A rainbow of potential—capturing and analyzing the spectra of variable stars to understand their physical properties and processes.
What We Do
The AAVSO Spectroscopy Special Interest Group promotes and advances astronomical spectroscopy for observers at all skill levels. We help members produce high‑quality spectra of variable stars, engage in observing programs and campaigns, and share our knowledge with each other. Our community ranges from beginners to advanced spectroscopists—all working together to acquire spectra that have real scientific value. We also seek to develop our skills in interpreting the observed spectral features to expand our knowledge of the physical nature of variable stars.
How We Do It
Observers collect spectra using a monochrome CCD or CMOS detector and spectrograph attached to a telescope and then process these spectra using widely available software to produce a fully calibrated spectrum that can be made available to others for research and publication. Calibration steps include dark and flat images to correct noise and image field variations and calibration lamp images to transform the image pixel values to wavelength. Once reduced, these spectra are submitted to AVSpec, our repository of variable star spectra, where they are vetted and archived.Our members have access to instructional materials and tools to help them develop their skills and knowledge, including the AAVSO Spectroscopy Manual {Link}. We conduct a regular monthly Zoom meeting which includes instructional presentations, updates on member observing programs, and general discussion in which we share our knowledge, improve our skills, and share our scientific insights.
Is It Right for Me?
Level: Moderate to Advanced. Astronomical spectroscopy is a rewarding endeavor for those who wish to contribute to science in a meaningful way but may not be for everyone as it involves a level of technical skill and personal commitment to achieve useful results. Many individuals start off in astronomical spectroscopy using relatively inexpensive and technically simpler grating filters. This allows the user to “test the waters” to see if spectroscopy is right for them. Later they typically upgrade to more advanced equipment and further develop their knowledge and skills. This special interest group welcomes and supports all levels of observers, from beginners to those more advanced.
Equipment: A telescope with a spectrograph or diffraction grating on a stable mount is required. For many projects, a small to mid-sized aperture telescope is fine but more advanced work, such as high-resolution line profiles, benefits from larger apertures. While a calibration lamp is not required for an observer using a diffraction grating, it is necessary for other spectrograph types. For many spectrographs, a method for autoguiding is required as well as a capability to adjust the orientation of the slit to the vertical.
Observing Requirements: Observers often monitor targets over months or years. Indeed, long-term spectral monitoring is one of the most valuable contributions since many variable stars lack extensive spectroscopy. Some targets, such as binary stars, pulsators, cataclysmic variables, and flare stars, require more frequent observations to detect rapid variations—often on a time scale of minutes to hours. While some observers do it on their own, others will team up with others geographically dispersed to provide observations not limited by daylight or cloud cover at a given location. Some observers choose to participate in structured campaigns typically organized and conducted by professional researchers. For all the above, the most important requirement is a passion for contributing to the science of variable stars and the commitment to produce spectra of scientific value.
Additional Considerations: To be successful in astronomical spectroscopy you should be comfortable with data reduction workflows including spectral extraction, wavelength calibration and normalization). Submissions into AVSpec require metadata (equipment, site, etc.) to be provided. Participation is often collaborative: working with other spectroscopists, discussing physical interpretation of spectra, and contributing to long-term campaigns are core to the SIG.