Sébastien Vievard
A5075421385- Stellar, planetary, and galactic studies
- Adaptive optics and wavefront sensing
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Optical Systems and Laser Technology
- Calibration and Measurement Techniques
- Advanced optical system design
- Optical Coherence Tomography Applications
- Astronomical Observations and Instrumentation
- Photonic and Optical Devices
- Advanced Optical Sensing Technologies
- Optical measurement and interference techniques
- Gamma-ray bursts and supernovae
- CCD and CMOS Imaging Sensors
- Optical Wireless Communication Technologies
- Semiconductor Lasers and Optical Devices
- Advanced Fiber Laser Technologies
- Astrophysical Phenomena and Observations
- Advanced Measurement and Metrology Techniques
- Atmospheric Ozone and Climate
- Spectroscopy and Laser Applications
- Photonic Crystal and Fiber Optics
- Optical Network Technologies
- Optical Polarization and Ellipsometry
National Astronomical Observatory of Japan
2018-2025
Astrobiology Center
2018-2025
Subaru (Japan)
2020-2025
National Institutes of Natural Sciences
2018-2024
The Graduate University for Advanced Studies, SOKENDAI
2024
Canada–France–Hawaii Telescope
2019-2023
University of Arizona
2020-2023
Sorbonne Université
2014-2022
Laboratoire d’études spatiales et d’instrumentation en astrophysique
2014-2022
Las Cumbres Observatory Global Telescope Network
2022
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 serves as testbed technologies ELTs. It multi-band which makes use light from 600 to 2500nm allowing coronagraphic direct exoplanet inner 3 lambda/D stellar host. Wavefront sensing control are key operation SCExAO. A partial correction low-order modes provided by Subaru's facility adaptive optics...
Abstract We present the direct-imaging discovery of a substellar companion in orbit around Sun-like star member Hyades open cluster. So far, no other companions have been unambiguously confirmed via direct imaging main-sequence stars Hyades. The HIP 21152 is an accelerating as identified by astrometry from Gaia and Hipparcos satellites. detected companion, B, multiple epochs using high-contrast SCExAO/CHARIS Keck/NIRC2. also obtained stellar radial-velocity data Okayama 188 cm telescope....
Context. In the age of JWST, temperate terrestrial exoplanets transiting nearby late-type M dwarfs provide unique opportunities for characterising their atmospheres, as well searching biosignature gases. this context, benchmark TRAPPIST-1 planetary system has garnered interest a broad scientific community. Aims. We report here discovery and validation two super-Earths LP 890-9 (TOI-4306, SPECULOOS-2), relatively low-activity (32 pc) M6V star. The inner planet, b, was first detected by TESS...
Direct imaging of gas giant exoplanets provides information on their atmospheres and the architectures planetary systems. However, few planets have been detected in blind surveys with direct imaging. Using astrometry from Gaia Hipparcos spacecraft, we identified dynamical evidence for a planet around nearby star HIP 99770. We confirmed detection this using Subaru Coronagraphic Extreme Adaptive Optics instrument. The planet, 99770 b, orbits 17 astronomical units its host star, receiving an...
We obtained spectra of the pre-main sequence star AU Microscopii during a transit its Neptune-sized planet to investigate orbit and atmosphere. used high-dispersion near-infrared spectrograph IRD on Subaru telescope detect Doppler "shadow" from constrain projected stellar obliquity. Modeling observed planetary shadow suggests spin-orbit alignment system ($\lambda=-4.7_{-6.4}^{+6.8}$ degrees), but additional observations are needed confirm this finding. use both data with NIRSPEC Keck-II...
We present the MKID Exoplanet Camera (MEC), a z through J band (800–1400 nm) integral field spectrograph located behind The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) at Telescope on Maunakea that utilizes Microwave Kinetic Inductance Detectors (MKIDs) as enabling technology for high contrast imaging. MEC is first permanently deployed near-infrared instrument and designed to operate both an IFU, focal plane wavefront sensor in multi-kHz feedback loop with SCExAO. read noise free,...
Abstract We present the direct imaging discovery of a substellar companion to nearby Sun-like star, HD 33632 Aa, at projected separation ∼20 au, obtained with SCExAO/CHARIS integral field spectroscopy complemented by Keck/NIRC2 thermal infrared imaging. The companion, Ab, induces 10.5 σ astrometric acceleration on star as detected Gaia and Hipparcos satellites. JHK (1.1–2.4 μ m) spectra L p (3.78 photometry are best matched L/T transition object: an older, higher-gravity, less dusty...
Abstract Characterisation of exoplanets is key to understanding their formation, composition and potential for life. Nulling interferometry, combined with extreme adaptive optics, among the most promising techniques advance this goal. We present an integrated-optic nuller whose design directly scalable future science-ready interferometric nullers: Guided-Light Interferometric Technology, deployed at Subaru Telescope. It combines four beams delivers spatial spectral information. demonstrate...
ABSTRACT Exoplanets in their infancy are ideal targets to probe the formation and evolution history of planetary systems, including planet migration atmospheric dissipation. In this paper, we present spectroscopic observations analyses two transits K2-33b, which is known be one youngest transiting planets (age ≈ 8–11 Myr) around a pre-main-sequence M-type star. Analysing K2-33’s near-infrared spectra obtained by IRD instrument on Subaru, investigate spin-orbit angle transit-induced excess...
We present the confirmation and characterisation of GJ 3473 b (G 50--16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal ($P=1.1980035\pm0.0000018\mathrm{\,d}$) was first detected by Transiting Exoplanet Survey Satellite (TESS). Through joint modelling follow-up radial velocity observations with CARMENES, IRD, HARPS together extensive ground-based photometric LCOGT, MuSCAT, MuSCAT2, we determined precise planetary mass, $M_b =...
Abstract We report the direct imaging discovery of a low-mass companion to nearby accelerating A star, HIP 109427, with Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument coupled Microwave Kinetic Inductance Detector Exoplanet Camera (MEC) and CHARIS integral field spectrograph. data reduced reference star point spread function (PSF) subtraction yield 1.1–2.4 μ m spectra. MEC reveals in Y J band at comparable signal-to-noise ratio using stochastic speckle discrimination, no PSF...
Detailed chemical analyses of M dwarfs are scarce but necessary to constrain the formation environment and internal structure planets being found around them. We present elemental abundances 13 (2900 < Teff 3500 K) observed in Subaru/IRD planet search project. They mid-to-late whose abundance individual elements has not been well studied. use high-resolution (~70,000) near-infrared (970-1750 nm) spectra measure Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, Sr by line-by-line analysis based on model...
The atmospheres of gas giant planets are thought to be inhomogeneous due weather and patchy clouds. We present two full nights coronagraphic observations the HR 8799 using CHARIS integral field spectrograph behind SCExAO adaptive optics system on Subaru Telescope search for spectrophomometric variability. did not detect significant variability signals, but placed lowest upper limits c d. Based injection-recovery tests, we expected have a 50% chance signals down 10% H-band photometric 30%...
Context. Exoplanet direct imaging is a key science goal of current ground-based telescopes as well future extremely large and space-based telescopes. Several high-contrast (HCI) systems for exoplanet have been developed are implemented on Despite recent developments in HCI systems, the contrast they deliver limited by non-common path aberrations (NCPAs) residual wavefront errors adaptive optics (AO) system. To overcome this limitation reach higher contrast, need focal plane wavefront-sensing...
Abstract Recent high-sensitivity observations reveal that accreting giant planets embedded in their parental circumstellar disks can emit H α at final formation stages. While the origin of this emission is not yet determined, magnetospheric accretion currently most plausible hypothesis. In order to test hypothesis further, we develop a simplified but physics-based model and apply it our taken toward HD 163296 with Subaru/SCExAO+VAMPIRES. We specify under which conditions undergo hydrogen...
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is an extremely modular high- contrast installed on the telescope in Hawaii. SCExAO has a dual purpose. Its position northern hemisphere 8-meter makes it prime for detection and characterization of exoplanets stellar environments over large portion sky. In addition, SCExAO's unique design ideal to test innovative technologies algorithms quickly laboratory setup subsequently deploy them on-sky. benefits from first stage...
Context. High-contrast imaging (HCI) observations of exoplanets can be limited by the island effect (IE). The IE occurs when main wavefront sensor (WFS) cannot measure sharp phase discontinuities across telescope’s secondary mirror support structures (also known as spiders). On current generation telescopes, becomes a severe problem ground wind speed is below few meters per second. During these conditions, air that in close contact with spiders cools down and not blown away. This create...
We present observations of two bright M dwarfs (TOI-1634 and TOI-1685: $J=9.5-9.6$) hosting ultra-short period (USP) planets, identified by the TESS mission. The stars are similar in temperature, mass, radius ($T_\mathrm{eff}\,\approx\,3500$ K, $M_\star\,\approx\,0.45-0.46\,M_\odot$, $R_\star\approx 0.45-0.46\,R_\odot$), planets both super-Earth-sized ($1.25\,R_\oplus<R_p<2.0\,R_\oplus$). For systems, light curves from ground-based photometry exhibit planetary transits, whose depths...
Adaptive optics (AO) has become an indispensable tool for ground-based telescopes to mitigate atmospheric seeing and obtain high angular resolution observations. Predictive control aims overcome latency in AO systems: the inevitable time delay between wavefront measurement correction. A current method of predictive uses empirical orthogonal functions (EOFs) framework borrowed from weather prediction, but advent modern machine learning rise neural networks (NNs) offer scope further...
Abstract We obtained high-resolution spectra of the ultracool M-dwarf TRAPPIST-1 during transit its planet “b” using two high-dispersion near-infrared spectrographs, Infrared Doppler (IRD) instrument on Subaru 8.2m telescope, and Habitable Zone Planet Finder (HPF) 10 m Hobby–Eberly Telescope. These spectroscopic observations are complemented by a photometric observation for APO/ARCTIC, which assisted us in capturing correct times our spectroscopy. Using data new IRD HPF observations, as well...
We report a search for excess absorption in the 1083.2 nm line of ortho (triplet) helium during transits TOI-1807b and TOI-2076b, 1.25 2.5R$_{\rm Earth}$ planets on 0.55- 10.4-day orbits around nearby $\sim$200~Myr-old K dwarf stars. limit equivalent width any transit-associated to $<$4 $<$8 mA, respectively. escape solar-composition atmospheres from TOI-2076b $\lesssim$1 $\lesssim$0.1M$_{\rm Gyr$^{-1}$, respectively, depending wind temperature. The absence H/He signature is consistent with...
Abstract We present follow-up SCExAO/CHARIS H- and K -band ( R ∼ 70) high-contrast integral field spectroscopy Keck/NIRC2 photometry of directly imaged brown dwarf companion HD 33632 Ab new radial-velocity data for the system from SOPHIE spectrograph, complemented by Hipparcos Gaia astrometry. These enable more robust spectral characterization compared to lower-resolution spectra discovery paper than double available astrometric baseline. Ab’s spectrum is well reproduced a L8.5–L9.5 dwarf....
Adaptive optics (AO) systems are critical in any application where highly resolved imaging or beam control must be performed through a dynamic medium. Such applications include astronomy and free-space optical communications, light propagates the atmosphere, as well medical microscopy vision science, biological tissues. Recent works have demonstrated common-path wavefront sensors (WFSs) for adaptive using photonic lantern (PL), slowly varying waveguide that can efficiently couple multi-moded...
Abstract The abundances of five elements, Na, Mg, Al, Si, and Sr, are investigated for 44 very metal-poor stars ($-4.0 &lt; [{\rm Fe/H}] -1.5$) in the Galactic halo system based on a local thermodynamic equilibrium (LTE) analysis high-resolution near-infrared spectra obtained with Infrared Doppler instrument (IRD) Subaru Telescope. Mg Si determined all stars. from up to 29 lines, which provide reliable abundance ratios compared previous results few optical lines. levels these...