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Register a new userAccretion Properties of PDS 70b with MUSE
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We report a new evaluation of the accretion properties of PDS~70b obtained with VLT/MUSE. The main difference from previous studies in Haffert et al. (2019) and Aoyama & Ikoma (2019) is in the mass accretion rate. Simultaneous multiple line observations, such as H$alpha$ and H$beta$, can better constrain the physical properties of an accreting planet. While we clearly detected H$alpha$ emissions from PDS~70b, no H$beta$ emissions were detected. We estimate the line flux of H$beta$ with a 3-$sigma$ upper limit to be 2.3~$times$~10$^{-16}$~erg~s$^{-1}$~cm$^{-2}$. The flux ratio $F_{rm Hbeta}$/$F_{rm Halpha}$ for PDS~70b is $<$~0.28. Numerical investigations by Aoyama et al. (2018) suggest that $F_{rm Hbeta}$/$F_{rm Halpha}$ should be close to unity if the extinction is negligible. We attribute the reduction of the flux ratio to the extinction, and estimate the extinction of H$alpha$ ($A_{rm Halpha}$) for PDS~70b to be $>$~2.0~mag using the interstellar extinction value. %The expected $A_{rm Halpha}$ value in the gap of the protoplanetary disk at the PDS~70b location is 2.4~mag, which is consistent with the estimated extinction. By combining with the H$alpha$ linewidth and the dereddening line luminosity of H$alpha$, %we derive the PDS~70b dynamical mass and mass accretion rate to be hashimotor{12~$pm$~3~$M_{rm Jup}$} and $gtrsim$~5~$times$~10$^{-7}$~$M_{rm Jup}$~yr$^{-1}$, respectively. we derive the PDS~70b mass accretion rate to be $gtrsim$~5~$times$~10$^{-7}$~$M_{rm Jup}$~yr$^{-1}$. The PDS~70b mass accretion rate is an order of magnitude larger than that of PDS~70. We found that the filling factor $f_{rm f}$ (the fractional area of the planetary surface emitting H$alpha$) is $gtrsim$0.01, which is similar to the typical stellar value. The small value of $f_{rm f}$ indicates that the H$alpha$ emitting areas are localized at the surface of PDS~70b.
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We present a high-contrast imaging search for Pa$beta$ line emission from protoplanets in the PDS~70 system with Keck/OSIRIS integral field spectroscopy. We applied the high-resolution spectral differential imaging technique to the OSIRIS $J$-band data but did not detect the Pa$beta$ line at the level predicted using the parameters of cite{Hashimoto2020}. This lack of Pa$beta$ emission suggests the MUSE-based study may have overestimated the line width of H$alpha$. We compared our Pa$beta$ detection limits with the previous H$alpha$ flux and H$beta$ limits and estimated $A_{rm V}$ to be $sim0.9$ and 2.0 for PDS~70~b and c respectively. In particular, PDS~70~bs $A_{rm V}$ is much smaller than implied by high-contrast near-infrared studies, which suggests the infrared-continuum photosphere and the hydrogen-emitting regions exist at different heights above the forming planet.
Advances in high-resolution imaging have revealed H$alpha$ emission separated from the host star. It is generally believed that the emission is associated with forming planets in protoplanetary disks. However, the nature of this emission is still not fully understood. Here we report a modeling effort of H$alpha$ emission from the planets around the young star PDS 70. Using standard magnetospheric accretion models previously applied to accreting young stars, we find that the observed line fluxes can be reproduced using a range of parameters relevant to PDS 70b and c, with the mean mass accretion rate of log(${rm dot{M}}$) = $-8.0pm0.6$ M$_{rm Jup}$ yr$^{-1}$ and $-8.1pm0.6$ M$_{rm Jup}$ yr$^{-1}$ for PDS 70b and PDS 70c, respectively. Our results suggest that H$alpha$ emission from young planets can originate in the magnetospheric accretion of mass from the circumplanetary disk. We find that empirical relationships between mass accretion rate and H$alpha$ line properties frequently used in T Tauri stars are not applicable in the planetary mass regime. In particular, the correlations between line flux and mass accretion rate underpredict the accretion rate by about an order of magnitude, and the width at the 10% height of the line is insensitive to the accretion rate at ${rm dot{M}}$ $< 10^{-8}$ M$_{rm Jup}$ yr$^{-1}$.
We present K-band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained K-band spectra and 100 $mu$as precision astrometry of both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of $0.17 pm 0.06$, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of PDS 70 b of 10 $M_textrm{Jup}$, while the mass of PDS 70 c was unconstrained. The GRAVITY K-band spectra rules out pure blackbody models for the photospheres of both planets. Instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. Any circumplanetary dust around these planets is not well constrained by the planets 1-5 $mu$m spectral energy distributions (SEDs) and requires longer wavelength data to probe with SED analysis. However with VLTI/GRAVITY, we made the first observations of a circumplanetary environment with sub-au spatial resolution, placing an upper limit of 0.3~au on the size of a bright disk around PDS 70 b.
As host to two accreting planets, PDS 70 provides a unique opportunity to probe the chemical complexity of atmosphere-forming material. We present ALMA Band 6 observations of the PDS~70 disk and report the first chemical inventory of the system. With a spatial resolution of 0.4-0.5 ($sim$50 au), 12 species are detected, including CO isotopologues and formaldehyde, small hydrocarbons, HCN and HCO+ isotopologues, and S-bearing molecules. SO and CH3OH are not detected. All lines show a large cavity at the center of the disk, indicative of the deep gap carved by the massive planets. The radial profiles of the line emission are compared to the (sub-)mm continuum and infrared scattered light intensity profiles. Different molecular transitions peak at different radii, revealing the complex interplay between density, temperature and chemistry in setting molecular abundances. Column densities and optical depth profiles are derived for all detected molecules, and upper limits obtained for the non detections. Excitation temperature is obtained for H2CO. Deuteration and nitrogen fractionation profiles from the hydro-cyanide lines show radially increasing fractionation levels. Comparison of the disk chemical inventory to grids of chemical models from the literature strongly suggests a disk molecular layer hosting a carbon to oxygen ratio C/O>1, thus providing for the first time compelling evidence of planets actively accreting high C/O ratio gas at present time.
The recent high spatial/spectral resolution observations have enabled constraining formation mechanisms of giant planets, especially at the final stages. The current interpretation of such observations is that these planets undergo magnetospheric accretion, suggesting the importance of planetary magnetic fields. We explore the properties of accreting, magnetized giant planets surrounded by their circumplanetary disks, using the physical parameters inferred for PDS 70 b/c. We compute the magnetic field strength and the resulting spin rate of giant planets, and find that these planets may possess dipole magnetic fields of either a few 10 G or a few 100 G; the former is the natural outcome of planetary growth and radius evolution, while the resulting spin rate cannot reproduce the observations. For the latter, a consistent picture can be drawn, where strong magnetic fields induced by hot planetary interiors lead both to magnetospheric accretion and to spin-down due to disk locking. We also compute the properties of circumplanetary disks in the vicinity of these planets, taking into account planetary magnetic fields. The resulting surface density becomes very low, compared with the canonical models, implying the importance of radial movement of satellite-forming materials. Our model predicts a positive gradient of the surface density, which invokes the traps for both satellite migration and radially drifting dust particles. This work thus concludes that the final formation stages of giant planets are similar to those of low-mass stars such as brown dwarfs, as suggested by recent studies.
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