941 research outputs found
An eclipsing post common-envelope system consisting of a pulsating hot subdwarf B star and a brown dwarf companion
Hot subdwarf B stars (sdBs) are evolved, core helium-burning objects located
on the extreme horizontal branch. Their formation history is still puzzling as
the sdB progenitors must lose nearly all of their hydrogen envelope during the
red-giant phase. About half of the known sdBs are in close binaries with
periods from 1.2 h to a few days, a fact that implies they experienced a
common-envelope phase. Eclipsing hot subdwarf binaries (also called HW Virginis
systems) are rare but important objects for determining fundamental stellar
parameters. Even more significant and uncommon are those binaries containing a
pulsating sdB, as the mass can be determined independently by asteroseismology.
Here we present a first analysis of the eclipsing hot subdwarf binary
V2008-1753. The light curve shows a total eclipse, a prominent reflection
effect, and low--amplitude pulsations with periods from 150 to 180 s. An
analysis of the light-- and radial velocity (RV) curves indicates a mass ratio
close to , an RV semi-amplitude of , and an
inclination of . Combining these results with our spectroscopic
determination of the surface gravity, , the best--fitting
model yields an sdB mass of 0.47 and a companion mass of . As the latter mass is below the hydrogen-burning limit,
V2008-1753 represents the first HW Vir system known consisting of a pulsating
sdB and a brown dwarf companion. Consequently, it holds great potential for
better constraining models of sdB binary evolution and asteroseismology.Comment: 9 pages, 8 figures, accepted for A&
Virtual Compton Scattering at Low Energy and the Generalized Polarizabilities of the Nucleon o
Virtual Compton Scattering on the nucleon: is a new
and rapidly developing field at low and high energies. This lecture is about
the low energy part, i.e. for energies in the center-of-mass
mainly up to the resonance region. I review the concept of
Generalized Polarizabilities of the Nucleon, and the experiments dedicated to
their measurement.Comment: 16 pages, 8 figures. lecture given at the Erice School "Lepton
Scattering and the Structure of Hadrons and Nuclei," Erice, 16 - 24 Sept.
2004; to appear in "Progress in Particle and Nuclear Physics
Cross sections for the production of fragments with Z greater than or equal to 8 by fragmentation of Z greater than or equal to 9 and less than or equal to 26 nuclei
Charge changing nuclear collisions in plastic nuclear track detectors were studied using a new experimental technique of automatic track measurement for etched tracks in plastic detectors. Partial cross sections for the production of fragments of charge Z approximately 8 were measured for projectile nuclei of charge 9 approximately Z approximately 26 in the detector material CR39 and in silver. for this purpose three independent experiments were performed using Bevalac beams. The first one was an exposure of a stack of CR39 plastic plates to 1.8 GeV/nucl. Ar-40 nuclei. The second one was an exposure of another CR39 stack of 1.7 GeV/nucl. Fe-56 projectiles. In the third experiment a mixed stack of CR39 plates and silver foils was irradiated with 1.7 GeV/nucl. Fe-56 nuclei. Thus the measurement of nuclear cross sections in a light target (CR39 = C12H18O7) and as well in a heavy target (silver) was possible
Double polarization experiments at intermediate energy
At modern electron accelerators with highly polarized, intense, high duty
factor beams double polarization coincidence experiments became feasible with
good statistical accuracy. The strong potential towards the precise
determination of small nucleon structure quantities is illustrated by two
recent examples from MAMI. The measurement of in the quasifree reaction
lead to a new parametrization of which is
significantly above the previously preferred one from elastic scattering.
A experiment at the energy of the resonance
yields preliminary results for the longitudinal quadrupole mixing. Both
experimental errors and model uncertainties are complementary to unpolarized
measurements.Comment: 8 pages, 6 figures, plenary talk given at PANIC'9
A new HW Vir binary from the Palomar Transient Factory: PTF1 J072455.75+125300.3 - An eclipsing subdwarf B binary with a M-star companion
We report the discovery of an eclipsing binary -- PTF1 J072456125301--
composed of a subdwarf B (sdB) star () with a faint companion.
Subdwarf B stars are core helium-burning stars, which can be found on the
extreme horizontal branch. About half of them reside in close binary systems,
but few are known to be eclipsing, for which fundamental stellar parameters can
be derived.\newline We conducted an analysis of photometric data and spectra
from the Palomar 60'' and the 200" Hale telescope respectively. A quantitative
spectral analysis found an effective temperature of
\,K, log g = and
log(, typical for an sdB star. The
companion does not contribute to the optical light of the system, except
through a distinct reflection effect. From the light curve an orbital period of
0.09980(25)\,d and a system inclination of 83.56\pm0.30\,^{\circ} were
derived. The radial velocity curve yielded an orbital semi-amplitude of
K_1=95.8\pm 8.1\,\text{km s^{-1}}. The mass for the M-type dwarf companion
is . PTF1\,J072456125301 has similar atmospheric
parameters to those of pulsating sdB stars (V346 Hya stars). Therefore it could
be a high-priority object for asteroseismology, if pulsations were detected
such as in the enigmatic case of NY Vir.Comment: Accepted to A&A, 7pages, 4 figure
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