Open Comet Photometry Tool

1. In the Image Viewer, go to Photometry → Comet Photometry.
   
2. The Comet Photometry window opens.

Update ICQ Settings

1. In the Comet Photometry window, click Update ICQ Settings.
   
2. Fill out the following fields:
   •    Observer: Enter your ICQ or COBS observer code.
   •    Method, Telescope, Camera, Chip: Select the appropriate ICQ keys from the drop-down menus to match your imaging setup.
   •    Calibration Type: Choose the calibration method used for your images. (Preferred: Bias, Dark, and Flat).

Tips:

• If your FITS images contain the CALSTAT keyword, Tycho Tracker can automatically detect the calibration type.
  
• Enable Include Location and Include Comet Altitude to add these details to the comment section of the ICQ report line.
  

Define Star Image and Comet Image

1. In the Image Viewer:
   •    Set Dynamic Stacking to Zero motion.
   •    In the Comet Photometry window, click Apply from Image Viewer under Star Image.
   •    A View button now appears next to Star Image.
   
2. Set Dynamic Stacking to Tracked.
   
3. Right-click the image in Image Viewer → Create Stack → Ephemeris.
   A stacked image, centered and aligned on the comet, is displayed.
   
4. In the Comet Photometry window, click Apply from Image Viewer under Comet Image.
   •    A View button now appears next to Comet Image.
   
5. Double-click on the center of the comet’s coma.
   •    The image is centered on the comet’s nucleus.
   •    In the Comet Photometry window, click Apply from Image Viewer under Origin.
   •    A View button now appears next to Origin. 
   

Note: 

• Comet information is retrieved automatically from the attached ephemeris.
  

Set Comparison Star Aperture

1. In the Comet Photometry window, click View next to Star Image.
   
2. Click Update Comp Star Aperture.
   
3. In the Aperture – Target window:
   •    Under Aperture Type, select Comp Stars.
   •    Zoom in and double-click on an isolated star (the view centers on that star). 
   
4. In the Image Viewer, click View PSF… to open the Object Profile window. 
   
5. Measure the FWHM of several stars to get an average.
   
6. Check the Image Plate Scale (PSc).
    
   Formula for Radius:
   

   Radius = FWHM × 4 / PSc

   
   
7. Set aperture parameters:
   •    Aperture Shape: Circle
   •    Radius 1: Calculated radius (rounded)
   •    Dead Zone: ~1/3 of calculated radius
   •    Sky Annulus: Radius + Dead Zone
   
   Example:
   •    FWHM ≈ 3.6″, PSc = 1.17″/px
   •    Radius = 12.3 px → use 13
   •    Dead Zone = 4.3 px → use 5
   •    Sky Annulus = 18

Select Comparison Stars

1. In the Comet Photometry window → Actions → Select Comparison Stars.
   •    The Comp Star Finder window opens, showing star list, filters, and a plot of True Magnitude vs. Instrument Magnitude.
2. Since we want total visual magnitude, select solar-like stars with B–V = 0.5–0.8.
   •    Set Min(B–V) = 0.5, Max(B–V) = 0.8.
   •    Click Refresh.
   
3. In the Image Viewer, go to Photometry → Show Photometry Stars.
   •    Select a point from the plot → the viewer centers on the star.
   •    If acceptable, right-click the star → Add to Active Comp Stars.
   •    Repeat for 5–7 stars.
   
4. To evaluate star quality:
   •    In Active Comparison Stars window, go to Graph → Generate Data.
   •    Good comparison stars should have ΔMagnitude ≤ ±0.1.
5. Once satisfied, close the Active Comparison Stars, Comp Star Finder, and Aperture – Comp Stars windows.

Tips:

• Choose stars near the comet, not at the frame edges.
• Favor stars lying close to the fitted line in the plot.
• Use stars in a magnitude range close to the expected comet magnitude.

Set the Coma Aperture Radius

1. Enhance the comet’s coma visibility by increasing Contrast (≈ 250 works well as a starting point).
   
2. Adjust the Coma Aperture Inner Radius until it fully covers the visible comet coma. 
   

Tips:

• For very large comets, adjust the Scale Factor to allow a larger radius.
  
• The Lock Aspect option will keep the Middle and Sky annuli scaled automatically with the Inner radius.
  

Measure Comet Tail Length

1. With contrast enhanced, the comet tail should be clearly visible.
   
2. In the Comet Photometry window, click Measure Comet Tail.
   •    A Markers window opens, and the mouse pointer centers on the comet’s coma.
   
3. Place the first marker:
   •    Without moving the mouse, left-click to set Marker 1 at the coma center.
   
4. Place the second marker:
   •    Move the mouse to the visible end of the tail.
   •    Left-click to set Marker 2. 
   

Tips:

• Try not to move the mouse after clicking the Measure Tail Length button as it automatically centers on the coma.
• Zoom out the image to view the entire tail before placing Marker 2.
  

Apply Star Removal filter

1. Set the Ignore radius and Coefficient of the Star Removal filter in the Comet Photometry window.
   
2. Reset the Image Contrast back to 0
   
3. Click on the Update Comet Image and observer the effect of star removal filter.

Notes & Tips:

• Ignore radius of 7 means that first 7 pixels from the coma center are not influenced by the star removal filter
  
• Coefficient value should usually be set between 1-3. Value of 3 should work in most cases. Do not over do it will not make a significant difference on the comet magnitude.
• Tycho Tracker defaults to Inner radius = 7 and Coefficient = 3, which work well in most cases.

How the star removal filter works

The Star Removal filter is designed to reduce the effect of background stars in comet photometry.

How it works:

1. The filter starts from the center of the comet’s coma.
   
2. The defined Ignore radius (inner coma region) is skipped, leaving the comet nucleus untouched.
   
3. Beyond the ignore radius, the filter moves outward in 2-pixel wide rings.
   
4. For each ring, the filter calculates the average pixel value.
   
5. Any pixel that is significantly brighter than the average (exceeding average × coefficient) is considered part of a star and is replaced with the calculated average value.
   

About the Coefficient:

• The coefficient defines the threshold for identifying stars.
  
• For example, a coefficient of 2 means that any pixel with a value greater than 2 × the average in its ring will be replaced.
  Examples:
  •    Coefficient < 2 → Aggressive filtering. Higher chance of also suppressing fine comet details.
  •    Coefficient = 2–3 → Balanced setting. Bright stars are removed while comet structure is preserved.
  •    Coefficient > 3 → Conservative filtering. Faint stars may remain visible.
  

Generating the Measurement Report

1. In the Comet Photometry window, click Generate Report.
   
2. Two windows will appear:
   •    Comet – Graph
   •    Comet – Report
   
   Comet – Graph Window
   •    Displays the magnitude growth curve, which helps verify if the selected coma diameter is appropriate.
   •    A correct curve shows a smooth, linear increase in brightness in the end points. This indicates that each additional data point adds only the background value.
   
   Comet – Report Window
   •    At the top, you will see the ICQ report line.
   •    Below that:
   Fixed aperture size measurements
   Coma growth curve measurements

 Notes:

• For COBS reporting, only the ICQ report line is needed. Simply copy and paste the entire line into the COBS multiple submission form.
  •    Important: Be sure to include the leading spaces, since the ICQ format uses a fixed-width layout.
  
• Additional measurements can be useful for other organizations:
  •    The BAA, for example, collects fixed-aperture magnitudes to track nucleus brightness and detect possible cometary outbursts.