O9.7V Garrison94 lists the B0V anchor as Ups Ori (= HD 36512). However Sota11 considers Tau Sco as the B0V standard, and Ups Ori as an O9.7V star. Unfortunately there have been some subtle shifts at the OB boundary: MK43 JM53 Walborn72 MK73 MK78 Keenan85 Walborn90 Garrison94 Garrison96 Sota11 HD93027 ... ... O9.5V ... ... ... O9.5V ... ... O9.5IV Sig_Ori O9.5V O9.5V ... O9.5V ... ... ... ... ... ... Ups_Ori ... B0V B0V B0V ... ... B0V B0V ... O9.7V Tau_Sco B0V B0V B0.2V B0V B0V B0V B0.2V ... B0V B0V HD2083 ... ... ... ... ... ... ... ... ... B0.2V HD36960 ... ... B0.5V ... ... ... B0.5V ... ... B0.5V Bet_Sco B0.5V B0.5V ... ... ... ... ... ... B0.5V ... Teff(O9.7V) = 33400 +- 200 K ; ups Ori (Nieva14; adopting Mota revised SpT) Teff(O9.7V) = 33619 K ; Simon-Diaz14 linear fit for O9.7V Mv(O9.7V) = -4.00 mag ; Bowen08 # Primary Standard HD 36512 = ups Ori = HR 1855 *O9.7V: Sota11(standard) B0V: Jaschek78(JM53),Jaschek64(all but one),Lesh68(stan),Walborn71,Walborn72,MK73,Abt77(B0Vs),Garcia89,Walborn90,Garrison94,Houk99(Garrison),Russeil07 B0.5V: Lesh68(stan) B3: Cannon Considered B0V standard in many publications and by Walborn90 and Garrison94, but now considered O9.7V standard by Sota11 (Walborn is coauthor), and it does appear to be somewhat hotter than other B0V stars [these are the only reason I've deprecated this now as a B0V standard and simply adopted O9.7V]. Teffs: 31500K(Philip80), 31500K(Kilian94), 31560K(Cunha94), 31622K(Brown94), 31812K(Paunzen05), 32200K(LeBorgne03), 32340+-2200K(Zorec09), 32533K(U-Bo=>Bessell98), 32900K(Sokolov95) => median Teff ~ 32000K. logg=4.13(LeBorgne03), [Fe/H]=0.25(LeBorgne03). Ups Ori has the third bluest B-V in Johnson66's compilation of UBV photometry, and the 2nd bluest U-B, so it could be useful for defining the sequence of intrinsic UBV colors of hot stars. M91: V=4.618+-0.013, B-V=-0.264+-0.007, U-B=-1.068+-0.008. V=4.62 (Johnson66), V=4.618+-0.013 (Mermilliod91), B-V=-0.26 (Johnson66), B-V=-0.264+-0.007 (Mermilliod91), U-B=-1.07 (Johnson66), U-B=-1.068+-0.008 (Mermilliod91). logN_HI[cm^-2] = 20.35+-0.10 (Shull85; from Lyman alpha absorption). Adopting the Savage & Mathis (1979) logNH/E(B-V) = 4.8e21 atoms/cm^2/mag, the Shull85 logN_HI value translates to E(B-V) = 0.047. So (B-V)o = (B-V)obs - E(B-V) = -0.264 - 0.047 = -0.311. Then E(U-B) = 0.72*E(B-V) = 0.72*0.047 = 0.034 mag. So (U-B)o = (U-B)obs - E(U-B) = -1.068 - 0.034 = -1.102 mag. 10/8/2011: Using revised Q-method calibration on Mermilliod91 colors (B-V=-0.264+-0.007, U-B=-1.068+-0.008) => (B-V)o = -0.310, (U-B)o = -1.100, E(B-V) = 0.046, Av=0.146 mag. Vanleeuwen07 plx = 1.14+-0.25 mas => 877+-202 pc. I adopt D = 400 pc as typical distance to Ori OB1. The star is out of the plane and not particularly fast moving, so it is doubtful that it is much beyond Ori OB1, and is likely ~300-500 pc. Star seems to be associated with Ori OB1, but it is not among the belt or sword stars - it is a couple degrees SW of the Orion Nebula Cluster (ONC), but it does not share the motion of the hot stars near it. It could be a "slow" runaway star from the belt or sword region of Ori OB1. Its U and W motion are discrepent compared to the ONC (deltaU ~ +13 km/s, deltaW ~ -4 km/s). More work would be needed to test this idea. Adopting d=400 pc, then Mv ~ -3.54, logL ~ 4.47 dex.