Sh2-115

Sh2-115 is a nebula in the constellation Cygnus.

It is located in the northern part of the constellation, about 2.5° northwest of the bright star Deneb; The most suitable period for its observation in the evening sky falls between the months of July and December and is greatly facilitated for observatories located in the regions of the Earth's northern hemisphere.

It is an H II region of considerable size with an oval shape and crossed in a northwest-southeast direction by a dark band that apparently divides it into two equal parts: the eastern part is dominated by the presence of a small open cluster, known as Berkeley 90, with which it is physically associated, while the western part lies in the direction of the variable star α2 CVn HD 196178 (V2015 Cyg), with an average apparent magnitude of 5.63; however, the distance of this star from the Sun is only 148 parsecs (481 light-years), much less than that estimated for the nebula, about 2300 parsecs (7500 light-years). The stars responsible for the ionization of gases are LS III +46 12, spectral class O6III, DM46 2972, class O9.5V, and DM46 2978, class B0III; the first of these dominates the Berkeley 90 cluster. The star BD+46 2972 also appears in the same field, but its distance is greater than the nebula, so its physical relationship with it should be excluded.

Sh2-115 corresponds to the ionized part of a large molecular cloud whose mass has been estimated to be about 4400 M⊙, extending for more than 30 parsecs. According to the Avedisova catalogue, the star-forming region to which this nebula belongs also includes several sources of infrared radiation observable in its direction, such as IRAS 20328+4639, IRAS 20334+4636, IRAS 20335+4637 and IRAS 20334+4654, identified during the 1980s; to these is added the W71 radio wave source. Its distance of 2300 parsecs corresponds to a region of the Orion Arm located just beyond the large Cygnus X nebula system, from which it would be about 500 parsecs.