Editing Supergiant (section)

===Surface gravity===
The supergiant luminosity class is assigned on the basis of spectral features that are largely a measure of surface gravity, although such stars are also affected by other properties such as [[microturbulence]].  Supergiants typically have surface gravities of around log(g) 2.0 cgs  and lower, although bright giants (luminosity class II) have statistically very similar surface gravities to normal Ib supergiants.<ref name=grayII>{{cite journal|bibcode=2001AJ....121.2159G|title=The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. II. Basic Parameters of Program Stars and the Role of Microturbulence|journal=The Astronomical Journal|volume=121|issue=4|pages=2159|last1=Gray|first1=R. O.|last2=Graham|first2=P. W.|last3=Hoyt|first3=S. R.|year=2001|doi=10.1086/319957|doi-access=free}}</ref>  Cool luminous supergiants have lower surface gravities, with the most luminous (and unstable) stars having log(g) around zero.<ref name=levesque/>  Hotter supergiants, even the most luminous, have surface gravities around one, due to their higher masses and smaller radii.<ref name=clark>{{cite journal|bibcode=2012A&A...541A.145C|arxiv=1202.3991|title=On the nature of the galactic early-B hypergiants|journal=Astronomy & Astrophysics|volume=541|pages=A145|last1=Clark|first1=J. S.|last2=Najarro|first2=F.|last3=Negueruela|first3=I.|last4=Ritchie|first4=B. W.|last5=Urbaneja|first5=M. A.|last6=Howarth|first6=I. D.|year=2012|doi=10.1051/0004-6361/201117472|s2cid=11978733}}</ref>