Radiation accretive

Fig. 5.23. Possible outcomes of accretion on to a CO white dwarf, according to its mass and accretion rate. Medd is the critical (Eddington) rate above which radiation pressure drives material out. After Nomoto and Kondo (1991). Courtesy Ken-ichi Nomoto.

One of the present authors proposed a model for superoutbursts and superhumps of SU UMa stars [1], In this model, the normal outbursts of SU UMa stars are thought to be essentially the same as the ordinary outbursts of dwarf nova and they are supposed to be caused by the disk instability (see e.g., Smak [2]). Superoutbursts are explained in the following way. The heating of the secondary s atmosphere by strong far UV and soft X-ray radiation due to accretion and the resulting increase in mass-overflow rate from the secondary may lead to a positive feed back instability between accretion and mass overflow in a certain circumstance. This "irradiation-induced mass-overflow instability" is the suggested mechanism of "superoutburst" of SU UMa stars. 

In 1964 Ya.B. [20 ], and independently of him E. Salpiter (USA), showed that a black hole may be found by its influence on the surrounding gas. The heating of the gas produces radiation which may then be detected. It was only after the publication of these papers that astronomers realized that black holes could be observed. It was, in fact, the papers of Ya.B. and his students that pointed out the very important role of accretion of matter... 

Under Ya.B. s guidance the theory of disc accretion was developed and received recognition and experimental verification. We note that all this work was basically performed before the experimental discoveries. Still awaiting experimental confirmation is the burst of neutrino radiation accompanying the collapse of a star, which Ya.B. examined together with O. Kh. Guseinov... 

Detected rotational H2 and ro-vibrational CO, CO2, C2H2, HCN, as well as H2O and OH lines trace hot gas in the inner, planet-forming disk zone with T > 300 K (Brittain et al. 2003 Lahuis et al. 2006 Salyk et al. 2008), see Fig. 4.3. These lines are a good measure of temperature and high-energy radiation fields, and presumably sensitive to disk accretion, which could be a stress-test for advanced chemo-dynamical models. In Table 4.1 the various molecules used to study protoplanetary disks are overviewed. 

Disk temperatures would have decreased rapidly with distance from the Sun as accretional energy release, optical depth, and solar radiation all declined. For example, some meteorite samples from main-belt asteroids contain hydrated silicates, formed by reactions between anhydrous rock and water ice. This implies that temperatures at 2-3 AU became low enough for ice to condense while the asteroids were forming. 

The rate at which the planetary cores accreted gas increased slowly until their masses reached 30M . After this, gas accretion was very rapid (Pollack et al., 1996). The growth timescale depends on the opacity of the planet s gas envelope, since this determines the rate at which the energy of accretion could be radiated away. Eor interstellar dust opacities, a lOM core would require 10 Myr to grow to Jupiter s mass (Pollack et al., 1996). However, growth would have been quicker if the opacity was lower due to coagulation of grains in the envelope (Ikoma et al., 2000). 

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