|
Harvard University
Astronomy Lab and Clay Telescope
|
|
Day Labs | Evening Labs | Cloudy Day Labs | MaximDL Help
Spectra of Betelgeuse and Rigel
The spectrum of a star can give us a lot of information about the star, including information about its composition and its temperature. In this lab, you will take the spectrum of two different stars and identify their spectral type. Stars are divided into groups (O, B, A, F, G, K, M) from hottest to coolest, from about 40,000K - 2,000K. A popular mnemonic to remember the spectral sequence is "Oh, be a fine girl and kiss me!". These groups are then further subdivided from (0-9) where the B0 would be the hottest stars in the subclass and B9 would be the cooler.
Procedure:
- Let's first get the spectrograph setup. Click here if you need further instructions.
- Now that we are setup, let's slew the telescope to Betelgeuse. Click here for detailed instructions on how to align Betelgeuse on the slit and take a spectrum.
- Immediately after you take the spectrum of Betelgeuse, you need to take calibration spectra. We have a Mercury-Argon light source that emits light at certain discrete wavelengths. We will use this calibration spectrum to convert our object spectrum from pixels to wavelengths.
- Now, let's repeat the process to take a spectrum of Rigel and a similar calibration spectrum.
Reductions/Analysis:
- Before we can analysis our spectra, we need to convert the pixels to wavelengths so we can determine what lines we observed. The following link will guide you through calculating a wavelength solution for each spectrum.
- Now that we have a wavelength solution, we can begin to dive into the analysis of what we are seeing in each of these very different spectrums.
- It is good to note that different stars have different spectral features and this is what distinguishes them from each other. In general, hotter stars tend to have stronger H and He lines while cooler stars are full of metal rich lines. Figure 17-11 in your book is a good visual of what prominent lines you can expect to see in different stars.
- Name as many lines as you can and give your best estimate of what spectral type of star Betelgeuse and Rigel are based on your observations.