G0IV Garrison94 lists eta Boo (HD 121370 = HR 5235) as the G0IV anchor standard, the hottest subgiant standard on his list. MK43 standard: eta Boo - G0IV zet Her - G0IV JM53 standards: eta Boo - G0IV zet Her - G0IV Cowley76 standard: eta Boo - G0IV MK78: eta Boo - G0IV Houk88 standard: eta Boo (= HD 121370) - G0IV [from JM53] Keenan89 standards: eta Boo (= HD 121370) - G0IV zet Her (= HD 150680) - G0IV HD 160269 - G0IV-V GrayAtlas standard: eta Boo - G0IV GrayNstars lists eta Boo as their G0IV DSO standard. But there is only one G0IV among the Gray03 and Gray06 papers (HIP 23831). In SIMBAD, the only G0IV stars brighter than V=6 are eta Boo(V=2.7), zet Her(V=2.8), 64 Cet(V=5.6), HD 33093(V=6.0). Corbally84 classifies the bright binary HD 147722+147722 as a pair of G0IV stars (see below). Among Gray03 and Gray06 stars within 40 pc: B-V(G0IV) = 0.652 (+-0.016 sem, +-0.027 stdev; N=3) V-I(G0IV) = 0.713 (+-0.015 sem, +-0.025 stdev; N=3) For Hipparcos stars within 75pc with parallax S/N > 8 (N=13): (G0IV) = 0.586 (+-0.017 sem, +-0.047 stdev) (G0IV) = 0.648 (+-0.016 sem, +-0.050 stdev) (G0IV) = 1.063 (+-0.051 sem, +-0.119 stdev) (G0IV) = 1.294 (+-0.061 sem, +-0.146 stdev) (G0IV) = 1.381 (+-0.054 sem, +-0.134 stdev) G(G0IV) = 0.249 (+-0.010 sem, +-0.051 stdev) (G0IV) = 0.067 (+-0.006 sem, +-0.023 stdev) (G0IV) = 0.638 (+-0.021 sem, +-0.064 stdev) (G0IV) =-0.062 (+-0.003 sem, +-0.009 stdev) (G0IV) = 6048 K ; pri. stan. eta Boo ([Fe/H]=+0.27) (G0IV) = 5968 K ; non-stan. HD 147723 (G0IV) = 5944 K ; non-stan. HD 147722 (G0IV) = 5766 K ; sec. stan. zet Her ([Fe/H]=+0.01) => adopt Teff(G0IV) = 5950 K [last updated 7/10/2017] (B-V)(G0IV) = 0.567(+-0.004 sem,+-0.010 stdev) ; SIMBAD median G0IV d<75pc,V<6.5(N=5) (B-V)(G0IV) = 0.580 ; pri. stan. eta Boo (B-V)(G0V) = 0.611 ; poly fit to FGKIV standards & exemplars (B-V)(G0IV) = 0.650 ; deprecated stan. zet Her => adopt (B-V)(G0IV) = 0.58 [updated 1/29/2022] Absolute magnitudes of nearby G0IV stars w/i 50pc (spt,plx from SIMBAD) Mv(G0IV) = 2.18 ; HD_66011 Mv(G0IV) = 2.28 ; HD_175986 Mv(G0IV) = 2.396 ; pri. stan. * eta Boo plx= 87.75 mas,Vmag= 2.680 Mv(G0IV) = 2.557 ; * 64 Cet plx= 24.37 mas,Vmag= 5.623 Mv(G0IV) = 2.74 ; deprecated stan. * zet Her A plx= 93.32 mas,Vmag= 2.89 Mv(G0IV) = 2.8 ; GrayCorbally09 Mv(G0IV) = 2.89 ; quadratic fit Mv(G0IV-K2IV) standards+exemplars for G0IV Mv(G0IV) = 3.107 ; HD 33093 plx= 26.93 mas,Vmag= 5.956 Mv(G0IV) = 3.580 ; HD 155875 plx= 25.83 mas,Vmag= 6.52 => adopt Mv(G0IV) = 2.89 mag [adopted 1/28/2022] logg(G0IV) = 3.80 ; pri. stan. eta Boo => adopt logg(G0IV) = 3.80 [updated 1/28/2022] # No standards MK73 and MorganAbt72 do not list a G0IV standard. # Primary Standards eta Boo = HD 121370 = HR 5235 (J1354+1823) F7IV/V: Adams35 F9: Bidelman85 F9III: Morgan38 *G0IV: Maury1897,Keenan41,MK43,Barry70,Cowley76(stan),Jaschek78(JM53),Jaschek64(most),Keenan80,Keenan89,Gray01 G0: Cannon One of only four subgiant (IV) anchor standards (Garrison94): eta Boo (G0IV), mu Her (G5IV), bet Aql (G8IV), gam Cep (K1IV) - so eta Boo is basically the prototype for the early G subgiants. B-V=0.580(HIP), V=2.68(HIP), V-I=0.65+-0.00(HIP), plx=87.75+-1.24mas(vanLeeuwen07), safely nearby and presumably unreddened. Revised HIP astrometry leads to => Mv=2.40, i.e. 1.94 mag above MS. PASTEL compendium: = 6048K(N=30), =3.80(N=22), <[Fe/H]>=+0.27(N=22). 2MASS photometry is poor, but there are plenty of ground-based near-IR mags reported (see Gezari). Blackwell90 lists J=1.66 => M_J = 1.38+-0.03. # Deprecated Standard zet Her = HD 150680 = HR 6212 = HIP 81693 G0IV: Maury1897,MK43,Stephenson69,Barry70(G0IVb,uv metals weak),Keenan80,Keenan89(stan), G0: Bidelman85 G0V: Adams35 G2IV: Gray01 G1IV: MK73(dagger),Abt81(standard) G3IV: Houk88(standard) *F9IV+G7V: Edwards76 1.5" binary. Morel01 presents detailed study of this binary, and considers the primary a subgiant in the Hertzsprung gap "where the star loci move rapidly". This star is what gives spectral types a bad name: considered "standard" for G0IV, G1IV, and G3IV over the years. It is clearly redder than eta Boo, which seems to have most consistent use as G0IV standard. HIP lists del(Hp)=2.68+-0.03. WDS lists mag1=2.95, mag2=5.40, which appear to be from TYC2: Vt(A)=2.952+-0.009, Vt(B)=5.400+-0.009, del(Vt)=2.448. ASCC lists V(A)=2.844+-0.004, V(B)=5.308+-0.008. Struve54 calls companion K0V. PASTEL lists 15 published Teff values: = 5766 K. 11 published [Fe/H] values: <[Fe/H]>=0.01. 2MASS photometry is poor. V(AB)=2.81(HIP), V(AB)=2.809+-0.010(Mermilliod91), B-V=0.650+-0.011(HIP), B-V(AB)=0.643+-0.010(Mermilliod91), V-I=0.70+-0.03(HIP). plx=93.32+-0.47mas(HIP2) => Mv(AB)=2.66. Assuming del(Hp) ~ del(V) => V(AB)=2.81 => V(A)=2.90, V(B)=5.58. Assuming del(Vt) ~ del(V) => V(AB)=2.81 => V(A)=2.92, V(B)=5.37. Morel01 solution: B-V(A)=0.649+-0.088(Morel01), V(A)=2.890+-0.033(Morel01), B-V(B)=0.81+-0.140(Morel01), V(B)=5.556+-0.059(Morel01), Teff(A)=5820+-50K(Morel01), Teff(B)=5300+-150K(Morel01). Adopting V(A)=2.89 and plx=93.32(HIP2) => Mv=2.74. # Other Stars HD 147722 = HR 6105 B (V=6.6) *G0IV: Evans57,Corbally84 G0V: Abt81,Gray06 F6/8V: Houk82 4.5" pair with HD 147723. Corbally84 classifies unresolved spectrum of pair as G0IV. PASTEL lists 3 published Teffs: = 5941K. 2 published metallicities: <[Fe/H]> = 0.04. B-V(AB)=0.625+-0.126(HIP). HD 147723 = HR 6105 A (V=5.8) *G0IV: Evans57, Abt81, Corbally84 F9IV: Gray06 F6/8V: Houk82 4.5" pair with HD 147722. PASTEL: 2 published Teffs: <[Fe/H]> = 5968K. published metallicities: <[Fe/H]> = 0.13. B-V(AB)=0.625+-0.126(HIP). HD 13421 = HIP 10212 F8IV/V: Adams35 F8IV: Harlan74 G0: HD G0IV: Cowley79(Montes97) plx=24.56+-0.30mas(HIP2), V=5.64(HIP), B-V=0.569+-0.007(HIP). 2MASS: JH photometry, poor but Ks=4.308+-0.016(2MASS). HR 1665 = HD 33093 = HIP 23831 F7V: Malaroda75 F9V: Wilson50 *G0IV: Gray06 G2V: Houk88 V=5.97(HIP), B-V=0.606+-0.003(HIP), V-I=0.67+-0.02(HIP). Mv=3.15, which is 1.36 mag above the Wright04 MS. Gray06 lists Teff=5768K, logg=3.40, [M/H]=-0.08. Luck17: logg=3.92+-0.01, Teff=5935K. Teffs: 5913+-53K(Masana06), 5958+-80K(Casagrande11). plx=26.9300+-0.0461mas(GaiaDR2) => Mv=3.12+-0.01. 2MASS photometry is flagged EEA, so only Ks is graded A: Ks=4.516+-0.024(2MASS). V-Ks=1.454. HD 13421 = 64 Cet = HR 635 = HIP 10212 F8IV/V: Adams35 F8IV: Harlan74 G0IV: Cowley79 V=5.64(HIP), B-V=0.569+-0.007(HIP), V-I=0.63+-0.07(HIP). plx=24.3716+-0.1475mas(GaiaDR2) => Mv=2.57. # COMMENTS ON ABSOLUTE MAGNITUDES FOR SUBGIANTS Combining subgiant standards and selected nearby exemplar stars, I looked at the trend of subtype vs. absolute magnitude. Remarkably plotting G0-K2 subgiants, the overall trend is surprisingly flat: Mv(G0IV-K2IV) ~ 2.97 (rms=0.65 mag). A line only marginal improves the fit: Mv(G0-K2IV) ~ 3.022 - 7.10384(SpT) (rms=0.648 mag) where SpT=0 for G0IV and SpT=12 for K2IV. Quadratic fit: Mv(G0-K2IV) = 2.88653 + 0.074884*SpT - 6.72325544e-3*SpT^2 Sandage03 shows that the subgiant branch for the old open cluster NGC 6791 (8.0 Gyr, [Fe/H] = +0.23) around Mv ~ 4.0 between 0.75 < B-V < 1.0 (their Fig. 11), or approximately ~G4IV and ~K1IV. Very few field subgiants have absolute magnitudes fainter than Mv ~ 4.0. The younger clusters NGC 188 (6.2 Gyr) and M67 (4.0 Gyr) have somewhat brighter and bluer subgiant sequences. Using SIMBAD, selecting all lum III stars (no mixed lum classes) for d<75pc, V<6.5 (fairly well-characterized bright stars with good photometry), retaining those with BVG photometry.. after clipping some obvious dwarf (Mv>4) and giant outliers... the absolute magnitudes are well fit by a trinomial as f(B-V): Mv = 5.6962949573530886e-001*(B-V) + 6.7769119865259801e+000*(B-V)^2 - 1.1637597308113921e+001*(B-V)^3 - 7.4435045496610677e+000*(B-V)^4 + 1.1447287468224590e+002*(B-V)^5 - 2.2291395198008181e+002*(B-V)^6 + 1.6507226866827122e+002*(B-V)^7 - 4.2885954328234050e+001*(B-V)^8 (-0.16 < B-V < 1.20; rms=0.606) # COMMENTS ON COLORS OF F SUBGIANTS VS. F DWARFS B-V color of G0IV primary standard Eta Boo: 0.580. Mean B-V color of G0IV stars from Gray03/06 (N=3): 0.652+-0.016 (stdev=0.027) Mean B-V color of G0IV stars in Hipparcos (d<75pc): 0.586+-0.017 (stdev=0.047) Note that the mean colors that I use for G dwarfs are based on the Keenan/Gray standards, and these differ a bit from those used by Houk (where most of the types in the Hipparcos catalog come from). <(B-V)GIV> - <(B-V)GV> = 0.007+-0.005 (stdev = 0.056; N=93) It is amazing that the color differences cancel out, given the trends among the individual subtypes: <(B-V)G0IV> - <(B-V)G0V> = 0.001+-0.009 (stdev = 0.033 mag; N=10) <(B-V)G1IV> - <(B-V)G1V> = 0.010+-0.005 (stdev = 0.009 mag; N=3)* <(B-V)G2IV> - <(B-V)G2V> = -0.010+-0.011 (stdev = 0.031 mag; N=9) <(B-V)G3IV> - <(B-V)G3V> = -0.047+-0.010 (stdev = 0.041 mag; N=15) <(B-V)G4IV> - <(B-V)G4V> = -0.034+-0.024 (stdev = 0.036 mag; N=4)* <(B-V)G5IV> - <(B-V)G5V> = 0.005+-0.008 (stdev = 0.047 mag; N=21) <(B-V)G6IV> - <(B-V)G6V> = 0.031+-0.010 (stdev = 0.023 mag; N=7) <(B-V)G7IV> - <(B-V)G7V> = 0.101+-0.027 (stdev = 0.038 mag; N=2)* <(B-V)G8IV> - <(B-V)G8V> = 0.044+-0.011 (stdev = 0.057 mag; N=21) <(B-V)G9IV> - <(B-V)G9V> = 0.154+-NA (stdev = inf mag; N=1)* B-V SpT (B-V)V (B-V)-(B-V)V 0.696 G0 0.588 0.108 0.556 G0 0.588 -0.032 0.590 G0 0.588 0.002 0.582 G0 0.588 -0.006 0.623 G0 0.588 0.035 0.598 G0 0.588 0.01 0.538 G0 0.588 -0.05 0.596 G0 0.588 0.008 0.559 G0 0.588 -0.029 0.610 G0 0.588 0.022 0.609 G1 0.604 0.005 0.625 G1 0.604 0.021 0.609 G1 0.604 0.005 0.585 G2 0.642 -0.057 0.637 G2 0.642 -0.005 0.665 G2 0.642 0.023 0.620 G2 0.642 -0.022 0.612 G2 0.642 -0.03 0.640 G2 0.642 -0.002 0.603 G2 0.642 -0.039 0.636 G2 0.642 -0.006 0.678 G2 0.642 0.036 0.708 G3 0.661 0.047 0.596 G3 0.661 -0.065 0.613 G3 0.661 -0.048 0.620 G3 0.661 -0.041 0.561 G3 0.661 -0.1 0.600 G3 0.661 -0.061 0.567 G3 0.661 -0.094 0.623 G3 0.661 -0.038 0.616 G3 0.661 -0.045 0.590 G3 0.661 -0.071 0.671 G3 0.661 0.01 0.590 G3 0.661 -0.071 0.657 G3 0.661 -0.004 0.599 G3 0.661 -0.062 0.672 G3 0.661 0.011 0.652 G4 0.674 -0.022 0.624 G4 0.674 -0.05 0.683 G4 0.674 0.009 0.603 G4 0.674 -0.071 0.635 G5 0.680 -0.045 0.764 G5 0.680 0.084 0.690 G5 0.680 0.01 0.680 G5 0.680 0 0.656 G5 0.680 -0.024 0.664 G5 0.680 -0.016 0.761 G5 0.680 0.081 0.650 G5 0.680 -0.03 0.687 G5 0.680 0.007 0.682 G5 0.680 0.002 0.671 G5 0.680 -0.009 0.664 G5 0.680 -0.016 0.748 G5 0.680 0.068 0.667 G5 0.680 -0.013 0.740 G5 0.680 0.06 0.829 G5 0.680 0.149 0.676 G5 0.680 -0.004 0.680 G5 0.680 0 0.727 G5 0.680 0.047 0.654 G5 0.680 -0.026 0.627 G5 0.680 -0.053 0.737 G6 0.704 0.033 0.730 G6 0.704 0.026 0.774 G6 0.704 0.07 0.742 G6 0.704 0.038 0.715 G6 0.704 0.011 0.747 G6 0.704 0.043 0.689 G6 0.704 -0.015 0.787 G7 0.713 0.074 0.841 G7 0.713 0.128 0.814 G8 0.737 0.077 0.690 G8 0.737 -0.047 0.734 G8 0.737 -0.003 0.769 G8 0.737 0.032 0.770 G8 0.737 0.033 0.794 G8 0.737 0.057 0.770 G8 0.737 0.033 0.753 G8 0.737 0.016 0.790 G8 0.737 0.053 0.765 G8 0.737 0.028 0.865 G8 0.737 0.128 0.655 G8 0.737 -0.082 0.864 G8 0.737 0.127 0.793 G8 0.737 0.056 0.840 G8 0.737 0.103 0.782 G8 0.737 0.045 0.805 G8 0.737 0.068 0.872 G8 0.737 0.135 0.780 G8 0.737 0.043 0.501 G8 0.737 -0.236 0.744 G8 0.737 0.007 0.931 G9 0.777 0.154