B0.2V

HD 2083 is the primary B0.2V standard. 

Walborn71 took the B0V standard Tau Sco, and using Ups Ori as the B0V
standard, called Tau Sco the "B0.2V" standard, and as adopted it as
such since then. Sota11 (Walborn is coauthor) now considers Tau Sco a
B0V (but not standard).

Walborn71 standard:  Tau Sco - B0.2V 
Walborn72 standard:  Tau Sco - B0.2V
Walborn90 standard:  Tau Sco - B0.2V
Sota11 standard:     HD 2083 - B0.2V (Tau Sco now considered B0V)

(B-V)(B0.2V) = -0.300 ; EEM dereddened B0.2V standard HD 2083 via Q-method
(B-V)(B0.2V) = -0.297 ; EEM dereddened B0.2V non-standard tet Car via Q-method

(U-B)(B0.2V) = -1.068 ; EEM dereddened B0.2V standard HD 2083 via Q-method
(U-B)(B0.2V) = -1.057 ; EEM dereddened B0.2V non-standard tet Car via Q-method

Mv(B0.2V) = -3.70 mag ; Bowen08

Teff(B0.2V)  = 29684 K ; U-B=-1.06 => Bessell98 calibration

# No Standard

Keenan85 does not list a B0.2V standard. 

# Primary Standard

HD 2083 (V=6.90)
  *B0.2V: Sota11(stan)
   B1V: Hiltner56(Jaschek64)
   O9.5III: Hill77(Kennedy83)
   B2: Cannon  

   Mermilliod91 lists B-V=0.03, U-B=-0.830, Vmag=6.890 => using
   updated Q-method (10/9/2011) => (B-V)o = -0.300, (U-B)o = -1.068,
   E(B-V)=0.330, Av=1.066.

# Weak Standard

HD 149438 = tau Sco = HR 6165
 *B0V: MK43,Lesh68(stan),Jaschek78(JM53),Bertiau58,Jaschek64(all),Garrison67,Hiltner69(stan),MK73,Garrison77(stan),MK78,Garrison79(stan),Houk82,Keenan85,Garcia89,Garrison96,Sota11(stan)
  B0.2V: Walborn71,Walborn90
  B0: Cannon

  Tau Sco was called B0V until Walborn called it B0.2V, but now it is
  considered B0V standard again by Sota11.  Hauck97 ubvy photometry =>
  dereddened following Castelli91 => (b-y)o = -0.114, co = -0.094,
  e(b-y) = 0.021, T(Balona94) = 31048K, T(Napiwotski93) = 32689 K.

  LogN_HI = 20.43+-0.10 (Shull85), 20.49+-0.04 (Bohlin78), 20.05
  (Hobbs78). Adopting logN_HI = 20.46, and the Savage & Mathis (1979)
  logNH/E(B-V) = 4.8e21 atoms/cm^2/mag, then E(B-V) = 0.060. Then
  (B-V)o = (B-V) - E(B-V) = -0.252 - 0.060 = -0.312, and (U-B)o =
  (U-B) - 0.72*E(B-V) = -1.023 - 0.72*0.06 = -1.066.

  Mermilliod91 photometry: V=2.825+-0.009, B-V=-0.252+-0.007,
  U-B=-1.023+-0.013 => Q-method => (B-V)o=-0.296, (U-B)o=-1.055,
  E(B-V)= 0.044, Av=0.143.

# Non-standard stars

tet Car = theta Car = HR 4199 = HD 93030
   *B0.2Vp: Walborn76
    B0V: AbtMorgan72(B0Vp),Whiteoak61(B0V),Hoffleit61(B0V)
    B0.5Vp: Hiltner69
    B1.5III: Cucchiaro80(UV)
    O9.5V: DeVaucoleurs57

    Comments on spectra from Skiff's compilation: "N strong, C weak,
    spec var?" (Walborn76), "NIII strong, CIII weak" (AbtMorgan72),
    "NII, SiIV strong; HeI weak" (Hiltner69).  V=2.759+-0.010
    (Mermilliod91), V=2.76(Johnson66),
    B-V=-0.227+-0.005(Mermilliod91), B-V=-0.22(Johnson66),
    U-B=-1.006+-0.012 (Mermilliod91), U-B=-1.00(Johnson66).  Bohlin78
    report logN_HI = 20.28+-0.09. Using Savage & Mathis 1979 relation,
    this suggests E(B-V) = 0.040. Hence, Q=-0.843, (B-V)o = -0.267,
    (U-B)o = -1.035. Mermilliod91 and updated Q-method (10/9/2011)
    yields (B-V)o = -0.297, (U-B)o = -1.057, E(B-V) = 0.07, Av=0.225
    mag.