A0IV

JM53 lists gam Gem as the A0IV standard

MK73 does not list a A0IV standard

GarrisonGray94 list HR 7211 (HD 177074) as their low-vsini A0IV
standard, and HR 8451 (HD 210419) as their high-vsini A0IV standard.

Houk88 adopts gam Gem (HR 2421, HD 47105) from JM53 as their A0IV standard.

GrayNstars used the A0IV star HR 7211 as a fiducial standard for their
CTIO survey.

# Primary Standards
HD 177074 = HR 7211 (J1904-3102,V=5.5)
  A0IV:deVaucouleurs57,GrayGarrison87(low-vsini stan.),GarrisonGray94 
  A0V: Evans66

HD 210419 = HR 8451 (J2210-0353)
  A0IVnn: GrayGarrison87(high-vsini stan.),GarrisonGray94
  A0V: Houk99
  A0Vn: Abt95
  A1Vnn: Cowley69
  Houk99 note: "HR 8451; vSINi=370"

# Weak Standard
HD 47105 = HR 2421 = gam Gem (J0638+1624)
  A0IV: JM53,Osawa59,Jaschek64(most),Cannon(A0)
  A1V: MK43
  A1IVs: GrayGarrison87
  A1IV: Cowley69
  A1III: Palmer68
  A1.5IV+: Gray03
  A2IV: Abt95
  B-V=0.001, Mv=-0.70, 1.81 mag above MS. 
  Type has migrated over the years. Clearly evolved. 
  Do not use as standard.