44 research outputs found
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
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
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Applications of Morphochronology to the Active Tectonics of Tibet
The Himalayas and the Tibetan Plateau were formed as a result of the collision of India and Asia, and provide an excellent opportunity to study the mechanical response of the continental lithosphere to tectonic stress. Geophysicists are divided in their views on the nature of this response advocating either (1) homogeneously distributed deformation with the lithosphere deforming as a fluid continuum or (2) deformation is highly localized with the lithosphere that deforms as a system of blocks. The resolution of this issue has broad implications for understanding the tectonic response of continental lithosphere in general. Homogeneous deformation is supported by relatively low decadal, geodetic slip-rate estimates for the Altyn Tagh and Karakorum Faults. Localized deformation is supported by high millennial, geomorphic slip-rates constrained by both cosmogenic and radiocarbon dating on these faults. Based upon the agreement of rates determined by radiocarbon and cosmogenic dating, the overall linearity of offset versus age correlations, and on the plateau-wide correlation of landscape evolution and climate history, the disparity between geomorphic and geodetic slip-rate determinations is unlikely to be due to the effects of surface erosion on the cosmogenic age determinations. Similarly, based upon the consistency of slip-rates over various observation intervals, secular variations in slip-rate appear to persist no longer than 2000 years and are unlikely to provide reconciliation. Conversely, geodetic and geomorphic slip-rate estimates on the Kunlun fault, which does not have significant splays or associated thrust faults, are in good agreement, indicating that there is no fundamental reason why these complementary geodetic and geomorphic methods should disagree. Similarly, the geodetic and geomorphic estimates of shortening rates across the northeastern edge of the plateau are in reasonable agreement, and the geomorphic rates on individual thrust faults demonstrate a significant eastward decrease in the shortening rate. This rate decrease is consistent with the transfer of slip from the Altyn Tagh Fault (ATF) to genetically-related thrust mountain building at its terminus. Rates on the ATF suggest a similar decrease in rate, but the current data set is too small to be definitive. Overall, the high, late Pleistocene-Holocene, geomorphic slip velocities on the major strike-slip faults of Tibet, suggests that they absorb as much of India's convergence relative to Siberia as the Himalayan Main Frontal Thrust on the southern edge of the plateau
Spectroscopic Study of SU UMa-type Dwarf Nova YZ Cnc during its 2002 Superoutburst
We report time-resolved spectroscopic observations of the SU Ursae Majoris
dwarf nova, YZ Cnc, for 2 nights over 11 hrs during its 2002 January
superoutburst. The spectra only show absorption-line profiles in the first day.
But the lines display blue and red troughs, with ``W'' profiles in the second
day. The radial velocity curve of the absorption troughs and emission peaks of
H has an amplitude of km s and a phase offset of
, which are very similar to those measured in quiescence;
however, the velocity deviates strongly from the systemic velocity
measured in quiescence, showing variation of the order of 60 km s.
And large shifts of 70 km s and 0.09, for the
orbital-averaged velocity and phase respectively, are also found in our
observations. All these phenomena can be well explained with a precession of an
eccentric disk and we conclude that these phenomena are the characteristic
products of an eccentric accretion disk.Comment: 11 pages, 4 figures, accepted for publication in ChJA
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
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