Aqueye+ is a new ultrafast optical single photon counter, based on single photon avalanche photodiodes (SPAD) and a 4-fold split-pupil concept. It is a completely revisited version of its predecessor, Aqueye, successfully mounted at the 182 cm Copern
icus telescope in Asiago. Here we will present the new technological features implemented on Aqueye+, namely a state of the art timing system, a dedicated and optimized optical train, a high sensitivity and high frame rate field camera and remote control, which will give Aqueye plus much superior performances with respect to its predecessor, unparalleled by any other existing fast photometer. The instrument will host also an optical vorticity module to achieve high performance astronomical coronography and a real time acquisition of atmospheric seeing unit. The present paper describes the instrument and its first performances.
The Crab nebula pulsar was observed in 2009 January and December with a novel very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we computed accurate phase
coherent timing solutions for the two observing runs and over the entire year 2009. Our statistical uncertainty on the determination of the phase of the main pulse and the rotational period of the pulsar for short (a few days) time intervals are $approx 1 , mu$s and ~0.5 ps, respectively. Comparison with the Jodrell Bank radio ephemerides shows that the optical pulse leads the radio one by ~240 $mu$s in January and ~160 $mu$s in December, in agreement with a number of other measurements performed after 1996. A third-order polynomial fit adequately describes the spin-down for the 2009 January plus December optical observations. The phase noise is consistent with being Gaussian distributed with a dispersion $sigma$ of $approx 15 , mu$s in most observations, in agreement with theoretical expectations for photon noise-induced phase variability.
We observed the Crab pulsar in October 2008 at the Copernico Telescope in Asiago - Cima Ekar with the optical photon counter Aqueye (the Asiago Quantum Eye) which has the best temporal resolution and accuracy ever achieved in the optical domain (hund
reds of picoseconds). Our goal was to perform a detailed analysis of the optical period and phase drift of the main peak of the Crab pulsar and compare it with the Jodrell Bank ephemerides. We determined the position of the main peak using the steepest zero of the cross-correlation function between the pulsar signal and an accurate optical template. The pulsar rotational period and period derivative have been measured with great accuracy using observations covering only a 2 day time interval. The error on the period is 1.7 ps, limited only by the statistical uncertainty. Both the rotational frequency and its first derivative are in agreement with those from the Jodrell Bank radio ephemerides archive. We also found evidence of the optical peak leading the radio one by ~230 microseconds. The distribution of phase-residuals of the whole dataset is slightly wider than that of a synthetic signal generated as a sequence of pulses distributed in time with the probability proportional to the pulse shape, such as the average count rate and background level are those of the Crab pulsar observed with Aqueye. The counting statistics and quality of the data allowed us to determine the pulsar period and period derivative with great accuracy in 2 days only. The time of arrival of the optical peak of the Crab pulsar leads the radio one in agreement with what recently reported in the literature. The distribution of the phase residuals can be approximated with a Gaussian and is consistent with being completely caused by photon noise (for the best data sets).
This paper reports a detailed analysis of the optical light curve of PSR B0540-69, the second brightest pulsar in the visible band, obtained in 2009 (Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon counting photometer Iqueye
mounted at the ESO 3.6-m NTT in La Silla (Chile). The optical light curve derived by Iqueye shows a double structure in the main peak, with a raising edge steeper than the trailing edge. The double peak can be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms respectively. Our new values of spin frequencies allow to extend by 3.5 years the time interval over which a reliable estimate of frequency first and second derivatives can be performed. A discussion of implications on the braking index and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the overall braking index from 1987 to 2009 is derived. The braking index corrected age is confirmed around 1700 years.
We review some applications of self-consistent Greens function theory to studies of one- and two-nucleon structure in finite nuclei. Large-scale microscopic calculations that employ realistic nuclear forces are now possible. Effects of long-range c
orrelations are seen to play a dominant role in determining the quenching of absolute spectroscopic factors. They also enhance considerably (e,epn) cross sections in superparallel kinematics, in agreement with observations.
The cratering history of main belt asteroid (2867) Steins has been investigated using OSIRIS imagery acquired during the Rosetta flyby that took place on the 5th of September 2008. For this purpose, we applied current models describing the formation
and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models coupled with appropriate crater scaling laws, allow the cratering history to be estimated. Hence, we derive Steins cratering retention age, namely the time lapsed since its formation or global surface reset. We also investigate the influence of various factors -like bulk structure and crater erasing- on the estimated age, which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted scaling law and asteroid physical parameters. Moreover, a marked lack of craters smaller than about 0.6km has been found and interpreted as a result of a peculiar evolution of Steins cratering record, possibly related either to the formation of the 2.1km wide impact crater near the south pole or to YORP reshaping.
The space-time correlations of streams of photons can provide fundamentally new channels of information about the Universe. Todays astronomical observations essentially measure certain amplitude coherence functions produced by a source. The spatial c
orrelations of wave fields has traditionally been exploited in Michelson-style amplitude interferometry. However the technology of the past was largely incapable of fine timing resolution and recording multiple beams. When time and space correlations are combined it is possible to achieve spectacular measurements that are impossible by any other means. Stellar intensity interferometry is ripe for development and is one of the few unexploited mechanisms to obtain potentially revolutionary new information in astronomy. As we discuss below, the modern use of stellar intensity interferometry can yield unprecedented measures of stellar diameters, binary stars, distance measures including Cepheids, rapidly rotating stars, pulsating stars, and short-time scale fluctuations that have never been measured before.
The single-particle spectral function of 56Ni has been computed within the framework of self-consistent Greens functions theory. The Faddeev random phase approximation method and the G-matrix technique are used to account for the effects of long- and
short-range physics on the spectral distribution. Large scale calculations have been performed in spaces including up to ten oscillator shells. The chiral N3LO interaction is used together with a monopole correction that accounts for eventual missing three-nucleon forces. The single-particle energies associated with nucleon transfer to valence 1p0f orbits are found to be almost converged with respect to both the size of the model space and the oscillator frequency. The results support that 56Ni is a good doubly magic nucleus. The absolute spectroscopic factors to the valence states on A=55,57 are also obtained. For the transition between the ground states of 57Ni and 56Ni, the calculations nicely agree with heavy-ion knockout experiments.
We respond to a Comment on our recent paper (Phys.Rev.C77:024304,2008) by Paar (arXiv:0803.0274).
The occurrence of a pygmy dipole resonance in proton rich Ar-32 and Ar-34 is studied using the unitary correlator operator method interaction Vucom, based on Argonne V18. Predictions from the random phase approximation (RPA) and the shell model in a
no-core basis are compared. It is found that the inclusion of configuration mixing up to two-particle--two-holes broadens the pygmy strength slightly and reduces sensibly its strength, as compared to the RPA predictions. For Ar-32 a clear peak associated with a pygmy resonance is found. For Ar-34, the pygmy states are obtained close to the giant dipole resonance and mix with it.
