This is a three-year award to sustain the Center for Astrophysics Supernova Program, which obtains observations of supernovae in low redshift galaxies using the 1.5 meter, 1.2 meter, and robotic 1.3 meter telescopes at Mount Hopkins Observatory in Arizona as well as the 6.5 meter MMT and Magellan telescopes. It will obtain spectra and multi-color optical light curves for supernovae north of -20º and brighter than 18 mag. This work is aimed at answering questions about supernovae: which stars explode, by what mechanism, and with what result? The work has also been applied to cosmology, providing part of the foundation for the discovery of dark energy.
The broader impacts of this work include training of students and outreach through public lectures
AST-0907903 Supernovae are exploding stars that, for a month, shine as brightly as billions of stars like the Sun. Because they are so bright, we can see them at very great distances-- up to halfway across the visible Universe. We have puzzled out that there are at least two broad classes of supernova explosions: those that get their energy from gravity when a star collapses and those that get their energy from the thermoculear detonation of a dead star's core. Aside from their intrinsic interest as stupendous events in nature that we would like to understand, supernovae are broadly important in two ways. One broad impact on our overall understanding of the history on the grandest scale is that they are violent events that create and disperse the elements that make up planets and people. If you want to understand where we came from, you need to understand supernova explosions. This is a theme that I incorporate into my undergraduate course at Harvard for students who are not goint to take any other science course. The other is that the supernovae that erupt as a result of a thermonuclear explosion in a compact burned-out core of a star can be used to gauge the distances between galaxies. This turns out to be of great importance in astronomy and fundamental physics. The 2011 Nobel Prize in Physics was awarded to Saul Perlmutter, Brian Schmidt, and Adam Riess for the discovery that the expansion of the universe is accelerating. They did this by using supernovae of this "SN Ia" type to determine distances. The physical explanation for this acceleration is the presence of some dark energy that makes up 2/3 of the Universe. At present, we do not know what the dark energy is, so further investigation, of the type carried out by this NSF grant lies at the center of understanding the way physics works on the grandest scale. Schmidt and Riess were both graduate students at Harvard of this grant's PI, Robert Kirshner. Each of them was supported in part by preceding NSF awards. More specifially, in the period from 8/2012 to 7/2013, we published 15 papers on a number of topics related to supernova explosions. These include a detailed study of SN 1987A, the brightest supernova seen since Kepler's time, which we have been following from space and from the ground. Amazingly, the supernova is getting brighter, no longer powered by the radioactivity of elements produced in the explosion 27 years ago, but now illuminated by light emitted as a result of the collision between the expanding debris of the vanished star and the gas that was in the neighborhood as a result of mass lost from the star about 20 000 years before the explosion took place. Another significant contribution is a paper written in collaboration with a postdoc at the Harvard-Smithsonian Center for Astrophysics, Ryan Foley. We identify a new variety of thermonuclear supernova explosion, dubbed SN Iax, that has a less powerful explosion than the standard explosion that has been used to trace the histroy of cosmic expansion. Our ongoing work at Harvard includes finishing up the Ph.D. thesis work for Andrew Friedman, who took a postdoc at MIT and Kaisey Mandel who, after finishing, went to University College, London. Andy's thesis contains a rich set of observations of SN Ia made at infrared wavelengths using our telescopes in Arizona. As our group has demonstrated, these supernovae make even better measuring rods for the Universe when the observations are done in the infrared. Kaisey's work is an exceptionally well-executed mathematical method for taking those observations and extracting the very best estimate of the distance. This work will be the foundation for future measurements that will do a superior job of measuring cosmic distances and inferring the properties of the dark energy.
