While taking data on the stars you need only record their names which can be their right ascension and declination and their B and V magnitudes. U magnitudes are not used in the analysis so please do not take U magnitudes unless you just enjoy doing extra work for no purpose. This data table of names, B, V, and B-V (which you compute via subtraction) will be one of the things you turn in.
This is a big hint, if the Mean Sky box says NO SKY! you have not taken a NO SKY reading yet. You will not get a B or V until you read the sky, that means someplace without an obvious star. You need to read a place with no star so that the light there can be subtracted from what it is when you are on a star. You will not get a Magnitude reading until you read the EMPTY SKY with both the B and V filter. You will then be able to get reading of B and V on stars.
You should also turn in the graph of the zero age main sequence absolute magnitudes versus B-V (on the CLEA & GALAXSee CD-ROM in the Astronomy directory is the file ZAMS.ga3 which is the zero age main sequence using the Vernier Graphic Analysis software); and the graph of your data of apparent V versus B-V (on the CLEA & GALAXSee CD-ROM in the Astronomy directory is the file CLEA_pho.ga3 which is for your data using the Vernier Graphic Analysis software). It is important that both graphs have the same numerical scale on both x and y and that they be printed on the same printer at the same scale since you are going to visually superimpose them on top of each other to get the difference between apparent and absolute magnitude. This feat is very easy to do using the Vernier Graphic Analysis software, but very difficult to do using Excel. If you would like your H-R, Hertzsprung-Russell, diagram to have the bright stars at the top and the dim stars at the bottom like the text you will need to invert the y-axis numbers, as Julia Parker discovered how to do this. (Click on the graph window, Graph Options, Axis Options, Scaling Manual, then make top -6 and bottom 17. Please do this to both graphs so you can compare them.) This distance modulus, m-M, the difference between apparent, m, and absolute magnitude, M, will be use in the formulae to get the distance to the Pleiades cluster in parsecs. d(pc)=10*10^((m-M)/5) . Then take the distance in parsecs and convert it to light years by using the conversion factor 3.26 Light year is equal to 1 parsec. Then compare the distance in light years to that accepted value of 410 light years and this will be your present difference.
Suppose that your distance modulus, m-M was 5, it won't be or at least shouldn't be this. Using the formulae d(pc)=10*10^(5/5)=100 parsecs. 100 parsecs x 3.26 light years/1 parsec = 326 light years. Comparing this to 410 light years for a present difference yields (410-326)/410*100=20.49%.
Suppose that your distance modulus, m-M was 6, it won't be or at least shouldn't be this. Using the formulae d(pc)=10*10^(6/5)=158.49 parsecs. 158.49 parsecs x 3.26 light years/1 parsec = 516.68 light years. Comparing this to 410 light years for a present difference yields (410-516)/410*100=-25.85%.
Your distance modulus from the interpolation of the two graphs
keeping color the same will be something between 5 and 6. Your
percentage differences will be much smaller than my examples of 20.49%
and -25.85%.
Some Adobe Acrobat pdf files of the ZAMS, Zero Age Main Sequence,
calibration curve done with Graphic Analysis 3.11 and converted to pdf
files for you to look at and use.
ZAMS
graph with ZAMS data.
Just
the ZAMS graph.
CLEA
photometry blank graph with blank data table.
CLEA
photometry blank graph.
Graphic Analysis files useful once you have Graphic Analysis
installed on your computer:
ZAMS.ga3
.
CLEA_pho.ga3
.
If you have Excel on your computer and want to use it instead of the
Graphic Analysis programs then the following Excel spreadsheet file
will be very useful.
It has the ZAMS calibration graph already inputted whose data is
on
page 11 of the "Photoelectric Photometry of the Pleiades" and another
graph
set up for you to input your (B-V,V), color versus apparent visual
magnitude,
ordered pairs from the photometry of the stars you have measured.
CLEApho.xls
. You may have to save this file and then open it in Excel.
You will have to print out both graphs on the same printer to the
same scale.
Last changed by Dr. Harold Williams, October 13, 2003.