This 127-hour deep field of NGC 7331, the Deer Lick Group and Stephan’s Quintet was captured from my observatory in Prades, Catalonia (Spain).
The field also contains SN 2026 aaiv, a supernova in NGC 7331, together with an extensive network of extremely faint hydrogen-alpha emission extending across much of the image.
The image combines data captured with two Takahashi refractors:
Takahashi FSQ-106 — LRGB
L: 481 × 300″ — 40h 05′
RGB: 3 × (90 × 300″) — 22h 30′
Total LRGB: 62h 35′
Takahashi FSQ-85 — Hα
Hα: 781 × 300″ — 65h 05′
Total integration: 127h 40′
Processing: three layers of information
One of the main challenges of this image was combining more than 65 hours of Hα data with the broadband image without simply turning the entire field red. The processing was therefore divided into three main components.
1. Broadband LRGB
The LRGB data form the foundation of the image, preserving the natural colors and structures of the galaxies, stars and background.
2. Faint diffuse Hα
The 65 hours of Hα reveal an extremely faint network of hydrogen emission extending across the field. This signal was processed separately and carefully integrated into the background while preserving the broadband appearance of the galaxies and stars.
3. HII regions inside the galaxies
The emission regions within the galaxies required a different approach. The broadband continuum was subtracted from the Hα data, allowing the genuine hydrogen emission to be separated from the normal stellar continuum of the galaxies.
This continuum-subtracted Hα signal was then used to integrate only the HII star-forming regions, while keeping the underlying galaxies in broadband color.
The goal throughout the processing was to reveal the extremely faint information contained in 127 hours and 40 minutes of data, while keeping the broadband light, diffuse hydrogen emission and HII regions as distinct and natural as possible.
The full image covers an area of 2º 58′ x 1º 26′ at a resolution of 1.46″/pixel.
Image Details
FSQ106:
L: 481 x 300″ (40h 05′)
RGB: (90,90,90 x 300″) (22h 30′)
FSQ85:
Ha: 781 x 300″ (65h 05′)
Calibrated with darks, flats and dark-flats.
Total exposure: 127h 40′
Moon at 20% (on average)
Image resolution: 1.46”/pixel
FOV (full image): 2º 58′ x 1º 26′
Equipment
FSQ106 EDX4 + ASI2600MM + LRGB Astrodon filters + Ha3nm Antlia – with ZWO EFW 7 pos
FSQ85 + ASI294MM + SHO LRGB Baader filters – with ZWO EFW 8 pos
Mesu200 mount
Guiding with ASI120MM and ZWO Mini Guide Scope
Software
SGP, PHD2, APP, PIX, PS.
Aleix Roig, September 2026.
Prades (Tarragona, Catalonia – Spain).