[en] All recent analyses of RR Lyrae stars show that the (V - K) color index is well suited to parameterize SV. The CORS method is used to compute new radii determinations for SW Dra and X Ari, taking into account even slight deviations from the single valued relation between SV and (V - K), assuming therefore the spectroscopically determined effective gravity curve as a second independent degree of freedom. A radius of 5.6 solar radii is obtained for SW Dra and 7.3 solar radii for X Ari. The results support Simon's suggestion that X Ari could be an anomalous Cepheid. 10 refs

[en] The first adaptive optics system for laser beam geometrical fluctuations correction, based on interferometric detection of aberrations, is presented. The bandwidth of the resulting feed-back is of several hundreds Hz and the residual fluctuations, measured on the error signal, are better than what can be obtained by typical Shack-Hartmann technique, encouraging for use in long baseline interferometers for GW detection

[en] Since a few years, the LISA-PF group in Napoli has been working to the development of an optical read-out system, based on optical levers and position sensitive detectors, for the LISA Gravitational Reference Sensor (GRS). This is intended as a more sensitive extra sensing device, in addition to capacitive readout that is the reference solution already tested on flight by the LISA-Pathfinder mission. The reliability of the proposed ORO device and the fulfillment of the sensitivity goals have been already demonstrated in bench-top measurements and tested with torsion pendulum facilities. In this paper we report on the present status of this activity, presenting the results obtained so-far and the perspectives for the future LISA mission. (paper)

[en] In this paper, we analyse the application of an optical readout system to the gravitational reference sensor of LISA. The goal is not the replacement of the capacitive sensor with an optical one, but the integration of the optical sensor in the present design of LISA. The main motivation is the implementation of a back-up solution, so that there is a significant risk reduction for the mission in case the main sensor fails for some reason. Furthermore, an optical system is potentially more sensitive than the capacitive one for some degrees of freedom. In this paper, we report some preliminary experimental results on the sensitivity of the sensor and describe a possible set-up for the implementation according to the present design of the gravitational reference sensor

[en] The LISA test-mass (TM) is sensitive to weak forces along all 6 Degrees of Freedom (DoFs). Extensi ve ground test ing is required in order to evaluate the influence of cross-talks of read-outs and actuators operating on different DoFs. To best represent the flight conditions, we developed in Firenze a facility with 2 soft DoFs. Using this facility we measure the forces and stiffnesses acting simultaneously along the 2 soft DoFs, and, more specifically, we will be able to de b ug residual couplings between the TM and the capacitive position sensor that reads the TM position, and to measure actuation cross talks with closed feedback loop. The facility is now ready, and here we report on the commissioning tests, and on the first measurements.

[en] Ground testing with torsion pendulums played a key role in the development and characterization of the Gravitational Reference Sensor (GRS) of LISA-Pathfinder (LPF). We report on a torsion pendulum facility with 2 soft degrees of freedom (DOF), realized by off-axis cascading two torsion fibers. This instrument, developed for testing on two DOFs the LPF GRS, allows simultaneous measurement of force and torque acting on the suspended test mass (TM), approaching free-fall condition on two DOFs down to a few mHz. We will report on the results of some measurement campaigns devoted in particular to the characterization of force to torque and torque to force actuation cross-talks (CT). (paper)

[en] In the last few years the Lisa group in Napoli has developed an Optical Read-Out (ORO) system based on optical levers as an auxiliary and backup readout for the Gravitational Reference Sensor (GRS) of LISA. Bench-top measurements, with a rigid set-up have successfully proven that the ORO fits the requirements for sensitivity both in translational and rotational DOFs, exceeding the capacitive sensor performance in a wide range of frequencies. Last year an ORO system designed in Napoli in collaboration with the Trento LISA group, has been installed, as an auxiliary readout system, on the four mass torsion pendulum developed in Trento. In this paper we report on the testing of this ORO device and its performances in comparison with the capacitive one; we also outline further improvements and their advantages for the torsion pendulum facility performances.

[en] In this paper the enhancement of the sensitivity and of the duty-cycle of a double stage suspended torsion pendulum are described. The increase in sensitivity, both for force and torque measurements, was obtained rearranging the pendulum mechanics, reducing the value of the suspended masses and moments of inertia and by adopting additional read-outs based on optical levers. The improvement of the duty-cycle was obtained by controlling the suspension point of the pendulum to reduce the effect of seismic noise on the translation resonances of the system. The reduction of these motions allowed continuous operation for three weeks, in high sensitivity regime of the read-out electronics, resulting in a force sensitivity of and a torque sensitivity of around 10 mHz. (paper)

[en] We present an adaptive optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack-Hartman-based AO system, we show that this technique is of particular interest when high sensitivity and high band-pass are required for correction of small perturbations such as, for instance, the control of the input beam of gravitational waves interferometric detectors

[en] The status of advancement of the VIRGO Project is presented: the first-generation results from the Pisa seismic noise super attenuator give an upper limit to the noise transfer function of 2x10^-8 at 10 Hz. The upper limit to the absolute noise of the 400 kg test mass at 10 Hz has been measured to be 1.5x10^-13 m/√Hz. The scheme and the related problems of the VIRGO interferometer, which is supposed to work down to 10 Hz, are also presented. At the 3rd Pisa Meeting in 1986 we presented the idea of what could be a very efficient seismic noise reduction system able to give a sensitivity h∝10^-25 at 10 Hz, in a 3 km interferometer for 1 year integration time. Now we have two new facts to present: the first is that the attenuator has been built, is working in Pisa, and shows remarkable characteristics. The second is the Italian-French interferometer VIRGO, a 3 km long antenna for low and high frequency (10-1000 Hz) gravitational wave (GW) detection. These two items will be presented in this article. (orig.)