Exercise in spectral classification

Today, you will do a little spectral classification. In the old days, this was done by comparing by eye the tiny photographic spectrum of a star to a chart of template spectra; very tedious, and somewhat qualitative. These days, fortunately, you can use a nice software package that makes it relatively simple.

The Contemporary Laboratory Exercises in Astronomy (or CLEA for short) project has created several nice projects you can do on a computer. One of them involves the classification of stellar spectra. Let's do that today.

Part I: classify stars

Log into the computer and find the "CLEA" entry under all programs
Choose the Stellar Spectra item from the list of CLEA projects
When the program starts, choose File -> Log in. Enter any name you like -- we won't be using the automatic recording facility
Choose File -> Run -> Classify Spectra This should cause a new window to appear.
In the new window, choose File -> Atlas of standard spectra , then pick "Main Sequence". A new, smaller window will pop up. Move it to the side. You can move up and down through the list of standard spectra with the "Up" and "Down" buttons in the "Classify Spectra" window.
In the "Classify Spectra" window, choose File -> Spectral line table . Again, a new, smaller window will appear. Drag it to the side. This window shows a list of lines produced by specific elements and ions. Double-click on a line in the table, and the line will be highlighted in the spectrum. Double-click on a feature in the spectrum, and the corresponding line and element will be highlighted in the table.
In the "Classify Spectra" window, choose File -> Unknown Spectrum -> Program List . This will load a list of stars which you must classify.
In the "Classify Spectra" window, choose File -> Preferences -> Display -> Comb. (Photo & Trace) . Play wih the "Display" settings to see the different ways that you can present spectra. I suspect you'll want to return to the default "Intensity Trace" option.

You must go through the list of stars and estimate the spectral class of each one. Fill in the Data Table handout (shown below) with your answers.

Part II: make an HR diagram

Okay, you should have a list of stars and their spectral classifications. In the table below, I show the apparent V-band magnitudes and the measured parallaxes to the stars you have classified. The parallax values are taken from the Hipparcos catalog; each one has an uncertainty of about +/- 1 milliarcsecond.

# name          parallax(mas)   Bmag   Vmag
HD_124320         5.14        8.98   8.84
HD_37767          1.66        9.03   8.93
HD_35619          0.38        8.79   8.66

HD_23733          7.11        8.73   8.41
O_1015                                      ignore -- no information
HD_24189         10.08        8.97   8.46

HD_107399        13.61        9.62   9.00
HD_240344         1.50        9.42   8.97
HD_17647         15.95        9.38   8.68

BD+63_137        66.46       10.28   8.98
HD_66171         21.15        8.82   8.20
HZ_948            4.33        9.29   8.67 

HD_35215          1.22        9.49   9.42
Feige_40          0.73       11.1   11.1
Feige_41          0.30       11.09  11.00

HD_6111          13.77        9.43   8.89
HD_23863          5.98        8.36   8.15
HD_221741         0.47        9.05   8.93

HD_242935         0.41        9.39   9.42
HD_5351          41.45       10.13   9.10
SAO_81292  V    213.0        10.97   9.43

HD_27685         26.96        8.501  7.841
HD_21619          3.97        9.03   8.80
HD_23511          4.00        9.75   9.28

HD_158659         0.20       10.45  10.31

You must use this information to

calculate the absolute V-band magnitude of each star (and, if you wish, the range in absolute magnitude, based on the uncertainty in the parallax)
make an HR diagram for the stars. Place absolute V-band magnitude on the vertical axis, and spectral class on the horizontal axis. You can divide the horizontal axis into 7 pieces, one each for O, B, A, F, G, K, M; try to sub-divide each piece into smaller sections so that you can place each star into its proper subclass.
indicate on your HR diagram the following regions:
- main sequence
- giant branch
- white dwarf area
Note that some of these regions may not contain any of the stars you have classified, so they may be empty
Place a special mark on your diagram for each of the following stars, and tell me what sort of star each one must be:
- star Q1: spectral class G7, apparent mag V=8.8, parallax 20.03 milliarcsec
- star Q2: spectral class B5, apparent mag V=8.5, parallax 434 milliarcsec
- star Q3: spectral class K2, apparent mag V=9.3, parallax 1.84 milliarcsec

Homework for tomorrow's class

If you did not finish all the steps above during the class period, then do them as homework. Bring your HR diagram and all your answers to the questions to class tomorrow.

For more information

The CLEA home page describes the many CLEA experiments, one of which is "The Classification of Stellar Spectra", on which this exercise is based.