Near and Far: White Dwarfs, Brown Dwarfs and a New Standard Candle

点击翻译按钮获取中文摘要

The research of the scientific program funded by this grant will take us from stars in the neighbourhood of the Sun to the furthest reaches of the universe. It will exploit the most sophisticated modern telescopes currently available to the world community, justifying Canada's contributions to these frontline facilities. It will expose HQP to a high impact international collaboration and provide a unique science experience that spans all of space and time.  The nearby region: (a) The fact that we can see stars means they are losing energy and hence evolving. For almost all stars, this energy is produced by nuclear reactions in the hot dense stellar core which consumes the star's hydrogen and produces heavier elements. At the end of this nuclear processing the star ejects all the material above its nuclear burning region, exposing the extremely dense and hot core which then slowly cools with time. The resulting stellar object is called a white dwarf (WD); typically half the mass of the Sun with a radius roughly that of the Earth. The most massive star capable of forming a WD is an extremely important quantity, all stars more massive than this limit explode as supernovae (SN) which control the chemical evolution and star formation rate in a galaxy. To determine this upper mass limit we have been exploring young star clusters that contain massive stars up to 10 or more times the mass of the Sun and establishing which of them produced WDs. It has been extremely challenging to locate WDs whose progenitor was more than 6 times the mass of the Sun, but some new ideas and techniques we have been developing is showing promise.   (b) We were successful in obtaining 20.5 hours of time on the soon-to-be-launched James Webb Space Telescope to search for (among other things) possible evidence of planetary systems around very old stars. The search will be in an ancient star cluster, imaging its WDs in the infrared (IR). About 5% of young WDs in the galaxy are known to be anomalously bright in the IR due to dust resulting from the destruction of planets or asteroids when the host star transitioned to a WD. Our search will be amongst the 12 billion year WDs in this ancient stellar system looking for evidence of planet formation in the very early universe. The distant region: The Hubble Constant, measuring the expansion rate of the universe, is one of the most fundamental cosmological parameters. Currently, the value from the standard cosmological model is in conflict with measurements in the local universe. Suggested causes range from systematic biases in one or both techniques to underestimated uncertainties in distance calibration, to the possibility of new physics in the early universe. To explore this conflict further we have developed a new distance technique using very luminous carbon-rich red giant stars. While still in its infancy, the method is proving to be extremely powerful and requires significantly less observing time than the standard techniques.