Sh 2-28 and RCW 145 are the same object. This becomes clear by comparing the direction and size of RCW 145 with the corrected BFS coordinates for Sh 2-28. For more information on errors in the original Sharpless catalog, see this article
Unfortunately SIMBAD uses the incorrect original Sharpless coordinates for Sh 2-28 rather than the corrected BFS coordinates.
Perhaps because of the errors in the original Sharpless coordinates for Sh 2-28, the RCW catalog identifies RCW 145 and Sh 2-26. Sh 2-26 is a smaller even fainter nebula further from the galactic plane (although part of it does appear to intersect the top of the boundaries the RCW catalog gives for RCW 145.).
The W 28 supernova remnant appears to be further away at a distance of 1800 to 3300 pc [1
] but, on the other hand, a 1978 paper by Crampton and Georgelins concludes that the nebula is the optical equivalent of W 28 and includes the supernova remnant. It appears to be associated with M 20, the Trifid nebula. Crampton and Georgelins conclude that Sh 2-28 is ionised by LSS 4551 and LSS 4538. [2
A 1993 paper finds a distance of 1500 pc for LS 4551. [3
1. ^ Giuliani, A., Tavani, M., Bulgarelli, A., et al. (2010). "AGILE detection
of GeV γ-ray emission from the SNR W28", Astronomy and Astrophysics, Vol.
516, L11. [2010A&A...516L..11G]
2. ^ Crampton, D., Georgelin, Y. M., & Georgelin, Y. P. (1978). "First optical
detection of W51 and observations of new H II regions and exciting stars",
Astronomy and Astrophysics, Vol. 66, 1-11. [1978A&A....66....1C]
3. ^ Kilkenny, D. (1993). "A study of reddened luminous stars in the Southern
Milky Way. II. Hβ photometry, reddening and distances.", South African
Astronomical Observatory Circular, Vol. 15, 53-64. [1993SAAOC..15...53K]