653 research outputs found
PG 1002+506: A Be Star Apparently at z \u3e +10 Kiloparsecs
PG 1002+506 is found to be a Be star, one of three found so far by the Palomar-Green survey. Its spectrum is classified as a B5 ± 1 Ve, with Teff = 14,900 ± 1200, log g = 4.2 ± 0.2, and v sin i = 340 ± 50 km s-1. At b = +51°, its height above the Galactic plane would therefore be z = +10.8 kpc, putting this apparently young, rapidly rotating star well into the Galactic halo. Its heliocentric radial velocity is found to be -2 ± 15 km s-1, consistent with either having been formed in the Galactic disk and subsequently ejected or having been formed in the halo
Evolution of elastic and mechanical properties during fault shear. The roles of clay content, fabric development, and porosity
Phyllosilicates weaken faults due to the formation of shear fabrics. Although the impacts of clay abundance and fabric on frictional strength, sliding stability, and porosity of faults are well studied, their influence on elastic properties is less known, though they are key factors for fault stiffness. We document the role that fabric and consolidation play in elastic properties and show that smectite content is the most important factor determining whether fabric or porosity controls the elastic response of faults. We conducted a suite of shear experiments on synthetic smectite-quartz fault gouges (10–100 wt% smectite) and sediment incoming to the Sumatra subduction zone. We monitored Vp, Vs, friction, porosity, shear and bulk moduli. We find that mechanical and elastic properties for gouges with abundant smectite are almost entirely controlled by fabric formation (decreasing mechanical and elastic properties with shear). Though fabrics control the elastic response of smectite-poor gouges over intermediate shear strains, porosity is the primary control throughout the majority of shearing. Elastic properties vary systematically with smectite content: High smectite gouges have values of Vp ~ 1,300–1,800 m/s, Vs ~ 900–1,100 m/s, K ~ 1–4 GPa, and G ~ 1–2 GPa, and low smectite gouges have values of Vp ~ 2,300–2,500 m/s, Vs ~ 1,200–1,300 m/s, K ~ 5–8 GPa, and G ~ 2.5–3 GPa. We find that, even in smectite-poor gouges, shear fabric also affects stiffness and elastic moduli, implying that while smectite abundance plays a clear role in controlling gouge properties, other fine-grained and platy clay minerals may produce similar behavior through their control on the development of fabrics and thin shear surfaces
CCD-based observations of PG 0856+121 and a theoretical analysis of its oscillation modes
BVRI CCD-based and near-IR (J) imaging, together with unfiltered photometry
of the hot subdwarf B star PG 0856+121 are reported. Two close, faint, red,
point-like sources are resolved. They account for the previously reported IR
excess observed in this hot subdwarf. In addition, the new unfiltered
differential photometry of PG 0856+121 confirms its previously reported
pulsational nature. A comparison with the oscillation modes of stellar models
suggests the possible presence of g modes.Comment: Accepted for publication in A&A. Seven pages, four figures include
Spectroscopic analysis of DA white dwarfs from the McCook & Sion catalog
For some years now, we have been gathering optical spectra of DA white dwarfs
in an effort to study and define the empirical ZZ Ceti instability strip.
However, we have recently expanded this survey to include all the DA white
dwarfs in the McCook & Sion catalog down to a limiting visual magnitude of
V=17.5. We present here a spectroscopic analysis of over 1000 DA white dwarfs
from this ongoing survey. We have several specific areas of interest most
notably the hot DAO white dwarfs, the ZZ Ceti instability strip, and the DA+dM
binary systems. Furthermore, we present a comparison of the ensemble properties
of our sample with those of other large surveys of DA white dwarfs, paying
particular attention to the distribution of mass as a function of effective
temperature.Comment: 8 pages, 7 figures, to appear in Journal of Physics Conference
Proceedings for the 16th European White Dwarf Worksho
Close Binary White Dwarf Systems: Numerous New Detections and Their Interpretation
We describe radial velocity observations of a large sample of apparently
single white dwarfs (WDs), obtained in a long-term effort to discover close,
double-degenerate (DD) pairs which might comprise viable Type Ia Supernova (SN
Ia) progenitors. We augment the WD sample with a previously observed sample of
apparently single subdwarf B (sdB) stars, which are believed to evolve directly
to the WD cooling sequence after the cessation of core helium burning. We have
identified 18 new radial velocity variables, including five confirmed sdB+WD
short-period pairs. Our observations are in general agreement with the
predictions of the theory of binary star evolution. We describe a numerical
method to evaluate the detection efficiency of the survey and estimate the
number of binary systems not detected due to the effects of varying orbital
inclination, orbital phase at the epoch of the first observation, and the
actual temporal sampling of each object in the sample. Follow-up observations
are in progress to solve for the orbital parameters of the candidate velocity
variables.Comment: 30 pages (LaTeX) + 6 figures (Postscript), aaspp4 styl
EMG/ENG services rendered by clinical neurophysiology technologists in solo practice
CITATION: Bill, P. L. A., et al. 1998. EMG/ENG services rendered by clinical neurophysiology technologists in solo practice. South African Medical Journal, 88(11):1360.The original publication is available at http://www.samj.org.za[No abstract available]Publisher’s versio
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap
The Influence of Social Evaluation on Heart Rate Variability and Motor Performance: A Study of “Real-Life” Competition
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