Galaxies for Fun Astronomical CMOS and CCD photos of peculiar galaxies and other astronomical stuff.
www.galaxies.se - by Ivar Hamberg
OBJECT: M42, the Great Nebula of Orion
This well known Great Nebula in Orion is so bright that individual exposures longer than 60 seconds easily gets overexposed.
- Here I present an RGB image with very limited exposure time. 13min.
- The closeup of the Trapezium is from the same RGB image.
- Further below is an SHO image of 40min.
OBJECT | M42 | Orion |
OPTICS | 12" RC f/8 1:1 flattener | f.l. 2432 mm |
FILTERS | LRGB SHO | - |
CAMERA | QHY600M PH | BIN2. 0.6"/pixel |
EXPOSURE | Ha: 3x5min OIII: 3x5min SII 2x5min L: 5x1min R: 5x1min G: 4x1min B: 4x1min | RGB: 13min SHO: 40min LRGB: 18min |
PROCESSING | Maxim DL / Pixinsight | BlurXT NoiseXT |
COLOUR Scheme | ||
DATE | 2024-11-22 | - |
SPECTRUM | 2022-02-28 | Area N 360 sec, Area S 540 sec |
SPECTROGRAPH | 300L/mm |
1. Spectrum of the Orion nebula
I captured spectra in 2 regions with the 300 L/mm slit spectrograph. The slit was placed horizontally just north (N), and south (S), of the Trapezium. There was no major difference observed for these two positions at this resolution. Logarithmic Y-axis scale.
Date: 2022-02-28 12" RC f/8
2. Spectrum across "the Orion Bar Ionisation Front" and Regio Huygheniana:
I separated the raw spectrum "S" into 3 slit sections. The ratio of Hydrogen versus Oxygen changes in this LINEAR view. (Matches with the RGB colors.)
S1: H-alpha and H-beta are strong. Nitrogen, Sulfur apparent.
S2: Oxygen is now stronger.
S3: Oxygen strongest.
He-I is present in all spectra.
(Approximate slit positions. Relative scaling of spectra.)
Date: 2022-02-28 12" RC f/8
3. Spectrum Line Ratio Calculations
A simple estimate of some Standard Line ratios can be done:
- E-Class: The Excitation Class in the Emission Nebula is determined by the sum of the two [O III] line intensities divided by the H-beta line intensity. The measured result is ~3.4. Hence the Excitation Class is E1 (Ratios 0-5).
- The [O III] line ratios should always be close to 3. The measured result is 3.0. Ok.
- The Balmer Decrement is the Flux ratio of H-alpha/H-Beta. The simplified measured result is ~3.2. The theoretical value is around 2.85. It can vary.
(Instrument response function compensation not done yet for this one. Tbd.)
