Observational Constraints on the Stellar Radiation Field Impinging on Transitional Disk Atmospheres

Abstract

Mid-infrared atomic and ionic line ratios measured in spectra of pre-main sequence stars are sensitive indicators of the hardness of the radiation field impinging on the disk surface. We present a low-resolution Spitzer IRS search for [Ar II] at 6.98 $\mu$m, [Ne II] at 12.81 $\mu$m, and [Ne III] 15.55 $\mu$m lines in 56 transitional disks. These objects, characterized by reduced near-infrared but strong far-infrared excess emission, are ideal targets to set constraints on the stellar radiation field onto the disk because their spectra are not contaminated by shock emission from jets/outflows or by molecular emission lines. After demonstrating that we can detect [Ne II] lines and recover their fluxes from the low-resolution spectra, here we report the first detections of [Ar II] lines towards protoplanetary disks. We did not detect [Ne III] emission in any of our sources. Our [Ne II]/[Ne III] line flux ratios combined with literature data suggest that a soft-EUV or X-ray spectrum produces these gas lines. Furthermore, the [Ar II]/[Ne II] line flux ratios point to a soft X-ray and/or soft-EUV stellar spectrum as the ionization source of the [Ar II] and [Ne II] emitting layer of the disk. If the soft X-ray component dominates over the EUV than we would expect larger photoevaporation rates hence a reduction of the time available to form planets.

Accepted for publication in ApJ

References in corpus (17)

• On the Diversity of the Taurus Transitional Disks: UX Tau A & Lk Ca 15
• H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
• Demographics of Transition Objects
• The Disk Population of the Chamaeleon I Star-Forming Region
• Line Emission from Gas in Optically Thick Dust Disks around Young Stars
• c2d Spitzer IRS Spectra of Disks around T Tauri Stars. III. [Ne II], [Fe I], and H_2 gas-phase lines
• Neon Fine-Structure Line Emission By X-ray Irradiated Protoplanetary Disks
• HD 98800: A 10-Myr-Old Transition Disk
• The Formation and Evolution of Planetary Systems: Description of the Spitzer Legacy Science Database
• Medium-separation binaries do not affect the first steps of planet formation
• [NeII] emission line profiles from photoevaporative disc winds
• The mid-infrared spectrum of the transiting exoplanet HD 209458b
• Free-free Emission and Radio Recombination Lines from Photoevaporating Disks
• High-resolution Spectroscopy of [Ne II] Emission from TW Hya
• Spitzer Spectroscopy of Circumstellar Disks in the 5 Myr Old Upper Scorpius OB Association
• An outflow origin of the [NeII] emission in the T Tau triplet
• A slowly accreting ~10 Myr old transitional disk in Orion OB1a

Cited by in corpus (11)

• Accretion of Jupiter-mass Planets in the Limit of Vanishing Viscosity
• Understanding the origin of the [OI] low-velocity component from T Tauri stars
• The Evolution of Disk Winds from a Combined Study of Optical and Infrared Forbidden Lines
• Uncertainties in water chemistry in disks: An application to TW Hya
• JWST Observations of Young protoStars (JOYS): Linked accretion and ejection in a Class I protobinary system
• Tracing High-Energy Radiation from T Tauri Stars Using Mid-Infrared Neon Emission from Disks
• MINDS. JWST-MIRI reveals a peculiar CO${}_2$-rich chemistry in the drift-dominated disk CX Tau
• Using Multiwavelength Variability to Explore the Connection between X-ray Emission, the Far-Ultraviolet H2 Bump, and Accretion in T Tauri Stars
• Testing protoplanetary disc dispersal with radio emission
• Modeling JWST MIRI-MRS Observations of T Cha: Mid-IR Noble Gas Emission Tracing a Dense Disk Wind
• MINDS. Young binary systems with JWST/MIRI: Variable water-rich primaries and extended emission