1,078 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
Rotational Broadening and Doppler Tomography of the Quiescent X-Ray Nova Centaurus X-4
We present high and intermediate resolution spectroscopy of the X-ray nova
Centaurus X-4 during its quiescent phase. Our analysis of the absorption
features supports a K3-K5V spectral classification for the companion star,
which contributes approximately 75 % of the total flux at Halpha. Using the
high resolution spectra we have measured the secondary star's rotational
broadening to be V_rot*sin(i) = 43 +/- 6 km/s and determined a binary mass
ratio of q=0.17 +/- 0.06. Combining our results for K_2 and q with the
published limits for the binary inclination, we constrain the mass of the
compact object and the secondary star to the ranges 0.49 < M_1 < 2.49 Msun and
0.04 < M_2 < 0.58 Msun. A Doppler image of the Halpha line shows emission
coming from the secondary star, but no hotspot is present. We discuss the
possible origins of this emission.Comment: 10 pages, 4 figures, accepted by MNRA
A possible black hole in the gamma-ray microquasar LS 5039
The population of high energy and very high energy gamma-ray sources,
detected with EGRET and the new generation of ground-based Cherenkov
telescopes, conforms a reduced but physically important sample. Most of these
sources are extragalactic (e.g., blazars), while among the galactic ones there
are pulsars and SN remnants. The microquasar LS 5039, previously proposed to be
associated with an EGRET source by Paredes et al. (2000), has recently been
detected at TeV energies, confirming that microquasars should be regarded as a
class of high energy gamma-ray sources. To model and understand how the
energetic photons are produced and escape from LS 5039 it is crucial to unveil
the nature of the compact object, which remains unknown. Here we present new
intermediate-dispersion spectroscopy of this source which, combined with values
reported in the literature, provides an orbital period of 3.90603+/-0.00017 d,
a mass function f(M)=0.0053+/-0.0009 M_sun, and an eccentricity e=0.35+/-0.04.
Atmosphere model fitting to the spectrum of the optical companion, together
with our new distance estimate of d=2.5+/-0.1 kpc, yields R_opt=9.3+0.7-0.6
R_sun, log (L_opt/L_sun)=5.26+/-0.06, and M_opt=22.9+3.4-2.9 M_sun. These,
combined with our dynamical solution and the assumption of
pseudo-synchronization, yield an inclination i=24.9+/-2.8 degree and a compact
object mass M_X=3.7+1.3-1.0 M_sun. This is above neutron star masses for most
of the standard equations of state and, therefore, we propose that the compact
object in LS 5039 is a black hole. We finally discuss about the implications of
our orbital solution and new parameters of the binary system on the CNO
products, the accretion/ejection energetic balance, the SN explosion scenario,
and the behaviour of the TeV emission with the new orbital period.Comment: 10 pages, 8 figures. Accepted for publication in MNRAS. Minor changes
according to referee repor
The mass of X-Ray Nova Scorpii 1994 (=GRO J1655--40)]
We have obtained high and intermediate resolution optical spectra of the
black-hole candidate Nova Sco 1994 in May/June 1998, when the source was in
complete (X-ray) quiescence. We measure the radial velocity curve of the
secondary star and obtain a semi-amplitude of K_2=215.5+/-2.4 km/s, which is 6
per cent lower than the only previously determined value. This new value for
K_2 thus reduces the binary mass function to f(M) = 2.73+/-0.09 Mo. Using only
the high resolution spectra we constrain the rotational broadening of the
secondary star, vsini, to lie in the range 82.9-94.9 km/s (95 per cent
confidence) and thus constrain the binary mass ratio to lie in the range
0.337--0.436 (95 per cent confidence). We can also combine our results with
published limits for the binary inclination to constrain the mass of the
compact object and secondary star to the ranges 5.5 -- 7.9 and 1.7 -- 3.3 Mo
respectively (95 per cent confidence). Finally, we report on the detection of
the Lithium resonance line at 6707.8 A, with an equivalent width of 55+/-8 mA.Comment: 5 pages, 5 figures, accepted by MNRA
Correlated X-ray and Optical Variability in V404 Cyg in Quiescence
We report simultaneous X-ray and optical observations of V404 Cyg in
quiescence. The X-ray flux varied dramatically by a factor of >20 during a 60ks
observation. X-ray variations were well correlated with those in Halpha,
although the latter include an approximately constant component as well.
Correlations can also be seen with the optical continuum, although these are
less clear. We see no large lag between X-ray and optical line variations; this
implies they are causally connected on short timescales. As in previous
observations, Halpha flares exhibit a double-peaked profile suggesting emission
distributed across the accretion disk. The peak separation is consistent with
material extending outwards to at least the circularization radius. The prompt
response in the entire Halpha line confirms that the variability is powered by
X-ray (and/or EUV) irradiation.Comment: 5 pages; Accepted for publication in the Astrophysical Journal
Letter
On the Origin of the Absorption Features in SS433
We present high-resolution optical spectroscopy of the X-ray binary system
SS433, obtained over a wide range of orbital phases. The spectra display
numerous weak absorption features, and include the clearest example seen to
date of those features, resembling a mid-A type supergiant spectrum, that have
previously been associated with the mass donor star. However, the new data
preclude the hypothesis that these features originate solely within the
photosphere of the putative mass donor, indicating that there may be more than
one region within the system producing an A supergiant-like spectrum, probably
an accretion disc wind. Indeed, whilst we cannot confirm the possibility that
the companion star is visible at certain phase combinations, it is possible
that all supergiant-like features observed thus far are produced solely in a
wind. We conclude that great care must be taken when interpreting the behaviour
of these weak features.Comment: Accepted for publication in MNRAS, 8 pages, 6 figure
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