105 research outputs found
VLT spectroscopy of XTE J2123-058 during quiescence
We present VLT low resolution spectroscopy of the neutron star X-ray
transient XTE J2123-058 during its quiescent state. Our data reveal the
presence of a K7V companion which contributes 77 % to the total flux at 6300 A
and orbits the neutron star at K_2 = 287 +/- 12 km/s. Contrary to other soft
X-ray transients (SXTs), the Halpha emission is almost exactly in antiphase
with the velocity curve of the optical companion. Using the light-center
technique we obtain K_1 = 140 +/- 27 km/s and hence q=K_1/K_2=M_2/M_1= 0.49 +/-
0.10. This, combined with a previous determination of the inclination angle
(i=73 +/- 4) yields M_1 = 1.55 +/- 0.31 Msun and M_2 = 0.76 +/- 0.22 Msun. M_2
agrees well with the observed spectral type. Doppler tomography of the Halpha
emission shows a non-symmetric accretion disc distribution mimicking that seen
in SW Sex stars. Although we find a large systemic velocity of -110 +/- 8 km/s
this value is consistent with the galactic rotation velocity at the position of
J2123-058, and hence a halo origin. The formation scenario of J2123-058 is
still unresolved.Comment: 10 pages, 3 figures, accepted for publication in MNRAS with very
minor change
New Insights into X-ray Binaries
X-ray binaries are excellent laboratories to study collapsed objects. On the
one hand, transient X-ray binaries contain the best examples of stellar-mass
black holes while persistent X-ray binaries mostly harbour accreting neutron
stars. The determination of stellar masses in persistent X-ray binaries is
usually hampered by the overwhelming luminosity of the X-ray heated accretion
disc. However, the discovery of high-excitation emission lines from the
irradiated companion star has opened new routes in the study of compact
objects. This paper presents novel techniques which exploits these irradiated
lines and summarises the dynamical masses obtained for the two populations of
collapsed stars: neutron stars and black holes.Comment: 12 pages, 5 figures, 2 tables, Invited review to plenary session in
"Highlights of Spanish Astrophysics V", Proceedings of the VIII Scientific
Meeting of the Spanish Astronomical Society (SEA) held in Santander, 7-11
July, 2008. Edited by J. Gorgas, L. J. Goicoechea, J. I. Gonzalez-Serrano, J.
M. Dieg
Dust in Supernovae and Supernova Remnants I : Formation Scenarios
Supernovae are considered as prime sources of dust in space. Observations of local supernovae over the past couple of decades have detected the presence of dust in supernova ejecta. The reddening of the high redshift quasars also indicate the presence of large masses of dust in early galaxies. Considering the top heavy IMF in the early galaxies, supernovae are assumed to be the major contributor to these large amounts of dust. However, the composition and morphology of dust grains formed in a supernova ejecta is yet to be understood with clarity. Moreover, the dust masses inferred from observations in mid-infrared and submillimeter wavelength regimes differ by two orders of magnitude or more. Therefore, the mechanism responsible for the synthesis of molecules and dust in such environments plays a crucial role in studying the evolution of cosmic dust in galaxies. This review summarises our current knowledge of dust formation in supernova ejecta and tries to quantify the role of supernovae as dust producers in a galaxy.Peer reviewe
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 He II, whilst phase 0.5 absorption is confined to Hα. 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
Multicolour observations of V404 Cyg with ULTRACAM
We present high-time-resolution multicolour observations of the quiescent soft X-ray transient V404 Cyg obtained with ULTRACAM. Superimposed on the ellipsoidal modulation of the secondary star are large flares on time-scales of a few hours, as well as several distinct rapid flares on time-scales of tens of minutes. The rapid flares, most of which show further variability and unresolved peaks, cover shorter time-scales than those reported in previous observations. The power density spectrum of the 5-s time-resolution data shows a quasi-periodic oscillation (QPO) feature at 0.78 mHz (=21.5 min). Assuming this periodicity represents the Keplerian period at the transition between the thin and advective disc regions, we determine the transition radius. We discuss the possible origins for the QPO feature in the context of the advection-dominated accretion flow model.We determine the colour of the large flares and find that the i-band flux per unit frequency interval is larger than that in the g band. The colour is consistent with optically thin gas with a temperature of ~8000 K arising from a region with an equivalent blackbody radius of at least 2 RΘ, which covers 3 per cent of the surface of the accretion disc. Our timing and spectral analysis results support the idea that the rapid flares (i.e. the QPO feature) most likely arise from regions near the transition radius
Bowen Fluorescence from the Companion Star in X1822-371
We present a clear evidence for the motion of the companion star in the Low
Mass X-Ray Binary (LMXB) X1822-371. We detect NIII lambda 4640 emission moving
in antiphase with the radial velocity curve of the neutron star and produced on
the X-ray heated hemisphere of the donor star. From the motion of this feature
we derive a lower limit to the radial velocity semi-amplitude of the companion
star K2 > 300 +_ 8 km/s, which, combined with a previous determination of the
inclination angle and the pulsar's radial velocity curve, yield M2 > 0.36(2)
Msun and M1 > 1.14(6) Msun. The HeI lambda 4471 absorption line moves at lower
velocities (~ 225 km/s) and with a -0.05 phase shift, suggests a likely origin
on the gas stream near the L1 point. In addition, we detect an S-wave emission
of OVI lambda 3811 produced by illumination of the hot-spot bulge by the
central source. The Balmer lines are dominated by broad absorptions probably
due to obscuration of the accretion disc by vertically extended cool material
from the splash region and overflowing stream. We also derive a more accurate,
and significantly different (compared to earlier work) systemic velocity of
gamma = -44 +_ 5 km/s based on the motion of the HeII lambda 4686 wings and
Doppler tomography. This work confirms the power of imaging the companion stars
in LMXBs and outbursting transients using the Bowen fluorescence transitions.Comment: 19 pages, 6 figures. accepted by Ap
The Distance and Interstellar Sight Line to GX 339-4
The distance to the black hole binary GX339-4 remains a topic of debate. We
examine high-resolution optical spectra of the NaD lines resolving the velocity
structure along the line of sight. We find this to be complex, with at least
nine components, mostly blue-shifted, spanning a velocity range of nearly
200km/s. The presence of components with a large blue-shift rules out a nearby
location and requires that the binary be located at or beyond the tangent
point, implying a lower limit to the distance of ~6kpc. The presence of a
significant red-shifted component at +30km/s is even more intriguing as GX339-4
also has a slightly positive systemic velocity, suggesting that the source, and
this cloud, could be on the far side of the Galaxy, where the radial velocities
due to Galactic rotation become positive again. If this is the case, we require
a distance of ~15kpc. This is less secure than the 6kpc lower limit however. We
discuss the implications of these possible distances for the outburst and
quiescent luminosities, and the nature of the companion star, and argue that a
large distance is consistent with these characteristics. In particular, it
would explain the non-detection of the companion star during the faintest
states.Comment: Accepted for publication in the Astrophysical Journa
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