Inner disc and circumplanetary material in the PDS 70 system: Insights from multi-epoch, multi-frequency ALMA observations

¹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France
² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁴ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, Milano, Italy
⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Department of Astronomical Science, The Graduate University for Advanced Studies, SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁷ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
⁸ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁹ Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
¹⁰ Department of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, TX 77005, USA
¹¹ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

^★ Corresponding author: daniele.fasano@oca.eu

Received: 1 April 2025
Accepted: 4 June 2025

Abstract

Context. The two giant protoplanets directly detected in the dust-depleted cavity of PDS 70 offer a unique opportunity to study the processes of ongoing planet formation. The planets have been detected both in IR thermal light and in the Hα line, indicating that they are actively accreting material from their surroundings.

Aims. We calibrated and analysed archival Atacama Large Millimeter/subMillimeter Array (ALMA) band 6 and 7 observations of PDS 70 to detect circumplanetary material in independent datasets taken at different epochs in 2019, 2021, and 2023 and assess its possible motion.

Methods. We performed 2D visibility modelling of the high-resolution ALMA band 6 (∼0.11^′′ × 0.08^′′) and band 7 (∼0.05^′′ × 0.05^′′) dust continuum emission of the outer disc. After subtracting the model from the data, we imaged the dust continuum emission in the cavity of PDS 70 at multiple epochs.

Results. We re-detect the compact dust emission around PDS 70 c in all our datasets in band 6 and 7, with a more than 3.8σ significance, and tentatively detect compact emission around PDS 70 b at ∼3σ in the band 6 datasets, with a peak emission of 59 ± 17 μJy/beam and 46 ± 14 μJy/beam. We find the astrometric relative position of the compact emission around PDS 70 c to be consistent with the expected position of the planet in the 2019–2023 time range. We measure a peak flux difference of up to 64 ± 34 μJy/beam at a 1σ confidence level for the continuum emission coming from the region around PDS 70 c and perform a Bayesian test on our measurements, finding that they are not consistent with significant variable emission. We find no evidence of flux variability in the inner disc. We measure the dust mass of the material co-located with PDS 70 c and the inner disc to be in the range of 0.008−0.063 M_⊕ and 0.04−0.31 M_⊕, respectively, consistent with previous measurements. Additionally, we obtain band 6–7 spectral indices of 2.5 ± 1.2 and 3.2 ± 0.5 for the dust emission around PDS 70 c and in the inner disc, respectively, suggesting the inner disc emission is dominated by optically thin dust.