Spectroscopy Analysis

During our Foundations of Science class on March 31, we will be producing reduced spectra. For this we will open each spectrum using a program called “RSPEC” and then within the program is the capability for opening image files and setting the width of the spectrum, and calibrating the spectrum using some known lines. This post is to help with this process, by providing a set of line lists, and comparison spectra for use.

Some of the main features you will be finding within the spectra are standard parts of the MK spectral classification system. The temperature and luminosity of stars are often plotted on what is known as an “HR Diagram.” You can explore how the temperature and radius of the star affect the locations on the HR diagram, and other aspects of spectral typing at the site: http://astro.unl.edu/naap/hr/hr_background1.html and http://astro.unl.edu/naap/hr/animations/hr.html.

With our spectra, we will open them with RSPEC with the lower left corner dialog (use “Image File” and select the image, after downloading the .jpg from the previous post). Then you will need to define the width of the spectrum using the yellow box on the side to just select the spectrum. This will produce a nice graph of wavelength and intensity for you to view. If you “calibrate” the spectrum by identifying a pair of pixel/wavelength locations (by comparing with other similar stars), then you will have a wonderful wavelength calibrated spectrum!  Below are some useful guides for identifying lines within your spectra.

List of 300 brightest stars is at http://www.atlasoftheuniverse.com/stars.html.

Some useful guides for spectral classification are found at these links:

http://www.skyandtelescope.com/astronomy-equipment/the-spectral-types-of-stars/

http://www.atnf.csiro.au/outreach/education/senior/astrophysics/spectral_class.html

http://www.astro.virginia.edu/class/majewski/astr551/lectures/LECTURE2/lec2b.html

http://skyserver.sdss.org/dr5/en/proj/basic/spectraltypes/lines.asp

A wonderful guide to astronomical spectroscopy from Steve Majewski (a U of C graduate school mate of mine!) can be found at:

https://www.astro.virginia.edu/class/majewski/astr313/lectures/spectroscopy/spec.html

Line lists and good images of standard spectral classifications are found at:

http://casswww.ucsd.edu/archive/public/tutorial/images/O-Gspect.gif

http://casswww.ucsd.edu/archive/public/tutorial/images/G-Mspect.gif

Within hot stars (O and B stars) the Hydrogen lines are very strong. Here are their wavelengths! In the second table are some key wavelengths of lines in cooler stars – the H and K lines are from the element CaII (or Ca+) and are very strong in solar-type stars, as are the G lines for which the sun’s spectral type is named.

hydrogen.lines

screenshot_1622

 

Here are some images for comparing with your spectra:

comparison.spectra2

comparison.spectra1

These spectra when plotted look like this:

screenshot_1623

A great blog post with a LOT of plots of stellar spectra (with labelled features) can be found at http://www.galaxyzooforum.org/index.php?topic=279364.0