The Kinematics And Excitation Of Infrared Wwater Vapor Emission From Planet-forming Disks: Results From Spectrally-resolved Surveys And Guidelines For JWST Spectra

By Keith Cowing
Press Release
September 19, 2022
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The Kinematics And Excitation Of Infrared Wwater Vapor Emission From Planet-forming Disks: Results From Spectrally-resolved Surveys And Guidelines For JWST Spectra
Overview of near- and mid-infrared water emission bands as observed from space and the ground (see Section 1.1). Top: Earth’s atmospheric transmission (in green), with the principal observing bands labelled in orange. Middle: water emission model with a temperature of 700 K and column density of 1018 cm−2 . The coverage of different spectrographs is shown with black boxes to illustrate which parts of the spectrum can be observed: high-resolution (R ∼ 30,000–95,000) spectrographs from the ground can spectrally-resolve relatively weak high-energy lines in small spectral windows, while JWST from space can observe a wider spectral range but only at moderate resolution (R ∼ 1,500–3,700). Bottom: zoomed-in spectral regions to illustrate the difference in resolution between JWST and ground-based data, and including models for OH and CO lines for identification (the CRIRES, iSHELL, and TEXES spectra are for DR Tau and adopted from Banzatti et al. 2017, 2022; Salyk et al. 2019).

This work presents water emission spectra at wavelengths covered by JWST (2.9-12.8 μm) as spectrally-resolved with high resolving powers (R = 30,000-100,000) using ground-based spectrographs.

Two new surveys with iSHELL and VISIR are combined with previous spectra from CRIRES and TEXES to cover parts of multiple ro-vibrational and rotational bands observable within telluric transmission bands, for a total of 85 disks and ≈160 spectra. The general expectation of a range of regions and excitation conditions traced by infrared water spectra is for the first time supported by the combined kinematics and excitation as spectrally resolved at multiple wavelengths.

The main findings from this analysis are: 1) water lines are progressively narrower going from the ro-vibrational bands at 2-9 μm to the rotational lines at 12 μm, and partly match a broad (BC) and narrow (NC) emission components, respectively, as extracted from ro-vibrational CO spectra; 2) rotation diagrams of resolved water lines from upper level energies of 4000-9500 K show curvatures indicative of optically thick emission (≈1018 cm−2) from a range of excitation temperatures (≈ 800-1100 K); 3) the new 5 μm spectra demonstrate that slab model fits to the rotational lines at >10μm strongly over-predict the ro-vibrational emission bands at <9μm, implying non-LTE excitation.

We discuss these findings in the context of a emission from a disk surface and a molecular inner disk wind, and provide a list of detailed guidelines to support the analysis and interpretation of spectrally-unresolved JWST spectra.

Andrea Banzatti, Klaus M. Pontoppidan, José Pérez Chávez, Lindsey Diehl, Colette Salyk, Simon Bruderer, Greg J. Herczeg, Ilaria Pascucci, Sean Brittain, Stanley Jensen, Arthur D. Bosman, Ewine F. van Dishoeck, Sierra Grant, Inga Kamp, Andres Carmona, Karin I. Öberg, Geoff A. Blake, Michael R. Meyer, Caleb Wheeler

Comments: Posted on arXiv as submitted to AJ, for immediate access by teams working on the analysis of JWST spectra
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2209.08216 [astro-ph.EP] (or arXiv:2209.08216v1 [astro-ph.EP] for this version)
Submission history
From: Andrea Banzatti Dr.
[v1] Sat, 17 Sep 2022 02:13:15 UTC (9,110 KB)

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