Little Rosette Nebula (Sh 2-170)
History
In the late 1950-ies the American astronomer Stewart Sharpless discovered the large nebula Sh 2-170 on the 48 inch Schmidt telescope photo plates of the «Palomar Observatory Sky Survey». In 1959 he published his discovery together with 313 H-II regions in a catalogue. He classified it as circular, structure between amorphous and filamentary with medium brightness, 20 arc minutes in diameter. [310]
In Beverly Lynds «Catalogue of Bright Nebulae», which was published in 1965, this nebula is listed as LBN 117.62+02.29 or LBN 577. [270]
The nebula resembles the larger and brighter Rosette Nebula (NGC 2237), hence the nickname «Little Rosette Nebula»
Physical Properties
Sh 2-170 is a young, almost circular, diffuse H-II region, ionized by a single main sequence O star, located near the periphery of a small dense molecular cloud. From the thermal continuum emission the mass of ionized gas within a radius of ∼7 pc is estimated to 350 solar masses. The H-I (λ21 cm) and far-infrared observations show an extended low-density atomic component, of ∼1000 solar masses, within an irregular boundary surrounding the ionized gas of mean radius ∼10 pc. CO emission shows a molecular cloud of ∼1150 solar masses within an area 6 pc × 4 pc. A compact infrared component coincides with the cloud. The exciting 10 mag star (LS I +64 11) is located on the near side of the cloud, just inside the southern periphery. It is is a member of the small open cluster Stock 18 [628]. Estimated distances range from 2.8 kpc to 5.8 kpc. [145]
Finder Chart
The H-II region Sh 2-170 is located in the constellation Cassiopeia and is circumpolar for Central Europe. Circa 2.5° to the south lies the supernova remnant CTB 1 and 2.5° to the north is Cederblad 214 (NGC 7822, Sh 2-171). The best time to observe is July to January, when the constellation is highest at night.
Visual Observation
400 mm Aperture: Determining the position based on surrounding stars is not quite straightforward. Unfortunately, neither without nor with an O-III filter is any nebula discernible. — 400 mm f/4.5 Taurus Dobsonian, Hasliberg, 16. 12. 2023, SQM 21.2, Bernd Nies