An image of the Keyhole Nebula, a region within the Carina Nebula, was captured on March 3rd and 5th, with a total integration time of 13.5 hours.
As one of the brightest deep-sky objects in the Chilean sky, the Carina Nebula, especially the Keyhole region was a prime target for a long exposure. We were eager to see the intricate details that could be revealed. On March 3rd, we captured 85 frames using 120-second exposures with the R filter, and 55 frames each for the V and B filters, totaling 6.5 hours of integration time.
On March 5th, we continued the data collection using 240-second exposures per frame. The relatively low wind speed that night allowed for longer exposures, as the tracking errors in right ascension (RA) and declination (Dec) were minimal. We captured 45 frames for the R filter and 30 frames for each of the V and B filters. The reason behind capturing more frames for the R filter in both sessions was due to the higher abundance of red emission in the nebula, primarily from ionized hydrogen (H-alpha) regions.
To stack images from two different nights with varying exposure times and separate sets of dark frames, we used the Weighted Batch Preprocessing (WBPP) script in PixInsight instead of the Fast Batch Preprocessing (FBPP) tool. WBPP offers greater flexibility and makes it easier to manage large datasets that require customized calibration settings. We then proceeded with our standard post-processing workflow. Thanks to the high signal-to-noise ratio of the stacked image, only minimal noise reduction was necessary.
Thoughts from Sharon (Telescope Operator):
This was my first time working with such a long total integration time, both in my personal projects and at Thunderbird South. I was genuinely amazed at how minimal the noise was in the final image. I really enjoyed experimenting with the post-processing tools on such a detailed image, though probably need to work on better techniques for handling the faint background gas structures that only become visible in deep exposures.