Casitas de Gila, Gila, New Mexico, October 20-25, 2022

NGC 1499 was a late-night target that was shot after imaging M31.  I captured narrowband Hydrogen-alpha, Oxygen-III and Sulfur-II filter data for the nebula and Red, Green and Blue broadband subframes for the stars.

In post processing with PixInsight, I used the calibrated and integrated red, green and blue master images for the stars.  The stars image was denoised, stretched and saturated.  I decided to emulate Jacques Deacon’s approach to producing a vibrant false color image with the narrowband master images (see 2022-08-28 | TAIC Workshop: California Nebula YouTube presentation).  I combined the denoised and cropped Ha, OIII and SII master images using a PixInsight expression with rescaling to produce an RGB color image with the following proportions per channel: Red – 80% SII and 20% Ha, Green – 60% Ha and 40% OIII, Blue – 20% Ha and 120% OIII.  The result was a good starting point for color manipulation.  It was difficult and time consuming to make color adjustments with the ColorMask script and version 2 of the Color Mask PixelMath formulas.  Note that Adam Block has two recent YouTube tutorials documenting an error in the ColorMask script when using the standard color mask button selections.  The user must not use these buttons and instead, put Start and End Cie h values in the text boxes.  Download an image of a Hue chart with numerical values to test your mask for proper color selection.  It was very time consuming to create and then blur desired color range masks.  Once the mask was applied, CurvesTransform and ColorSaturation tools were used.  The rest of the image processing workflow was straight forward, made easy with starless images.  The stretched, sharpened and saturated starless nebula was combined with the stars using the PixelMath combine function with the opscreen() parameter.

The California Nebula (NGC 1499/Sh2-220) is an emission nebula located in the constellation Perseus. As with many astronomer-named deep sky objects, its name comes from its resemblance to the outline of the State of California.  It is almost 2.5° long on the sky and, because of its very low surface brightness, it is extremely difficult to observe visually.  Most astrophotographers use narrowband filters to capture the nebulosity.   It lies at a distance of about 1,000 light years from Earth.  Its fluorescence is due to excitation of the Hβ line in the nebula by the nearby prodigiously energetic O7 star, Xi Persei (Menkib).  The California Nebula was discovered by E. E. Barnard in 1884.  Fun fact: the California Nebula transits in the zenith in central California as the latitude matches the declination of the object. (Wikipedia and SkySafari Pro).

Imaging details:

Stellarvue SVX102T with SFR0.74 focal reducer (FL = 528mm, f/5.2)
ZWO off-axis guider (OAG-L) with a ZWO ASI 174MM mini guide camera
Losmandy G11 mount with Gemini 2
ZWO ASI 2600MM Pro cooled monochrome camera (-10oC)
Chroma 36mm filters:  5nm Hydrogen-alpha, 3nm Oxygen-III, 3nm Sulfur-II, Luminance, Red, Green, and Blue
Equatorial camera rotation: 0o

Software:    Sequence Generator Pro, ASTAP plate solving, PHD2 guiding, 
    Losmandy Gemini ASCOM mount control and web client interface,
    SharpCap Pro for polar alignment with the Polemaster camera,
    PixInsight 1.8.9 with StarXTerminator (AI version 10) and NoiseXTerminator,
    Photoshop CC 2022

Hydrogen-a    10 min x 28 subframes (280 min), Gain 100, Offset 68, 1x1 binning
Oxygen-III      10 min x 24 subframes (240 min), Gain 100, Offset 68, 1x1 binning
Sulfur-II          10 min x 25 subframes (250 min), Gain 100, Offset 68, 1x1 binning
Red        4 min x 8 subframes (32 min), Gain 100, Offset 68, 1x1 binning
Green    4 min x 12 subframes (48 min), Gain 100, Offset 68, 1x1 binning
Blue       4 min x 12 subframes (48 min), Gain 100, Offset 68, 1x1 binning