The β Pictoris b Hill sphere transit campaign

I. Photometric limits to dust and rings^★

¹ Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
e-mail: kenworthy@strw.leidenuniv.nl
² Department of Physics & Astronomy, University of Rochester, Rochester, NY 14627, USA
³ Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93106, USA
⁴ NOVA Optical IR Instrumentation Group at ASTRON, PO Box 2, 7990AA Dwingeloo, The Netherlands
⁵ Institut de Recherche sur les Exoplanètes, Département de Physique, Université de Montréal, Montréal, QC H3C 3J7, Canada
⁶ South African Astronomical Observatory, Observatory Rd, Observatory Cape Town, 7700 Cape Town, South Africa
⁷ NASA Headquarters, 300 E Street SW, Washington, DC 20546, USA
⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, M/S321-100, Pasadena, CA 91109, USA
⁹ DOTA, ONERA, Université Paris Saclay, 92322 Châtillon, France
¹⁰ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹¹ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
¹² Department of Astronomy, University of Cape Town, Rondebosch, 7700 Cape Town, South Africa
¹³ Astrofica Technologies Pty Ltd, 2 Francis Road, Zonnebloem, Woodstock, Cape town, 7925, South Africa
¹⁴ Southern African Large Telescope, Observatory Rd, Observatory Cape Town, 7700 Cape Town, South Africa
¹⁵ Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria
¹⁶ Institut für Kommunikationsnetze und Satellitenkommunikation, Technical University Graz, Inffeldgasse 12, 8010 Graz, Austria
¹⁷ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
¹⁸ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
²⁰ Concordia Station, IPEV/PNRA, Dome C, Antarctica
²¹ Department of Mathematics, Computer Science and Physics, University of Udine, Italy
²² European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
²³ Astronomy Department, University of California, Berkeley, CA 94720, USA
²⁴ SETI Institute, Carl Sagan Center, 189 Bernardo Ave., Mountain View, CA 94043, USA
²⁵ Institute of Astrophysics, FORTH, 71110 Heraklion, Greece
²⁶ Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
²⁷ Space Telescope Science Institute, Baltimore, MD 21218, USA
²⁸ JHU Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, MD 20723, USA
²⁹ Astrophysics Research Centre, Queen’s University Belfast, Belfast BT7 1NN, UK
³⁰ School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, Glasnevin, Dublin 9, Ireland
³¹ IPAG, Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³² LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
³³ IMCCE – Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris, France
³⁴ Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
³⁵ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
³⁶ Shanghai Observatory, Chinese Academy of Sciences, PR China
³⁷ Purple Mountain Observatory, Chinese Academy of Science, Nanjing 210008, PR China

Received: 4 December 2020
Accepted: 8 February 2021

Abstract

Aims. Photometric monitoring of β Pic in 1981 showed anomalous fluctuations of up to 4% over several days, consistent with foreground material transiting the stellar disk. The subsequent discovery of the gas giant planet β Pic b and the predicted transit of its Hill sphere to within a 0.1 au projected separation of the planet provided an opportunity to search for the transit of a circumplanetary disk (CPD) in this 21 ± 4 Myr-old planetary system. We aim to detect, or put an upper limit on, the density and nature of the material in the circumplanetary environment of the planet via the continuous photometric monitoring of the Hill sphere transit that occurred in 2017 and 2018.

Methods. Continuous broadband photometric monitoring of β Pic requires ground-based observatories at multiple longitudes to provide redundancy and to provide triggers for rapid spectroscopic follow-up. These include the dedicated β Pic monitoring bRing observatories in Sutherland and Siding Springs, the ASTEP400 telescope at Concordia, and the space observatories BRITE and the Hubble Space Telescope (HST). We search the combined light curves for evidence of short-period transient events caused by rings as well as for longer-term photometric variability due to diffuse circumplanetary material.

Results. We find no photometric event that matches with the event seen in November 1981, and there is no systematic photometric dimming of the star as a function of the Hill sphere radius.

Conclusions. We conclude that the 1981 event was not caused by the transit of a CPD around β Pic b. The upper limit on the long-term variability of β Pic places an upper limit of 1.8 × 10²² g of dust within the Hill sphere (comparable to the ~100 km radius asteroid 16 Psyche). Circumplanetary material is either condensed into a disk that does not transit β Pic, condensed into a disk with moons that has an obliquity that does not intersect with the path of β Pic behind the Hill sphere, or is below our detection threshold. This is the first time that a dedicated international campaign has mapped the Hill sphere transit of an extrasolar gas giant planet at 10 au.