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.

HD 64568 is the only O3V dwarf in the Sota14 GOSSS (Galactic O-Star
Spectroscopic Survey ; Vizier /III/274/main)

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 (stdev=0.4 mag)
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
Mv(O3V)   = -5.26+-0.17 mag ; pri. stan. HD 64568 (seems significantly fainter than trend?)
=> 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) = 3.921+-0.15 (stdev) ; Martins05
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]

Mass(O3V) =  56.0+-4.0 Msun ; HD93205A Weidner10
Mass(O3V) = 57.95 Msun      ; Martins05/obs. Teff scale 
Mass(O3V) = 58.34 Msun      ; Martins05/theo. Teff scale
Mass(O3V) = 59.0 Msun       ; MIST/Choi16 solar tracks for logT=4.652,logL=5.82
Mass(O3V) =  65+8-7 Msun    ; Weidner10
=> adopt Mass(O3V) = 59 Msun [updated 4/16/2022]

# 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,Markova11
 *O3V((f*))z: Soto14
  O4((f)): Garrison77
  O5:: MacConnell76
  O5: Crampton71,Loden65
  O5/6: Houk88

  
  Star in NGC 2467 region, apparently ejected from Haffner 18 cluster
  - with HD 64315AB [O5.5Vz+O7V; 1262" away] ejected in the opposite
  direction (Maiz-Appelaniz18).  Consistently classified O3V (variant)
  by Walborn82 and Walborn02, and is the only O3V (or variant) in
  Soto14 GOSSS survey.  Appears to be binary and is referred to as HD
  64568a in Markova18.  V=9.397+-0.018(Mermilliod91),
  V=9.380+-0.006(Hauck97), B-V=0.071+-0.020(Mermilliod91),
  U-B=-0.895+-0.029(Mermilliod91). G=9.312+-0.003(GaiaEDR3).  G-V =
  9.312 - 9.397 = -0.085 (ignoring extinction).  V-I=0.07+-0.00(HIP)
  [estimate; but does not appear to be Cousins Ic reported anywhere].
  QBV method by EEM => (B-V)o=-0.330, (U-B)o=-1.178, E(B-V)=0.401,
  Av=1.294.  Dereddening Paunzen15 ubvy\beta photometry => using
  Castelli91: (b-y)0=-0.128, c0=-0.190, E(b-y)=0.261, Av=1.101 =>
  using Shobbrook83: (b-y)0=-0.130, c0=-0.190, E(b-y)=0.263, Av=1.153.
  It appears that (b-y)0 doesn't vary much between ~O3V and ~O7.5V,
  and is not useful for Teff estimates in this regime.
  MaizAppelaniz18 estimates Av=1.388+-0.018 and monochromatic
  reddneing E(4405-5495) = 0.373+-0.007 and which traces E(B-V) very
  well in this regime for hot stars (Fig.5 of MaizAppelaniz18).
  Reddening estimates: E(B-V)=0.32+-0.02(Bowen08),
  E(B-V)=0.355(Hauck97 ubvy\beta dered using Castelli91,
  E(B-V)=Av/3.1), E(B-V)=0.3601+-0.0686(Stassun19/TIC),
  E(B-V)=0.37(Savage85), E(B-V)=0.372(Hauck97 ubvy\beta dered using
  Shobbrook83, E(B-V)=Av/3.1), E(B-V)~E(4405-5495)=0.373+-0.007,
  E(B-V)=0.38(Friedemann92), E(B-V)=0.40(Heiles00), E(B-V)=0.401(see
  previous UBV estimate) => Adopt the values from MaizApellaniz18:
  0.373+-0.007, Av=1.388+-0.018, which is consistent with the other
  estimates.  plx=0.1367+-0.0386mas(GaiaDR2).
  plx=0.2241+-0.0177mas(GaiaEDR3); note that cluster Haffner_19 has
  plx=0.169+-0.010mas(Cantat-Gaudin20),
  plx=0.236+-0.011mas(MaizAppelaniz18).  Adopt plx=0.2241+-0.0177mas
  from GaiaEDR3, consistent with Haffner_18 group parallax from
  MaizApellaniz18 => Mv=-5.26+-0.17 [previously I had used
  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).
  plx=0.2241+-0.0177(GaiaEDR3).  V=9.397, plx=0.2241mas, Av=1.294 =>
  Mv=-5.15+-0.17.
  
# Secondary Standard

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

# 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).
  
# 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.