VLT/SPHERE exploration of the young multiplanetary system PDS70

Abstract

Context. PDS 70 is a young (5.4 Myr), nearby (∼113 pc) star hosting a known transition disk with a large gap. Recent observations with SPHERE and NACO in the near-infrared (NIR) allowed us to detect a planetary mass companion, PDS 70 b, within the disk cavity. Moreover, observations in H α with MagAO and MUSE revealed emission associated to PDS 70 b and to another new companion candidate, PDS 70 c, at a larger separation from the star. PDS 70 is the only multiple planetary system at its formation stage detected so far through direct imaging. Aims. Our aim is to confirm the discovery of the second planet PDS 70 c using SPHERE at VLT, to further characterize its physical properties, and search for additional point sources in this young planetary system. Methods. We re-analyzed archival SPHERE NIR observations and obtained new data in Y, J, H and K spectral bands for a total of four different epochs. The data were reduced using the data reduction and handling pipeline and the SPHERE data center. We then applied custom routines (e.g. ANDROMEDA and PACO) to subtract the starlight. Results. We re-detect both PDS 70 b and c and confirm that PDS 70 c is gravitationally bound to the star. We estimate this second planet to be less massive than 5 M Jup and with a T eff around 900 K. Also, it has a low gravity with log g between 3.0 and 3.5 dex. In addition, a third object has been identified at short separation (∼0.12 ) from the star and gravitationally bound to the star. Its spectrum is however very blue, so that we are probably seeing stellar light reflected by dust and our analysis seems to demonstrate that it is a feature of the inner disk. We, however, cannot completely exclude the possibility that it is a planetary mass object enshrouded by a dust envelope. In this latter case, its mass should be of the order of few tens of M ⊕ . Moreover, we propose a possible structure for the planetary system based on our data that, however, cannot be stable on a long timescale.

Detectability of embedded protoplanets from hydrodynamical simulations

“…This second source is very close to an extended disc feature, consequently its photometry should be done with caution. In Mesa et al (2019), the planetary nature of this companion has been confirmed, and absolute magnitudes in J-, H-, and K-bands could be inferred for two SPHERE epochs. The spectrum in the J-band is very faint, and indistinguishable from the adjacent disc feature, thus the J-band magnitude should be regarded as upper limit.…”

“…The NaCo Lband map detected emission that is partly covered by the disc, therefore its L-band magnitude should also be taken as an upper limit. Using various atmospheric models, Mesa et al (2019) constrained the mass PDS 70c to be between 1.9 and 4.4 M J .…”

Accretion Properties of PDS 70b with MUSE*

“…The planetary mass is commonly estimated by comparing photometric and spectroscopic observations with planetary evolution and atmospheric models (e.g., Müller et al 2018;Keppler et al 2018;Christiaens et al 2019a;Haffert et al 2019;Mesa et al 2019). On the other hand, our method based on the accretion shock model can estimate a dynamic planetary mass (Aoyama & Ikoma 2019).…”

The paradox of youth for ALMA planet candidates

“…Additionally, albedo of dusty molecular gas is ∼ 0.5 in the optical/NIR wavelengths (Woitke et al 2019), implying that a significant fraction of the stellar luminosity incident onto the protoplanets could be reflected and hence be observable. Emission from several cold clumps of unknown nature with AU-scale sizes at distance of tens of AU from the host star has been recently detected in PDS 70 (Mesa et al 2019), which is one of the objects included in our study. Additionally, if the disruption process is less abrupt than we assumed here then the clumps may be surrounded by emission elongated mainly along their orbits of both gas and dust that could stand out much better than point-like pre-disruption protoplanets.…”