Tycho Tracker: A Comprehensive All-in-One Tool for Comet Photometry

Introduction

Comet photometry is essential for studying comet activity, dust production, and brightness evolution. However, achieving accurate measurements presents several challenges, including low surface brightness, complex coma morphology, and contamination by background stars and sky gradient. Furthermore, traditional comet photometry workflows often involve using multiple software packages, which can hinder both efficiency and consistency.

Tycho Tracker v12 addresses these issues with an integrated solution, combining image calibration, plate solving, alignment, photometric measurement, and reporting in a single environment. Originally designed for asteroid and satellite detection, its new comet photometry module greatly simplifies and enhances comet observations.

Using Tycho Tracker for Comet Photometry

Image Calibration and Alignment

Accurate photometric results require careful image calibration using master bias, dark, and flat frames. Tycho Tracker allows users to apply master calibration frames directly, saving calibrated images automatically for streamlined processing. Plate solving uses standard star catalogs, and alignment can be done either on fixed stars or the moving comet. This ensures precise registration of images before photometric analysis.

Comet Photometry Module

The comet photometry module enables users to measure the comet’s brightness by comparing the flux within a user-defined coma aperture against a selection of carefully chosen comparison stars from photometric star catalogs such as APASS and ATLAS. These stars are chosen based on their color indices to ensure accurate transformations to standard photometric systems.

A standout feature is the visual star removal filter, which compensates for contaminating stars and bright tail structures within the photometric aperture. Assuming circular symmetry, it replaces anomalous bright pixels with the median flux at a given radial distance. This can be seen in Figure 1, which shows the effect of different filter settings applied on the images of comet P/2023 S1.

Figure 1: Comparison of coma aperture appearance with different star removal filter coefficients: no filter (left), moderate filtering with coefficient 3 (middle), and strong filtering with coefficient 1 (right).

Tests show that enabling the star removal filter can improve photometric accuracy by up to 0.5 magnitudes, especially in dense star fields.

Sky background selection is another critical factor. Tycho Tracker offers two flexible approaches: a traditional sky annulus or a manually drawn region to avoid gradients and nearby structures. Figure 2 illustrates a user-defined rectangular background region.

Figure 2: Example of manually defining a background region for sky subtraction using a rectangular selection tool.

Tail analysis tools are also included for measuring tail length and position angle from stacked images. Additionally, the module supports atmospheric extinction correction using the method described by Green [1], allowing users to correct for altitude-dependent dimming effects, critical for low-altitude observations.

Tycho Tracker outputs comet photometry results in the standardized ICQ-format line [2], facilitating direct submission to databases such as COBS [3] or the International Comet Quarterly. In addition to total magnitudes, the software calculates Afρ values across a range of increasing coma aperture sizes, providing insight into the dust production rate and coma structure. A magnitude growth curve is automatically generated, displaying the change in measured magnitude as a function of aperture radius. This diagnostic plot helps users assess whether their chosen aperture adequately captures the full coma flux while avoiding contamination from the tail or background gradients.

Figure 3: Tycho Tracker comet photometry module interface, showing the visualized magnitude growth curve (bottom left) and the automatically generated ICQ-format report line (upper right).

Example Observations

To validate the capabilities of Tycho Tracker’s comet photometry module, four comets exhibiting a broad range of brightness levels, coma structures, and environmental conditions were analyzed:

• 29P/Schwassmann–Wachmann
• C/2023 A3 (Tsuchinshan–ATLAS)
• P/2023 S1
• C/2022 U1 (Leonard)

Each dataset was processed with Tycho Tracker, KOPR [4], and Comphot [5] under consistent conditions: same apertures and comparison stars from the APASS catalog. An additional comparison was conducted between Tycho Tracker results with and without using its star removal filter. Table 1 summarizes total magnitudes and measured coma diameter from each software tool and configuration. For each comet, the first row reports the measured visual total magnitude; the second row shows the corresponding coma diameter in arcminutes, as determined by each software and method.

Table 1: Summary of total magnitude measurements for four comets processed using Tycho Tracker (with and without star removal), KOPR, and Comphot (manual and automatic apertures).

Comet	Predicted Mag	Tycho Tracker Star Filter On	Tycho Tracker Star Filter Off	KOPR	Comphot Manual aperture	Comphot Auto aperture
29P/Schwassmann–Wachmann	12.6	11.6	11.5	11.6	11.45	11.20
	(4.65')	(4.65')	(4.80')	(4.7')	(6.4')
C/2023 A3 (Tsuchinshan–ATLAS)	10.3	10.3	9.8	10.4	10.31	10.23
	(2.54')	(2.54')	(2.60')	(2.63')	(3.00')
P/2023 S1	16.0	15.8	15.6	15.9	15.81	16.21
	(0.74')	(0.74')	(0.80')	(0.94')	(0.56')
C/2022 U1 (Leonard)	18.5	18.4	18.3	18.3	19.42	19.42
	(0.27')	(0.27')	(0.28')	(0.38')	(0.38')

 

Conclusion

Across all targets, Tycho Tracker showed excellent agreement with established tools, delivering total magnitude measurements that typically differed by less than ±0.1 magnitude. For comets observed in dense star fields or featuring prominent dust tails, the application of Tycho Tracker’s star removal filter proved crucial, improving the reliability of photometric results by effectively minimizing contamination. Without the filter, magnitude overestimations of up to 0.5 mag was observed, especially for bright, active comets.

The analysis also highlighted Tycho Tracker’s robustness when dealing with faint objects near the detection threshold, such as C/2022 U1 (Leonard), where precise background region selection was critical.

Tycho Tracker redefines accessibility in comet photometry, eliminating the need for multiple tools while delivering high-quality, reproducible measurements.