Photonic technologies offer numerous advantages for astronomical instruments such as spectrographs and interferometers owing to their small footprints and diverse range of functionalities. Operating ...at the diffraction-limit, it is notoriously difficult to efficiently couple such devices directly with large telescopes. We demonstrate that with careful control of both the non-ideal pupil geometry of a telescope and residual wavefront errors, efficient coupling with single-mode devices can indeed be realised. A fibre injection was built within the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument. Light was coupled into a single-mode fibre operating in the near-IR (J − H bands) which was downstream of the extreme adaptive optics system and the pupil apodising optics. A coupling efficiency of 86% of the theoretical maximum limit was achieved at 1550 nm for a diffraction-limited beam in the laboratory, and was linearly correlated with Strehl ratio. The coupling efficiency was constant to within <30% in the range 1250–1600 nm. Preliminary on-sky data with a Strehl ratio of 60% in the H-band produced a coupling efficiency into a single-mode fibre of ~50%, consistent with expectations. The coupling was >40% for 84% of the time and >50% for 41% of the time. The laboratory results allow us to forecast that extreme adaptive optics levels of correction (Strehl ratio >90% in H-band) would allow coupling of >67% (of the order of coupling to multimode fibres currently) while standard levels of wavefront correction (Strehl ratio >20% in H-band) would allow coupling of >18%. For Strehl ratios <20%, few-port photonic lanterns become a superior choice but the signal-to-noise, and pixel availability must be considered. These results illustrate a clear path to efficient on-sky coupling into a single-mode fibre, which could be used to realise modal-noise-free radial velocity machines, very-long-baseline optical/near-IR interferometers and/or simply exploit photonic technologies in future instrument design.
Context.
Exoplanet direct imaging is a key science goal of current ground-based telescopes as well as of future ground-based extremely large telescopes and space-based telescopes. Several ...high-contrast imaging (HCI) systems for direct exoplanet imaging have been developed and are implemented on current telescopes. Despite recent developments in HCI systems, the contrast they deliver is limited by non-common path aberrations (NCPAs) and residual wavefront errors of the adaptive optics (AO) system. To overcome this limitation and reach higher contrast, HCI systems need focal plane wavefront-sensing and control (FPWFS&C) techniques.
Aims.
We propose a method that provides both deep contrast and a 100% duty cycle by combining two complementary FPWFS&C methods: electric field conjugation (EFC), and spatial linear dark field control (LDFC). The ultimate goal of this work is to generate the high contrast zone, which is called the dark hole, in the focal plane by using EFC and to maintain the contrast within the high-contrast zone by using spatial LDFC without interrupting science observations. We describe the practical implementation, quantify the linearity range over which LDFC can operate, and derive its photon-noise-limited dynamical performance.
Methods.
We implemented EFC+LDFC on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument using its internal light source (off-sky). We first deployed the implicit EFC (iEFC) algorithm to generate the dark hole with a classical Lyot coronagraph (CLC) with a 114 mas diameter focal-plane mask at 1550 nm wavelength. This iEFC algorithm was deployed with pair-wise probes. Using iEFC with pair-wise probes, we directly measured the response matrix of the deformable mirror (DM) modes and built the control matrix by inverting the response matrix. After the calibration process, we generated the dark hole by closing the iEFC loop. When the dark hole was generated, we implemented spatial LDFC to restore and maintain the contrast of the dark hole. In the tests shown here, we introduced static and quasi-static speckles, and then we operated spatial LDFC in closed loop to verify its performance. We used numerical simulations to derive linearity range and photon-noise-limited dynamical performance.
Results.
Using iEFC, we generated the dark hole with a ~2×10
−7
contrast in a narrow-band filter (
λ
= 1550 ± 25 nm). We reached a contrast floor limited by the camera noise. Comparison between pre- and post-iEFC images shows that with iEFC in closed-loop operation, an improvement in contrast of a factor ≈ 100–500× was reached across the dark hole. In the spatial LDFC experiments, we were able to nearly fully remove the speckles generated by the DM perturbation and maintain the contrast of the dark hole.
Conclusions.
This work presents the first laboratory demonstration of combining two FPWFS&C methods, iEFC and spatial LDFC. Linear range and photon-noise-limited sensitivity are provided to derive close-loop performance for on-sky systems. Our results provide a promising approach for taking advantages of both high contrast and a 100% science duty cycle for HCI systems.
We present high-resolution, H-band imaging observations, collected with Subaru/HiCIAO, of the scattered light from the transitional disk around SAO 206462 (HD 135344B). Although previous sub-mm ...imagery suggested the existence of a dust-depleted cavity at r < or =, slant 46 AU, our observations reveal the presence of scattered light components as close as 0".2 (~28 AU) from the star. Moreover, we have discovered two small-scale spiral structures lying within 0".5 (~70 AU). We present models for the spiral structures using the spiral density wave theory, and derive a disk aspect ratio of h ~ 0.1, which is consistent with previous sub-mm observations. This model can potentially give estimates of the temperature and rotation profiles of the disk based on dynamical processes, independently from sub-mm observations. It also predicts the evolution of the spiral structures, which can be observable on timescales of 10-20 years, providing conclusive tests of the model. While we cannot uniquely identify the origin of these spirals, planets embedded in the disk may be capable of exciting the observed morphology. Assuming that this is the case, we can make predictions on the locations and, possibly, the masses of the unseen planets. Such planets may be detected by future multi-wavelength observations.
Context.
One of the key noise sources that currently limits high-contrast imaging observations for exoplanet detection is quasi-static speckles. Quasi-static speckles originate from slowly evolving ...non-common path aberrations (NCPA). These NCPA are related to the different optics encountered in the wavefront sensing path and the science path, and they also exhibit a chromatic component due to the difference in the wavelength between the science camera and the main wavefront sensor. These speckles degrade the contrast in the high-contrast region (or dark hole) generated by the coronagraph and make the calibration in post-processing more challenging.
Aims.
The purpose of this work is to present a proof-of-concept on-sky demonstration of spatial Linear Dark Field Control (LDFC). The ultimate goal of LDFC is to stabilize the point spread function by addressing NCPA using the science image as additional wavefront sensor.
Methods.
We combined spatial LDFC with the Asymmetric Pupil vector-Apodizing Phase Plate (APvAPP) on the Subaru Coronagraphic Extreme Adaptive Optics system at the Subaru Telescope. To allow for rapid prototyping and easy interfacing with the instrument, LDFC was implemented in Python. This limited the speed of the correction loop to approximately 20 Hz. With the APvAPP, we derive a high-contrast reference image to be utilized by LDFC. LDFC is then deployed on-sky to stabilize the science image and maintain the high-contrast achieved in the reference image.
Results.
In this paper, we report the results of the first successful proof-of-principle LDFC on-sky tests. We present results from two types of cases: (1) correction of instrumental errors and atmospheric residuals plus artificially induced static aberrations introduced on the deformable mirror and (2) correction of only atmospheric residuals and instrumental aberrations. When introducing artificial static wavefront aberrations on the DM, we find that LDFC can improve the raw contrast by a factor of 3–7 over the dark hole. In these tests, the residual wavefront error decreased by ∼50 nm RMS, from ∼90 nm to ∼40 nm RMS. In the case with only residual atmospheric wavefront errors and instrumental aberrations, we show that LDFC is able to suppress evolving aberrations that have timescales of < 0.1–0.4 Hz. We find that the power at 10
−2
Hz is reduced by a factor of ∼20, 7, and 4 for spatial frequency bins at 2.5, 5.5, and 8.5
λ
/
D
, respectively.
Conclusions.
We have identified multiplied challenges that have to be overcome before LDFC can become an integral part of science observations. The results presented in this work show that LDFC is a promising technique for enabling the high-contrast imaging goals of the upcoming generation of extremely large telescopes.
VLT/NaCo angular differential imaging at L' (3.8 mu m) revealed a probable giant planet comoving with the young and early-type HD 95086, also known to harbor an extended debris disk. The discovery ...was based on the proper motion analysis of two datasets spanning 15 months. However, the second dataset suffered from bad atmospheric conditions, which limited the significance of the re-detection at the 3sigma level. In this Letter, we report new VLT/NaCo observations of HD 95086 obtained on 2013 June 26 and 27 at L' to recover the planet candidate. We unambiguously re-detect the companion HD 95086 b with multiple independent pipelines at a signal-to-noise ratio greater than or equal to 5. Combined with previously reported measurements, our astrometry decisively shows that the planet is comoving with HD 95086 and inconsistent with a background object. With a revised mass of 5 + or - 2 Jupiter masses, estimated from its L' photometry and "hot-start" models at 17 + or - 4 Myr, HD 95086 b becomes a new benchmark for further physical and orbital characterization of young giant planets.
Context. The SAO 206462 (HD 135344B) disk is one of the few known transitional disks showing asymmetric features in scattered light and thermal emission. Near-infrared scattered-light images revealed ...two bright outer spiral arms and an inner cavity depleted in dust. Giant protoplanets have been proposed to account for the disk morphology. Aims. We aim to search for giant planets responsible for the disk features and, in the case of non-detection, to constrain recent planet predictions using the data detection limits. Methods. We obtained new high-contrast and high-resolution total intensity images of the target spanning the Y to the K bands (0.95–2.3 μm) using the VLT/SPHERE near-infrared camera and integral field spectrometer. Results. The spiral arms and the outer cavity edge are revealed at high resolutions and sensitivities without the need for aggressive image post-processing techniques, which introduce photometric biases. We do not detect any close-in companions. For the derivation of the detection limits on putative giant planets embedded in the disk, we show that the knowledge of the disk aspect ratio and viscosity is critical for the estimation of the attenuation of a planet signal by the protoplanetary dust because of the gaps that these putative planets may open. Given assumptions on these parameters, the mass limits can vary from ~2–5 to ~4–7 Jupiter masses at separations beyond the disk spiral arms. The SPHERE detection limits are more stringent than those derived from archival NaCo/L′ data and provide new constraints on a few recent predictions of massive planets (4–15 MJ) based on the spiral density wave theory. The SPHERE and ALMA data do not favor the hypotheses on massive giant planets in the outer disk (beyond 0.6′′). There could still be low-mass planets in the outer disk and/or planets inside the cavity.
We present the direct imaging discovery of an extrasolar planet, or possible low-mass brown dwarf, at a projected separation of 55 + or - 2 AU (1".58 + or - 07007) from the B9-type star Kappa And. ...The planet was detected with Subaru/HiCIAO during the SEEDS survey and confirmed as a bound companion via common proper motion measurements. Observed near-infrared magnitudes of J = 16.3 + or - 0.3, H = 15.2 + or - 0.2, K sub(s) = 14.6 + or - 0.4, and L' = 13.12 + or - 0.09 indicate a temperature of ~1700 K. The galactic kinematics of the host star are consistent with membership in the Columba Association, implying a corresponding age of (ProQuest: Formulae and/or non-USASCII text omitted) Myr. The system's age, combined with the companion photometry, points to a model-dependent companion mass ~12.8 M sub(Jup). The host star's estimated mass of 2.4-2.5 M sub(middot in circle) places it among the most massive stars ever known to harbor an extrasolar planet or low-mass brown dwarf. While the mass of the companion is close to the deuterium burning limit, its mass ratio, orbital separation, and likely planet-like formation scenario imply that it may be best defined as a "super-Jupiter" with properties similar to other recently discovered companions to massive stars.
Using the NASA/IRTF SpeX and BASS spectrometers we have obtained 0.7-13 m observations of the newly imaged 3-10 Myr old HD 36546 disk system. The SpeX spectrum is most consistent with the ...photospheric emission expected from an L* ∼ 20 L , solar abundance A1.5V star with little to no extinction, and excess emission from circumstellar dust detectable beyond 4.5 m. Non-detections of CO emission lines and accretion signatures point to the gas-poor circumstellar environment of a very old transition disk. Combining the SpeX + BASS spectra with archival WISE/AKARI/IRAS/Herschel photometry, we find an outer cold dust belt at ∼135 K and 20-40 au from the primary, likely coincident with the disk imaged by Subaru, and a new second inner belt with a temperature ∼570 K and an unusual, broad SED maximum in the 6-9 m region, tracing dust at 1.1-2.2 au. An SED maximum at 6-9 m has been reported in just two other A-star systems, HD 131488 and HD 121191, both of ∼10 Myr age. From Spitzer, we have also identified the ∼12 Myr old A7V HD 148657 system as having similar 5-35 m excess spectral features. The Spitzer data allows us to rule out water emission and rule in carbonaceous materials-organics, carbonates, SiC-as the source of the 6-9 m excess. Assuming a common origin for the four young A-star systems' disks, we suggest they are experiencing an early era of carbon-rich planetesimal processing.
HD 95086 is an intermediate-mass debris-disk-bearing star. VLT/NaCo 3.8 μm observations revealed it hosts a 5 ± 2 MJup companion (HD 95086 b) at ≃56 AU. Follow-up observations at 1.66 and 2.18 μm ...yielded a null detection, suggesting extremely red colors for the planet and the need for deeper direct-imaging data. In this Letter, we report H-(1.7 μm) and K1-(2.05 μm) band detections of HD 95086 b from Gemini Planet Imager (GPI) commissioning observations taken by the GPI team. The planet position in both spectral channels is consistent with the NaCo measurements and we confirm it to be comoving. Our photometry yields colors of H − L′ = 3.6 ± 1.0 mag and K1 − L′ = 2.4 ± 0.7 mag, consistent with previously reported 5-σ upper limits in H and Ks. The photometry of HD 95086 b best matches that of 2M 1207 b and HR 8799 cde. Comparing its spectral energy distribution with the BT-SETTL and LESIA planet atmospheric models yields Teff ~ 600–1500 K and log g ~ 2.1–4.5. Hot-start evolutionary models yield M = 5 ± 2 MJup. Warm-start models reproduce the combined absolute fluxes of the object for M = 4–14 MJup for a wide range of plausible initial conditions (Sinit = 8–13 kB/baryon). The color−magnitude diagram location of HD 95086 b and its estimated Teff and log g suggest that the planet is a peculiar L − T transition object with an enhanced amount of photospheric dust.
PDF
