1,209 research outputs found
Doppler Tomography of XTE J2123-058 and Other Neutron Star LMXBs
We describe Doppler tomography obtained in the 1998 outburst of the neutron
star low mass X-ray binary (LMXB) XTE J2123-058. This analysis, and other
aspects of phase-resolved spectroscopy, indicate similarities to SW Sex
systems, except that anomalous emission kinematics are seen in HeII, whilst
phase 0.5 absorption is confined to H alpha. This separation of these effects
may provide tighter constraints on models in the LMXB case than is possible for
SW Sex systems. We will compare results for other LMXBs which appear to show
similar kinematics and discuss how models for the SW Sex phenomenon can be
adapted to these systems. Finally we will summarise the limited Doppler
tomography performed on the class of neutron star LMXBs as a whole, and discuss
whether any common patterns can yet be identified.Comment: 8 pages, 5 postscript figures. To appear in Proceedings of
Astro-Tomography Workshop, Brussels, July 2000, Eds. H. Boffin, D. Steeghs,
Springer-Verlag Lecture Notes in Physic
Fast Photometry of Quiescent Soft X-ray Transients with the Gemini-South Acquisition Camera
We present a compilation of high time-resolution photometric observations of
quiescent soft X-ray transients obtained with the acquisition camera of
Gemini-South. A0620-00 was observed with a short cycle time and high precision.
Superimposed on the ellipsoidal modulation we find several prominent flares
together with weaker continual variability. The flares seen sample shorter
timescale than those reported in previous observations, with rise times as low
as 30s or less; most flares show unresolved peaks. The power density spectrum
(PDS) of A0620-00 appears to exhibit band-limited noise closely resembling the
X-ray PDS of black hole candidates in their low states, but with the
low-frequency break at a lower frequency. X-ray Nova Mus 1991 shows much larger
amplitude flares than A0620-00 and if a break is present it is at a lower
frequency. X-ray Nova Vel 1993 shows very little flaring and is, like A0620-00,
dominated by the ellipsoidal modulation. We discuss the possible origins for
the flares. They are clearly associated with the accretion flow rather than an
active companion, but whether they originate in the outer disc, or are driven
by events in the inner region is not yet resolved. The similarities of the PDS
to those of low/hard state sources would support the latter interpretation, and
the low break frequency is as would be expected if this frequency approximately
scales with the size of an inner evaporated region. We also report the
discovery of a new variable star only 14arcsec from XN Mus 1991. This appears
to be a W UMa star, with an orbital period of about 6hrs.Comment: 11 pages, accepted for publication in MNRA
Disentangling jet and disc emission from the 2005 outburst of XTE J1118+480
The black hole X-ray transient, XTE J1118+480, has now twice been observed in
outburst - 2000 and 2005 - and on both occasions remained in the low/hard X-ray
spectral state. Here we present radio, infrared, optical, soft X-ray and hard
X-ray observations of the more recent outburst. We find that the lightcurves
have very different morphologies compared with the 2000 event and the optical
decay is delayed relative to the X-ray/radio. We attribute this lesser degree
of correlation to contributions of emission from multiple components, in
particular the jet and accretion disc. Whereas the jet seemed to dominate the
broadband spectrum in 2000, in 2005 the accretion disc seems to be more
prominent and we use an analysis of the lightcurves and spectra to distinguish
between the jet and disc emission. There also appears to be an optically thin
component to the radio emission in the 2005 data, possibly associated with
multiple ejection events and decaying as the outburst proceeds. These results
add to the discussion that the term "low/hard state'" covers a wider range of
properties than previously thought, if it is to account for XTE J1118+480
during these two outbursts.Comment: Accepted for publication in MNRA
Autonomía y orientación en el Espacio Europeo de Educación Superior mediante el portafolio y la tutoría
En el nuevo rol del profesor y del estudiante
universitario, según el cual el primero asume funciones
de guía, orientador, asesor y facilitador de recursos para
el aprendizaje activo del segundo, se le da más importancia
al aprendizaje que a la enseñanza. En este trabajo
mostramos la percepción que tienen 290 estudiantes
de distintas especialidades de Magisterio y
Fisioterapia sobre el uso del portafolios y de la tutoría
como elementos de interés para los procesos de innovación
docente (Espacio Europeo de Educación Superior).
Para tal fin se ha pasado un cuestionario, efectuándose
un análisis descriptivo y comparativo,
obteniendo evidencias de interés
Evidence for a black-hole in the X-ray transient XTE J1859+226
We present the results of time-resolved optical photometry and spectroscopy
of the X-ray transient XTE J1859+226 (V406 Vul). Photometric observations taken
during 2000 and 2008 reveals the presence of the secondary star's ellipsoidal
modulation. Further photometry obtained in 2010 shows the system ~1 mag
brighter than its quiescence level and the ellipsoidal modulation diluted by
strong flaring activity. Spectroscopic data obtained with the 10.4-m GTC in
2010 reveals radial velocity variations of ~500 km/s over 3 h. A simultaneous
fit to the photometry and spectroscopy using sinusoids to represent the
secondary star's ellipsoidal and radial velocity variations, yields an orbital
period of 6.58+-0.05 h and a secondary star's radial velocity semi-amplitude of
K_2= 541+-70 km/s. The implied mass function is f(M)=4.5+-0.6 Msun,
significantly lower than previously reported but consistent with the presence
of a black hole in XTE J1859+226. The lack of eclipses sets an upper limit to
the inclination of 70 degrees which yields a lower limit to the black hole mass
of 5.42 Msun.Comment: Accepted for publication in MNRAS. Contains 5 pages and 4 figure
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