No abstract

Two studies utilizing sparse aperture-masking (SAM) interferometry and H α differential imaging have reported multiple jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly formed planets ("protoplanets"). We present new near-infrared direct imaging/spectroscopy from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with the Coronagraphic High 2 Angular Resolution Imaging Spectrograph (CHARIS) integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets, and thus offer the first decisive test of their existence.The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed H α detection of LkCa 15 b.We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen jovian companion. To identify jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling.

Direct images of protoplanets embedded in disks around infant stars provide the key to understanding the formation of gas giant planets like Jupiter. Using the Subaru Telescope and Hubble Space Telescope, we find evidence for a jovian protoplanet around AB Aurigae orbiting at a wide projected separation (~93 au), likely responsible for multiple planet-induced features in the disk. Its emission is reproducible as reprocessed radiation from an embedded protoplanet. We also identify two structures located at 430-580 au that are candidate sites of planet formation. These data reveal planet formation in the embedded phase and a protoplanet discovery at wide, > 50 au separations characteristic of most imaged exoplanets. With at least one clump-like protoplanet and multiple spiral arms, the AB Aur system may also provide the evidence for a long-considered alternative to the canonical model for Jupiter's formation: disk (gravitational) instability.

We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a <20 M Jup widely separated (∼8″, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color–magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256 b with JWST's NIRSpec IFU and MIRI MRS modes for coverage from 1 to 20 μm at resolutions of ∼1000–3700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the JWST spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.

Based on two decades of radial velocity (RV) observations using Keck/HIRES and McDonald/Tull, and more recent observations using the Automated Planet Finder, we found that the nearby star HR 5183 (HD 120066) hosts a 3M J minimum mass planet with an orbital period of 74 +43 −22 years. The orbit is highly eccentric (e 0.84), shuttling the planet from within the orbit of Jupiter to beyond the orbit of Neptune. Our careful survey design enabled high cadence observations before, during, and after the planet's periastron passage, yielding precise orbital parameter constraints. We searched for stellar or planetary companions that could have excited the planet's eccentricity, but found no candidates, potentially implying that the perturber was ejected from the system. We did identify a bound stellar companion more than 15,000 au from the primary, but reasoned that it is currently too widely separated to have an appreciable effect on HR 5183 b. Because HR 5183 b's wide orbit takes it more than 30 au (1") from its star, we also explored the potential of complimentary studies with direct imaging or stellar astrometry. We found that a Gaia detection is very likely, and that imaging at 10 µm is a promising avenue. This discovery highlights the value of long-baseline RV surveys for discovering and characterizing long-period, eccentric Jovian planets. This population may offer important insights into the dynamical evolution of planetary systems containing multiple massive planets.

WISEA J080822.18-644357.3, an M star in the Carina association, exhibits extreme infrared excess and accretion activity at an age greater than the expected accretion disk lifetime. We consider J0808 as the prototypical example of a class of M star accretion disks at ages 20 Myr, which we call "Peter Pan" disks, since they apparently refuse to grow up. We present four new Peter Pan disk candidates identified via the Disk Detective citizen science project, coupled with Gaia astrometry. We find that WISEA J044634.16-262756.1 and WISEA J094900.65-713803.1 both exhibit significant infrared excess after accounting for nearby stars within the 2MASS beams. The J0446 system has > 95% likelihood of Columba membership. The J0949 system shows > 95% likelihood of Carina membership. We present new GMOS optical spectra of all four objects, showing possible accretion signatures on all four stars. We present ground-based and TESS lightcurves of J0808 and 2MASS J0501-4337, including a large flare and aperiodic dipping activity on J0808, and strong periodicity on J0501. We find Paβ and Brγ emission indicating ongoing accretion in near-IR spectroscopy of J0808. Using observed characteristics of these systems, we discuss mechanisms that lead to accretion disks at ages 20 Myr, and find that these objects most plausibly represent long-lived CO-poor primordial disks, or "hybrid" disks, exhibiting both debris-and primordial-disk features. The question remains: why have gas-rich disks persisted so long around these particular stars?

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 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 M J 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. Unified Astronomy Thesaurus concepts: Exoplanets (498); Brown dwarfs (185); Astronomical instrumentation (799); Astronomical optics (88); Direct imaging (387); Coronagraphic imaging (313); Exoplanet detection methods (489); Astronomical techniques (1684)

We present new, near-infrared (1.1-2.4 μm) 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 ρ∼0 2 (r proj ∼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 tworing 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 (ρ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 Å) 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.