Antonio Cali

Metal Abundances of Red Clump Stars in Open Clusters. I. NGC 6819

We present an analysis of high-dispersion spectra (R ~ 40,000) of three red clump stars in the old open cluster NGC 6819. The spectra were obtained with SARG, the high-dispersion spectrograph of the Telescopio Nazionale Galileo. The spectra were analyzed using both equivalent widths measured with an automatic procedure and comparisons with synthetic spectra. NGC 6819 is found to be slightly metal-rich ([Fe/H] = +0.09 ± 0.03, internal error); there are no previous high-resolution studies to compare. Most element-to-element abundance ratios are close to solar; we find a slight excess of Si and a significant Na overabundance. Our spectra can also be used to derive the interstellar reddening toward the cluster by comparing the observed colors with those expected from line excitation: we derive E(B-V) = 0.14 ± 0.04, in agreement with the most recent estimate for this cluster.

Progress on photon-counting intensified APS

We report on the progress of the activity, started one year ago, to obtain a photon counting, MCP-based detector, optimized for high count-rate. A new electronic board, hosting both the APS and the electronics processing unit, has been developed. The new architecture of the system, designed to drive the detector, to acquire the images and compute the photon event centers, is described in detail in this paper. We also report the functional tests carried out on the sub-parts of the detector along with a preliminary characterization of the system.

Photon counting system based on intensified CMOS-APS: PC-IAPS

A progress report on the work, started ten months ago, aimed to evaluate the use of a new type of position sensor (Complementary Metal Oxide Semiconductor Active Pixel Sensor or CMOS-APS) as readout system in MCP-based intensified photon counting systems, is presented in this paper. The main differences respect to the more classical Photon Counting Intensified CCDs (PC-ICCD), the advantages and the disadvantages of their use as image photon counters, the adopted solutions to acquire the images and compute the photon event center, are described. The adopted optics and the designed mechanical assembly are also shown. The selected CMOS-APS, heart of the system, is treated in detail, as well as the electronics designed to drive the detector, to compute the center of the luminous spot on the MCP phosphor screen, and to send and receive data from a host computer. Finally we present preliminary results and achieved performances.

Comparison between the EUV performances of cryogenically cooled CCDs and a MAMA detector

The results of some measurements to characterize the performance of various cryogenically cooled CCDs and of a Multi Anode Microchannel Array detector in the Extreme UltraViolet region (EUV) are presented. A performance comparison between the two different types of detector was made: from these measurements some indications can be obtained which say in what conditions and for what applications one detector is preferable to the other. This can have some important implications, for example in choosing a detector for a space mission.

Characterization of SPAD Arrays: First Results

SPAD detectors are very promising for astrophysical applications. Large arrays are crucial to cover as much of the focal plane as possible. STMicroelectronics has developed various monolithic arrays of SPAD. At present, the manufacturing of 5×5 arrays (each with an active area of 40 μm and pitch between adjacent pixels of 240 μm) is completed and improvements in terms of pixels and technology are under study and development. An appropriate cryogenic system to host the packaged SPAD arrays and detection electronics to drive them have been designed and realized. Electro-optical characteristics of various arrays in different operating conditions have been measured and the obtained results are presented herein.

A New Photon Counting Detector: Intensified CMOS-APS

A new type of position sensor (CMOS-APS) used as readout system in MCP-based intensified photon counter is presented. Thanks to CMOS technology, the pixel addressing and the readout circuits as well as the analogue-to-digital converters are integrated into the chip. These unique characteristics make the CMOS-APS a very compact, low power consumption, photon counting system. The more classical Photon Counting Intensified CCDs (PC-ICCD), the selected CMOS-APS, the driving and interface electronics based on Field Programmable Gate Array (FPGA), and the adopted algorithm to compute the center of the luminous spot on the MCP phosphor screen are described.

Tests of SARG: the high-resolution spectrograph for TNG

We present results of laboratory test of the high resolution spectrograph, that will be soon in operation at TNG telescope, La Palma. These first result shows that the instruments performs according to specifications, providing the expected very high resolution; and that can be operated remotely according to the TNG standards.

High-resolution spectrograph of TNG: a status report

The high resolution spectrograph of the TNG (SARG) was projected to cover a spectral range from (lambda) equals 0.37 up to 0.9 micrometer, with resolution ranging from R equals 19,000 up to R equals 144,000. The dispersing element of the spectrograph is an R4 echelle grating in Quasi-Littrow mode; the beam size is 100 mm giving an RS product of RS equals 46,000 at order center. Both single object and long slit (up to 30 arcsec) observing modes are possible: in the first case cross-dispersion is provided by means of a selection of four grisms; interference filters are used for the long slit mode. A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048 X 4096 EEV CCDs (pixel size: 13.5 micrometer) allowing complete spectral coverage at all resolving power for (lambda) less than 0.8 micrometer. Confocal image slicers are foreseen for observations at R greater than or equal to 76,000; an absorbing cell for accurate radial velocities is also considered. SARG will be rigidly fixed to one of the arms of the TNG fork by means of an optical table and a special thermally insulating enclosure (temperature of all spectrograph components will be kept constant at a preset value by a distributed active thermal control system). All functions are motorized in order to allow very stable performances and full remote control. The architecture of SARG controls will be constructed around a VME crate linked to the TNG LAN and the instrument Workstation B by a fiber optic link.