How to create an ID Card for a high proper motion Target star


This section outlines how to create an ID Card for a Target star with high proper motion1. We'll illustrate this with an example FITS image of EV Lac, used with kind premission of Stephen M. Brincat. EV Lac is a nearby flare star with a notable proper motion.


Here is the image acquired by Stephen M. Brincat with EV Lac marked by the yellow arrow.




Standard procedure producing wrong results


  1. Open the Variable ID Card menu and select the New commannd to create a new ID Card.

  2. In the Name field, enter EV Lac, and click the AAVSO Lookup button. This will automatically retrieve the J2000.0 coordinates, RA = 22h 46m 49.73s and Dec = +44° 20' 02.40", along with the AAVSO chart ID and AAVSO designation info. 

  3. Click the FITS image button to select the provided image as reference image. 


At this point, Phoranso will generate the following screen. However, you'll notice that the aperture rings are incorrectly positioned at the J2000.0 coordinates of EV Lac. This misplacement occurs because EV Lac has a significant proper motion and has shifted to the northwest since the J2000.0 epoch, as shown in the above image.



Correct steps to follow


  1. We first have to determine the current position of EV Lac for the present epoch. To do so, ensure that the zoom factor of your image is set to 150% or higher. Then move the mouse cursor over EV Lac. The real-time coordinates will be displayed in the fields below the image. You should obtain the following approximate coordinates: RA = 22h 46m 48.06s and Dec = +44° 19' 50.41". Although this position might not be entirely precise, it is sufficiently accurate to proceed with photometry.
     
  2. Open the Variable ID Card menu and select the New commannd to create a new ID Card.

  3. In the Name field, enter the target star name: EV Lac  

  4. In the RA field, enter the corrected RA of the target star: 22 46 48.06

  5. In the Dec field, enter the Dec of the target star, +44 19 50.41

  6. Click the AAVSO chart ID field. This will expand the New Variable ID Card window, revealing the Select reference image section

  7. Here you can select a DSS image, FITS image or AAVSO chart. Choose FITS image and select the previously used FITS image of EV Lac

  8. Phoranso will solve the image and retrieve catalog data for all stars present. Your Variable ID Card window should now resemble the example below, where Phoranso successfully identified the correct position of EV Lac. Note that in addition it still marks the J2000.0 coordinates of EV Lac with a second set of aperture rings, but those will be ignored when adding the ID Card to the ID Cards manager, and later on during photometry.


From this point, continue by selecting the Reference, Check and Comparison stars as described in the New command.  



1 Proper motion refers to the apparent movement of a star across the sky relative to more distant background stars, due to its motion through space.