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Published November 1, 2014 | Published
Journal Article Open

Low Extreme-ultraviolet Luminosities Impinging on Protoplanetary Disks

Abstract

The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the extreme-ultraviolet (EUV) luminosity impinging on 14 disks around young (~2-10 Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 10^(42) photons s^(–1) for all sources without jets and lower than 5 × 10^(40) photons s^(–1) for the three older sources in our sample. These latter values are low for EUV-driven photoevaporation alone to clear out protoplanetary material in the timescale inferred by observations. In addition, our EUV upper limits are too low to reproduce the [Ne II] 12.81 μm luminosities from three disks with slow [Ne II]-detected winds. This indicates that the [Ne II] line in these sources primarily traces a mostly neutral wind where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative mass loss rates than those predicted by EUV-driven models alone. In summary, our results suggest that high-energy stellar photons other than EUV may dominate the dispersal of protoplanetary disks around sun-like stars.

Additional Information

© 2014 American Astronomical Society. Received 2014 June 27; accepted 2014 August 21; published 2014 October 8. The authors thank the anonymous referee for a prompt and useful report. I.P. thanks Cathie Clarke for stimulating discussion. I.P., U.G., and D.H. acknowledge support from an NSF Astronomy & Astrophysics Research Grant (ID: 1312962). Facility: ATCA

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