Application of Pade Approximants to Determination of alpha_s(M_Z^2) from Hadronic Event Shape Observables in e+e- Annihilation

We have applied Pade approximants to perturbative QCD calculations of event shape observables in e+e- --> hadrons. We used the exact O(alpha_s^2) prediction and the [0/1] Pade approximant to estimate the O(alpha_s^3) term for 15 observables, and in each case determined alpha_s(M_Z^2) from comparison with hadronic Z^0 decay data from the SLD experiment. We found the scatter among the alpha_s(M_Z^2) values to be significantly reduced compared with the standard O(alpha_s^2) determination, implying that the Pade method provides at least a partial approximation of higher-order perturbative contributions to event shape observables.Comment: 15 pages, 1 EPS figure, Submitted to Physics Letters

A simple toy model of the advective-acoustic instability I. Perturbative approach

Some general properties of the advective-acoustic instability are described and understood using a toy model which is simple enough to allow for analytical estimates of the eigenfrequencies. The essential ingredients of this model, in the unperturbed regime, are a stationary shock and a subsonic region of deceleration. For the sake of analytical simplicity, the 2D unperturbed flow is parallel and the deceleration is produced adiabatically by an external potential. The instability mechanism is determined unambiguously as the consequence of a cycle between advected and acoustic perturbations. The purely acoustic cycle, considered alone, is proven to be stable in this flow. Its contribution to the instability can be either constructive or destructive. A frequency cut-off is associated to the advection time through the region of deceleration. This cut-off frequency explains why the instability favours eigenmodes with a low frequency and a large horizontal wavelength. The relation between the instability occurring in this highly simplified toy model and the properties of SASI observed in the numerical simulations of stellar core-collapse is discussed. This simple set up is proposed as a benchmark test to evaluate the accuracy, in the linear regime, of numerical simulations involving this instability. We illustrate such benchmark simulations in a companion paper.Comment: 14 pages, 10 figures, ApJ in pres

The Broadband Infrared Emission Spectrum of the Exoplanet TrES-3

We use the Spitzer Space Telescope to estimate the dayside thermal emission of the exoplanet TrES-3 integrated in the 3.6, 4.5, 5.8, and 8.0 micron bandpasses of the Infrared Array Camera (IRAC) instrument. We observe two secondary eclipses and find relative eclipse depths of 0.00346 +/- 0.00035, 0.00372 +/- 0.00054, 0.00449 +/- 0.00097, and 0.00475 +/- 0.00046, respectively in the 4 IRAC bandpasses. We combine our results with the earlier K band measurement of De Mooij et al. (2009), and compare them with models of the planetary emission. We find that the planet does not require the presence of an inversion layer in the high atmosphere. This is the first very strongly irradiated planet that does not have a temperature inversion, which indicates that stellar or planetary characteristics other than temperature have an important impact on temperature inversion. De Mooij & Snellen (2009) also detected a possible slight offset in the timing of the secondary eclipse in K band. However, based on our 4 Spitzer channels, we place a 3sigma upper limit of |ecos(w)| < 0.0056 where e is the planets orbital eccentricity and w is the longitude of the periastron. This result strongly indicates that the orbit is circular, as expected from tidal circularization theory.Comment: Accepted by Ap

Detection of a Temperature Inversion in the Broadband Infrared Emission Spectrum of TrES-4

We estimate the strength of the bandpass-integrated thermal emission from the extrasolar planet TrES-4 at 3.6, 4.5, 5.8, and 8.0 micron using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We find relative eclipse depths of 0.137 +/- 0.011%, 0.148 +/- 0.016%, 0.261 +/- 0.059%, and 0.318 +/- 0.044% in these four bandpasses, respectively. We also place a 2 sigma upper limit of 0.37% on the depth of the secondary eclipse in the 16 micron IRS peak-up array. These eclipse depths reveal that TrES-4 has an emission spectrum similar to that of HD 209458b, which requires the presence of water emission bands created by an thermal inversion layer high in the atmosphere in order to explain the observed features. TrES-4 receives more radiation from its star than HD 209458b and has a correspondingly higher effective temperature, therefore the presence of a temperature inversion in this planet's atmosphere lends support to the idea that inversions might be correlated with the irradiance received by the planet. We find no evidence for any offset in the timing of the secondary eclipse, and place a 3 sigma upper limit of |ecos(omega)|<0.0058 where e is the planet's orbital eccentricity and omega is the argument of pericenter. From this we conclude that tidal heating from ongoing orbital circulatization is unlikely to be the explanation for TrES-4's inflated radius.Comment: 10 pages in emulateapj format, 7 figures (some in color), accepted for publication in Ap

Equation-of-State Dependent Features in Shock-Oscillation Modulated Neutrino and Gravitational-Wave Signals from Supernovae

We present 2D hydrodynamic simulations of the long-time accretion phase of a 15 solar mass star after core bounce and before the launch of a supernova explosion. Our simulations are performed with the Prometheus-Vertex code, employing multi-flavor, energy-dependent neutrino transport and an effective relativistic gravitational potential. Testing the influence of a stiff and a soft equation of state for hot neutron star matter, we find that the non-radial mass motions in the supernova core due to the standing accretion shock instability (SASI) and convection impose a time variability on the neutrino and gravitational-wave signals. These variations have larger amplitudes as well as higher frequencies in the case of a more compact nascent neutron star. After the prompt shock-breakout burst of electron neutrinos, a more compact accreting remnant radiates neutrinos with higher luminosities and larger mean energies. The observable neutrino emission in the direction of SASI shock oscillations exhibits a modulation of several 10% in the luminosities and ~1 MeV in the mean energies with most power at typical SASI frequencies of 20-100 Hz. At times later than 50-100 ms after bounce the gravitational-wave amplitude is dominated by the growing low-frequency (<200 Hz) signal associated with anisotropic neutrino emission. A high-frequency wave signal is caused by nonradial gas flows in the outer neutron star layers, which are stirred by anisotropic accretion from the SASI and convective regions. The gravitational-wave power then peaks at about 300-800 Hz with distinctively higher spectral frequencies originating from the more compact and more rapidly contracting neutron star. The detectability of the SASI effects in the neutrino and gravitational-wave signals is briefly discussed. (abridged)Comment: 21 pages, 11 figures, 45 eps files; revised version including discussion of signal detectability; accepted by Astronomy & Astrophysics; high-resolution images can be obtained upon reques

Crucial Physical Dependencies of the Core-Collapse Supernova Mechanism

We explore with self-consistent 2D F{\sc{ornax}} simulations the dependence of the outcome of collapse on many-body corrections to neutrino-nucleon cross sections, the nucleon-nucleon bremsstrahlung rate, electron capture on heavy nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and neutrino-nucleon scattering. Importantly, proximity to criticality amplifies the role of even small changes in the neutrino-matter couplings, and such changes can together add to produce outsized effects. When close to the critical condition the cumulative result of a few small effects (including seeds) that individually have only modest consequence can convert an anemic into a robust explosion, or even a dud into a blast. Such sensitivity is not seen in one dimension and may explain the apparent heterogeneity in the outcomes of detailed simulations performed internationally. A natural conclusion is that the different groups collectively are closer to a realistic understanding of the mechanism of core-collapse supernovae than might have seemed apparent.Comment: 25 pages; 10 figure

Spatial distribution and broad-band spectral characteristics of the diffuse X-ray background, 0.1 - 1.0 keV

Preliminary maps covering more than 85 percent of the sky are presented for three energy bands: the B band, the C band, and the M band. The study was undertaken to find evidence that most of the diffuse X-ray background at energies less than 1 keV is local to the galaxy and that it is most probably due to thermal radiation from a low density plasma which fills a substantial fraction of interstellar space. A preliminary analysis of the data is provided including a report that most of the B and C band flux has a common origin, probably in a 10 to the 6th power K region surrounding the Sun, and that most of the M band flux does not originate from the same material

Evolution of "51Peg b-like" Planets

About one-quarter of the extrasolar giant planets discovered so far have orbital distances smaller than 0.1 AU. These ``51Peg b-like'' planets can now be directly characterized, as shown by the planet transiting in front the star HD209458. We review the processes that affect their evolution. We apply our work to the case of HD209458b, whose radius has been recently measured. We argue that its radius can be reproduced only when the deep atmosphere is assumed to be unrealistically hot. When using more realistic atmospheric temperatures, an energy source appears to be missing in order to explain HD209458b's large size. The most likely source of energy available is not in the planet's spin or orbit, but in the intense radiation received from the parent star. We show that the radius of HD209458b can be reproduced if a small fraction (~1%) of the stellar flux is transformed into kinetic energy in the planetary atmosphere and subsequently converted to thermal energy by dynamical processes at pressures of tens of bars.Comment: 11 pages including 9 figures. A&A, in press. Also available at http://www.obs-nice.fr/guillot/pegasi-planets

Gravitational Wave Background from Neutrino-Driven Gamma-Ray Bursts

We discuss the gravitational wave background (GWB) from a cosmological population of gamma-ray bursts (GRBs). Among various emission mechanisms for the gravitational waves (GWs), we pay a particular attention to the vast anisotropic neutrino emissions from the accretion disk around the black hole formed after the so-called failed supernova explosions. The produced GWs by such mechanism are known as burst with memory, which could dominate over the low-frequency regime below \sim 10Hz. To estimate their amplitudes, we derive general analytic formulae for gravitational waveform from the axisymmetric jets. Based on the formulae, we first quantify the spectrum of GWs from a single GRB. Then, summing up its cosmological population, we find that the resultant value of the density parameter becomes roughly \Omega_{GW} \approx 10^{-20} over the wide-band of the low-frequency region, f\sim 10^{-4}-10^1Hz. The amplitude of GWB is sufficiently smaller than the primordial GWBs originated from an inflationary epoch and far below the detection limit.Comment: 6 pages, 4 figures, accepted for publication in MNRA

Studies of high latitude current systems using MAGSAT vector data

The magnetic disturbance fields caused by global external current systems are considered with particular emphasis on improving the understanding of the physical processes which control high latitude current systems. Following processing the MAGSAT data were routinely plotted in the Universal Time (UT) format as well as in a polar plot format. The H'D'U' coordinate system, was adopted as the standard for representing the MAGSAT residual magnetic field vectors. A data file was generated and the TPOLAR computer code was developed to determine from the orbital elements, the time, latitude, and MLT of the extremum latitude of each transpolar segment of orbit. The precision of the vector data set from MAGSAT prompted an extended exploratory phase for data analysis procedures, modeling techniques and phenomenology