Abstract

Context. The two main advantages of exoplanet imaging are the discovery of objects in the outer part of stellar systems, which constrains the models of planet formation, and its ability to spectrally characterize the planets to study their atmospheres. It is, however, challenging because exoplanets are up to 1010 times fainter than their stars and are separated by a fraction of an arcsecond. Current instruments like SPHERE-VLT or GPI-Gemini detect young and massive planets only because of non-common path aberrations (NCPA) that are not corrected by the adaptive optics system. To probe fainter exoplanets a new instruments capable of minimizing the NCPA is needed. One solution is the self-coherent camera (SCC) focal plane wavefront sensor which is able to attenuate the starlight by factors of up to several 108 in the laboratory in space-like conditions. Aims. In this paper, we demonstrate the SCC on the sky for the first time. Methods. We installed an SCC on the stellar double coronagraph instrument at the Hale telescope. We minimize the NCPA that limited the vortex coronagraph performance. We then compared this procedure to the standard procedure used at Palomar. Results. On internal sources, we demonstrated that the SCC improves the coronagraphic detection limit by a factor of 4–20 between 1.5 and 5 λ/D. Using this SCC calibration, the on-sky contrast is improved by a factor of 5 between 2 and 4 λ/D. These results prove the ability of the SCC to be implemented in an existing instrument. Conclusions. This paper highlights two interests of the self-coherent camera. First, the SCC can minimize the speckle intensity in the field of view, especially the ones that are very close to the star where many exoplanets are to be discovered. Then the SCC has a 100% efficiency with science time as each image can be used for both science and NCPA minimization.

Highlights

  • Imaging of exoplanets is one priority for astronomers because it is the only technique that can discover long orbital period planets and that enables the spectral characterization of their atmospheres

  • This performance is far from the best performance reached in the laboratory with attenuation of the starlight by a factor of 109 to 1010 (Baudoz et al 2018a; Lawson et al 2013) because wavefront aberrations upstream of the coronagraph can be measured and minimized down to a few picometers rms in the laboratory using the technique of focal plane wavefront sensing and control, for example the pair-wise technique (Give’on et al 2011) coupled with electric field conjugation (Give’on et al 2007), speckle nulling (Bordé & Traub 2006), or the self-coherent camera (Galicher et al 2008)

  • We present the coronagraphic performance obtained at the Palomar telescope using a self-coherent camera

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Summary

Introduction

Imaging of exoplanets is one priority for astronomers because it is the only technique that can discover long orbital period planets and that enables the spectral characterization of their atmospheres. The coronagraphic images produced by these instruments enable the detection of planets that are up to ∼106 times fainter than the host star This performance is far from the best performance reached in the laboratory with attenuation of the starlight by a factor of 109 to 1010 (Baudoz et al 2018a; Lawson et al 2013) because wavefront aberrations upstream of the coronagraph can be measured and minimized down to a few picometers rms in the laboratory using the technique of focal plane wavefront sensing and control, for example the pair-wise technique (Give’on et al 2011) coupled with electric field conjugation (Give’on et al 2007), speckle nulling (Bordé & Traub 2006), or the self-coherent camera (Galicher et al 2008). After presenting the procedures for non-common path aberration (NCPA) calibration in Sect. 4, we present the performance of the self-coherent camera on internal source and on-sky in Sects. 5 and 6

Principle of the self-coherent camera
Implementation in the stellar double coronagraph instrument
MGS algorithm limitation
SCC procedure
Performance
Comparison with other techniques
Current limitation at Palomar
On-sky performance
Findings
Conclusion
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