HII region around California Nebula (NGC 1499)

Around the California Nebula (NGC 1499) there is a huge HII region which lies behind the dust in constellations Perseus and Taurus and thus is only visible in the voids and less dense regions of these molecular clouds. That nebula was already partially depicted in the view of the Milky Way from Taurus to Perseus. The 30°×30° wide-field view of this page (probably) shows entire nebula.

Full views

Click on the images to load a full resolution version with more than 100 megapixels using a JavaScript viewer.

Discoveries

The view above show some nebulae that cannot be found in catalogs. (The JavaScript Viewer allows identifying objects using catalogs or SIMBAD and defining new objects.) Some (probably not all) of these unexplored nebulae have been collected in the list below. Click on the following links for a presentation.

• C7-C7,C10,C11 and H2-H7: Objects that are not cataloged by now and objects the are related to them. The list does not contain nebulae that are only minor extensions of known structures. (Objects whose name starts with the letter 'C' have been earlier identified in the view "Milky Way from Taurus to Perseus".)
• Huge HII region, labeled H1, that lies behind Molecular clouds in Taurus and Perseus because it is only visible in the voids and less dense regions of the dust. The brightest part is the California nebula (NGC 1499). Since the entire region has a similar filamentary structure, it seems to belong together. The apparent diameter is about 35°× 24°.

  It is assumed that the California nebula is ionized by Xi Persei. Distance estimations are 370pc to 460pc (Gaia EDR3) and 320pc to 470pc (Hipparcos). That interval can be refined slightly by considering the distances of the foreground nebulae:

  There are two other HII regions that seem to lie in front of H1, labeled "LBN 749A" and "LBN 749B" here. They are at a similar position as LBN 749 (coordinates of LBN catalog are often inaccurate), which is categorized as a HII region, and together they have a similar dimension as LBN 749.

  The brighter part, here labeled LBN 749A, is most likely ionized by HD 278942 at a distance of about 383pc (=1250ly, Gaia EDR3, +/-14pc). The dark nebulae that lies in front of LBN 749A belongs to the Perseus molecular at a distance of about 305pc, see [3]. At this distance the diameter of LBN 749A would be about 5pc (1° apparent), which means that it is almost impossible that this nebula lies within the Perseus molecular cloud.

  Another molecular cloud lies between LBN 749A and LBN 749B and H1: that molecular cloud obscures the background nebulae but is does not obscure LBN 749A. The existence of two molecular cloud in that region was also detected by [4], a CO radio survey which observed double lines in that region. That survey also measured the northern parts of the molecular cloud that obscure H1.

  The fainter part of LBN 749, LBN 749B, may be ionized by omi Per. Most exact distance estimations are from Gaia EDR3: 290pc to 380pc. That does not lead to additional information. Also, it is not clear whether IC 348, the nebula south of omi Per and whose distance is about 320 pc (long baseline measurements from [3] and Gaia EDR3 data) lies in front of LBN 749B or not.

  Near VdB 24 there are two young stellar objects that may belong to the molecular cloud that lies between H1 and LBN 749A, BD+38 811 and 2MASS J03494092+3859051, both in a distance of about 430 pc (=1400ly). Unfortunately it cannot be safely detected from visual inspection, whether the large HII region lies in front of that star formation region.

  Furthermore the Taurus Molecular Cloud obviously lies in front of H1. Distance according to [2] is 130pc to 200pc, much closer than LBN 749A.

  Thus, the only constraint that can derived from the given data is that the minimum distance of the molecular clouds that lies in front of H1 (and behind LBN 749A) is about 380pc.

Notes

• In the JavaScript viewer, the object outlines can be toggled on and off by pressing the '2' key. This can be helpful to make certain structures (e.g. rings) visible.
• False color images containing H-alpha and continuum:
• False color images containing H-alpha and continuum:
  • H-alpha is mapped to red, blue continuum is mapped to green, and red continuum (without H-alpha) is mapped to blue.
  • Color of molecular clouds and reflection nebulae in the false color image is something between green (bluish in reality) and blue (reddish in reality).
  • HII regions (ionized hydrogen) appear red to orange, depending on the amount of OIII (doubly ionized oxygen) detected by the blue continuum filter.
  • HII regions can be obscured (i.e. their radiation is scattered and/or absorbed) by molecular clouds that lie in front of them. However, emission nebulae do not obscure molecular clouds. This means that a HII region lies farther away if it appears to be hidden by a visible molecular cloud or a dark nebula. If molecular clouds and HII regions look somehow mixed (pinky red), the HII region is either nearer, or the molecular cloud is very thin. The latter aspect is the reason why it is difficult to determine whether an unobscured HII region lies in front of the molecular cloud.
    An improved visualization of the correlation between HII regions and molecular clouds is planned as soon as better data are available, namely NIR data, which better indicate regions that are optically thick for H-alpha emission.
• SIMBAD queries for certain object types can be made easily in the JavaScript Viewer by drawing a circle and pressing a shortcut key or via the menu
• A repository with the discoveries can also be found on GitHub

Image data

Images where captured with a camera array which is described on the instruments page.

Image data are:

Projection type:	Stereographic
Center position:	RA: 3h48', DEC: 35°
Orientation:	North is up
Scale:	10 arcsec/pixel (in center at maximum resolution)
FOV:	30°×30° (through center)
Exposure times:	Sum of exposure times of all frames used to calculate the image. H-alpha: 11.1 d Continuum channels: 5.8 d

Image processing

All image processing steps are deterministic, i.e. there was no manual retouching or any other kind of non-reproducible adjustment. The software which was used can be downloaded here.

Image processing steps where:

1. Bias correction, dark current subtraction, flatfield correction
2. Alignment and brightness calibration using stars from reference image
3. Stacking with masking unlikely values and background correction
4. Star subtraction
5. Denoising and deconvolution both components (stars and residual)
6. RGB-composition (same factor for stars and residual for the true color composite)
7. Dynamic range compression using non-linear high-pass filter
8. Tonal curve correction

References

1. Gibson, S.J.; Nordsieck, K.H. (2003). "The Pleiades Reflection Nebula. II. Simple Model Constraints on Dust Properties and Scattering Geometry". The Astrophysical Journal. 589 (1): 362–377.
2. P. A. B. Galli 1, L. Loinard 2,3 H. Bouy 1, L. M. Sarro 4, G. N. Ortiz-León 5, S. A. Dzib 5, J. Olivares 1, M. Heyer 6, J. Hernandez 7, C. Román-Zúñiga 7, M. Kounkel 8, and K. Covey, (2019). "Structure and kinematics of the Taurus star-forming region from Gaia-DR2 and VLBI astrometry". Astronomy & Astrophysics 630: A137.
3. Gisela N. Ortiz-León et al. (2018.) "The Gould's Belt Distances Survey (GOBELINS). V. Distances and Kinematics of the Perseus Molecular Cloud." The Astrophysical Journal, 865 (1): 73
4. Ungerechts, H. & Thaddeus, P. (1987). "A CO survey of the dark nebulae in Perseus, Taurus, and Auriga". Astrophysical Journal Supplement Series, 63: 645-660.