources with super Eddington
luminosities. The results of UV observations of these X-ray sources will allow
to find the origin of these sources as accreting intermediate mass black holes.Comment: 6 pages, 3 figure
Gravitationally lensed QSOs in the ISSIS/WSO-UV era
Gravitationally lensed QSOs (GLQs) at redshift z = 1-2 play a key role in
understanding the cosmic evolution of the innermost parts of active galaxies
(black holes, accretion disks, coronas and internal jets), as well as the
structure of galaxies at intermediate redshifts. With respect to studies of
normal QSOs, GLQ programmes have several advantages. For example, a monitoring
of GLQs may lead to unambiguous detections of intrinsic and extrinsic
variations. Both kinds of variations can be used to discuss central engines in
distant QSOs, and mass distributions and compositions of lensing galaxies. In
this context, UV data are of particular interest, since they correspond to
emissions from the immediate surroundings of the supermassive black hole. We
describe some observation strategies to analyse optically bright GLQs at z of
about 1.5, using ISSIS (CfS) on board World Space Observatory-Ultraviolet.Comment: 7 pages, 4 figures, Accepted for publication in Astrophysics & Space
Scienc
Tracing the evolution of nearby early-type galaxies in low density environments. The Ultraviolet view from GALEX
We detected recent star formation in nearby early-type galaxies located in
low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of
star formation may be present in the nucleus and in outer rings/arm like
structures. Our study suggests that such star formation may be induced by
different triggering mechanisms, such as the inner secular evolution driven by
bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV)
color vs. Mg2 correlation, and suggest that it relates to "downsizing" in
galaxy formation.Comment: Conference "UV Universe 2010" S. Petersburg 31 May - 3 June, 2010
Accepted for publication in Astrophysics & Space Science . The final
publication is available at http://www.springerlink.co
Merging of Components in Close Binaries: Type Ia Supernovae, Massive White Dwarfs, and Ap stars
The "Scenario Machine" (a computer code designed for studies of the evolution
of close binaries) was used to carry out a population synthesis for a wide
range of merging astrophysical objects: main-sequence stars with main-sequence
stars; white dwarfs with white dwarfs, neutron stars, and black holes; neutron
stars with neutron stars and black holes; and black holes with black holes.We
calculate the rates of such events, and plot the mass distributions for merging
white dwarfs and main-sequence stars. It is shown that Type Ia supernovae can
be used as standard candles only after approximately one billion years of
evolution of galaxies. In the course of this evolution, the average energy of
Type Ia supernovae should decrease by roughly 10%; the maximum and minimum
energies of Type Ia supernovae may differ by no less than by a factor of 1.5.
This circumstance should be taken into account in estimations of parameters of
acceleration of the Universe. According to theoretical estimates, the most
massive - as a rule, magnetic - white dwarfs probably originate from mergers of
white dwarfs of lower mass. At least some magnetic Ap and Bp stars may form in
mergers of low-mass main sequence stars (<1.5 mass of the Sun) with convective
envelopes.Comment: 15 pages, 4 figure
Open Issues on the Synthesis of Evolved Stellar Populations at Ultraviolet Wavelengths
In this paper we briefly review three topics that have motivated our (and
others') investigations in recent years within the context of evolutionary
population synthesis techniques. These are: The origin of the FUV up-turn in
elliptical galaxies, the age-metallicity degeneracy, and the study of the
mid-UV rest-frame spectra of distant red galaxies. We summarize some of our
results and present a very preliminary application of a UV grid of theoretical
spectra in the analysis of integrated properties of aged stellar populations.
At the end, we concisely suggest how these topics can be tackled once the World
Space Observatory enters into operation in the midst of this decade.Comment: 8 pages, 4 figures, accepted for publication in Astrophysics & Space
Science, UV Universe special issu
The ECHELON-2 Trial: 5-year results of a randomized, phase III study of brentuximab vedotin with chemotherapy for CD30-positive peripheral T-cell lymphoma
Background: For patients with peripheral T-cell lymphoma (PTCL), outcomes using frontline treatment with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) or CHOP-like therapy are typically poor. The ECHELON-2 study demonstrated that brentuximab vedotin plus cyclophosphamide, doxorubicin, and prednisone (A+CHP) exhibited statistically superior progression-free survival (PFS) per independent central review and improvements in overall survival versus CHOP for the frontline treatment of patients with systemic anaplastic large cell lymphoma or other CD30-positive PTCL. Patients and methods: ECHELON-2 is a double-blind, double-dummy, randomized, placebo-controlled, active-comparator phase III study. We present an exploratory update of the ECHELON-2 study, including an analysis of 5-year PFS per investigator in the intent-to-treat analysis group. Results: A total of 452 patients were randomized (1: 1) to six or eight cycles of A+CHP (N = 226) or CHOP (N = 226). At median follow-up of 47.6 months, 5-year PFS rates were 51.4% [95% confidence interval (CI): 42.8% to 59.4%] with A+CHP versus 43.0% (95% CI: 35.8% to 50.0%) with CHOP (hazard ratio = 0.70; 95% CI: 0.53-0.91), and 5-year overall survival (OS) rates were 70.1% (95% CI: 63.3% to 75.9%) with A+CHP versus 61.0% (95% CI: 54.0% to 67.3%) with CHOP (hazard ratio = 0.72; 95% CI: 0.53-0.99). Both PFS and OS were generally consistent across key subgroups. Peripheral neuropathy was resolved or improved in 72% (84/117) of patients in the A+CHP arm and 78% (97/124) in the CHOP arm. Among patients who relapsed and subsequently received brentuximab vedotin, the objective response rate was 59% with brentuximab vedotin retreatment after A+CHP and 50% with subsequent brentuximab vedotin after CHOP. Conclusions: In this 5-year update of ECHELON-2, frontline treatment of patients with PTCL with A+CHP continues to provide clinically meaningful improvement in PFS and OS versus CHOP, with a manageable safety profile, including continued resolution or improvement of peripheral neuropathy
GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy
We propose to perform a continuously scanning all-sky survey from 200 keV to
80 MeV achieving a sensitivity which is better by a factor of 40 or more
compared to the previous missions in this energy range. The Gamma-Ray Imaging,
Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in
ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS
has its focus on the evolving, violent Universe, exploring a unique energy
window. We propose to investigate -ray bursts and blazars, the
mechanisms behind supernova explosions, nucleosynthesis and spallation, the
enigmatic origin of positrons in our Galaxy, and the nature of radiation
processes and particle acceleration in extreme cosmic sources including pulsars
and magnetars. The natural energy scale for these non-thermal processes is of
the order of MeV. Although they can be partially and indirectly studied using
other methods, only the proposed GRIPS measurements will provide direct access
to their primary photons. GRIPS will be a driver for the study of transient
sources in the era of neutrino and gravitational wave observatories such as
IceCUBE and LISA, establishing a new type of diagnostics in relativistic and
nuclear astrophysics. This will support extrapolations to investigate star
formation, galaxy evolution, and black hole formation at high redshifts.Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic
Vision 2010; 25 p., 25 figs; see also www.grips-mission.e
The Multiplicity of Main Sequence Turnoffs in Globular Clusters
We present color-magnitude diagrams of globular clusters for models with
self-enrichment and pre-enrichment. The models with self-enrichment turn out to
have two or more main sequence turnoff points in the color-magnitude diagram if
the fraction of mass lost by the globular cluster under supernova explosions
does not exceed 95-97%. The models with pre-enrichment can have only one main
sequence turnoff point. We argue that the cluster wCen evolved according to a
self-enrichment scenario.Comment: 13 pages, 7 figure
Stability of Yellow Fever Virus under Recombinatory Pressure as Compared with Chikungunya Virus
Recombination is a mechanism whereby positive sense single stranded RNA viruses exchange segments of genetic information. Recent phylogenetic analyses of naturally occurring recombinant flaviviruses have raised concerns regarding the potential for the emergence of virulent recombinants either post-vaccination or following co-infection with two distinct wild-type viruses. To characterize the conditions and sequences that favor RNA arthropod-borne virus recombination we constructed yellow fever virus (YFV) 17D recombinant crosses containing complementary deletions in the envelope protein coding sequence. These constructs were designed to strongly favor recombination, and the detection conditions were optimized to achieve high sensitivity recovery of putative recombinants. Full length recombinant YFV 17D virus was never detected under any of the experimental conditions examined, despite achieving estimated YFV replicon co-infection levels of ∼2.4×106 in BHK-21 (vertebrate) cells and ∼1.05×105 in C710 (arthropod) cells. Additionally YFV 17D superinfection resistance was observed in vertebrate and arthropod cells harboring a primary infection with wild-type YFV Asibi strain. Furthermore recombination potential was also evaluated using similarly designed chikungunya virus (CHIKV) replicons towards validation of this strategy for recombination detection. Non-homologus recombination was observed for CHIKV within the structural gene coding sequence resulting in an in-frame duplication of capsid and E3 gene. Based on these data, it is concluded that even in the unlikely event of a high level acute co-infection of two distinct YFV genomes in an arthropod or vertebrate host, the generation of viable flavivirus recombinants is extremely unlikely
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