O4V Garrison94 does not list an O4V anchor standard, however it appears that from all recent literature that HD 46223 is the primary O4V standard. MK73 lists HD 46223 as the "O4" dagger standard, and indeed all subsequent published types (mostly by Walborn and MK78) consider the star to be O4V (or variant). Abt68 standard: HD 46223 - O4 (no luminosity class) Walborn71 standard: HD 46223 - O4V((f)) MK73 standard: HD 46223 - O4 (no luminosity class) Garrison77 standard: HD 46223 - O4V MK78 standard: HD 46223 - O4V Keenan85 standard: HD 46223 - O4V Garcia89 standard: HD 46223 - O4V Walborn90 standard: HD 46223 - O4V((f)) Walborn02 standards: HD 46223 - (O4V), HDE 303308 (O4V, formerly O3V), W28-5 (O4V) GrayAtlas standard: HD 46223 - O4V GrayNStars standard: HD 46223 - O4V Skiff08 lists only one O4V standard: HD 46223 Walborn72 classified three stars as O4V or variant: HD 45223 (O4V((f))), HD 46233 (O4V((f))), and HD 96715 (O4V). B-V(O4V) = -0.28 ; Martins06 B-V(O4) = -0.291 ; EEM dereddened zet Pup O4I (just for comparison) B-V(O4V) = -0.32 ; Bohm-Vitense81 B-V(O4V) = -0.324 ; exemplar HD 96715 Q-method B-V(O4V) = -0.325 ; exemplar HD 164794 = 9 Sgr Q-method B-V(O4V) = -0.326 ; pri. stan. HD 46223 Q-method B-V(O4V) = -0.326 ; U-B=-1.16 using Q-method => adopt (B-V)(O4V) = -0.326 [updated 2/7/2020] U-B(O4) = -1.125 ; EEM dereddened zet Pup O4I (just for comparison) U-B(O4V) = -1.15 ; Martins06 U-B(O4V) = -1.153 ; exemplar HD 96715 (Q method) U-B(O4V) = -1.156 ; exemplar HD 164794 = 9 Sgr (Q method) U-B(O4V) = -1.161 ; pri. stan. HD 46223 (Q method) U-B(O4V) = -1.20 ; Bessell98 U-B(O4V) = -1.20 ; Schmidt-Kaler82 => adopt (U-B)(O4V) = -1.16 [updated 2/7/2020] Teff(O4V) = 41000 K ; weak stan. HD 303308 (Repolust04; O4 V ((f+))) Teff(O4V) = 41500 K ; non-stan. NGC 345 MPG 324 (Heap06) & Heap06 adopted for O4V((f)) Teff(O4V) = 42241 K ; Simon-Diaz14 linear fit for O4V Teff(O4V) = 42857 K ; Martins05(Theoretical scale),GrayCorbally09 Teff(O4V) = 42900 K ; Holgado18 Teff(O4V) = 42900 K ; EEM trend for O dwarfs 1/2020 ** Teff(O4V) = 43000 K ; pri. stan. HD 46223 (median Teff) Teff(O4V) = 43419 K ; Martins05(Obs. scale) Teff(O4V) = 43652 K ; Simon-Diaz17 median for O4V (N=3) Teff(O4V) = 44000 K ; Massey05(Milky Way) Teff(O4V) = 44000 K ; Bessell98 Teff(O4V) = 44000 K ; Crowther97/Fig.3 Teff(O4V) = 48000 K ; Schmidt-Kaler82 => adopt Teff(O4V) = 42900 K (logTeff = 4.632) [updated 1/20/2020] Mv(O4V) = -5.22 mag ; pri. stan. HD 46223 ; Martins11 Mv(O4V) = -5.29 mag ; weak stan. HD 303308 ; Repolust04 Mv(O4V) = -5.44 mag ; pri. stan. HD 46223 (Q-method,NGC2244 dist) Mv(O4I) = -5.49 mag ; O4I(n)f zet Pup *supergiant* Mv(O4V) = -5.5 mag ; GrayCorbally09 Mv(O4V) = -5.50 mag ; Martins05 (stdev=0.4 mag) Mv(O4V) = -5.52 mag ; Russeil03 Mv(O4V) = -5.525 mag ; logL/Teff trend for O dwarfs: logL=5.652,BCv=-3.92 Mv(O4V) = -5.526 mag ; EEM trend for O dwarfs Mv(O4V) = -5.56 mag ; Martins06/theor.scale Mv(O4V) = -5.57 mag ; Martins06/obs.scale Mv(O4V) = -5.65 mag ; Bowen08 Mv(O4V) = -5.76 mag ; exemplar HD 164794 = 9 Sgr Mv(O4V) = -5.9 mag ; Schmidt-Kaler82 Mv(O4V) = -6.1 mag ; Conti71(ZAMS) => adopt Mv(O4V) = -5.5 mag [updated 2/9/2020] BCv(O4V) = -3.588 mag ; Balona94(Teff=42900K, set so BCv(5772K)=-0.085) BCv(O4V) = -3.85 mag ; Martins06(obs.scale) BCv(O4V) = -3.870 mag ; LanzHubeny03(Teff=42900K,Z/Zsun=1) BCv(O4V) = -3.89 mag ; Martins06(theor.scale) BCv(O4V) = -3.92 mag ; Martins05(obs.scale) BCv(O4V) = -3.95 mag ; Martins05(theor.scale) BCv(O4V) = -4.008 mag ; Chen19 PARSEC Teff=44900K,solar,logg=3.77 BCv(O4V) = -4.144 mag ; Flower96(Teff=42900K, set so BCv(5772K)=-0.085) BCv(O4V) = -4.32 mag ; Schmidt-Kaler82(BCv=-4.45 + 0.13 offset) => adopt BCv(O4V) = -3.89 [updated 1/31/2020] logL(O4V) = 5.68 dex ; Martins05(Theoretical scale) logL(O4V) = 5.67 dex ; Martins05(Obs. scale) logL(O4V) = 5.652 dex ; Mv = -5.5, BCv= -3.89, Mbol=-9.390 logL(O4V) = 5.60 dex ; HD 46223 (Martins11) logL(O4V) = 5.53 dex ; weak stan. HD 303308 (Repolust04) => adopt logL(O4V) = 5.652 dex [updated 2/9/2020] => adopt Mbol(O4V) = -9.390 mag [updated 2/9/2020] logg(O4V) = 3.92+-0.15 (stdev) ; Martins05 logg(O4V) = 3.90 dex ; weak stan. HD 303308 (Repolust04) logg(O4V) = 3.77 dex ; Holgado18 => adopt logg(O4V) = 3.77 dex [updated 1/31/2020] Mass(O4V) = 39.0 Msun ; weak stan. HD 303308 (Repolust04) Mass(O4V) = 46.16 Msun ; Martins05/theo. Teff scale Mass(O4V) = 46.94 Msun ; Martins05/obs. Teff scale Mass(O4V) = 48.3 Msun ; MIST/Choi16 solar tracks for logT=4.632,logL=5.652 Mass(O4V) = 54+7-6 Msun ; Weidner10 => adopt Mass(O4V) = 48 Msun [updated 4/16/2022] Rad(O4V) = 12.4090 Rsun ; Teff=42900K, logL=5.672 Rad(O4V) = 12.324 Rsun ; Martins05 (Teff=42858K,logL=5.664) Rad(O4V) = 11.5 Rsun ; HD303308/Repolust04 => adopt Rad(O4V) = 12.127 Rsun [updated 2/9/2020] # Primary Standards HD 46223 = NGC 2244 Johnson 3 O4: Morgan65,Abt68,MK73(dagger) O4V: Garrison77(stan),MK78(stan),Keenan85,Garcia89,GrayAtlas O4V((f)): Walborn71(stan),Walborn72,Walborn73,Walborn90,Martins11 *O4V((f+)): Walborn02 Morgan65 classified the star as O4, and it has been a primary standard since. Considered O4V (variant) standard by all Walborn papers. Adopt "O4V((f+))" M91: V=7.266+-0.015, B-V=0.217+-0.008, U-B=-0.774+-0.013 => QBV => (B-V)o=-0.326, (U-B)o=-1.161, E(B-V)=0.543, Av=1.754. Its a long way to redden, however. E(B-V)=0.470(Zejda12), E(B-V)=0.481(Kervella19,STILISM), E(B-V)=0.51(Slyk08). Bohannon90 gives Teff=46000+-1000, (B-V)o=-0.31, (U-B)o=-1.10. Teffs: 42200+-500K(Holgado18), 43000K(Martins11), 46000+-1000K(Bohannon90) => median Teff = 43000K. logg = 3.73+-0.04(Holgado18). plx = 0.2777+-0.0321 mas(GaiaDR2) => 1/plx(corr.Lindegren18) => 3260.5 pc (m-M)o=12.566. Dist = 3254pc (BailerJones18; (m-M)o=12.562). *However*, it is member of NGC2244 which has closer distance: Cantat-Gaudin20 quotes D=1548.8pc(mode). Using own GaiaDR2, it seems too luminous (Mv=-7.05), but at mean cluster distance (D=1548.8pc), I get: V=7.266, plx=0.646mas, Av=1.754 => Mv=-5.44. # Secondary Standards W28-5 = W61 28-5 = 2MASS J05342846-6943568 O4V((f+)): Walborn02,Massey04 O4V((f)): Massey00 LMC member from from Westerlund61, but will be lower metallicity than Galactic O4V stars. # Exemplars HD 96715 *O4V((f))z: Holgado18,Sota14 O4V((f)): Walborn73[Snow94 adopts] O4V: Walborn72,Garrison77 O5: Houk75 O5:: 1972A&AS...16..323T Good agreement on O4V since mid-70s. V=8.255+-0.011, B-V=0.106+-0.013, U-B=-0.847+-0.020(Mermilliod91) => Q-method => (B-V)o=-0.324, (U-B)o=-1.153, E(B-V)=0.430, Av=1.388. Teffs: 39000+-2000K(Garcia04), 40400+-1800K(William11), 45200+-1200K(Holgado18), 46400K(Snow94) => adopting recent 45200+-1200K(Holgado18). logg=4.0+-0.2(Garcia04), logg=3.91+-0.13(Holgado13), logg=3.84+-0.11(William11). Mv = -6.3(Snow94) HD 164794 = 9 Sgr = NGC 6530 7 = HR 6736 O4V: Bisiachhi82 *O4((f))z: Sota14 O4((f)): Walborn72,Walborn73,Walborn85,Conti74,Maiz-Apellaniz16 O4f: Conti71,Conti73,Conti73 O5V: Jaschek78(Hiltner69(Stan)) O5: Morgan53,Morgan55,Jaschek64(most),Hiltner65 O6: Houk88 O7: Weaver53 Member of NGC 6530 Lagoon Nebula. Hiltner69 used as O5V standard, but recent types have converged on O4V subtype. V=5.973+-0.009, B-V=0.025+-0.009, U-B=-0.908+-0.012(Mermilliod91) => Q-method => (B-V)o=-0.325, (U-B)o=-1.156, E(B-V)=0.350, Av=1.128. E(B-V)=0.392(Kervella19,STILISM). plx = 0.8505+-0.0952mas(GaiaDR2). For NGC 3630, Damiani19 estimates D = 1325pc (plx=0.755mas, m-Mo=10.611). Mv=-5.50+-0.29(NebotGomez-Moran18). V=5.973, plx=0.755mas, Av=1.128 => Mv = -5.76. Cl* NGC 346 ELS 7 = Cl* NGC 346 W 6 = Cl* NGC 346 MPG 324 = 2MASS J00585738-7210336 *O4V((f)): Massey89,Walborn00 O4V((f+)): Evans06 O4/5V: 1986PASP...98.1133N O5V: Massey09 SMC exemplar. 0 58 57.38 -72 10 33.7(ICRS). V=13.74, B-V=-0.29, U-B=-1.00(Massey02). # Deprecated Standard HDE 303308 = Cl* Trumpler 16 MJ 480 O3V: Walborn71, Garmany82(Humphreys78), O3V((f)): Walborn73,Walborn90,Massey93 O3: Conti77 O4V((f)): Alexander16(near 4100A) O4V((f+)): Walborn02 O4V((fc)): Walborn10 *O4.5V((fc)): Sota14 O5: Vijapurkar93 O5/6V: Alexander16(near 4400A) Walborn02 redefined this star from an O3V standard (Walborn73,Walborn90) to a primary O4V standard (Walborn02). # Other Stars HD 66811 = zet Pup (not O4 dwarf, but instructive for UBV colors) *O4I(n)f: Walborn72 O4fe: Conti74 O4f: Conti71 O5: MK43 O5Ik: Hiltner69 While not a dwarf, the O4I star zet Pup has the bluest U-B in Johnson66's UBV catalog, and the 2nd bluest B-V, so it might be useful for constraining the intrinsic UBV sequence for O stars. MaizAppellaniz18 has it as the O star with the lowest reddening and extinction in their sample of 562 O stars(!), with a corresponding E(B-V)=0.012+-0.009 and Av=0.059. plx=3.01+-0.10mas(HIP2). Unfortunately the Gaia photometry is fairly poor as it is a 2nd mag star. B-V=-0.27(Johnson66), B-V=-0.274+-0.009(Mermilliod91), B-V=-0.280+-0.013(Cousins71), U-B=-1.113+-0.012(Mermilliod91), U-B=-1.10(Cousins71), U-B=-1.09(Johsnon66), V=2.249+-0.012(Mermilliod91), V=2.25(Johnson66), V=2.255+-0.006(Cousins71). Good consensus on estimate of interevening hydrogen: logNH = 19.99, 19.99, 20.00 (Hobbs78, Bohlin78, Shull85), I adopt logNH = 19.99, which using Savage & Mathis 1979 conversion leads to E(B-V) = 0.0168 mag (similar to MaizApellaniz18 estimate of E(B-V)=0.012+-0.009). So (B-V)o = (B-V)obs - E(B-V) = -0.274 - 0.0168 = -0.291, and (U-B)o = (U-B)obs - E(U-B) = -1.113 - (0.0168*0.72) = -1.125. MaizApellaniz18 estimate the de-extincted Johnson V mag to be Vo=2.175+-0.059. GaiaEDR3 does not list astrometery. Vizier lists a *corrected* GaiaEDR3 Gmag = 2.2543+-0.0090. Using MaizApellaniz18 Vo and Av (assume +-0.03 err), HIP2 plx => Mv = -5.49+-0.10, which is surprisingly similar to the Mv estimates for O4 dwarfs! (see above)