Stellar Spectroscopy 
Stellar Spectroscopy is actually a method of classifying stars based on their spectra. The spectra, which reveals the chemical composition of the star, helps to understand where the star is on its evolutionary journey on the Hertzsprung-Russell [H-R] Diagram. All stars start as Main Sequence stars. The Main Sequence is a line on the H-R diagram running roughly from the lower right to the upper left on the diagram. Only stars that are fusing hydrogen to helium are located in the main sequence. As stars exhaust their supply of hydrogen, they leave the main sequence for one of the branched areas on the diagram.
Click on the diagram below for an enlarged view of the H-R
diagram
Main Stellar Types
| Type | Color | Approximate Surface Temperature | Main Characteristics | Examples |
|---|---|---|---|---|
| O | Blue | > 25,000 K | Singly ionized helium lines either in emission or absorption. Strong ultraviolet continuum. | 10 Lacertra |
| B | Blue | 11,000 - 25,000 | Neutral helium lines in absorption. | Rigel Spica |
| A | Blue | 7,500 - 11,000 | Hydrogen lines at maximum strength for A0 stars, decreasing thereafter. | Sirius Vega |
| F | Blue to White | 6,000 - 7,500 | Metallic lines become noticeable. | Canopus Procyon |
| G | White to Yellow | 5,000 - 6,000 | Solar-type spectra. Absorption lines of neutral metallic atoms and ions (e.g. once-ionized calcium) grow in strength. | Sun Capella |
| K | Orange to Red | 3,500 - 5,000 | Metallic lines dominate. Weak blue continuum. | Arcturus Aldebaran |
| M | Red | < 3,500 | Molecular bands of titanium oxide noticeable. | Betelgeuse Antares |
There are also several subtypes for star classification which are too involved to mention here. More information can be found here.
Equipment:
I am currently using an grating type spectrometer, named the SGS [Self Guiding Spectrometer] , which is manufactured by SBIG. This is a single beam spectrometer which uses a CCD camera as a detector. I have made several modifications to the equipment which are listed below. I wrote a paper on the Classification of the Nova V475 Sct 04 that makes good use of the SGS. The paper can be downloaded here.
Spectra:
Click on the picture to see the full size graph.
Regulus is a class B7V star [Strong Helium lines and a longer toe into the UV
spectrum].
Arcturus is a K2IIIp [More to the red end of the spectrum and with a spectrum
dominated by metallic lines]
Izar is a class A0 star [Slightly more to the red than the B stars]. 
The Nova V475 Sct on October 1, 2003
The Hydrogen alpha line is clearly visible at 6562 Å as are the Fe lines at 4900
to 5400 Å
More information on this nova is available at the Nova and Supernova page.
Handy Things to Know
For those of you using the ST-10XME camera along with the SGS, here is a
third order polynomial correction factor that I have worked up for the QE
[Quantum Efficiency] of the KAF-3200XME chip:
QE= ((-6E-06 * A2) + (0.0761 * A) - (155.25)) * 0.01
Equipment Modifications:
Those Darn Cover Screws!: Removing the cover screws something that is done a lot and is very time consuming. To make the process easier, I purchased some 4-40 x 1/4" plastic headed thumb screws from McMaster-Carr. www.mcmaster.com
The thumb screws are Part Number: 1185A221
Putting the object
on the chip: One big problem with the SGS spectrometer is that
there is no
provision to use an eyepiece for centering the program object on the guider
chip. The optical inlet to the spectrometer is a
rather elaborate
threaded ring which attaches to the visual back of the typical SCT scope.
I removed this ring and inserted a T-adapter [the SGS chassis is already threaded
for a T-adapter] which is mated to a 2" Meade flip-mirror. Because the actual inlet aperture
of the SGS is so small [~1/2"] there is no problem with vignetting of the
light cone as it enters the instrument. The image to the right shows the flip
mirror between the scope back and the SGS.
Grating Lock-Down: Another
problem with the SGS is the rotary carousel which is used for the low resolution
and high resolution gratings. The carousel rotates to provide the
particular grating which is needed for the program application. This is a
handy option for the SGS, but the method used to lock the carousel in place [two
spring loaded detents] is not sufficient to keep the carousel from
rotating while in use. Even 
a change of a few arc seconds in the rotation
of the carousel causes the calibration to drift. Slewing the scope from
one position to the next moves the carousel sufficiently to require a new
calibration spectra to be taken. This is a problem mentioned by Alan
Holmes in the operating manual for the instrument. I solved this problem
by replacing the outboard spring loaded detent set screw with a custom sharp pointed set screw
which is accessible from outside of the SGS case. See image above. The set screw positively
locks the carousel in place and is loosened when moving from one grating to the
other. The inboard spring loaded detent remains and locates the grating before it is
locked down.
Camera Attachment: The attachment of the camera to
the SGS and the
subsequent alignment of the camera to the SGS is a rather tedious
procedure. I made the attachment easier by machining a new clamping ring
screw so that it extends outside of the SGS case and does not necessitate
removing the instrument cover from the case to access the camera clamp.
As supplied, the SGS requires that the normal camera adapter plate be removed and replaced with a special SGS adapter plate each time that the camera is to be used with the spectrometer. This is also a tedious procedure. It also requires that the camera be realigned to the SGS before each use. I machined a new nosepiece for the camera which on one end has a ring to fit in the normal camera adapter plate and on the other end has a short tube to fit into the SGS clamp ring. This adapter stays permanently attached to the SGS and attaches to the standard camera adapter plate via the normal three set screws supplied with the camera. I put a mark on the machined adapter and the camera adapter plate so that they may be aligned during the assembly process. This alignment is close enough that a final tweaking can take place on the scope via the extended clamp ring screw mentioned earlier.
Calibration Light Sources:
The SGS has an opal diffuser on the outside of the
case where a calibration
light source can be placed for the purposes of taking a calibration frame.
There is, however, no provision for attaching the light source to the diffuser.
[It is mentioned in the
operating manual to "tape" the calibration source to the case] I have machined a small metal adapter which will hold
two - three neon bulb sized calibration lamp sources in close contact with the opal diffuser and also
block out any extraneous light. It attaches to the case by means of the
screw which was originally used to hold the light shield over the diffuser.
Remote
Control of Slit Illumination: The SGS uses an LED to illuminate the
internal
slit so that the program object may be centered on the slit. The on-off switch
and intensity control for this LED are mounted on the body of the SGS.
This is very inconvenient in that touching the controls makes the unit vibrate. It also necessitates that the operator move from the computer
console over to the telescope [which may be several feet away or in a different room altogether]. To help solve this problem, I removed the 9 volt
battery, the Power Indicator LED, the Power Switch and the Intensity control
from the SGS, plugged the holes with nylon bolts and remounted the controls in a small plastic 'Radio Shack' project
box. Only two wires are required to re-connect these controls to the LED
inside of the SGS. These are attached back to the SGS body via a 1/8"
phone jack. [You can also see the heads of those plastic headed 4-40
thumb screws in these pictures]