arXiv subjects

Yasushi Suto

Publications and source records attributed to Yasushi Suto.

At least 37 records · Page 2Linked to original sources

arXiv2020

Search for Alignment of Disk Orientations in Nearby Star-Forming Regions: Lupus, Taurus, Upper Scorpius, $ρ$ Ophiuchi, and Orion

Spatial correlations among proto-planetary disk orientations carry unique information on physics of multiple star formation processes. We select five nearby star-forming regions that comprise a number of proto-planetary disks with spatially-resolved images with ALMA and HST, and search for the mutual alignment of the disk axes. Specifically, we apply the Kuiper test to examine the statistical uniformity of the position angle (PA: the angle of the major axis of the projected disk ellipse measured counter-clockwise from the north) distribution. The disks located in the star-forming regions, except the Lupus clouds, do not show any signature of the alignment, supporting the random orientation. Rotational axes of 16 disks with spectroscopic measurement of PA in the Lupus III cloud, a sub-region of the Lupus field, however, exhibit a weak and possible departure from the random distribution at a $2σ$ level, and the inclination angles of the 16 disks are not uniform as well. Furthermore, the mean direction of the disk PAs in the Lupus III cloud is parallel to the direction of its filament structure, and approximately perpendicular to the magnetic field direction. We also confirm the robustness of the estimated PAs in the Lupus clouds by comparing the different observations and estimators based on three different methods including sparse modeling. The absence of the significant alignment of the disk orientation is consistent with the turbulent origin of the disk angular momentum. Further observations are required to confirm/falsify the possible disk alignment in the Lupus III cloud.

astro-ph.SR↗

arXiv2020

Beyond a pale blue dot : how to search for possible bio-signatures on earth-like planets

The Earth viewed from outside the Solar system would be identified merely like a pale blue dot, as coined by Carl Sagan. In order to detect possible signatures of the presence of life on a second earth among several terrestrial planets discovered in a habit-able zone, one has to develop and establish a methodology to characterize the planet as something beyond a mere pale blue dot. We pay particular attention to the periodic change of the color of the dot according to the rotation of the planet. Because of the large-scale inhomogeneous distribution of the planetary surface, the reflected light of the dot comprises different color components corresponding to land, ocean, ice, and cloud that cover the surface of the planet. If we decompose the color of the dot into several principle components, in turn, one can identify the presence of the different surface components. Furthermore, the vegetation on the earth is known to share a remarkable reflection signature; the reflection becomes significantly enhanced at wave-lengths longer than 760nm, which is known as a red-edge of the vegetation. If one can identify the corresponding color signature in a pale blue dot, it can be used as a unique probe of the presence of life. I will describe the feasibility of the methodology for future space missions, and consider the direction towards astrobiology from an astrophysicist's point of view.

astro-ph.EP↗

arXiv2020

Obliquity of an Earth-like planet from frequency modulation of its direct imaged lightcurve: mock analysis from general circulation model simulation

Direct-imaging techniques of exoplanets have made significant progress recently, and will eventually enable to monitor photometric and spectroscopic signals of earth-like habitable planets in the future. The presence of clouds, however, would remain as one of the most uncertain components in deciphering such direct-imaged signals of planets. We attempt to examine how the planetary obliquity produce different cloud patterns by performing a series of GCM (General Circulation Model) simulation runs using a set of parameters relevant for our Earth. Then we use the simulated photometric lightcurves to compute their frequency modulation due to the planetary spin-orbit coupling over an entire orbital period, and attempt to see to what extent one can estimate the obliquity of an Earth-twin. We find that it is possible to estimate the obliquity of an Earth-twin within the uncertainty of several degrees with a dedicated 4 m space telescope at 10 pc away from the system if the stellar flux is completely blocked. While our conclusion is based on several idealized assumptions, a frequency modulation of a directly-imaged earth-like planet offers a unique methodology to determine its obliquity.

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arXiv2020

Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

We study shapes and alignments of 45 dark matter (DM) haloes and their brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble (CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of the DM haloes by strong gravitational lensing, whereas BCG shapes are derived from their light profiles in Hubble Space Telescope images. Our measurements from a large sample of massive clusters presented here provide new constraints on dark matter and cluster astrophysics. We find that DM haloes are on average highly elongated with the mean ellipticity of $0.482\pm 0.028$, and position angles of major axes of DM haloes and their BCGs tend to be aligned well with the mean value of alignment angles of $22.2\pm 3.9$ deg. We find that DM haloes in our sample are on average more elongated than their BCGs with the mean difference of their ellipticities of $0.11\pm 0.03$. In contrast, the Horizon-AGN cosmological hydrodynamical simulation predicts on average similar ellipticities between DM haloes and their central galaxies. While such a difference between the observations and the simulation may well be explained by the difference of their halo mass scales, other possibilities include the bias inherent to strong lensing measurements, limited knowledge of baryon physics, or a limitation of cold dark matter.

astro-ph.CO↗

arXiv2020

Architecture of three-planet systems predicted from the observed protoplanetary disk of HL Tau

A number of protoplanetary disks observed with ALMA potentially provide direct examples of initial conditions for planetary systems. In particular, the HL Tau disk has been intensively studied, and its rings/gaps are conventionally interpreted to be a result of unseen massive planets embedded in the gaps. Based on this interpretation, we carried out N-body simulations to investigate orbital evolution of planets within the protoplanetary disk and after the disk dispersal. Before the disk dispersal, our N-body simulations include both migration and mass-growth of the planet coupled with evolution of the disk. By varying the disk parameters, we produce a variety of widely-separated planetary systems consisting of three super-Jupiters at the end of disk dispersal. We found the outer planet is more massive than the inner one, and the migration of the innermost planet is inefficient due to the accretion of outer planet(s). We also showed how the final configuration and the final planetary mass depend on disk parameters. The migration is found to be convergent and no planet-pair has a period ratio less than 2. After the disk dispersal, we switch to pure gravitational N-body simulations and integrate the orbits up to 10 Gyr. Most simulated systems remain stable for at least 10 Gyr. We discuss implications of our result in terms of the observed widely-separated planetary systems HR 8799 and PDS 70.

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arXiv2020

A strategy to search for an inner binary black hole from the motion of the tertiary star

There are several on-going projects to search for stars orbiting around an invisible companion. A fraction of such candidates may be a triple, instead of a binary, consisting of an inner binary black hole (BBH) and an outer orbiting star. In this paper, we propose a methodology to search for a signature of such an inner BBH, possibly a progenitor of gravitational-wave sources discovered by {\it LIGO}, from the precise radial velocity (RV) follow-up of the outer star. We first describe a methodology using an existing approximate RV formula for coplanar circular triples. We apply this method and constrain the parameters of a possible inner binary objects in 2M05215658+4359220, which consists of a red giant and an unseen companion. Next we consider co-planar but non-circular triples. We compute numerically the RV variation of a tertiary star orbiting around an inner BBH, generate mock RV curves, and examine the feasibility of the BBH detection for our fiducial models. We conclude that the short-cadence RV monitoring of a star-BH binary provides an interesting and realistic method to constrain and/or search for possible inner BBHs. Indeed a recent discovery of a star--BH binary system LB-1 may imply that there are a large number of such unknown objects in our Galaxy, which are ideal targets for the methodology proposed here.

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arXiv2020

Star-disk alignment in the protoplanetary disks: SPH simulation of the collapse of turbulent molecular cloud cores

We perform a series of three-dimensional smoothed particle hydrodynamics (SPH) simulations to study the evolution of the angle between the protostellar spin and the protoplanetary disk rotation axes (the star-disk angle $ψ_{\rm sd}$) in turbulent molecular cloud cores. While $ψ_{\rm sd}$ at the protostar formation epoch exhibits broad distribution up to $\sim 130^{\circ}$, $ψ_{\rm sd}$ decreases ($\lesssim 20^{\circ}$) in a timescale of $\sim 10^{4}$ yr. This timescale of the star-disk alignment, $t_{\rm alignment}$, corresponds basically to the mass doubling time of the central protostar, in which the protostar forgets its initial spin direction due to the mass accretion from the disk. Values of $ψ_{\rm sd}$ both at $t=10^2$ yr and $t=10^5$ yr after the protostar formation are independent of the ratios of thermal and turbulent energies to gravitational energy of the initial cloud cores: $α=E_{\rm thermal}/|E_{\rm gravity}|$ and $γ_{\rm turb}=E_{\rm turbulence}/|E_{\rm gravity}|$. We also find that a warped disk is possibly formed by the turbulent accretion flow from the circumstellar envelope.

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arXiv2019

Cosmological evolution of orientations of cluster-sized dark matter haloes and their central galaxies in the Horizon-AGN simulation

It is known observationally that the major axes of galaxy clusters and their brightest cluster galaxies are roughly aligned with each other. To understand the origin of the alignment, we identify 40 cluster-sized dark matter (DM) haloes with masses higher than $5\times10^{13}~M_{\odot}$ and their central galaxies (CGs) at $z\approx 0$ in the Horizon-AGN cosmological hydrodynamical simulation. We trace the progenitors at 50 different epochs between $0 1$. The alignment becomes tighter with cosmic time; the major axes of the CGs and their host DM haloes at present are aligned on average within $\sim 30^{\circ}$ in the three dimensional space and $\sim 20^{\circ}$ in the projected plane. The orientations of the major axes of DM haloes on average follow one of the eigen-vectors of the surrounding tidal field that corresponds to the {\it slowest collapsing} (or even stretching) mode, and the alignment with the tidal field also becomes tighter. This implies that the orientations of CGs and DM haloes at the present epoch are largely imprinted in the primordial density field of the Universe, whereas strong dynamical interactions such as mergers are important to explain their mutual alignment at each epoch.

astro-ph.CO↗

arXiv2019

Second Data Release of the Hyper Suprime-Cam Subaru Strategic Program

This paper presents the second data release of the Hyper Suprime-Cam Subaru Strategic Program, a wide-field optical imaging survey on the 8.2 meter Subaru Telescope. The release includes data from 174 nights of observation through January 2018. The Wide layer data cover about 300 deg^2 in all five broadband filters (grizy) to the nominal survey exposure (10min in gr and 20min in izy). Partially observed areas are also included in the release; about 1100 deg^2 is observed in at least one filter and one exposure. The median seeing in the i-band is 0.6 arcsec, demonstrating the superb image quality of the survey. The Deep (26 deg^2) and UltraDeep (4 deg^2) data are jointly processed and the UltraDeep-COSMOS field reaches an unprecedented depth of i~28 at 5 sigma for point sources. In addition to the broad-bands, narrow-band data are also available in the Deep and UltraDeep fields. This release includes a major update to the processing pipeline, including improved sky subtraction, PSF modeling, object detection, and artifact rejection. The overall data quality has been improved, but this release is not without problems; there is a persistent deblender problem as well as new issues with masks around bright stars. The user is encouraged to review the issue list before utilizing the data for scientific explorations. All the image products as well as catalog products are available for download. The catalogs are also loaded to a database, which provides an easy interface for users to retrieve data for objects of interest. In addition to these main data products, detailed galaxy shape measurements withheld from the Public Data Release 1 (PDR1) are now available to the community. The shape catalog is drawn from the S16A internal release, which has a larger area than PDR1 (160 deg^2). All products are available at the data release site, https://hsc-release.mtk.nao.ac.jp/.

astro-ph.IM↗

arXiv2019

Asteroseismic determination of the stellar rotation period of the Kepler transiting planetary systems and its implications for the spin-orbit architecture

We measure the rotation periods of 19 stars in the {\it Kepler} transiting planetary systems, $P_{\rm rot, astero}$ from asteroseismology and $P_{\rm rot, phot}$ from photometric variation of their lightcurve. Two stars exhibit two clear peaks in the Lomb-Scargle periodogram, neither of which agrees with the seismic rotation period. Other four systems do not show any clear peak, whose stellar rotation period is impossible to estimate reliably from the photometric variation; their stellar equators may be significantly inclined with respect to the planetary orbital plane. For the remaining 13 systems, $P_{\rm rot, astero}$ and $P_{\rm rot, phot}$ agree within 30\%. Interestingly, three out of the 13 systems are in the spin-orbit resonant state in which $P_{\rm orb, b}/P_{\rm rot, astero} \approx 1$ with $P_{\rm orb, b}$ being the orbital period of the inner-most planet of each system. The corresponding chance probability is ($0.2$-$4.7$) \% based on the photometric rotation period data for 464 {\it Kepler} transiting planetary systems. While further analysis of stars with reliable rotation periods is required to examine the statistical significance, the spin-orbit resonance between the star and planets, if confirmed, have important implications for the star-planet tidal interaction, in addition to the origin of the spin-orbit (mis-)alignment of transiting planetary systems.

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arXiv2019

The misaligned orbit of the Earth-sized planet Kepler-408b

Kepler-408 is one of the 33 planet-hosting {\it Kepler} stars for which asteroseismology has been used to investigate the orientation of the stellar rotation axis relative to the planetary orbital plane. The transiting "hot Earth," Kepler-408b, has an orbital period of 2.5 days and a radius of $0.86$~$R_\oplus$, making it much smaller than the planets for which spin-orbit alignment has been studied using the Rossiter-McLaughlin effect. Because conflicting asteroseismic results have been reported in the literature, we undertake a thorough re-appraisal of this system and perform numerous checks for consistency and robustness. We find that the conflicting results are due to the different models for the low-frequency noise in the power spectrum. A careful treatment of the background noise resolves these conflicts, and shows that the stellar inclination is $\is=42^{+5}_{-4}$ degrees. Kepler-408b is, by far, the smallest planet known to have a significantly misaligned orbit.

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arXiv2018

Cool core disturbed: Observational evidence for coexistence of sub-sonic sloshing gas and stripped shock-heated gas around the core of RX J1347.5-1145

RXJ1347.5-1145 (z = 0.451) is one of the most luminous X-ray galaxy clusters, which hosts a prominent cool core and exhibits a signature of a major merger. We present the first direct observational evidence for sub-sonic nature of sloshing motion of the cool core. We find that a residual X-ray image from the Chandra X-ray Observatory after removing the global emission shows a clear dipolar pattern characteristic of gas sloshing, whereas we find no significant residual in the Sunyaev-Zel'dovich effect (SZE) image from the Atacama Large Millimeter/submillimeter Array (ALMA). We estimate the equation of state of perturbations in the gas from the X-ray and SZE residual images. The inferred velocity is 420 +310 -420 km s-1, which is much lower than the adiabatic sound speed of the intracluster medium in the core. We thus conclude that the perturbation is nearly isobaric, and gas sloshing motion is consistent with being in pressure equilibrium. Next, we report evidence for gas stripping of an infalling subcluster, which likely shock-heats gas to high temperature well in excess of 20 keV. Using mass distribution inferred from strong lensing images of the Hubble Space Telescope (HST), we find that the mass peak is located away from the peak position of stripped gas with statistical significance of > 5σ. Unlike for the gas sloshing, the velocity inferred from the equation of state of the excess hot gas is comparable to the adiabatic sound speed expected for the 20 keV intracluster medium. All of the results support that the southeast substructure is created by a merger. On the other hand, the positional offset between the mass and the gas limits the self-interaction cross section of dark matter to be less than 3.7 h-1 cm2 g-1 (95% CL).

astro-ph.HE↗

arXiv2018

Projected alignment of non-sphericities of stellar, gas, and dark matter distributions in galaxy clusters: analysis of the Horizon-AGN simulation

While various observations measured ellipticities of galaxy clusters and alignments between orientations of the brightest cluster galaxies and their host clusters, there are only a handful of numerical simulations that implement realistic baryon physics to allow direct comparisons with those observations. Here we investigate ellipticities of galaxy clusters and alignments between various components of them and the central galaxies in the state-of-the-art cosmological hydrodynamical simulation Horizon-AGN, which contains dark matter, stellar, and gas components in a large simulation box of $(100 h^{-1}$ Mpc$)^3$ with high spatial resolution ($\sim1$ kpc). We estimate ellipticities of total matter, dark matter, stellar, gas surface mass density distributions, X-ray surface brightness, and the Compton $y$-parameter of the Sunyaev-Zel'dovich effect, as well as alignments between these components and the central galaxies for 120 projected images of galaxy clusters with masses $M_{200}>5\times10^{13}M_{\odot}$. Our results indicate that the distributions of these components are well aligned with the major-axes of the central galaxies, with the root mean square value of differences of their position angles of $\sim 20^\circ$, which vary little from inner to the outer regions. We also estimate alignments of these various components with total matter distributions, and find tighter alignments than those for central galaxies with the root mean square value of $\sim 15^\circ$. We compare our results with previous observations of ellipticities and position angle alignments and find reasonable agreements. The comprehensive analysis presented in this paper provides useful prior information for analyzing stacked lensing signals as well as designing future observations to study ellipticities and alignments of galaxy clusters.

astro-ph.GA↗

arXiv2018

Reliability of stellar inclination estimated from asteroseismology: analytical criteria, mock simulations and Kepler data analysis

Advances in asteroseismology of solar-like stars, now provide a unique method to estimate the stellar inclination $i_{\star}$. This enables to evaluate the spin-orbit angle of transiting planetary systems, in a complementary fashion to the Rossiter-McLaughlin effect, a well-established method to estimate the projected spin-orbit angle $λ$. Although the asteroseismic method has been broadly applied to the Kepler data, its reliability has yet to be assessed intensively. In this work, we evaluate the accuracy of $i_{\star}$ from asteroseismology of solar-like stars using 3000 simulated power spectra. We find that the low signal-to-noise ratio of the power spectra induces a systematic under-estimate (over-estimate) bias for stars with high (low) inclinations. We derive analytical criteria for the reliable asteroseismic estimate, which indicates that reliable measurements are possible in the range of $20^\circ \lesssim i_{\star} \lesssim 80^\circ$ only for stars with high signal-to-noise ratio. We also analyse and measure the stellar inclination of 94 Kepler main-sequence solar-like stars, among which 33 are planetary hosts. According to our reliability criteria, a third of them (9 with planets, 22 without) have accurate stellar inclination. Comparison of our asteroseismic estimate of $v\sin{i_{\star}}$ against spectroscopic measurements indicates that the latter suffers from a large uncertainty possibly due to the modeling of macro-turbulence, especially for stars with projected rotation speed $v\sin{i_{\star}} \lesssim 5$ km/s. This reinforces earlier claims, and the stellar inclination estimated from the combination of measurements from spectroscopy and photometric variation for slowly rotating stars needs to be interpreted with caution.

astro-ph.SR↗

arXiv2018

Systematic Search for Rings around Kepler Planet Candidates: Constraints on Ring Size and Occurrence Rate

We perform a systematic search for rings around 168 Kepler planet candidates with sufficient signal-to-noise ratios that are selected from all the short-cadence data. We fit ringed and ringless models to their lightcurves, and compare the fitting results to search for the signatures of planetary rings. First, we identify 29 tentative systems, for which the ringed models exhibit statistically significant improvement over the ringless models. The lightcurves of those systems are individually examined, but we are not able to identify any candidate that indicates evidence for rings. In turn, we find out several mechanisms of false-positives that would produce ring-like signals, and the null detection enables us to place upper limits on the size of rings. Furthermore, assuming the tidal alignment between axes of the planetary rings and orbits, we conclude that the occurrence rate of rings larger than twice the planetary radius is less than 15 percent. Even though the majority of our targets are short-period planets, our null detection provides statistical and quantitative constraints on largely uncertain theoretical models of origin, formation, and evolution of planetary rings.

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arXiv2017

First Data Release of the Hyper Suprime-Cam Subaru Strategic Program

The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most outstanding questions in astronomy today, including the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope and it started in March 2014. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 years of observations (61.5 nights) and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i~26.4, ~26.5, and ~27.0 mag, respectively (5sigma for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0.6 arcsec in the i-band in the Wide layer. We show that we achieve 1-2 per cent PSF photometry (rms) both internally and externally (against Pan-STARRS1), and ~10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp/.

astro-ph.IM↗

arXiv2017

Towards Detection of Exoplanetary Rings Via Transit Photometry: Methodology and a Possible Candidate

Detection of a planetary ring of exoplanets remains as one of the most attractive but challenging goals in the field. We present a methodology of a systematic search for exoplanetary rings via transit photometry of long-period planets. The methodology relies on a precise integration scheme we develop to compute a transit light curve of a ringed planet. We apply the methodology to 89 long-period planet candidates from the Kepler data so as to estimate, and/or set upper limits on, the parameters of possible rings. While a majority of our samples do not have a sufficiently good signal-to-noise ratio for meaningful constraints on ring parameters, we find that six systems with a higher signal-to-noise ratio are inconsistent with the presence of a ring larger than 1.5 times the planetary radius assuming a grazing orbit and a tilted ring. Furthermore, we identify five preliminary candidate systems whose light curves exhibit ring-like features. After removing four false positives due to the contamination from nearby stars, we identify KIC 10403228 as a reasonable candidate for a ringed planet. A systematic parameter fit of its light curve with a ringed planet model indicates two possible solutions corresponding to a Saturn-like planet with a tilted ring. There also remain other two possible scenarios accounting for the data; a circumstellar disk and a hierarchical triple. Due to large uncertain factors, we cannot choose one specific model among the three.

astro-ph.EP↗

arXiv2016

Possible Outcomes of Coplanar High-eccentricity Migration: Hot Jupiters, Close-in Super-Earths, and Counter-orbiting Planets

We investigate the formation of close-in planets in near-coplanar eccentric hierarchical triple systems via the secular interaction between an inner planet and an outer perturber (Coplanar High-eccentricity Migration, CHEM). We generalize the previous work on the analytical condition for successful CHEM for point masses interacting only through gravity by taking into account the finite mass effect of the inner planet. We find that efficient CHEM requires that the systems should have m_1<<m_0 and m_1<<m_2. In addition to the gravity for point masses, we examine the importance of the short-range forces, and provide an analytical estimate of the migration time scale. We perform a series of numerical simulations in CHEM for systems consisting of a sun-like central star, giant gas inner planet and planetary outer perturber, including the short-range forces and stellar and planetary dissipative tides. We find that most of such systems end up with a tidal disruption, a small fraction of the systems produce prograde hot Jupiters (HJs), but no retrograde one. In addition, we extend CHEM to super-Earth mass range, and show that the formation of close-in super-Earths in prograde orbits is also possible. Finally, we carry out CHEM simulation for the observed hierarchical triple and counter-orbiting HJ systems. We find that CHEM can explain a part of the former systems, but it is generally very difficult to reproduce counter-orbiting HJ systems.

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