Abstract
Giant planets around young stars serve as a clue to unveiling their formation history and orbital evolution. CI Tau is a 2 Myr-old classical T Tauri star hosting an eccentric hot Jupiter, CI ...Tau b. The standard formation scenario of a hot Jupiter predicts that planets formed further out and migrated inward. A high eccentricity of CI Tau b may be suggestive of high-
e
migration due to secular gravitational perturbations by an outer companion. Also, the Atacama Large Millimeter/submillimeter Array 1.3 mm-continuum observations show that CI Tau has at least three annular gaps in which unseen planets may exist. We present high-contrast imaging around CI Tau taken from the Keck/NIRC2
L
′
-band filter and vortex coronagraph that allows us to search for an outer companion. We did not detect any outer companion around CI Tau from angular differential imaging (ADI) using two deep imaging data sets. The detection limits from ADI-reduced images rule out the existence of an outer companion beyond ∼30 au that can cause the Kozai–Lidov migration of CI Tau b. Our results suggest that CI Tau b may have experienced type II migration from ≲2 au in megayears. We also confirm that no planets with ≥2–4
M
Jup
are hidden in two outer gaps.
Abstract
Recent high-sensitivity observations reveal that accreting giant planets embedded in their parental circumstellar disks can emit H
α
at their final formation stages. While the origin of this ...emission is not yet determined, magnetospheric accretion is currently the most plausible hypothesis. In order to test this hypothesis further, we develop a simplified but physics-based model and apply it to our observations taken toward HD 163296 with Subaru/SCExAO+VAMPIRES. We specify under which conditions embedded giant planets can undergo magnetospheric accretion and emit hydrogen lines. We find that when the stellar accretion rates are high, magnetospheric accretion becomes energetic enough to self-regulate the resulting emission. On the other hand, when massive planets are embedded in disks with low accretion rates, earlier formation histories determine whether magnetospheric accretion occurs. We explore two different origins for the hydrogen emission lines (magnetospheric accretion flow heated by accretion-related processes versus planetary surfaces via accretion shock). The corresponding relationships between the accretion and line luminosities dictate that the emission from accretion flow achieves higher line flux than that from accretion shock, and the flux decreases with increasing wavelengths (i.e., from H
α
to Pa
β
and up to Br
γ
). Our observations do not detect any point-like source emitting H
α
, and they are used to derive the 5
σ
detection limit. The observations are therefore not sensitive enough, and a reliable examination of our model becomes possible when the observational sensitivity is improved by a factor of 10 or more. Multi-band observations increase the possibility of efficiently detecting embedded giant planets and carefully determining the origin of the hydrogen emission lines.
We report the detection of an excess in dust continuum emission at 233 GHz (1.3 mm in wavelength) in the protoplanetary disk (PPD) around TW Hya revealed through high-sensitivity observations at ∼3 ...au resolution with the Atacama Large Millimeter/submillimeter Array. The sensitivity of the 233 GHz image has been improved by a factor of 3 with regard to that of our previous cycle 3 observations. The overall structure is mostly axisymmetric, and there are apparent gaps at 25 and 41 au as previously reported. The most remarkable new finding is a few astronomical-unit-scale excess emission in the southwest part of the PPD. The excess emission is located at 52 au from the disk center and is 1.5 times brighter than the surrounding PPD at a significance of 12 . We performed a visibility fitting to the extracted emission after subtracting the axisymmetric PPD emission and found that the inferred size and the total flux density of the excess emission are 4.4 × 1.0 au and 250 Jy, respectively. The dust mass of the excess emission corresponds to 0.03 M⊕ if a dust temperature of 18 K is assumed. Because the excess emission can also be marginally identified in the Band 7 image at almost the same position, the feature is unlikely to be a background source. The excess emission can be explained by a dust clump accumulated in a small elongated vortex or a massive circumplanetary disk around a Neptune-mass-forming planet.
Direct imaging of gas giant exoplanets provides information on their atmospheres and the architectures of planetary systems. However, few planets have been detected in blind surveys with direct ...imaging. Using astrometry from the Gaia and Hipparcos spacecraft, we identified dynamical evidence for a gas giant planet around the nearby star HIP 99770. We confirmed the detection of this planet with direct imaging using the Subaru Coronagraphic Extreme Adaptive Optics instrument. The planet, HIP 99770 b, orbits 17 astronomical units from its host star, receiving an amount of light similar to that reaching Jupiter. Its dynamical mass is 13.9 to 16.1 Jupiter masses. The planet-to-star mass ratio (7 to 8) × 10
is similar to that of other directly imaged planets. The planet's atmospheric spectrum indicates an older, less cloudy analog of the previously imaged exoplanets around HR 8799.
Abstract
We present Keck/NIRC2
K
p
L
p
high-contrast imaging observations of a J0337 protoplanetary disk. The data discover the spatially-resolved large cavity, which is the second report among ...protoplanetary disks in the Perseus star-forming region after the LkH
α
330 system. Our data and forward modeling using RADMC-3D suggests ∼80 au for the cavity radius. There is discrepancy between J0337's spectral energy distribution (SED) and the modeled SED at ∼10
μ
m and this suggests an unseen inner disk. We also searched for companions around J0337 but did not detect any companion candidates at separations between 0.″1 and 2.″5. The
L
p
-band detection limit corresponds to ∼20
M
Jup
at 60 au, ∼9–10
M
Jup
at 90 au, and ∼3
M
Jup
at >120 au. Compared with other young systems with large cavities such as PDS 70 and RX J1604, multiple Jovian planets, a single eccentric Jovian planet, or a massive brown dwarf at an inner separation could exist within the cavity.
We present the direct imaging discovery of a substellar companion to the nearby Sun-like star, HD 33632 Aa, at a projected separation of ∼20 au, obtained with SCExAO/CHARIS integral field ...spectroscopy complemented by Keck/NIRC2 thermal infrared imaging. The companion, HD 33632 Ab, induces a 10.5σ astrometric acceleration on the star as detected with the Gaia and Hipparcos satellites. SCExAO/CHARIS JHK (1.1–2.4 μm) spectra and Keck/NIRC2 L(sub p) (3.78 μm) photometry are best matched by a field L/T transition object: an older, higher-gravity, and less dusty counterpart to HR 8799 cde. Combining our astrometry with Gaia/Hipparcos data and archival Lick Observatory radial velocities, we measure a dynamical mass of 46.4 ± 8 MJ and an eccentricity of e < 0.46 at 95% confidence. HD 33632 Ab’s mass and mass ratio (4.0% ± 0.7%) are comparable to the low-mass brown dwarf GJ 758 B and intermediate between the more massive brown dwarf HD 19467 B and the (near-)planet-mass companions to HR 2562 and GJ 504. Using Gaia to select for direct imaging observations with the newest extreme adaptive optics systems can reveal substellar or even planet-mass companions on solar system–like scales at an increased frequency compared to blind surveys
We present new, near-infrared (1.1-2.4 m) high-contrast imaging of the debris disk around HD 15115 with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with the Coronagraphic ...High Angular Resolution Imaging Spectrograph (CHARIS). The SCExAO/CHARIS resolves the disk down to ∼ 0 2 (rproj ∼ 10 au), a factor of ∼3-5 smaller than previous recent studies. We derive a disk position angle of PA ∼ 279 4-280 5 and an inclination of i ∼ 85 3-86.2 . While recent SPHERE/IRDIS imagery of the system could suggest a significantly misaligned two-ring disk geometry, CHARIS imagery does not reveal conclusive evidence for this hypothesis. Moreover, optimizing models of both one- and two-ring geometries using differential evolution, we find that a single ring having a Hong-like scattering phase function matches the data equally well within the CHARIS field of view ( 1″). The disk's asymmetry, well evidenced at larger separations, is also recovered; the west side of the disk appears, on average, around 0.4 mag brighter across the CHARIS bandpass between 0 25 and 1″. Comparing Space Telescope Imaging Spectrograph (STIS) 50CCD optical photometry (2000-10500 ) with CHARIS near-infrared photometry, we find a red (STIS/50CCD−CHARIS broadband) color for both sides of the disk throughout the 0 4-1″ region of overlap, in contrast to the blue color reported at similar wavelengths for regions exterior to ∼2″. Further, this color may suggest a smaller minimum grain size than previously estimated at larger separations. Finally, we provide constraints on planetary companions and discuss possible mechanisms for the observed inner disk flux asymmetry and color.
We present Subaru/SCExAO+Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) broadband (JHK-band) integral field spectroscopy of HD 34700 A. CHARIS data recover HD 34700 A's disk ring ...and confirm multiple spirals discovered by Monnier et al. We set limits on substellar companions of ∼12 MJup at 0 3 (in the ring gap) and ∼5 MJup at 0 75 (outside the ring). The data reveal darkening effects on the ring and spiral, although we do not identify the origin of each feature such as shadows or physical features related to the outer spirals. Geometric albedos converted from the surface brightness suggest a greater scale height and/or prominently abundant submicron dust at position angles between ∼45° and 90°. Spiral fitting resulted in very large pitch angles (∼30°-50°); a stellar flyby of HD 34700 B or infall from a possible envelope is perhaps a reasonable scenario to explain the large pitch angles.
We present high-contrast observations of 68 young stellar objects (YSOs) that have been explored as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey on the Subaru ...telescope. Our targets are very young (<10 Myr) stars, which often harbor protoplanetary disks where planets may be forming. We achieve a typical contrast of ∼10−4-10−5.5 at an angular distance of 1″ from the central star, corresponding to typical mass sensitivities (assuming hot-start evolutionary models) of ∼10 MJ at 70 au and ∼6 MJ at 140 au. We detected a new stellar companion to HIP 79462 and confirmed the substellar objects GQ Lup b and ROXs 42B b. An additional six companion candidates await follow-up observations to check for common proper motion. Our SEEDS YSO observations probe the population of planets and brown dwarfs at the very youngest ages; these may be compared to the results of surveys targeting somewhat older stars. Our sample and the associated observational results will help enable detailed statistical analyses of giant planet formation.
Abstract
We present a high-resolution (2.5 au) multiband analysis of the protoplanetary disk around TW Hya using Atacama Large Millimeter/submillimeter Array (ALMA) long baseline data at Bands 3, 4, ...6, and 7. We aim to reconstruct a high-sensitivity millimeter continuum image and revisit the spectral index distribution. The imaging is performed by combining new ALMA data at Bands 4 and 6 with available archive data. Two methods are employed to reconstruct the images: multifrequency synthesis (MFS) and the fiducial image-oriented method, where each band is imaged separately and the frequency dependence is fitted pixel by pixel. We find that MFS imaging with a second-order Taylor expansion can reproduce the frequency dependence of the continuum emission between Bands 3 and 7 in a manner consistent with previous studies, and that it is a reasonable method for reconstructing the spectral index map. The image-oriented method provides a spectral index map consistent with the MFS imaging, but with a two times lower resolution. Mock observations of an intensity model were conducted to validate the images from the two methods. We find that the MFS imaging provides a high-resolution spectral index distribution with an uncertainty of <10%. Using the submillimeter spectrum reproduced from our MFS images, we directly calculate the optical depth, power-law index of the dust opacity coefficient (
β
), and dust temperature. The derived parameters are consistent with previous works, and the enhancement of
β
within the intensity gaps is also confirmed, supporting a deficit of millimeter-sized grains within the gaps.
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