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Sh2-235

Aur

• H alpha
• Oxy 3

• 16 x 900 sec - 4 hours
• 1 x 900 sec - 3 hours 45 min

• UNBINNED
• UNBINNED

Sh2-235 and the associated nebula system are found in the central part of the constellation of Auriga, on the edge of a region rich in background stars due to the presence of the Milky Way trail; their position is easily recovered around 4 ° at WSW of the bright star iga Aurigae, which has an apparent magnitude of 2.65. Sh2-235 is the brightest nebula of the complex to which it belongs and is visible with a powerful amateur telescope or better still in long exposure photographs as a very pale light spot; the surrounding clouds are instead visible especially in near infrared sensitive images. The most suitable period for the observation of this nebulous system in the evening sky falls generally in the months between November and April. From the northern hemisphere, visibility is greatly facilitated, thanks to the fact that it is moderately northern; around 36 ° N the area of ​​sky that hosts the nebulae is perfectly visible at the zenith in the evenings of the first half of winter. From the southern hemisphere, however, its observation is made more difficult, although it is still visible up to a latitude of 54 ° S. Sh2-235 is the most central and brightest nebula of an H II region known as G174 + 2.5; it is observed in the direction of the northern part of the OB Aur OB1 association and includes the nebulae cataloged as Sh2-231, Sh2-232, Sh2-233 and Sh2-235, identified as single nebulae in the census of the H II regions completed in 1959. [ 4] Although in optical images they appear as distinct nebulae, in reality they all belong to a single giant molecular cloud, some parts of which appear illuminated by young and hot stars. [2] This cloud is found in the Arm of Perseus at a galactic latitude which places it slightly off-center with respect to the center of the galactic disk; distance measurements indicate a range between 1600 and 2000 parsecs, therefore it is normally indicated as equal to about 1800 parsecs (about 5870 light years). It is an H II region in a highly evolved phase, as evidenced by its irregular and uneven appearance. The exciter star of the gases is a blue dwarf cataloged as BD + 35 ° 1201, with spectral class O9.5V and an apparent magnitude of 10.54; it is also the brightest star in the whole complex. Inside there are three small subregions associated with young stars, which have been indicated as Sh2-235A, Sh2-235B and Sh2-235C; the first two are the most conspicuous and present within them water masers, a methanol and a silicon monoxide maser, which, being associated with young stellar objects, are clear evidence of the presence of star formation phenomena in act within them. Between regions A and B, about a first arc to the south of the main nebula complex, there is also a very compact thickening of gas smaller than half a parsec, in which there is a quadripolar jet, a cluster of infrared sources immersed deep in the cloud and two sources of radio waves, cataloged as VLA-1 and VLA-2, all objects representing different initial stages of stellar evolution; the VLA-1 radio source coincides with one of the masers previously detected, while the VLA-2 source is located near the region B and could be associated with a star in a more advanced phase.