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Register a new userHigh-contrast H$alpha$ imaging with Subaru/SCExAO+VAMPIRES
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We present current status of H$alpha$ high-contrast imaging observations with Subaru/SCExAO+VAMPIRES. Our adaptive optics correction at optical wavelengths in combination with (double) spectral differential imaging (SDI) and angular differential imaging (ADI) was capable of detecting a ring-like feature around omi Cet and the H$alpha$ counterpart of jet around RY Tau. We tested the post-processing by changing the order of ADI and SDI and both of the contrast limits achieved $sim10^{-3}-5times10^{-4}$ at $0.3^{primeprime}$, which is comparable to other H$alpha$ high-contrast imaging instruments in the southern hemisphere such as VLT/SPHERE, VLT/MUSE, and MagAO. Subaru/VAMPIRES provides great opportunities for H$alpha$ high-contrast imaging for northern hemisphere targets.
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MWC758 is a young star surrounded by a transitional disk. Recently, a protoplanet candidate has been detected around MWC758 through high-resolution $L$-band observations. The candidate is located inside the disk cavity at a separation of $sim$111 mas from the central star, and at an average position angle of $sim$165.5 degrees. We have performed simultaneous adaptive optics observations of MWC758 in the H$_{alpha}$ line and the adjacent continuum using SPHERE/ZIMPOL at the Very Large Telescope (VLT). We aim at detecting accreting protoplanet candidates through spectral angular differential imaging observations. The data analysis does not reveal any H$_{alpha}$ signal around the target. The derived contrast curve in the B_Ha filter allows us to derive a 5$sigma$ upper limit of $sim$7.6 mag at 111 mas, the separation of the previously detected planet candidate. This contrast translates into a H$_{alpha}$ line luminosity of $L_{rm H_{alpha}}lesssim$ 5$times$10$^{-5}$ $L_{odot}$ at 111 mas, and an accretion luminosity of $L_{acc} <$3.7$times$10$^{-4},L_{odot}$. For the predicted mass range of MWC758b, 0.5-5 $M_{rm Jup}$, this implies accretion rates of $dot M lesssim$ 3.4$times$(10$^{-8}$-10$^{-9}),M_{odot}/yr$, for an average planet radius of 1.1 $R_{rm Jup}$. Therefore, our estimates are consistent with the predictions of accreting circumplanetary accretion models for $R_{rm in} = 1 R_{rm Jup}$. In any case, the non-detection of any H$_{alpha}$ emitting source in the ZIMPOL images does not allow us to unveil the true nature of the $L$ detected source.
We present new, near-infrared (1.1--2.4 $mu m$) high-contrast imaging of the bright debris disk surrounding HIP 79977 with the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) coupled with the CHARIS integral field spectrograph. SCExAO/CHARIS resolves the disk down to smaller angular separations of (0.11; $r sim 14$ au) and at a higher significance than previously achieved at the same wavelengths. The disk exhibits a marginally significant east-west brightness asymmetry in $H$ band that requires confirmation. Geometrical modeling suggests a nearly edge-on disk viewed at a position angle of $sim$ 114.6$^{o}$ east of north. The disk is best-fit by scattered-light models assuming strongly forward-scattering grains ($g$ $sim$ 0.5--0.65) confined to a torus with a peak density at $r_{0}$ $sim$ 53--75 au. We find that a shallow outer density power law of $alpha_{out}=$-1-- -3 and flare index of $beta = 1$ are preferred. Other disk parameters (e.g.~inner density power law and vertical scale height) are more poorly constrained. The disk has a slightly blue intrinsic color and its profile is broadly consistent with predictions from birth ring models applied to other debris disks. While HIP 79977s disk appears to be more strongly forward-scattering than most resolved disks surrounding 5--30 Myr-old stars, this difference may be due to observational biases favoring forward-scattering models for inclined disks vs. lower inclination, ostensibly neutral-scattering disks like HR 4796As. Deeper, higher signal-to-noise SCExAO/CHARIS data can better constrain the disks dust composition.
We present $H$-band scattered light imaging of a bright debris disk around the A0 star HD 36546 obtained from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system with data recorded by the HiCIAO camera using the vector vortex coronagraph. SCExAO traces the disk from $r$ $sim$ 0.3 to $r$ $sim$ 1 (34--114 au). The disk is oriented in a near east-west direction (PA $sim$ 75$^{o}$), is inclined by $i$ $sim$ 70--75$^{o}$ and is strongly forward-scattering ($g$ $>$ 0.5). It is an extended disk rather than a sharp ring; a second, diffuse dust population extends from the disks eastern side. While HD 36546 intrinsic properties are consistent with a wide age range ($t$ $sim$ 1--250 $Myr$), its kinematics and analysis of coeval stars suggest a young age (3--10 $Myr$) and a possible connection to Taurus-Aurigas star formation history. SCExAOs planet-to-star contrast ratios are comparable to the first-light Gemini Planet Imager contrasts; for an age of 10 $Myr$, we rule out planets with masses comparable to HR 8799 b beyond a projected separation of 23 au. A massive icy planetesimal disk or an unseen superjovian planet at $r$ $>$ 20 au may explain the disks visibility. The HD 36546 debris disk may be the youngest debris disk yet imaged, is the first newly-identified object from the now-operational SCExAO extreme AO system, is ideally suited for spectroscopic follow up with SCExAO/CHARIS in 2017, and may be a key probe of icy planet formation and planet-disk interactions.
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its $sim$130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescopes overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L (3.8 $mu$m), as opposed to the shorter wavelength near-infrared bands (1-2.4 $mu$m) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent ($sim$0.1-1 Gyr) stars. LEECHs contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5$mu$m in preparation for JWST.
Current and future high-contrast imaging instruments require extreme adaptive optics (XAO) systems to reach contrasts necessary to directly image exoplanets. Telescope vibrations and the temporal error induced by the latency of the control loop limit the performance of these systems. One way to reduce these effects is to use predictive control. We describe how model-free Reinforcement Learning can be used to optimize a Recurrent Neural Network controller for closed-loop predictive control. First, we verify our proposed approach for tip-tilt control in simulations and a lab setup. The results show that this algorithm can effectively learn to mitigate vibrations and reduce the residuals for power-law input turbulence as compared to an optimal gain integrator. We also show that the controller can learn to minimize random vibrations without requiring online updating of the control law. Next, we show in simulations that our algorithm can also be applied to the control of a high-order deformable mirror. We demonstrate that our controller can provide two orders of magnitude improvement in contrast at small separations under stationary turbulence. Furthermore, we show more than an order of magnitude improvement in contrast for different wind velocities and directions without requiring online updating of the control law.
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