G2.5V Keenan80 standard: 70 Vir (=HD 117176) - G2.5Va (but later G4V in Keenan88!) Keenan83 standard: psi Ser (=HD 140538) - G2.5V 16 Cyg B (=HD 186427= "16 Cyg fol") - G2.5V Keenan85 standard: zet^1 Ret (=HD 20766) - G2.5V Fe 1 hdel 1 58 Eri (=HD 30495) - G2.5V psi Ser (=HD 140538) - G2.5V Keenan88 standard: 9 Cet (=HD 1835) - G2.5V psi Ser (HD 140538) - G2.5V 58 Eri (=HD 30495) - G2.5IV-V Keenan89 standard: 9 Cet (=HD 1835) - G2.5V psi Ser (HD 140538) - G2.5V zet^1 Ret (=HD 20766) - G2.5V Hdel1 58 Eri (=HD 30495) - G2.5IV-V Teff(G2.5V) = 5739 K ; Teff from smoothed SpT(Teff) trend => adopt Teff(G2.5V) = 5740 K (logTeff = 3.759) [updated 10/27/2017] BCv(G2.5V) = -0.086 [last updated 8/3/2018, on scale where BCv(5772K)=-0.08] # Standard HD 1835 = 9 Cet = BE Cet = HR 88 = GJ 17.3 = GJ 9012 G2V: Keenan85 G2.5V: Keenan88(stan),Keenan89,Keenan99 G2V m+0.25: Gray89 G5V CH-0.5: Gray06 Neither of Gray's published types agrees with Keenan's. Probably not a good standard. HD 140538 = psi Ser = HR 5853 G2.5V: Keenan85,Keenan88 No Teff estimates # Weak Standard HD 117176 = 70 Vir = HR 5072: HIP[B-V] = 0.714+-0.007 G4V: Keenan83, Keenan89(G4Va) G2.5Va: Keenan80 G5V: Gray01,JM53 G5IV-V: MK43 This star is similar to 16 Cyg B in that its temperature type has moved around quite a bit over the years. Mamajek02 suggests "IV-V" may be a more appropriate luminosity class. The majority of Skiff07 refs show G5V, Keenan89 is only G4V, and Keenan80 had as G2.5V! The B-V=0.714 is redder than mean G4V (0.659) Given its range of published types by Keenan alone (G5 in MK43, G2.5 in Keenan80, and G4 in Keenan83 and Keenan89), I would say that this is a poor standard. HD 186427 = 16_Cyg_B = HR 7504 = GJ 765.1B (J1941+5031) *G3V: Keenan85,Keenan88,Keenan89,Gray03,Gray06 G4V: Keenan80 G2.5V: Keenan83 G2V: Gray01 G5V: JM53, Wilson62 G4.5V: Stebbins57 G2V: Adams35 16 Cyg B has been considered a standard G2.5V, G3V, G4V, and G5V at different times by Morgan and Keenan. It appears that Keenan stopped at G3V in the 80s, and Gray03/06 adopted this (although Gray01 said G2V). I adopt Keenan's final "G3V" and consider it a primary standard. B-V[HIP]=0.661+-0.005. # Variant HD 20766 = zet^1 Ret = HR 1006 G2.5V Fe1 Hdel1 : Keenan85 *G2.5V H delta1 : Keenan99 HD 30495 = 58 Eri G2.5V: Keenan85 *G2.5V-IV: Keenan88(stan),Keenan89