Kaleidoscope of irradiated disks: MUSE observations of proplyds in the Orion Nebula Cluster

I. Sample presentation and ionization front sizes

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
e-mail: mariliis.aru@eso.org
² Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
³ Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
⁴ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁵ Department of Physics, Institute for Computational Cosmology, University of Durham, South Road, Durham DH1 3LE, UK
⁶ Space Telescope Science Institute, 3700 San Martin Dr, Baltimore, MD 21218, USA
⁷ Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁸ Instituto de Astrofísica e Ciências do Espaco, Universidade de Lisboa, OAL, Tapada da Ajuda, 1349-018 Lisboa, Portugal
⁹ Université Cote d’Azur, Observatoire de la Cote d’Azur, CNRS, Laboratoire Lagrange, 06300 Nice, France
¹⁰ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹¹ NASA Headquarters, 300 E Street SW, Washington, DC 20546, USA

Received: 18 December 2023
Accepted: 2 April 2024

Abstract

In the Orion Nebula Cluster (ONC), protoplanetary disks exhibit ionized gas clouds in the form of a striking teardrop shape as massive stars irradiate the disk material. We present the first spatially and spectrally resolved observations of 12 such objects, known as proplyds, using integral field spectroscopy observations performed with the Multi-Unit Spectroscopic Explorer (MUSE) instrument in Narrow Field Mode (NFM) on the Very Large Telescope (VLT). We present the morphology of the proplyds in seven emission lines and measure the radius of the ionization front (I-front) of the targets in four tracers, covering transitions of different ionization states for the same element. We also derive stellar masses for the targets. The measurements follow a consistent trend of increasing I-front radius for a decreasing strength of the far-UV radiation as expected from photoevaporation models. By analyzing the ratios of the I-front radii as measured in the emission lines of Hα, [O I] 6300 A, [O II] 7330 A, and [O III] 5007 A, we observe the ionization stratification, that is, the most ionized part of the flow being the furthest from the disk (and closest to the UV source). The ratios of ionization front radii scale in the same way for all proplyds in our sample regardless of the incident radiation. We show that the stratification can help constrain the densities near the I-front by using a 1D photoionization model. We derive the upper limits of photoevaporative mass-loss rates (Ṁ_loss) by assuming ionization equilibrium, and estimate values in the range 1.07–94.5 × 10⁻⁷ M_⊙ yr⁻¹, with Ṁ_loss values decreasing towards lower impinging radiation. We do not find a correlation between the mass-loss rate and stellar mass. The highest mass-loss rate is for the giant proplyd 244–440. These values of Ṁ_loss, combined with recent estimates of the disk mass with ALMA, confirm previous estimates of the short lifetime of these proplyds. This work demonstrates the potential of this MUSE dataset and offers a new set of observables to be used to test current and future models of external photoevaporation.