Avedisova says this nebula is ionised by the O9.5 III giant
LS II +26 6 at a distance of 4500 +/- 1000 parsecs.
(Note, however, that several other authorities have concluded that LS II +26 6 is not an ionising star for Sh 2-90. [
1])
Avedisova places Sh 2-90 in the star formation region
SFR 63.18+0.45 along with the infrared HII region
IRAS 19471+2641, a water maser and at least 3 molecular clouds.
Humphreys gives a similar distance estimate for LS II +26 6 (4550 parsecs) but a distance for Vul OB1 of only 2000 parsecs. If LS II +26 6 is the ionising star for Sh 2-90 then either this nebula is not associated with Vul OB1 or the distance estimates for LS II +26 6 or Vul OB1 are incorrect.
A blister on a 60 thousand solar mass molecular cloud.[
2]
Sharpless 90 is associated with Vul OB1 and contains a cometary elephant trunk structure on its eastern edge which appears to have originated from a past disturbance from the southwest.[
3]
Notes
1. ^ Forbes, D. (1989). "Photometry and spectroscopy of stars in northern H II
regions", Astronomy and Astrophysics Supplement Series, Vol. 77, 439-445.
[1989A&AS...77..439F]
2. ^ Lafon, G., Baudry, A., de La Noe, J., et al. (1983). "The molecular
cloud-H II region complexes associated with SH 90 and SH 235", Astronomy
and Astrophysics, Vol. 124, 1-10. [1983A&A...124....1L]
3. ^ Turner, D. G. (1986). "The large globule LYNDS 810 as a possible member of
the Vulpecula OB1 complex", Astronomy and Astrophysics, Vol. 167, 157-160.
[1986A&A...167..157T]