The Star Formation Environment of S106

TIP Last Changed: JeffMangum - 17 June 2008

Table of Contents:

Background Reading

  1. Read the Radio Astronomy Tutorials on "Observing Modes Used in Radio Astronomy".
  2. Read the articles listed on the Star Formation References wiki page.
  3. Read the articles in the "General Information and Introductions" section of the Molecules in Radio Astronomy wiki page.

To Do

  1. Research past measurements and analysis of S106IR/FIR.
  2. Read background information on NH3 and its use as a temperature probe.
  3. Peruse NH3(1,1) and (2,2) image cubes.
  4. Derive Tk from image cubes.
  5. Compare dense gas structure derived from NH3 measurements to other molecular and dust continuum studies.
  6. Determine nature of IRS sources in region (i.e. compare infrared and continuum emission properties).
  7. Derive dynamical model which explains correlation between dense gas and dynamical (outflow or rotation) structures.


Sharpless 106 (S106) is an HII region in the constellation Cygnus. S106 possesses many of the "standard" features of an active star formation region: a bipolar emission nebula, molecular emission (both extended and compact), and an outflow. Distances to S106 range from 600 pc to 2.5 kpc (difficult to determine given its location near a galactic rotation tangent point).

The S106 HII region has been the subject of numerous observational investigations. The exciting star for the S106 bipolar HII region, called S106IR, has been studied at radio, infrared, and optical wavelengths. S106IR is buried within an ~30 arcsec diameter dense molecular cloud, which produces an optical dark lane through the center of the HII region, and appears to be a pre-main sequence stellar object that may still be accreting matter. Several investigations have attempted to derive the structure of the dense molecular cloud surrounding S106IR. For example, Bally & Scoville (1982), Harvey (1982), Bieging (1984), Mezger (1987), Barsony (1989), Crutcher etal. (1991), and Schneider (2002) have presented evidence suggesting that the molecular cloud surrounding S106IR is either a massive edge-on disk, a torus, or a collection of dense clumps. Unfortunately, inadequate spatial resolution and/or spatial frequency sensitivity at millimeter and submillimeter wavelengths have hampered efforts to resolve any disk-like structures less than ~30 arcsec in size and resolve the question as to the structure of the molecular material. Even at the lower limit of traditional distances, 600 pc, a disk of 0.09 pc extent poses problems owing to its immensity. Rayner (1994) has argued persuasively for a distance of 1.2+-0.2 kpc for the system, which exacerbates the disk size problem. Rayner pointed out that a cluster of ~260 stars is located only 30 arcsec northeast of S106IR. This suggests that the molecular material may be involved in the production of more stars than just S106IR.

High-resolution (Theta_B < 20 arcsec) submillimeter spectral line and continuum measurements by Richer (1993) have shown that the molecular material in the vicinity of S106IR is composed of an extended emission region located to the east and an unresolved compact source located to the west of the exciting source. This western compact (Theta_s < 6 arcsec) emission source, designated S106FIR, is a warm (T_k ~ 50 K), dense (n(H_2) > 10^7 cm^{-3}) dust and gas condensation. Richer (1993) suggest that S106FIR is a very young star in the process of formation.

The NH_3 (1,1) and (2,2) emission lines have received extensive use as a probe of the kinetic temperature in dense molecular clouds (see Ho 1979; Walmsley & Ungerechts 1983; Mangum 1992). High spatial (Theta_B ~ 3 arcsec, or 3500 AU at 1.2 kpc) and spectral (Delta V ~ 0.3km s^{-1}) resolution measurements of the NH_3 emission toward the S106 core region have been made using the Very Large Array (VLA). The figure below shows the integrated NH3 (1,1) (solid contour) and integrated NH3 (2,2) (dashed contour) emission from the region. Note the high degree of overlap between the NH3 (1,1) and (2,2) emission, indicating a relatively uniform, yet warm, temperature for the dense gas in this region.

The star marks the position of the more-evolved infrared source S106IR, while the box marks the position of the younger S106FIR object. The bulk of the NH3 emission extends to the NE (upper left). The connection between this dense gas emission and the infrared sources is one of the things that will be researched (and solved!) during this project.

The goal of this research project is to determine the dense gas kinetic temperature within S106IR on both large and small scales using these VLA NH3 measurements. The kinetic temperature structure derived can then be compared to other dense gas measurements to correlate density and temperature in this active star formation region.

Water Maser Measurements


Notes and Reports

Topic revision: r6 - 2008-06-17, JeffMangum
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback