Sh2-129 and Ou4, the Flying Bat and the Squid

About the Subject
Sh2-129, also known as the "Flying Bat" is an emission nebula in Cepheus, a cloud of glowing, ionized hydrogen gas at distance of roughly 2,300 light-years. In 2011 an amateur astronomer named Nicolas Outters found a very faint area of O III emissions apparently embedded within Sh2-129. It had not been noticed before because of the exceptionally low surface brightness. This very faint bipolar outflow, cataloged as Ou4 and known as the "Squid" nebula, is so faint that with my 12" telescope, each pixel receives only about 19 photons per hour per pixel from the very brightest regions of the squid nebula (4 ADU above background for the brightest regions of the nebula with five minute exposures, 0.33 e-/ADU gain, QE around 85% at O III wavelength). No wonder this object had been previously overlooked. Since 2011 it has become a favorite summertime target for advanced amateur astrophotographers, both because it pushes one's equipment and skills to do the subject justice, and because of the color contrasts and photogenic composition.

Since its discovery, there have been a few attempts to determine whether the Squid Nebula, Ou4, actually resides within the larger Flying Bat, and whether the triple star system HR 8119, the  which appears to be at the center of OU 4 is, actually, the source.  In 2014, Corradi et al published their findings in Astronomy & Astrophysics, Volume 570. Based on emission-line spatial distribution and kinetic modeling, they determined that Ou4 likely did reside within Sh2-129, and that HR 8119 was the likely source of the outflow. They believe the outflow was launched some 90,000 years ago. While the findings stated that the observed characteristics of the Squid were consistent with a bipolar outflow from HR 8119, they could not rule out other possible unrelated sources.

About the Image
This is a bi-color image of the Flying Bat and Squid with H-alpha (656nm) mapped to red, and O III (501nm) mapped to both blue and green. In order to provide a more natural appearance, the bi-color image was blended with an RGB image of the star field. Total integration time was 18h 55m for O III, 8h 55m for H-alpha, and 1h10m for the RGB stars. The intent was to approximately match SNR between the H-alpha and O III datasets. The image could definitely benefit from additional integration time, but given the weather in late July and early August and the relatively short duration of full dark in the summer, I had to make do with just under thirty hours in total. Seeing conditions were typical for northern New Mexico in the summer with each channel having FWHM values of around 2.2 arc seconds prior to processing.  In order to maximize image depth, nearly all exposures were incorporated into the final image, regardless of sharpness, due to the low surface brightness of the subject.  The telescope mount was controlled by APCC with a high precision pointing and tracking model that incorporated atmospheric conditions.  NINA was used for control of all equipment and for configuring the capture sequence. PHD2 was used to provide supplementary guiding, though the pointing model and absolute encoders alone would likely have been sufficient for the five minute sub exposures. All image processing was performed in PixInsight.