Exoplanet detections have revolutionized astronomy, offering new insights into solar system architecture and planet demographics. While nearly 1,900 exoplanets have now been discovered and confirmed, ...none are still in the process of formation. Transition disks, protoplanetary disks with inner clearings best explained by the influence of accreting planets, are natural laboratories for the study of planet formation. Some transition disks show evidence for the presence of young planets in the form of disk asymmetries or infrared sources detected within their clearings, as in the case of LkCa 15 (refs 8, 9). Attempts to observe directly signatures of accretion onto protoplanets have hitherto proven unsuccessful. Here we report adaptive optics observations of LkCa 15 that probe within the disk clearing. With accurate source positions over multiple epochs spanning 2009-2015, we infer the presence of multiple companions on Keplerian orbits. We directly detect Hα emission from the innermost companion, LkCa 15 b, evincing hot (about 10,000 kelvin) gas falling deep into the potential well of an accreting protoplanet.
PurposeTo compare the long-term outcomes of accelerated corneal collagen crosslinking (CXL) to conventional CXL for progressive keratoconus.Patients and methodsComparative clinical study of ...consecutive progressive keratoconic eyes that underwent either accelerated CXL (9 mW/cm
ultraviolet A (UVA) light irradiance for 10 min) or conventional CXL (3 mW/cm
UVA light irradiance for 30 min). Eyes with minimum 12 months' follow-up were included. Post-procedure changes in keratometry readings (Flat meridian: K1; steep meridian: K2), central corneal thickness (CCT), best spectacle-corrected visual acuity (BSCVA), and manifest refraction spherical equivalent (MRSE) were analysed.ResultsA total of 42 eyes were included. In all, 21 eyes had accelerated CXL (20.5±5.5 months' follow-up) and 21 eyes had conventional CXL group (20.2±5.6 months' follow-up). In the accelerated CXL group, a significant reduction in K2 (P=0.02), however no significant change in K1 (P=0.35) and CCT (P=0.62) was noted. In the conventional CXL group, a significant reduction was seen in K1 (P=0.01) and K2 (P=0.04), but not in CCT (P=0.95). Although both groups exhibited significant reductions in K2 readings, no noteworthy differences were noted between them (P=0.36). Improvements in BSCVA (accelerated CXL; P=0.22 and conventional CXL; P=0.20) and MRSE (accelerated CXL; P=0.97 and conventional CXL; P=0.54) were noted, however were not significant in either group.ConclusionAccelerated and conventional CXL appear to be effective procedures for stabilising progressive keratoconus in the long-term.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems ...and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multiband instrument which makes use of light from 600 to 2500 nm, allowing for coronagraphic direct exoplanet imaging of the inner 3λ/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subaru's facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well-corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase-induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1λ/D. Noncommon path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid-2016) can take deeper exposures and/or perform angular, spectral, and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable subdiffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.
We present new 0.6-4 m imaging of the SR 21 transition disk from Keck/NIRC2 and Magellan/MagAO. The protoplanetary disk around SR 21 has a large (∼30-40 au) clearing first inferred from its spectral ...energy distribution and later detected in submillimeter imaging. Both the gas and small dust grains are known to have a different morphology, with an inner truncation in CO at ∼7 au, and micron-sized dust detected within the millimeter clearing. Previous near-infrared imaging could not distinguish between an inner dust disk with a truncation at ∼7 au or one that extended to the sublimation radius. The imaging data presented here require an inner dust disk radius of a few au, and complex structure such as a warp or spiral. We present a parametric warped disk model that can reproduce the observations. Reconciling the images with the spectral energy distribution gathered from the literature suggests grain growth to 2-5 m within the submillimeter clearing. The complex disk structure and possible grain growth can be connected to dynamical shaping by a giant-planet-mass companion, a scenario supported by previous observational and theoretical studies.
Abstract
We report adaptive optics (AO) follow-up imaging of OGLE-2014-BLG-1050, which is the second binary microlensing event with space-based parallax measurements. The degeneracy in microlens ...parallax
π
E
led to two sets of solutions, either a ∼ (0.9, 0.35)
M
⊙
binary at ∼3.5 kpc or a ∼(0.2, 0.07)
M
⊙
binary at ∼1.1 kpc. We measure the flux blended with the microlensed source by conducting Magellan AO observations, and find that the blending is consistent with the predicted lens flux from the higher-mass solution. From the combination of the AO flux measurement together with previous lensing constraints, it is estimated that the lens system consists of a
primary and a
secondary at
kpc.
Precision wavefront control on future segmented-aperture space telescopes presents significant challenges, particularly in the context of high-contrast exoplanet direct imaging. We present a new ...wavefront control architecture that translates the ground-based artificial guide star concept to space with a laser source on board a second spacecraft, formation flying within the telescope's field of view. We describe the motivating problem of mirror segment motion and develop wavefront sensing requirements as a function of guide star magnitude and segment motion power spectrum. Several sample cases with different values for transmitter power, pointing jitter, and wavelength are presented to illustrate the advantages and challenges of having a non-stellar-magnitude noise limited wavefront sensor for space telescopes. These notional designs allow increased control authority, potentially relaxing spacecraft stability requirements by two orders of magnitude and increasing terrestrial exoplanet discovery space by allowing high-contrast observations of stars of arbitrary brightness.
We utilized the new high-order 585 actuator Magellan Adaptive Optics system (MagAO) to obtain very high-resolution visible light images of HD 142527 with MagAO's VisAO science camera. In the median ...seeing conditions of the 6.5 m Magellan telescope (0".5-0".7), we find MagAO delivers 24%-19% Strehl at H alpha (0.656 mu m). We detect a faint companion (HD 142527B) embedded in this young transitional disk system at just 86.3 + or - 1.9 mas (~12 AU) from the star. The companion is detected in both H alpha and a continuum filter ( Delta mag = 6.33 + or - 0.20 mag at H alpha and 7.50 + or - 0.25 mag in the continuum filter). This provides confirmation of the tentative companion discovered by Biller and co-workers with sparse aperture masking at the 8 m Very Large Telescope. The H alpha emission from the ~0.25 solar mass companion (EW = 180 A) implies a mass accretion rate of ~5.9 x 10 super(-10) M sub(sun) yr super(-1) and a total accretion luminosity of 1.2% L sub(sun). Assuming a similar accretion rate, we estimate that a 1 Jupiter mass gas giant could have considerably better (50-1000x) planet/star contrasts at H alpha than at the H band (COND models) for a range of optical extinctions (3.4-0 mag). We suggest that ~0.5-5-M sub(jup) extrasolar planets in their gas accretion phase could be much more luminous at H alpha than in the NIR. This is the motivation for our new MagAO GAPplanetS survey for extrasolar planets.
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.
Abstract
The Large Binocular Telescope (LBT) has two 8.4 m primary mirrors that produce beams that can be combined coherently in a “Fizeau” interferometric mode. In principle, the Fizeau point-spread ...function (PSF) enables the probing of structure at a resolution up to three times better than that of the adaptive-optics-corrected PSF of a single 8.4 m telescope. In this work, we examined the nearby star Altair (5.13 pc, type A7V, hundreds of Myr to ≈1.4 Gyr) in the Fizeau mode with the LBT at Br
α
(4.05
μ
m) and carried out angular differential imaging to search for companions. This work presents the first filled-aperture LBT Fizeau science data set to benefit from a correcting mirror that provides active phase control. In the analysis of the
λ
/
D
angular regime, the sensitivity of the data set is down to ≈0.5
M
⊙
at 1″ for a 1.0 Gyr system. This sensitivity remains limited by the small amount of integration time, which is in turn limited by the instability of the Fizeau PSF. However, in the Fizeau fringe regime we attain sensitivities of Δ
m
≈ 5 at 0.″2 and put constraints on companions of 1.3
M
⊙
down to an inner angle of ≈0.″15, closer than any previously published direct imaging of Altair. This analysis is a pathfinder for future data sets of this type, and represents some of the first steps to unlocking the potential of the first Extremely Large Telescope. Fizeau observations will be able to reach dimmer targets with upgrades to the instrument, in particular the phase detector.
We utilized the new high-order (250-378 mode) Magellan Adaptive Optics system (MagAO) to obtain very high spatial resolution observations in "visible light" with MagAO's VisAO CCD camera. In the ...good-median seeing conditions of Magellan (0".5-0".7), we find MagAO delivers individual short exposure images as good as 19 mas optical resolution. Due to telescope vibrations, long exposure (60 s) r' (0.63 mu m) images are slightly coarser at FWHM = 23-29 mas (Strehl ~28%) with bright (R < 9 mag) guide stars. These are the highest resolution filled-aperture images published to date. Images of the young (~1 Myr) Orion Trapezium theta super(1) Ori A, B, and C cluster members were obtained with VisAO. In particular, the 32 mas binary theta super(1) Ori C sub(1)C sub(2) was easily resolved in non-interferometric images for the first time. The relative positions of the bright trapezium binary stars were measured with ~0.6-5 mas accuracy. We are now sensitive to relative proper motions of just ~0.2 mas yr super(-1) (~0.4 km s super(-1) at 414 pc)-this is a ~2-10 x improvement in orbital velocity accuracy compared to previous efforts. For the first time, we see clear motion of the barycenter of theta super(1) Ori B sub(2)B sub(3) about theta super(1) Ori B sub(1). All five members of the theta super(1) Ori B system appear likely to be a gravitationally bound "mini cluster," but we find that not all the orbits can be both circular and co-planar. The lowest mass member of the theta super(1) Ori B system (B sub(4); mass ~0.2 M sub(middot in circle)) has a very clearly detected motion (at 4.1 + or - 1.3 km s super(-1); correlation = 99.9%) w.r.t. B sub(1). Previous work has suggested that B sub(4) and B sub(3) are on long-term unstable orbits and will be ejected from this "mini cluster." However, our new "baseline" model of the theta super(1) Ori B system suggests a more hierarchical system than previously thought, and so the ejection of B sub(4) may not occur for many orbits, and B sub(3) may be stable against ejection in the long-term. This "ejection" process of the lowest mass member of a "mini cluster" could play a major role in the formation of low-mass stars and brown dwarfs.
PDF
