20,438 research outputs found
X-Ray Eclipse Timing in the LMXB EXO0748-676
Orbital period changes are an important diagnostic for understanding low mass
X-ray binary (LMXB) accretion-induced angular momentum exchange and overall
system evolution. We present our most recent results for the eclipse timing of
the LMXB EXO0748-676. Since its discovery in 1985 it has apparently undergone
three distinct orbital period "epochs", each characterized by a different
orbital period than the previous epoch. We outline the orbital period behavior
for EXO0748-676 over the past 18 years and discuss the implications of this
behavior in light of current theoretical ideas for LMXB evolution.Comment: 4 Pages, 3 Figures, Submitted to the X-Ray Timing 2003: Rossi and
Beyond conference, November 200
Normal loads program for aerodynamic lifting surface theory
A description of and users manual are presented for a U.S.A. FORTRAN 4 computer program which evaluates spanwise and chordwise loading distributions, lift coefficient, pitching moment coefficient, and other stability derivatives for thin wings in linearized, steady, subsonic flow. The program is based on a kernel function method lifting surface theory and is applicable to a large class of planforms including asymmetrical ones and ones with mixed straight and curved edges
Plotting program for aerodynamic lifting surface theory
A description of and users manual for a USA FORTRAN IV computer program which plots the planform and control points of a wing are presented. The program also plots some of the configuration data such as the aspect ratio. The planform data is stored on a disc file which is created by a geometry program. This program, the geometry program, and several other programs are used together in the analysis of lifting, thin wings in steady, subsonic flow according to a kernel function lifting surface theory
Boundary condition program for aerodynamic lifting surface theory
Users manual for a U.S.A. FORTRAN 4 computer program which determines boundary conditions for a thin wing lifting surface program is described. This program, the geometry program, and several other programs are used together in the analysis of lifting, thin wings in steady, subsonic flow according to a kernel function lifting surface theory. The program calculates specific types of boundary conditions automatically such as those necessary to determine pitch and roll damping derivatives. The program also accepts descriptions of the camber or downwash and twist in the form of tables and/or coefficients of equations. The program performs interpolations so that tables and/or coefficients can apply at stations selected by the user and not at stations dictated by the control point locations
Possible Magnetic Activity in the Low Mass X-ray Binary EXO 0748-676
We report evidence of magnetic activity associated with the secondary star in
the EXO 0748-676 low mass X-ray binary system. An analysis of a sequence of
five consecutive X-ray eclipses observed during December 2003 with the RXTE
satellite brings out a feature occurring during ingress we interpret as the
X-ray photoelectric absorption shadow, as seen by an observer at Earth, of a
plasma structure suspended above the surface of the secondary star. The light
curve feature consists of an initial drop in count rate to near zero (the
absorption shadow) with a very short rebound to a significant fraction of the
pre-ingress count rate and then a final plunge to totality over a total time
scale of ~25 s. The ingress feature persists for at least 5 consecutive orbital
periods (a total of ~19 hr), and possibly up to 5 days in our data. Our data
also show significant post-egress dipping during this eclipse sequence, unusual
for this source, indicating possible secondary star mass ejection during this
episode.Comment: Accepted by Astrophysical Journal Letters; 11 Pages including 3
figures and 1 tabl
Classical T Tauri-like Outflow Activity in the Brown Dwarf Mass Regime
Over the last number of years spectroscopic studies have strongly supported
the assertion that protostellar accretion and outflow activity persists to the
lowest masses. In this paper we present the results of our latest investigation
of brown dwarf (BD) outflow activity and report on the discovery of two new
outflows. Here ISO-Oph 32 is shown to drive a blue-shifted outflow with a
radial velocity of 10-20 km/s and spectro-astrometric analysis constrains the
position angle of this outflow to 240 +/- 7 degrees. The BD candidate ISO-Cha1
217 is found to have a bipolar outflow bright in several key forbidden lines
(radial velocity = -20 km/s, +40 km/s) and with a PA of 190-210 degrees. A
striking feature of the ISO-Cha1 217 outflow is the strong asymmetry between
the red and blue-shifted lobes. This asymmetry is revealed in the relative
brightness of the two lobes (red-shifted lobe is brighter), the factor of two
difference in radial velocity (the red-shifted lobe is faster) and the
difference in the electron density (again higher in the red lobe). Such
asymmetries are common in jets from low mass protostars and the observation of
a marked asymmetry at such a low mass supports the idea that BD outflow
activity is scaled down from low mass protostellar activity.
In addition to presenting these new results, a comprehensive comparison is
made between BD outflow activity and jets launched by CTTSs. In particular, the
application of current methods for investigating the excitation conditions and
mass loss rates in CTT jets to BD spectra is explored.Comment: Accepted by Astrophysical Journa
A generalized family of anisotropic compact object in general relativity
We present model for anisotropic compact star under the general theory of
relativity of Einstein. In the study a 4-dimensional spacetime has been
considered which is embedded into the 5-dimensional flat metric so that the
spherically symmetric metric has class 1 when the condition
is satisfied (
and being the metric potentials along with a constant ). A set of
solutions for the field equations are found depending on the index involved
in the physical parameters. The interior solutions have been matched smoothly
at the boundary of the spherical distribution to the exterior Schwarzschild
solution which necessarily provides values of the unknown constants. We have
chosen the values of as and =10 to 20000 for which interesting and
physically viable results can be found out. The numerical values of the
parameters and arbitrary constants for different compact stars are assumed in
the graphical plots and tables as follows: (i) LMC X-4 : ,
for and , for , (ii) SMC
X-1: , for , and , for . The investigations on the physical features of the model include
several astrophysical issues, like (i) regularity behavior of stars at the
centre, (ii) well behaved condition for velocity of sound, (iii) energy
conditions, (iv) stabilty of the system via the following three techniques -
adiabatic index, Herrera cracking concept and TOV equation, (v) total mass,
effective mass and compactification factor and (vi) surface redshift. Specific
numerical values of the compact star candidates LMC X-4 and SMC X-1 are
calculated for central and surface densities as well as central pressure to
compare the model value with actual observational data.Comment: 20 pages, 9 figures, 2 Table
A Strong X-Ray Burst from the Low Mass X-Ray Binary EXO0748-676
We have observed an unusually strong X-ray burst as a part of our regular
eclipse timing observations of the low mass binary system EXO0748-676. The
burst peak flux was 5.2x10^-8 ergs cm^-2 s^-1, approximately five times the
normal peak X-ray burst flux observed from this source by RXTE. Spectral fits
to the data strongly suggest that photospheric radius expansion occurred during
the burst. In this Letter we examine the properties of this X-ray burst, which
is the first example of a radius expansion burst from EXO0748-676 observed by
RXTE. We find no evidence for coherent burst oscillations. Assuming that the
peak burst luminosity is the Eddington luminosity for a 1.4 solar mass neutron
star we derive a distance to EXO0748-676 of 7.7 kpc for a helium-dominated
burst photosphere and 5.9 kpc for a hydrogen-dominated burst photosphere.Comment: 15 pages including 2 figures and 1 table. Accepted for publication in
the Astrophysical Journa
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