K2.5V Keenan99 standard: HD 283750 (=BD+26_730) - K2.5Ve (B-V)(K2.5V) = 0.866 ; exemplar HD 191408 (B-V)(K2.5V) = 0.917 ; exemplar HD 115404 (B-V)(K2.5V) = 0.938 ; Gray03/06 N=84 K2.5V B-V (+-0.003 sem, +-0.036 stdev) (B-V)(K2.5V) = 0.942 ; Koen10 d<25pc median K2.5V (B-V)(K2.5V) = 0.949 ; exemplar HR 1982 = HD 38392 (B-V)(K2.5V) = 1.12 ; deprecated stan. HD 283750 => adopt (B-V)(K2.5V) = 0.938 ; updated 5/19/2018 => adopt (U-B)(K2.5V) = 0.691 => adopt (Bt-Vt)(K2.5V) = 1.101 => adopt (V-Ic)(K2.5V) = 0.974 => adopt (V-Rc)(K2.5V) = 0.513 => adopt (R-Ic)(K2.5V) = 0.460 => adopt (V-J)(K2.5V) = 1.711 => adopt (V-H)(K2.5V) = 2.170 => adopt (V-Ks)(K2.5V) = 2.274 => adopt (H-Ks)(K2.5V) = 0.104 => adopt (J-H)(K2.5V) = 0.459 => adopt (K-W1)(K2.5V) = 0.032 => adopt (V-Hp)(K2.5V) = -0.142 => adopt (W1-W2)(K2.5V) = -0.071 => adopt (W1-W3)(K2.5V) = -0.032 => adopt (W1-W4)(K2.5V) = -0.006 => adopt (G-J)(K2.5V) = 1.361 => adopt (G-Ks)(K2.5V) = 1.925 (G-V)(K2.5V) = -0.315 ; HD 203850 PM* K2.5V (G-V)(K2.5V) = -0.308 ; HD 154577 PM* K2.5Vk: (G-V)(K2.5V) = -0.303 ; HD 40307 PM* K2.5V (G-V)(K2.5V) = -0.300 ; HD 5133 PM* K2.5Vk: (G-V)(K2.5V) = -0.293 ; HD 53927 PM* K2.5V (G-V)(K2.5V) = -0.293 ; smooth fit f(SpT) G9V-M0V (G-V)(K2.5V) = -0.292 ; trend for SIMBAD d<20pc for V-Ks=2.274 (G-V)(K2.5V) = -0.291 ; BD+21 3245 PM* K2.5V (G-V)(K2.5V) = -0.287 ; HD 223374 PM* K2.5V (G-V)(K2.5V) = -0.284 ; HD 155712 PM* K2.5V (G-V)(K2.5V) = -0.280 ; HD 25665 PM* K2.5V (G-V)(K2.5V) = -0.277 ; exemplar HD 191408 PM* K2.5V (G-V)(K2.5V) = -0.274 ; HD 4628 PM* K2.5V (G-V)(K2.5V) = -0.272 ; HD 4635 PM* K2.5V+ (G-V)(K2.5V) = -0.271 ; HD 216259 PM* K2.5V (G-V)(K2.5V) = -0.264 ; HD 197396 PM* K2.5V (G-V)(K2.5V) = -0.252 ; BD+31 3330 PM* K2.5V (G-V)(K2.5V) = -0.246 ; HD 208038 PM* K2.5V => adopt (G-V)(K2.5V) = -0.29 [updated 9/21/2021] (Bp-Rp)(K2.5V) = 1.0885 HD_191408 K2.5V (Bp-Rp)(K2V) = 1.10 K2V mean (Bp-Rp)(K2.5V) = 1.146 fit for V-Ks=2.274 (Bp-Rp)(K2.5V) = 1.1560 V*_AK_Lep K2.5V(k) (Bp-Rp)(K3V) = 1.21 K3V mean => adopt (Bp-Rp)(K2.5V) = 1.15 [updated 7/17/2020] (G-Rp)(K2.5V) = 0.6088 ; HD_191408 K2.5V (G-Rp)(K2V) = 0.62 ; K2V mean (G-Rp)(K2.5V) = 0.6341 ; V*_AK_Lep K2.5V(k) (G-Rp)(K2.5V) = 0.636 ; fit for V-Ks=2.274 (G-Rp)(K3V) = 0.66 ; K3V mean => adopt (G-Rp)(K2.5V) = 0.64 [updated 7/17/2020] => adopt (Bp-G)(K2.5V) = 0.51 [updated 7/17/2020; Bp-Rp=1.15, G-Rp=0.64] (V-Ks)(K2.5V) = 3.15 ; deprecated stan. HD 283750 Teff(K2.5V) = 5047 +- 19 K ; GJ 33 (Pecaut13) Teff(K2.5V) = 5035 K ; non-stan. GJ 505 (slightly metal-poor) Teff(K2.5V) = 4994 K ; Gray03/06 K2.5V stars trend w/PASTEL Teff (for [Fe/H]=0.00 Teff(K2.5V) = 4967 K ; exemplar HR 1982 = HD 38392 (solar metallicity) Teff(K2.5V) = 4923 K ; smoothed Teff(SpT) trend Teff(K2.5V) = 4920 K ; exemplar HD 160346 (solar metallicity) => adopt Teff(K2.5V) = 4990 K (logT = 3.698) ; updated 5/19/2018 BCv(K2.5V) = -0.283+-0.021 mag ; GJ 33 (Pecaut13) BCv(K2.5V) = -0.288 ; median of 5 calibrations for Teff=4990K (systematic rms scatter 0.031) BCv(K2.5V) = -0.312 ; interp K2V(logT=3.708,BCv=-0.26), K3V(logT=3.687,BCv=-0.37) => adopt BCv(K2.5V) = -0.31 [last updated 8/3/2018, adjusted so that BCv(5772K)=-0.08] Mv(K2V) = 6.17 ; adopted for K2V Mv(K2.5V) = 6.31 ; Gray01/03/06 dwarfs, xHIP B-V/Mv, Gaspar16 |[Fe/H]|<0.05 "solar": fit for B-V=0.938 Mv(K2.5V) = 6.32 ; Koen10 d<25pc median K2.5V Mv(K2.5V) = 6.34 ; B-V=0.938 Mv(K2.5V) = 6.41 ; exemplar HR 1982 = HD 38392 Mv(K2.5V) = 6.43 ; adopted for K3V => adopt Mv(K2.5V) = 6.31 [updated 9/26/2020] => adopt M_G(K2.5V) = 6.02 [updated 9/21/2021] (Mv=6.31, G-V=-0.29) => adopt M_Ks(K2.5V) = 4.036 [updated 9/26/2020] (Mv=6.31, V-Ks=2.274) M_G(K2.5V) = 6.148 ; SIMBAD d<20pc trend for V-Ks=2.274 logL(K2.5V) = -0.504 ; Mv=6.31, BCv=-0.31, Mbol=6.000 => adopt logL(K2.5V) = -0.504 [updated 9/26/2020] => adopt Mbol(K2.5V) = 6.000 [updated 9/26/2020] Rad(K2.5V) = 0.749 Rsun ; Teff=4990K, logL=-0.504 => adopt Rad(K2.5V) = 0.749 [updated 9/26/2020] Mass(K2.5V) = 0.831 Msun ; EEM fit to Torres10 binaries for Mv=6.34 Mass(K2.5V) = 0.798 Msun ; EEM calib for logL=-0.512 Mass(K2.5V) = 0.794 Msun ; Eker15 calib for logL=-0.512 Mass(K2.5V) = 0.76 Msun ; 0.78 Msun for K2V, 0.75 Msun for K3V Mass(K2.5V) = 0.746 Msun ; Mann18 calib for M_Ks=4.066 => adopt Mass(K2.5V) = 0.76 Msun [last updated 8/2/2018] # Deprecated Standard HD 283750 = BD+26_730 = V833 Tau K2V: Oswalt88 *K2.5Ve : Keenan89,Keenan99 K3IVke: Gray03 K5: Metreveli68 K5Vep: Eggen65 128" common proper motion pair with DA white dwarf. VSX reports as BY Dra variable with min and max magnitude 9.10 and 9.90. V=8.39, B-V=1.12, U-B=0.86 (Mermilliod87). J=5.945+-0.023(2MASS), H=5.400+-0.011(2MASS), Ks=5.240+-0.023(2MASS). V-Ks=8.39-5.24 = 3.15. PASTEL: only one set of spectroscopic parameters: 4831+-6K, logg=4.8+-0.2, [Fe/H]=0.34+-0.05 dex (all Mishenina08, Mishenina12 identical). Not a well characterized star, is very active variable, very metal-rich, and not much use as a standard beyond Keenan's late compendia. # Exemplars HR 1982 = HD 38392 = gam Lep B = AK Lep K2V: Roman49,Levato78 *K2.5V(i): Gray06 K3V: Munch44,Bidelman85(K3),Abt08 K6V: Adams35 Surprisingly bright star missing from Hipparcos, but in Tycho. Ursa Major stream member, unclear if associated with cluster. V=6.16(TYC), V=6.160+-0.012(Mermilliod91), B-V=0.954+-0.009(TYC), B-V=0.949+-0.007(Mermilliod91), U-B=0.740+-0.000(Mermilliod91), 2MASS photometry is flagged CCD so poor all around. plx=112.4005+-0.0302mas(GaiaDR2). Mv=6.414+-0.012(M91,GaiaDR2). PASTEL: =4967K(N=5), =4.50(N=4), <[Fe/H]>=-0.01(N=4). HD 191408 = HR 7703 = GJ 783A = HJ 5173 A K2V: Wilson62,Houk82,Bidelman85(K2) *K2.5V: Gray06 K3V: Evans57,BSC,Gliese91 K4V: Adams35,1942HarCi.448....1H K5V: 1923AnHar..98.....C M5V V=12 companion 4" away on ~millenium period orbit. Separation has shrunk from 15" to 4" since J. Herschel discovered it in 1834. Type has steadily marched hotter since 1923! Presumably the range in types is due to metal poorness. V=5.318+-0.006(Mermilliod91), B-V=0.866+-0.007(Mermilliod91), U-B=0.442+-0.042(Mermilliod91). PASTEL: = 4953K(N=9), <[Fe/H]> = -0.535(N=8) , logg=4.61(N=8). Ramirez13: Teff=4969+-66K, logg=4.62+-0.02, [Fe/H]=-0.52+-0.05. Ages: 6.1+-0.9Gyr(Ramirez12),7.0Gyr(Gaspar13). Masses: 0.69+-0.03Msun(Ramirez12). Soubiran05 and Ramirez12 classify it as thick disk. Using Bensby14, I estimate P(thin)=1.5%, P(thick)=95.3%, P(halo)=0.2%, P(Hercules)=3.1%. [alpha/Fe] = +0.28 (Soubiran05). Luminosities: L=0.286Lsun(Eiroa13), L=0.28309+-0.00784Lsun(Stassun19; logL = -0.5481+-0.0120), L=0.297+-0.001Lsun(GaiaDR2). logLx/Lbol=-6.1(Eiroa13). GaiaDR2: plx= 166.2274+-0.1256mas (=> 6.01481+-0.00454 pc). Rad=0.697+-0.044Rsun(Stassun19), Rad= 0.718+-0.022(Teff from Ramirez13, Lum from Stassun19), Rad=0.73+-0.01Rsun(GaiaDR2). Masses: 0.69+-0.00Msun(Maldonado19), 0.694+-0.017Msun(Ramirez13), 0.7508+-0.0378Msun(Anders19), 0.76+-0.02Msun(Casagrande11) Mass=0.840+-0.095Msun(Stassun19). HD 115404 = GJ 505 K1V: Abt81 K2V: Wilson62,Cowley67 *K2.5V(k): Gray03 K3V: 1927MeUpp..28....1L,Adams35,Bidelman85(K3) M1V companion 7.25" away. V=6.537+-0.024(Mermilliod91), B-V=0.917+-0.021(Mermilliod91), U-B=0.623+-0.020(Mermilliod91), b-y=0.532(Hauck97). All 2MASS photometry low quality. Metal poor. PASTEL: = 5035K, [Fe/H] ~ -0.15 [excluding Luck05/06, which had [Fe/H]=-0.34, 4100K?] HD 23356 = UGP 67 K2V: Houk88 K2IV-V: Upgren72 *K2.5V: Gray06 K3: Bidelman85 # Notes Gray03/06 K2.5V stars queried through PASTEL w/182 pairs of Teff,[Fe/H]. Trend for K2.5V stars: Teff = 4994K + 1.211633e2*[Fe/H] ; rms=85K