Exoplanet detection in angular and spectral differential imaging: local learning of background correlations for improved detectionsFlasseur, Olivier; Denis, Loïc; Thiébaut, Éric M.; Langlois, Maud
doi: 10.1117/12.2313601pmid: N/A
The search for new exoplanets by direct imaging is a very active research topic in astronomy. The detection is particularly challenging because of the very high contrast between the host star and the companions. They thus remain hidden by a nonstationary background displaying strong spatial correlations. We propose a new algorithm named PACO (for PAtch COvariances) for reduction of differential imaging datasets. Contrary to existing approaches, we model the background correlations using a local Gaussian distribution that locally captures the spatial correlations at the scale of a patch of a few tens of pixels. The decision in favor of the presence or the absence of an exoplanet in then performed by a binary hypothesis test. The method is completely parameter-free and produces both stationary and statistically grounded detection maps so that the false alarm rate, the probability of detection and the contrast can be directly assessed without post-processing and/or Monte-Carlo simulations. We describe in a forthcoming paper its detailed principle and implementation. In this paper, we recall the principle of the PACO algorithm and we give new illustrations of its benefits in terms of detection capabilities on datasets from the VLT/SPHERE-IRDIS instrument. We also apply our algorithm on multi-spectral datasets from the VLT/SPHERE-IFS spectrograph. The performance of PACO is compared to state-of-the-art algorithms such as TLOCI and KLIP-PCA.
SAMplus: adaptive optics at optical wavelengths for SOARFaes, Daniel M.; Tokovinin, Andrei; Vieira, Tarcio; Mello, Alexandre; Domingues, Marcia; Andrade, Denis; Quint, Bruno C.; dos Santos, Jesulino B.
doi: 10.1117/12.2312205pmid: N/A
Adaptive Optics (AO) is an innovative technique that substantially improves the optical performance of groundbased telescopes. The SOAR Adaptive Module (SAM) is a laser-assisted AO instrument, designed to compensate ground-layer atmospheric turbulence in near-IR and visible wavelengths over a large Field of View. Here we detail our proposal to upgrade SAM, dubbed SAMplus, that is focused on enhancing its performance in visible wavelengths and increasing the instrument reliability. As an illustration, for a seeing of 0.62 arcsec at 500 nm and a typical turbulence profile, current SAM improves the PSF FWHM to 0.40 arcsec, and with the upgrade we expect to deliver images with a FWHM of ≈ 0.34 arcsec - up to 0.23 arcsec FWHM PSF under good seeing conditions. Such capabilities will be fully integrated with the latest SAM instruments, putting SOAR in an unique position as observatory facility.
Demonstration of a speckle nulling algorithm and Kalman filter estimator with a fiber injection unit for observing exoplanets with high-dispersion coronagraphyXin, Yeyuan; Llop Sayson, Jorge; Klimovich, Nikita; Mawet, Dimitri; Ruane, Garreth; Delorme, Jacques; Jovanovic, Nemanja
doi: 10.1117/12.2312357pmid: N/A
High-dispersion coronagraphy (HDC) combines high contrast imaging techniques with high spectral resolution spectroscopy to observe exoplanets and determine characteristics such as chemical composition, temperature, and rotational velocities. It has been demonstrated in lab that with monochromatic light, a fiber injection unit (FIU), in which an optical fiber is used to couple to light from the exoplanet, could be used to direct exoplanet light to a high-resolution spectrograph, with robust performance and speckle suppression that exceeds conventional image-based speckle nulling. We now demonstrate in lab a FIU based speckle nulling scheme with a Kalman filter estimator. We currently find that speckle nulling with a Kalman filter is more stable and outperforms traditional speckle nulling by 10% in suppression in the presence of white detector noise.
Point spread function reconstruction coupling AO telemetry and focal plane imagesBeltramo-Martin, O.; Correia, C. M.; Neichel, B.; Fusco, T.; Ragland, S.; Wizinowich, P. L.
doi: 10.1117/12.2313233pmid: N/A
Scientific exploitation in ground-based astronomy is improved thanks to adaptive optics (AO) that restore diffraction-limit angular resolution. Besides, the ultimate data interpretation is delivered by post-processing techniques that usually relies on a Point spread function (PSF) model. Nevertheless, existing methods to constrain this model based on standard pipeline encounter the spatial and time variations of the AO PSF. In order to improve accuracy on key science observables, such as photometry and astrometry, alternative methods are investigated, such as PSF reconstruction (PSF-R), designed to estimate the PSF from AO control-loop data and key atmosphere and system parameters. We aim in this paper at retrieving directly these relevant inputs we need to reconstruct the PSF using an hybrid approach, that couples AO telemetry with focal plane images, named as Focal plane profiling and reconstruction (FPPR). It adjusts atmosphere parameters (the C2n (h) profile) and optical gains in the system. We describe the FPPR method that is applied to on-sky Keck images in engineering mode operated with either natural or laser guide star and show we get 1% of accuracy on respectively the Strehl-ratio and the PSF FWHM reconstruction.
CATS: an autonomous station for atmospheric turbulence characterizationZiad, Aziz; Chabé, Julien; Fantei-Caujolle, Yan; Aristidi, Eric; Renaud, Catherine; Ben Rahhal, Malak
doi: 10.1117/12.2313386pmid: N/A
From its long expertise in Atmospheric Optics, the J.L. Lagrange Laboratory of the Observatoire de la Côte d'Azur has developed a new generation of autonomous stations of atmospheric turbulence measurement. Since two years, the Calern Observatory is equipped with this kind of stations called CATS for Calern Atmospheric Turbulence Station. CATS is an autonomous station consisting of a set of complementary instruments within original techniques for measuring optical turbulence since the first meters above the ground to the borders of the atmosphere including the dome seeing. Indeed, one of the CATS instruments is the PML (Profiler of Moon Limb) measuring the vertical distribution of turbulence using lunar and solar limbs with a resolution reaching 100m in the ground layer. The second instrument is a Generalized DIMM dedicated to provide wavefront parameters at ground level (seeing, outer scale, coherence time and isoplanatic angle). A third instrument called INTENSE (INdoor TurbulENce Sensor) is occasionally associated with CATS station to measure the turbulence inside the dome of the 1.5m MeO telescope to evaluate its contribution to the whole turbulence. The CATS station is also a support for our educative activities as part of our Masters in Astronomy and Optics, through the organization of on-sky training works.
A calibration source for ELT AO systemsEsposito, S.; Bonaglia, M.; Briguglio, R.; Busoni, L.; Fusco, T.; Neichel, B.
doi: 10.1117/12.2314963pmid: N/A
The paper describes the possible implementation of a calibration source to be installed in the ELT optical train providing a single pass test beam for AO systems calibration. The source could be used by SCAO systems like those of MICADO/MAORY, HARMONI and METIS and to monitor M4 shape and differential pistons. Additional functionalities could be provided in order to use it for LGS based AO systems calibrations like the MCAO system of MAORY/MICADO or the foreseen LTAO system of HARMONI. In this work, we show a straw man optical design for such an on-axis source and describe options to provide off-axis sources to support engineering and commissioning phases of AO systems at the ELT.
Application of the phase diversity to estimate the non-common path aberrations in the Gemini planet imager: results from simulation and real dataLamb, Masen; Norton, Andrew; Macintosh, Bruce ; Correia, Carlos; Véran, Jean-Pierre; Marois, Christian; Sivanandam, Suresh
doi: 10.1117/12.2313458pmid: N/A
We explore the application of phase diversity to calibrate the non common path aberrations (NCPA) in the Gemini Planet Imager (GPI). This is first investigated in simulation in order to characterize the ideal technique parameters with simulated GPI calibration source data. The best working simulation parameters are derived and we establish the algorithm's capability to recover an injected astigmatism. Furthermore, the real data appear to exhibit signs of de-centering between the in and out of focus images that are required by phase diversity; this effect can arise when the diverse images are acquired in closed loop and are close to the non-linear regime of the wavefront sensor. We show in simulation that this effect can inhibit our algorithm, which does not take into account the impact of de-centering between images. To mitigate this effect, we validate the technique of using a single diverse image with our algorithm; this is first demonstrated in simulation and then applied to the real GPI data. Following this approach, we find that we can successfully recover a known astigmatism injection using the real GPI data and subsequently apply an NCPA correction to GPI (in the format of offset reference slopes) to improve the relative Strehl ratio by 5%; we note this NCPA correction application is rudimentary and a more thorough application will be investigated in the near future. Finally, the estimated NCPA in the form of astigmatism and coma agree well with the magnitude of the same modes reported by Poyneer et al. 2016.