Stellar discovery: Swarthmore student discovers star

A couple of years ago, Astronomy Professor David Cohen began a project to look into the relationship between x-rays and stellar winds. Most theory on this subject applies to highly luminous stars with very strong, turbulent winds. However, Professor Cohen was interested in examining the stars of lesser luminosity. Using the Chandra x-ray telescope, he began to examine beta Crucis, a star in the Crux or Southern Cross constellation.

According to Professor Cohen, the project really “got started” when Michael Kuhn ’07, an astrophysics major, joined the research team. Like many astrophysics majors, Kuhn was encouraged to do research during the summer before his senior year. According to Kuhn, Professor Cohen “thought it would be interesting for [him] to work on [the project] because of the unusual spectral line profiles of the primary star and the presence of a new x-ray source which could be a young stellar companion to beta Crucis.”

The project took a surprising turn this past year when an accidental observation lead to an unexpected discovery. While observing beta Crucis, another strong x-ray source not from the star itself was visible. “The separation between the two sources is an angle of 4 arcseconds — one 900th of a degree,” suggesting that the second mystery x-ray source “would be roughly 11th magnitude in the optical” and visible through a telescope. In other words, the team had found a new star unlisted in any astrological catalogue.

Astronomy professor Eric Jensen believes that the star remained undiscovered because beta Crucis itself is so bright and would overwhelm the light from its companion star. After observing several characteristics of the star, the research team suspects that the new star is a low mass star due to its high energy x-ray emission, time variability of x-ray brightness, and the proximity of other young stars. The new star is also likely a “physical companion” of beta Crucis bound by gravity. In order to affirm these claims, more observations will have to be done to show that beta Crucis and the new star are moving across the sky together.

As beta Crucis is the 19th brightest star in the sky, it is curious that this star had never been previously observed. Its discovery was purely chance and not part of the original goals of the project. If more observation proves that it is truly a young, low-mass star, Kuhn suggests that it would be interesting to further examine its relationship to the “stellar nursery of x-ray bright pre-main sequence stars (young stars that have not finished collapsing out of interstellar gas, and haven’t started nuclear fusion of hydrogen in their cores) within a degree of beta Crucis.”

Kuhn “really enjoyed” his work on the project and with Professor Cohen, spending the majority of his time creating and refining models of x-ray concepts pertaining to both stars. He ultimately went to present the findings at the American Astronomical Society meeting held in January in Seattle, WA. Professor Cohen asserts that sending students to conferences such as these is a good way for students to meet people and network in the astrophysics world. The project itself will not be truly finished until the resulting paper is published. With his career just beginning, Kuhn himself plans either to attend graduate school for astronomy or search for an astronomy-related job.


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