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NASA's James Webb Space Telescope:

Molecular Spectroscopy of Protoplanetar y Disks

During the gas-rich phase of planet formation, protoplanetary disks act as "chemical factories." The high densities and high temperatures in the inner disk, coupled with strong UV and X-ray irradiation impinging on the disk surface, lead to a rich volatile chemistry that drives the composition of planetesimals, and ultimately the make-up of fully assembled planetary bodies and their atmospheres. The main spectroscopic tracer of molecular gas on scales of a few AU is infrared line emission by gaseous molecules such as H2O, CO, CO2, OH and a growing list of organics. The spectroscopic modes of JWST NIRSpec and MIRI cover the main molecular bands of gas in planet-forming regions, tracing gas at temperatures of 100-1000 K. The integral field units of JWST will resolve the molecular emission in nearby protoplanetary disks, while the high sensitivity will allow observations of disks as far away as the Magellanic Clouds, constraining the chemistry of planet formation in a wide range of environments. The resolving power of l/Dl~2700 separate individual lines in complex molecular bands, and allow for accurate measurements of weak lines critical for constraining chemical models, including those of rare isotopologues. Molecular spectroscopy with JWST is not restricted to protoplanetary disks. NIRSpec and MIRI will enable detailed observations of the chemistry of protostars, molecular out flows, and the atmospheres of cool and evolved stars throughout the Galaxy. The same molecular bands will be observable in exoplanetary atmospheres. Beyond the Milky Way, JWST can constrain the chemistry of the interstellar medium of both nearby and distant galaxies. The improvements in sensitivity and spectral resolving power in the 3-28 mm waveband, compared to previous facilities, opens a vast new discovery space in the molecular universe.

Orion Proplyds

HD 141569


Molecular spectroscopy of protoplanetar y disks with JWST

1.5 Flux [Jy] 1.0 0.5

H2O + OH rotational lines 1
5

2
10

3
15 Wavelength [micron]
0.40 0.35 0.30 0.25 0.20 0.15 0.10 Flux [Jy]

20

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Model parameters Protoplanetary disk around a young solar-type star: Teff=4250 K; L * =1 Lsol; 0.01 Mdisk=Msol disk, distance=125 pc. Abundances based on Spitzer and ground-based IR spectroscopy What does it mean? The mid-IR molecular lines from protoplanetary disks are formed in the disk surfaces at 1-10 AU. JWST observing modes NIRSpec: 1-5 mm @ R~2700 MIRI: 5-28 mm @ R~2700

CO fundamental
4.5 4.6 4.7 Wavelength [micron] 4.8 4.9

1
5.0

0.40 0.35 0.30 0.25 0.20 0.15 0.10 5.5
0.55

Flux [Jy]

H2O stretch
6.0 6.5 Wavelength [micron] 7.0

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7.5

Flux [Jy]

0.50 0.45 0.40 0.35

C2H2
13.5

HCN
14.0 14.5

CO2
15.0 Wavelength [micron] 15.5 16.0

3
16.5

NIRSpec

Near-Infrared Spectrograph (NIRSpec) Micro · · Fixed · · -Shutter Assembly (MSA) 4 separate quadrants over 3.4' by 3.4' FOV 365 x 171 user configurable shutters per quadrant slits (FS) Always open, no overlap with MSA on detectors Four narrow slits and one 1.6'' square for high throughput Integral Field Unit (IFU ) · 3'' x 3'' FOV in 30 slices, each 0.1'' (dispersion) x 3'' (spatial)

MIRI Spitzer-IRS/Keck /Gemini/ VLT

Spectroscopy of disks throughout the Milky Way Galaxy
· NIRSpec (R~2700/1-5 mm) can reach protoplanetary disks around Solar mass stars out to 40 kpc (Herbig Ae disks out to 100 kpc, including the Magellanic Clouds). · MIRI can obtain 5-28 mm R~2700 spectra of protoplanetary disks out to 7 kpc. · Several orders of magnitude improvement over current capabilities for mid-IR spectroscopy of molecular gas.

Mid-Infrared Instrument (MIRI) Direct Imaging · nine photometric bands from 5 to 28 µm Coronagraphic Imaging · three four-quadrant phase masks (4QPMs) at 10.65, 11.4, & 15.5 µm, Lyot coronagraph at 23 µm Low-Resolution Spectroscopy (LRS) · 5-14 µm, l/Dl ~ 100 at 7.5 µm, 0.6'' x 5.5'' slit LRS Slitless Spectroscopy for exoplanet studies Medium Resolution Spectrometer (MRS) · l/Dl ~ 2200 ­ 3500 · 4.9 to 28.8 µm, enabled by four IFUs · 3.7'' to 7.7'' field-of-views (wavelength-dependent)

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