tot from the Sun in the direction opposite that of the Galactic center. The computed values of the radial velocity are given by

Transcription

1 THE ASTRONOMICAL JOURNAL, 116:284È292, 1998 July ( The American Astronomical Society. All rights reserved. Printed in the U.S.A. THE AGE RANGE OF HYADES STARS OLIN J. EGGEN Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories,1 Casilla 603, La Serena, Chile; oeggen=noao.edu Received 1997 December 29; revised 1998 March 12 ABSTRACT On the basis of canonical models, the age of Hyades supercluster stars, whether in the Hyades and Praesepe clusters or the noncluster Ðeld, ranges from (5È6) ] 108 to 109 yr. The di erence between the parallax derived from the supercluster motion and that obtained from Hipparcos observations has a dispersion only twice that of the mean dispersion of the individual Hipparcos values. The supercluster appears not to contain red giants on the Ðrst ascent of the red giant branch, but only asympic giant branch ( clump ÏÏ) stars. The masses obtained for individual components of binary stars in the supercluster show a dispersion of less than 10% when compared with model predictions. Key words: open clusters and associations: individual (Hyades) È stars: evolution 1. INTRODUCTION The Hyades cluster, because of its depth-to-distance ratio, has become the basis for the universal metric. The lowest mass cluster members form a cluster halo, and the cluster itself, together with its near-twin the Praesepe cluster, is part of the Hyades supercluster. This supercluster, together with another, the NGC 1901 supercluster, forms the main constituent of star stream I, for which the apex of the proper motions is (a, d) \ (6h.4, 6.5) (B1950.0). Previous investigations of the cluster and superclusters have shown a wider range of agesè8 ] 108 to 2 ] 109 yrèthan can be easily explained as one, prolonged star birth event. The present discussion will be divided into two parts, with the upper main sequence of the supercluster discussed in 2.1 and red giants in 2.2. The b photometry is mainly from the compilation by Hauck & Mermilliod (1980), and the RI photometry is on the system deðned in Eggen (1979). The proper motions are on the FK5 system and are from the references in the notes to Table 1. The observed radial velocities are mainly from Abt & Biggs (1972) and Barbier-Brossat, Petit, & Figon (1994). For the upperè main-sequence stars, the values of log T are based on b. A previous discussion (Eggen 1995) found that log T \ ] 0.53(b [ 2.800), (1) derived from spectrophotometry (Smalley & Dworetsky 1993) for a range of Am, ultraèshort-period Cepheid (USPC; d Scuti), and normal AF stars, as well as fundamental values of T (Andersen 1991) derived from eclipsing binaries. The mean dispersion of the di erence between the spectrophotometric values and those from equation (1) is ^100 K. The temperatures for the red giants are from BessellÏs (1979) calibration of the [(R[I), log T ] relation. C The convergent point of the proper motion of stars in stream I is at (a, d) \ (6h.4, 6.5) (Eggen 1996). The stars discussed here are mainly of magnitude V \ 7 and peculiar velocity P.V. ¹ 0.1V, with M (clus) [ M (phot) \ 0.25 mag. Here V V P.V. \ 4.74qD(pc), (2) ÈÈÈÈÈÈÈÈÈÈÈÈÈÈÈ 1 The National Optical Astronomy Observatories are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. where (t, q) are the components of the proper motion in the direction of the convergent point (a, d) and perpendicular to that direction, respectively; and n \ 4.74t/(V sin j), (3) clus where V is al space motion of the supercluster relative to the Sun and j is the angular distance between the star and (a, d). The photometric luminosities have been derived from the photometric calibrations listed in Eggen (1996). 2. HYADES SUPERCLUSTER 2.1. Upper Main Sequence The parameters for upperèmain-sequence members of the Hyades supercluster are listed in Table 1, where the stars are identiðed by HR, HD, and Hipparcos (ESA 1997) numbers. Only stars not known to have photometrically unresolved companions from 0.2 to 3.2 mag fainter are considered. The al space motion is V \ 43.5 ] 0.045X (4) (Eggen 1992b), where X is the distance in parsecs of the star from the Sun in the direction opposite that of the Galactic center. The computed values of the radial velocity are given by o \ V cos j. (5) comp The mean di erence, o [ o, omitting the variable- velocity stars, is [0.3 ^ obs 2.4 (1 comp p) kms~1, or[0.35 ^ 2.50 km s~1 if we include those with variable velocity. The dispersion in the mean peculiar velocity is higher, as expected, from the supercluster members, [0.27 ^ 2.50 km s~1, than it is for the members of the Hyades cluster, ]0.26 ^ 0.66 km s~1. The mean modulus for the Hyades cluster members in Table 1 is 3.29 mag from the cluster motion and 3.37 mag from the Hipparcos parallaxes. The motion parallaxes from the Hipparcos convergent point (Perryman et al. 1998) yield a mean modulus of 3.33 mag, and Schwan (1991) found 3.40 mag. The comparison between the cluster parallaxes in Table 1 and the Hipparcos results is almost identical to that discussed by Perryman et al. The overall comparison for the supercluster stars in Table 1 yields n [ n \ 0.13 ^ 1.84 mas. Four stars are omitted from this clus comparison, Hip listed in Table 2. The convergent point of the proper motions of a critically selected 20 cluster members (Perryman et al. 1998) is (a, d) \ (6h. 52, 6.66), com- 284

2 TABLE 1 MEMBERS OF THE HYADES SUPERCLUSTER o (km s~1) k X V P.V. SPECTRAL HR (HD) REFERENCEa (pc) (km s~1) Obs. Comp. (km s~1) M log T Cluster Hip. p TYPE NOTES HIP V [ [2V [2.9 ]1.2 ] A1 E ]2.3 ]1.4 ]0.8 ] F3 IV ]9.4 ]9.1 ]0.5 ] A7 V (8391)... 2 [ ]4.2 ]4.2 ]1.4 ] F1 V ]7V ]10.0 ]0.2 ] A5 IV [ ]8.0 ]4.6 ]2.9 ] A1 V ]15.0 ]18.5 ]4.0 ] A5 III ]24V ]18.4 ]1.3 ] F0 III ]28.5 ]27.0 ]0.2 ] F5 IV ]34.5 ]31.3 ]0.9 ] A3 Vp 5, ]30.0 ]32.2 [1.0 ] F2 V ]35.0 ]35.1 [0.3 ] F4 V ]36: ]34.6 ]0.5 ] F5 V ]36.4 ]36.7 [0.1 ] F3 V (26345) ]35.0 ]36.8 ]0.1 ] F6 V ]36.8 ]37.4 [0.6 ] F4 V ]36.4 ]37.5 ]2.2 ] F5 V (26737) ]3.75 ]38.4 ]0.8 ] F5 V ]42.0 ]38.4 ]0.1 ] F0 V 7, ]42.0 ]38.0 [0.8 ] F2 V ]36.2 ]38.4 [0.6 ] F0 IV 7, (27534) ]3.1 ]37.8 ]0.4 ] F5 V ]41.2 ]38.5 [0.6 ] Am 7, ]37.5 ]38.1 [0.3 ] A8 V (27848) ]37.1 ]37.8 ]0.4 ] F6 V ]36.6 ]38.6 ]1.2 ] F3 V ]40.1 ]38.9 ]0.5 ] A6 V ]33.0 ]38.0 ]0.4 ] A5 Vm 7, ]40.2 ]38.9 ]0.6 ] A2 IV ]36.4 ]38.9 [0.6 ] F7 V 6, 7, ]37.5 ]38.3 ]0.2 ] Am ]44.2 ]39.0 ]0.8 ] F2 V ]39.5 ]38.9 ]0.4 ] A7 IV 7, ]33.4 ]39.5 ]0.4 ] A7 V (28394) ]39.8 ]39.0 ]0.1 ] F8 V 7, ]37.5 ]39.2 ]0.7 ] A7 V 6, ]39.3 ]39.2 ]0.5 ] Am ]38.8 ]39.4 ]0.2 ] F0 V (28608) ]41.3 ]39.7 [0.1 ] F7 V ]36.0 ]39.4 [0.4 ] F2 V ]39.8 ]39.6 [0.3 ] F5 V ]43.3 ]38.6 ]0.5 ] F5 IV ]38.4 ]40.1 [0.3 ] F2 V ]45.0 ]40.2 ]1.0 ] A6 V ]36.9 ]40.4 ]1.6 ] A6 IV ]36.3 ]40.5 [0.6 ] A9 III ]39.4 ]41.0 [0.4 ] A3 IV ]43.0 ]41.4 ]1.7 ] Am 7, ]38.5 ]40.9 ]0.4 ] A9 V 6, ]38.0 ]40.7 ]1.0 ] F2 IV ]35.0 ]41.3 ]0.7 ] F1 V ]42.2 ]41.5 ]0.5 ] A7 V ]45.0 ]40.5 [0.6 ] Am ]39.2 ]43.0 ]0.4 ] Am 7, ]8.0 ]7.5 ]3.5 ] A1 V ]41.0 ]43.8 ]0.3 ] F0 V ]40.9 ]42.0 ]0.2 ] Am ]28: ]29.0 [3.5 ] Am ]40V ]43.6 [0.6 ] A4 IV [ ]9.0 ]10.1 [2.3 ] A4 V ]32.0 ]31.6 [3.0 ] A5 IV ]17.0 ]20.8 [3.1 ] A2 III ]23.0 ]22.7 ]3.0 [ A2 Vp (97840)... 2 [ ]5.2 ]8.4 [4.5 ] F4 IV/V [ ]9.0 ]4.4 [2.8 ] A2 IV/V ]7.0 ]7.7 [2.5 ] Am [ ]9.1 ]6.2 ]2.3 ] F3 IV [ [2.4 [2.3 [1.4 ] Ap 6, ]4.0 ]3.2 [1.6 ] F0 V V ]3.9 [4.0 ] F3 IV

3 286 EGGEN Vol. 116 TABLE 1ÈContinued o (km s~1) k X V P.V. SPECTRAL HR (HD) REFERENCEa (pc) (km s~1) Obs. Comp. (km s~1) M log T Cluster Hip. p TYPE NOTES HIP V [1.5 ]1.1 [1.2 ] A7 V (112734)... 2 [ [6V [3.1 ]4.2 ] A [ [7V [3.6 ]4.5 ] Am [ [14.5 [11.5 ]3.3 ] A8 IV (121141)... 2 [ [16V [13.6 [0.7 ] F2 V [ [20V [18.0 ]0.8 ] F0 IV [ [9V [5.7 [2.9 ] Am [ [30V [28.1 ]1.9 ] A9 V [ [21.1 [22.6 ]0.5 ] A7 V [8.4 [6.2 ]3.6 ] A2 Vp 6, [ [24.0 [22.0 [0.2 ] A6 V [ [31.0 [28.5 [0.3 ] Am [ [20V [22.2 [2.2 ] A0 V [ [12.4 [15.0 [0.1 ] A4 V [ [18.9 [17.6 [4.5 ] F2 V [ [7.0 [7.0 [4.5 ] A6 Vm [18.8 [15.5 [4.5 ] G0 V NOTES.È(1) V526 Cas, USPC (P \ 0.05 days); (2) suspected variable (HR 343 \ CSV ); (3) d Cas, unconðrmed eclipsing binary; (4) TY For, USPC (P \ 0.05 days); (5) CHARA 10; (6) equal components; (7) Hyades cluster star; (8) V696 Tau, USPC (P \ 0.05 days); (9) V696 Tau, USPC (P \ 0.04 days); (10) V773 Tau, USPC (P \ 0.06 days); (11) i2 Tau (period?); (12) P \ 13 yr; (13) h2 Tau (see Eggen 1995), USPC (P \ 0.07 days); (14) spectroscopic binary, P \ 239 days; (15) spectroscopic binary; (16) spectroscopic binary, P \ 156 days; (17) spectroscopic binary, P \ 24 days; (18) AI CVn, USPC (P \ 0.14 days); (19) BP Oct, USPC (P \ 0.08 days). a Proper-motion references: (1) FK5, Fricke et al. 1988; (2) FK5 supplement, Schwan et al. 1993; (3) FK5 Extension, Fricke, Schwan, & Corbin 1991; (4) Hipparcos Catalogue, ESA pared with (a, d) \ (6h.4, 6.5) for the stars in stream I (Eggen 1996). The (log T, M ) array for the stars in Table 1 is shown V in Figure 1. The Hyades cluster stars are represented by Ðlled circles, and the noncluster, supercluster members by open circles. The Praesepe cluster stars are mostly fainter in apparent magnitude than the objects in Table 1, but the cluster is almost an identical twin of the Hyades cluster. The Praesepe stars that are not known to have photometrically unresolved companions between 0.2 and 3.0 mag fainter are listed in Table 3. These stars are represented in Figure 1 by crosses. The adopted modulus of Praesepe is 6.35 mag, derived from the 3.0 mag di erence between the Hyades and Praesepe main sequences and the mean modulus of 3.35 mag for the Hyades. The Praesepe cluster, as a member of the Hyades group, is discussed in Eggen (1992a, 1996). The adopted parallax of 5.4 mas agrees well with the main Hipparcos value in Table 4 of 5.51 ^ 0.96 mas. The supercluster members with T [ 7500 K are shown in Figure 1a, and the lower temperature objects are in Figure 1b. The isochrones in the Ðgure are from Castellani, Chii, & Straniero (1992). The models have Y \ 0.27 and Z \ 0.02, whereas the expected value for the supercluster is probably nearer Z \ However, this small di erence has been compensated for by subtracting 0.10 mag from the model values of M (see Eggen 1986, Fig. 19). Based on the V arguments by Castellani et al. (1992) against the presence of convective overshoot at the core, the canonical models have been adopted here. Use of models with convective over- TABLE 2 STARS OMITTED FROM HYADES PARALLAX COMPARISON HR Cluster Hip. p 1408a a b b a Hyades cluster (Perryman et al. 1998). b Supercluster. FIG. 1.È Hyades supercluster members in the (log T, M V )-plane

4 No. 1, 1998 AGE RANGE OF HYADES STARS 287 TABLE 3 MEMBERS OF THE PRAESEPE CLUSTER Spectral Spectral HD/BD M V log T Type Notes HD/BD M V log T Type Notes ] G0 III ] A9 V ] K9 V ] F0 V 6, ] F0 V ] Am ] Am ] A6 III ] F0 IV ] F0 V ] A5 V ] A9 V ] F0 V ] A9 III ] F2 V ] F0 V ] A9 V ] Am ] A9 V ] A6 V ] A9 V ] F5 V ] F0 III ] A5 V ] A7 V ] F2 V ] F2 V ] ] F4 V ] F2 V ] A7 V ] Am ] ] F6 V ] Am 5, 6 ] ] F5 V ] Ap 7 ] ] F ] Am ] ] F ] Am NOTES.È (1) BR Cnc, USPC (P \ 0.04 days); (2) CY Cnc, USPC (P \ 0.1: days); (3) BT Cnc, USPC (P \ 0.10 days); (4) BU Cnc, USPC (P \ days); (5) spectroscopic binary, P \ 12 days; (6) equal components; (7) 40 Cnc (binary?); (8) BQ Cnc, USPC (P \ 0.07 days); (9) BV Cnc, USPC (P \ 0.21: days); (10) BN Cnc, USPC (P \ 0.04 days); (11) BW Cnc, USPC (P \ 0.07 days); (12) BX Cnc, USPC (P \ 0.05 days). shoot at the core (e.g., Maeder & Meynet 1991) would increase the ages by a factor near 1.5. The minimum age of the supercluster stars, including both the Hyades and Praesepe cluster members, appears to be (5È6) ] 108 yr. However, both Figures 1a and 1b show evidence that older stars exist in all three components (two clusters and noncluster Ðeld) of the supercluster. The Am stars and USPC (d Scuti) variables in the supercluster are represented in Figures 2a and 2b, respectively. The complicated double star HR 1412 has been omitted from the Ðgure. The symbols are as in Figure 1. Two stars not in Table 1 or 3 have been added to Figure 2b: the largeamplitude USPC stars VZ Cnc and d Sct (Table 5). 1. VZ Cnc is about 10, or 30 pc, from the center of the Praesepe cluster. Eleven cluster members in the Hipparcos Catalogue, as well as VZ Cnc, yield the results shown in Table 4. The variable and the cluster appear to be at the same distance with nearly the same proper motion. The mean cluster radial velocity is ]34 km s~1, and Abt (1955) TABLE 4 ASTROMETRY OF PRAESEPE MEMBERS AND VZ CANCRI a (J2000.0) d (J2000.0) k a k d p(k a, k d ) n p(n) HD HIP (hr) (deg) (mas yr~1) (mas yr~1) (mas yr~1) (mas) (mas) ]19.59 [35.66 [ , ]20.34 [35.96 [ , ]19.50 [36.65 [ , ]19.27 [35.55 [ , ]20.04 [35.02 [ , ]19.97 [34.86 [ , ]19.67 [35.22 [ , ]19.54 [33.74 [ , ]19.72 [34.26 [ , ]19.58 [33.61 [ , ]19.87 [34.85 [ , Mean ]19.74 [34.9 [ p... ^0.90 ^1.3 ^0.96 VZ Cnc ]9.82 [29.88 [ , TABLE 5 COMPARISON STARS IN FIGURE 2b M V P STAR n n n n Mean log T (days) clus phot PvL Hip VZ Cnc... ]1.30 ]1.51 ]1.45 ]1.25 ] d Sct ]1.38 ]1.37 ]1.06 ]

5 288 EGGEN Vol. 116 TABLE 6 SUPERCLUSTER MEMBERS WITH T D 7450 K Spectral Age HR (HD) M V log T Type d (yr) Notes (73210)... ] A5 V ] (73819)... ] A6 V (73785)... ] A9 III ] A5 IV... 8 ] ] A3 Vp , 3 (73756)... ] A7 V , 4 (74028)... ] A7 V , ] A9 V , ] A8 IV ] A7 V ] A4 V (73619)... ] Am... 1, ] A7 V ] F0 IV... 4, ] Am , ] F0 V ] F0 V (112734)... ] A ] 108 NOTES.È(1) Praesepe cluster; (2) spectroscopic binary; (3) equal components; (4) USPC; (5) Hyades cluster. FIG. 2.ÈRecognized (a) Am and (b) USPC members of the supercluster in the (log T, M V )-plane. found a mean of ]30 km s~1 for the variable from 92 plates. McNamara & Rogers (1962) and Balona & Stobie (1983), from 14 and 103 plates, respectively, found ranges from about 0 to ]55 km s~1 for the variable. The value of M from n is derived from the Praesepe modulus of 6.35 V clus mag and n from the parallax in Table 4. The period- Hip luminosity relation (Eggen 1994b) gives M \[2.80 log P V [ 0.60 \]1.45 mag. The periods of the fundamental modes (Templeton et al. 1997; Fitch 1976) are listed in Table d Sct, at B coordinates (18h.65, [9.1), is very near the antapex of the stream I proper motions, so the predicted stream motion in the tangential direction is nearly zero and the star is an FK5 standard with the very small motion of (k, k ) \ (9, 2) mas yr~1. The predicted radial velocity is [45.6 a d km s~1, compared with an observed value of [44 km s~1 from 23 plates, and this agreement, together with that of the luminosities from photometric parallaxes and the period-luminosity relation, is the basis for accepting the star as a member of the Hyades supercluster. This object is labeled in Figure 2b. The stars in Table 6 represent a cross section of the (M, log T )-plane of Figure 1a at T \ 7450 ^ 85 K, where V the dependence of M on d changes very little with temperature change. One V main-sequence object and three highly evolved members of the Praesepe cluster give the same age, 6 ] 108 yr, as the other hotter stars, but members of all three supercluster componentsèpraesepe, Hyades, and nonclusterèdeðne a main-sequence turno with an age of 8 ] 108 yr. The location in Figure 1 of these stars is not inñuenced by undetected binaries, as shown by Figure 3, where the cluster luminosities are correlated with the luminosity parameter, d, of the Geneva photometric system (Rufener 1988). The d-parameter is Geneva equivalent of [c ] in the Stro mgren system; d \ (U[B) [ ] 1 (B1 [ B2), where the median e ective wavelengths are 3464 Ó for U, 4015 Ó for B1 and 4476 Ó for B2. It is therefore possible to conclude that these supercluster stars have a range of ages at least from 5È6 to8]108 yr. Much of the dispersion in Figure 3 can be accounted for by the temperature range adopted in Table 6 and the strong dependence of F on temperature, in the expression M \ A V ] F *d. The same procedure has been applied to the stars in Table 7 with T between 6950 and 7330 K that populate the main-sequence turno region of models with age near 109 yr. Values of the cluster luminosity are correlated with the photometric luminosity parameter d in Figure 4, where, FIG. 3.ÈCross section in M of the temperature-luminosity array near T \ 7450 K. The d-index is a V luminosity parameter in the Geneva photometry.

6 No. 1, 1998 AGE RANGE OF HYADES STARS 289 TABLE 7 SUPERCLUSTER MEMBERS WITH TEMPERATURE NEAR 7100 K AND AGE NEAR 109 yr Spectral Age HR (HD) M V log T Type d (yr) Notes VZ Cnc... ] USPC (73798)... ] F Praesepe, USPC ] F2 IV ] F0 V (73993)... ] F0 IV (73746)... ] F0 V Praesepe, USPC ] F2 V Hyades ] Am Hyades, USPC ] F1 V Hyades (73397)... ] F2 V Praesepe ] F2 V Hyades again, most of the dispersion can be accounted for by the substantial temperature range included. Figure 3 quantiðes the dispersion around the isochrones seen in Figure 1. It is difficult to avoid the conclusion that, like the Pleiades supercluster (see, e.g., Herbig 1964; Eggen 1977), FIG. 4.ÈSame as Fig. 3, but for T near 7150 K all of the components of the Hyades supercluster (cluster and noncluster members) show a larger range in age than can easily be understood as representing a single, prolonged epoch of star formation Red Giants The red giants in the supercluster are listed in Table 8, where the data are of the same type as provided in Tables 1 and 2. The temperatures are derived from BessellÏs (1979) calibration of R[I (Eggen 1994a). The Hyades cluster, Praesepe cluster, and noncluster supercluster members of Table 8 are represented in Figure 5, which also contains an isochrone for 6 ] 108 yr (Z \ 0.02, Y \ 0.27). These evolved stars are apparently part of the youngest population in the supercluster, (5È6) ] 108 yr. Figure 5 seems to conðrm earlier indications that there are no red stars on the Ðrst-ascent giant branch but that, instead, they populate the asympic giant branch, or clump.ïï The mean di erence of n [ n \ 0.71 ^ 1.70 mas is very similar to the result clus Hip obtained from the stars in Table Masses Twenty visual binaries, and the double-lined eclipsing variable HD (V818 Tau), are members of the supercluster and are described in Table 9. The two binaries of lowest luminosity are not in the Hipparcos Catalogue, and the mean, ground-based parallaxes are listed in the table. It is notable that the dispersion in the Hipparcos parallax for most of these binaries is nearly double that of the single stars in Table 1 but that the mean di erence is n clus TABLE 8 EVOLVED RED STARS IN THE HYADES SUPERCLUSTER o (km s~1) X V P.V. SPECTRAL HR (HD) (pc) (km s~1) Obs. Comp. (km s~1) M Cluster Hip. p log T TYPE HIP NOTES V 1346a ]38.6 ]38.0 ]0.5 ] K0 III a ]37.6 ]38.2 ]1.3 ] K0 III , 2, a ]38.4 ] ] G9 III b ]37.3 ]38.5 ]3.0 ] K0 III (73598)... ] K0 III (73665)... ] K0 III (73710)... ] K0 III (73974)... ] K0 III b ]16.2 ]17.6 [0.2 ] G6 III b ]15.8 ]16.6 [1.7 ] G8 III b... [ ]4.3 ]6.1 ]3.6 ] K0 III NOTES.È(1) Hyades cluster; (2) spectroscopic binary; (3) P \ 530 days; (4) Praesepe cluster. a FK5 proper motion (Fricke et al. 1988). b Hipparcos proper motion (ESA 1997).

7 290 EGGEN Vol. 116 FIG. 5.ÈThe (log T, M ) relation for the evolved red stars in the V supercluster. [ n \ 0.79 ^ 1.97 mas, omitting HD 38. The individual Hip components for 17 systems are listed in Table 10, where the individual magnitudes and colors are based on the results for the combined light and the observed di erence in visual magnitude (Eggen 1984). The references for the orbital parameters are listed in the last column of the table. The (log T, M ) relation for the stars in Table 10 is shown in V Figure 6, where Hyades cluster members are represented by Ðlled circles and noncluster supercluster members by open circles. The adopted temperatures are from the (B[V, log T ) relation of Bessell (1979). The isochrones for 6 ] 108 and 109 yr (Z \ 0.025) are those for Z \ with M V decreased by 0.1 mag (Castellani et al. 1992). The I magnitudes and R[I colors of components of the three systems of lowest luminosity (HD 38AB, UW Cet AB FIG. 6.ÈThe (log T, M ) relation for the individual components of visual binaries in the supercluster. V and Wolf 424AB), together with the C component of HD , are listed in Table 11, where the values of M (clus) I are based on the cluster parallax (Table 1) and the orbital parameters, with references, are in the rightmost columns of the table. Previously (Eggen 1993), it was found that the lower main sequence of the Hyades cluster is well repre- TABLE 9 VISUAL BINARIES IN THE HYADES SUPERCLUSTER o (km s~1) X V P.V. HD (pc) (km s~1) Obs. Comp. Cluster Hip. p ADS HIP (km s~1) NOTES ]0.1 ] [ ]5V ] [3.7 BD ] Var. ] [4.5 UV Ceta Var. ] (367) [ ]32.9 ] [ ]38.1 ] ]1.5 1, ]36.8 ] ] ]37.9 ] ]0.2 1, ]38V ] [ ]41.0 ] ] ]42V ] ]1.1 1, Var. ] ] ]39.0 ] ] ] ] ]23.1 ] [0.6 Wolf 424a [3: [ [ [ Var. [ ] [ [ [ [2V [ [ [14V [ ]4.3 NOTES.È(1) Hyades cluster; (2) V818 Tau, double-lined eclipsing binary (P \ 5.61 days); (3) component A is spectroscopic binary, P \ 4 days; (4) component B is spectroscopic binary, P \ days. a Proper motions from Hipparcos (ESA 1997) except for UV Cet and Wolf 424, for which proper motion is the mean of results from parallax determinations.

8 No. 1, 1998 AGE RANGE OF HYADES STARS 291 TABLE 10 COMPONENTS OF SUPERCLUSTER BINARIES P a HD V B[V M V (yr) (mas) Reference 6114A ] B ]2.62 BD ]1 194A ] BD ]1 194B ] A ] B (1.50) ] A ] days B ] A ] B ] AA@ ] B ] A ] B ] A ] B ] A ] BB@ ] A ] B ] A ] B ] A ] B ] A ] B ] A ] B ] A ] B ] C ] A ] B ] A ] B ]2.08 REFERENCES.È(1) Heintz 1964; (2) Eggen 1965; (3) Hopmann 1995; (4) Schiller & Milone 1987; (5) McAlister 1990; (6) Peterson & Solensky 1988; (7) Baize 1980; (8) Heintz 1996; (9) Heintz 1960; (10) Eggen 1984; (11) Heintz sented by M \ 4.56(R[I) ] 3.95 mag, (6) I and this is the origin of the values of M (phot) in Table 11. The mean di erence M (clus) [M (phot) I \]0.04 ^ 0.06 mag. The orbit for HD I 38AB is obviously I still indeterminate, but the well-observed systems UV Cet and Wolf 424 give reliable masses for stars that are near the end of the hydrogen-burning main sequence: UV Cet, 1 ; \ 0.13 M ; Wolf 424, 1 ; \ 0.10 M. 2 mass _ 2 mass _ The al mass obtained from the orbital elements in Table 10 and the cluster parallax in Table 1, ; \ a3/p2n3 M, (7) mass _ is listed in Table 12 ( Obs. ÏÏ). The values obtained from the luminosities of the individual components and the stellar model with t \ 8 ] 108 yr and Z \ (Castellani et al. 1992) are labeled Model ÏÏ in the table. Two systems in which one component is known to be a spectroscopic binary, HD 27691AA@B and HD 28363ABB@, indicate that TABLE 11 LOW-LUMINOSITY SUPERCLUSTER BINARIES M I P a STAR I R[I Cluster Phot. (yr) (mas) REFERENCE HD 38A ]7.20 ] HD 38B ]7.24 ]7.19 BD ] ]7.96 ]7.83 UV Cet A ]11.80 ] UV Cet B ]11.80 ]11.70 Wolf 424A ]11.13 ] Wolf 424B ]11.13 ]11.16 HD C ]5.54 ]5.51 REFERENCES.È(1) Heintz 1996; (2) Worley & Behall 1973; (3) Heintz 1993.

9 292 EGGEN TABLE 12 TOTAL MASSES ; mass (M _ ) ; mass (M _ ) HD Obs. Model NOTES HD Obs. Model NOTES BD ]1 194AB AB AB AB AB AB AB AB AA@B , AB AB AB AB AB ABB@ , AB NOTES.È (1) Hyades cluster; (2) component A is spectroscopic binary, P \ 4 days; (3) component B is spectroscopic binary, P \ 21.2 days; (4) up \ 215 yr, orbit uncertain. the unseen companion has approximately 0.5 solar masses. The errors are probably equally distributed between the components, so the dispersion for the mass of a single component is less than 10%. Although the masses are of interest in themselves, they are included here because the extreme dependence of the mass determination on the parallax further conðrms the parallaxes adopted here. REFERENCES Abt, H. A. 1995, ApJ, 122, 390 Abt, H. A., & Biggs, E. S. 1972, Bibliography of Stellar Radial Velocities (Kitt Peak: KPNO) Andersen, J. 1991, A&A Rev., 3, 91 Baize, P. 1980, A&AS, 39, 83 Balona, L. A., & Stobie, R. S. 1983, South African Astron. Obs. Circ., No. 7, 19 Fricke, W. S., Schwan, H., & Corbin, T. E. 1991, Vero Astron. Rechen- Inst. Heidelberg, No. 33 Hauck, B., & Mermilliod, M. 1980, A&AS, 40, 1 Heintz, W. D. 1960, Astron. Nachr., 285, 256 ÈÈÈ. 1964, Vero Sternw. Mu nchen, 5, 247 ÈÈÈ. 1993, A&A, 277, 452 ÈÈÈ. 1996, A&AS, 98, 209 Barbier-Brossat, M., Petit, M., & Figon, R. 1994, Catalogue Biblio- Herbig, G. 1964, R. Obs. Bull., No. 82 graphique de Vitesses Stellaires: 1970È1990 (Marseille: Obs. Marseilles) Bessell, M. S. 1979, PASP, 91, 589 Castellani, V., Chii, A., & Straniero, O. 1992, ApJS, 78, 517 Eggen, O. J. 1965, AJ, 70, 19 ÈÈÈ. 1977, PASP, 89, 187 ÈÈÈ. 1979, ApJS, 41, 413 ÈÈÈ. 1984, AJ, 89, 839 ÈÈÈ. 1986, AJ, 92, 910 ÈÈÈ. 1992a, AJ, 104, 1482 ÈÈÈ. 1992b, AJ, 104, 2141 ÈÈÈ. 1993, AJ, 106, 1885 ÈÈÈ. 1994a, AJ, 107, 594 ÈÈÈ. 1994b, AJ, 107, 2131 ÈÈÈ. 1995, AJ, 110, 823 ÈÈÈ. 1996, AJ, 111, 1615 Hopmann, J. 1955, Mitt. Univ. Sternw. Wien, 10, 269 Maeder, A., & Meynet, G. 1991, A&AS, 89, 451 McAlister, H. A. 1990, in ASP Conf. Ser. 38, New Frontiers in Binary Star Research, ed. K.-C. Leung & I. Na (San Francisco: ASP), 57 McNamara, D. H., & Rogers, M. C. 1962, PASP, 74, 420 Perryman, M., et al. 1998, A&A, 331, 81 Peterson, D. M., & Solensky, R. 1988, ApJ, 333, 256 Rufener, F. 1988, Catalogue of Stars Measured in the Geneva Observatory Photometric System (4th ed.; Sauverny: Obs. Genève) Schiller, S. J., & Milone, E. F. 1987, AJ, 93, 1471 Schwan, H. 1991, A&A, 243, 386 Schwan, H., Bastian, U., Bien, R., Ja hrling, R., Jahreiss, H., & Roser, S. 1993, Vero. Astron. Rechen-Inst. Heidelberg, No. 34 Smalley, B., & Dworetsky, M. M. 1993, A&A, 271, 515 Templeton, M. R., McNamara, B. J., Guzik, J. A., Bradley, P. A., Cox, ESA. 1997, The Hipparcos and Tycho Catalogues (ESA SP-1200) A. N., & Middleditch, J. 1997, AJ, 114, 1592 (Noordwijk: ESA) Worley, C. E., & Behall, A. L. 1973, AJ, 78, 650 Fitch, W. S. 1976, in IAU Colloq. 29, Multiple Periodic Variable Stars, ed. W. S. Fitch (Dordrecht: Reidel), 167