|
Michael Caligiuri's Spectroscopy
Last Update: 10/19/08 |
 |
|
Be Star Basics: A Be star is a main sequence B-type star with prominent emission lines of hydrogen in its spectrum. A Be star is a normal B star in which sudden events eject matter into a thin dense equatorial disk that emits hydrogen. The main part of the star is characterized by a high-velocity polar wind that can be observed as a blue- or red-shifted spectrum. What makes the study of Be stars so interesting is the periodic variability in the emission line profile. Emission lines of Be stars are usually double peaked. Interestingly, the shape of this twin peak profile can signal a Doppler shift in the disk of gas surrounding the star. Longer-term variations (on the order of years or months) in the intensity and shape of the emission line can indicate change in disk structure. The study of very short-term variability is far more feasible to the amateur. Oudmaijer and Drew (1997) demonstrated rapid variability in some Be stars with time scales on the order of minutes. Very short-term variability in the emission line profile is thought to be due to changes in the photosphere or immediate circumstellar environment rather than disk variation (Porter and Rivinius, 2003). Why Image Spectra from Be Stars? Providing reliable systematic data on variability of the stellar properties of hot young emission stars can enhance the understanding of stellar physics. Characterizing this variability can help astronomers understand the origin of these emissions (e.g. photospheric, circumstellar environment, or disk dynamics). Thus, setting out to characterise the variability of Be stars appears to be a worthwhile exercise. There are many challenges to obtaining reliable accurate data on Be star dynamics and meeting these challenges can be satisfying. Unlike color or narrowband CCD imaging of deep sky objects, which can take hours of work under steady skies, useful data from stellar spectroscopy can be acquired in a matter of minutes under average skies. Goals: At least two goals are attainable with a modest backyard spectrographic telescope: 1) cataloging Be stars and their short-term profile variability; and 2) reconciling observations with current theories and models. For example, previous work has shown that 90% of early Be stars (B1-B5) show significant short-term variability, while late Be stars are relatively stable (Balona et al., 1992). |
|
Equipment |
Spectra of Be Stars |
Emission Line Profile Variability |
