Subaru Seminars

Debris disks have optically thin dust components around main-sequence stars. Recently, several debris disks harboring a gas component have been discovered in survey observations at optical, infrared, and radio wavelengths, and its origin has been discussed in terms of the evolution of protoplanetary disks and the formation of planetary bodies. In fact, many debris disks are known to reveal submillimeter-wave CO emission, e.g., 49 Ceti, β Pictoris, and 15 others or more. In addition to the CO emission, the submillimeter-wave [C I] emission has been observed toward a few debris disks. I will present recent observations of gaseous debris disks and also present our result of the first subarcsecond images of 49 Ceti in the [C I] 3P1-3P0 emission and the 614 um dust continuum emission observed with ALMA.

Why do massive galaxies in the early universe stop forming new stars and become quiescent? The nature of this quenching process is one of the most important missing pieces in the puzzle of galaxy formation. A number of physical mechanisms have been proposed, but observational evidence is still lacking. Using deep near-infrared spectroscopy, I have explored the stellar ages, stellar kinematics, and ionized gas properties for quiescent galaxies at 1<z<2.5. I will present recent results from these studies and discuss their implications for quenching.

Thermal infrared (IR) emission from dust is a key probe of the evolution and death of short-lived, massive stars. Dust itself is a key component of the interstellar medium; however, the dominant channels of dust production throughout cosmic time are uncertain. In this talk, I will discuss our JWST Director's Discretionary Early Release Science (DD ERS) program, where we will investigate the formation mechanism and chemical composition of dust formed in the colliding winds of a Carbon-rich Wolf-Rayet (WC) binary. With dust production rates ranging from 10^-8 - 10^-6 Msun/yr, such massive stellar binaries may have a significant influence on the dust abundance in galaxies in both the local and early Universe. Dust abundances, composition and formation pathways in the hostile and luminous environment around WC+OB binaries are, however, uncertain due to observational challenges in achieving both high spatial resolution and sensitivity in the mid-IR. Our planned JWST/MIRI+MRS and NIRISS+AMI observations of the archetypal periodic dust forming Wolf-Rayet binary system WR140 will address these uncertainties and also demonstrate the utility of these observing modes for IR bright targets with faint extended emission.

Enhanced mid-infrared emission from CH4 and other stratospheric hydrocarbons has been observed coincident with Jupiter's ultraviolet auroral emission in previous work. This suggests Jupiter's stratosphere and external magnetosphere and solar-wind environment are coupled, however, the exact nature of this coupling remains unknown. A time series of Subaru-COMICS 7.8-micron images of Jupiter will be presented, which demonstrate that both the morphology and magnitude of Jupiter's auroral CH4 emission varied in relation to external solar-wind conditions. The southern auroral CH4 emission increased by 3.8 K in brightness temperature and the northern auroral CH4 emission exhibited a dusk-side brightening after the arrival of a solar-wind compression at Jupiter. These results suggest the solar-wind compression perturbed the jovian magnetosphere and ultimately deposited energetic particles as deep as the neutral stratosphere and modified either the thermal structure, abundance of CH4 or population of energy states of CH4. Such a coupling of the polar stratosphere and external magnetosphere/solar-wind environment could be ubiquitous in Jupiter-like exoplanets.

Ryan Lyman will discuss the history, and provide an overview and explaination of the products and services of the Maunakea Weather Center. In addition, he will share his knowledge on the construction and interpretation of the weather forecast for the Maunakea Observatories, with particular emphasis on atmospheric turbulence and 'Seeing.'

The Subaru Telescope has done amazing work with its Prime-Focus-Camera. In the first 10-15 years we used SuprimeCam, and more recently Hyper SuprimeCam (HSC). Most of you know that the combination of the Subaru Telescope and HSC has produced extraordinary images of great size and quality. But do you know of the existence of the Atmospheric Dispersion Corrector (ADC) in the middle of the camera, and how it works? The image of a star made by an ordinary camera is elongated, and becomes like a rainbow, due to the effects of the atmosphere. This distortion is a strong function of the zenith distance to the star, and so we do not usually recognize changes in this distortion because the focal length of a camera is usually short. But with a big telescope like Subaru, whose focal length is 15m, it matters. We need to design a specialized camera in order to compensate for this atmospheric diffraction. As the first man to design a camera for JNLT, I used two direct-vision prisms for ADC and I boasted to be the designer of the largest camera in the world. But it did not last long. Kunio Takeshi of CANON company invented a sliding type ADC and made a better design of SC. In this seminar, I will explain how the Atmospheric Dispersion Corrector invented by late Dr. Takeshi works.

A major bottleneck for the exploitation of data from the Kepler mission for stellar astrophysics and exoplanet research has been the lack of precise properties for most of the observed stars. In this talk, I will present the first reclassification of radii for ~180,000 Kepler stars derived by combining parallaxes from the Gaia Data Release 2 with the DR25 Kepler Stellar Properties Catalog. The median radius precision is ~8%, a typical improvement by a factor of 4-5 over previous estimates. Using Gaia-revised properties for >4000 exoplanets and their host stars I will discuss several intriguing features in the planet radius versus incident flux plane, including a re-investigation of the radius gap for small planets, the discovery that several confirmed exoplanets occupy a previously described "hot super-Earth desert" at high irradiance, and the relation between gas-giant planet radius and stellar incident flux. I will furthermore present the first bona fide sample of 38 Kepler planets smaller than two earth radii in the habitable zone. Finally, I will present first estimates of homogeneously derived masses and ages of all Kepler host stars using Gaia parallaxes, and discuss trends of Kepler exoplanet properties as a function of these parameters, including the utility that Subaru-HDS spectra provide. These results demonstrate the transformative impact of Gaia data on the characterization of stellar and exoplanet populations.

Extremely Large Telescopes have chosen the Pyramid Wave-Front Sensor (PWFS) over the widely used Shack-Hartmann Wave-Front Sensor (SHWFS) to perform their Single Conjugate Adaptive Optics (SCAO) mode. The PWFS is a Fourier-filtering based sensor which has proven to be strongly efficient for astronomical purposes. It however shows non-linearity behaviors that lead to a reduction of its sensitivity while working around a non-null phase. This effect degrades the performance of the closed loop and prevent from accurate correction of Non-Common-Path Aberrations (NCPA). Thanks to a new breakthrough in the theoretical description of the PFWS which use a convolutive model to describe the sensor, we show that it is possible to analytically predict the behavior of the PWFS in closed-loop operation. This model allows us to explore the impact of residual phases on the properties of the PFWS measurements in term of sensitivity and dynamic range. We used the benefits of this theoretical approach to demonstrate that it is possible to build robust and agile strategies to control our system by compensating the measurements of the PWFS with a minimum knowledge of the turbulence shape.

The James Webb Space Telescope (JWST) will be the premier infrared astronomical facility after its launch in 2021, and its extragalactic observations will revolutionize our understanding of galaxy evolution by breaking the redshift and sensitivity barriers of existing facilities. I will introduce the JWST Advanced Deep Extragalactic Survey (JADES), a joint program of the NIRCam and NIRSpec GTO teams that will be observed in JWST Cycle 1. The design of JADES relied heavily on mock catalogs that we produced using a novel phenomenological model for the evolution of galaxy properties across cosmic time. I will present our model designed for mock JWST observations, and show its science predictions out to z~15 for the JADES survey, including the rest-frame UV galaxy counts beyond the current redshift frontier (z>10), the emergence of the first quenched galaxies at z>4, and constraints on the ionization properties and ISM of early galaxies at 4 < z < 9. The JWST mock data products are publicly available to facilitate GO Cycle 1 proposal planning, and will serve as a powerful future JWST data analysis tool after launch.

Although thermonuclear (Type Ia) supernovae and neutron star mergers are some of the most important astrophysical events, our understanding of these explosions is vague. I will present abundance measurements of elements across the periodic table (Mg, Fe, Co, Ba, and others) that address the nature of both types of explosions. The measurements are based on Keck/DEIMOS spectroscopy of red giants in dwarf galaxies, which experienced a large number of Type Ia supernovae. The iron-peak elemental abundances strongly suggest that the majority of Type Ia supernovae in dwarf galaxies exploded below the Chandrasekhar mass, i.e., the double-degenerate model or the single-degenerate, double-detonation model. The DEIMOS spectra also reveal that barium comes from the r-process and appears in the dwarf galaxies on a timescale similar to iron (at least 100 Myr). Therefore, the mostly likely origin is not supernovae but neutron star mergers. The evolution of the [Ba/Fe] ratio indicates a neutron star merger rate consistent with results from LIGO.

In this talk, I will present a novel survey of the most massive overdensities of galaxies in the peak of cosmic star formation and QSO activities (z=2--4). These structures are traced by the strongest intergalactic Hi (Lyman-alpha) absorption on large scales of 10-30 Mpc. I will present the survey of the strong Hi absorption due to intergalactic medium (IGM) overdensities, and further present our discovery of a sample of extremely massive overdensies at z~2.3 by utilizing Subaru/HSC, KPNO-4m, and CFHT. I will further discuss the discovery of largest and most luminous Lyman alpha nebulae in these fields, which are unique laboratories to study the IGM-galaxy interactions. I will present our newest observations of these Lyman alpha nebulae using Keck Cosmic Web Imager (KCWI). In the end, I will talk about the future prospects.

The most distant quasars provide unique probes to the formation of the earliest supermassive black holes, the co-evolution of early massive galaxies and their central black holes and the reionization of the intergalactic medium. More than 100 quasars have been discovered at z>6. I will present progress on surveys of the most distant quasars, focusing on three recent discoveries: the most distant quasar at z=7.54; the most luminous quasar at z>6 powered by a twelve billion solar mass black hole; and the first gravitationally lensed quasar during the epoch of reionization.

Recently, direct detection of the molecular signature in exoplanet atmosphere using high-resolution spectroscopy is a hot topic in the exoplanet characterisation research field. Unlike low-resolution spectroscopy, it is able to resolve molecular bands into individual absorption lines. By observing the planet during its orbital movement, it is possible to distinguish the exoplanet lines from telluric and stellar lines owing to the variation of Doppler shifts and detect specific molecule unambiguously, which is why it is called planet radial velocity (PRV) technique. It has been predicted that titanium oxide (TiO) and/or vanadium oxide (VO) causing thermal inversions in the atmosphere of the the very hot Jupiters. To find the thermal inversion agent, we observed WASP-33 b before its secondary eclipse using High Dispersion Spectrograph (HDS; R~165,000) on Subaru telescope in the wavelength range of 0.62-0.88 μm. We remove the systematics from the instrument, the telluric and stellar lines using SYSREM and cross-correlate it with model spectrum. We are able to detect TiO emission signature and confirm the existence of stratosphere in the dayside atmosphere of WASP-33b (one of the hottest Hot Jupiter, Teq= 3300 K) by 4.8 sigma. This is the first direct detection of TiO emission signature in the dayside of exoplanet atmosphere using PRV technique in the optical wavelength regime. Our result strengthens the prediction that cold trap effect is inefficient in the atmosphere of a very hot jupiter (Teq > 2500K) and demonstrate the capability of HDS on Subaru telescope to do PRV observation.

Ultra-diffuse galaxies (UDGs) have been the latest of the hypes in the galaxy evolution field. Although known to exist for a while, only recently we have had the opportunity to start studying them thanks to deep photometric observations. The largest compilation of UDGs in a cluster is in fact from Subaru's Suprime-Cam, leading to an incredible pool of candidates to be followed-up spectroscopically. In this talk I will present a detailed study of the stellar populations and star formation histories of some Coma and field UDGs from new DEIMOS and KCWI data (Keck). Comparing such properties with the different formation scenarios that have been simulated to date, I will thus reveal the nature of UDGs and they role in the broader picture of galaxy evolution.