Version 1.0 PAGE 7 When you have had a look at the Help function, close all the help windows and proceed to log in to the program as described on the following page. Part II  Entering Student Accounting Information Position the cursor over the LOG IN... on the menu bar at the top of the logo screen and click the mouse button once to activate the Student Accounting screen. Enter your name (first and last), and those of your lab partners.  Do not use punctuation marks.  Press tab after each name is entered, or click in each student block to enter the next name.  Enter the Laboratory Table Number or Letter you are seated at for this experiment if it is not already filled in for you. You can change and edit your entries by clicking in the appropriate field and making your changes.  When all the information has been entered to your satisfaction, click OK to continue, and click yes when you are asked if you are finished logging in.  The opening screen of the Spectral Classification lab will then appear. Part III  Spectral Classification Of Main-Sequence Stars Purpose To become familiar with the appearance of the spectra of main sequence stars.  To learn how to classify the spectra of main sequence stars by comparing a spectrum with an atlas of spectra of  selected standard stars. Method You will examine the digital spectra of 25 unknown stars, determine the spectral type of each star, and record your results along with the reason for making each classification. The spectra can be compared visually and digitally (point by point) with an representative atlas of 13 standard spectra, and by looking at the relative strengths of characteristic absorption lines, you will be able to estimate the spectral type of unknown stars to about a tenth of a spectral class, even if they lie between spectral types of these stars given in the atlas. Procedure 1.  Select the CLASSIFY SPECTRA function from the RUN  pull-down menu by clicking on the RUN option and dragging down to the CLASSIFY SPECTRA choice (this is a procedure you will use frequently to access items and make menu choices).  Answer no to any questions the computer may ask at this time about stored spectra (later you may want to examine these spectra, but not now). You are now in the classification tool.  (See FIGURE 2 on the following page.)  The screen that you see shows three panels, one above another with some control buttons at the right and a menu bar at the top.  The center panel will be used to display the spectrum of an unknown star, and the top and bottom panels will show you spectra of standard stars which can be compared with the unknown.  Let us now run through the features of the classification tool by classifying the first of the 25 unknown spectra provided for practice. 2.  Call up the spectra of a practice unknown star by dragging down the LOAD pull-down menu.  You will see 3 choices:  Unknown Spectrum, Atlas of Standard Spectra, and Spectral Line Table.  Choose Unknown Spectrum  by dragging the mouse cursor to the right as indicated by the arrow on that choice, and then selecting Program List.  A window will appear displaying a list of practice stars by name. Highlight the first star on the list — HD124320 — by dragging the mouse (it should be highlighted already) and then click on the OK button.  You will see the spectrum of HD 124320 displayed in the center panel of the classification screen. Look at the spectrum carefully.  Note that what you are seeing is a graph of intensity versus wavelength. The spectrum spans a range from 3900 Å to 4500 Å, and the intensity can range from 0 (no light) to 1.0 (maximum light).