2,728 research outputs found
On Completely Mixed Stochastic Games
In this paper, we consider a zero-sum undiscounted stochastic game which has
finite state space and finitely many pure actions. Also, we assume the
transition probability of the undiscounted stochastic game is controlled by one
player and all the optimal strategies of the game are strictly positive. Under
all the above assumptions, we show that the -discounted stochastic games
with the same payoff matrices and sufficiently close to 1 are also
completely mixed. We give a counterexample to show that the converse of the
above result in not true. We also show that, if we have non-zero value in some
state for the undiscounted stochastic game then for sufficiently close
to 1 the -discounted stochastic game also possess nonzero value in the
same state
Circumstellar dust shells of hot post-AGB stars
Using a radiative transfer code (DUSTY) parameters of the circumstellar dust
shells of 15 hot post-AGB stars have been derived. Combining the optical, near
and far-infrared (ISO, IRAS) data of the stars, we have reconstructed their
spectral energy distributions (SEDs) and estimated the dust temperatures, mass
loss rates, angular radii of the inner boundary of the dust envelopes and the
distances to these stars. The mass loss rates
(10Myr) are intermediate between stars at the
tip of the AGB and the PN phase. We have also studied the ISO spectra of 7 of
these stars. Amorphous and crystalline silicate features were observed in
IRAS14331-6435 (Hen3-1013), IRAS18062+2410 (SAO85766) and IRAS22023+5249 (LSIII
+5224) indicating oxygen-rich circumstellar dust shells. The presence of
unidentified infrared (UIR) band at 7.7, SiC emission at 11.5 and the
"26" and "main 30" features in the ISO spectrum of IRAS17311-4924
(Hen3-1428) suggest that the central star may be carbon-rich. The ISO spectrum
of IRAS17423-1755 (Hen3-1475) shows a broad absorption feature at 3.1 due
to CH and/or HCN which is usually detected in the circumstellar
shells of carbon-rich stars.Comment: 18 pages, accepted for publication in A&
UV (IUE) spectra of the central stars of high latitude planetary nebulae Hb7 and Sp3
We present an analysis of the UV (IUE) spectra of the central stars of Hb7
and Sp3. Comparison with the IUE spectrum of the standard star HD 93205 leads
to a spectral classification of O3V for these stars, with an effective
temperature of 50,000 K. From the P-Cygni profiles of CIV (1550 A), we derive
stellar wind velocities and mass loss rates of -1317 km/s +/- 300 km/s and
2.9X10^{-8} solar mass yr^{-1} and -1603 km/s +/- 400 km/s and 7X10^{-9} solar
mass yr^{-1} for Hb7 and Sp3 respectively. From all the available data, we
reconstruct the spectral energy distribution of Hb7 and Sp3.Comment: 4 pages, 3 figures, latex, accepted for publication in Astronomy &
Astrophysic
Photometry and low resolution spectroscopy of hot post-AGB candidates
We have obtained Johnson U, B, V and Cousins R, I photometry and low
resolution spectra of a small sample of hot post-AGB candidates. Using the
present data in combination with JHK data from 2MASS, infrared data from the
MSX catalog and the IRAS fluxes, we have studied the spectral energy
distribution (SED) of these stars. Using the DUSTY code we have estimated the
dust temperatures, the distances to the stars, the mass-loss rates, angular
radii of the inner boundary of the dust envelopes and dynamical ages from the
tip of the AGB. These candidates have also been imaged through a narrow band
H-alpha filter, to search for nebulosity around the central stars. Our H-alpha
images revealed the bipolar morphology of the low excitation PN IRAS 17395-0841
with an angular extent of 2.8arcsec. The bipolar lobes of IRAS 17423-1755 in
H-alpha were found to have an angular extent of 3.5arcsec (south-east lobe) and
2.2arcsec (north-west lobe). The dust envelope characteristics, low resolution
spectrum and IRAS colors suggest that IRAS 18313-1738 is similar to the
proto-planetary nebula (PPN) HD 51585. The SED of IRAS 17423-1755, IRAS
18313-1738 and IRAS 19127+1717 show a warm dust component (in addition to the
cold dust) which may be due to recent and ongoing mass-loss.Comment: 20 pages, 6 figures, h-alpha figure compressed with XV, paper
accepted for publication in Astronomy & Astrophysic
High resolution spectroscopy of the high velocity hot post-AGB star LS III +52 24 (IRAS 22023+5249)
The first high-resolution (R~50,000) optical spectrum of the B-type star, LS
III +52 24, identified as the optical counterpart of the hot post-AGB candidate
IRAS 22023+5249 (I22023) is presented. We report the detailed identifications
of the observed absorption and emission features in the full wavelength range
(4290-9015 A) as well as the atmospheric parameters and photospheric abundances
(under the Local Thermodinamic Equilibrium approximation) for the first time.
The nebular parameters (Te, Ne) are also derived. We estimate Teff=24,000 K,
log g=3.0, xi=7 kms-1 and the derived abundances indicate a slightly
metal-deficient evolved star with C/O<1. The observed P-Cygni profiles of
hydrogen and helium clearly indicate on-going post-AGB mass loss. The presence
of [N II] and [S II] lines and the non-detection of [O III] indicate that
photoionisation has just started. The observed spectral features, large
heliocentric radial velocity, atmospheric parameters, and chemical composition
indicate that I22023 is an evolved post-AGB star belonging to the old disk
population. The derived nebular parameters (Te=7000 K, Ne=1.2x104 cm-3) also
suggest that I22023 may be evolving into a compact, young low-excitation
Planetary Nebula. Our optical spectroscopic analysis together with the recent
Spitzer detection of double-dust chemistry (the simultaneous presence of
carbonaceous molecules and amorphous silicates) in I22023 and other B-type
post-AGB candidates may point to a binary system with a dusty disk as the
stellar origin common to the hot post-AGB stars with O-rich central stars.Comment: Accepted for publication in MNRAS (22 pages, 4 figures, and 8
tables). arXiv admin note: substantial text overlap with arXiv:0707.059
Comment on ``Intermittent Synchronization in a Pair of Coupled Chaotic Pendula"
The main aim of this comment is to emphasize that the conditional Lyapunov
exponents play an important role in distinguishing between intermittent and
persistent synchronization, when the analytic criteria for asymptotic stability
are not uniformly obeyed.Comment: 2 pages, RevTeX 4, 1 EPS figur
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