Radiation-hydrodynamic models of X-ray and EUV photoevaporating protoplanetary discs

By James E. Owen, Barbara Ercolano, C. Clarke, Richard Alexander. 2009

264 citations recorded by the source corpus.

We present the first radiation-hydrodynamic model of a protoplanetary disc irradiated with an X-ray extreme ultraviolet (X-EUV) spectrum. In a model where the total ionizing luminosity is divided equally between X-ray and EUV luminosity, we find a photoevaporation rate of 1.4 x 10 -8 M ☉ yr -1 , which is two orders of magnitude greater than the case of EUV photoevaporation alone. Thus, it is clear that the X-rays are the dominant driving mechanism for photoevaporation. This can be understood inasmuch as X-rays are capable of penetrating much larger columns (~ 10 22 cm -2 ) and can thus effect heating in denser regions and at larger radius than the EUV. The radial extent of the launching region of the X-ray-heated wind is 1-70 au compared with the pure EUV case where the launch region is concentrated around a few au. When we couple our wind mass-loss rates with models for the disc's viscous evolution, we find that, as in the pure EUV case, there is a photoevaporative switch, such that an inner hole develops at ~1 au at the point when the accretion rate in the disc drops below the wind mass-loss rate. At this point, the remaining disc material is quickly removed in the final 15-20 per cent of the disc's lifetime. This is consistent with the 10 5 yr transitional time-scale estimated from observations of T Tauri stars. We however note several key differences to previous EUV-driven photoevaporation models. The two orders of magnitude higher photoevaporation rate is now consistent with the average accretion rate observed in young stars and will cut the disc off in its prime. Moreover, the extended mass-loss profile subjects the disc to a significant period (~20 per cent of the disc's lifetime) of 'photoevaporation-starved accretion'. We also caution that although our mass-loss rates are high compared to some accretion rates observed in young stars, our model has a rather large X-ray luminosity of 2 x 10 30 erg s -1 ; further modelling is required in order to investigate the evolutionary implications of the large observed spread of X-ray luminosities in T Tauri stars.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/652b5073409f043b2109ee5177e9b6568aaa7ba5

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Citations in the corpus

Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics (2017, methodology): “Fully self-consistent calculations would require coupling radiative transfer and chemistry (including photochemistry) with dynamics (as in some photo-evaporation simulations, e.g., Owen et al. 2010; Wang & Goodman 2017).”
Planetary evaporation by UV and X‐ray radiation: basic hydrodynamics (2012, methodology): “…parameters expected, since the escape temperature from a planetary atmosphere is similar to the escape temperature from the inner disk (1-10 AU) around a solar-type star, we will make use of the temperature-ionization parameter relation of Owen et al. (2010) in this work, as shown in Fig.”
RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “However, there is growing consensus that X-rays drive substantially higher wind mass-loss rates, and therefore that photoevaporation has a much more prominent effect on disk structures at early times (Ercolano et al. 2008, 2009; Drake et al. 2009; Owen et al. 2010).”
The coronal X-ray - age relation and its implications for the evaporation of exoplanets (2011, background): “Studies of the photoevaporation of protoplanetary discs (e.g. Ercolano, Clarke & Drake 2009; Owen et al. 2010) have shown this means that in the case of strong X-ray driven outflows the EUV does not penetrate far enough to drive further evaporation and instead just heats the outflow.”
Dynamics of Protoplanetary Disks (2010, background): “Owen et al. (2010) computed radiation hydrodynamic models of X-ray irradiated disks, assuming a luminosity LX = 2×1030 erg s−1.”
UNVEILING THE STRUCTURE OF PRE-TRANSITIONAL DISKS (2010, background): “2009, ApJ, 703, 1964 Goldreich, P., & Tremaine, S. 1980, ApJ, 241, 425 Goldreich, P., & Ward, W. R. 1973, ApJ, 183, 1051 Gorti, U., & Hollenbach, D. 2009, ApJ, 690, 1539 Gullbring, E., Hartmann, L., Briceno, C., & Calvet, N. 1998, ApJ, 492, 323 Hartigan, P., Edwards, S., & Ghandour, L. 1995, ApJ, 45”
TRANSITIONAL AND PRE-TRANSITIONAL DISKS: GAP OPENING BY MULTIPLE PLANETS? (2010, background): “More recent estimates suggest higher values, perhaps as much as∼10−8M⊙ yr −1 due to the inclusion of X-rays (Gorti & Hollenbach 2009; Owen et al. 2010); however, the highest values are problematic, because then it becomes difficult to understand why so many T Tauri disks last for several Myr with…”
KEPLER PLANETS: A TALE OF EVAPORATION (2013, background): “If the adopted X-ray spectrum -while based on observed spectra (see Owen et al. 2010)- is overly soft or overly hard, then the X-ray heating will be overor under-estimated, respectively.”
On the theory of disc photoevaporation (2011, methodology): “The most convincing argument that the higher energy photons ( 0.3–0.4 keV) are dominating the heating to temperatures 5000 K is provided by the exercise conducted in Owen et al. (2010).”
Protoplanetary Disks and Their Evolution (2011, background): “• Photoevaporative flows from disk surfaces have been observed but the models disagree on the relative importance of FUV, EUV, and X-ray photoevaporation.”
Protoplanetary disc evolution and dispersal: the implications of X-ray photoevaporation (2010, methodology): “Therefore, we adopt the unattenuated spectrum shown in Owen et al. (2010) and expect our results to generalise to cases of moderate screening.”