J.-P. Rivet

Temporal intensity interferometry: photon bunching in three bright stars

We report the first intensity correlation measured with star light since Hanbury Brown and Twiss historical experiments. The photon bunching g (2) (τ, r = 0), obtained in the photon counting regime, was measured for 3 bright stars, α Boo, α CMi, and β Gem. The light was collected at the focal plane of a 1 m optical telescope, was transported by a multi-mode optical fiber, split into two avalanche photodiodes and digitally correlated in real-time. For total exposure times of a few hours, we obtained contrast values around 2 × 10 −3 , in agreement with the expectation for chaotic sources, given the optical and electronic bandwidths of our setup. Comparing our results with the measurement of Hanbury Brown et al. on α CMi, we argue for the timely opportunity to extend our experiments to measuring the spatial correlation function over existing and/or foreseen arrays of optical telescopes diluted over several kilometers. This would enable µas long-baseline interferometry in the optical, especially in the visible wavelengths with a limiting magnitude of 10.

A single-shot optical linear polarimeter for asteroid studies

Polarimetric studies of minor Solar System bodies are useful to access physical parameters, such as albedo and diameter, which are both important and difficult to derive by other techniques. Current activities in this field are limited since most instruments adopted in recent observing campaigns involve photomultipliers detectors. These sensors are suitable for observations of objects with fast polarization variations, but usually suffer from low quantum efficiency. This severely limits the number of accessible targets. For asteroids, the polarization evolves slowly enough to allow more sensitive albeit slower detectors (CCD-based polarimeters). However, polarimetric measurement accuracy may be hampered with usual sequential polarimeters. Indeed, retarder plate swapping time, readout and exposure time add up. Consequently, the time laps between complementary polarization measurements (some minutes) may be non-negligible in some cases, compared to the evolution time of the polarization parameters. Moreover, polarimetric accuracy may also be limited by airmass variations between complementary exposures. We are developing a new single-shot CCD polarimeter based on a double-Wollaston configuration already described in literature [9][10]. This allows simultaneous acquisition of the three Stokes parameters I, Q, U without any moving parts. So, the linear polarization degree can be measured accurately, even for targets with fast polarization and/or airmass variations. Presently, the polarization analyzer is in calibration phase, and will be installed soon at the F/12.5 Cassegrain focus of the West telescope at the Centre Pédagogique Planète et Univers facility (C2PU, Observatoire de la Côte dAzur, Plateau de Calern, France).

Spatial intensity interferometry on three bright stars

The present articlereports on the first spatial intensity interferometry measurements on stars since the observations at Narrabri Observatory by Hanbury Brown et al. in the 1970s. Taking advantage of the progresses in recent years on photon-counting detectors and fast electronics, we were able to measure the zero-time delay intensity correlation

The phase-polarization curve of asteroid (3200) Phaethon†

g^{(2)}(tau = 0, r)

A CATALOG OF ECLIPSING BINARIES AND VARIABLE STARS OBSERVED WITH ASTEP 400 FROM DOME C, ANTARCTICA

between the light collected by two 1-m optical telescopes separated by 15 m. Using two marginally resolved stars (

Rotational variation of the linear polarization of the asteroid (3200) Phaethon as evidence for inhomogeneity in its surface properties

alpha

Six winters of photometry from Dome C, Antarctica: challenges, improvements, and results from the ASTEP experiment

Lyr and

Transiting planet candidates with ASTEP 400 at Dome C, Antarctica

beta

ASTEP: Towards the detection and characterization of exoplanets from Dome C

Ori) with R magnitudes of 0.01 and 0.13 respectively, we demonstrate that 4-hour correlation exposures provide reliable visibilities, whilst a significant loss of contrast is found on alpha Aur, in agreement with its binary-star nature.

SPECTROSCOPIC AND POLARIMETRIC SURVEY OF L-TYPE ASTEROIDS

A multi-colour phase-polarization curve of asteroid (3200)~Phaethon has been obtained during the December 2017 apparition by merging measurements taken at the observing station of Calern (France) and at the Rhozen observatory (Bulgaria). All the observations were obtained in the positive polarization branch, the phase angle ranging from 36