O7.5V

There are no known O7.5V standards, including in Walborn90

HIP contains only one O7.5V star: HIP 30496 = HD 44811.

B-V(O7.5V)  = -0.321  ; exemplar HD 152590
B-V(O7.5V)  = -0.317  ; U-B=-1.125 trend Q-method
B-V(O7.5V)  = -0.314  ; exemplar HD 53975
B-V(O7.5V)  = -0.31   ; Fitzgerald70
B-V(O7.5V)  = -0.291  ; EEM dereddened HD 44811
=> adopt (B-V)(O7.5V) = -0.317 [updated 2/7/2020]

U-B(O7.5V)  = -1.16   ; Fitzgerald70
U-B(O7.5V)  = -1.155  ; EEM dereddened HD 44811
U-B(O7.5V)  = -1.143  ; exemplar HD 152590
U-B(O7.5V)  = -1.125  ; interp O3-O9V
U-B(O7.5V)  = -1.116  ; exemplar HD 53975
=> adopt (U-B)(O7.5V) = -1.125 [updated 2/7/2020]

Teff(O7.5V) = 34419 K ; Martins05(theo. scale)
Teff(O7.5V) = 34750 K ; Massey05(Milky Way)
Teff(O7.5V) = 35874 K ; Martins05(obs. scale),GrayCorbally09
Teff(O7.5V) = 36100 K ; EEM trend for O dwarfs 1/2020 **
Teff(O7.5V) = 36728 K ; Simon-Diaz17 median for O7.5V (N=4)
Teff(O7.5V) = 36947 K ; Simon-Diaz14 linear fit for O7.5V
Teff(O7.5V) = 37230 K ; Holgado18
Teff(O7.5V) = 37500 K ; Crowther97/Fig.3 
=> adopt Teff(O7.5V) = 36100 K (logT = 4.558) [updated 1/20/2020]

Mv(O7.5V) = -4.88  mag ; Russeil03
Mv(O7.5V) = -4.835 mag ; Wegner07 (halfway between O7V and O8V)
Mv(O7.5V) = -4.8   mag ; GrayCorbally09
Mv(O7.5V) = -4.75  mag ; Bowen08
Mv(O7.5V) = -4.68  mag ; EEM trend for O7.5V
Mv(O7.5V) = -4.6   mag ; halfway between O7V (-4.8) and O8V (-4.4)
Mv(O7.5V) = -4.6   mag ; Conti71(V)
Mv(O7.5V) = -4.56  mag ; Martins06/obs.scale
Mv(O7.5V) = -4.55  mag ; Martins06/theor.scale
Mv(O7.5V) = -4.55  mag ; Garmany92 (O7.5V,IV)
Mv(O7.5V) = -4.48  mag ; Martins05
Mv(O7.5V) = -4.1   mag ; Conti71(ZAMS)
=> adopt Mv(O7.5V) = -4.65 mag [updated 2/8/2020]

BCv(O7.5V) =   -3.570 mag ; Flower96 calibration for (Teff=36100K)
BCv(O7.5V) =  -3.39  mag ; Martins05(obs.scale)
BCv(O7.5V) =  -3.346 mag ; Bessell98 calibration for (Teff=36100K)
BCv(O7.5V) =  -3.334 mag ; LanzHubeny03/07 calibration (Teff=36100K)
BCv(O7.5V) = -3.325 mag ; EEM interp O7V(-3.41),O8V(-3.24)
BCv(O7.5V) =  -3.32  mag ; Martins06(obs.scale)
BCv(O7.5V) =   -3.275 mag ; Balona94 calibration (Teff=36100K)
BCv(O7.5V) =  -3.27  mag ; Martins05(obs.scale)
BCv(O7.5V) =  -3.20  mag ; Martins06(theor.scale)
=> adopt BCv(O7.5V) = -3.33 [updated 1/31/2020]

logL(O7.5V) = 5.088 dex ; Mv=-4.65, BCv=-3.33 => Mbol = -7.980
logL(O7.5V) = 5.05  dex ; Martins05(obs. scale)
logL(O7.5V) = 5.040 dex ; EEM O dwarf trend for O7.5V
logL(O7.5V) = 5.00  dex ; Martins05(theo. scale)
=> adopt logL(O7.5V) =  5.088 dex [updated 2/8/2020]
=> adopt Mbol(O7.5V) = -7.980 mag [updated 2/8/2020]

logg(O7.5V) = 3.84 dex ; Holgado18
=> adopt logg(O7.5V) = 3.84 dex [updated 1/31/2020]

Rad(O7.5V) = 8.9462 Rsun ; Teff=36100K, logL=5.088
Rad(O7.5V) = 8.639 Rsun ; Martins05 (Teff=35876K,logL=5.047)
=> adopt Rad(O7.5V) = 8.946 Rsun [updated 2/8/2020]

Mass(O7.5V) = 25+7-5 Msun ; Weidner10
Mass(O7.5V) = 26.06 Msun  ; MIST/Choi16 solar tracks for logT=4.558,logL=5.088
=> adopt Mass(O7.5V) = 26 Msun [updated 4/16/2022]

# No Standards

MK73, MK78, Walborn90, Garrison94 do not list O7.5V standards.

# Exemplars

HD 152590
   O7V: Garrison77,Schild69(O7)
  *O7.5Vz: Sota14
   O7.5V: Walborn72,Mathys88
   O8: Houk78

   V=8.454+-0.023, B-V=0.135+-0.014, U-B=-0.817+-0.011(Mermillio91) =>
   Q-method(1/2020) => (B-V)o=-0.321, (U-B)o=-1.143, E(B-V)=0.456, Av=1.473.

HD 53975
   O7V: Bisiacchi76,Bisacchi82
   O7.5V: Conti71,Walborn72
  *O7.5Vz: Sota11
   O8: Morgan55,Lesh68,Claria74
   B7Iab/Ib: Houk88(apparently erroneous)

   V=6.473+-0.016, B-V=-0.099+-0.005, U-B=-0.963+-0.016(Mermilliod91)
   => Q-method(1/2020) => (B-V)o=-0.314, (U-B)o=-1.116, E(B-V)=0.215,
   Av=0.693. 

HD 53975 = BD-12_1788
   O7.5V: Conti71,Walborn72
   O8: Morgan55,Lesh68,Jaschek64(all)
   O7V: Bisiacchi76,Bisiacchi82
   B7IAB/B: Houk88
   B5p: Cannon

# Other Stars

Morgan55 classified three stars as O7.5V or variant: HD 44811 (O7.5V;
V=8.4), HD 194334 (O7.5V; V=8.8) and HD 165921 (O7.5V:nn; V=7.3).

Conti71 classified three stars as O7.5V or variant: HD 53975 (O7.5V;
V=6.5), HD 46573 (O7.5Vf; V=8.0) and HD 171589 (O7.5Vf; V=8.3).

Walborn72 classified two stars as O7.5V: HD 53975 and HD 152590.

HD 152590 
  O7.5V: Walborn72
  O7V: Garrison77
  O7: Jaschek78(Schild69)
  O8: Houk78
  B5: Cannon

BD+60 513

HD 35619

HD 46573

HD 155806
  *O7.5V((f))(e): Maiz-Apellaniz16
   O7.5V((f))z(e): Sota14
   O7.5IIIe: Conti73,Conti74,Negueruela04
   O7.5Ve: Bisiacchi82
   O7.5V[n]e: Walborn73
   O7.5((f)): Mathys88
   O8IIIe: Garrison77
   O8Ve: Hiltner69
   O8e: Weaver53
   O9: Houk82

   Emission lines. There are some other pre-1970 classifications. Good
   agreement on O7.5 subtype in recent decades. V=5.525+-0.008,
   B-V=0.005+-0.008, U-B=-0.965+-0.014(Mermilliod91).  Q-method =>
   (B-V)o=-0.336, (U-B)o=-1.202, E(B-V)=0.341, Av=1.097 (perhaps
   corrupted by the emission lines).