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CFHS. Killer Asteroid Project. Astrometrica: Advanced NEO Search Prepared by Harlan Devore Cape Fear High School. CFHS. KAP2008. Why Use Advanced Techniques?. o Astrometrica’s moving object detection function generally cannot find targets that are dimmer than about magnitude 18 or 18.5.
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CFHS Killer Asteroid Project Astrometrica:Advanced NEO SearchPrepared byHarlan DevoreCape Fear High School CFHS
KAP2008 Why Use Advanced Techniques? o Astrometrica’s moving object detection function generally cannot find targets that are dimmer than about magnitude 18 or 18.5. o Under normal seeing conditions, targets dimmer than 19.5 will usually not be found using manual detection. o Most asteroids brighter than magnitude 19 have already been discovered. Most of the NEOs we need to measure are in the range of magnitude 19 to 22.5. o To measure targets in this range, we use a technique called “Stack and Track”. S&T measurements are generally more precise and accurate than measurements made from single images.
KAP2008 What is Stack & Track? o By stacking several images of the target area, pixel counts for an object are added together to make objects such as stars brighter. Stacking makes asteroids look like streaks because they are moving. Image 1 + Image 2 = Stacked image o Stacking alone does not brighten the asteroid, but may make a bright one more obvious by turning it into a streak. + = Asteroid
KAP2008 Tracking o Tracking involves offsetting each image in the direction opposite of that the asteroid is moving. Each image is offset by the distance the asteroid would have moved in each successive image. The asteroid appear to be stationary, but turns the stars into streaks. Image 1 + Image 2 = Image after S&T o By tracking the image before stacking, the asteroid becomes brighter in the stacked image and does not form a streak. + =
KAP2008 An Analogy o Suppose a helicopter flies above a truck on the interstate. If the helicopter moves at the same speed and direction as the truck, the truck will appear to be stationary with respect to the helicopter. If the pilot photographed the truck, it would stay in the same place in the image frame, but trees and houses along the road would appear be streaks moving backwards. That is the effect produced by stack and track.
KAP2008 Opening Astrometrica o To start the program, double click on the Astrometrica icon o As Astrometrica opens, it will ask you if you want to delete files from the previous session. Clicking [Yes] will delete the MPC report created in the previous session.
KAP2008 Updating the Astrometrica’s Minor Planet Database o Before beginning a new session, you should update Astrometrica’s Minor Planet Center orbitals database. - From the Main menu bar, click [Internet], [Update MPCOrb].
KAP2008 Downloading Updates CFHS o When the Select Files window appears, check all items in the list, then click [OK]. o Astrometrica will then link with the Minor Planet Center through the Internet and obtain update files for the program’s MP orbital database.
KAP2008 Updating Database CFHS o When all files have been downloaded from the Internet, the File Download window will appear. Click [OK]. o Astrometrica will then begin an update of its MPCOrb database. This process will take a few minutes. o When the Update MPCOrb window appears, click [OK]. Astrometrica will then reload its MPCOrb database.
KAP2008 Setting the Configuration o o To set up the program configuration, click [File], [Settings…] on the Main toolbar. (Alternative method: Click the Edit Program Settings icon on the Main toolbar.)
KAP2008 Observing Site Settings o o In the Program Settings window, click the Observing Site tab. - Enter your first initial and last name as Measurer. - For Telescope, enter: Astro-Research 0.61m (for the 24” telescope), or Astro-Research 0.81m (for the 32” telescope)
KAP2008 CCD Settings o o Click the CCD tab. - Enter Focal Length: 3718.0 mm (for the 32” telescope) or 3195.0 mm (for the 24” telescope)
KAP2008 Program Settings o o Click the Program tab. - In the Residuals box, set Astrometric and Photometric Limits. - The limit numbers to use vary with the seeing conditions for the image batch. Lower numbers yield more accurate measurements. - Start with 0.25 (Astrometric Limit) and 0.35 (Photometric Limit), then adjust them up or down as need while working with the images. o Click [OK] to continue, then [YES] save your settings.
KAP2008 Loading Image Files o o Click [File], [Load Images…] o Browse to the folder containing the current image sets.
KAP2008 Selecting Image Files o Select images from a set: - Hold down the <Ctrl> key, and click on 5 images from an image set. (Space them out if the set contains more than 5 images.) - Click [Open] to start loading the images. Start of image set End of image set *Note: Only the first and last few files in an image set will be labeled with the NEO’s name.
KAP2008 Opening Image Files - As each image file opens, Astrometrica will calculate the date–time for the middle of the image exposure. - Click [OK] to accept the calculation.
KAP2008 Image Data Reduction o Astrometrica must next perform astrometric data reduction of the images. This involves: - Extraction and inventory all objects in the images. - Aligning the images. - Downloading star catalog data from the Internet. - Comparing objects inventoried to star catalog data to create the “best fit” image coordinate system. - Analyzing position and magnitude differences between image and catalog objects. - Evaluating whether inventory objects are known or unknown.
KAP2008 Performing Data Reduction o To begin data reduction, click on the Data Reduction icon on the Main toolbar. o When the Coordinates window appears, click [OK].
KAP2008 Astrometric Solution o If Astrometrica is able to obtain an astrometric solution, it will display a circle around each object in the image. Color code is as follows:
KAP2008 Data Reduction Table dRA = delta Right Ascension dDe = delta Declination dMag = delta Magnitude These values represent the average differences between the positions (and magnitudes) of the reference stars in the image versus their catalog values. • o Astrometrica will also display a Data Reduction Table window. • Note the values in the dRA, dDe, and dMag columns. For precision measurements, these values need to be as small as possible. When possible, dRA and dDe should be less than 0.10 arcsec. • Lowering Astrometric Limits in the Program Settings window can sometimes be used to reduce dRA and dDe values that are too large.
KAP2008 No Astrometric Solution? o Sometimes Astrometrica will fail to find an astrometric solution on the first try. o Check Automatic Reference Star Match using 80 Stars, then click [OK] o If Astrometrica again fails to find a solution, try again with 160 stars.
KAP2008 Manual Solutions o If Astrometrica again fails to find a solution, you can try to obtain a manual star match. o Click [OK] to start the Manual Reference Star Match.
KAP2008 Manual Solutions o Click the directional arrows to move the star pattern overlay to match it to the stars in the image. Most overlay star patterns must be moved up and to the right to match image stars.
KAP2008 Adjusting Focal Length • o After most of the stars near the image center are centered in their reference overlay circles, adjust the focal length as needed to shrink or expand the overlay. • Reduce focal length to shrink the overlay. • Increase focal length to expand the overlay. Here, Focal Length must be adjusted down to shrink the overlay. Stars near the center are centered, but not those around the edges.
KAP2008 Adjusting Position Angle • o Position angle can be adjusted to rotate the reference star overlay if needed. • Increasing position angle rotates the overlay clockwise. • o Click [OK] when you have a good match between the overlay and the image. Here, Position Angle must be increased to rotate the overlay clockwise. Reference circles on the right need to move down. Those on the left need to move up.
KAP2008 When Automatic and Manual Solutions Fail… o When astrometric solutions fail, try the following: 1) Check the CCD Settings to verify that the focal length is correct. 2) Click [Window] [Tile Windows]. Check images to ensure: A) Images are of the same star field and are aligned. B) All images have about the same seeing conditions C) None of the images have major artifacts (streaks, airplanes, satellites, Moon, bright planets, etc). D) Stars are not distorted in shape by telescope movement. 3) Discard any images that are misaligned, have poor seeing, or artifacts that might cause astrometric solution problems, then retry the Automatic solution.
KAP2008 When Automatic and Manual Solutions Fail… 4) If the automatic solution still fails, click [Settings], select the Program tab, then adjust the Astrometric and Photometric Limit residuals upward by 0.05 and try the automatic solution again. Repeat this step until a solution is obtained.
KAP2008 Moving Object Detection o Once an astrometric solution has been found, Astrometrica can automatically detect moving objects -- if they are fairly bright. o To initiate this feature, click on the Moving Object Detection icon. Then click [OK].
KAP2008 Evaluating Moving Objects o If Astrometric detects moving objects, it will display them in a verification window. o In this example, Astrometrica has detected a 19th magnitude asteroid. The six digit “packing” number that proceeds its designation (2004 ER94) is an indication that additional data is not needed for this object. o Click the [Reject] button.
KAP2008 More Moving Objects o This is an example, Astrometrica has found 2003 YG23. It may be either an asteroid or a NEO. o 2003 YG23 does not have a pack number, so the MPC may need data on it. It is fairly well defined and has a fairly good Signal-to-Noise Ratio (SNR), so click [Accept] to record data for it.
KAP2008 New Asteroids o Astrometric is unable to match the next object detected to a known asteroid, so it displays a [ ] in the Object Designation box. ? o This object has a good SNR and is well defined with a full-width at half maximum (FWHM) of 2.2”. Click the Object Designation button to see if it might be a known asteroid.
KAP2008 New Asteroids o There are no nearby objects with similar magnitudes, so this is probably a new asteroid. o Click [Cancel ] to reject the highlighted designation.
KAP2008 Measuring New Asteroids o Assign a name to this asteroid in the Object Designation box by entering your initials and a four digit serial number. (Ex: ) HVD1234 • - Click [Accept] to record measurements for this object. • In your log book, list the serial number used to avoid reusing it in the future. HVD1234
KAP2008 Displaying the Known Object Overlay o After completing the automated moving object search, you can do a manual search for dimmer asteroids not found in the automated search. o Begin by clicking the Known Object Overlay button This will display all known asteroids in the image area.
KAP2008 Stack &Track with NEO 2008 CY4 o 2008 CY4 was a 19.9 magnitude NEO imaged on Feb 16, 2008. Seeing conditions were excellent, and it is visible near the lower • right corner of its tracking box. • Manual measurements from single images produced poor results. • S&T was needed.
KAP2008 Getting Started with S &T o Before setting up for stack and track, it is a good idea to get the speed and position angle for the target object. • Click on the Stop icon on the menu bar to stop the blinking. • Click on the target object (or anywhere in the target box if object is not visible).
KAP2008 Gathering Target Information o When the object verification window opens, note low signal to noise ratio (SNR = 2.2). This is too low to yield good measurements. o Click on the Object Designation button.
KAP2008 Speed and PA o In the Object Identification window, note the Magnitude, Speed and PA (position angle) for 2008 CY4. • Note file date, target name, magnitude, speed, and PA in your lab book. • Click [Cancel] to close Object Identification window. • Click [Reject] to close Object Verification window.
KAP2008 Starting Image Stacks o Before starting to stack images, close all image windows by clicking on the Close all Windows icon. o Next, click on the Stack Images icon.
KAP2008 Adding Images o When the Select Images window opens, click the [Add] button. When the Open window appears, browse to the file folder containing the target image set.
KAP2008 Creating Image Stack #1 o There are 35 images in the 2008 CY4 set. Because the target was fairly bright, we will make four image stacks instead of three. • Click on the first image in the set, hold down the [Shift] key, and click on the 9th image in the set. • Next, click [Open].
KAP2008 Building the Image Stack o Click [OK] to start building the stack. o Astrometrica will then calculate the mean date-time for each image. As each results windows appears click [OK] or just press the [Enter] key.
KAP2008 Opening Object Browser o After calculating the last date-time, the Tracking window will open. - Click on the Object Browse button.
KAP2008 Browsing for Object o When the Object Browser window opens, enter the target name in the Filter window. • Next, click [OK] • Astrometrica will then calculate speed and PA for the target object using orbital data from its MPC database.
KAP2008 Checking Speed and PA o Astrometrica will then display the calculated Speed and PA for the target in the Tracking window. • Check calculated speed and PA against the values recorded in your lab book…Astrometrica frequently calculates speed and PA for the wrong object ! • If calculated speed and PA are wrong, manually enter speed and PA in Object Motion window. • Click [OK] to accept values.
KAP2008 Aligning Images o Astrometrica will then align and stack the images to make a single combined image. This process may take a few minutes.
KAP2008 No Astrometric Solution? o If Astrometrica is unable to find an astrometric solution, it is usually because sky seeing conditions changed (large magnitude residuals), focal length setting is incorrect, or an image is bad (large RA or Dec residuals). o You can: 1) try an Automatic Reference Star match using more reference stars, 2) try a Manual Reference Star Match, 3) load single images from the stack and check for a bad image, eliminate it from the stack list, and reload the stack, or 4) adjust the photometric and astrometric residual limits on the Program tab of the Settings window.
KAP2008 Stack Data Reduction o After creating the image stack, Astrometrica will compare RA, Dec, and mag for the combined image with those in the USNO star catalog. o Check to see that deltas (dRA, dDe, dmag) are acceptable.
KAP2008 Loading Additional Stacks o To start the creation of the second image stack, click the Stack Images icon.
KAP2008 Opening Second Stack o When the Select Images window opens, click the [Add] button. When the Open window appears, use the mouse cursor and Shift key to select the next nine images for the second stack. • Click [OK] to load the images. • When the Add window appears again, click [OK] to start building the stack. • Click [OK] as each date-time calculation window appears.