We shall describe here the main features of the PSPT telescope, in its definitive version, according to the conditions of the three sites. Small differences among the three systems do not affect the validity of the present overall description.


FIGURE 2: PSPT telescope during observation.

The PSPT is a refracting telescope with a small diameter, working on the diffraction limit and acquiring full-disk images of the Sun through five interferential filters with a relatively narrow band. The telescope, endowed with an equatorial mount and a computer-controlled time movement, has an optical design which lowers the level of scattered light in the instrument.

The images have been acquired, until the 11 March 2022, by a CCD 2048×2048 detector, with a very short exposure (generally of the order of 40ms). In order to increase the photometric accuracy of acquired data, several exposures are joint so as to create a single image. An active mirror stabilizes the image field so as to prevent a series of exposures from significantly affecting the resolution quality of the acquired image. The system also included a scintillation monitor as well as flux channels, which could be used to measure the change in atmospheric transparency during the acquisition as well as to select images.

Telescope sighting and the movement of its mechanisms have been controlled by a software running on PC 486 and DSP (Digital Signal Processor), whereas data acquisition and system check during acquisition have been handled by special programs in C and IDL language, running on a Sun Ultra Sparc 1 workstation.

From 17 March 2023 new optical elements, novel electronics, a new Andor Zyla 4.2+ sCMOS camera, and a new control software were installed at the telescope. The new sCMOS camera, which has a sensor of 2048×2048 pixels (16 bit/pixel) with a pixel size of 6.5 ɥm, allows for frame rate of 53 imm/s at (2048×2048) and 1578 imm/s at (128×128) and a read noise of 1.1 e-. These characteristics allow for acquisition of images with exposure times of the order of 1 ms, which are significantly smaller than the ones used with the previous camera requiring the image stabilization during data acquisition. Accordingly, the optical path and control system of the Rome/PSPT were simplified by removing all the components needed for the image stabilization. Besides, new electronics and software were realized to control the telescope and to acquire the data. The telescope and data acquisition are now operated through a simple GUI in Windows 10 OS.