R. Stanga

The Virgo interferometer

The Virgo gravitational wave detector is an interferometer with 3 km long arms in construction near Pisa to be commissioned in the year 2000. Virgo has been designed to achieve a strain sensitivity of a few times at 200 Hz. A large effort has gone into the conception of the mirror suspension system, which is expected to reduce noise to the level of at 10 Hz. The expected signals and main sources of noise are briefly discussed; the choices made are illustrated together with the present status of the experiment.

Measurement of the VIRGO superattenuator performance for seismic noise suppression

Below a few tens of hertz interferometric detection of gravitational waves is masked by seismic vibrations of the optical components. In order to isolate the mirrors of the VIRGO interferometer, a sophisticated suspension system, called superattenuator, has been developed. Its working principle is based on a multistage pendulum acting on seismic vibrations as a chain of second order mechanical low-pass filters. A complete superattenuator has been built and tested. This apparatus allows extending the VIRGO detection band down to a few Hz. A detailed description of the attenuation system and its performance are presented in this article.

An inverted pendulum preisolator stage for the VIRGO suspension system

The design of a new preisolator stage for the VIRGO superattenuator is presented. The device is essentially a 6 m high inverted pendulum with horizontal resonant frequency of 30 mHz. An isolation of 65 dB at 1 Hz has been achieved. Very low forces are needed to move the whole superattenuator acting on the inverted pendulum. For this reason, the system is a suitable platform for the active control of the mirror suspension.

The linear variable differential transformer (LVDT) position sensor for gravitational wave interferometer low-frequency controls

Low-power, ultra-high-vacuum compatible, non-contacting position sensors with nanometer resolution and centimeter dynamic range have been developed, built and tested. They have been designed at Virgo as the sensors for low-frequency modal damping of Seismic Attenuation System chains in Gravitational Wave interferometers and sub-micron absolute mirror positioning. One type of these linear variable differential transformers (LVDTs) has been designed to be also insensitive to transversal displacement thus allowing 3D movement of the sensor head while still precisely reading its position along the sensitivity axis. A second LVDT geometry has been designed to measure the displacement of the vertical seismic attenuation filters from their nominal position. Unlike the commercial LVDTs, mostly based on magnetic cores, the LVDTs described here exert no force on the measured structure.

Inertial control of the mirror suspensions of the VIRGO interferometer for gravitational wave detection

In order to achieve full detection sensitivity at low frequencies, the mirrors of interferometric gravitational wave detectors must be isolated from seismic noise. The VIRGO vibration isolator, called the superattenuator, is fully effective at frequencies above 4 Hz. But the residual motion of the mirror at the mechanical resonant frequencies of the system is too large for the interferometer locking system and must be damped. A multidimensional feedback system, using inertial sensors and digital processing, has been designed for this purpose. An experimental procedure for determining the feedback control of the system has been defined. In this article a full description of the system is given and experimental results are presented.

A MULTI-ELECTRODE SILICON DETECTOR FOR HIGH-ENERGY EXPERIMENTS

Abstract A detector has been developed in our laboratory for proposed use in high energy experiments. It works as a MWPC in which the ionizing medium consists of a thin layer of silicon crystal. The results of the test carried out at CERN show that the detector is ideally suited for the detection of minimum ionizing particles and can provide very high spatial resolution.

Electronic measurement of the lifetime of D± mesons

Abstract Charmed meson pairs have been photoproduced coherently on an active silicon target. Ninety-eight decays have been analyzed and the lifetime of charged Ds has been measured.

Morphology of the 12 micron Seyfert galaxies. II. Optical and near-infrared image atlas

We present 263 optical and near-infrared (NIR) images for 42 1s and 48 Seyfert 2s, selected from the Extended 12 μm Galaxy Sample. Elliptically averaged profiles are derived from the images, and isophotal radii and magnitudes are calculated from these. We also report virtual aperture photometry that, judging from comparison with previous work, is accurate to roughly 0.05 mag in the optical, and 0.07 mag in the NIR. Our B-band isophotal magnitude and radii, obtained from ellipse fitting, are in good agreement with those of Third Reference Catalogue of Bright Galaxies. When compared with the B band, V, I, J, and K isophotal diameters show that the colors in the outer regions of Seyfert galaxies are consistent with the colors of normal spirals. Differences in the integrated isophotal colors and comparison with a simple model show that the active nucleus + bulge are stronger and redder in the NIR than in the optical. Finally, roughly estimated Seyfert disk surface brightnesses are significantly brighter in B and K than those in normal spirals of similar morphological type.

ARNICA, THE ARCETRI NEAR-INFRARED CAMERA

ARNICA (ARcetri Near-Infrared CAmera) is the imaging camera for the near-infrared bands between 1.0 and 2.5 microns that the Arcetri Observatory has designed and built for the Infrared Telescope TIRGO located at Gornergrat, Switzerland. We describe the mechanical and optical design of the camera, and report on the astronomical performance of ARNICA as measured during the commissioning runs at the TIRGO (December, 1992 to December 1993), and an observing run at the William Herschel Telescope, Canary Islands (December, 1993). System performance is defined in terms of efficiency of the camera+telescope system and camera sensitivity for extended and point-like sources.

A new fast and programmable trigger logic

Abstract The NAl (FRAMM) experiment, under construction for the CERN-SPS North Area, deals with more than 1000 counter signals which have to be combined together in order to build sophisticated and highly selective triggers. These requirements have led to the development of a low cost, combinatorial, fast electronics which can replace, in an advantageous way, the standard NIM electronics at the trigger level. The essential performances of the basic circuit are: 1. 1) programmability of any desired logical expression; 2. 2) trigger time independent of the chosen expression; 3. 3) reduced cost and compactness due to the use of commercial RAMs, PROMs, and PLAs; 4. 4) short delay, less than 20 ns, between input and output pulses.