707 research outputs found
In situ stress magnitude and rock strength in the Nankai accretionary complex: a novel approach using paired constraints from downhole data in two wells
We present a method to simultaneously constrain both far-field horizontal stress magnitudes (S hmin and S Hmax) and in situ rock unconfined compressive strength (UCS), using geophysical logging data from two boreholes located 70Â m apart that access the uppermost accretionary prism of the Nankai subduction zone . The boreholes sample the same sediments and are affected by the same tectonic stress field, but were drilled with different annular pressures, thus providing a unique opportunity to refine estimates of both in situ stress magnitudes and rock strength. We develop a forward model to predict the angular width of compressional wellbore failures (borehole breakouts), and identify combinations of S Hmax and UCS that best match breakout widths observed in resistivity images from the two boreholes. The method requires knowledge of S hmin, which is defined by leak-off tests conducted during drilling. Our results define a normal to strike-slip stress regime from 900 to 1386Â m below seafloor, consistent with observations from seismic and core data. Our analysis also suggests that in situ values of UCS are generally slightly lower that commonly assumed on the basis of published empirical relations between UCS and P-wave velocity
Huntington's Disease In a Coloured Family
A South African Coloured (of mixed descent) family with Huntington's disease in which all four members of one sibship, ranging in age from 16 to 23 years, are affected, is described. One generation back, definitely two, and possibly three, members of a sibship of six were affected with the adult form. The offspring of the one affected male all show some evidence of this condition, the age of onset being between 13 and 16 years. The offspring of the one female carrier who was definitely affected do not at this time appear to have been affected. The literature concerning juvenile Huntington's disease, especially with regard to its clinical presentation, EEG, and air encephalographic findings, is reviewed and compared with the family described. The predominance of rigidity and akinesia in the juvenile form, as opposed to chorea, which is the main adult extrapyramidal manifestation, is stressed. This is, to our knowledge, the first report of a Coloured (mixed descent) family's manifesting the clinical features of juvenile Huntington's disease
Stellar adiabatic mass loss model and applications
Roche-lobe overflow and common envelope evolution are very important in
binary evolution, which is believed to be the main evolutionary channel to hot
subdwarf stars. The details of these processes are difficult to model, but
adiabatic expansion provides an excellent approximation to the structure of a
donor star undergoing dynamical time scale mass transfer. We can use this model
to study the responses of stars of various masses and evolutionary stages as
potential donor stars, with the urgent goal of obtaining more accurate
stability criteria for dynamical mass transfer in binary population synthesis
studies. As examples, we describe here several models with the initial masses
equal to 1 Msun and 10 Msun, and identify potential limitations to the use of
our results for giant-branch stars.Comment: 7 pages, 5 figures,Accepted for publication in AP&SS, Special issue
Hot Sub-dwarf Stars, in Han Z., Jeffery S., Podsiadlowski Ph. ed
The Influence of Social Evaluation on Heart Rate Variability and Motor Performance: A Study of âReal-Lifeâ Competition
Click the PDF icon to download the abstract
K-band spectroscopy of pre-cataclysmic variables
Aims. There exists now substantial evidence for abundance anomalies in a number of cataclysmic variables (CVs), indicating that the photosphere of the secondary star incorporates thermonuclear processed material. However, the spectral energy distribution in CVs is usually dominated by the radiation produced by the accretion process, severely hindering an investigation of the stellar components.
On the other hand, depending on how the secondary star has acquired such material, the above mentioned abundance anomalies could also be present in pre-CVs, i.e. detached white/red dwarf binaries that will eventually evolve into CVs, but have not yet started mass transfer, and therefore allow for an unobstructed view on the secondary star at infrared wavelengths.
Methods. We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to examine them for anomalous chemical abundances. In particular, we study the strength of the 12CO and 13CO absorption bands that have been found diminished and enhanced, respectively, in similar studies of CVs.
Results. All our systems show CO abundances that are within the range observed for single stars. The weakest 12CO bands with respect to the spectral type are found in the pre-CV BPM 71214, although on a much smaller scale than observed in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account that our sample is subject to the present observational bias that favours the discovery of young pre-CVs with secondary stars of late spectral types, we can conclude the following: 1) our study provides
observational proof that the CO anomalies discovered in certain CVs are not due to any material acquired during the common envelope phase, and 2) if the CO anomalies in certain CVs are not due to accretion of processed material during nova outburst, then the progenitors of these CVs are of a significantly different type than the currently known sample of pre-CVs
High ions towards white dwarfs: circumstellar line shifts and stellar temperature
Based on a compilation of OVI, CIV, SiIV and NV data from IUE, FUSE, GHRS,
STIS, and COS, we derive an anti- correlation between the stellar temperature
and the high ion velocity shift w.r.t. to the photosphere, with positive (resp.
negative) velocity shifts for the cooler (resp. hotter) white dwarfs. This
trend probably reflects more than a single process, however such a dependence
on the WD's temperature again favors a CS origin for a very large fraction of
those ion absorptions, previously observed with IUE, HST-STIS, HST-GHRS, FUSE,
and now COS, selecting objects for which absorption line radial velocities,
stellar effective temperature and photospheric velocity can be found in the
literature. Interestingly, and gas in near-equilibrium in the star vicinity. It
is also probably significant that the temperature that corresponds to a null
radial velocity, i.e. \simeq 50,000K, also corresponds to the threshold below
which there is a dichotomy between pure or heavy elements atmospheres as well
as some temperature estimates for and a form of balance between radiation
pressure and gravitation. This is consistent with ubiquitous evaporation of
orbiting dusty material. Together with the fact that the fraction of stars with
(red-or blue-) shifted lines and the fraction of stars known to possess heavy
species in their atmosphere are of the same order, such a velocity-temperature
relationship is consistent with quasi-continuous evaporation of orbiting CS
dusty material, followed by accretion and settling down in the photosphere. In
view of these results, ion measurements close to the photospheric or the IS
velocity should be interpreted with caution, especially for stars at
intermediate temperatures. While tracing CS gas, they may be erroneously
attributed to photospheric material or to the ISM, explaining the difficulty of
finding a coherent pattern of the high ions in the local IS 3D distribution.Comment: Accepted by A&A. Body of paper identical to v1. This submission has a
more appropriate truncation of the original abstrac
The Unseen Population of F to K-type Companions to Hot Subdwarf Stars
We present a method to select hot subdwarf stars with A to M-type companions
using photometric selection criteria. We cover a wide range in wavelength by
combining GALEX ultraviolet data, optical photometry from the SDSS and the
Carlsberg Meridian telescope, near-infrared data from 2MASS and UKIDSS. We
construct two complimentary samples, one by matching GALEX, CMC and 2MASS, as
well as a smaller, but deeper, sample using GALEX, SDSS and UKIDSS. In both
cases, a large number of composite subdwarf plus main-sequence star candidates
were found. We fit their spectral energy distributions with a composite model
in order to estimate the subdwarf and companion star effective temperatures
along with the distance to each system. The distribution of subdwarf effective
temperature was found to primarily lie in the 20,000 - 30,000 K regime, but we
also find cooler subdwarf candidates, making up ~5-10 per cent. The most
prevalent companion spectral types were seen to be main-sequence stars between
F0 and K0, while subdwarfs with M-type companions appear much rarer. This is
clear observational confirmation that a very efficient first stable Roche-lobe
overflow channel appears to produce a large number of subdwarfs with F to
K-type companions. Our samples thus support the importance of binary evolution
for subdwarf formation.Comment: 30 pages, 10 figures, 11 tables. Accepted for publication in MNRA
Detached white dwarf main-sequence star binaries
We considered the formation of detached white dwarf main-sequence star (WDMS)
binaries through seven evolutionary channels subdivided according to the
evolutionary process that gives rise to the formation of the white dwarf or its
helium-star progenitor: dynamically stable Roche-lobe overflow (Algol-type
evolution), dynamically unstable Roche-lobe overflow (common-envelope
evolution), or stellar winds (single star evolution). We examine the
sensitivity of the population to changes in the amount of mass lost from the
system during stable Roche-lobe overflow, the common-envelope ejection
efficiency, and the initial mass ratio or initial secondary mass distribution.
In the case of a flat initial mass ratio distribution, the local space density
of WDMS binaries is of the order of 10^{-3}/pc^3. This number decreases to
10^{-4}/pc^3 when the initial mass ratio distribution is approximately
proportional to the inverse of the initial mass ratio. More than 75% of the
WDMS binary population stems from wide systems in which both components evolve
as if they were single stars. The remaining part of the population is dominated
by systems in which the white dwarf is formed in a common-envelope phase. The
birthrate of WDMS binaries forming through a common-envelope phase is about 10
times larger than the birthrate of WDMS binaries forming through a stable
Roche-lobe overflow phase. The ratio of the number of helium white dwarf
systems to the number of carbon/oxygen or oxygen/neon/magnesium white dwarf
systems derived from large samples of observed WDMS binaries by, e.g., future
planet-search missions such as SuperWASP, COROT, and Kepler may furthermore
constrain the common-envelope ejection efficiency.Comment: 22 pages, accepted for publication in A&
The rapidly pulsating sdO star, SDSS J160043.6+074802.9
A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system
containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields
Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely
type of K3V for the secondary star. We compare our results with atmospheric
parameters derived by Fontaine et al. (2008) and in the context of existing
evolution models for sdO stars. New and more extensive photometry is also
presented which recovers most, but not all, frequencies found in an earlier
paper. It therefore seems probable that some pulsation modes have variable
amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO
models show those having log g > 5.3 to be more likely to be unstable and
capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009
September
A Spectroscopic Analysis of Blue Stragglers, Horizontal Branch and Turn-Off Stars in Four Globular Clusters
We present a spectroscopic analysis of HST/STIS and FOS low- and
intermediate-resolution spectroscopy of 55 stars (turn-off stars, horizontal
branch stars and blue stragglers) in four globular clusters (47 Tucanae, M3,
NGC6752, and NGC6397). Stars were analyzed with non-Local Thermodynamic
Equilibrium model atmospheres, and values for their effective temperatures and
gravities and some rotation rates were obtained. Using photometric fluxes, we
also obtained radii, luminosities and spectroscopic masses.Comment: 71 pages, 28 figures. Electronic figures only in the published
versio
- âŠ