OBSERVATIONAL CONSTRAINTS ON THE STELLAR RADIATION FIELD IMPINGING ON TRANSITIONAL DISK ATMOSPHERES

Journal Article · Thu Nov 01 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/759/1/47· OSTI ID:22086461

Szulagyi, Judit ^[1]; Pascucci, Ilaria ^[2]; Abraham, Peter; Moor, Attila ^[3]; Apai, Daniel ^[4]; Bouwman, Jeroen ^[5]

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1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
2. Lunar and Planetary Laboratory, University of Arizona, 1629 East University Boulevard, Tucson, AZ 85721 (United States)
3. Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest (Hungary)
4. Department of Astronomy, The University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721 (United States)
5. Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)

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 toward 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, then we would expect larger photoevaporation rates and, hence, a reduction of the time available to form planets.

• OSTI ID: 22086461
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 759; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ARGON IONS
ASTRONOMY
ASTROPHYSICS
EXTREME ULTRAVIOLET RADIATION
IONIZATION
JETS
MAIN SEQUENCE STARS
NEON IONS
PHOTON EMISSION
PLANETS
PROTOPLANETS
SOFT X RADIATION
STELLAR ATMOSPHERES
STELLAR RADIATION
X-RAY SPECTRA