2,280 research outputs found
Partial waves of baryon-antibaryon in three-body B meson decay
The conspicuous threshold enhancement has been observed in the
baryon-antibaryon subchannels of many three-body B decay modes. By examining
the partial waves of baryon-antibaryon, we first show for B- -->pp-bar K- that
the pK- angular correlation rules out dominance of a single pp-bar partial wave
for the enhancement, for instance, the resonance hypothesis or the strong
final-state interaction in a single channel. The measured pK- angular
correlation turns out to be opposite to the naive expectation of the
short-distance picture. We study the origin of this reversed angular
correlation in the context of the pp-bar partial waves and argue that NN-bar
bound states may be the cause of this sign reversal. Dependence of the angular
correlation on the pp-bar invariant mass is very important to probe the
underlying problem from the experimental side.Comment: 16 pages, 9 figures, the version for journal publicatio
Dust in Intermediate Polars: Light Curves from the Spitzer Space Telescope
Here we present Spitzer 4.5 ÎŒm light curves of two intermediate polars (IPs)âDQ Her and EX Hyaâobtained with Cycle 6 observations. Our initial evaluation of the light curves of DQ Her and EX Hya shows that these two IPs exhibit similar behavior as that seen in nonâmagnetic systems (specifically WZ Sge). The binary eclipses seen in the Spitzer light curves of DQ Her and EX Hya are about three times longer than their optical counterparts, indicating that a reservoir of dust extends beyond the outer edge of the optically visible accretion disk
Establishing Visible Interferometer System Responses: Resolved and Unresolved Calibrators
The propagation of errors through the uniform disk visibility function is
examined. Implications of those errors upon measures of absolute visibility
through optical and near-infrared interferometers are considered within the
context of using calibration stars to establish system visibilities for these
instruments. We suggest a simple ratio test to establish empirically whether or
not the measured visibilities produced by such an instrument are relative
(errors dominated by calibrator angular size prediction error) or absolute
(errors dominated by measurement error).Comment: 20 pages, 7 figures, to be published in the PAS
Spitzer Space Telescope Observations of Circumbinary Dust Disks around Polars
We present Spitzer Space Telescope IRAC photometry of the magnetic cataclysmic variables EF Eri, MR Ser, VV Pup, V834 Cen, GG Leo and V347 Pav. When we combine our results with the 2MASS data, we find that at least five of the polars have flux densities in the mid-IR in excess of the emission expected from the stellar components alone. We are unable to model this mid-IR excess with cyclotron emission, but we can recreate the observed spectral energy distributions with the inclusion of a simple circumbinary dust disk model. Importantly, we find that the masses of our modelled disks are approximately 12 orders of magnitude lower than required to significantly affect CV evolution. The accretion disk-less polars are ideal places to search for these disks, since the luminous accretion disk in most CVs would drown out the faint IR signature of the cooler, dimmer circumbinary disks
Outbursts of EX Hydrae Revisited
We present optical spectroscopy of EX Hya during its 1991 outburst. This
outburst is characterised by strong irradiation of the front face of the
secondary star by the white dwarf, an overflowing stream which is seen strongly
in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the
binary and spin phases. Strong irradiation of the accretion curtain and that of
the inner regions of the disc led to strong emission of HeII and to the
suppression of the Hg and Hb emission.
Disc overflow was observed in quiescence in earlier studies, where the
overflow stream material was modulated at high velocities close to 1000 km/s.
In outburst, the overflowing material is modulated at even higher velocities
(~1500 km/s). These are streaming velocities down the field lines close to the
white dwarf. Evidence for material collecting near the outer edge of the disc
and corotating with the accretion curtain was observed. In decline, this
material and the accretion curtain obscured almost all the emission near binary
phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse
minimum. This has provided additional evidence for an extended accretion
curtain, and for the corotation of material with the accretion curtain at the
outer edge of the disc. From these observations we suggest that a mechanism
similar to that of Spruit & Taam, where outbursts result due to the storage and
release of matter outside the magnetosphere, triggers the outbursts of EX Hya.
This is followed by the irradiation of the secondary star due to accretion
induced radiation.Comment: 12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low
resolution. Paper accepted by the Monthly Notices of the Royal Astronomical
Societ
EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae
We present simultaneous X-ray (lambda_peak ~ 44A) and EUV (lambda_peak = 89A)
light curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with
the EUVE satellite. We find that the unique shape of the X-ray light curve is
different from previously obtained X-ray light curves of QQ Vul and provides
evidence for two-pole accretion. Detailed examination of the photometric data
indicates that QQ Vul undergoes a stellar eclipse of the X-ray emitting region,
indicative of a high binary inclination. We discuss possible implications for
the nature of this system given the observed shape of its EUV and X-ray light
curves.Comment: 12 pages including 4 figures, accepted to PAS
First Spitzer Space Telescope Observations of Magnetic Cataclysmic Variables: Evidence for Excess Emission at 3--8 microns
We present the first observations of magnetic cataclysmic variables with the
Spitzer Space Telescope. We used the Infrared Array Camera to obtain photometry
of the polars EF Eri, GG Leo, V347 Pav, and RX J0154.0-5947 at 3.6, 4.5, 5.8,
and 8.0 m. In all of our targets, we detect excess mid-infrared emission
over that expected from the component stars alone. We explore the origin of
this IR excess by examining bremsstrahlung, cyclotron emission, circumbinary
dust, and L/T brown dwarf secondary stars. Bremsstrahlung and cyclotron
emission appear unlikely to be significant contributors to the observed fluxes.
At present, the most likely candidate for the excess emission is dust that is
probably located in a circumbinary disk with an inner temperature near 800 K.
However, a simple dust disk plus any reasonable low mass or brown dwarf-like
secondary star is unable to fully explain the observed flux densities in the
3--8 m region.Comment: Accepted to ApJ Letter
Simultaneous X-ray and Optical Observations of EX Hydrae
The intermediate polar, EX Hydrae, was the object of a large simultaneous
multiwavelength observational campaign during 2000 May - June. Here we present
the Rossi X-ray Timing Explorer photometry and optical photometry and
spectroscopy from ground-based observatories obtained as part of this campaign.
Balmer line radial velocities and Doppler maps provide evidence for an extended
bulge along the outer edge of the accretion disk and some form of
extended/overflowing material originating from the hot spot. In addition, the
optical binary eclipse possesses an extended egress shoulder, an indication
that an additional source (other than the white dwarf) is coming out of
eclipse. We also compare the X-ray and optical results with the results
obtained from the EUV and UV observations from the multiwavelength data set.Comment: to appear in the Astronomical Journal, April 200
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