High-Energy Astrophysics at UBC
We recently discovered an ultramassive white dwarf that escaped from the nearby Hyades cluster (2023ApJ…956L..41M). It is one of only three white dwarfs with a mass likely greater than 1.3 solar masses, but unlike the other two, it is not strongly magnetic, so we can use spectroscopy to estimate its mass as well, yielding a test of the mass-radius relation for white dwarfs!
Paul successfully defended his thesis on Studies of evolved stellar populations : from giants to remnants. He will be continuing his research at UBC. Congratulations Paul!
As reported in Nature (2023Natur.620…61C), the ZTF survey discovered a rapidly rotating white dwarf (ZTF J203349.8+322901.1 or Janus) that follow-up spectroscopy reveal is half-covered with helium and the other half-covered with hydrogen, a white dwarf with two faces!
IXPE finally measures the long-predicted polarization of X-rays from the surface and magnetosphere of a magnetar (4U 0142+61) as published in Science, 2022Sci…378..646T. The extent of polarization from 2-4 keV is about ten percent indicating the surface is likely to be solid or liquid. Above 4 keV, the mode of polarization switches and increases to about 30% as expected from resonant Compton scattering in the magnetosphere. This is an amazing validation and probe of the magnetar model!
Javiera defended her thesis on Red giant stars as standard candles. Congratulations Javiera!
We have completed a comprehensive study of massive white dwarfs with Gaia EDR3 10.1093/mnras/stac458. We can account for the numbers of white dwarfs between 0.95 and 1.15 solar masses with white dwarf cooling models and the rate of star formation in the Galaxy over the past few billion years. In fact, these massive white dwarfs provide an excellent method to trace star formation. The most massive and rare white dwarfs with masses greater than 1.15 solar masses appear to be form through a combination of mergers and the evolution of single stars with about equal numbers forming through these two avenues over the past few billion years.
We developed a novel method to reconstruct and determine the ages of all the young clusters within 200 pc of the Sun using Gaia EDR3 including the Pleiades 10.3847/1538-4357/ac45fc and four other clusters 2110.04296. In the process we found two white dwarfs lost from the Pleiades bringing the total number of Pleiad WDs to three and three from the Alpha Persei cluster 10.3847/2041-8213/ac50a5. These are the most massive white dwarfs to have been associated with clusters using the unprecedentedly precise astrometry of Gaia.
Alumna Ilaria Caiazzo led a team based at Caltech and elsewhere to discover the smallest and therefore most massive white dwarf ever found. It is within about one percent of the maximum mass that a white dwarf can be, the Chandrasekhar mass. It rotates every seven minutes and harbours a magnetic field more than a billion times stronger than Earth’s 10.1038/s41586-021-03615-y.
Our JWST proposal (on ADS) to look for brown dwarfs and planetary disks was chosen for Cycle 1! Learn about our motivation for the proposal arxiv:1702.00091 and arxiv:1903.06769.
Our second paper on carbon stars as standard candles has just been accepted 10.1093/mnras/staa3750. Check it out!
Here is the first paper too 10.1093/mnras/staa1346.