Using MPO Canopus for Photometry of LONEOS Asteroids

Background

At Lowell Observatory, we made extensive use of MPO Canopus for the Near-Earth Asteroid Photometric Survey (NEAPS). Since NEAPS has come to an end, we have used it to find stellar and cometary lightcurves. We found it to be very useful, and its author, Brian Warner is always gracious in helping us use it. While MPO Canopus is certainly not a requirement for any of our photometric projects, it is the only commercial software for which we have experience. Hence, we can offer some support for those amateurs who use it. If you choose to use another photometric product, you should get support from its author.

Image Requirements

Images, at a minimum, must be in FITS format. Ideally, the header for the FITS file should adhere to the SBIG FITS convention. The SBIG convention defines certain "often used" keywords so that commercial software (notably, MPO Canopus) can reliably access the information in the header. All SBIG cameras produce headers with the expected conventions and many other cameras also use it. If you are active in a LARI photometric project and your camera does not produce SBIG convention headers, we can write some software that will modify the header in the expected way.

Images must be carefully "flattened" so that MPC Software can produce the best possible photometric results. MPO Canopus has procedures that produce the required flattened image. At Lowell, we have our own flatting procedures so we do not use the MPO Canopus procedures. We will provide flattened images so that you do not have to flatten them.

MPO Canopus General Concepts

MPO Canopus uses "photometry sessions" as a general organizational concept. The user normally uses the Windows file system for basic organization of image frames. The LONEOS project was not envisioned as a photometric effort so our image cadence does not match the expectations of MPO Canopus. Canopus prefers images organized by each unique date/object, and it responds well to having a sub-directory for each related set of images. The photometry section of the software allows the user to create a session and "attach" the images in the sub-directory to the new session. The session name is generally the name of the object to be analyzed. There can often be many sessions with the same name, corresponding to set of images obtained on different nights. When MPO Canopus begins its period analysis, it gathers all the sessions of the same name together and allows the user to select any or all of them to be used in the analysis.

LONEOS images and the KBLR project are organized in a slightly different way. We cannot obtain the asteroid's rotational period. We can only obtain accurate absolute photometry for four images in a single night. So we will use "sessions" to identify a set of four asteroid images. For a single set of images, there will be multiple sessions all with the same date and time, each session referencing a different asteroid.

In summary, Canopus expects a group of sessions with the same name should contain information about the same object. Each session normally corresponds to a different night. All (or some of) the sessions can be used to perform the period analysis. The KBLR project must modify this paradigm only slightly so that all photometric information can be found in a single night for a single asteroid with no intent to perform period analysis.

MPO Canopus also keeps a description of your instrumentation and other observational information. If you have multiple instruments, you can keep a profile on each one. Sometimes, you might have multiple telescopes and multiple interchangeable cameras. You should probably create a different profile for each combination that you use. This information is published whenever you send information to the Minor Planet Center, AAVSO, etc. and it may be used within Canopus to estimate image characteristics.

If you are participating in the KBLR project, you should provide Canopus a description of the LONEOS telescope and instrument. The instructions below provide a link that describes this operation.

MPO Canopus provides a good set of photometric catalogs. We have found the Carlsberg catalog (superset) provides excellent estimates of the r' magnitude of most stars in the declination range -30 ≤ δ ≤ +60. Using this catalog, we can perform absolute photometry using on-chip reference stars. If you are not observing in the Carlsberg declination range, other available catalogs provide magnitude references that are not as accurate but often "good enough".

MPO Canopus runs under the Microsoft operating system du jour. Windows 7 is probably a good choice.

FAIR WARNING: Photometry is as much an art as a science. As with any art, the artist gets better with practice. Folks new to the art will make mistakes in a variety of wonderful ways. Have no fear! Press On! Many folks will be happy to (helpfully) criticize your work and you will get better. MPO Canopus not only does photometry but period analysis. Period analysis is as much an art as a science so the same comments apply. Good Luck.

Support and Documentation

I recommend that you get the MPO Canopus/PhotoRed User's Guide. It has "everything you ever wanted to know" about Canopus and I believe it is free (but I may be mistaken on this point).

Also, you should create an account for the MPO support Forum at Yahoo Groups (http://tech.groups.yahoo.com/group/MPOSoftware/). Lots of astronomers participate in this group, most notably, Brian Warner, who wrote Canopus. You can get your best help here.

Procedure

Step 1. Load your images on the computer. This is not an MPO Canopus operation but a Windows operation. In the procedure below, we assume that MPO Canopus is running on the same machine on which your images are stored. If you have just come from the "astrometry" procedures page, you have already performed this step, so skip to Step 2.

Procedure Sub-steps Expected Result
We suggest that you create a sub-directory for images. For example, "Images". You should probably put this in your home directory. That is, "C:\Users\FredFlintstone\Images".  
If you have multiple instrument configurations, we suggest that you create a sub-directory under "Images" for each of them. For example, "C:\Users\FredFlintstone\Images\SBIG_ten_inch". This step is not necessary if you have a single configuration.
We suggest you create a sub-directory under the appropriate configuration directory that is named for the date of the images. For example, "C:\Users\FredFlintstone\Images\SBIG_ten_inch\2012-04-16".
Copy or Move the data images into the appropriate directory. You have probably already done this in the astrometry procedure but, if not, review that procedure to get instructions.

Step 2. Verify that Canopus is using the proper configuration.

Procedure Sub-steps Expected Result
Invoke MPO Canopus The main Canopus window should appear.
From the "File" drop-down menu on the main Canopus window, select "Configuration". The "Configuration Settings" window appears.
Select the "General" tab in the "Configuration Settings" dialog box. The "General" tab information appears.
Verify that you are using the "LONEOS" profile. If not, select the "LONEOS" profile. If the "LONEOS" profile does not exist, refer to the astrometric procedure for instructions on how to create and select it. You have verified Canopus is using the "LONEOS" profile.
Select the MPC tab in the "Configuration Settings" dialog box. The "MPC" tab information appears.
Put your name in the "MEA" field. Use the "F. M. Last" name format. (First two initials separated by one space followed by one space and the last name) Also put the observer's name in the "OBS" field. You can get the observer's name from the FITS header. Use the same format. Then depress the "OK" button. Canopus saves/selects the "LONEOS" configuration.

Step 3. Create sessions for the images just stored.

Procedure Sub-steps Expected Result
Invoke MPO Canopus if not already invoked. The main Canopus window should appear.
Select the "Photometry" menu item near the top of the page. A drop-down menu should appear.
Select "Session" from the drop-down menu. A new window should appear. It is the "Photometry Session Data" (PSD) window.
In the PSD window, depress the "New" button. The "Session Data" portion of the window becomes active. (It is the lower left corner of the window.)
Type in the values for "Object Name", "Mid-Date", "Mid-Time". Mid-Date and Mid-Time correspond to the time of night halfway between the night's first observation and last observation. Select a "Filter" from the pull down menu. (The "Mag Band" may spontaneously match.) If you want to use a different Mag Band for analysis, select "Mag Band" from the pull down menu and pick a different value. (Sloan filters and mag bands are typically two letter values with the first letter as an "S".) Select a "Telescope: from the pull down menu. If you cannot find your telescope in the pull down menu, type in its name. Also enter the "F.L." (focal length of the telescope) "Camera" option (again, type it in if your camera does not appear), "Temp." (generally the CCD temperature), and the "Exp." (exposure time in seconds).

If you are in the KBLR project and using LONEOS data, most of this information is available from the configuration (details in the previous step) or in the FITS header. Here is some short-cut information. Use "SR" for the mag band and the filter. LONEOS was unfiltered but we are pretending it used an r' filter. Telescope is LONEOS, F.L. is 1100 mm., camera is LONEOS CCD, Temp. is -110 C., Exp. is 45.
Comment: Some of this information seems redundant. For example, the Camera and F.L. should be part of the of the configuration. We can obtain the Exp. value from the FITS header. Put it in anyway.

Remember that Brian Warner designed Canopus for asteroid lightcurves. If you are creating stellar lightcurves, some of this information (mid-time, for example) is not useful.
If you know the name of the asteroid with which you are currently working, depress the "Calc M/D/P" button at the bottom of the PSD window. If you don't know the name of the asteroid, skip this step and the next. You will be prompted for the name of the asteroid by the "Asteroid Lookup" dialog box.
Supply the name of the asteroid. You can use either the name or the number, but if the number is available, use it. Also select "MPC" as the source. Then depress the "OK" button. The "Asteroid Dialog" box will disappear. Canopus will calculate some aspect numbers and display them on the bottom of the PSD window.
Depress the "Save" button on the PSD window. Canopus saves the information you just supplied and all the editable fields on the PSD become inactive.
Depress the "OK" button on the PSD window. If you did not supply an asteroid name, Canopus will post a warning message about "Light-time correction". Answer "Yes" to the "Continue?" question. If you supplied the asteroid name or answered "Yes" to the warning message, the PSD window will disappear and Canopus will use the selected session in the following steps.

Step 4. Begin the photometric analysis phase by selecting the first image in a time series. Also select the comparison stars (generally called comp stars).

Procedure Sub-steps Expected Result
From Canopus, open the first in a sequence of four LONEOS frames by selecting Image -> Open The "Open Image File" dialog box appears.
From the "Open Image File" dialog box, select the first of the four frames and depress the "Open" button. The "Open Image File" dialog box disappears and the selected frame image appears in the main Canopus window.
You have already performed this step but you must do it again right here.

Measure the position of some of the stars on the frame by selecting Image -> Auto Match/Measure
This process will take a little time so be patient. When the process concludes, each of the selected measurement stars will appear with concentric circles about them. Also a window labeled "Photometry Residuals" should appear. You may dismiss this window.
Verify that you have selected the proper session by invoking the session manager. "Photometry" -> "Session...". The session you want to use should be highlighted. Depress the "OK" button. If not, find it, highlight it and depress the "OK" button. You have verified the session.
From the "Photometry" drop-down menu item near the top of the main Canopus window, select the "Lightcurve wizard..." option. A small pop-up window may appear asking, "Clear current settings?". If not, the "Lightcurve Photometry Wizard" window appears.
If the pop-up window appears, answer "Yes" to the "Clear current settings?" question. The pop-up window disappears. A second pop-up window might appear or you might go directly to the "Lightcurve Photometry Wizard".
If the second "Confirm" dialog box appears, it will likely state that "There are observation data in the current session. Continue?" Respond by depressing the "Yes" button. The second "Confirm" dialog box disappears. Then the "Lightcurve Photometry Wizard" dialog box appear.
Enter the name of the first image in the provided field. You may depress the small box to the right of the name field to get a list of images. If you have reversed black and white on your images, you may want to select "Black Numbers". Also select "Star Subtraction". Depress the "Next>>" button. The "Lightcurve Photometry Wizard" window provides some instructions on how to proceed and the selected image should appear in the main window.
Read the instructions. Then depress the "Next>>" button. The "Lightcurve Photometry Wizard" changes to the form where comp stars are identified.
This is a non-sequential step but it has to be done sometime.

Invoke the image magnifier by simultaneously depressing the Ctrl/Shift/4 keys.
The magnifier appears. When you put the pointer on the image, the magnifier should show a magnified version of the region near the pointer. It should also show three circles. The inner circle corresponds to the area that will be measured for star signal. The outer annulus corresponds to the area measured for the sky background value and the middle annulus is the dead area.

Details about setting the apertures can be found in the astrometry procedure.
Now back to the photometry and the "Lightcurve Photometry Wizard". Depress the "Selector" button in the Wizard. A Comp Star Selector window appears.
From the "Comp Star Selector" verify that the "Plot" tab has been selected and then depress the "Plot Comps" button. The "Comp Star Selector" works for several seconds and then presents a graph that plots the catalog magnitudes as a function of the instrumental magnitudes.
We are now ready to select the comp stars. In general terms, we want to select the stars from the set on the DS9 display. Unfortunately, Canopus does not have all of those stars in its catalog so we will have to scramble around until we find comp stars that are in both DS9 and Canopus.

Bring your DS9 display up with its potential comp stars identified. It should also display the area where the asteroid is located. (Note: You can used the printed DS9 image you created earlier but, because the frames are so large, I found the printed copy to be hard to use.)

Place the mouse pointer on an isolated potential comp star in the DS9 display. You can read its pixel coordinates at the top of the DS9 display. Find the star at the same pixel coordinates on the Canopus display and, using the magnifier, carefully center it and then left click it. (If your pattern recognition skills are good, you can just pick the star off the Canopus display without referring to the pixel coordinates.)
Canopus should put a "bullseye" around the star you just selected. If the star is in the Canopus catalog, you will see a green dot appear in the "Comp Star Selector" window. If the green dot does not appear, this star should not be used for a comp star. If the green dot does not lie on the "very" straight line formed in the graph, it should not be used as a comp star. In either case, repeat this step with a different potential comp star until you find an acceptable comp star.
When you find an acceptable comp star, depress the "Set Comp 1" button in the "Comp Star Selector" window. Repeat the preceding step and each time depress the next "Set Comp n" button where n = 2..5.

Warning! Do not use the Lightcurve Photometry Wizard window to select the comp stars. Things just won't work correctly if you do that.
You have just selected five comp stars and their pixel coordinates should appear in the "Lightcurve Photometry Wizard" next to the "Star n" buttons where n = 1..5.
Now locate the asteroid in the main MPO Canopus window. Carefully center it in the annulus of the magnifier and left click it.

If you earlier used DS9 to locate the asteroid, you can go to frame 1 of DS9, find its pixel coordinates and easily locate the asteroid on the Canopus window.
Canopus should put a bullseye around the asteroid.
Move to the "Lightcurve Photometry Wizard" and depress the target button. The pixel coordinates of the asteroid should appear next to the target button.
Back in the Comp Star Selector window, select the "Comps" tab. The "Comps" window should appear and each of your selected comp stars should be listed with a magnitude in several, if not all, the bands.
Verify that every comp star has a magnitude in the r' band. If one or more of the r' values is missing, go back a few steps and re-select the comp star that has no r' values and try to get it to put the r' value in. If it won't put value in, select another comp star. Every comp star has an r' magnitude.
Within the "Comps" tab of the "Comp Star Selector", check the "Set Comp Mags" checkbox. Then depress the "Transfer" button. This step transfers the comp star magnitudes into lightcurve wizard so that the asteroid magnitudes will be on an absolute scale rather than a relative scale.
From the "Lightcurve Photometry Wizard", depress the ">>Next" button. A new step appears asking you to supply the name of the last image in the series.
Within the "Lightcurve Photometry Wizard" put in the name of the last LONEOS frames to be examined. You can get an "Open" dialog box to help you find the file by depressing the box just to the right of the filename field. This is a standard MS-Windows operation so I won't describe the details. Then depress the ">> Next" button The last image appears in the main Canopus window and some instructions appear in the Wizard window.
Read the instructions and depress the ">>Next" button. More instructions appear in the Wizard window.
We are to identify the comp stars in the final image.

Move to the location of the comp stars. You will find a set a numbers corresponding to the set of comp stars you originally found. If you are lucky, the numbers will be very near the correct stars. Place your pointer over the first comp star and carefully center it in the magnifier. When it is centered, left click the star. Then click the "Star 1" button in the Wizard.
The positions of all the comp stars should be immediately defined in the wizard.
Place your pointer over the asteroid and carefully center it in the magnifier. When it is centered, left click the asteroid. Then click the "Target" button in the Wizard. The pixel coordinates of the asteroid should display in the wizard.
Depress the "Show Path" button in the Wizard. Then depress the ">>Next" button. The wizard displays some instructions about the star subtraction feature.
Depress the ">>Next" button in the wizard. The next set of instructions appear in the wizard.
Depress the "Load Image #1" button in the wizard. The first image in the series is reloaded and becomes visible in the main Canopus window.
Select a bright isolated unsaturated star by clicking on it with the left mouse button. Then depress the "Set Ref Star 1" button. The coordinates of the star appear next to the button and the next button is enabled.
Select a second bright isolated unsaturated star by clicking on it with the left mouse button. Then depress the "Set Ref Star 2" button. The coordinates of the second star appear next to the button.
While watching the magnifier, move the mouse pointer along the path of the asteroid. Whenever a star, however faint, enters the background annulus of the magnifier, move the pointer to the star and left click it. Then depress the "Add" button in the "Lightcurve Photometry Wizard" window. WARNING: Be very careful not to select the asteroid itself. Repeat this operation until all the stars near the path of the asteroid have been added. Then depress the "Next" button. You should have a "short" list of stars along the path of the asteroid. These stars will be "removed" when the photometric values of the asteroid are calculated. After depressing the "Next" button, the wizard will take you to an informational window.

Step 5. Perform the photometric reductions on each frame in the time series.

Procedure Sub-steps Expected Result
Select the "Save Comps" button in the "Lightcurve Photometry Wizard" window. The "Save Comps" option produces a PNG formatted image file with the comp stars and targets labeled. Be sure to note where Canopus saved it and be sure to print it for future reference. (Normally, Canopus saves it with the data frames.)
Depress the "Finish" button. A dialog box with all the image filenames appears.
Select all the four filenames that correspond to the images in this set. (This is an MS Windows selection process that you surely know.) (There are exceptions to this rule but generally, it is correct.) Depress the "Open" button. An "Image" dialog box appears.
Double click the first image name in the dialog box. Canopus attempts to highlight each of the comp stars and the target on the image.
Verify that each of the comp stars is accurately centered within a bullseye. If not, move the mouse pointer to the first comp star, accurately center it using the magnifier and left click the mouse. Don't move the mouse until you read the expected results. All the comp stars should simultaneously locate properly with their respective bullseyes. The magnifier should show the asteroid centered in its annulus.
If the asteroid is not centered in its annulus, move the pointer to the asteroid and center it within the annulus. Then, while holding the "Ctrl" key down, depress the left mouse button. The asteroid becomes centered in the annulus.
Depress the "Accept" button in the "Images" window. The values are pulled from the image, the computer beeps and the image selector moves to the next image in the "Images" window.
Repeat the previous steps in the obvious way until all the images have been processed. Depress the "Close" button in the "Images" window. The "Images" window disappears.

Step 6. Photometric Sanity Check

Procedure Sub-steps Expected Result
Open the "Sessions" window by selecting the "Photometry" drop-down menu item on the main Canopus page. Then select the "Session..." option. The PSD window appears.
Verify that the correct session is still selected. If not, select it. The depress the "Edit" button. The editing fields on the bottom half of the window become enabled.
Depress the "Calc DC" button in the PSD window. The PSD displays the raw photometric data. (You may also get a "Confirm" pop up window asking if you will accept the new value.) You should be able to see numerical values for the magnitude of the target on each frame.
If the pop up window appears, answer "yes" to the question. If not, go to the next step. The pop up window disappears.
Select the "Comparison Plots" tab at the top of the PSD. The "Comparison Plots" section of the PSD appears.
Select the "Avg" option from the "Data" box. Then, in turn, select each of the comp stars, 1 through 5, in the comp box. Note the spread in the plot of comp star values. The spread in the comp star values should be small, i.e., on the order of 0.02 mag peak-to-peak or smaller. If it is much larger, re-reduce. If it is still too large, seek advice.
Select the "Observations" tab in the PSD window. The asteroid and comp star raw photometric data appear.
The bottom half of the window contains the information we need. Using the scroll bar at the bottom of the lower pane, scroll to the right end of the data. Although these data are unlabeled, the last two values are the r' magnitude and corresponding uncertainty, one set of values for each frame. You should record these someplace because the magnitudes need to go into the MPC report and I sure would like to keep the uncertainties. You have recorded asteroid r' magnitude and uncertainty.
DO NOT OMIT THIS STEP or you will loose your reduction values. Select the "Session Data" tab and depress the "Save" button. Then depress the "OK" button. Canopus saves your reduction values.

Congratulations! You now have reasonably accurate magnitudes for one asteroid.