512 research outputs found
Extending emission line Doppler tomography ; mapping modulated line flux
Emission line Doppler tomography is a powerful tool that resolves the
accretion flow in binaries on micro-arcsecond scales using time-resolved
spectroscopy. I present an extension to Doppler tomography that relaxes one of
its fundamental axioms and permits the mapping of time-dependent emission
sources. Significant variability on the orbital period is a common
characteristic of the emission sources that are observed in the accretion flows
of cataclysmic variables and X-ray binaries. Modulation Doppler tomography maps
sources varying harmonically as a function of the orbital period through the
simultaneous reconstruction of three Doppler tomograms. One image describes the
average flux distribution like in standard tomography, while the two additional
images describe the variable component in terms of its sine and cosine
amplitudes. I describe the implementation of such an extension in the form of
the maximum entropy based fitting code MODMAP. Test reconstructions of
synthetic data illustrate that the technique is robust and well constrained.
Artifact free reconstructions of complex emission distributions can be achieved
under a wide range of signal to noise levels. An application of the technique
is illustrated by mapping the orbital modulations of the asymmetric accretion
disc emission in the dwarf nova IP Pegasi.Comment: 8 pages, 4 figures; accepted for publication in MNRA
3D Finite Volume Simulation of Accretion Discs with Spiral Shocks
We perform 2D and 3D numerical simulations of an accretion disc in a close
binary system using the Simplified Flux vector Splitting (SFS) finite volume
method. In our calculations, gas is assumed to be the ideal one, and we
calculate the cases with gamma=1.01, 1.05, 1.1 and 1.2. The mass ratio of the
mass losing star to the mass accreting star is unity. Our results show that
spiral shocks are formed on the accretion disc in all cases. In 2D calculations
we find that the smaller gamma is, the more tightly the spiral winds. We
observe this trend in 3D calculations as well in somewhat weaker sense.Comment: 2 pages, LaTeX with 2 ps figures using crckapb.sty. To appear in the
Proceedings of Numerical Astrophysics 1998, Tokyo, Japan, 10-13 March, 1998,
eds. S. M. Miyama, K. Tomisaka and T. Hanawa (Kluwer Academic Publishers
Spiral shocks in the accretion disc of IP Peg during outburst maximum
In response to our recent discovery of spiral arms in the accretion disc of
IP Peg during rise to outburst, we have obtained time-resolved
spectrophotometry of IP Peg during outburst maximum. In particular, indirect
imaging of HeII 4686, using Doppler tomography, shows a two-arm spiral pattern
on the disc image, which confirms repeatability over different outbursts. The
jump in HeII intensity (a factor of more than two) and in velocity (~200--300
km/s) clarifies the shock nature of the spiral structure. The HeII shocks show
an azimuthal extent of ~90 degrees, a shallow power-law emissivity ~V^{-1}, an
upper limit of 30 degrees in opening angle, and a flux contribution of 15 per
cent of the total disc emission. We discuss the results in view of recent
simulations of accretion discs which show that spiral shocks can be raised in
the accretion disc by the secondary star.Comment: 5 pages, 4 figures, MNRAS journal paper. in pres
Spiral Structure in IP Peg: Confronting Theory and Observations
The first convincing piece of evidence of spiral structure in the accretion
disc in IP Pegasi was found by Steeghs et al. (1997). We performed two kinds of
2D hydrodynamic simulations, a SFS finite volume scheme and a SPH scheme, with
a mass ratio of 0.5. Both results agreed well with each other. We constructed
Doppler maps and line flux-binary phase relations based on density
distributions, the results agreeing well with those obtained by observation.Comment: 4 pages, LaTeX with 2 ps figures using crckapb.sty. To appear in the
Proceedings of Numerical Astrophysics 1998, Tokyo, Japan, 10-13 March, 1998,
eds. S. M. Miyama, K. Tomisaka and T. Hanawa (Kluwer Academic Publishers
Spectroscopy of Candidate Members of the Eta Cha and MBM12 Young Associations
We present an analysis of candidate members of the Eta Cha and MBM 12A young
associations. For an area of 0.7 deg^2 toward Eta Cha, we have performed a
search for members of the association by combining JHK_s photometry from 2MASS
and i photometry from DENIS with followup optical spectroscopy at Magellan
Observatory. We report the discovery of three new members with spectral types
of M5.25-M5.75, corresponding to masses of 0.13-0.08 M_sun by theoretical
evolutionary models. Two and three of these members were found independently by
Lyo and coworkers and Song and coworkers, respectively. Meanwhile, no brown
dwarfs were detected in Eta Cha down to the completeness limit of 0.015 M_sun.
For MBM 12A, we have obtained spectra of three of the remaining candidate
members that lacked spectroscopy at the end of the survey by Luhman, all of
which are found to be field M dwarfs. Ogura and coworkers have recently
presented four "probable" members of MBM 12A. However, two of these objects
were previously classified as field dwarfs by the spectroscopy of Luhman. In
this work, we find that the other two objects are field dwarfs as well.Comment: to be published in The Astrophysical Journal, 19 pages, 7 figure
Precision Ephemerides For Gravitational Wave Searches: II. Cyg X-2
Accreting neutron stars in low-mass X-ray binaries (LMXBs) are candidate
high-frequency persistent gravitational wave sources. These may be detectable
with next generation interferometers such as Advanced LIGO/VIRGO within this
decade. However, the search sensitivity is expected to be limited principally
by the uncertainty in the binary system parameters. We combine new optical
spectroscopy of Cyg X-2 obtained with the Liverpool Telescope (LT) with
available historical radial velocity data, which gives us improved orbital
parameter uncertainties based on a 44-year baseline. We obtained an improvement
of a factor of 2.6 in the orbital period precision and a factor of 2 in the
epoch of inferior conjunction T_0. The updated orbital parameters imply a mass
function of 0.65 +/- 0.01 M_sun, leading to a primary mass (M_1) of 1.67 +/-
0.22 M_sun (for i=62.5 +/- 4 deg). In addition, we estimate the likely orbital
parameter precision through to the expected Advanced LIGO and VIRGO detector
observing period and quantify the corresponding improvement in sensitivity via
the required number of templates.Comment: 7 pages, 3 figures, accepted for publication by Ap
Quiescent NIR and optical counterparts to candidate black hole X-ray binaries
We present near-infrared and optical imaging of fifteen candidate black hole
X-ray binaries. In addition to quiescent observations for all sources, we also
observed two of these sources (IGR J17451-3022 and XTE J1818-245) in outburst.
We detect the quiescent counterpart for twelve out of fifteen sources, and for
the remaining three we report limiting magnitudes. The magnitudes of the
detected counterparts range between = 17.59 and = 22.29 mag. We
provide (limits on) the absolute magnitudes and finding charts of all sources.
Of these twelve detections in quiescence, seven represent the first quiescent
reported values (for MAXI J1543-564, XTE J1726-476, IGR J17451-3022, XTE
J1818-245, MAXI J1828-249, MAXI J1836-194, Swift J1910.2-0546) and two
detections show fainter counterparts to XTE J1752-223 and XTE J2012+381 than
previously reported. We used theoretical arguments and observed trends, for
instance between the outburst and quiescent X-ray luminosity and orbital period
to derive an expected trend between and of
. Comparing this to observations we
find a different behaviour. We discuss possible explanations for this result.Comment: 18 pages, 6 figures. Accepted for publication in MNRA
On the mass of the neutron star in V395 Car/2S 0921-630
We report high-resolution optical spectroscopy of the low-mass X-ray binary
V395 Car/2S 0921-630 obtained with the MIKE echelle spectrograph on the
Magellan-Clay telescope. Our spectra are obtained near superior conjunction of
the mass donor star and we exploit the absorption lines originating from the
back-side of the K-type object to accurately derive its rotational velocity.
Using K0-K1 III templates, we find vsini=32.9 +/- 0.8 km/s. We show that the
choice of template star and the assumed limb darkening coefficient has little
impact on the derived rotational velocity. This value is a significant revision
downwards compared to previously published values. We derive new system
parameter constraints in the light of our much lower rotational velocity. We
find M_1=1.44 +/- 0.10 Msun, M_2=0.35 +/- 0.03 Msun, and q=0.24 +/- 0.02 where
the errors have been estimated through a Monte-Carlo simulation. A possible
remaining systematic effect is the fact that we may be over-estimating the
orbital velocity of the mass donor due to irradiation effects. However, any
correction for this effect will only reduce the compact object mass further,
down to a minimum mass of M_1=1.05 +/- 0.08 Msun. There is thus strong evidence
that the compact object in this binary is a neutron star of rather typical mass
and that the previously reported mass values of 2-4Msun were too high due to an
over-estimate of the rotational broadening.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
The component masses of the cataclysmic variable V347 Puppis
We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km sâ1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km sâ1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 Mâ for the white dwarf primary and M2= 0.52 ± 0.06 Mâ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc
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