O5V

HD 46150 appears to be the O5V primary standard. 

MK43 standard:        Zet Pup   - O5 (no luminosity class, from Plaskett 1922)
Abt68 standard:       HD 46150  - O5 (no luminosity class)
Hiltner69 standard:   HD 164794 = 9 Sgr - O5V
Walborn71 standard:   HD 46150  - O5V((f))
MK73 dagger standard: HD 46150  - O5 (no luminosity class; dagger standard), and
                      Zet Pup   - O5f (dagger standard)
Garrison77 standard:  HD 46150  - O5V
MK78 standard:        HD 46150  - O5V
Keenan85 standard:    HD 46150  - O5V
Garcia89 standard:    HD 46150  - O5V
Walborn90 standard:   HD 46150  - O5V((f))
GrayAtlas standard:   HD 46150  - O5V

Skiff08 lists only one O5V standard: HD 46150 (MK78)

B-V(O5V)  = -0.33   ; SchmidtKaler82
B-V(O5V)  = -0.323  ; U-B=-1.15 trend/Q-method
B-V(O5V)  = -0.325  ; pri. stan. HD 46150 
B-V(O5V)  = -0.32   ; Johnson58,Johnson63,Johnson66,Fitzgerald70,Morgan71
B-V(O5V)  = -0.28   ; Martins06
=> adopt (B-V)(O5V) = -0.323 [updated 2/7/2020]

U-B(O5V)  = -1.14   ; Martins06
U-B(O5V)  = -1.14   ; Johnson66
U-B(O5V)  = -1.15   ; Johnson58,Johnson63
U-B(O5V)  = -1.157  ; pri. stan. HD 46150 (Q-method)
U-B(O5V)  = -1.19   ; Bessell98
U-B(O5V)  = -1.19   ; Fitzgerald70
U-B(O5V)  = -1.19   ; Schmidt-Kaler82
=> adopt (U-B)(O5V) = -1.15  [updated 2/7/2020]
=> adopt Q(O5V)     = -0.921 [updated 2/7/2020]

(g-r)(O5V) = -0.62 ; Covey07 interp O5V -0.62 to O9V -0.62

Teff(O5V) =  40300 K ; Bohm-Vitense81
Teff(O5V) =  40500 K ; non-stan. HD 15629 (Repolust04)
Teff(O5V) = 40728 K ; Simon-Diaz14 linear fit for O5V
Teff(O5V) = 40738 K ; Simon-Diaz17 median for O5V (N=1; HD46150)
Teff(O5V) = 40862 K ; Martins05(Obs. scale), GrayCorbally09
Teff(O5V) = 41000 K ; Massey05(Milky Way)
Teff(O5V) = 41280 K ; Holgado18
Teff(O5V) = 41400 K ; EEM trend for O dwarfs 1/2020 **
Teff(O5V) = 41540 K ; Martins05(Theoretical scale)
Teff(O5V) = 42000 K ; pri. stan. HD 46150 (median Teff)
Teff(O5V) =  43000 K ; Bessell98
Teff(O5V) =  43000 K ; Crowther97/Fig.3 
Teff(O5V) =  44500 K ; Schmidt-Kaler82
Teff(O5V) =  47034 K ; EEM N=6 Teffs
=> adopt Teff(O5V) = 41400 K (logTeff = 4.617) [updated 1/20/2020]

Mv(O5V) =  -5.7  mag ; Schmidt-Kaler82
Mv(O5V) = -5.67 mas ; pri. stan. HD 46150 (see below)
Mv(O5V) = -5.6  mag ; Conti71(ZAMS)
Mv(O5V) = -5.5  mag ; GrayCorbally09
Mv(O5V) = -5.50 mag ; non-stan. HD 15629 (Repolust04)
Mv(O5V) = -5.50 mag ; Bowen08
Mv(O5V) = -5.48 mag ; pri. stan. HD 46150 (Martins11)
Mv(O5V) = -5.41 mag ; Russeil03
Mv(O5V) = -5.34 mag ; EEM trend for O dwarfs
Mv(O5V) = -5.300 mag ; EEM logL/Teff trend for O dwarfs
Mv(O5V) = -5.27 mag ; Martins06/obs.scale
Mv(O5V) = -5.27 mag ; Martins06/theor.scale
Mv(O5V) = -5.21 mag ; Martins05
Mv(O5V) =  -5.10 mag ; Wegner07
=> adopt Mv(O5V) = -5.35 mag [updated 2/8/2020]

BCv(O5V) =  -4.27  mag ; Schmidt-Kaler82(BCv=-4.40 + 0.13 offset)
BCv(O5V) =  -4.027 mag ; Flower96(Teff=41400K, set so BCv(5772K)=-0.085)
BCv(O5V) = -3.894 mag ; Chen19 PARSEC Teff=41400K,solar,logg=3.75
BCv(O5V) = -3.82  mag ; Martins05(theor.scale)
BCv(O5V) = -3.76  mag ; Martins06(theor.scale)
BCv(O5V) = -3.758 mag ; LanzHubeny03(Teff=41400K,Z/Zsun=1)
BCv(O5V) = -3.78  mag ; Martins05(obs.scale)
BCv(O5V) = -3.71  mag ; Martins06(obs.scale)
BCv(O5V) =  -3.526 mag ; Balona94(Teff=41400K, set so BCv(5772K)=-0.085)
=> adopt BCv(O5V) = -3.76 [updated 1/31/2020]

logL(O5V) = 5.50  ; Martins05(Obs. scale)
logL(O5V) = 5.51  ; Martins05(Theoretical scale)
logL(O5V) = 5.521 ; logL/Teff trend for O dwarfs for Teff=41300K
logL(O5V) = 5.540 ; Mv=-5.35, BCv=-3.76 => Mbol = -9.110
logL(O5V) = 5.60  ; non-stan. HD 15629 (Repolust04)
=> adopt logL(O5V) =  5.540 dex [updated 2/8/2020]
=> adopt Mbol(O5V) = -9.110 mag [updated 2/8/2020]

Mass(O5V) =  30.4 Msun  ; non-stan. HD 15629 (Repolust04)
Mass(O5V) = 31.98 Msun  ; EEM Teff vs. Mass fit for binaries (Teff=41000K)
Mass(O5V) = 37.28 Msun  ; Martins05/theo. Teff scale
Mass(O5V) = 38.08 Msun  ; Martins05/obs. Teff scale 
Mass(O5V) = 42.96 Msun  ; MIST/Choi16 solar tracks for logT=4.617,logL=5.540
Mass(O5V) = 44+7-6 Msun ; Weidner10
=> adopt Mass(O5V) = 43 Msun [updated 4/16/2022]

logg(O5V) = 3.70 dex ; non-stan. HD 15629 (Repolust04)
logg(O5V) = 3.79 dex ; Holgado18
logg(O5V) = 3.919+-0.15 (stdev) ; Martins05
=> adopt logg(O5V) = 3.79 dex [updated 1/31/2020]

Rad(O5V) = 12.8    Rsun ; HD15629/Repolust04
Rad(O5V) = 11.4460 Rsun ; logL=5.540, Teff= 41400K
Rad(O5V) = 11.112  Rsun ; Martins05 (Teff=40863K,logL=5.492)
=> adopt Rad(O5V) = 11.446 Rsun [updated 2/8/2020]

# No Standards

GrayNstars does not list an O5V standard.

# Primary Standard

HD 46150 = Cl* NGC 2244 John 2
  O5: Morgan65,Abt68,MK73(dagger)
  O5V: Garrison77(stan),MK78(stan),Keenan85,Garcia89,GrayAtlas,Abt08
  O5V((f)): Walborn71(stan),Walborn72,Walborn73,Bisiacchi76,Walborn90,Walborn02
 *O5V((f))z: Martins11,Sota11
  O5.5((f)): Conti74,Conti77
  O6: JM53
  B5Iab: Houk99

  NGC 2244 member classified by Morgan65 as "O5" and it has been a
  primary standard since.  M91: V=6.745, B-V=0.129+-0.008,
  U-B=-0.834+-0.012 => QBV => (B-V)o=-0.325, (U-B)o=-1.157,
  E(B-V)=0.424, Av=1.465.  plx= 0.6263+-0.0788mas(GaiaDR2), however it
  is NGC2244 member and Cantat-Gaudin18 estimate D=1548.8pc(mode) =>
  plx=0.646mas, (m-M)o=10.950. E(B-V)=0.45+-0.03(Fan17),
  Av=1.444+-0.019(MaizApellaniz18) => Mv=-5.72.
  Mv=-5.5(Snow94). V=6.745, plx=0.646mas, Av=1.465 => Mv =
  -5.67. logL=3.98(Simon-Diaz17).  Teffs: 40738K(Simon-Diaz17),
  42000K(Martins11), 44300K(Snow94) => <Teff> = 42000K.


# Deprecated Standard

HD 93204
  O5V((f)): Walborn73,Walborn02
  O5.5V(fc): Walborn10
 *O5.5V((f)): Sota14
  O6V((f)): Markova11
  O6/7V: Alexander18

  It appears that Walborn and subsequent authors moved this star 0.5-1
  subtype later.  V=8.440+-0.019(Mermilliod91),
  B-V=0.099+-0.010(Mermilliod91), U-B==0.884+-0.005(Mermilliod91).
  E(B-V)=0.41(Savage01),
  Av=1.611+-0.032(MaizApellaniz18). plx=0.4486+-0.0378mas(GaiaDR2).
  Mv=-4.912.
 
HD 164794 = 9 Sgr
  O4V: Bisiachhi82
 *O4((f))z: Sota14
  O4((f)): Walborn72,Walborn73,Conti74,Maiz-Apellaniz16
  O4f: Conti71,Conti73,Conti73
  O5V: Jaschek78(Hiltner69(Stan))
  O5: Morgan53,Morgan55,Jaschek64(most),Hiltner65
  O6: Houk88
  O7: Weaver53

  Hiltner69 used as O5V standard, but recent types have converged on
  O4V subtype.

# Other Stars
HD 66811 = Zet Pup = HR 3165 
  O5: MK43,MK73(dagger)
  O5If: MK78
  O3f: Heap77
  O4fe: Conti74,Conti77
  O4If: Bisiacchi76
  O4I(n)f: Walborn72
  O4f: Conti71
  O5Ik: Buscombe69
  O5f: Morgan55,Hiltner69
  O5f/WN7: Smith55
  O6/7III: Zorec09
  Never considered a "O5V" standard. MK78 considers "O5If" standard. 

Walborn72 classifies three stars as O5V or variant: HD 15629
(O5V((f))), HD 192281 (O5Vn((f))p), and HD 46150 (O5V((f))).