Imaging exoplanets with coronagraphic instruments

Galicher, R.; Mazoyer, Johan

doi:10.5802/crphys.133

Cited by 14 publications

(7 citation statements)

References 221 publications

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“…In that respect, an extreme adaptive optics (AO) system like SPHERE is able to routinely achieve Strehl ratio larger than 80% in the near IR (J, H and Ks bands) for bright stars (R<10) and can even provide a Strehl of 50% at visible wavelengths for R<9 [44], allowing to deliver exquisite image quality with angular resolution of 15 to 50 mas for wavelengths in the range 0.6-2.0 µm. Such a low wavefront error level is necessary for a coronagraph to provide a large rejection of the starlight (see [45] this proceeding for a review of coronagraphic techniques). The SPHERE coronagraph [46] has a diameter of about 0.2 ′′ which means that no off-axis object can be recovered below the Inner Working Angle of ∼ 0.1 ′′ .…”

Section: Detection Methodsmentioning

confidence: 99%

Observations of circumstellar disks in scattered light with SPHERE at the VLT

Boccaletti¹

2024

Comptes Rendus. Physique

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The technological developments initiated in the early 21 st century have led to the implementation of "planet finders" instruments on 8-m class telescopes which are in operation since 2014-2015. Such facilities are at the inception of significant progresses in the study of exoplanetary systems by enabling high contrast imaging of the environment of young nearby stars. One of the most productive science in this field is certainly the observations at high angular resolution of circumstellar disks, from the very young gas-rich protoplanetary disks all the way to more elusive dust-rich debris disks. In this paper, we summarize the main results obtained for these two categories of objects focusing on their morphological characteristics, as well as on the measurement of optical properties of the small dust particles to which the near IR spectral range is sensitive to. We mostly provide exemples based on observations performed with the SPHERE instrument at the VLT.Résumé. Les développements technologiques initiés au début du 21 ème siècle ont conduit à la mise en place d'instruments "découvreurs de planètes" sur des télescopes de la classe 8m en fonctionnement depuis 2014-2015. De telles installations sont à l'origine de progrès significatifs dans l'étude des systèmes exoplanétaires en permettant l'imagerie à haut contraste de l'environnement des jeunes étoiles proches. L'une des sciences les plus productives dans ce domaine est certainement l'observation à haute résolution angulaire des disques circumstellaires, depuis les très jeunes disques protoplanétaires riches en gaz jusqu'aux disques de débris plus insaisissables, riches en poussières. Dans cet article, nous résumons les principaux résultats obtenus pour ces deux catégories d'objets en nous concentrant sur leurs caractéristiques morphologiques, ainsi que sur la mesure des propriétés optiques des petites particules de poussière auxquelles la gamme spectrale du proche IR est sensible. Nous présentons surtout des exemples basés sur des observations réalisées avec l'instrument SPHERE au VLT.

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Section: Detection Methodsmentioning

confidence: 99%

Observations of circumstellar disks in scattered light with SPHERE at the VLT

Boccaletti¹

2024

Comptes Rendus. Physique

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“…They also use active optics during the observations to control non-common path aberrations introduced by any optical defects between the astrophysical and the AO sensing channels. It results in a starlight attenuation in the raw coronagraphic images within an area referred to as the dark hole (Galicher & Mazoyer 2023). Potier et al (2020) demonstrate that utilizing pair-wise probing (Give'on et al 2007) in conjunction with electric field conjugated correction (Malbet et al 1995) results in a ten-fold reduction in starlight intensity between 200 mas and 700 mas when using the internal source of the SPHERE instrument.…”

Section: Introductionmentioning

confidence: 99%

“…instruments. This allows starlight to seep into the instrument and reach the detector, forming speckles in the coronagraphic image (Galicher & Mazoyer 2023).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, both ground-based and space-based coronagraphs will also be limited by wavefront aberrations introduced by optics. Adding a coronagraph by itself behind a telescope will provide images limited by stellar residuals (AO halo and quasi-static speckles; Galicher & Mazoyer 2023). Currently, the speckles are removed using post-processing methods as reference differential imaging (RDI; Smith & Terrile 1984;Beuzit et al 1997;Lafrenière et al 2009;Ruane et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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Increasing the raw contrast of VLT/SPHERE with the dark hole technique

Galicher,

Potier,

Mazoyer

et al. 2024

A&A

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Imaging exoplanetary systems is essential to characterizing exoplanet atmospheres and orbits as well as circumstellar disks and to studying planet-disk interactions to understand the planet formation processes. Imaging exoplanets or circumstellar disks in the visible and near-infrared is challenging, however, because these objects are very faint relative to their star, even though only fractions of an arcsecond away. Coronagraphic instruments have already allowed the imaging of a few exoplanets, but their performance is limited by wavefront aberrations. Adaptive optics systems partly compensate for the Earth's atmosphere turbulence, but they cannot fully control the wavefront. Some of the starlight leaks through the coronagraph and forms speckles in the astrophysical image. Focal plane wavefront control, used as a second stage after the adaptive optics system, has been proposed to minimize the speckle intensity within an area called the dark hole. We previously demonstrated the on-sky performance of dark hole techniques, pairwise probing coupled with electric field conjugation, using the apodized pupil Lyot coronagraph of the VLT/SPHERE instrument. In this paper, we probe their performance using the SPHERE four-quadrant phase mask coronagraph, and we demonstrate the interest of combining dark hole techniques and reference differential imaging. We used these dark hole techniques on-sky to create a dark hole in the narrow band around $1.7\ observing HR\,4796. We then recorded broadband images of HR\,4796 and a reference star at the H band. The dark hole techniques improved the H-band detection limit by a factor of three. The dark hole was stable from one star to a nearby star enabling reference differential imaging. This stability offers two new strategies of observation. First, one can quickly create a dark hole observing a bright star before pointing to a faint target star. Furthermore, one can couple dark hole techniques and reference differential imaging. A very interesting point is that the performance of these methods does not depend on the astrophysical signal.

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“…Nevertheless, they are not necessarily the most representative of the population of planets in our galaxy [2]. The detection techniques of exoplanets will be presented in other reviews of this special issue [3,4]. Here, we focus on a few specificities of the population of exoplanets as we know it today, in comparison to the solar system planets.…”

Section: Introduction: the Population Of Hot Exoplanets And The Solar...mentioning

confidence: 99%

Interactions of exoplanets with their environment

Strugarek¹

2024

Comptes Rendus. Physique

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Exoplanets on close-in orbit are subject to intense interactions with their host star. They receive a strong irradiation from the star, trigger tides within their host, and stars and close-in planets can be magnetically connected. In this review, I introduce the physical concepts behind these three types of interaction. I provide simple scaling-laws for their relative strengths, and highlight the aspects of the interactions that still elude our understanding. For each interaction, I also review their detectable effects on both specific star-planet systems and on the population of exoplanets as we know it today.Résumé. Les exoplanètes en orbite rapprochée sont soumises à des interactions intenses avec leur étoile hôte. Elles reçoivent une forte irradiation de l'étoile, déclenchent des phénomènes de marées dans leur hôte, et les étoiles et les planètes proches peuvent être connectées magnétiquement. Dans cette revue, je présente les concepts physiques qui sous-tendent ces trois types d'interaction. Je présente des lois d'échelle simples pour estimer leurs forces relatives et je souligne les aspects des interactions qui échappent encore à notre compréhension. Pour chaque interaction, je passe également en revue leurs effets détectables à la fois sur des systèmes étoile-planète spécifiques et sur la population d'exoplanètes telle que nous la connaissons aujourd'hui.

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Imaging exoplanets with coronagraphic instruments

Cited by 14 publications

References 221 publications

Observations of circumstellar disks in scattered light with SPHERE at the VLT

Observations of circumstellar disks in scattered light with SPHERE at the VLT

Increasing the raw contrast of VLT/SPHERE with the dark hole technique

Interactions of exoplanets with their environment

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