PI Highlight
Dr. Allen Shafter
Dr. Allen Shafter is a professor and chair of SDSU’s astronomy department. His research involves the study of a class of variable stars known as Classical Novae.
Most people are surprised to learn that stars are neither constant in brightness nor eternal. Stars are born as a result of the gravitational collapse of large diffuse clouds of gas and dust in the interstellar medium, they "live" for a finite period of time ranging from tens of millions to tens of billions of years depending on their initial mass. During their lifetimes stars vary in brightness on a variety of time scales and amplitudes, from tiny and frequent fluctuations in brightness exhibited by run-of-the-mill stars like our sun, to the relatively rare, but colossal explosions that take place at the end of a massive star's life, supernovae.
The brightness of supernovae can, for a brief period of weeks to months, rival the combined luminosity of an entire galaxy containing billions of "normal" stars.
Professor Shafter and his students in the astronomy department at SDSU have been studying another type of explosive variable star known as classical novae. While not as bright as supernovae, classical novae are nevertheless among the most spectacular of cosmic explosions. For example, a classical nova releases as much energy in a few weeks as the sun does in ten thousand years!
The explosions of classical novae result from the fact that they are not single stars, but "binary" stars. That in itself is not that unusual, roughly half of the stars in the sky are not single, but consist of pairs of stars orbiting one another on timescales of minutes to centuries. In the case of classical novae one of the stars is a relatively normal star like the sun in a close orbit with a small and very dense companion star known as a white dwarf. The close proximity of the stars in combination with the strong gravitational pull of the white dwarf results in the transfer of material from the normal star onto the surface of its white dwarf companion. This material builds up over time (from a few years to many thousands of years) before burning explosively, resulting in the nova eruption.
Click here to view two erupting novae (circled) in the nearby Andromeda galaxy.
The high luminosities of the classical nova explosions enables them to be seen at great distances from earth, all the way to other galaxies millions of light years away. By studying novae in external galaxies, Professor Shafter is trying to understand how the rate and brightness of classical nova eruptions depend on the detailed physical properties (e.g., mass, chemical composition, age) of the component stars in the nova binary. He is particularly interested in studying nova systems that have been seen to have more than one eruption, the so called "Recurrent Novae". In his latest research, professor Shafter and his students, Stephanie Lauber, and Chris Curtin (now pursuing a PhD in Astronomy at Swinburne University in Australia) have been studying classical novae in the nearby Andromeda galaxy (with Lauber) and in several giant elliptical galaxies that are members of the distant Virgo cluster of galaxies (with Curtin). This research is currently funded through grants from NASA and the NSF.
With the exception of the work on the distant Virgo cluster galaxies, which was done with the large (3.6 meter) Canada-France-Hawaii Telescope (CFHT), much of Dr. Shafter's work and that of his colleagues takes place at SDSU's Mount Laguna Observatory (MLO). The MLO is located 50 miles east of San Diego, at an altitude of 6100 ft. (1859 meters) on the remote eastern edge of the Cleveland National Forest.
Currently, there are four telescopes in operation at MLO ranging in size from a 21-in reflector used for public nights and student training to 24-in and 40-in reflectors used for research. The latest addition is the new Phillips Claud 50-in telescope, which is currently being commissioned.
For further information, Professor Shafter can be reached at ashafter@mail.sdsu.edu or at 619-594-6170.
Further information about Mount Laguna Observatory can be found at: http://mintaka.sdsu.edu/.