Pub. Astron. Soc. Pacific, Volume 83, June 1971 the ARCTURUS GROUP O. J. EGGEN Mount Stromlo and Siding Spring Observatories, Re

Pub. Astron. Soc. Pacific, Volume 83, June 1971

O. J. EGGEN Mount Stromlo and Siding Spring Observatories, Research School of Physical Sciences, The Australian National University Received 15 March 1971

Fifty-three probable members of a group of old disk population stars, moving with Arcturus, are discussed. The group includes the long period (250e1) variable RT Hydrae. The {My, B—V) and (Mboi, fí—/) diagrams of the group stars show the members to be among the oldest of the old disk population, similar in age, but not in chemical composition, to members of the old cluster NGC 188. Apogalactium for the group members is near the sun and there is some evidence for a nonrandom distribution of the U vectors of the space motions. The ultraviolet excess, 8(C/—ß)o.6' of the main-sequence members is +0Φ11 and spectroscopic analyses of three giant members give [Fe/H] near —0.5. The values of S{U— B)q q for seven groups of old disk population stars range from + 0Φ17 (σ Puppis group) to + 0^03 ( ε Indi group) with the old disk cluster M67 being similar to the latter. The value of E{B—V) = +0^06 for M67 is confirmed by early-type field stars in the vicinity of the cluster. The members of some of the old disk population groups that populate the (Μ^,Κ — Ι) plane near the clump of red giants (M^ol == 0m to + lm) are tabulated and discussed in connection with the suggested "supermetallicity" of some of these stars. It is concluded that the old disk population clusters and groups contain stars with values of [Fe/H] ranging from that of the Hyades to about 20 percent that of the sun. Available narrow-band photometric indices of early K-type giants are not directly useful for determining [Fe/H]. Key words: old disk stars — elemental abundances — photometry

I. Introduction The (UBV) observations have been made in The large and well-determined parallax, several programs over many years. The (RI) σ/091 (weight 50), of Arcturus (HR 5340 = a results were mainly determined with the 40-inch Bootis) leads to space motion vectors of ((7, V, W) reflector at Siding Spring or with the Mount = ( — 25, —116, —3) km/sec. The common Wilson and Palomar Observatories' facilities. space motion of Arcturus and HR 7405 (a Vul- In a few cases, as noted, observations by others peculae has already been noted (Eggen 1969α), have been used. All {RI) results are on the Kron and recent studies of the motions of subgiants system (Kron, Gascoigne, and White 1957; Eggen and main-sequence stars have shown that among 1968α, 1971α). the relatively small number of objects near the The U vectors of the group members are dis- sun with space velocities of this size a significant tributed between —15 and —75 km/sec as percentage may be moving with Arcturus. These shown in Figure 1. A search for possible group stars are listed in Table I together with the (UBV) members with U vectors between 0 and —10 and {Rl) photometric results; the number (N, N) km/sec and between —75 and —85 km/sec of (UBV) and (RI) observations, respectively; yielded no additional members. the group parallax, ng, and the resulting modulus, m — M; the space motion vectors {U, V, W) II. (Mbob R—l) and (My, B—V) Relations and their change for a 100-parsec increase in The members of the Arcturus group listed in the distance (dU, dV, dW); the proper motions, Table I are shown as open circles in the (My, μ; the radial velocity, p, and spectral type; and B—V) plane of Figure 2. A few members of the either individual trigonometric parallax deter- very old, disk population cluster NGC 188 minations with their weights, designated by the (Eggen and Sandage 1969) are also shown in usual observatory abbreviations, or the mean Figure 2, as crosses. The cluster and the group parallax and its total weight, in parentheses. are probably of about the same age although the

271

TABLE I Members of the Arcturus Group

HD Ve V-V U-B m-M U V W Ha Name R R-I Ν, Ν π. dU dV dW Sp. T. km/sec (O'/OOl) (o:'ooi) 3266A 8?43 +0^66 - 15 -116 - 72 + 180 - 52.0 2 8 A ( 2 0 ) ADS497A 4,- 0.017 + 11 -129 -167 -405 G2 V Β 9.25 +0.69 +0.14 4,- G5 V 4308 6.54 +0.655 +0.11 1.88 - 52 -116 - 26 + 160 + 98.4 40C(8) -66053 5.99 + 0.19 2.1 0.042 - 78 -276 +217 -741 G3 V 61Y (7) -53077 9. 84 + 0. 84 +0.44 4.16 - 25 -116 + 114 + 70 - 58.2 19C(6) LTT 195 9.47 +0.35 2.2 0.015 - 63 -198 + 92 -474 K3 V 0Y ( 8) 4744 7.60 + 1.06 +0.79 3.95 - 16 -116 + 87 +224 -162.8 -6A(20) +290141 7.15 +0.39 1.1 0.016 + 66 - 65 - 14 - 30 G8 IV 6497 6. 42 + 1.18 + 1.26 4.95 - 16 -116 - 42 + 107 - 95.5 HR 316 5. 86 + 0.42 2, A* 0.010 + 42 - 36 - 53 -116 K2 III 6734 6. 45 +0.85 +0. 47 3.30 - 50 -116 + 40 + 138 - 95.4 22Y(12) 29 Cet 6.02 +0.335 2.2 0.022 - 41 -186 + 94 -422 KO IV 12369 7.00 + 1.42 7.68 - 64 -116 + 70 + 27 - 68.6 -2507 89 0.003 - 13 - 36 + 1 - 76 Κ4 III +480739 9. 82 +0.96 + 0.68 3.68 - 48 -116 + 9 + 76 - 97.0 18M ( 8 ) LTT 10 887 9.31 +0.36 1,1 0.0185 + 50 100 -150 -398 dK6 64Yk(6) 17820 8. 40 +0.53 -0.06 4.20 - 23 -117 - 84 + 45 + 6.1 +10o380 0.0145 - 59 -169 -116 -439 GO 22225 7.52 + 1.50 8.24 - 18 -116 - 43 + 6 - 8.5 GC 4276 6. 40 +0.935 1,2 0.002 - 3 - 26 - 11 - 40 gM2 24002 8.59 +0.84 +0.42 2.91 - 47 -116 - 15 + 260 - 16.0 25 (52) +0o659 0.026 - 88 -307 - 65 -635 Kl V 31560 3.12 + 1.08 4.95 - 67 -116 + 40 + 192 + 12.5 24C(7) ~2801839 0.010 - 76 -112 + 49 -234 K5 50806 6.02 +0.715 +0.255 3.20 - 53 -116 0 + 177 +171.5 34Y(10) -2 803554 5.69 +0.235 2,2 0.023 -206 -133 + 34 -440 G5 IV 3 8C(7) + 330169 4 10.11 +1.02 +0.82 3.15 - 70 -116 - 68 0 - 78.0 30V(10) G51-10 9.69 + 0.42 2.1 0.0235 - 13 -302 - 61 -640 dK6 4 4M ( 7 ) 71250 5.56 + 1.61 +1. 88 7.30 35 -116 - 79 - 23 - 7.3 26W(8) 27 Cnc 4.26 + 1.08 2.2 0.0035 10 - 42 - 26 -106 gM3 71887 7. 40 + 1.62 + 1.05 8.35 60 -116 15 + 17 + 40.0 253d RT HYA 4. 85 + 1.74 MAX 0.002 20 - 19 - 55 gM6e 75530 9.19 +0.73 +0.215 3.80 28 -116 - 90 -166 + 35.0 14C(7) -402 46 8 8.94 +0.275 2.3 0.0175 80 - 50 -180 -492 G8 V +10o2122 9.92 +0. 88 +0.555 3.45 - 58 -116 - 70 - 50 - 16.6 -7V(12) G 43-34 9. 44 +0.325 2,2 0.0205 -105 -254 -119 -626 dK5 23Y(7) 233719 9.54 + 1.10 +0.94 2.61 - 29 -116 + 21 + 96 - 24.5 2 6M(7) +5301395 8. 83 +0.47 2,2 0.030 - 44 -334 + 120 -748 dMO 69Yk(6) 90508 6.46 +0.605 +0.04 2.33 25 -116 + 30 + 84 - 6.6 53A(28) +4901961 6.20 + 0.24 3.4 0.034 74 -395 + 122 -885 G1 V 40M (7) 94518 3. 35 +0.60 -0.03 3.53 27 -116 - 33 -100 + 92.5 37C(7) -30o8807 0.020 39 - 64 -143 -326 G2 V

TABLE I (C

HP Ve B-V U-B m— M u V W μα 7r(tríg) Name R R-I Ν, Ν dU dV dW Μδ Sp. T. km/sec (orooi) (o':ooi) Wolf 397 + 1. 19 - 26 - 116 - 68 - 250 + 37.0 33(40) G 10-25 9.48 +0.525 3, 4 0.048 -148 - 480 -221 -1130 dMO 106516 6.12 + 0. 47 -0.14 2. 80 - 67 - 116 -101 + 33 + 6.4 28(25) HR 4657 5.99 + 0.14 2,1 0.0275 -334 - 306 -289 -1018 F6 V 111515 8. 13 +0.69 + 0.10 3.40 - 56 - 116 - 67 - 72 - 3.9 31(15) + 2025 85 7.99 +0.255 2, 1 0.021 -122 - 248 -134 - 646 G8 V 115577 6. 80 +0.98 +0.655 3.70 - 75 - 116 + 69 - 61 +152.5 -2 709145 6.47 +0.38 1.1 0.018 + 12 - 36 - 30 G8 IV 115062 6.94 +1.575 +1.875 8.20 - 11 - 116 - 34 30 + 273 56 Vir 5.90 +0.795 2.2 0.002 + 2 - 24 - 12 48 gM2 123598 7. 10 +1.595 + 1. 80 8.42 69 - 116 - 54 4 + 58.0 5. 87 +1.065 6,6 0.002 7 - 19 - 19 58 M3 III 124897 - 0.06 + 1.23 + 1.26 0.20 - 25 - 116 - 3 -1100 - 5.2 0.091(50) α Boo - 0.64 + 0. 47 3.3 0.091 -241 -1053 + 16 -2000 K2 IIIp Ross 5 3 11.08 + 1. 32 + 1.02 1.38 - 41 - 116 + 59 - 900 + 24.0 64M(7) G 166-57 10.26 +0.63 2.4 0.053 -180 - 657 +201 -1200 dM2 140385 8.54 + 0. 70 +0. 10 5.60 - 36 - 116 - 10 87 - 44.8 + 30ο269 5 2,- 0.0065 - 41 - 72 + 19 158 G2 V 153075 7.00 +0.58 -0.01 3.59 - 47 - 116 - 25 165 + 98.7 2,- 0.019 + 75 - 134 - 18 281 GO V 155918 7.03 +0.605 -0.005 2.02 - 11 - 116 + 62 970 + 58.9 48Y(12) -750136 8 6. 83 +0.195 1 r 2 0.0395 + 118 - 314 + 330 206 G2 V 29C(8) +2 702 891 9.50 + 0.64 + 0.12 4.95 - 50 116 + 1 - 135 - 55.5 18M LTT 15276 4,- 0. 010 - 82 78 + 25 - 206 dG2 164064 5. 86 + 1.56 + 1.90 7.50 - 24 116 - 58 9 - 31.7 HR 6706 5.07 + 0.72 4,3 0.003 - 17 33 - 17 - 86 gK5 167768 6.00 + 0.90 + 0.50 5. 45 - 71 116 - 82 + 10 + 2.0 5(30) HR 6840 5.62 +0.335 2,2 0.008 - 55 94 - 66 - 268 G3 III 171911 6.67 + 1.58 + 1.63 8.00 - 46 116 + 29 - 48 - 86.5 GC 25404 2,- 0.0025 - 15 9 + 16 - 24 gM4 175545 7. 45 + 1.22 7.65 - 50 116 - 90 + 12 - 19.0 -0o3595 1, - 0.003 - 20 31 - 26 - 92 K2 III 176704 5.64 + 1.23 + 1.26 5.88 - 14 116 - 40 - 16 0.0 HR 7195 2,- 0.007 - 9 78 - 27 - 173 K3 III 177758 7. 25 + 0.58 0.00,3. 80 - 48 116 - 2 - 190 - 2.5 6(16) -1205278 1,- 0.017 - 85 192 - 4 - 400 GO V 183439 4. 42 + 1. 50 + 1. 81 5.20 - 23 116 + 2 6 - 128 - 85.5 17A(20) α Vul 3.55 + 0.69 8,4 0.009 - 60 38 + 28 - 103 MO III -4M (7) 184700 8. 84 +0.66 + 0.10 4.55 - 46 116 - 29 - 79 - 21.8 14(16) -0o37 86 3,- 0.012 - 90 127 - 40 - 329 G2 V 184768 7.57 + 0.67 + 0.15 4.50 - 55 116 - 62 9 - 14.1 13(37) -0o37 88 3,- 0.0125 - 89 136 - 81 - 386 dG4 186776 6. 15 + 1.60 + 1. 88 7.10 - 29 116 + 47 - 70 - 97.0 HR 7523 5.00 +0.925 MAX 0.004 - 20 9 + 24 - 15 M3 III 189558 7.72 + 0.53 -0.01 3.90 - 64 116 + 37 - 305 - 14.7 13(25) -1205613 2,- 0.0165 -125 180 + 54 - 365 F9 V

TABLE I {Continued)

HD Ve B-Y U-B m-M U V w μα fl'(trig) Name R R-I Ν, Ν dU dV dW μδ Sp. T. km/sec (orooi) (o':ooi) 190333 9?20 + 0^66 +0?15 - 47 - 116 - 24 - 57 + 58.2 -15C(7) -43δ13796 2,- 0.010 + 2 - 115 + 7 - 235 G2 V 191046 7.06 + 1. 15 + 1.02 6.35 - 56 - 116 + 30 - 88 - 93.3 20M(10) +3503962 6.60 +0.39 2,1 0.0055 - 44 - 14 + 18 - 61 K0 III 196866 6.90 + 1.22 6.72 - 65 - 116 - 33 - 27 - 78.0 GC 28775 1,- 0.0045 - 42 - 20 - 21 - 103 K2 III 197484 8. 86 + 0.63 5.60 - 22 - 116 - 2 - 37 + 21.1 GC 28907 0.0065 - 4 - 96 + 9 - 198 G2 V 199288 6.52 +0.61 -0.05 2.00 - 26 - 116 + 51 - 517 - 8.2 51Υ(10) -44014214 6.36 +0.21 2,3 0.040 -130 - 469 + 183 - 965 GO V 43C(7) +904955 10.50 +0.98 +0.77 4.03 - 70 - 116 - 51 + 51: - 16: lOY(lO) G 18-14 If - 0.0155 -117 - 160 -156 - 530: dK4 2 4M(8) 213893 6.69 + 1.54 + 1. 83 7.10 - 41 - 116 + 35 - 22 - 88.0 5.71 +0.71 3,3 0.004 - 24 - 23 - 11 - 68 K5 III 219215 4.21 + 1.56 + 1. 88 5.80 38 - 116 - 59 + 37 - 0.4 7(33) HR 8834 3.22 + 0. 81 2,2 0.007 27 - 81 - 41 - 192 M2 III Argue (19 67)

IV1V ^ θο 0 - 0 * o

12 +2 - . V\o O xQ ** O +4 - o Ν +6 -

+8 - -20 -40 -60 U +10 - X' NGC 188 Fig. 1 — Histogram of the U vectors in the Arcturus +0-4 +0-8 +1-2 +1-6 group. Β -V Fig. 2 — The {Mv,B—V) diagram for members of the difference in the chemical composition of the Arcturus group in Table I (open circles). Stars in Table members, indicated by the ultraviolet excess of IV are shown as filled circles and selected members of the cluster NGC 188 are represented by crosses. the main-sequence stars, 0{U—B)06= +(7^03 for NGC 188 (Eggen and Sandage 1969) and m -hO^ll for the Arcturus group (§IV, below), may are derived from the relation Μ(Ι;) + l , as be the cause of slight differences in the subgiant discussed previously (cf. Eggen 1969α). The sequences. following transformation equations between the {RI)K and {RI)J systems were used (Eggen The group stars with (RI) observations are 1971α) represented by open circles in the (Mboi, R~ I) plane of Figure 3. The bolometric magnitudes RK= Rj + (Γ38; (R-I)K > +(Γ4

- "bol -! 1 1 1 1 1 1 r TABLE II < CU -4 - Observations of RT Hydrae 0 0 JD Ve B-V U-B R R-I 0% -2 - * o* 2440267 81. 3 6 + 1^50 + 0^81 313 8. 35 + 1.54 + 0.78 314 5 . 40 + 1.9 7 0 - 315 5.45 + 1.93 337 8.29 + 1. 52 + 0. 80 338 8.24 + 1. 52 + 0 . 74 + 2 - 340 5.44 + 1.93 o O o 341 5. 47 + 1.94 xx · O 347 8. 19 + 1.54 + 0 . 78 +4 - 529 8.29 + 1.53 + 0.66 xo 534 5. 37 + 1. 87 543 X 0 547 5. 25 +1.805 +6 - ^o 548 7. 79 + 1. 55 + 0. 82 550 7.81 + 1.54 + 0 . 85 χ * σ Pup Group 559 7. 81 + 1.55 + 0. 88 +8 - 563 5. 18 + 1.90 571 7. 85 +0-2 +1-4 581 5.05 + 1. 90 583 7. 79 + 1. 54 + 0.96 586 7. 76 + 1.56 + 0. 88 591 7. 72 + 1.56 + 0.89 Fig. 3 — The (Μ^ι, R—I) diagram for members of the 592 7. 80 Arcturus group in Table I (open circles). Stars in Table 618 7, 42 622 7. 52 4.84 +1.735 IV are shown as filled circles and members of the σ Puppis 624 7. 50 4. 82 + 1.74 group are represented by crosses. 626 7. 49 4. 82 + 1. 74 627 7. 39 + 1.07 628 4. 81 + 1.75 631 4. 81 + 1. 76 RK= Rj + (Γ18 + 0.5 {R- I)K; 641 7.61 4.93 +1.735 644 7.65 + 0.99 4.92 + 1. 79 {R—I)k < +0^4 645 7.74 4.92 +1.785 647 7. 78 4.94 + 1. 81 {R—I)K — 0.80 {R—I)j — 0^5 . 657 7. 82 +0.945 658 4.99 +1.805 662 7. 84 4.98 + 1. 82 The members of the very similar σ Puppis group 664 7. 84 4.97 +1.825 666 7. 83 4.97 +1.805 (Eggen 1971fe) are represented in Figure 3 by 667 7. 84 4.98 + 1. 82 680 7. 81 + 1. 49 + 0.96 crosses. The ultraviolet excess of the main- 681 5.00 + 1. 89 sequence members of the σ Puppis group is the 683 7.74 + 1.51 + 0.94 684 4. 89 +1.825 largest thus far found in the old disk population, 688 7. 79 +1.495 +0.925 4.96 +1.865 689 7. 85 4.97 + 1. 84 8{U-B)o.6 = +0^17 (§IV below). 705 8.05 + 1.51 +0.775 ? 708 The reddest star in Figure 3 is the variable 709 8. 10 +1.485 +0.755 721 8. 11 +1.585 +0.745 RT Hydrae, which is represented at maximum 734 5. 46 +1.815 735 light. The observations of this variable, which 736 5. 50 +1.835 has a period near 250d, are listed in Table II and the light and color curves are shown in Figure 4. A few observations of Ve and R from an earlier cycle have been advanced by 253d and are shown as filled circles in Figure 4. Like the long-period variables in other old disk population groups, such as R Leonis (313d) in the Wolf 630 group (Eggen 1971c, Fig. 14), S Pavonis (386d) in the € Indi group (Eggen 1971b, Fig. 11), S Sculptons (365d) in the 61 Cygni group (Eggen 1971α, Fig. 12), and R Horologii (403d) in the σ Puppis group (Eggen 1971b, Fig. 10), RT Hya shows variations in amplitude from cycle to cycle. The other known variable in Table I is 540 580 HD 186776 (V 973 Cyg). The visual amplitude JD 2440000 + is near (TO and from observations published elsewhere (Eggen 1967), and by analogy with similar Fig. 4 — Light and color curves of RT Hya.

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 276 O. J. EGGEN stars in the other old disk population groups (cf. Eggen 1971c), the period is probably 80 to 90 days. III. Kinematics -40 If we adopt {U\ V)©' with respect to the local standard of rest, of (+10, —16) km/sec (Eggen 1970α), the Arcturus group has V = —100 υ o km/sec with respect to that standard. The parameters of the orbits of the group stars, based on the galactic potential field discussed by +40 Eggen, Lynden-Bell, and Sandage (1962) are ■ G.R. listed in Table III. The group stars, U ' between — 20 and —60 km/sec, are now at apogalactium, + 400 ps Rmax between 10.1 and 10.4 kpc, in orbits with Fig. 5 — The correlation between the U vectors of the e = (Hmax - ßmin)/(ßmax + ^min) = 0.45. space motion and Y, the distance from the sun in the direction of galactic rotation, for members of the Arc- turus group in Table I (open circles). Stars in Table IV TABLE III are shown as crosses and the filled circles are members of Orbital Parameters for Stars with the V Cephei group. V = —100 km/sec and the Listed Values of U ' IT R(Max) R(Min) e The η Cephei group members (Eggen 1971fc) (km/sec) Kpc have values of U between + 20 and + 50 km/sec + 40 10.10 3.87 0.445 and V( —97 km/sec) is only about 10 percent + 20 10.08 3.90 0.44 less than that for the Arcturus group stars. The ± 0 10.08 3.90 0.44 U vectors of η Cephei group members are shown - 20 10.08 3.90 0.44 as filled circles in Figure 5. The trigonometric - 40 10.10 3.87 0.445 parallax of Arcturus is too well established to - 60 10.40 3.84 0.46 allow a change from —119 to —97 km/sec and - 80 10.90 3.80 0.485 the value of V = — 97 km/sec for η Cep is -100 11.10 3.73 0.495 based on a trigonometric parallax of 0'/071 (weight 52) whereas V= —116 km/sec would require a value of 0'Ό27. Although the difference The values of Uand Y for thein membersthe V velocity of the of the two groups is small, it Arturus group are shown as open circles in the is nevertheless real. The gaps in the distribution {U,Y) plane of Figure 5 where Y is the distance of the U velocities in Figure 5 may indicate that from the sun, in the direction of galactic rotation. either there are two, or perhaps three, groups The group stars are not only distributed in a represented, with U = +10 to 0, —15 to —30, nonrandom way in Figure 5 but within the two and —45 to —70 km/sec, but all with V — —116 obvious dumpings of points, between [/=-15 km/sec or, as seems more probable from the con- to —30 km/sec and —45 to —70 km/sec, there sistency of the color-luminosity arrays, one is a suggestion that Udecreases,group numerically, with a nonrandom distribution of U vec- from left to right in the diagram. It has already tors. To avoid difficulties with possible uncer- been mentioned that group members with tainties due to the overlap with the η Cephei between —10 and 0 km/sec were not found. A group, only those stars shown as open circles in search for possible group members, in a catalog Figure 5 (Table I) will be referred to here as of high velocity stars (Eggen 1964α), with members of the Arcturus group. between 0 and +20 km/sec yielded the stars listed in Table IV. These stars are represented IV. Ultraviolet Excess by filled circles in Figures 2 and 3 and by crosses The Arcturus group stars are shown in the in Figure 5. (U~B, B—V) plane of Figure 6 where the filled

TABLE IV Possible Members of the Arcturus Group HP Ve B-V U-B 771— M U V W "(trig) Name R R-I Ν, Ν dU dV dW μδ Sp. T. km/sec (0".001) (0".001) 19735 6^74 0 - 116 - 25 + 77 - 36.1 HR 9 49 5.58 +0.575 2,A* 0.0045 + 13 - 43 -14 - 80 K5 III 38014 8.56 +0.86 +0.58 2.92 + 7 - 116 - 22 + 230 + 55.5 29 (34) + 2o10 41 8.23 +0. 30 2,3 0 ; 026 -100 - 248 - 24 - 525 dK4 65583 7.00 + 0.70 + 0.18 1.70 + 11 - 116 - 41 - 152 + 12.5 56 (48) +2901664 6.66 +0.275 3, A* 0.046 - 1 - 517 -212 -1171 G8 V 115322* 7.10 + 1.60 + 1.60 8.40 - 116 - 54 - 30 - 22.8 5.40 + 1.30 Max 0.002 - 26 ,- 7 - 52 gM4 149161 4. 84 + 1.50 +1. 83 5-90 - 116 + 74 - 182 + 3.1 -11(19) HR 6159 4.00 +0.63 4,2 0.0065 - 78 + 49 - 77 K5 III

153344o 7.04 +0.66 +0.20 3.58 - 116 + 16 - 338 - 82.1 13A(20) +62 1520 6. 82 +0. 22 2,2 0.019 - 97 + 127 - 51 G5 IV 175305 7. 78 +0.76 + 0.16 4.34 + 13 - 116 -123 + 314 -188.0 -8(27) +5901925 7. 45 +0.30 2,1 0.0135 + 75 + 46 -130 + 85 G5 III 191584 6.20 + 1.22 + 1.29 6. 80 - 116 - 1 - 15 - 0.8 HR 7706 5.65 +0.415 2,2 0.0045 - 50 - 1 - 104 K2 III * A = Argue (1967) HD 115322, A new variable. Period 70 and visual amplitude of 0.3.

U-B • Subgiants o Dwarfs and open circles, respectively, represent stars Hyades M.S. brighter and fainter than My = + 4m. The rela- Hyades GTS tions for Hyades main-sequence and giant stars are also shown. The mean value of 8(11—8), reduced to the value at (B—V) = +011^ (Sand- age 1969), for the stars with (B—V) between -f(F5 and +(Γ8 is +0^11 ± (Γ02 (A.D.). This +0-4 - value is listed in Table V together with the values derived from a similar analysis of the members of six other, old disk population groups. The value derived by Eggen and Sandage (1964) for the stars in M 67 is also given for comparison. The ultraviolet excess for the M 67 stars depends +0-8 - upon the reddening, E(B—V) = +0^06 (Eggen and Sandage 1964). To strengthen this reddening determination a search was made for blue field stars in the vicinity of the cluster. Only two objects, with negative values of (B—V), were found and are listed in Table VI together with the blue straggler, Fagerholm 81, in the cluster. The previously derived value of E{B— V) = -fCTW does not appear to be greatly +0-6 +10 B-V in error, and values as high as 0^10 to 0^12 (Spin- Fig. 6 —The Arcturus group members (Table I) in the rad and Taylor 1969; Spinrad et al. 1970) seem (t/—β, β—V) plane. unlikely.

TABLE V Ultraviolet Excess of Main-Sequence Stars in Old Disk Population Groups Group 8([/—B)o.6 NO. aPup* + 0^17 ± (TOS A.D. 10 Arctums* + 0.11 ± 0.02 24 η Cep* + 0.09 ±0.02 7 61 Cyg + 0.075 ±0.02 7 Wolf 630* + 0.065 ±0.02 10 ζ Her + 0.045 ±0.03 9 e Ind + 0.03 ± (FO3 3 M 67 + 0^3 (Eggen and Sandage 1964)

*Notes to Table V aPuppis: HD 37160, G8 III; [Fe/H] = -0.73 (Hel- fer and Wallerstein 1968). HD 107328, KO III; [Fe/H] = -0.72 (Helfer + 0-3 +0-4 +0-5 + 0-6 and Wallerstein 1968). R -I Arcturus: HD 6497, K2 III; [Fe/H] = — 0.4 Cayrel De Strobel 1966). Fig. 7 — The stars near the clump of red giants in the HD 124897 (a Boo), K2 III; [Fe/H] = -0.5 old disk population groups. The numbers are those of (Griffin and Griffin 1967). the stars in Table VII. HD 191046, KO IIIp; [Fe/H] = — 0.5(Green- stein and Keenan 1958). VCephei: HD 1688322, K0 III; [Fe/H] = -0.3 (Green- population stars. Two such clusters are shown in stein and Keenan 1958). Figure 8; the data for M 67 (Eggen 1969b) and eiCygni: HD 95272, K0 III; [Fe/H] = -0.12 (Helfer IC 4651 (Eggen 1971b) are given elsewhere. and Wallerstein 1968). Wolf 630; HD 94264,K0 III-IV; [Fe/H] = -0.15 (Cayrel IC 4651 is slightly younger than M 67, and the De Strobel 1966). stars shown in Figure 7 and the clump stars are slightly bluer, but the presence of the clump is well illustrated in both cases (cf. Eggen 1968b; V. K-Type Giants and (Supermetallicity ?) Cannon 1970). The early K-type giants and subgiants in the This isolated region of clump stars is almost Arcturus group and four other old disk popula- certainly of importance in the evolutionary tion groups (ζ Herculis, σ Pup, € Ind, and η Cep, history of old disk population objects of 1 to 1.5 Eggen 1971fc) are listed in Table VII together solar masses. The luminosity of the clump stars with the bolometric luminosity, the {R—I) color is also apparently little effected by chemical index, and the spectral type (cf. Jaschek, Conde, composition. The groups represented in Figure and de Sierra 1964). These stars are represented 7 contain stars with ultraviolet excesses ranging in Figure 7 by the running number in Table VII. from +0^17 (σ Pup) to +0^3 (e Ind). The The stars in two other old disk groups, 61 Cygni giants and subgiants in the globular cluster 47 and Wolf 630 (Eggen 1971c), show very similar Tucanae, where the chemical composition is results. The six stars fainter than Mboi = +1°1 probably nearly the same as that of the σ Puppis in Figure 7 represent the top of the steeply rising group stars, are shown in the (Mboi, R—I) and subgiant sequence and those redder than (R—I) (My, B—V) planes of Figure 9. A modulus of = +0^48 represent the beginning of the very 13^4, which would give a median visual lumi- slowly rising giant branch for stars of type K2 nosity of 0^45 for the two short-period cepheids and later. The stars between these limits, and in the cluster, has been adopted. These observa- clearly separated from the two sequences men- tions will be discussed in more detail elsewhere tioned, represent the "clump" of early K-type but are displayed here to support the assump- giants found in nearly every cluster of old disk tion that the clump of red giants in old disk

TABLE VI Blue Stars Near M 67 Name Ve B-V υ-Β E{B-V) (m-M)* + 12° 1872 8^10 -(Γ04 -0n45 3 + (F025 7^2 + 14° 2113 7.87 -0.10 -0.45 2 + 0.06 8.35 Fag 81 1(Γ03 -0n)73 — 0^385 Std + 0^)65 9^5 *Main-sequence luminosity assumed.

TABLE VII Early K-Type Giants in Some Old Disk Population Groups No. HD ^bol R—I Sp. No. HD ^bol R-I Sp. Arcturus Group ε Indi Group 6497 +0?95 +0^42 K2 III 20 22231 -0?4 +0^385 K3 III 124897 -0. 85 +0.47 K2 IIIp 21 40409 + 1.55 +0.375 gK3 167768 +0. 35 +0.335 G3 IIIp 22 72324 + 0.8 +0. 37 G9 IIIp 191046 +0. 35 +0.39 K0 IIIp 23 90170 +0.3 +0.315 K0 24 115539 +0.5 +0.355 G8 IV ζ Herculis Group 25 219430 +0.75 +0.385 KO III 26 219615 + 1.4 +0.355 G8 III 5 9106 +0. 8 +0.44 K3 III 6 43899 +0.6 +0.395 gKl η Cephei Group 7 90250 +0.75 +0.37 K1 III1 8 108570 + 1.65 +0.38 dG8 27 4730 -0, +0. 49 gK5 9 119425 + 1. 45 +0.38 K1 III-IV 28 6254 +1. + 0 , 385 G8 IV 10 121416 +0. 65 +0.425 KO IV 29 27370 + 0.55 +0. 40 gG5 30 43380 -0.15 +0. 39 K2 III σ Puppis Group 31 62044 -0.65 +0, 42 Klp 32 72184 0.0 +0. 395 K2 III 11 3457 -1.05 +0.53 Κ4 III 33 114971 -0.05 + 0, 385 K0 12 37160 +0. 55 +0.38 G8 IIIp 34 121146 +0.55 +0 . 42 sg K2 13 37763 + 0.45 +0.39 Κ4 III 35 125932 -0.7 +0. 50 K5 III 14 40801 +0.6 +0.36 KO III 36 126271 -0.15 + 0, 455 gK4 15 77729 -1.0 +0.595 Κ4 III 37 129336 +0.3 +0, 33 G8 III 16 100470 -0.15 +0.37 KO III 38 168322 +0. 35 + 0 , 365 K0 III 17 107328 -0.15 +0.44 KO III 39 203344 + 1.25 +0 , 38 KO IV 18 130227 0.0 +0.415 K2 III 19 130694 -1. 1 +0.57 gK4 population clusters and groups represent the be- the weakness of CN. The asymptotic branch ginnings of an asymptotic branch to the giant star No. 3 has been described as "Lines slightly sequence. The obvious distortion of the (B—V) weak; CH strong" by Keenan and Keller (1953) scale for the asymptotic branch stars (filled who also found the stars Nos. 9 and 39 to have circles) in Figure 9 compared with the subgiants "4172 slightly strong" and Ήδ, Ηγ slightly (open circles) causes the asymptotic branch to strong?" respectively. Four of the clump stars. collapse into the clump near Mboi = + 0^5 in Nos. 4, 12, 22, and 38, have been discussed by the (Mbob R—I) plane. This same effect can be Greenstein and Keenan (1958) as stars with ab- seen in comparing Figures 2 and 3 and is also normal CN or CH bands. They found that rela- probably, at least in part, the explanation of the tive to four standard stars, all of which are young difference, described by Sandage and Walker disk population giants, stars 4, 12, and 38 are (1966), between the positions of asymptotic underabundant in CH by a factor of ten or more. branch stars and subgiants of M 92 in the Star No. 22 has normal CN and CH and the CH (U-B, B-V) plane. in No. 12 is also normal, but that in star No. 4 Many of the stars in Figure 7 have been is underabundant by a factor of three or four. described as having peculiar spectra, mainly in Although the clump stars are spread over less

0 3 0 4 · (R-l)0 ·

Fig. 8 — The stars near the clump of red giants in two old disk population clusters. Fig. 9 — The asymptotic branch (filled circles) and giant- subgiant (open circles) stars of the cluster 47 Tue, shown in the (My, B—V) and (Mbob R~ Ό planes. than a magnitude in luminosity for a given temperature, the variation in surface gravity may lected in Table VIII. These indices are plotted be large. A model computed by Iben (1968) against values of (R—I) in Figure 10 where the with 1.25 solar masses and (X, Z) = (0.71, 0.02) members of various groups are distinguished by passes through the clump region in 3 X 107 symbols: filled circle, Arcturus; plus signs, σ years while nearly doubling its radius. The evi- Pup; triangles, ζ Her; inverted triangles, η Cep; dence for rapid changes in this region of the open squares. Wolf630; and filled squares, 61 Cyg. color-luminosity array, both within the star and The continuous curves are the mean relations on its surface, would appear to complicate any for Hyades and Pleiades group stars of the young attempt to determine the chemical composition disk population (cf. Eggen 1966). It is obvious of these objects from narrow-band photometric from Figure 10 that, although with some rejec- indices. The available spectroscopic analyses tion of isolated stars, reasonably consistent mean have led to the values of [Fe/H], for G- and values of departures from the Hyades-Pleiades early K-type giants, given in the notes to Table relations could be obtained for several stars in V. These results are as consistent (for members a given group, for a given star large errors could of the same group, and with the mean values of occur. For example, four members of the η Ce- d{U— B)oq derived for each group from the phei group (inverted triangles) are consistent in main-sequence members) as could be expected. having Mg b lines that are stronger by 0.09 ± 0.02 To test the usefulness of narrow-band indices of (A.D.) than the Hyades-Pleiades stars, and five some of these stars in determining chemical com- members are consistent in showing Caí lines position, the indices derived at Cambridge Ob- that differ by —0.02 ± 0.03 (A.D.) from the servatory for the Caí triplet (Peat 1964) and standards, but it is a different combination of the the Mg b line (Deeming 1960) have been col- six group stars in each case. Four of the five

TABLE VIII Narrow-Band Indices for Early K-Type Group Giants HD R-I Ca ι Mg b Group 37160 +0^38 1.060 2.33 σ Pup 40801 +0.36 1.075 40 σ Pup 43380 +0.39 1.089 49 η Cep 49520 +0.46 1.203 41 61 Cyg 62044 +0.42 1.100 46 η Cep 72184 +0.395 1.101 46 η Cep 90250 +0.37 1.083 2.35 ζ Her 94264 +0.40 1.085 2.37 Wolf 630 94669 +0.42 1.090 2.40 Wolf 630 98824 +0.41 1.097 2.30 61 Cyg 106760 +0.415 1.081 2.39 Wolf 630 107328 +0.44 1.080 2.37 σ Pup 119425 +0.38 1.098 2.42 ζ Her 121146 +0.42 1.131 2.49 η Cep 124679 +0.345 1.081 2.28 Wolf 630 124897 +0.47 1.094 2.43 Arcturus 129336 +0.33 1.079 2.18 η Cep 131111 +0.38 1.089 2.31 61 Cyg 136514 +0.435 1.131 2.42 Wolf 630 168322 +0.365 1.067 2.28 η Cep

Wolf 630 group members (open squares) in Figure 10 lie on the standard (Mg b, R— I) relation, but these same stars have Ca ι lines ranging from 0.25 fainter to 0.25 brighter than the standards. In the mean, the run of Caí intensity parallels the [Fe/H] and ô{U—B)06 results in Table V with the one member of the Arcturus group and four members of the σ Puppis group showing the weakest lines, displaced from the standard relation by about 0.25, and the ζ Her- culis group members showing little or no difference from the standards. Apparently the narrow- band indices are no more capable of recognizing such small abundance differences as between the sun and the Hyades than is the usual spectroscopic analysis. The situation concerning the Mg b line is more confused, pardy, perhaps, because of the effect of luminosity on these indices (cf. Deeming 1960). Perhaps the most ambitious attempt to use narrow-band indices for determining the composition of K-type giants is that of Spinrad and Taylor (1969). Because their use of a randomly Fig. 10 — The Cambridge, narrow-band indices for Mg b and Ca ι lines in members of the old disk popula- selected collection of field giants as a standard tion groups; Arcturus, filled circle; σ Pup, plus signs; ζ seemed open to criticism, their results for the Her, triangles; V Cep, inverted triangles; Wolf 630, open giants and subgiants in the range discussed here squares; and 61 Cyg, filled squares. The continuous have been reanalyzed in the following way. The curves represent the Hyades group giants. first six stars in Table IX are probable members of the Hyades group and the last four are pos- Spinrad and Taylor for Caí, Mg, GH, Na D, sible members of the Pleiades group. The values and CN are also listed as well as (R—I). The of Τ and the blocking fractions, w, measured by {w, T) relations for these young disk stars are

TABLE IX Possible Members of the Hyades 0-3 and Pleiades Groups HR Ca ι Mg CH D CN R—I (4200) w 941 389 0.13 0. 15 0. 32 0.05 +0^34 951 412 0.16 0. 16 0. 33 0.05 +0.355 01 0Ν(λ4200) 1346 386 0.09 0. 13 0.29 0.06 +0.335 1373 391 0.10 0. 12 0. 31 0.05 +0.335 1409 394 0.11 0. 13 0. 31 0.05 +0.34 1411 382 0.12 0. 14 0. 31 0.05 +0. 33 2478 446 0.22 0. 19 0. 32 0.07 +0. 43 4737 434 0. 18 0.21 0.31 0.09 +0. 38 5889 374 0.07 0. 12 0.28 0.03 0.08 +0.285 01 6644 448 0. 19 0.25 0.31 0.07 0.29 +0.41 shown in Figure 11 where the continuous curves represent the adopted relation for Hyades- Pleiades stars. The giants in the old disk popula- 0-3 tion groups and clusters, with temperatures and luminosities that place them near the clump in CH the color-luminosity array and which were also observed by Spinrad and Taylor, are listed in Table X. The values of {w, T) for these stars are 0-2 shown in Figure 12 where the continuous curves represent the Hyades-Pleiades stars in Figure 11. 01 The member of the 61 Cygni group is represented by a cross, σ Puppis group by a plus sign, e Indi group by open circles, ζ Herculis group by a triangle, and η Cephei group by an inverted tri- Ca I angle. Members of the cluster M 67 are shown in 0-2 Figure 12 as filled circles. The star e Virginis (HR4932), often used as a standard in spectro- 01 scopic analysis of Κ giants, and found from a direct comparison with the sun by Cayrel and Cayrel (1963) to have solar abundance, is represented in Figure 12 by the circled dot at Τ = 400 440 393. Fig. 11— Hyades-Pleiades group giants in the {w, T) If we discuss the data in Figure 12 with the plane for CN, Na D, CH, and Ca i. The continuous same detail, and confidence, as Spinrad and curves are adopted as standard relations. Taylor have for similar results on other stars, we arrive at interesting, if confusing, conclusions. overabundance occurs in many old disk popula- For example, HR 1907 (HD 37160) in the σ tion stars. In fact, the available evidence sug- Puppis group (plus sign) shows Hyades abund- gests that the overabundance of all α-process ance of Caí and Mg but a relatively large de- elements, relative to Fe, is [alFe] ~ 0.2 for ficiency of Na. The CH is relatively strong and such relatively Fe-weak stars as members of the CN very weak. The spectroscopic analysis σ Puppis group, and that this overabundance (Heifer and Wallerstein 1968) gives [Fe/H] = decreases with increasing Fe abundance (cf. — 0.73, which is consistent both with the Peat and Pemberton 1968). This result, plus the ultraviolet excess of the main-sequence group already noted tendency for stars in the region of stars and the abundance determination for the red giant clump to have abnormal CN and other group stars (Table V). The overabund- CH strengths, leaves only the (T, Na D) relation ance of both Caí and Mg, seen in Figure in Figure 12 as a reliable index of [Fe/H], and 12, is also found in the spectroscopic analyses by even this index may be suspect. The young disk Heifer and Wallerstein who also note that this population star e Vir, used as the solar standard

TABLE X Photometric Parameters for Old Disk Population Group and Cluster Stars HR HD Τ Caí Mg CH NaD CN Group (4200)

495 10486 401 0. 15 0.23 0. 30 0. 10 0.26 +0^43 61 Cyg 1907 37160 402 0.13 0.17 0.36 0.02 0.14 +0.38 σ Pup 3369 72324 402 0.15 0.14 0.32 0.05 0.26 +0.37 ε Ind 5159 119425 436 0.20 0.22 0.34 0.07 0.30 +0.38 ζ Her 5227 121146 460 0.28 0.31 0.36 0.07 0.29 +0.42 η Cep 8841 219430 426 0.21 0.19 0.40 0.05 0.26 +0.385 ε Ind 8852 219615 395 0.11 0.14 0.35 0.03 0.15 +0.355 ε Ind

Fag M 67

84 392 0.18 0.17 0.35 0.06 0.27 +0.375 105 442 0.28 0.25 0.35 0.09 0.31 +0.46 108 479 0.36 0.30 0.35 0.11 0.34 +0.51 141 396 0.18 0.18 0.37 0.06 0.28 +0.395 151 390 0.19 0.17 0.34 0.07 0.27 +0.39 170 475 0.30 0.28 0.33 0.09 0.34 +0.51 224 408 0.20 0.22 0.31 0.09 0.29 +0.415 in Figure 12, is consistent in its displacement have the strongest Fe lines. Whether this metal from the Hyades stars in M g and Caí as well as line strength is that of the sun, or factors of two in CH and CN, with the only anomaly being in to three times stronger or weaker than the sun, Na D, but again this is reasonably consistent cannot easily be determined because of the un- with the spectroscopic analysis by Cayrel and certainties involved. The old disk groups and Cayrel (1963) who found the composition to be cluster in Table V, and represented in Figure solar except for an overabundance of Na by a 12, are known from both the values of ô{U— B)o,e factor of two. and spectroscopic analyses to have values of In view of these uncertainties, the small dis- [Fe/H] ranging from solar to one-fifth of solar placements of individual stars in Figure 12 seem value. With this range as a scale factor a de- a wholly inadequate basis upon which to derive tailed interpretation of Figure 12 might run as values of [Fe/H] that can be then used to cor- follows. rect results that have been previously derived 1. If we accept the arguments discussed from what Spinrad and Taylor (1969) refer to as above that the most reliable indicator of [Fe/H] the "astrophysical mythology" that old stars may be the Na D lines, the total displacement cannot have greater Fe abundances than the from the Hyades (Na, T) relation of 0.07 repre- Hyades. sents a factor of five in values of [Fe/H]. We It is well known from (UBV) photometry of must also remember that the M 67 stars are main-sequence stars (cf. Eggen 1964fc, 1970α) fainter than the other objects by a factor of 100 that within the old disk population there exists a or more and small errors in both Τ and w can whole range of metal abundances, from that of be expected. A small, systematic difference of the Hyades {8(11-3)0^=0^) to that of the Γ(Μ67) — r(standard stars) = 30 ± 20 (A.D.) σ Puppis group {8{U—B)o.6= +0^17) but the was derived from comparisons between Τ and maximum in the frequency distribution moves (R—I) so that the M67 stars in Figure 12 may to larger values of 8{U~-B) with increasing age. need to be shifted to the right by up to 30 in T. This range of ultraviolet excesses is reflected in There is certainly very little difference between the groups and cluster in Table V where values the (Na, T) relations for all of these old disk of δ(ϊ7-β)ο.6 = -l-CPOS for members of M 67 stars and for the Hyades-Pleiades stars except and the e Indi group indicate that these stars that the member of the σ Puppis group (plus

Ί 1 1 2. The CN strengths are all within about ·· 0.02 of the (CN, T) relation for Hyades-Pleiades · -Δ·4 ^ " stars except for a member of the group with the largest underabundance of Fe (σ Pup, plus sign) and a member of the group with the least underabundance of Fe (e Ind, open circle). In + view of the already noted tendency for stars

1 CN (λ4200) near the red giant clump to show CN anomalies, the (CN, T) relation can probably give little reliable information concerning [Fe/H]. Na D 3. Most of the old disk population group and cluster stars in Figure 12 have strong CH, aver- - ^ " aging about + 0.05, in w, compared with Hyades- + Pleiades stars or +0.07 compared with the sun o (e Vir). 4. The Caí lines are stronger in the M67 /9¾ Χ v · # stars ( + 0.08 in w, relative to the Hyades) and η Cephei group members ( + 0.05) than in the 0 CH other groups. On the other hand, the Mg b line is strongest ( + 0.08 in w, relative to the Hyades) in the members of the 61 Cygni and η Cephei - Mg groups. Until more is known of a possible correlation between [oJFe] and [Fe/H], neither the displacements in the (Mg, T) and (Ca, T) planes of Figure 12 nor the inconsistencies of ι these displacements with known values of 1 I [Fe/H] can be interpreted. Spinrad and Taylor (1969) apparently accept the evidence of the narrow-band system for Fe • Gal abundance determinations in main-sequence stars, although they find the evidence from the • ν* - (UBV) photometry unacceptable, expecially in M 67. The reddening-free parameters, β and V» [mj, for main-sequence (My > +3m) members of six old disk population groups are listed in Table XI and represented in Figure 13 by the following symbols: Arcturus, filled circle; η Cep, I 1 1.. inverted triangle; 61 Cyg, cross; Wolf 630, boxes; 400 440 480 ζ Her, triangles; and € Ind, open circle. The con- Fig. 12 — The old disk population giants in the (u;, T) tinuous curve in Figure 13 represents the stan- plane: σ Pup, plus sign; 61 Cyg, cross; V Cep, inverted dard relation for Hyades cluster stars (Crawford triangle; ε Ind, open circle; ζ Her, triangle; and M 67, and Barnes 1969; Eggen 1969fc). The resulting filled circles. The solar standard, ε Vir, is represented by values of Δ [mj are compared, in Table XII, a circled dot at Τ = 393. The continuous curves are from Figure 11. with the values of ô(U—B)06 and [Fe/H], from Table V. In spite of the apparent "supermetal- sign), which is known to have the lowest Fe licity" of some of the group giants in some of the abundance in Figure 12, obviously has weaker panels of Figure 12, the broad- and narrow-band Na D lines. The solar standard, € Vir also falls photometry of main-sequence stars in these on the (Na, T) relation for Hyades stars, as groups is consistent with the spectroscopic already mentioned. analyses in conforming the previous conclusion

TABLE XI that the old disk population stars contain those Narrow-Band Indices for Main-Sequence with Fe abundances between that of the Hyades Stars in Old Disk Population Groups stars and of the σ Puppis group members. Taylor and Spinrad (1971) have said that their HD [mi] HD [mi] "results — including those for SMR (supermetal Arcturus Gp. Wolf 6 30 Gp. rich) stars —stand unretracted." It would seem 153075 2.603 0.239 126660 2.640 0.220 that more spectroscopic investigations of the 193307 2. 619 0.240 η Cep Gp. 200790 2.627 0.245 clump stars in Figure 7 (Table VII) may show 215648 2.625 0.215 10785 2.607 0.248 if their results are intractable. 61 Cyg Gp. ζ Her Gp. 207692 2.638 0.212 13974 2. 600 0.270 60532 2. 640 0.210 REFERENCES ε Ind Gp. 34411 2.600 Argue, A. N. 1967, M.N.R.A.S. 135, 23. Cannon, R. D. 1970, M.N.R.A.S. 150, 111. Cayrel, G., and Cayrel, R. 1963, Ap. J. 137, 431. Cayrel De Strobel, G. 1966, Ann. d'Ap. 29, 413. Crawford, D. L., and Barnes, J. V. 1969, A.J. 74, 818. Deeming, T. J. 1960, M.N.R.A.S. 121, 52. Eggen, O. J. 1964α, Roy. Obs. Bull. No. 84. 1964Z?, A.J. 69, 570. 1966, Roy. Obs. Bull. No. 125. 1967, Ap.J. Suppl. 14, 307 (No. 131). 1968û, Αρ. J. Suppl. 16, 49 (No. 142). 1968k, Ap. J. 152, 83. 1969a, Ap. J. 158, 225. 19696, Pub. A. S.P. 81, 553. 1970a, in Vistas in Astronomy, A. Beer, ed., 12, 367. 19702?, Pub. A.S.P. 82, 99. 1971a, Ap.J. Suppl. 22, 389 (No. 191). 1971b, Pub. A.S.P. 83, 251. 1971c, Ap.J. 165,317. Eggen, O. T., and Sandage, A. R. 1964, Ap. J. 140, 130. 1969, Ap.J. 158,669. 2-64 2-60 Ρ Eggen, O. J., Lynden-Bell, D., and Sandage, A. R. 1962, Ap.J. 136, 748. Fig. 13 — Main-sequence members of the Arcturus Greenstein, J. L., and Keenan, P. C. 1958, Ap. J. 127, (filled circle), 61 Cyg (cross), ε Ind (open circle), ζ Her 172. (triangles), η Cep (inverted, triangle), and Wolf 630 (open Griffin, R., and Griffin, R. 1967, M.N.R.A.S. 137, 253. boxes) groups in the reddening-free (β, [mi] ) plane. Heifer, H. L., and Wallerstein, G. 1968, Αρ. J. Suppl. 16, 1 (No. 141). Iben, I., Jr. 1968, Ap./. 154, 581. Keenan, P. C., and Keller, G. 1953, Ap. J. 117, 241. TABLE XII Kron, G. E., Gascoigne, S. C. B., and White, H. S. 1957, A.J. 62, 205. Comparison of ô{U—B) and Δ[?η1] Values Jaschek, J., Conde, Η., and Sierra, A. C. de 1964, Obs. for Main-Sequence Stars with [Fe/H] Astr. Univ. La Plata 27, 2. Determinations for Giants in Old Disk Peat, D.W. 1964, M.N.R.A.S. 128, 475. Population Groups Peat, D. W., and Pemberton, A. C. 1968, M.N.R.A.S. 140, 21. Group 8(1/-β)ο.6 Ν A[m1] Ν [Fe/H] Ν Sandage, A. 1969, Ap. J. 158, 1115. Sandage, ., and Walker, M. F. 1966, Ap. J. 143, 313. σ Pup + 0.17 10 -0. 72 Α Arcturus + 0 . 11 24 + 0.0 42 -0.5 Spinrad, H., and Taylor, B. J. 1969, Ap. J. 157, 1279. η Cep + 0.09 7 +0.027 -0.3 61 Cyg +0.075 7 +0.026 -0 . 12 Spinrad, H., Greenstein, J. L., Taylor, B. J., and King, I. Wolf 630 +0.065 10 +0.018 -0. 15 R. 1970, Ap.J. 162,891. ζ Her +0.045 9 +0.020 ε Ind + 0.03 3 +0.005 Taylor, B. J., and Spinrad, H. 1971, Bull. A.A.S. 3, 11. M 67 + 0.03