2021ApJ...915...90N -
Astrophys. J., 915, 90-90 (2021/July-2)
Photoevaporation of grain-depleted protoplanetary disks around intermediate-mass stars: investigating the possibility of gas-rich debris disks as protoplanetary remnants.
NAKATANI R., KOBAYASHI H., KUIPER R., NOMURA H. and AIKAWA Y.
Abstract (from CDS):
Debris disks are classically considered to be gas-less systems, but recent (sub)millimeter observations have detected tens of those with rich gas content. The origin of the gas component remains unclear, but it could be protoplanetary remnants and/or secondary products from large bodies. In order to be protoplanetary in origin, the gas component of the parental protoplanetary disk is required to survive for ≳10Myr. However, previous models predict ≲10Myr lifetimes because of efficient photoevaporation at the late stage of disk evolution. We investigate photoevaporation of gas-rich, optically-thin disks around intermediate-mass stars at a late stage of the disk evolution. The evolved system is modeled like those devoid of small grains (≲4µm). We find that grain depletion reduces photoelectric heating so that far-ultraviolet photoevaporation is not excited. Extreme-ultraviolet (EUV) photoevaporation is dominant and yields a mass-loss rate of the order of 1×10–11(ΦEUV/1038s–1)1/2M☉yr–1, where ΦEUV is the EUV emission rate of the host star. The estimated gas-disk lifetimes are ∼100(Mdisk/10–3M☉)(ΦEUV/1038s–1)1/2Myr and depend on the "initial" disk mass at the point small grains have been depleted in the system. We show that the gas component can survive for a much longer time around A-type stars than lower-mass (F-, G-, K-type) stars owing to their atypical low EUV (and X-ray) luminosities. This trend is consistent with the higher frequency of gas-rich debris disks around A-type stars, implying the possibility of the gas component being protoplanetary remnants.
Abstract Copyright:
© 2021. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Protoplanetary disks - Debris disks - Hydrodynamical simulations - Star formation - Planetary system formation
Simbad objects:
3
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