Date:
Sun, 08/02/202612:30-13:30
Title: The pulsating white dwarfs of novae and a path to supernovae Ia outbursts on "single" sub-Chandrasekhar white dwarfs
Abstract: This talk will have two parts. In the first half, I will review a "mystery" that we still have to solve. When shell hydrogen burning can be observed in the "supersoft X-ray sources", whose atmosphere have effective temperature up to a million K, flux modulations are clearly observed with periods ranging from about 30 s to an hour. When the periods are of at least several minutes, we have found evidence that this is the rotation period of the white dwarf, which is highly magnetized (B>=10^5 Gauss), although why the periods appear in this phase is not clear at all. Most supersoft X-ray sources - although not all - are novae in a late outburst phase, and a high magnetic field of their white dwrafs is a new factor to include in evolution and outburst models. For periods of the order of a minute or less, the possibility of stellar pulsations has not been ruled out yet, although accretion onto the white dwarf in principle can spin it up to such fast rotation.
In the second half of the talk I will review a series of articles published in the last 11 years, which suggest that thermonuclear supernovae may explode also without merging or accretion from a binary companion. Such supernovae would probably occur with white dwarf mass above 1 M(sol), however they will definitely be sub-Chandrasekhar. This may occur if a white dwarf is reheated by traces of uranium (with radioactive decay of 238U), or by rekindled nuclear burning of hydrogen or helium. He burning may occur because of increased abundance of alpha particles, again because of radioactive uranium. In both cases analytical calculations show that the white dwarf may be brought out of the pycnonuclear regime and C12+C12 may be ignited in the thermonuclear regime, at quite lower density than in almost-Chandrasekhar mass white dwarfs. This will be a new SN Ia model to explore.
Zoom link:
https://huji.zoom.us/j/87163167105?pwd=KuCPRWT4FlIUvEDpDS8Q9jsBX3kpJb.1
Meeting ID: 871 6316 7105
Passcode: 457989
Contact: David Barba González
Abstract: This talk will have two parts. In the first half, I will review a "mystery" that we still have to solve. When shell hydrogen burning can be observed in the "supersoft X-ray sources", whose atmosphere have effective temperature up to a million K, flux modulations are clearly observed with periods ranging from about 30 s to an hour. When the periods are of at least several minutes, we have found evidence that this is the rotation period of the white dwarf, which is highly magnetized (B>=10^5 Gauss), although why the periods appear in this phase is not clear at all. Most supersoft X-ray sources - although not all - are novae in a late outburst phase, and a high magnetic field of their white dwrafs is a new factor to include in evolution and outburst models. For periods of the order of a minute or less, the possibility of stellar pulsations has not been ruled out yet, although accretion onto the white dwarf in principle can spin it up to such fast rotation.
In the second half of the talk I will review a series of articles published in the last 11 years, which suggest that thermonuclear supernovae may explode also without merging or accretion from a binary companion. Such supernovae would probably occur with white dwarf mass above 1 M(sol), however they will definitely be sub-Chandrasekhar. This may occur if a white dwarf is reheated by traces of uranium (with radioactive decay of 238U), or by rekindled nuclear burning of hydrogen or helium. He burning may occur because of increased abundance of alpha particles, again because of radioactive uranium. In both cases analytical calculations show that the white dwarf may be brought out of the pycnonuclear regime and C12+C12 may be ignited in the thermonuclear regime, at quite lower density than in almost-Chandrasekhar mass white dwarfs. This will be a new SN Ia model to explore.
Zoom link:
https://huji.zoom.us/j/87163167105?pwd=KuCPRWT4FlIUvEDpDS8Q9jsBX3kpJb.1
Meeting ID: 871 6316 7105
Passcode: 457989
Contact: David Barba González