Takayuki Kotani

Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504

Several exoplanets have recently been imaged at wide separations of >10?AU from their parent stars. These span a limited range of ages ( 0.5?mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct-imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160?Myr, GJ 504b has an estimated mass of 4 Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5?AU exceeds the typical outer boundary of ~30?AU predicted for the core accretion mechanism. GJ 504b is also significantly cooler (510 K) and has a bluer color (J ? H = ?0.23?mag) than previously imaged exoplanets, suggesting a largely cloud-free atmosphere accessible to spectroscopic characterization. Thus, it has the potential of providing novel insights into the origins of giant planets as well as their atmospheric properties.

Infrared Doppler instrument for the Subaru Telescope (IRD)

Because of their large numbers, red dwarfs may be the most abundant planet hosts in our Galaxy. In order to detect Earth-like planets around nearby red dwarfs (in particular late-M stars), it is crucial to conduct the precise radial velocity (RV) measurements at near-infrared wavelengths where these stars emit most of light. We report the development of the Infrared Doppler (IRD) spectrometer for the Subaru telescope. IRD is a fiber-fed, high-precision, near infrared spectrometer with a spectral resolution of R~70,000 covering from 0.97 to 1.75 μm. To achieve 1m/s RV measurement precision, we employ our original laser frequency comb of a wide-wavelength coverage as an extremely stable wavelength standard in the near-infrared. The spectrometer optics is composed of a new wide-pitch Echelle-grating and Volume-Phase Holographic gratings. To achieve ultimate thermal stability, very low thermal expansion ceramic is used for most of the optical components including the optical bench. The spectrometer will utilize a 4096×4096-pixel HgCdTe array.

Precise wavefront correction with an unbalanced nulling interferometer for exo-planet imaging coronagraphs

Context. Coronagraphs of high dynamical range used for direct exo-planet detection (10 9 –10 10 contrast) on small angular separation (few λ/D units) usually require an input wavefront quality of approximately ten thousandths of a wavelength rms. Aims. We propose a novel method based on a pre-optics setup that behaves partly as a low-efficiency coronagraph, and partly as a high-sensitivity wavefront aberration compensator (phase and amplitude). The combination of the two effects results in a highly accurate corrected wavefront. Methods. First, an (intensity-) unbalanced nulling interferometer (UNI) performs a rejection of part of the wavefront electric field. Then, the input aberrations of the recombined output wavefront are magnified. Because of the unbalanced recombination scheme, aberrations can be free of phase singular points (zeros) and can therefore be compensated by a downstream phase and amplitude correction (PAC) adaptive optics system, using two deformable mirrors. Results. In the image plane, the central star’s peak intensity and the noise level of its speckled halo are reduced by the UNI-PAC combination: the output-corrected wavefront aberrations can be interpreted as an improved compensation of the initial (eventually already corrected) incident wavefront aberrations. Conclusions. The important conclusion is that not all of the elements in the optical setup using UNI-PAC need to reach the λ/10 000 rms surface error quality.

Nulling and adaptive optics for very high dynamic range coronagraph

We have started demonstrating a technique for high dynamic range observations in the lab. This method, proposed by Nishikawa et al., combines a nulling interferometer, a wavefront compensator, and a coronagraph. In the experiments, two beams are generated by a beam splitter and they are combined by another beam splitter under an intensity-unbalanced nulling condition. After the unbalanced nulling interferometer (UNI), normal wavefront sensor and two deformable mirrors are applied for phase and amplitude correction (PAC). Wavefront errors of the two original beams, large errors after the UNI, and compensated errors after the PAC by the deformable mirrors will be measured. After the UNI-PAC method is applied, a downstream coronagraph optics will be set to see that the peak intensity of the central star is dimmed and speckle noise level is also reduced relative to off-axis planet intensity. Possible applications of the method are also discussed.

Virtual wavefront compensation and speckle reduction in coronagraph by unbalanced nulling interferometer (UNI) and phase and amplitude correction (PAC)

We proposed a novel method based on a pre-optics setup that behaves partly as a low-efficiency coronagraph, and partly as a high-sensitivity wavefront aberration compensator (phase and amplitude). The combination of the two effects results in a highly accurate corrected wavefront. First, an (intensity-) unbalanced nulling interferometer (UNI) performs a rejection of part of the wavefront electric field. Then the recombined output wavefront has its input aberrations magnified. Because of the unbalanced recombination scheme, aberrations can be free of phase singular points (zeros) and can therefore be compensated by a downstream phase and amplitude correction (PAC) adaptive optics system, using two deformable mirrors. In the image plane, the central stars peak intensity and the noise level of its speckled halo are reduced by the UNI-PAC combination: the output-corrected wavefront aberrations can be interpreted as an improved compensation of the initial (eventually already corrected) incident wavefront aberrations. The important conclusion is that not all the elements in the optical setup using UNI-PAC need to reach the lambda/10000 rms surface error quality. In the experiments, we observed the aberration magnification of more than 5 times and compensated to about lambda/70 rms which is the current limit of the AO system. This means that we reached to lambda/350 level virtually. We observed the speckle reduction in the focal plane with a coronagraph.

Precise wavefront correction with unbalanced nulling interferometer for direct detection of exo-planet

We propose a pre-optical system for a stellar coronagraph to reduce the speckle noise. It consists of an (amplitude-) unbalanced nulling interferometer (UNI) and phase and amplitude correction (PAC) with two deformable mirrors. We have demonstrated that an initial wavefront error of lambda/82 is 3.9 times magnified to lambda/22 by the UNI.

The mid-infrared imager, spectrometer, coronagraph (MISC) for the Origins Space telescope (OST)

The Mid-infrared Imager, Spectrometer, Coronagraph (MISC) is one of the instruments studied both for the Origins Space Telescope (OST) Mission Concept 1 and 2. The MISC for OST Mission Concept 1 consists of the MISC imager and spectrometer module (MISC I and S), the MISC coronagraph module (MISC COR) and the MISC transit spectrometer module (MISC TRA). The MISC I and S offers (1) a wide field (3 arcminx3 arcmin) imaging and low-resolution spectroscopic capability with filters and grisms for 6-38 μm, (2) a medium-resolution (R~1,000) Integral Field Unit (IFU) spectroscopic capability for 5- 38 μm and (3) a high-resolution (R~25,000) slit spectroscopic capability for 12-18 μm and 25-36 μm. The MISC COR module employs PIAACMC coronagraphy method and covers 6-38 μm achieving 10-7 contrast at 0.5 arcsec from the central star. The MISC TRA module employs a densified pupil spectroscopic design to achieve 3-5 ppm of spectro-photometric stability and covers 5-26 μm with R=100-300. The MISC for OST Mission Concept 2 consists of the MISC wide field imager module (MISC WFI) and the MISC transit Spectrometer module (MISC TRA). The MISC WFI offers a wide field (3 arcmin ×3 arcmin) imaging and low-resolution spectroscopic capabilities with filters and grisms for 6-28μm. The MISC TRA module in the OST Mission Concept 2 also employs the densified pupil spectroscopic design to achieve <5 ppm of spectro-photometric stability and covers 4-22 μm with R=100-300. The highest ever spectrophotometric stability achieved by MISC TRA enables to detect bio-signatures (e.g., ozone, water, and methane) in habitable worlds in both primary and secondary transits of exoplanets and makes the OST a powerful tool to bring an revolutionary progress in exoplanet sciences. Combined with the spectroscopic capability in the FIR provided by other OST instruments, the MISC widens the wavelength coverage of OST down to 5μm, which makes the OST a powerful tool to diagnose the physical and chemical condition of the ISM using dust features, molecules lines and atomic and ionic lines. The MISC also provides the OST with a focal plane guiding function for the other OST science instruments as well as its own use.

FIRST, the pupil-remapping fiber interferometer at Subaru telescope: towards photonic beam-combination with phase control and on-sky commissioning results (Conference Presentation)

FIRST (Fibered Imager foR a Single Telescope) is a post-AO instrument module that enables high-contrast imaging and spectroscopy at sub-diffraction limited spatial scales. FIRST achieves this through a unique combination of sparse aperture masking, spatial filtering, pupil remapping Fizeau interferometry, and cross-dispersion in the visible. The telescope pupil is divided into sub-pupils using a honeycomb array of micro-electro-mechanical mirrors, and the light from each sub-pupil injected into a separate single mode fiber that provides spatial filtering. The fibers, which are pathlength-matched to within a few tens of micrometers, reformat the sub-apertures into a linear non-redundant array allowing for the extraction of fringes from each possible baseline as well as wavelength dispersion to create ~130 spectral channels for every baseline combination over the 600-900nm spectral range.n nIn this presentation, we will first report on the latest on-sky results obtained with FIRST. In its current design, the instrument was successfully integrated on the 3-m telescope at Lick Observatory and is now a module of the SCExAO extreme adaptive optics instrument on the 8-m Subaru Telescope. The latest on-sky results obtained from commissioning data show the detection of the stellar companion of the Alpha Equu binary system at an angular separation of 0.6 λ/D (11mas). Even at such a separation, the FIRST data delivers information on the companion spectrum, providing valuable constraints on the stellar parameters of the system such as the effective temperatures.nThe second part of this presentation will focus on the ongoing instrument upgrades with the aim of increasing the instrument’s stability and sensitivity, thus improving the dynamic range. We initiated a comprehensive upgrade of FIRST’s interferometric components to a new series of photonic on-chip beam combiners and automated optoelectronic delay lines for rapid phasing of each sub-pupil. The new photonic beam combining chips split light from each sub-aperture and combines them to provide a simultaneous measurement of the fringes from every baseline. Another function of the new photonic chips is the inclusion of waveguides in crystalline electro-optic material (Lithium niobate) that enable on-chip active phase control of the light at high speeds (up to kHz). This type of photonic architecture has not been implemented previously for astronomical interferometry of this kind and could potentially provide FIRST with key advantages (see Martin et al., these proceedings). nnWhile the beam-combiner output no longer requires non-redundancy, the fiber array that feeds the chip input still requires accurate pathlength-matching to achieve high fringe contrasts. The existing fibers were individually manufactured to ensure identical length. However, while this method was successful, it was not very flexible particularly if any photonic components are added that change the overall fiber length. Thus, another key FIRST upgrade is the use of actively controlled fiber delay lines capable of compensating for up to 100 mm of differential pathlength in each fiber, with sub-micron accuracy. This type of active pathlength control allows FIRST to not only correct for unwanted environmental phase delays, but also makes it entirely reconfigurable regardless of the back-end photonics used.

PIAA coronagraph for Origins Space telescope (OST) mid-infrared imager, spectrometer, coronagraph (MISC) instrument

The Mid-infrared Imager, Spectrometer Coronagraph (MISC) instrument studied for the Origins Space Telescope (OST) Mission Concept 1 is designed to observe at mid-infrared (MIR) wavelengths ranging from 5 to 38 microns for OST. In the OST Mission Concept 1 study, MISC consists of three separate optical modules providing imaging, spectroscopy, and coronagraph capabilities. The MISC Coronagraph module (MISC COR) employs Phase-Induced Amplitude Apodization (PIAA) coronagraph (Guyon et al. 2014) in which pupil apodization is modified by reflection on mirrors and central starlight is blocked by focal plane mask and Lyot mask. The performance target of MISC COR is to achieve 10-7 contrast at 0.5” from the central star with covering wavelength of 6-38 microns using 2 optical channels. MISC COR will be a powerful tool to bring a revolutionary progress in exoplanet sciences. In this paper, we present detailed design of its optics and optomechanics, and discuss expected performances for a variety of combination of focal plane mask and Lyot mask.

Contrast improvement with imperfect pre-coronagraph and dark-hole

We are studying a coronagraph system with an imperfect pre-coronagraph in the field of direct detection of exoplanets which can provide additional contrast to a main coronagraph. It is a kind of an unbalanced nulling interferometer (UNI) concept which consists of the first deformable mirror (DM), the pre-coronagraph, the second DM, and a main coronagraph. The pre-coronagraph and the DM1 reduce the star light and the speckle noise to about one-hundreds which would be added to the main coronagraph contrast. The DMs can be controlled by the dark-hole algorithm by changing the masks at the coronagraph foci.