Ground‐based Coronagraphy with High‐Order Adaptive Optics

Sivaramakrishnan, Anand; Koresko, C.; Makidon, Russell B.; Berkefeld, Thomas; Kuchner, Marc J.

doi:10.1086/320444

Cited by 138 publications

(147 citation statements)

References 15 publications

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“…Epochs 9 and 11 were obtained using "The Lyot Project" (Sivaramakrishnan et al 2007;Hinkley et al 2007Hinkley et al , 2009Leconte et al 2010), a diffraction-limited classical Lyot coronagraph (Lyot 1939;Sivaramakrishnan et al 2001) working in the infrared and recently decommissioned at AEOS. The thirteenth epoch of observations of the α Oph system was obtained using a recently commissioned coronagraph integrated with an integral field spectrograph (IFS) spanning the J and H bands (1.06 μm-1.76 μm) on the 200 in Hale Telescope at Palomar Observatory (Hinkley et al 2008(Hinkley et al , 2011.…”

Section: Astrometric Observationsmentioning

confidence: 99%

ESTABLISHING α Oph AS A PROTOTYPE ROTATOR: IMPROVED ASTROMETRIC ORBIT

Hinkley

Monnier

Oppenheimer

et al. 2010

ApJ

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The nearby star α Oph (Ras Alhague) is a rapidly rotating A5IV star spinning at ∼ 89% of its breakup velocity. This system has been imaged extensively by interferometric techniques, giving a precise geometric model of the star's oblateness and the resulting temperature variation on the stellar surface. Fortuitously, α Oph has a previously known stellar companion, and characterization of the orbit provides an independent, dynamically based check of both the host star and the companion mass. Such measurements are crucial to constrain models of such rapidly rotating stars. In this study, we combine eight years of adaptive optics imaging data from the Palomar, AEOS, and CFHT telescopes to derive an improved, astrometric characterization of the companion orbit. We also use photometry from these observations to derive a model-based estimate of the companion mass. A fit was performed on the photocenter motion of this system to extract a component mass ratio. We find masses of 2.40 +0.23 −0.37 M and 0.85 +0.06 −0.04 M for α Oph A and α Oph B, respectively. Previous orbital studies of this system found a mass too high for this system, inconsistent with stellar evolutionary calculations. Our measurements of the host star mass are more consistent with these evolutionary calculations, but with slightly higher uncertainties. In addition to the dynamically derived masses, we use IJHK photometry to derive a model-based mass for α Oph B, of 0.77 ± 0.05 M marginally consistent with the dynamical masses derived from our orbit. Our model fits predict a periastron passage on 2012 April 19, with the two components having a 50 mas separation from 2012 March to May. A modest amount of interferometric and radial velocity data during this period could provide a mass determination of this star at the few percent level.

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Section: Astrometric Observationsmentioning

confidence: 99%

ESTABLISHING α Oph AS A PROTOTYPE ROTATOR: IMPROVED ASTROMETRIC ORBIT

Hinkley

Monnier

Oppenheimer

et al. 2010

ApJ

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“…Moreover, this must be obtained in the presence of telescope central obstruction and over a broad band (typically 20%). The classical Lyot Coronagraph (Lyot 1939;Sivaramakrishnan et al 2001) does not provide sufficient starlight suppression to enable the detection of extrasolar planets, and several more advanced techniques have been proposed in the past few years (Roddier & Roddier 1997;Rouan et al 2000;Baudoz et al 2000;Aime et al 2002;Kuchner & Traub 2002;Soummer et al 2003b;Kasdin et al 2003;Guyon et al 2005;Mawet et al 2005;Foo et al 2005;Serabyn et al 2010;L. Pueyo et al 2011, in preparation;Crepp et al 2011).…”

Section: Introductionmentioning

confidence: 99%

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Soummer

Sivaramakrishnan

Pueyo

et al. 2011

ApJ

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107

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Direct imaging and spectroscopy of young giant planets from the ground requires broadband starlight suppression with coronagraphy. It is important to minimize the coronagraph chromatic sensitivity to help remove residual speckles through post-processing of images at multiple wavelengths. The coronagraph must also be able to mitigate the effects of ground-based telescopes with central obstruction. We present new properties of the Apodized Pupil Lyot Coronagraph (APLC) that enable quasi-achromatic starlight suppression over a broad bandpass (20%) and with central obstructions. We discuss the existence of these quasi-achromatic solutions using the properties of the generalized prolate spheroidal functions, which are used to define the apodizer profile. We discuss a broadband optimization method and illustrate its parameter space in terms of inner working angle and contrast. These new APLC solutions are implemented in the Gemini Planet Imager (GPI), a new facility instrument to detect and characterize young giant planets and disks, which will be commissioned in 2011. The coronagraph design delivers a contrast better than 10 −7 beyond a separation of 0.2 arcsec in the presence of Gemini's central obstruction over a 20% bandpass. The science camera is an integral field spectrograph observing in one of the Y, J, or H, or in about two-thirds of the K bandpass, at a single time. Similar solutions have also been used for the Palomar 1640 coronagraphic integral field spectrograph.

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“…A number of recently proposed coronagraphs can potentially be used to reduce the bright starlight (e.g., Guyon et al 2006a), but scattering by nonideal telescope optics and atmospheric seeing fluctuations severely limits the off-axis detection capabilities of all types of coronagraphs, with performance ultimately set by the quality of the corrected stellar wavefront (Malbet et al 1995). Indeed, classical ''Lyot'' coronagraphs employing opaque focal plane starlight blockers should yield significant contrast gains only for stellar Strehl ratios exceeding %90% (Sivaramakrishnan et al 2001). On the other hand, current-generation AO systems on large ground-based telescopes typically provide Strehl ratios of %50%Y 70%, limiting coronagraphic performance.…”

Section: Introductionmentioning

confidence: 99%

Extreme Adaptive Optics Imaging with a Clear and Well‐Corrected Off‐Axis Telescope Subaperture

Serabyn¹,

Wallace²,

Troy³

et al. 2007

ApJ

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Rather than using an adaptive optics (AO) system to correct a telescope's entire pupil, it can instead be used to more finely correct a smaller subaperture. Indeed, existing AO systems can be used to correct a subaperture 1 3 to 1 2 the size of a 5Y10 m telescope to extreme adaptive optics (ExAO) levels. We discuss the potential performance of a clear off-axis well-corrected subaperture (WCS), and describe our initial imaging results with a 1.5 m diameter WCS on the Palomar Observatory's Hale Telescope. These include measured Strehl ratios of 0.92Y0.94 in the infrared (2.17 m) and %0.12 in the B band, the latter allowing a binary of separation 0.34 00 to be easily resolved in the blue. Such performance levels enable a variety of novel observational modes, such as infrared ExAO, visible-wavelength AO, and high-contrast coronagraphy. One specific application suggested by the high Strehl ratio stability obtained (1%) is the measurement of planetary transits and eclipses. Also described is a simple ''dark hole'' experiment carried out on a binary star, in which a comatic phase term was applied directly to the deformable mirror, in order to shift the diffraction rings to one side of the point-spread function.

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Ground‐based Coronagraphy with High‐Order Adaptive Optics

Cited by 138 publications

References 15 publications

ESTABLISHING α Oph AS A PROTOTYPE ROTATOR: IMPROVED ASTROMETRIC ORBIT

ESTABLISHING α Oph AS A PROTOTYPE ROTATOR: IMPROVED ASTROMETRIC ORBIT

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Extreme Adaptive Optics Imaging with a Clear and Well‐Corrected Off‐Axis Telescope Subaperture

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