68 research outputs found
A Radial Velocity Survey of the Cygnus OB2 Association
We conducted a radial velocity survey of the Cygnus OB2 Association over a 6
year (1999 - 2005) time interval to search for massive close binaries. During
this time we obtained 1139 spectra on 146 OB stars to measure mean systemic
radial velocities and radial velocity variations. We spectroscopically identify
73 new OB stars for the first time, the majority of which are likely to be
Association members. Spectroscopic evidence is also presented for a B3Iae
classification and temperature class variation (B3 - B8) on the order of 1 year
for Cygnus OB2 No. 12. Calculations of the intial mass function with the
current spectroscopic sample yield Gamma = -2.2 +/- 0.1. Of the 120 stars with
the most reliable data, 36 are probable and 9 are possible single-lined
spectroscopic binaries. We also identify 3 new and 8 candidate double-lined
spectroscopic binaries. These data imply a lower limit on the massive binary
fraction of 30% - 42%. The calculated velocity dispersion for Cygnus OB2 is
2.44 +/- km/s, which is typical of open clusters. No runaway OB stars were
found.Comment: 56 pages, 23 figures, 5 tables, accepted for publication in the
Astrophysical Journa
A model of superoutbursts in binaries of SU UMa type
A new mechanism explaining superoutbursts in binaries of SU UMa type is
proposed. In the framework of this mechanism the accretion rate increase
leading to the superoutburst is associated with formation of a spiral wave of a
new "precessional" type in inner gasdynamically unperturbed parts of the
accretion disc. The possibility of existence of this type of waves was
suggested in our previous work (astro-ph/0403053). The features of the
"precessional" spiral wave allow explaining both the energy release during the
outburst and all its observational manifestations. The distinctive
characteristic of a superoutburst in a SU UMa type star is the appearance of
the superhump on the light curve. The proposed model reproduces well the
formation of the superhump as well as its observational features, such as the
period that is 3-7% longer than the orbital one and the detectability of
superhumps regardless of the binary inclination.Comment: LaTeX, 20 pages, 4 figures, to be published in Astron. Z
The Dwarf Novae During Quiescence
We present a synthetic spectral analysis of nearly the entire FUV IUE archive
of spectra of DNe in or near quiescence. We have examined all of the systems
for which S/N permitted an analysis. The study includes 53 systems of all DN
subtypes both above and below the period gap. The spectra were uniformly
analyzed using synthetic spectral codes for optically thick accretion disks and
stellar photospheres along with the best-available distance measurements or
estimates. We present newly determined approximate WD temperatures or upper
limits and estimated accretion rates. The average temperature of WDs in DNe
below the period gap is ~18,000K. For WDs in DNe above the period gap, the
average WD temperature is ~26,000K. There is a flux component, in addition to a
WD photosphere, which contributes >60% of the flux in the FUV in 53% of the
quiescent DNe in this study. We find that for 41% of the DNe in our sample, a
WD photosphere provides >60% of the FUV flux. Accretion rates estimated from
the FUV alone for the sample of DNe during quiescence ranged from 10^-12
Msun/yr to 10^-10 Msun/yr.The additional flux component is almost certainly not
an optically thick accretion disk since, according to the disk instability
model, the disk should be optically thin and too cool during DN quiescence to
be a significant FUV continuum emitter. Among the candidates for the second
component of FUV light are the quiescent inner disk, a hot equatorial accretion
belt, and a hot rotating ring. The implications of our study for disk accretion
physics and CV evolution are discussed.Comment: 36 pages, 3 tables, 8 figures, final accepted version of manuscrip
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Sustainability performance measurement with Analytic Network Process and balanced scorecard: Cuban practical case
A database of the coseismic effects following the 30 October 2016 Norcia earthquake in Central Italy
We provide a database of the coseismic geological surface effects following the Mw 6.5 Norcia earthquake that hit central Italy on 30 October 2016. This was one of the strongest seismic events to occur in Europe in the past thirty years, causing complex surface ruptures over an area of >400 km 2. The database originated from the collaboration of several European teams (Open EMERGEO Working Group; about 130 researchers) coordinated by the Istituto Nazionale di Geofisica e Vulcanologia. The observations were collected by performing detailed field surveys in the epicentral region in order to describe the geometry and kinematics of surface faulting, and subsequently of landslides and other secondary coseismic effects. The resulting database consists of homogeneous georeferenced records identifying 7323 observation points, each of which contains 18 numeric and string fields of relevant information. This database will impact future earthquake studies focused on modelling of the seismic processes in active extensional settings, updating probabilistic estimates of slip distribution, and assessing the hazard of surface faulting
Rapid response to the earthquake emergency of May 2012 in the Po Plain, northern Italy
No abstrac
Genetic landscape of pediatric acute liver failure of indeterminate origin.
BACKGROUND AIMS
Pediatric acute liver failure (PALF) is a life-threatening condition. In Europe, main causes are viral infections (12-16%) and inherited metabolic diseases (14-28%). Yet, in up to 50% of cases the underlying etiology remains elusive, challenging clinical management, including liver transplantation. We systematically studied indeterminate PALF cases referred for genetic evaluation by whole-exome sequencing (WES), and analyzed phenotypic and biochemical markers, and the diagnostic yield of WES in this condition.
METHODS
With this international, multicenter observational study, patients (0-18 y) with indeterminate PALF were analyzed by WES. Data on the clinical and biochemical phenotype were retrieved and systematically analyzed.
RESULTS
In total, 260 indeterminate PALF patients from 19 countries were recruited between 2011 and 2022, of whom 59 had recurrent PALF (RALF). WES established a genetic diagnosis in 37% of cases (97/260). Diagnostic yield was highest in children with PALF in the first year of life (46%), and in children with RALF (64%). Thirty-six distinct disease genes were identified. Defects in NBAS (n=20), MPV17 (n=8) and DGUOK (n=7) were the most frequent findings. When categorizing, most frequent were mitochondrial diseases (45%), disorders of vesicular trafficking (28%) and cytosolic aminoacyl-tRNA synthetase deficiencies (10%). One-third of patients had a fatal outcome. Fifty-six patients received liver transplants.
CONCLUSION
This study elucidates a large contribution of genetic causes in PALF of indeterminate origin with an increasing spectrum of disease entities. The high proportion of diagnosed cases and potential treatment implications argue for exome or in future rapid genome sequencing in PALF diagnostics
Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly
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