**Log In** To Log In to this CLEA Exercise: 1) Select "File"->"Log In..." from the main menu. The login dialog will appear. 2) Enter the appropriate name(s) in the fields provided. 3) The laboratory table number may already be set. If it is not, or is incorrect, enter the correct table number. 4) Press "OK". The selections on the file menu that control the exercise will be activated, while the "Log In..." selection will be deactivated. (You cannot return to the login dialog after you have completed it.) The information entered on the login dialog is used to generate names for data files, and will appear on data and printouts that are produced by the exercise. If you have entered no information, a box will warn you of this when you press "OK". If you select "Cancel" on the warning box you will return to the login dialog. If you select "OK" on the warning box, the program will continue. In this case, generated data and files will be identified as "NoLog". **Access Telescope Window** In order to make photometric measurements of stars, you must access the telescope window. Select "File"->"Run" from the main menu and the telescope window will appear, showing the telescope control panel. There may be some delay at this point as portions of the program are initialized. Do not attempt to press buttons or make menu selections until the message informing you that you have control of a telescope has appeared. It is not necessary to access the telescope window in order to load and process data that has been saved previously. See Help topic "Load Data" under "Data Operations" for details. **Telescope Controls** The following buttons are used to operate the telescope. They are located on the left side of the telescope control panel. "Dome" - Press this button to open and close the dome. This is the only button that is enabled when the dome is closed. The dome is closed when a telescope is first accessed, and closes automatically when the user elects to change telescopes. (See Help topic "Change Telescope"). "Tracking" - This button turns on the sidereal tracking that enables the telescope to remain pointed at a particular spot on the sky as the Earth turns. When tracking is off, the stars will drift through the telescope field. Tracking is off when a telescope is first accessed. The other telescope controls are enabled only when tracking is on. "Slew Rate" - This button sets the rate at which the telescope moves when a slew button (N,S,E,W) is pressed. The rate doubles each time the slew rate button is pressed, up to a maximum rate of 16. The rate resets to 1 if the slew rate button is pressed when the rate is 16. Slew Buttons ("N","S","E","W") - The slew buttons are used to move the telescope to point to a particular spot (direction) in the sky. To move the telescope, press and hold the appropriate button. The telescope will slew at a speed determined by the slew rate setting. Release the button to stop the slew. For long slews, the button will stay down if you slide the cursor off of it before releasing the mouse button. In this case, stop the slew by pressing and releasing the mouse button with the cursor over any slew button. If you slew some distance from the original field center, you may encounter delays as the sky display is updated, which may require loading a new field file. These delays can be fairly lengthy on slower machines. The wait cursor (hour glass) will be displayed during these pauses. Do not attempt to press buttons or make menu selections if you see the hour glass cursor. "Change View" - The telescope has two magnifications (or field sizes) available. The "Finder" field is 2 1/2 degrees on a side, and is used for locating particular stars and other objects. The "Instrument" field is 15 arc minutes on a side, and is used to center the object in the photometer aperture, which appears in the center of the photometer field. (The small square in the center of the finder field shows the relative size and location of the photometer field.) The photometer is enabled for use only when the photometer field is displayed. There may be some delay as the view is changed on slower machines. Do not attempt to press buttons or make menu selections when the "Changing View" message is displayed and/or the wait cursor (hour glass) is visible. "Set Coordinates" - Pressing this button activates a dialog which allows the pointing coordinates for the telescope to be entered directly. This is generally faster than using the slew buttons to move the telescope from object to object, unless the objects are very near each other in the sky. Some fine adjustments with the slew buttons may be necessary to center the object in the photometer slit after setting the coordinates. **Request Telescope Time** Access to the larger telescopes may be restricted. You may request time on telescopes that are not currently available to you (the selections are grayed). To request time, select "Telescope"->"Request Time"-> (telescope selection) from the main menu. If your request is granted: You will be informed of the number of uses you have been given (the number of stars you can measure with the restricted telescope). You may then access the telescope in the normal manner (see Help topic "Access Telescopes"), but a tally will be kept of your uses, and you will be informed when you have used up your allotment. You may then request more time if you wish. If your request is not granted: You will be informed that you may reapply after a certain number of minutes. Until that time has passed you will not be able to request time on that particular telescope. When the time has elapsed a message will appear informing you that you may reapply. You may do anything else you wish, including requesting and/or using other telescopes, while waiting to reapply. **Access Telescopes** To change telescopes, select "Telescope" from the main menu, and then make your selection from the "Access" list that appears. If a particular selection is grayed, you must request and be awarded time on that particular telescope in order to use it (see Help topic "Request Telescope Time"). When you have selected a telescope to access, the dome on the current telescope will close, and there will be a pause while the system attempts to access the telescope you have selected. If the selected telescope is available, you will be given control. Note that you must again open the dome and turn on the tracking before you can proceed to make photometric measurements with the new telescope. If the telescope you select is restricted and you have been granted a limited number of uses, you will be informed of your remaining uses before the telescope is accessed. **Change Star Field** The "Field..." selection on the main menu accesses a dialog from which you can select other star fields (if your exercise involves multiple fields). Note that the field cannot be changed unless the dome is open and the tracking drive is on. There will be some delay as the new field is accessed. Do not attempt to press buttons or make menu selections when a "Wait" message is displayed on the screen and/or the wait cursor (hour glass) has replaced the normal (arrow) cursor. **Access Photometer Window** You can access the photometer window only when the instrument (15 arc minute) field appears on the monitor. After you have carefully centered the object in the photometer aperture using the slew buttons, press the "Take Reading" button and the photometer window will appear. The photometer window has its own menu to control taking and saving photometric data of the object in the slit. Note that some selections from the main menu remain available when the photometer window is displayed. **Set Filter** To change the active filter, press the button labeled "Filter" on the photometer control panel. The color-coded indicator will cycle through the available selections. Note that you must take a sky reading with each filter that you plan to use. (See Help topic "Take Sky Readings".) **Set Integration Seconds** Press the button labeled "Seconds" on the photometer control panel to set the duration of each integration (the length of time that the photon counts accumulate when a reading is taken). The selections range from 0.1 second to 100 seconds by factors of 10. (See Help topics "Set Number of Integrations" and "Take Photometric Readings".) **Set Number of Integrations** Press the button labeled "Integrations" on the photometer control panel to set the number of integrations that make up a complete reading. The selections range from 1 to 5. (See Help topics "Set Integration Seconds" and "Take Photometric Readings".) **Take Sky Readings** You must take a sky reading through each filter before you can measure the brightness of stars through that filter. One set of sky readings is sufficient as long as you continue to use the same telescope. If you change telescopes you must take a new set of sky readings, even if you are returning to a telescope you have used previously. Take sky readings as follows: 1) Change to the "Instrument" view and position the telescope so that there is no star in or immediately adjacent to the red aperture circle. 2) Press "Take Reading" to access the photometer controls. If the telescope is properly positioned, the box labeled "Object" should say "Sky". 3) Set the filter to the desired color. (If a sky reading has been taken with a particular filter, the box labeled "Mean Sky" will contain the mean sky counts per second for that filter. Otherwise, the entry will indicate "NO SKY!".) 4) Set the integration time to 10 seconds and the number of integrations to 5. 5) Press "Start Count" and wait for the readings to appear. You will see the raw counts as each integration is completed. When the reading is complete the mean sky count in that color will appear in the box labeled "Mean Sky". 6) Repeat for each filter you will be using. 7) Select "Record Readings" from the menu to save the sky readings. (You may not need to do this if the program is set to automatically compute the stellar magnitudes for you. If you are computing the magnitudes yourself from the photon counts you MUST record the sky readings.) (See other Help topics under "Taking Data".) **Take Photometric Readings** You must take sky readings before you can take photometric measurements of stars. When you have completed the sky measurements, take photometric readings of stars as follows: 1) Roughly center the star in the red square on the "Finder" view. Change to the "Instrument" view and accurately center the star in the red aperture circle. (If the star has a nearby companion, be sure to keep the companion outside of the aperture circle. In this case the star you are measuring may not be well centered.) 2) Press "Take Reading" to access the photometer controls. The box labeled "Object" may contain some identification of the star you are measuring. It should not say "Sky". 3) Set the filter to the desired color. (If the "Mean Sky" box indicates "NO SKY!" you cannot take a measurement in that color. Return to the telescope controls, move the star out of the red aperture circle, then return to the photometer controls ("Take Reading") and read the sky.) 4) Set the desired integration time and number of integrations. (Some trial & error may be required here - see Step 5 below.) 5) Press "Start Count" and wait for the readings to appear. You will see the raw counts as each integration is completed. When the reading is complete, the mean counts per second, signal to noise ratio, and computed magnitude will appear in the labeled boxes. For greatest accuracy, your readings should be reflect signal to noise ratios of 100 or more. If you get a S/N of less than this, you should increase the integration time, number of integrations, or both, and take a new reading (don't record the old one). (If your S/N is REALLY low, you may need to use a larger telescope to get accurate photometry.) If your S/N is very high (> ~500), you may want to decrease your integration time and/or number of integrations on future stars of about the same magnitude to save time. 6) Repeat readings for each filter you are using. Note that most stars appear fainter in the blue (B), and fainter yet in the ultraviolet (U), than in the visual (V). This is due to the combined effects of stellar temperature and interstellar reddening. You may have to increase the integration time and number of integrations - always check the signal to noise ratio. 7) Select "Record Readings" from the menu to save the photometric readings. IF YOU RETURN TO THE MAIN DISPLAY WITHOUT RECORDING THE READINGS YOU WILL LOOSE THEM AND HAVE TO REPEAT THE MEASUREMENTS! (See other Help topics under "Taking Data".) **Record Readings** To record photometric measurements you have taken, select "Record Readings" from the Photometer Window menu. A dialog box will appear with information about the object and telescope, and the readings you have taken. You may enter any notes or comments you want to record in the box labeled "Remarks". Press "OK" to record all the data. Normally, you should not record the data for each color (filter) as you take it. Wait until you have measured the star (or sky) in all desired colors. (Each time you record data you create a separate record, even if the record contains data for only one color. You might need to do this only if you require very accurate timing for variability studies.) Note that the records are time-tagged with the Julian date to 6 decimal places (about 0.1 second). This is the time the last measurement you took (regardless of the filter) was completed. NOTE: Recording your readings in this manner saves them internally for additional processing, but does NOT write them to a file. To do that, you must return to the main display and select "File"-> "Data"->"Save" from the main menu. (See Help topics under "Data Operations".) **Return to Telescope Window** You should complete your photometric measurements of the star in all required colors (filters) and record your measurements before returning to the telescope window. Select "Ok" to close the "Record Readings" dialog (if you have not already done so), then select "Return" from the photometer menu. You will be warned and given a chance to cancel the return if you have not recorded all the data you have taken. When you return to the telescope window your recorded data for the star you have been working with is placed in a list in memory, but is not saved to a file. (See Help topics under "Data Operations".) **Load Data** You can load a file of data that was previously created and saved using this program. This feature allows you to: o Accumulate data over several sessions as part of a project. You can delay computing and/or plotting the final results until all stars have been measured. o Recover from a system crash, at least to the point at which data was last saved. o Use a spreadsheet program or other means to calculate results and plot graphs. To load a file, select "File"->"Data"->"Load" from the main menu, then locate or enter the file name on the "File Open" dialog, and press "OK". Before you attempt this you should be aware of the following: o When a file is loaded, it replaces any data currently present. You will be warned to save first if you attempt to load over existing data. o Any data generated after a file load is added to the loaded data in memory. You will have to save it to keep the complete set. o The format of the file to be loaded must be same as written (comma delimited text), except that string fields need not be enclosed in double quotes ("). (See other Help topics under "Data Operations.) **Review Data** To review data you have already generated or loaded, select "File"-> "Data"->"Review..." from the main menu. A list entitled "Review Photometric Data" will appear, from which you can use the mouse to select individual records. Once you have selected a record, you may either edit it (press "Edit") or delete it (press "Delete"). If you select "Edit", the "Photometric Data" dialog will appear. This is the same dialog that appears during the data-taking process. When you have finished editing a record, press "OK" to return to the "Review Photometric Data" list. When you have finished reviewing all records, press "Done" to close the "Review Photometric Data" list. A list of the data in each record appears on the "Review Measurements" display. Fields shown (separated by vertical bars) include the following: the object ID, the time tag (Julian Date minus 2,450,000.0), the U, B, and V values, the data type (1=mean counts, 2=computed magnitudes), the telescope (1=16", 2=1M, 3=4M), and the remarks field. **Save Data** To save all of your current data to a file, select "File"->"Data"-> "Save..." from the main menu. The software creates a file name for the saved data, and asks you to verify or change it. (If part of your data originated from an existing file that you loaded, the name of that file is used for the save file. If no previous file exists, the program generates a file name from the first login name and the qualifier ".csv".) If the file name you verify or provide already exists, you are given the option of overwriting the existing file or providing a different file name. Saved data can be reloaded at a later time (see Help topic "Load Data"), and can be analyzed and modified off-line, either with a text editor or a spreadsheet program (see topic "Use Spreadsheet Program"), as long as the original format is preserved. The saved data is written in text form, one record per line, with commas separating the values (comma delimited text). String fields (in this case, the ID and Remarks fields) and any empty fields are enclosed in double quotes ("). This format can be read and parsed into individual columns by most spreadsheet programs. (But not all can write it back in the same format - see "Use Spreadsheet Program"). Header information and column titles are also written in this file as string fields and will appear on a resulting spreadsheet. You should save your data often, as a protection against system crashes. You MUST save your data before you can print it (see Help topic "Print Data"). **Print Data** To print the exercise data, select "File"->"Data"->"Print" from the main menu. All records currently in memory are printed, along with identifying header information and column labels. Printing is accomplished via Windows, employing the Windows Print Manager if so specified in the Windows setup. Output is directed to the default printer, also specified in the Windows setup. NOTE: To avoid any possiblity of data loss, the software will execute the print only if the current data has been saved (see Help topic "Save Data"). As an alternative, saved data can be read into a spreadsheet program and printed from there (see Help topic "Use Spreadsheet Program"). **Use Spreadsheet Program** Computation of magnitudes (if required) and colors, as well as preparing color-magnitude and color-color diagrams, may be facilitated by making use of a spreadsheet program. If a spreadsheet program is available for your use, the "SpreadSheet" selection on the "File" menu will be dark black. (If this entry is grey, no spreadsheet program is available.) The following outlines the steps to follow in using a spreadsheet: o Take and record photometric measurements for all required stars. o Save your data to a file ("File"->"Data"->"Save"). You will need to make note of the file name. o Access the spreadsheet ("File"->"SpreadSheet"). o Load your data file into the spreadsheet (choose file type "Text" - qualifier .CSV). Your instructor will assist you with this and other spreadsheet activities. o If you are working with mean count data, use the spreadsheet to compute magnitudes. You will need to utilize the sky counts, the telescope factors, and the measurements of standard stars (stars with known magnitudes and colors). o Use the spreadsheet to compute the color indices B-V and U-B, in columns. o Use the spreadsheet program to generate required plots, such as V vs B-V and perhaps U-B vs B-V. You may have some difficulty getting the graphs to adhere to the astronomical convention of magnitude or color index values increasing downward along the Y-axis. With some plotting packages the only solution is to plot the negative of the correct value. o Print your completed graphs. In some older spreadsheet programs this may require saving the graph and running a second program to print it. o If so instructed, write the completed spreadsheet back out as a comma delimited file (in Excel, choose "File"->"Save As..." type CSV). o Exit the spreadsheet (in Excel, choose "File"->"Exit").