The PSPT in Rome
The first PSPT (Precision Solar Photometric Telescope),
which was planned and built by the National Solar
Observatory, in the frame of the RISE project,for the
acquisition of solar images endowed with a high
photometric preicision,for the study of solar
variability, has been operative at the Astronomical
Observatory of Rome since February 1996.
This telescope gives whole-disk images of the Sun, on
three different wavelengths, characterized by a nominal
spatial resolution of ~1arcsec/pixel (which corresponds
to about 750 km upon the Solar surface),and a
photometric precision of the order of 0.1% per pixel.
The images, calibrated for instrumental effects, are
available through Internet connection to the Website of
The PSPT project
In the frame of the RISE project, the section of
Sacramento Peak of the National Solar Observatory (New
Mexico, USA) takes care of the planning and realization
of the PSPT telescopes, optimized for the acquisition of
photometric images of the whole Solar disk.
Since the main scientific interests connected with the
usage of these images involve an understanding of the
origin of the variations of Solar irradiance and
luminosity, the main request of the project was the
accuracy of the differential photometry of the surface
of the Sun (both by pixel and observation) such as to
allow a direct comparison with variations of
irradiance as measured from space, equal to 0.1% of
solar irradiance on short time scales.
The PSPT instruments are now coordinating their activity
so as to allow the acquisition of homogeneous data; we
also foresee theacquisition of long continuous series of
The daily program of observations with the PSPT
telescopes includes the acquisition of individual
images, obtained at fixed intervals to monitor the
activity of the Sun, as well as series of
images acquired in order to make instrument
calibrations in all three spectrum bands of observation.
In the month of March 1995, the Astronomical Observatory
of Rome, in collaboration with the Physics Department of
the Tor Vergata University of Rome, started its
collaboration with the RISE/PSPT project, financing the
realization of the first PSPT, which was then installed
After the installation of the PSPT in Rome (Fig. 1), two
other instruments were realized and then installed,
respectively in the summer of 1998, at the Solar
Observatory of Mauna Loa (Hawaii, USA), and from the
start of the year 2000 at the Solar Observatory of
Sacramento Peak (New Mexico, USA).
Figure 1: The
PSPT telescope and the host-dome at the Astronomical
of Monte Porzio Catone (Rome)
A short history of the PSPT in Rome
A prototype of the PSPT was
installed in one of the small domes of the main building of
the Monte Mario branch of the Astronomical Observatory of
Rome in February 1996.
The images obtained with this
prototype were acquired through a CCD Thomson (A/D at 12
bit/pixel) detector of 1024x1024 elements, by using two
interferential filters centered on the continuous blue
(409.6nm, through band = 0.5nm) and on the CaII K line
(393.3nm, through band = 0.25nm).
The results of the calibration of data acquired with the
Rome prototype (stability of flat-field, compensation of the
active mirror, evaluation of diffuse lighting), as well as
the control of the procedures for the acquisition and the
calibration of data (connection between the Sun workstation
Sun and the Personal computer, calculation of flat-field)
suggested significant changes in the final versions of the
PSPT now operating in the three sites (Mauna Loa, Sacramento
Peak, and Roma).
In June 1997, the PSPT prototype active in Monte Mario was
replaced by a quasi-definitive version of the instrument.
On this occasion, the body of the telescope, the electronic
monitoring and data-acquisition system, as well as the CCD
detector, were replaced with other components, whose main
features will be described in the following.
Also interferential filtres used sofar were replaced with
other filtres centered upon the same wavelengths in the
continuous blue and on the CaII K line, with a narrower
through passband, and another filter was added and focussed
upon the continuous red.
Finally , in the month of September 2001, when the PSPT
telescope was transferred to the main branch of the
Astronomical Observatory of Rome in Monte Porzio Catone,
(Figure 1), the system was partly modified, so as to make it
identical to the telescopes realized and already working in
The main changes consist in the replacement of the old
objective with a new one with better reflectivity, and the
removal of a thermal filter inside the telescope.
the foreseen update of the software employed by the system
for the telescope monitoring and the data acquisition could
not be made because of an incompatibility of the hardware
used in the Rome telescope, with the telescopes operating in
April 2007 we are using two new
interferential filters: one
centered on the continuous Green (535.7nm;
band = 0.50nm)
and one in the
(430.6nm; band = 1.20nm).
Since September 2008 we replaced the Green filter with a new
CaII K with a
narrower through bandpass
(393.3nm, through band = 0.10nm).