Highly structured disk around the planet host PDS 70 revealed by high-angular resolution observations with ALMA

Abstract

Context. Imaged in the gap of a transition disk and found at a separation of about 195 mas (∼22 au) from its host star at a position angle of about 155 o , PDS 70 b is the most robustly detected young planet to date. This system is therefore a unique laboratory for characterizing the properties of young planetary systems at the stage of their formation. Aims. We aim to trace direct and indirect imprints of PDS 70 b on the gas and dust emission of the circumstellar disk in order to study the properties of this ∼5 Myr young planetary system. Methods. We obtained ALMA band 7 observations of PDS 70 in dust continuum and 12 CO (3 − 2) and combined them with archival data. This resulted in an unprecedented angular resolution of about 70 mas (∼8 au). Results. We derive an upper limit on circumplanetary material at the location of PDS 70 b of ∼0.01 M ⊕ and find a highly structured circumstellar disk in both dust and gas. The outer dust ring peaks at 0.65 (74 au) and reveals a possible second unresolved peak at about 0.53 (60 au). The integrated intensity of CO also shows evidence of a depletion of emission at ∼0.2 (23 au) with a width of ∼0.1 (11 au). The gas kinematics show evidence of a deviation from Keplerian rotation inside 0.8 (91 au). This implies a pressure gradient that can account for the location of the dust ring well beyond the location of PDS 70 b. Farther in, we detect an inner disk that appears to be connected to the outer disk by a possible bridge feature in the northwest region in both gas and dust. We compare the observations to hydrodynamical simulations that include a planet with different masses that cover the estimated mass range that was previously derived from near-infrared photometry (∼5-9 M Jup ). We find that even a planet with a mass of 10 M Jup may not be sufficient to explain the extent of the wide gap, and an additional low-mass companion may be needed to account for the observed disk morphology.

Accretion Properties of PDS 70b with MUSE*

“…Here, we estimate the contribution of the unseen dust to the extinction. Keppler et al (2019) conducted hydrodynamic simulations to reproduce the observed 12 CO (2-1) integrated intensity map and found that the azimuthally averaged gas surface density at the location of PDS 70b is ∼0.01 g cm −2 , which can be translated to a molecular hydrogen surface density of ∼3 × 10 21 cm −2 . By using the relationship between the interstellar dust extinction and the hydrogen column density (N H /A V = 1.9 × 10 21 cm −2 mag −1 ; Bohlin et al 1978), we derived A V ∼ 3.3 mag, which corresponds to A Hα ∼ 2.4 mag with A λ ∝ λ −1.75 (Draine 1989), where we assume that hydrogen atoms are in the form of hydrogen molecules.…”

“…A good example of robustly detected accreting planets at tens of au from a central star is the PDS 70 planetary system. This system includes a weakly accreting young star (spectral type of K7, mass of 0.8 M ⊙ , accretion rate of 6 × 10 −11 M ⊙ yr −1 , age of 5 Myr, distance of 113 pc; Pecaut & Mamajek 2016;Keppler et al 2019;Haffert et al 2019;Müller et al 2018;Gaia Collaboration et al 2018) associated with two planetary-mass companions (Haffert et al 2019;Isella et al 2019;Christiaens et al 2019a,b;Keppler et al 2018;Müller et al 2018;Wagner et al 2018). Aoyama & Ikoma (2019) estimated that PDS 70b's mass and mass accretion rate are ∼12 M Jup and ∼4 × 10 −8 M Jup yr −1 , respectively, while the values for PDS 70c are ∼10 M Jup and ∼1 × 10 −8 M Jup yr −1 .…”

A Multifrequency ALMA Characterization of Substructures in the GM Aur Protoplanetary Disk

“…The posterior medians are listed in Table 5, with error bars calculated from the 16th and 84th percentiles. As noted in Keppler et al (2019), the nominal error bars should be regarded with caution because there may also be systematic uncertainties associated with image-plane fitting and differences between the assumed model structure and true emission behavior.…”

Variable Accretion onto Protoplanet Host Star PDS 70

“…In this case, we may need to invoke an inner disk mass reservoir (e.g., dead zone) that can feed the star for a prolonged period of time with a low efficiency (Hartmann & Bae 2018). The presence of compact sub-millimeter continuum emission shown in ALMA observations (Long et al 2018;Keppler et al 2019) may support this inner reservoir scenario. Manara et al (2019) used the planet population synthesis models of Mordasini et al (2009Mordasini et al ( , 2012 to make predictions for stellar mass accretion rates and disk masses and compare them with observations of the Lupus and Chamaeleon star-forming regions.…”