699 research outputs found
Tidal Flows in asynchronous binaries: The beta-factor
We discuss the potential role that tidal flows in asynchronous binary stars
may play in transporting chemically enriched material from deep layers towards
the surface and the corresponding observational consequences of these
processes. We suggest that the time-dependent velocity field induced by
asynchronous rotation may contribute significantly to the mixing, thus
providing a channel for the formation of chemically enriched slowly rotating
massive stars.Comment: in Setting New Standards in Binary Star Research, A. Tkachenko & K.
Pavlovski (eds), EAS Publication Series, in Pres
Stellar Orbital Studies in Normal Spiral Galaxies II: Restrictions to Structural and Dynamical parameters on Spiral Arms
Making use of a set of detailed potential models for normal spiral galaxies,
we analyze the disk stellar orbital dynamics as the structural and dynamical
parameters of the spiral arms (mass, pattern speed and pitch angle) are
gradually modified. With this comprehensive study of ordered and chaotic
behavior, we constructed an assemblage of orbitally supported galactic models
and plausible parameters for orbitally self-consistent spiral arms models. We
find that, to maintain orbital support for the spiral arms, the spiral arm
mass, M, must decrease with the increase of the pitch angle, ; if
is smaller than , M can be as large as , ,
of the disk mass, for Sa, Sb, and Sc galaxies, respectively. If
increases up to , the maximum M is of the disk
mass independently in this case of morphological type. For values larger than
these limits, spiral arms would likely act as transient features. Regarding the
limits posed by extreme chaotic behavior, we find a strong restriction on the
maximum plausible values of spiral arms parameters on disk galaxies beyond
which, chaotic behavior becomes pervasive. We find that for smaller than
, , , for Sa, Sb, and Sc galaxies,
respectively, M can go up to , of the mass of the disk. If the
corresponding is around , , , M
is , , of the mass of the disk. Beyond these
values, chaos dominates phase space, destroying the main periodic and the
neighboring quasi-periodic orbits.Comment: 51 pages in preprint format, 30 figures, Accepted for publication in
Ap
On the Galactic Spiral Patterns: Stellar and Gaseous
The gas response to a proposed spiral stellar pattern for our Galaxy is
presented here as calculated via 2D hydrodynamic calculations utilizing the
ZEUS code in the disk plane. The locus is that found by Drimmel (2000) from
emission profiles in the K band and at 240 . The self-consistency of the
stellar spiral pattern was studied in previous work (see Martos et al. 2004).
It is a sensitive function of the pattern rotation speed, , among
other parameters which include the mass in the spiral and its pitch angle. Here
we further discuss the complex gaseous response found there for plausible
values of in our Galaxy, and argue that its value must be close to
from the strong self-consistency criterion and other
recent, independent studies which depend on such parameter. However, other
values of that have been used in the literature are explored to
study the gas response to the stellar (K band) 2-armed pattern. For our best
fit values, the gaseous response to the 2-armed pattern displayed in the K band
is a four-armed pattern with complex features in the interarm regions. This
response resembles the optical arms observed in the Milky Way and other
galaxies with the smooth underlying two-armed pattern of the old stellar disk
populations in our interpretation.Comment: Accepted for Publication in the Journal of the Korean Astronomical
Society, expanded from the proceedings of the 2004 Mexico-Korea meetin
Tidal effects on the radial velocity curve of HD77581 (Vela X-1)
The mass of the neutron star in Vela X-1 has been found to be more massive
than the canonical 1.5 Mo. This result relies on the assumption that the
amplitude of the optical component's measured radial velocity curve is not
seriously affected by the interactions in the system. In this paper we explore
the effect on the radial velocity curve caused by surface motions excited by
tidal interactions. We use a calculation from first principles that involves
solving the equations of motion of a Lagrangian grid of surface elements. The
velocities on the visible surface of the star are projected along the
line-of-sight to the observer to obtain the absorption-line profile in the
observer's reference frame. The centroid of the line-profiles for different
orbital phases is then measured and a simulated RV curve constructed. Models
are run for the "standard" (vsini=116 km/s) and "slow" (56 km/s) supergiant
rotation velocities. We find that the surface velocity field is complex and
includes fast, small-spatial scale structures. It leads to strong variability
in the photospheric line profiles which, in turn, causes significant deviations
from a Keplerian RV curve. The peak-to-peak amplitudes of model RV curves are
in all cases larger than the amplitude of the orbital motion. Keplerian fits to
RV curves obtained with the "standard" rotation velocity imply a neutron star
>1.7 Mo. However, a similar analysis of the "slow" rotational velocity models
allows for m_ns ~ 1.5 Mo. Thus, the stellar rotation plays an important role in
determining the characteristics of the perturbed RV curve. Given the
observational uncertainty in GP Vel's projected rotation velocity and the
strong perturbations seen in the published and the model RV curves, we are
unable to rule out a small (~1.5 Mo) mass for the neutron star companion.Comment: 14 pages, 16 figures; A&A, accepte
Six New Galactic Orbits of Globular Clusters in a Milky-Way-Like Galaxy
Absolute proper motions for six new globular clusters have recently been
determined. This motivated us to obtain the Galactic orbits of these six
clusters both in an axisymmetric Galactic potential and in a barred potential,
such as the one of our Galaxy. Orbits are also obtained for a Galactic
potential that includes spiral arms. The orbital characteristics are compared
and discussed for these three cases. Tidal radii and destruction rates are also
computed and discussed.Comment: 29 pages, 11 figures. Accepted for publication in Ap
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