科研之友
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摘要
The similar to 10 per cent of tidal disruption events ( IDEs) due to stars more massive than M-* greater than or similar to M-circle dot should show abundance anomalies due to stellar evolution in helium, carbon and nitrogen, but not oxygen. Helium is always enhanced, but only by up to similar to 25 per cent on average because it becomes inaccessible once it is sequestered in the high-density core as the star leaves the main sequence. However, portions of the debris associated with the disrupted core of a main sequence star can be enhanced in helium by factors of 2-3 for debris at a common orbital period. These helium abundance variations may be a contributor to the observed diversity of hydrogen and helium line strengths in IDEs. A still more striking anomaly is the rapid enhancement of nitrogen and the depletion of carbon due to the CNO cycle stars with M-* greater than or similar to M-circle dot quickly show an increase in their average N/C ratio by factors of 3-10. Because low-mass stars evolve slowly and high-mass stars are rare, IDEs showing high N/C will almost all be due to similar to 1-2 M-circle dot stars disrupted on the main sequence. Like helium, portions of the debris will show still larger changes in C and N, and the anomalies decline as the star leaves the main sequence. The enhanced [N/C] abundance ratio of these IDEs provides the first natural explanation for the rare, nitrogen-rich quasars and may also explain the strong nitrogen emission seen in ultraviolet spectra of ASASSN-141i.
- 出版日期2016-5-1
