O3V

There are no O3V anchor (Garrison94) or dagger (MK73) standards.

HDE 303308 *used to be* the O3V primary standard, but
it appears now that HD 64568 is.

Walborn02 states "HD 64568 and LH 10-3058 now redefine spectral type O3 V((f*))."

Walborn90 standard:  HDE 303308 O3V((f))
Walborn02 standards: HD 64568 O3V((f*)), LH 10-3058 O3V((f*))

Skiff08 does not flag any stars as O3V standards.

B-V(O3V)  = -0.28  ; Martins06
B-V(O3V)  = -0.330 ; pri. stan. HD 64568 (Q-method)
B-V(O3V)  = -0.331 ; U-B=-1.18 from trend/Q-method
=> adopt (B-V)(O3V) = -0.33 [updated 2/7/2020]

U-B(O3V)  = -1.16 ; Martins06
U-B(O3V)  = -1.178 ; pri. stan. HD 64568 (Q-method)
U-B(O3V)  = -1.22 ; Bessell98
U-B(O3V)  = -1.22 ; Schmidt-Kaler82
=> adopt (U-B)(O3V) = -1.175 [updated 2/7/2020]

Teff(O3V) =  52500 K  ; Schmidt-Kaler82
Teff(O3V) =  50000 K  ; Bessell98
Teff(O3V) =  50000 K  ; Crowther97/Fig.3 
Teff(O3V) = 46500 K   ; Massey05(Milky Way)
Teff(O3V) =  46500 K  ; non-stan. HD 93128 (Repolust04)
Teff(O3V) =  46000 K  ; non-stan. HD 93250 (Repolust04)
Teff(O3V) = 44900 K   ; pri. stan. HD 64568 (large scatter)
Teff(O3V) = 44852 K   ; Martins05(Obs. scale), adopted by GrayCorbally09
Teff(O3V) = 44616 K   ; Martins05(Theoretical scale)
Teff(O3V) = 44520 K   ; Holgado18(extrapolation past O4V)
=> adopt Teff(O3V) = 44900 K (logTeff = 4.652) [updated 2/9/2020]

Mv(O3V)   =  -6.14 mag ; non-stan. HD 93250 (Repolust04)
Mv(O3V)   =  -6.0  mag ; Schmidt-Kaler82
Mv(O3V)   = -5.86 mag ; Martins06/obs.scale
Mv(O3V)   = -5.85 mag ; Martins06/theor.scale
Mv(O3V)   = -5.80 mag ; Bowen08
Mv(O3V)   = -5.79 mag ; Martins05
Mv(O3V)   = -5.767 mag ; EEM trend for O dwarfs
Mv(O3V)   = -5.7 +-0.2 mag ; Walborn02 (n=7 O2-O3V((f*)) stars
Mv(O3V)   = -5.688 mag ; EEM trend for O dwarfs logL=5.784, BCv=-4.03
Mv(O3V)   = -5.65 mag ; Russeil03
Mv(O3V)   = -5.6  mag ; GrayCorbally09
=> adopt Mv(O3V) = -5.8 mag [updated 2/7/2020]

BCv(O3V)  =  -4.62  mag ; Schmidt-Kaler82(BCv=-4.75 + 0.13 offset)
BCv(O3V)  =  -4.290 mag ; Flower96(Teff=44900K,set so BCv(5772K)=-0.085)
BCv(O3V)  = -4.156 mag ; Chen19 PARSEC Teff=44900K,solar,logg=3.75
BCv(O3V)  = -4.05  mag ; Martins05(obs.scale)
BCv(O3V)  = -4.03  mag ; Martins05(theor.scale)
BCv(O3V)  = -4.013 mag ; LanzHubeny03(Teff=44900K,Z/Zsun=1)
BCv(O3V)  = -3.99  mag ; Martins06(obs.scale)
BCv(O3V)  = -3.97  mag ; Martins06(theor.scale)
BCv(O3V)  =  -3.664 mag ; Balona94(Teff=44900K,set so BCv(5772K)=-0.085]
=> adopt BCv(O3V) = -4.01 [updated 2/9/2020]

logL(O3V) =  5.66  dex ; non-stan. HD 93128 (Repolust04)
logL(O3V) =  5.784 dex ; EEM trend for O dwarfs
logL(O3V) =  5.820 dex ; Mv=-5.8, BCv=-4.01, Mbol=-9.810
logL(O3V) =  5.834 dex ; Martins05
logL(O3V) =  6.01  dex ; non-stan. HD 93250 (Repolust04)
=> adopt logL(O3V) =  5.820 dex [updated 2/9/2020]
=> adopt Mbol(O3V) = -9.810 mag [updated 2/9/2020]

logg(O3V) = 4.00 dex ; non-stan. HD 93128 (Repolust04)
logg(O3V) = 3.95 dex ; non-stan. HD 93250 (Repolust04)
logg(O3V) = 3.75 dex ; Holgardo18
=> adopt logg(O3V) = 3.75 dex [updated 1/31/2020]

Rad(O3V) = 15.9   Rsun ; HD93250/Repolust04
Rad(O3V) = 13.687 Rsun ; Martins05 (Teff=44853K,logL=5.834)
Rad(O3V) = 13.4326 Rsun ; Teff=44900, logL=5.820
Rad(O3V) = 10.4   Rsun ; HD93128/Repolust04
=> adopt Rad(O3V) = 13.433 Rsun [updated 2/9/2020]

# No Standards

MK78 and Keenan85 does not list an O3V standard (or earlier; only O4V and later).

# Primary Standards

HD 64568 = NGC 2467 77 = HD 64568a
  O3V(f*): Walborn82
 *O3V((f*)): Walborn02
  O4((f)): Garrison77
  O5:: MacConnell76
  O5: Crampton71,Loden65
  O5/6: Houk88
  
  Star was consistently called O3V (variant) by Walborn82 and
  Walborn02.  Appears to be binary and is referred to as HD 64568a in
  Markova18.  V=9.397+-0.018(Mermilliod91),
  B-V=0.071+-0.020(Mermilliod91), U-B=-0.895+-0.029(Mermilliod91). QBV
  method by EEM => (B-V)o=-0.330, (U-B)o=-1.178, E(B-V)=0.401,
  Av=1.294.  Mv=-6.22+-0.61. Teffs: 41000+-2000K(Garcia04),
  44900+-1700K(Williams11), 48000+-15000K(Markova18) => <Teff> =
  44900K(large scatter).  logg=3.91+-0.08(William11),
  logg=3.9+-0.2(Garcia04), logg=4.00+-0.10(Markova18).
  Rad=11.5Rsun(Markova18). logL=5.80(Markova18).
  
# Secondary Standard

LH 10-3058 
  O3V((f*)): Walborn02

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).
  
# Others

Walborn02 also lists Sk-71_51, P1163, P1311, & ST_5-52
as examples of O3V((f*))

Walborn71 defined O3 from 4 Carina Nebula stars.
Walborn82 discusses the O3 class in detail.
Walborn02 further bifurcates O3 into O2 and O3.5 also.