Lunch talk on Apr. 29th, 2019
An evolution scenario for metal pollution and circumstellar disks of white dwarfs
Speaker: 陈迪昌（南京大学）/ Dichang Chen (Nanjing University)
Venue: The 3rd floor, SWIFAR Building
Time: 12:30 PM, Monday, 29th April, 2019
White dwarf stars are the final evolution stage of main sequence stars with masses less than about eight solar masses, which includes over 97% of stars in our Milky Way. Planetary systems can survive stellar evolution, as is clear from the atmospheric metal pollution and circumstellar dusty disks of single white dwarfs. Therefore, the study on metal pollution and dusty disks offers a unique and powerful window into the structure, evolution and fate of planetary systems both around main sequence and beyond main sequence.
Recent observations show that 1-4% of single white dwarfs are accompanied by dusty disks, while the occurrence rate of metal pollution is about 25-50%. Dusty disks and metal pollution have been associated with accretion of remanent planetary systems around white dwarfs, yet the relationship between these two phenomena is still unclear. By analyzing a sample of metal-polluted white dwarfs, we find that the mass accretion rate onto the white dwarf generally follows a broken power-law decay, which matches well with the theoretical prediction, assuming that dust accretion is primarily driven by Poynting-Robertson drag and the dust source is primarily delivered via dynamically falling asteroids perturbed by a Jovian planet. The presence of disks is mainly at the early stage (0.1-0.7 Gyr) of the whole process of metal pollution, which is detectable until 8 Gyr, naturally explaining the fraction (2-16%) of metal-polluted white dwarfs with dusty disks. The success of this scenario also implies that the configuration of an asteroid belt with an outer gas giant might be common around stars of several solar masses.