Stellar Astronomy

Many areas of stellar astronomy are of interest to our group, such as pulsations of variable stars (asteroseismology), stellar populations and star formation histories of galaxies, cataclysmic variable studies, and even gamma-ray bursts.

Asteroseismology


Asteroseismology is the study of pulsations on other stars, using many of the techniques developed for solar oscillations. We want to learn about properties of stars, such as internal rotation, that cannot be found by any other means. The principle difference with the Sun is that we cannot spatially resolve most stars because they are so distant, and thus they are point sources of light. This complicates the analysis of the pulsation spectrum because far fewer frequencies are detectable. This is still a very young and promising field of stellar astronomy, with many interesting problems to study.

The asteroseismic community, over the next few years, will be provided with unprecedented space-based data. Satellite instruments like MOST and CoRoT have already been operating for several years, and the recently launched Kepler mission promises outstanding data. A less expensive but very flexible ground-based observing project, SONG, will likely become operational in the next 3-5 years as well.

At NMSU we have both photometric and spectroscopic observing opportunities at Apache Point Observatory. We are involved in Kepler projects for data analysis and follow-up ground observations of various target stars.

We have ongoing collaborations with Joyce Guzik (LANL), Markus Roth (Kiepenheuer Institute), J. Christensen Dalsgaard (Aarhus University, Denmark), Travis Metcalfe (HAO), Orlagh Creevey (IAS, Spain).

A few nice articles about asteroseismology are the following:

Gamma-ray bursts


Gamma-ray bursts (GRBs) are among the most energetic events in the universe. Explaining their energy output has been a formidable challenge. Theorists have responded by constructing highly collimated models, the most prominent of which is called the fireball model. An unescapable consequence of this model is that the number of orphan afterglows (afterglows not associated with prompt gamma-ray emission) must be substantially larger than the number of detected GRBs.

We use Sloan Digital Sky Survey (SDSS-II) data to search for these orphan afterglows. The widely used fire-ball model of GRBs predicts that about 22 orphan afterglows should be detected in this study. This value is higher by over a factor ten when compared to past or current studies. Therefore, this effort provides a strong test of the fire-ball model. Future studies will reach a fainter limiting magnitude than this study, but their temporal coverage will make the connection between their newly discovered transients and afterglows problematical. If no orphan afterglows are found in this investigation, the fire-ball model will require severe modification or a new energy mechanism must be sought to account for the GRB emission.

The SDSS-II data provides an exceedingly good match to the demands of this type of effort. It provides the means to discover transients, but also allows measurement of their decay light curves, color evolution, and spectral energy distributions. These latter quantities are essential in connecting transients to orphan afterglows.