22,642 research outputs found
Stability windows for proto-quark stars
We investigate the existence of possible stable strange matter and related
stability windows at finite temperature for different models that are generally
applied to describe quark stars, namely, the quark-mass density dependent
model, the MIT bag model and the Nambu-Jona-Lasinio model. We emphasize that,
although the limits for stable strange matter depend on a comparison with the
ground state of 56Fe, which is a zero temperature state, the quantity that has
to be used in the search for strange matter in proto-quark stars is the free
energy and we analyze stability windows up to temperatures of the order of 40
MeV. The effects of strong magnetic fields on stability windows are computed
and the resulting mass-radius relations for different stages of the proto-quark
star are analyzed.Comment: Published versio
A Radial Velocity Study of the Intermediate Polar EX Hydrae
A study on the intermediate polar EX Hya is presented, based on simultaneous
photometry and high dispersion spectroscopic observations, during four
consecutive nights. The strong photometric modulation related to with the
67-min spin period of the primary star is clearly present, as well as the
narrow eclipses associated to the orbital modulation. Since our eclipse timings
have been obtained almost 91,000 cycles since the last reported observations,
we present new linear ephemeris, although we cannot rule out a sinusoidal
variation suggested by previous authors. The system mainly shows double-peaked
H, H and HeI 5876 \AA emission lines. From the profile
of the H line, we find two components; one with a steep rise and
velocities not larger than 1000 km s and another broader component
extending up to 2000 km s, which we interpret as coming mainly
from the inner disc. A strong and variable hotspot is found and a stream-like
structure is seen at times. We show that the best solution correspond to km s from H, from the two emission components, which
are both in phase with the orbital modulation. We remark on a peculiar effect
in the radial velocity curve around phase zero, which could be interpreted as a
Rositter-MacLaughlin-like effect, which has been taken into account before
deriving . This value is compatible with the values found in
high-resolution both in the ultraviolet and X-ray. We find: M, M and
R. Doppler Tomography has been applied, to construct six Doppler
tomograms for single orbital cycles spanning the four days of observations to
support our conclusions. Our results indicate that EX Hya has a well formed
disc and that the magnetosphere should extend only to about
.Comment: 16 pages, 14 figures, accepted for publication in MNRA
Report of IAU Commission 30 on Radial Velocities (2006-2009)
Brief summaries are given on the following subjects: Radial velocities and
exoplanets (Toward Earth-mass planets; Retired A stars and their planets;
Current status and prospects); Toward higher radial velocity precision; Radial
velocities and asteroseismology; Radial velocities in Galactic and
extragalactic clusters; Radial velocities for field giants; Galactic structure
-- Large surveys (The Geneva-Copenhagen Survey; Sloan Digital Sky Survey;
RAVE); Working groups (WG on radial velocity standards; WG on stellar radial
velocity bibliography; WG on the catalogue of orbital elements of spectroscopic
binaries [SB9]).Comment: 11 pages, to appear in the IAU Transactions Vol. XXVIIA, Reports on
Astronomy 2006-2009, ed. Karel van der Hucht. Editor: G. Torre
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