Temporal intensity interferometry: photon bunching in three bright stars

Abstract

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.

Intensity interferometry of P Cygni in the H α emission line: towards distance calibration of LBV supergiant stars

“…Here, approximating the line shape by a Gaussian, the temporal correlation measurement corresponds to a line width of FWHM ∆λ 0.3 nm, in agreement with the actual spectrum. Note also that the contrast of the g (2) (τ ) function measured here is significantly higher than what it would be if it were determined by the 1-nm filter (the contrast would be ∼ 1.4 × 10 −3 ), which would be the case in the continuum [14]. This "intensity-correlation spectroscopy" technique [12,40,44] would be relevant for exotic, very narrow lines, that would be hard to characterize with standard spectroscopic techniques.…”

“…The SPADs have a timing jitter of 450 ps each, which gives a temporal resolution τ el √ 2 × 450 640 ps. Compared to our previous experiments [14,15], we have modified the CA in order to collimate the optical beam before its transmission through the filter, in order to have a more precise control on the filter width and central wavelength. This is indeed more critical when one wants to select a specific spectral line.…”

“…In this context our group started a number of pilot experiments in 2016 using two modest 1 m size optical telescopes. After the successful observations of temporal and spatial bunching on a few bright stars at 780 nm [14,15,26,43], we decided to observe emission-line stars. The LBV star P Cyg is a very good candidate due to its strong H and He emission lines.…”

Spatial intensity interferometry on three bright stars

“…In ref. (Guerin et al 2017), we used a single telescope and thus measured the temporal autocorrelation function g (2) (τ, r = 0). The shape of this function allows to identify the nature of the light source.…”

“…Recently, we reported the first measurement of the temporal intensity autocorrelation function from an unresolved star since the seminal work of HBT (Guerin et al 2017). The present article presents the first re-implementation of a two-telescope intensity interferometer, accessing the spatial intensity correlation function from two 1-m optical telescopes separated by an East-West baseline of 15 m. The first demonstrations were done on two marginally resolved stars, β Ori (Rigel) and α Lyr (Vega), to check the reliability of our setup.…”