JWST Detects Neon Line Variability in a Protoplanetary Disk

The Astrophysical Journal Letters, vol. 958, pp. L4

Abstract

Abstract We report the first detection of variability in the mid-infrared neon line emission of a protoplanetary disk by comparing a JWST Mid-InfraRed Instrument Medium Resolution Spectrometer spectrum of SZ Cha taken in 2023 with a Spitzer Infrared Spectrograph Short-High spectrum of this object from 2008. We measure the [Ne iii]-to-[Ne ii] line flux ratio, which is a diagnostic of the high-energy radiation field, to distinguish between the dominance of EUV- or X-ray-driven disk photoevaporation. We find that the [Ne iii]-to-[Ne ii] line flux ratio changes significantly from ∼1.4 in 2008 to ∼0.2 in 2023. This points to a switch from EUV-dominated to X-ray-dominated photoevaporation of the disk. We present contemporaneous ground-based optical spectra of the Hα emission line that show the presence of a strong wind in 2023. We propose that this strong wind prevents EUV radiation from reaching the disk surface while the X-rays permeate the wind and irradiate the disk. We speculate that at the time of the Spitzer observations, the wind was suppressed and EUV radiation reached the disk. These observations confirm that the MIR neon emission lines are sensitive to changes in high-energy radiation reaching the disk surface. This highlights the [Ne iii]-to-[Ne ii] line flux ratio as a tool to gauge the efficiency of disk photoevaporation in order to provide constraints on the planet formation timescale. However, multiwavelength observations are crucial to interpret the observations and properly consider the star–disk connection.

Authors 9

1. Catherine C. Espaillat

   Boston University

   Affiliation as printed

   Institute for Astrophysical Research & Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA; cce@bu.edu

   Institute for Astrophysical Research & Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

2. Thanawuth Thanathibodee

   Boston University

   Affiliation as printed

   Institute for Astrophysical Research & Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA; cce@bu.edu

   Institute for Astrophysical Research & Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

3. Caeley V. Pittman

   Boston University

   Affiliation as printed

   Institute for Astrophysical Research & Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA; cce@bu.edu

   Institute for Astrophysical Research & Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA

4. J. A. Sturm Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, The Netherlands

5. Melissa K. McClure Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, The Netherlands

6. Nuria Calvet

   University of Michigan

   Affiliation as printed

   Department of Astronomy, Univ`tpdelersity of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA

7. F. M. Walter

   Stony Brook University

   Affiliation as printed

   Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800, USA

8. R. Franco-Hernández

   Universidad de Guadalajara

   Affiliation as printed

   Instituto de Astronomía y Meteorología, Universidad de Guadalajara, Avenida Vallarta No. 2602, Col. Arcos Vallarta Sur, CP 44130, Guadalajara, Jalisco, Mexico

9. James Muzerolle

   Space Telescope Science Institute

   Affiliation as printed

   Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA