Compensation of high-order quasi-static aberrations on SPHERE with the coronagraphic phase diversity (COFFEE)

Paul, Baptiste; Sauvage, Jean-François; Mugnier, Laurent M.; Dohlen, Kjetil; Petit, Cyril; Fusco, Thierry; Mouillet, D.; Beuzit, Jean-Luc; Ferrari, Marc

doi:10.1051/0004-6361/201424133

Cited by 29 publications

(29 citation statements)

References 12 publications

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“…The K band is particularly interesting for this type of observations as adaptive optics systems are very efficient in this wavelength range, providing excellent correction of the atmospheric turbulence. Using a combination of coronagraphy and advanced processing techniques, the VLT/SPHERE instrument has demonstrated that sources with a contrast of 10 −4 or smaller can be detected down to an angular separation of ≈3λ/D = 0.2 with a high signal-to-noise ratio (Paul et al 2014). It has also been proposed recently that optimized correction techniques may significantly improve the accessible contrast (N'Diaye et al 2016), particularly in view of the E-ELT instrumentation.…”

Section: The Close Environment Of α Cen a And Bmentioning

confidence: 99%

Close stellar conjunctions ofαCentauri A and B until 2050

Kervella

Mignard

Mérand

et al. 2016

A&A

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The rapid proper motion of the α Cen pair (≈3.7 arcsec yr −1 ) and its location close to the galactic plane on a rich stellar background combine constructively to make them excellent candidates for close stellar conjunctions with more distant stars. Adding new differential astrometry to archival data, we have refined the orbital parameters, barycentric proper motion and parallax of α Cen and compute its apparent trajectory on sky over the coming decades. Based on NTT/SUSI2, NTT/SOFI, and VLT/NACO maps of the field stars around the trajectories of α Cen A and B, we present a catalog of the expected close conjunctions until 2050. An exceptional event will take place in early May 2028, when α Cen A will come within ρ min = 0.015 ± 0.135 arcsec of the m K = 7.8 star 2MASS 14392160-6049528 (hereafter S5). In terms of impact parameter and contrast, this is the most favorable stellar conjunction of α Cen within at least the next three decades. With an angular diameter of θ LD = 0.47 ± 0.05 mas, it is likely that S5 is a red giant or supergiant located at several kiloparsecs. The approached stars will act as moving light probes in transmission through the environment of α Cen. The observation of these close conjunctions holds great promises to search for planets and other low mass objects in the α Cen system using photometry and astrometry. The relativistic displacement of the approached star images will be observable, with significant deflection angles in the milliarcsecond range. The small impact parameter of the conjunction with S5 means that this star has a probability of 45% of entering the Einstein ring of α Cen A. The gravitational amplification of the flux of S5 could reach a factor five for the combination of the two lensed images. The proper motion, orbital parameters and parallax of α Cen will be measurable with an extreme accuracy from differential astrometry with the S stars. This will be valuable, for example to prepare the recently announced Breakthrough Starshot initiative to send interstellar nanocrafts to α Centauri.

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Section: The Close Environment Of α Cen a And Bmentioning

confidence: 99%

Close stellar conjunctions ofαCentauri A and B until 2050

Kervella

Mignard

Mérand

et al. 2016

A&A

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“…14 Though other variants, such as the coronagraphic focal plane wavefront estimation for exoplanet detection (COFFEE) 15 algorithm, have also been studied, stroke minimization and EFC have achieved the highest contrast of any controllers to date and are the primary control laws under consideration for the WFIRST-AFTA coronagraph system. In this section, we describe each, highlighting their differences and similarities.…”

Section: Monochromatic Model-based Control Algorithmsmentioning

confidence: 99%

“…(15) to be represented as the equality constraint ðI DH − C k Þ ¼ 0. Incorporating the equality constraint for the central wavelength into the minimization on stroke via a Lagrange multiplier, μ k , yields a quadratic cost function given by E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 1 6 ; 3 2 6 ; 2 9 9…”

Section: Stroke Minimization-lagrange Multipliersmentioning

confidence: 99%

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Methods and limitations of focal plane sensing, estimation, and control in high-contrast imaging

Groff

Riggs

Kern

et al. 2015

J. Astron. Telesc. Instrum. Syst

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Abstract. Coronagraphy is a very promising method for directly imaging exoplanets, but the performance of a coronagraph is highly sensitive to quasi-static aberrations within the telescope. The resultant speckles are suppressed in the final focal plane using a wavefront control system that estimates the field at the final focal plane to avoid any noncommon path error. This requires a set of probe images that modulate the field so that it may be estimated. With an estimate of the focal plane electric field, a control law is defined to suppress the speckle field so that the planet can be imaged. Characterizing the planet requires that the speckle field be suppressed simultaneously over the bandpass of interest. The choice of control law, bandpass, estimator, and probing methodology has implications in the control solutions and contrast performance. Here, we compare wavefront probing, estimation, and control algorithms, and describe their practical implementation. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

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“…ZELDA; N'Diaye et al 2013), coronagraphic phase diversity (e.g. COFFEE; Paul et al 2013Paul et al , 2014, energy minimization or electric field conjugation (Bordé & Traub 2006;Give'On et al 2007), or any combination of these methods.…”

Section: Experimental Results and Comparison To Simulationsmentioning

confidence: 99%

Apodization in high-contrast long-slit spectroscopy

Vigan

N’Diaye

Dohlen

et al. 2016

A&A

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Spectral characterization of young, giant exoplanets detected by direct imaging is one of the tasks of the new generation of highcontrast imagers. For this purpose, the VLT/SPHERE instrument includes a unique long-slit spectroscopy (LSS) mode coupled with Lyot coronagraphy in its infrared dual-band imager and spectrograph (IRDIS). The performance of this mode is intrinsically limited by the use of a non-optimal coronagraph, but in a previous work we demonstrated that it could be significantly improved at small inner-working angles using the stop-less Lyot coronagraph (SLLC). We now present the development, testing, and validation of the first SLLC prototype for VLT/SPHERE. Based on the transmission profile previously proposed, the prototype was manufactured using microdots technology and was installed inside the instrument in 2014. The transmission measurements agree well with the specifications, except in the very low transmissions (<5% in amplitude). The performance of the SLLC is tested in both imaging and spectroscopy using data acquired on the internal source. In imaging, we obtain a raw contrast gain of a factor 10 at 0.3 and 5 at 0.5 with the SLLC. Using data acquired with a focal-plane mask, we also demonstrate that no Lyot stop is required to reach the full performance, which validates the SLLC concept. Comparison with a realistic simulation model shows that we are currently limited by the internal phase aberrations of SPHERE. In spectroscopy, we obtain a gain of ∼1 mag in a limited range of angular separations. Simulations show that although the main limitation comes from phase errors, the performance in the non-SLLC case is very close to the ultimate limit of the LSS mode. Finally, we obtain the very first on-sky data with the SLLC, which appear extremely promising for the future scientific exploitation of an apodized LSS mode in SPHERE.

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Compensation of high-order quasi-static aberrations on SPHERE with the coronagraphic phase diversity (COFFEE)

Cited by 29 publications

References 12 publications

Close stellar conjunctions ofαCentauri A and B until 2050

Close stellar conjunctions ofαCentauri A and B until 2050

Methods and limitations of focal plane sensing, estimation, and control in high-contrast imaging

Apodization in high-contrast long-slit spectroscopy

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