VLA cm-wave survey of young stellar objects in the Oph A cluster: constraining extreme UV- and X-ray-driven disk photoevaporation

A pathfinder for Square Kilometre Array studies^★

¹ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
e-mail: audrey.coutens@u-bordeaux.fr
² European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
³ School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK
⁴ SKA Organisation, Jodrell Bank Observatory, Lower Withington, Macclesfield, Cheshire SK11 9DL, UK
⁵ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁶ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁷ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58089, México
⁸ Instituto de Astronomía, Universidad Nacional Autónoma de Mexico, Apartado Postal 70-264, Ciudad de México 04510, México
⁹ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Florence, Italy
¹⁰ Department of Astronomy, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
¹¹ Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland
¹² Max-Planck-Institüt für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
¹³ Observatorio Astronómico Nacional (OAG-IGN), Alfonso XII 3, 28014 Madrid, Spain
¹⁴ Université Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 38401 Grenoble, France
¹⁵ NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Rd, Victoria, BC, V9E 2E7, Canada
¹⁶ Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 5C2, Canada
¹⁷ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁸ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁹ Lund Observatory, Lund University, Box 43, 22100 Lund, Sweden
²⁰ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
²¹ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
²² Ural Federal University, 620002, 19 Mira street, Yekaterinburg, Russia
²³ Department of Physics and Astronomy, University College London, Gower St., London WC1E 6BT, UK
²⁴ Department of Chemistry, Ludwig Maximilian University, Butenandtstr. 5–13, 81377 München, Germany
²⁵ Max Planck Institute for Astronomy, Königstuhl 17, 69117, Heidelberg, Germany
²⁶ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA, Cambridge, UK
²⁷ NRAO, 520 Edgemont Road Charlottesville, VA 22903-2475 USA
²⁸ ASTRON Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
²⁹ Joint Institute for VLBI ERIC (JIVE), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
³⁰ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
³¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02 138, USA

Received: 22 February 2019
Accepted: 4 September 2019

Abstract

Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity that are intimately connected to the evolution of protoplanetary disks and the formation of planets. We carried out sensitive continuum observations toward the Ophiuchus A star-forming region, using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6′ and with a spatial resolution of θ_maj ×θ_min ~ 0.′′4 × 0.′′2. We achieved a 5 μJy beam⁻¹ rms noise level at the center of our mosaic field of view. Among the 18 sources we detected, 16 were YSOs (three Class 0, five Class I, six Class II, and two Class III) and two were extragalactic candidates. We find that thermal dust emission generally contributed less than 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission, such as gyro-synchrotron radiation from active magnetospheres, free–free emission from thermal jets, free–free emission from the outflowing photoevaporated disk material, and synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections for Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve over time. The sensitivity of our data cannot exclude photoevaporation due to the role of X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys using the Square Kilometre Array (SKA) will have the capacity to provide significant constraints to disk photoevaporation.