Abstract
We present a massive accreting gap planet model that ensures large gaps in transitional disks are kept dust free by the scattering action of three coplanar quasi-circular planets in a 1:2:4 ...mean motion resonance (MMR). This model uses the constraint of the observed gap size, and the dust-free nature of the gap, to determine within ∼10% the possible orbits for three massive planets in an MMR. Calculated orbits are consistent with the observed orbits and H
α
emission (the brightest line to observe these planets) for LkCa 15 b, PDS 70 b, and PDS 70 c within observational errors. Moreover, the model suggests that the scarcity of detected H
α
planets is likely a selection effect of the current limitations of non-coronagraphic, low (<10%) Strehl, H
α
imaging with adaptive optics (AO) systems used in past H
α
surveys. We predict that as higher Strehl AO systems (with high-performance custom coronagraphs; like the 6.5 m Magellan Telescope MagAO-X system) are utilized at H
α
, the number of detected gap planets will substantially increase by more than tenfold. For example, we show that >25 ± 5 new H
α
“gap planets” are potentially discoverable by a survey of the best 19 transitional disks with MagAO-X. Detections of these accreting protoplanets will significantly improve our understanding of planet formation, planet growth and accretion, solar system architectures, and planet–disk interactions.
PDS 70b is a recently discovered and directly imaged exoplanet within the wide ( 40 au) cavity around PDS 70. Ongoing accretion onto the central star suggests that accretion onto PDS 70b may also be ...ongoing. We present the first high-contrast images at H (656 nm) and nearby continuum (643 nm) of PDS 70 utilizing the MagAO system. The combination of these filters allows for the accretion rate of the young planet to be inferred, as hot infalling hydrogen gas will emit strongly at H over the optical continuum. We detected a source in H at the position of PDS 70b on two sequential nights in 2018 May, for which we establish a false positive probability of <0.1%. We conclude that PDS 70b is a young, actively accreting planet. We utilize the H line luminosity to derive a mass accretion rate of MJup yr−1, where the large uncertainty is primarily due to the unknown amount of optical extinction from the circumstellar and circumplanetary disks. PDS 70b represents the second case of an accreting planet interior to a disk gap, and is among the early examples of a planet observed during its formation.
We report the detection of a faint point-like feature possibly related to ongoing planet-formation in the disk of the transition disk star HD 169142. The point-like feature has a Amag(L) ~ 6.4, at a ...separation of ~0".'11 and position angle ~0degrees. Given its lack of an H or KS counterpart despite its relative brightness, this candidate cannot be explained by purely photospheric emission and must be a disk feature heated by an as yet unknown source. Its extremely red colors make it highly unlikely to be a background object, but future multi-wavelength follow up is necessary for confirmation and characterization of this feature.
Abstract
High-contrast imaging has afforded astronomers the opportunity to study light directly emitted by adolescent (tens of megayears) and “proto” (<10 Myr) planets still undergoing formation. ...Direct detection of these planets is enabled by empirical point-spread function (PSF) modeling and removal algorithms. The computational intensity of such algorithms, as well as their multiplicity of tunable input parameters, has led to the prevalence of ad hoc optimization approaches to high-contrast imaging results. In this work, we present a new, systematic approach to optimization vetted using data of the high-contrast stellar companion HD 142527 B from the Magellan Adaptive Optics Giant Accreting Protoplanet Survey (GAPlanetS). More specifically, we present a grid search technique designed to explore three influential parameters of the PSF subtraction algorithm
pyKLIP
: annuli, movement, and KL modes. We consider multiple metrics for postprocessed image quality in order to optimally recover at H
α
(656 nm) synthetic planets injected into contemporaneous continuum (643 nm) images. These metrics include peak (single-pixel) signal-to-noise ratio (S/N), average (multipixel average) S/N, 5
σ
contrast, and false-positive fraction. We apply continuum-optimized KLIP reduction parameters to six H
α
direct detections of the low-mass stellar companion HD 142527 B and recover the companion at a range of separations. Relative to a single-informed, nonoptimized set of KLIP parameters applied to all data sets uniformly, our multimetric grid search optimization led to improvements in companion S/N of up to 1.2
σ
, with an average improvement of 0.6
σ
. Since many direct imaging detections lie close to the canonical 5
σ
threshold, even such modest improvements may result in higher yields in future imaging surveys.
Abstract
Recent discoveries of young exoplanets within their natal disks offer exciting opportunities to study ongoing planet formation. In particular, a planet’s mass accretion rate can be ...constrained by observing the accretion-induced excess emission. So far, planetary accretion is only probed by the H
α
line, which is then converted to a total accretion luminosity using correlations derived for stars. However, the majority of the accretion luminosity is expected to emerge from hydrogen continuum emission, and is best measured in the ultraviolet (UV). In this paper, we present HST/WFC3/UVIS F336W (UV) and F656N (H
α
) high-contrast imaging observations of PDS 70. Applying a suite of novel observational techniques, we detect the planet PDS 70 b with signal-to-noise ratios of 5.3 and 7.8 in the F336W and F656N bands, respectively. This is the first time that an exoplanet has been directly imaged in the UV. Our observed H
α
flux of PDS 70 b is higher by
than the most recent published result. However, the light curve retrieved from our observations does not support greater than 30% variability in the planet’s H
α
emission in six epochs over a five month timescale. We estimate a mass accretion rate of
. H
α
accounts for 36% of the total accretion luminosity. Such a high proportion of energy released in line emission suggests efficient production of H
α
emission in planetary accretion, and motivates using the H
α
band for searches of accreting planets. These results demonstrate HST/WFC3/UVIS’s excellent high-contrast imaging performance and highlight its potential for planet formation studies.
Abstract
We present resolved images of the inner disk component around HD 141569A using the Magellan adaptive optics system with the Clio2 1–5
μ
m camera, offering a glimpse of a complex system ...thought to be in a short evolutionary phase between protoplanetary and debris disk stages. We use a reference star along with the Karhunen–Loéve image projection (KLIP) algorithm for point-spread function subtraction to detect the disk inward to about 0.″24 (∼25 au assuming a distance of 111 pc) at high signal-to-noise ratios at
L
′
(3.8
μ
m),
Ls
(3.3
μ
m), and narrowband
Ice
(3.1
μ
m). We identify an arc or spiral arm structure at the southeast extremity, consistent with previous studies. We implement forward modeling with a simple disk model within the framework of a Markov Chain Monte Carlo sampler to better constrain the geometrical attributes and photometry using our KLIP-reduced disk images. We then leverage these modeling results to facilitate a comparison of the measured brightness in each passband to find a reduction in scattered light from the disk in the
Ice
filter, implying significant absorption due to water ice in the dust. Additionally, our best-fit disk models exhibit peak brightness in the southwestern, back-scattering region of the disk, which we suggest to be possible evidence of 3.3
μ
m polycyclic aromatic hydrocarbon emission. However, we point out the need for additional observations with bluer filters and more complex modeling to confirm these hypotheses.
We report Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum upper limits for five planetary-mass companions DH Tau B, CT Cha B, GSC 6214-210 B, 1RXS 1609 B, and GQ Lup B. Our ...survey, together with other ALMA studies, have yielded null results for disks around young planet-mass companions and placed stringent dust mass upper limits, typically less than 0.1 M⊕, when assuming dust continuum is optically thin. Such low-mass gas/dust content can lead to a disk lifetime estimate (from accretion rates) much shorter than the age of the system. To alleviate this timescale discrepancy, we suggest that disks around wide companions might be very compact and optically thick in order to sustain a few Myr of accretion, yet have very weak (sub)millimeter flux so as to still be elusive to ALMA. Our order-of-magnitude estimate shows that compact optically thick disks might be smaller than 1000 RJup and only emit ∼ Jy of flux in the (sub)millimeter, but their average temperature can be higher than that of circumstellar disks. The high disk temperature could impede satellite formation, but it also suggests that mid- to far-infrared might be more favorable than radio wavelengths to characterize disk properties. Finally, the compact disk size might imply that dynamical encounters between the companion and the star, or any other scatterers in the system, play a role in the formation of planetary-mass companions.
Abstract
Multi-wavelength observations provide a complementary view of the formation of young, directly imaged planet-mass companions. We report the ALMA 1.3 mm and
Magellan
adaptive optics H
α
,
,
, ...and
Y
S
observations of the GQ Lup system, a classical T Tauri star with a
substellar companion at ∼110 au projected separation. We estimate the accretion rates for both components from the observed H
α
fluxes. In our ∼0.″05 resolution ALMA map, we resolve GQ Lup A’s disk in the dust continuum, but no signal is found from the companion. The disk is compact, with a radius of ∼22 au, a dust mass of ∼6
M
⊕
, an inclination angle of ∼56°, and a very flat surface density profile indicative of a radial variation in dust grain sizes. No gaps or inner cavity are found in the disk, so there is unlikely a massive inner companion to scatter GQ Lup B outward. Thus, GQ Lup B might have formed in situ via disk fragmentation or prestellar core collapse. We also show that GQ Lup A’s disk is misaligned with its spin axis, and possibly with GQ Lup B’s orbit. Our analysis on the tidal truncation radius of GQ Lup A’s disk suggests that GQ Lup B’s orbit might have a low eccentricity.
Abstract
We report an Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum detection of the accretion disk around SR 12 c, an ∼11
M
Jup
planetary-mass companion (PMC) orbiting its ...host binary at 980 au. This is the first submillimeter detection of a circumplanetary disk around a wide PMC. The disk has a flux density of 127 ± 14
μ
Jy and is not resolved by the ∼0.″1 beam, so the dust disk radius is likely less than 5 au and can be much smaller if the dust continuum is optically thick. If, however, the dust emission is optically thin, then the SR 12 c disk has a comparable dust mass to the circumplanetary disk around PDS 70 c but is about five times lower than that of the ∼12
M
Jup
free-floating OTS 44. This suggests that disks around bound and unbound planetary-mass objects can span a wide range of masses. The gas mass estimated with an accretion rate of 10
−11
M
☉
yr
−1
implies a gas-to-dust ratio higher than 100. If cloud absorption is not significant, a nondetection of
12
CO(3–2) implies a compact gas disk around SR 12 c. Future sensitive observations may detect more PMC disks at 0.88 mm flux densities of ≲100
μ
Jy.
We present the results of the largest L′ (3.8 m) direct imaging survey for exoplanets to date, the Large Binocular Telescope Interferometer Exozodi Exoplanet Common Hunt (LEECH). We observed 98 stars ...with spectral types from B to M. Cool planets emit a larger share of their flux in L′ compared to shorter wavelengths, affording LEECH an advantage in detecting low-mass, old, and cold-start giant planets. We emphasize proximity over youth in our target selection, probing physical separations smaller than other direct imaging surveys. For FGK stars, LEECH outperforms many previous studies, placing tighter constraints on the hot-start planet occurrence frequency interior to ∼20 au. For less luminous, cold-start planets, LEECH provides the best constraints on giant-planet frequency interior to ∼20 au around FGK stars. Direct imaging survey results depend sensitively on both the choice of evolutionary model (e.g., hot- or cold-start) and assumptions (explicit or implicit) about the shape of the underlying planet distribution, in particular its radial extent. Artificially low limits on the planet occurrence frequency can be derived when the shape of the planet distribution is assumed to extend to very large separations, well beyond typical protoplanetary dust-disk radii ( 50 au), and when hot-start models are used exclusively. We place a conservative upper limit on the planet occurrence frequency using cold-start models and planetary population distributions that do not extend beyond typical protoplanetary dust-disk radii. We find that 90% of FGK systems can host a 7-10 MJup planet from 5 to 50 au. This limit leaves open the possibility that planets in this range are common.
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