1,077 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
Radiatively-Driven Outflows and Avoidance of Common-Envelope Evolution in Close Binaries
Recent work on Cygnus X-2 suggests that neutron-star or black-hole binaries
survive highly super-Eddington mass transfer rates without undergoing
common-envelope evolution. We suggest here that the accretion flows in such
cases are radiation pressure-dominated versions of the "ADIOS" picture proposed
by Blandford and Begelman (1999), in which almost all the mass is expelled from
large radii in the accretion disk. We estimate the maximum radius from which
mass loss is likely to occur, and show that common-envelope evolution is
probably avoided in any binary in which a main-sequence donor transfers mass on
a thermal timescale to a neutron star or black hole, even though the mass
transfer rate may reach values of 0.001 solar masses per year. This conclusion
probably applies also to donors expanding across the Hertzsprung gap, provided
that their envelopes are radiative. SS433 may be an example of a system in this
state.Comment: 4 pages, submitted to Astrophysical Journal Letters, 26 March 199
Sexual isolation between Drosophila melanogaster females and Drosophila simulans males. I – Relation between homospecific and heterospecific mating success
International audienc
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
The Spectrum of the Black Hole X-ray Nova V404 Cygni in Quiescence as Measured by XMM-Newton
We present XMM observations of the black hole X-ray nova V404 Cygni in
quiescence. Its quiescent spectrum can be best fitted by a simple power-law
with slope 2. The spectra are consistent with that expected for the
advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in
luminosity compared to the previous observation of Chandra. We see variability
of a factor of 4 during the observation. We find no evidence for the presence
of fluorescent or H-like/He-like iron emission, with upper limits of 52 eV and
110 eV respectively. The limit on the fluorescent emission is improved by a
factor of 15 over the previous estimate, and the restriction on H-like/He-like
emission is lower than predicted from models by a factor of roughly 2.Comment: 6 pages, 7 figures, ApJ accepte
A Black Hole in the X-Ray Nova Velorum 1993
We have obtained 17 moderate-resolution (~2.5 A) optical spectra of the
Galactic X-ray Nova Velorum 1993 in quiescence with the Keck-II telescope. The
orbital period (P) is 0.285206 +/- 0.0000014 d, and the semiamplitude (K_2) is
475.4 +/- 5.9 km/s. Our derived mass function, f(M_1) = PK_2^3 /2 pi G = 3.17
+/- 0.12 M_sun, is close to the conventional absolute limiting mass for a
neutron star (~ 3.0-3.2 M_sun) -- but if the orbital inclination i is less than
80 degrees (given the absences of eclipses), then M_1 is greater than 4.2-4.4
M_sun for nominal secondary-star masses of 0.5 M_sun (M0) to 0.65 M_sun (K6).
The primary star is therefore almost certainly a black hole rather than a
neutron star. The velocity curve of the primary from H-alpha emission has a
semiamplitude (K_1) of 65.3 +/- 7.0 km/s, but with a phase offset by 237
degrees (rather than 180 degrees) from that of the secondary star. The nominal
mass ratio q = M_2/M_1 = K_1/K_2 = 0.137 +/- 0.015, and hence for M_2 =
0.5-0.65 M_sun we derive M_1 = 3.64-4.74 M_sun. An adopted mass M_1 ~ 4.4 M_sun
is significantly below the typical value of ~ 7 M_sun found for black holes in
other low-mass X-ray binaries.
Keck observations of MXB 1659-29 (V2134 Oph) in quiescence reveal a probable
optical counterpart at R = 23.6 +/- 0.4 mag.Comment: 16 pages, 9 figures, added references, revised per. referee's
comments Accepted for publication in August 1999 issue of PAS
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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