We describe and report first results from PALM-3000, the second-generation astronomical adaptive optics (AO) facility for the 5.1 m Hale telescope at Palomar Observatory. PALM-3000 has been engineered for high-contrast imaging and emission spectroscopy of brown dwarfs and large planetary mass bodies at near-infrared wavelengths around bright stars, but also supports general natural guide star use to V ≈ 17. Using its unique 66 × 66 actuator deformable mirror, PALM-3000 has thus far demonstrated residual wavefront errors of 141 nm rms under ~1'' seeing conditions. PALM-3000 can provide phase conjugation correction over a 6."4 × 6."4 working region at λ = 2.2 μm, or full electric field (amplitude and phase) correction over approximately one-half of this field. With optimized back-end instrumentation, PALM-3000 is designed to enable 10^(–7) contrast at 1" angular separation, including post-observation speckle suppression processing. While continued optimization of the AO system is ongoing, we have already successfully commissioned five back-end instruments and begun a major exoplanet characterization survey, Project 1640.

/pdf/palm-3000-exoplanet-adaptive-optics-for-the-5-m-hale-33l6x1z4v0.pdf

PALM-3000: EXOPLANET ADAPTIVE OPTICS FOR THE 5 m HALE TELESCOPE

Debris dust in the habitable zones of stars—otherwise known as exozodiacal dust—comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the solar system’s zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this article, we qualitatively assess the primary impact of exozodiacal dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This article represents the first report of NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG).

/pdf/the-exozodiacal-dust-problem-for-direct-observations-of-exo-5cg3fbm5c9.pdf

The Exozodiacal Dust Problem for Direct Observations of Exo-Earths

The Large Binocular Telescope Interferometer (LBTI) enables nulling interferometric observations across the N band (8 to 13 μm) to suppress a star's bright light and probe for faint circumstellar emission. We present and statistically analyze the results from the LBTI/Hunt for Observable Signatures of Terrestrial Systems survey for exozodiacal dust. By comparing our measurements to model predictions based on the solar zodiacal dust in the N band, we estimate a 1σ median sensitivity of 23 zodis times the solar system dust surface density in its habitable zone (HZ; 23 zodis) for early-type stars and 48 zodis for Sun-like stars, where 1 zodi is the surface density of HZ dust in the solar system. Of the 38 stars observed, 10 show significant excess. A clear correlation of our detections with the presence of cold dust in the systems was found, but none with the stellar spectral type or age. The majority of Sun-like stars have relatively low HZ dust levels (best-fit median: 3 zodis, 1σ upper limit: 9 zodis, 95% confidence: 27 zodis based on our N band measurements), while ~20% are significantly more dusty. The solar system's HZ dust content is consistent with being typical. Our median HZ dust level would not be a major limitation to the direct imaging search for Earth-like exoplanets, but more precise constraints are still required, in particular to evaluate the impact of exozodiacal dust for the spectroscopic characterization of imaged exo-Earth candidates.

https://www.repository.cam.ac.uk/bitstream/1810/303891/1/2003.03499v1.pdf

The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey

There is labelling mistake in Fig. 1 (Sect. 2), as this plot deals with the non-squared visibility: the correct label for the vertical axis should therefore read δV/V and the inserted texts should be V > 40% and V 16%. In the body of the article, Sect. 3, another reference is made to this result. The reader should read that the squared visibility limit is V 2 > 16%. The correction of this mistake does not change the main characteristics of the calibrator stars catalog.

/pdf/erratum-a-catalog-of-bright-calibrator-stars-for-200-m-lahxpdxngv.pdf

Erratum A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry

We report on the first nulling interferometric observations with the Large Binocular Telescope Interferometer (LBTI), resolving the N' band (9.81–12.41 μm) emission around the nearby main-sequence star η Crv (F2V, 1–2 Gyr). The measured source null depth amounts to 4.40% ± 0.35% over a field-of-view of 140 mas in radius (~2.6 AU for the distance of η Crv) and shows no significant variation over 35° of sky rotation. This relatively low null is unexpected given the total disk to star flux ratio measured by the Spitzer Infrared Spectrograph (IRS; ~23% across the N' band), suggesting that a significant fraction of the dust lies within the central nulled response of the LBTI (79 mas or 1.4 AU). Modeling of the warm disk shows that it cannot resemble a scaled version of the solar zodiacal cloud unless it is almost perpendicular to the outer disk imaged by Herschel. It is more likely that the inner and outer disks are coplanar and the warm dust is located at a distance of 0.5–1.0 AU, significantly closer than previously predicted by models of the IRS spectrum (~3 AU). The predicted disk sizes can be reconciled if the warm disk is not centrosymmetric, or if the dust particles are dominated by very small grains. Both possibilities hint that a recent collision has produced much of the dust. Finally, we discuss the implications for the presence of dust for the distance where the insolation is the same as Earth's (2.3 AU).

/pdf/first-light-lbt-nulling-interferometric-observations-warm-1nue3xy4tq.pdf

FIRST-LIGHT LBT NULLING INTERFEROMETRIC OBSERVATIONS: WARM EXOZODIACAL DUST RESOLVED WITHIN A FEW AU OF η Crv

A new "self-calibrated" statistical analysis method has been developed for the reduction of nulling interferometry data. The idea is to use the statistical distributions of the uctuating null depth and beam intensities to retrieve the astrophysical null depth (or equivalently the object’s visibility) in the presence of fast atmospheric uctuations. The approach yields an accuracy much better (about an order of magnitude) than is presently possible with standard data reduction methods, because the astrophysical null depth accuracy is no longer limited by the magnitude of the instrumental phase and intensity errors but by uncertainties on their probability distributions. This approach was tested on the sky with the two-aperture ber nulling instrument mounted on the Palomar Hale telescope. Using our new data analysis approach alone - and no observations of calibrators - , we

Improving interferometric null depth measurements using statistical distributions: theory and rst results with the Palomar Fiber Nuller

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Improving interferometric null depth measurements using statistical distributions: theory and rst results with the Palomar Fiber Nuller