Photon-counting Photometer Research Articles

Quantum Astronomy at the University and INAF Astronomical Observatory of Padova, Italy

Twenty years ago, we started to apply quantum optics to the astronomical research carried out inside the Department of Physics and Astronomy and the INAF Astronomical Observatory in Padova, Italy. The initial activities were stimulated by the project of the European Southern Observatory (ESO) to build a 100 m diameter telescope, the Overwhelmingly Large (OWL) telescope. The enormous photon flux expected from such an aperture suggested that quantum optics concepts be utilized in order to obtain novel astrophysical results. Following initial successful attempts to utilize the orbital angular momentum of the light beam to enhance the visibility of faint companions to bright stars, the Padova team concentrated its efforts on very high time resolution, in order to measure and store the arrival time of celestial photons to better than one nanosecond. To obtain observational results, we built two photon counting photometers (AquEye and IquEye) to be used with our telescopes of the Asiago Observatory and with 4 m class telescopes such as the ESO New Technology Telescope (NTT) in Chile. This paper firstly describes these two instruments and then expounds the results obtained on pulsar light curves, lunar occultations and the first photon counting intensity interferometry measurements of the bright star Vega. Indeed, the correlation of photon arrival times on two or more apertures can lead to extremely high angular resolutions, as shown around 1970 by Hanbury Brown and Twiss. Prospects for quantum intensity interferometry with arrays of Cherenkov light telescopes will also be described.

Aqueye and Iqueye, Very-High-Time-Resolution Photon-Counting Photometers

AbstractWe describe very high-time-resolution photometers capable of tagging the arrival time of each photon with a resolution and accuracy of few hundred picoseconds, for hours of continuous acquisition, and with a dynamic range of more than 6 orders of magnitude. The final goal is the conceptual definition of a “quantum” photometer for the E-ELT, capable of detecting and measuring second-order correlation effects in photon streams from celestial sources. Two prototype units have been built and operated, one for the Asiago 1.8-m telescope (AquEYE) and one for the 3.5-m NTT (IquEYE).Here we will present results obtained by IquEYE on the Crab Nebula pulsar in simultaneous radio observations with Jodrell Bank in December 2009.

The optical light curve of the Large Magellanic Cloud pulsar B0540−69 in 2009

This paper reports a detailed analysis of the optical light curve of PSR B0540−69, the second brightest pulsar in the visible band, obtained in 2009 (January 18 and 20, and December 14, 15, 16 and 18) with the very high speed photon-counting photometer Iqueye mounted at the ESO 3.6-m New Technology Telescope in La Silla (Chile). The optical light curve derived by Iqueye shows a double structure in the main peak, with a rising edge steeper than the trailing edge. The double peak can be fitted by two Gaussians with the same height and full width at half-maximum of 13.3 and 15.5 ms, respectively. Our new values of spin frequencies allow us to extend by 3.5 yr the time interval over which a reliable estimate of frequency first and second derivatives can be performed. A discussion of implications for the braking index and age of the pulsar is presented. A value of n= 2.087 ± 0.007 for the overall braking index from 1987 to 2009 is derived. The braking index corrected age is confirmed at around 1700 yr.

Iqueye, a single photon-counting photometer applied to the ESO new technology telescope

Context. A new extremely high speed photon-counting photometer, Iqueye, has been installed and tested at the New Technology Telescope, in La Silla. Aims. This instrument is the second prototype of a “quantum” photometer being developed for future Extremely Large Telescopes of 30–50 m aperture. Methods. Iqueye divides the telescope aperture into four portions, each feeding a single photon avalanche diode. The counts from the four channels are collected by a time-to-digital converter board, where each photon is appropriately time-tagged. Owing to a rubidium oscillator and a GPS receiver, an absolute rms timing accuracy better than 0.5 ns during one-hour observations is achieved. The system can sustain a count rate of up to 8 MHz uninterruptedly for an entire night of observation. Results. During five nights of observations, the system performed smoothly, and the observations of optical pulsar calibration targets provided excellent results.

AquEYE, a single photon counting photometer for astronomy

This paper describes the results obtained so far with AquEYE, a single photon counting, fixed aperture photometer for the Asiago 182 cm telescope. AquEYE has been conceived as a prototype of a truly ‘quantum’ photometer for future Extremely Large Telescopes of 30–50 m aperture. This prototype is characterized by four independent channels equipped with single photon avalanche diodes (SPADs) as detectors. The counts from the four channels are acquired by a TDC board which has a nominal 25 ps time tagging capability. Taking into account the 35 ps jitter in the SPAD itself, the overall precision of the time tags is of the order of 50 ps. The internal oscillator is locked to an external rubidium clock; a GPS pulse per second is collected by the TDC itself to obtain a UTC reference. The maximum photon count rate which the present system can sustain is 12 MHz.

A double-head photon-counting photometer for fast timing observations

The structure of the electronics of the two-head, high-speed photometer operating on the 152-cm G.D. Cassini telescope of Bologna University has been fully redesigned for high-time-resolution observations of fast variable sources, in particular, of the optical counterparts of X-ray binary systems. The fast photometer now permits sampling times from 0.1 ms to 100 s. The handling of the system clock and I/O configuration have been modified to provide rigorous synchronization of the sampling time with an external high-stability clock and the continuous acquisition of an uninterrupted data stream. The continuous data-acquisition process, which is driven by an external clock, is limited only by the capacity of the hard disk and is supported by a double-buffer SRAM memory designed to overcome any discontinuity in the asynchronous communication with the computer. Real-time monitoring of the data enables continuous evaluation of the weather conditions, and the directly displayed light curve can be used to determine the optimal management of the observations.

Determination of dead-time in photon counting photometers by a polarimetric method

Experiments are described which demonstrate that the dead-time constant associated with a photon counting stellar photometer/polarimeter is readily determinable by the application of the Malus law. It is also proposed that corrections for dead-time losses should be applied by an iteration technique to the exact equation rather than using the available approximation formulae.

Photoelectric Observations of AD Leo: 1989-1994

An investigation of the activity of the flare star AD Leo was made using U-band patrol observations. 60 cm computer-controlled telescopes with identical single channel photon-counting photometers at the National Astronomical Observatory at Rozhen and at the Belogradchik Observatory were used. The integration time was 1 sec. Differential photometry was carried out, the AD Leo measurements were made relative to BD+20°2475. The data was reduced with the program package APR (Kirov et al. 1991).Two simultaneous observing runs were made. The results of the first have already been published (Antov etal. 1991). The other was part of the observational campaign in May, 1991 with the ROSAT satellite. In Bulgaria, the observations were carried out at Rozhen in the U-band and at Belogradchik in the B-band. Four flares were detected by both.

MANIA Complex – Hardware and Software for the Investigation of Optical Variability on Time Scales 10−7−102 s

One of the basic astrophysical problems is the search for and investigation of brightness fluctuations of celestial objects on time scales comparable with the mean time between registered photons. To facilitate this a special mathematical formalism was developed (Shwartsman 1977, Plokhotnichenko 1983).At the Special Astrophysical Observatory, photometric equipment has been developed which allows these ideas to be explored observationally and which also allows to study light curves of astrophysical objects using classical methods.This equipment and these methods are used in the search for and study of variable objects with time resolution 10−7 s in the MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) experiment. The hardware consists of a photon-counting photometer for synchronous detection in different colour bands, a specialized “time-code” converter (Quantochron 3-16), measuring photon arrival times with an accuracy of 20 ns and a PC AT 386 and DAT-cassette recorder. Our equipment allows the uninterrupted accumulation of 108 photocounts with a rate up to 375 kHz without distortions in 28 or 216 parallel channels (Zhuravkov et al. 1994). The software permits the investigation of variability on time scales 10−7 − 102 s.

Calcium does not act as a second messenger for adrenergic and cholinergic agonists in corneal epithelial cells.

The role of changes in intracellular [Ca2+]i as a second messenger in response to either adrenergic or cholinergic agonists was determined in isolated bovine corneal epithelial cells. [Ca2+]i was measured in suspensions of cells loaded with either of the fluorescent indicators quin2 or indo-1, as well as in single cells loaded with fura-2. Fluorescence from the cell suspensions was measured in a spectrofluorometer while single cell fluorescence was measured using a modified fluorescence microscope with a photon counting photometer. Cells were loaded with these dyes by incubation in Ringer's (pH 8.1) containing 2-50 microM of the acetoxymethyl ester of the indicator. Fluorescence was measured before and after exposure to either, one of the adrenergic agonists isoproterenol, phenylephrine or epinephrine, or the cholinergic agonist carbachol. The resting [Ca2+]i level from the quin2 experiments was 115 nM +/- 41 nM (SEM) (n = 23) whereas with fura-2 it was 71 +/- 10 nM (n = 30). In no case did we see any change in [Ca2+]i within 15 min after addition of any agonist but we were able to observe increased calcium when 0.5 microM ionomycin was added to either the same or untreated cells. The disparity in the resting levels determined by the two methods may result from various calibration problems. Our results indicate that changes in [Ca2+]i have no second messenger role in response to these agonists.

Eine neue Methode zur Bestimmung der statistischen Zählverluste bei Photonenzählern

AbstractA simple method for the determination of statistical pulse losses of photon counting photometer in dependence on the pulse intensity was deveoloped. The slowly decereasin brightness of the clear sky in the dusk serves a light source. With the help of neutral filter one gets two different pulse rates for two intensities. From a series of such measurements with different intensities one can derive the correction in dependence on pulse density in form of a power sequence.

A MICROCOMPUTER-CONTROLLED PHOTOMETER

ABSTRACT The equipment of the Capilla Peak Observatory includes a 61-cm reflecting telescope and a photon-counting photometer designed for automated operation. To make the most effective use of a telescope for maximum scientific return requires flexible, intelligent operation. The obvious answer is computer control of the equipment. A description is presented of a microcomputer-controlled photometer. A microcomputer can do real-time data reduction while controlling a photometer's operation. This capability allows the observer to make informed decisions in the observing procedure while at the telescope. The computerized photometry greatly simplifies the postobservation data reduction because the data are already in a computer-readable form.

UBVRI PHOTOMETRY OF HR 7308.

ABSTRACT The star HR7308 (HD180583) is the shortest-period classical Cepheid known. It is also unique (so far as it is currently known) in having a variable amplitude. A description is presented of UBVRI photometry (all on the Johnson system) of HR7308 obtained during the second half of 1981. The data are used to derive interstellar reddening and, by application of the surface brightness technique of Barnes et al. (1977), to derive a distance, radius, and absolute magnitude for the star. All observations reported were obtained with a 0.5-m reflector equipped with a standard photon-counting photometer.

The three-channel photon-counting high-speed photometer of Beijing observatory

A photon-counting photometer capable of observing simultaneously a variable star, a comparison star and the sky background has been installed on the 60-cm Reflector of Beijing Observatory, Xinglong Station. It has a special purpose computer to make real time reduction of the data from the three channels and the result is printed out or, additionally for rapid phenomena, displayed on CRT or chart recorder. The photometer has already been in use over several years and has proved itself up to the appointed task.

Scintillation at two optical frequencies

Stellar scintillation data were obtained on a single night at a variety of zenith distances and azimuths, using a photon-counting photometer recording at 100 Hz simultaneously at wavelengths of 0.475 microm and 0.870 microm. Orientable apertures of 42-cm diam separated by 1 m were used to establish the average upper atmosphere wind direction and velocity. Dispersion in the earth's atmosphere separate the average optical paths at the two wavelengths, permitting a reconstruction of the spatial cross-correlation function for scintillations, independent of assumptions about differential fluid motions. Although there is clear evidence of a complicated velocity field, scintillation power was predominantly produced by levels at pressures of 130 +/- 30 mbar. The data are not grossly inconsistent with layers of isotropic Kolmogorov turbulence, but there is some evidence for deviation from the Kolmogorov spectral index and/or anisotropy.

UBV photometry of Vesta

A lightcurve of Vesta, obtained on four nights between June 23 and 30 June 1978 during the coordinated campaign for the determination of the rotation period, is presented. The observations were performed at the 91-cm telescope of the Catania Observatory employing UBV filters and a photon counting photometer. The V lightcurve apparently shows a single maximum, suggesting that the 5 h20 m29 s.2 period is the correct one. Features are evident near the maximum and the minimum closely resembling those of Johnson's lightcurve of 22 December 1950 and Taylor's of January 21, 1973. The amplitude in V light is 0 m.105 and small variations are also found in the color indices. The largest color variation is for the U-V with Δm = 0. m.05, which is slightly larger than the value 0 m.02 found by T. Gehrels [ Astron. J. 72, 929 (1967)]. The maximum and minimum values occur at the same phase with respect to the maximum V light as found by Gehrels, i.e., Vesta appears bluer near 0 p.25 and redder near 0 p.7. Corrections with the solar phase angle were made using the coefficients given by Gehrels for the B-V and U-V while a new value of 0.036 mag/deg was assumed for the V observations. The available amplitudes of Vesta's lightcurve were analyzed with respect to the longitude position and the solar phase angle.

Fluorescence polarization: measurements with a photon-counting photometer

A T-format, photon-counting polarization photometer was constructed to facilitate precise polarization measurements at low signal-to-noise ratios. The instrument optics and electronics are described. Several examples of the instrument's performance are given, including measurements on picomolar fluorescein solutions at low excitation resolution and the excitation polarization spectrum of indole (2 x 10(-4)M) at a resolution of 5 A.

The multifunction photoelectric photometer of Torino Observatory

The paper describes the design and the realization of a multiple-function photoelectric photometer made by Trieste Observatory for Torino Observatory. The system design shows a two-beam, sequential multiband photon counting and analog photoelectric photometer configuration based on a PDP8/E computer for the control and data acquisition and elaboration. The actual realization of the system and the use of it in the one-beam configuration operating now at torino Observatory shows the advantages of such a solution and the easiness in modifying and determining the system functions by software programs rather than by hardware specials.

A real-time spectrum analyser with on-line definition of the confidence levels

This paper describes a real-time spectrum analyser with on-line definition of the confidence levels built at Trieste Observatory for a research program on periodical components of unknown period in optical sources. The system is realized by a photon counting photometer on-line to a computer that elaborates in real-time the data from the photometer and displays the spectrum of the source measured. The spectrum is normalized to unity mean value and the display is calibrated by the confidence levels relative to the $$\chi _v^2 $$ distribution of the spectrum displayed. Some experimental data show the performance of the machine that operates in real-time at full efficiency up to 160 Hz.

Double beam photon counting photometer with dead time compensation

Double beam photon counting photometer with dead time compensation