Hipparcos Trigonometric Parallaxes Research Articles

Orbit of the mercury-manganese binary 41 Eridani

Context. Mercury-manganese (HgMn) stars are a class of slowly rotating chemically peculiar main-sequence late B-type stars. More than two-thirds of the HgMn stars are known to belong to spectroscopic binaries. Aims. By determining orbital solutions for binary HgMn stars, we will be able to obtain the masses for both components and the distance to the system. Consequently, we can establish the position of both components in the Hertzsprung-Russell diagram and confront the chemical peculiarities of the HgMn stars with their age and evolutionary history. Methods. We initiated a program to identify interferometric binaries in a sample of HgMn stars, using the PIONIER near-infrared interferometer at the VLTI on Cerro Paranal, Chile. For the detected systems, we intend to obtain full orbital solutions in conjunction with spectroscopic data. Results. The data obtained for the SB2 system 41 Eridani allowed the determination of the orbital elements with a period of just five days and a semi-major axis of under 2 mas. Including published radial velocity measurements, we derived almost identical masses of 3.17 +/- 0.07 M_Sun for the primary and 3.07 +/- 0.07 M_Sun for the secondary. The measured magnitude difference is less than 0.1 mag. The orbital parallax is 18.05 +/- 0.17 mas, which is in good agreement with the Hipparcos trigonometric parallax of 18.33 +/- 0.15 mas. The stellar diameters are resolved as well at 0.39 +/- 0.03 mas. The spin rate is synchronized with the orbital rate.

Accurate parameters for HD 209458 and its planet fromHSTspectrophotometry

We present updated parameters for the star HD 209458 and its transiting giant planet. The stellar angular diameter $\theta$=0.2254$\pm$0.0017 mas is obtained from the average ratio between the absolute flux observed with the Hubble Space Telescope and that of the best-fitting Kurucz model atmosphere. This angular diameter represents an improvement in precision of more than four times compared to available interferometric determinations. The stellar radius $R_\star$=1.20$\pm$0.05 R$_{\odot}$ is ascertained by combining the angular diameter with the Hipparcos trigonometric parallax, which is the main contributor to its uncertainty, and therefore the radius accuracy should be significantly improved with Gaia's measurements. The radius of the exoplanet $R_\text{p}$=1.41$\pm$0.06 $R_\text{J}$ is derived from the corresponding transit depth in the light curve and our stellar radius. From the model fitting, we accurately determine the effective temperature, $T_\text{eff}$=6071$\pm$20 K, which is in perfect agreement with the value of 6070$\pm$24 K calculated from the angular diameter and the integrated spectral energy distribution. We also find precise values from recent Padova Isochrones, such as $R_\star$=1.20$\pm$0.06 R$_{\odot}$ and $T_\text{eff}$=6099$\pm$41 K. We arrive at a consistent picture from these methods and compare the results with those from the literature.

Comparison of Hipparcos Trigonometric and Mount Wilson Spectroscopic Parallaxes for 90 Subgiants that Defined the Class in 1935

A history is given of the discovery between 1914 and 1935 of stars of intermediate luminosity between giants and dwarfs with spectral types between G0 to K3. The Mount Wilson spectroscopists identified about 90 such stars in their 1935 summary paper of spectroscopic absolute magnitudes for 4179 stars. Called “subgiants” by Strömberg, these 90 stars defined the group at the time. The position of the Mount Wilson subgiants in the HR diagram caused difficulties in comparisons of high weight trigonometric parallaxes being measured in the 1930s and with Russell's prevailing evolution proposal, and critics questioned the reality of the Mount Wilson subgiants. To show that the 1935 Mount Wilson subgiants are real, we compare, star-by-star, the Mount Wilson spectroscopic absolute magnitudes of the 90 stars defining their sample against those absolute magnitudes derived from Hipparcos trigonometric parallaxes. We address concerns over biases in the Mount Wilson calibration sample and biases created by the adopted methodology for calibration. Historically, these concerns were sufficient to discredit the discovery of subgiants in the Mount Wilson sample. However, as shown here, the majority of the Mount Wilson stars identified as subgiants that also have reliable Hipparcos trigonometric parallaxes do lie among the subgiant sequence in the Hipparcos HR diagram. Moreover, no significant offset is seen between the MV brightnesses derived from the Mount Wilson spectroscopic parallaxes and the MV values derived from Hipparcos trigonometric parallaxes with , which confirms in an impressive manner the efficacy of the original Mount Wilson assessments. The existence of subgiants proved that Russell's contraction proposal for stellar evolution from giants to the main sequence was incorrect. Instead, Gamow's 1944 unpublished conjecture that subgiants are post main-sequence stars just having left the main sequence was very nearly correct but was a decade before its time.

ON THE ACCURACY OFHIPPARCOSUSING BINARY STARS AS A CALIBRATION TOOL

Stellar binary systems, specifically those that present the most accurate available orbital elements, are a reliable tool to test the accuracy of astrometric observations. We selected all 35 binaries with these characteristics. Our objective is to provide standard uncertainties for the positions and parallaxes measured by Hipparcos relative to this trustworthy set, as well as to check supposed correlations between several parameters (measurement residuals, positions, magnitudes, and parallaxes). In addition, using the high-confidence subset of visual–spectroscopic binaries, we implemented a validation test of the Hipparcos trigonometric parallaxes of binary systems that allowed the evaluation of their reliability. Standard and non-standard statistical analysis techniques were applied in order to achieve well-founded conclusions. In particular, errors-in-variables models such as the total least-squares method were used to validate Hipparcos parallaxes by comparison with those obtained directly from the orbital elements. Previously, we executed Thompsonʼs τ technique in order to detect suspected outliers in the data. Furthermore, several statistical hypothesis tests were carried out to verify if our results were statistically significant. A statistically significant trend indicating larger Hipparcos angular separations with respect to the reference values in 5.2 ± 1.4 mas was found at the 10−8 significance level. Uncertainties in the polar coordinates θ and ρ of 1.°8 and 6.3 mas, respectively, were estimated for the Hipparcos observations of binary systems. We also verified that the parallaxes of binary systems measured in this mission are absolutely compatible with the set of orbital parallaxes obtained from the most accurate orbits at least at the 95% confidence level. This methodology allows us to better estimate the accuracy of Hipparcos observations of binary systems. Indeed, further application to the data collected by Gaia should yield a standard procedure to compare both data sets.

Dynamical and physical properties of 22 binaries discovered by W. S. Finsen

Using recent speckle measurements performed by different observers, in this paper we present revised orbital elements and dynamical masses for the binaries WDS 02396−1152 (FIN 312), 04515−3454 (FIN 320), 06253+0130 (FIN 343), 07003−2207 (FIN 334 Aa,Ab), 08291−4756 (FIN 315 Aa,Ab), 08345−3236 (FIN 335), 09173−6841 (FIN 363 AB), 09442−2746 (FIN 326), 12064−6543 (FIN 367 Aa,Ab), 12446−5717 (FIN 65 AB), 13117−2633 (FIN 305), 13320−6519 (FIN 369), 14373−4608 (FIN 318 Aa,Ab), 16057−0617 (FIN 384 Aa,Ab), 16115+0943 (FIN 354), 17221−7007 (FIN 373), 17542+1108 (FIN 381), 19035−6845 (FIN 357), 21044−1951 (FIN 328), 21158−5316 (FIN 329), 21477−3054 (FIN 330 AB) and 21579−5500 (FIN 307) discovered by W. S. Finsen using his eyepiece interferometer. A brief historical comment on Finsen’s work on binaries is included. The orbital and physical properties of these stars are discussed with detail. In addition to this, quantitative results about a likely overestimation of Finsen’s angular separations are provided. Moreover, the evaluation as well as the statistical significance determination of a suspected underestimation of the Hipparcos trigonometrical parallaxes at large distances is also accomplished.

Rotation and lithium abundance of solar-analog stars

Rotational velocity, lithium abundance, and the mass depth of the outer convective zone are key parameters in the study of the processes at work in the stellar interior, in particular when examining the poorly understood processes operating in the interior of solar-analog stars. We investigate whether the large dispersion in the observed lithium abundances of solar-analog stars can be explained by the depth behavior of the outer convective zone masses, within the framework of the standard convection model based on the local mixing-length theory. We also aims to analyze the link between rotation and lithium abundance in solar-analog stars. We computed a new extensive grid of stellar evolutionary models, applicable to solar-analog stars, for a finely discretized set of mass and metallicity. From these models, the stellar mass, age, and mass depth of the outer convective zone were estimated for 117 solar-analog stars, using Teff and [Fe/H] available in the literature, and the new HIPPARCOS trigonometric parallax measurements. We determine the age and mass of the outer convective zone for a bona fide sample of 117 solar-analog stars. No significant on-to-one correlation is found between the computed convection zone mass and published lithium abundance, indicating that the large A(Li) dispersion in solar analogs cannot be explained by the classical framework of envelope convective mixing coupled with lithium depletion at the bottom of the convection zone. These results illustrate the need for an extra-mixing process to explain lithium behavior in solar-analog stars, such as, shear mixing caused by differential rotation. To derive a more realistic definition of solar-analog stars, as well as solar-twin, it seems important to consider the inner physical properties of stars, such as convection, hence rotation and magnetic properties.

Distance determination for RAVE stars using stellar models

<i>Aims. <i/>We develop a method for deriving distances from spectroscopic data and obtaining full 6D phase-space coordinates for the RAVE survey's second data release.<i>Methods. <i/>We used stellar models combined with atmospheric properties from RAVE (effective temperature, surface gravity and metallicity) and (<i>J<i/>-<i>K<i/><sub>s<sub/>) photometry from archival sources to derive absolute magnitudes. In combination with apparent magnitudes, sky coordinates, proper motions from a variety of sources and radial velocities from RAVE, we are able to derive the full 6D phase-space coordinates for a large sample of RAVE stars. This method is tested with artificial data, Hipparcos trigonometric parallaxes and observations of the open cluster M 67.<i>Results. <i/>When we applied our method to a set of 16 146 stars, we found that 25% (4037) of the stars have relative (statistical) distance errors of <i><<i/>35%, while 50% (8073) and 75% (12 110) have relative (statistical) errors smaller than 45% and 50%, respectively. Our various tests show that we can reliably estimate distances for main-sequence stars, but there is an indication of potential systematic problems with giant stars owing to uncertainties in the underlying stellar models. For the main-sequence star sample (defined as those with log(<i>g<i/>) > 4), 25% (1744) have relative distance errors <i><<i/>31%, while 50% (3488) and 75% (5231) have relative errors smaller than 36% and 42%, respectively. Our full dataset shows the expected decrease in the metallicity of stars as a function of distance from the Galactic plane. The known kinematic substructures in the <i>U<i/> and <i>V<i/> velocity components of nearby dwarf stars are apparent in our dataset, confirming the accuracy of our data and the reliability of our technique. We provide independent measurements of the orientation of the <i>UV<i/> velocity ellipsoid and of the solar motion, and they are in very good agreement with previous work.<i>Conclusions. <i/>The distance catalogue for the RAVE second data release is available at http://www.astro.rug.nl/~rave, and will be updated in the future to include new data releases.

G 112-29 (=NLTT 18149): A VERY WIDE COMPANION TO GJ 282 AB WITH A COMMON PROPER MOTION, COMMON PARALLAX, COMMON RADIAL VELOCITY, AND COMMON AGE

We have made a search for common proper motion (CPM) companions to the wide binaries in the solar vicinity. We found that the binary GJ 282AB has a very distant CPM companion (NLTT 18149) at a separation $s=1.09 \arcdeg$. Improved spectral types and radial velocities are obtained, and ages determined for the three components. The Hipparcos trigonometric parallaxes and the new radial velocities and ages turn out to be very similar for the three stars, and provide strong evidence that they form a physical system. At a projected separation of 55733AU from GJ 282AB, NLTT 18149 ranks among the widest physical companions known.

The Cepheid PL zero-point based on the revised Hipparcos trigonometrical parallaxes

Revised Hipparcos data were released by van Leeuwen in 2007. In this article revised Hipparcos trigonometrical parallaxes are used to derive a period-luminosity zero-point in the optical V band. Adopting a fixed slope of −2.81 from the LMC, a zero-point value of ρ= −1.37±0.07 is derived based on the method by Feast and Catchpole (1997). This value yields an LMC distance modulus of 18.64 mag, which makes a minor change in H0 expected from Feast and Catchpole’s result in 1997.

On the distance to the Ophiuchus star‐forming region

AbstractThe Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest known embedded cluster within ∼300 pc of the Sun. Unfortunately, distance estimates to the Oph complex vary by nearly ∼40% (∼120–165 pc). Here I calculate a new independent distance estimate of 135±8 pc to this benchmark star‐forming region based on Hipparcos trigonometric parallaxes to stars illuminating reflection nebulosity in close proximity to Lynds 1688. Combining this value with recent distance estimates from reddening studies suggests a consensus distance of 139±6 pc (4% error), situating it within ∼11 pc of the centroid of the ∼5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The velocity vectors for Oph and Upper Sco are statistically indistinguishable within ∼1 km s–1 in each vector component. Both Oph and Upper Sco have negligible motion (&lt;1 km s–1) in the Galactic vertical direction with respect to the Local Standard of Rest, which is inconsistent with the young stellar groups having formed via the high velocity cloud impact scenario. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Eclipsing binaries observed with the WIRE satellite

We present the most precise light curve ever obtained of a detached eclipsing binary star and use it investigate the inclusion of non-linear limb darkening laws in eclipsing binary light curve models. This light curve, of the bright system beta Aurigae, was obtained using the star tracker aboard the WIRE satellite and contains 30000 datapoints with a scatter of 0.3 mmag. We analyse it using a version of the EBOP code modified to include non-linear limb darkening and to directly incorporate observed times of minimum light and spectroscopic light ratios into the solution as individual observations. We also analyse the dataset with the WD code to ensure that the two models give consistent results. EBOP provides an excellent fit to the WIRE data. Whilst the fractional radii are only defined to a precision of 5%, including an accurate published spectroscopic light ratio improves this dramatically to 0.5%. Using non-linear limb darkening improves the quality of the fit significantly and causes the measured radii to increase by 0.4%. It is possible to derive all of the limb darkening coefficients from the light curve, although they are strongly correlated with each other, and they agree with theoretical predictions. The radii and masses of the components of beta Aur are R_A = 2.762 +/- 0.017 Rsun, R_B = 2.568 +/- 0.017 Rsun, M_A = 2.376 +/- 0.027 Msun and M_B = 2.291 +/- 0.027 Msun. Theoretical stellar models can match these parameters for a solar metal abundance and an age of 450-500 Myr. The Hipparcos trigonometric parallax and an interferometrically-derived orbital parallax give distances to beta Aur which are in excellent agreement with each other and with distances derived using surface brightness relations and several sets of empirical and theoretical bolometric corrections (abridged).

Absolute magnitudes of OB and Be stars based on Hipparcos parallaxes - III

The absolute visual magnitudes, M v , of A-M stars are based on calculated Hipparcos trigonometric parallaxes. The sample used consists of 30986 unreddened and reddened A-M stars in luminosity classes Ia, Iab, Ib, II, III, IV and V. The colour excesses of the reddened stars were calculated using the mean colour indices, according to the SIMBAD data base and the intrinsic B - V values calibrated for the given spectral types and luminosity classes by Schmidt-Kaler. The values of the total-to-selective extinction, R v = A v /E(B-V), for all the reddened stars were calculated from previously published near-infrared photometric measurements. The calculated visual magnitudes, M v , of A-M stars compare with the earlier determinations of Schmidt-Kaler. The mean absolute magnitudes published by Schmidt-Kaler are generally brighter (except for the stars in luminosity classes V and IV) than those determined in this paper.

On the link between rotation, chromospheric activity and Li abundance in subgiant stars

The connection rotation–CaII emission flux–lithium abundance is analyzed for a sample of bona fide subgiant stars, with evolutionary status determined from HIPPARCOS trigonometric parallax measurements and from the Toulouse–Geneva code. The distribution of rotation and CaII emission flux as a function of effective temperature shows a discontinuity located around the same spectral type, F8IV. Blueward of this spectral type, subgiants have a large spread of values of rotation and CaII flux, whereas stars redward of F8IV show essentially low rotation and low CaII flux. The strength of these declines depends on stellar mass. The abundance of lithium also shows a sudden decrease. For subgiants with mass lower than about 1.2 the decrease is located later than that in rotation and CaII flux, whereas for masses higher than 1.2 the decrease in lithium abundance is located around the spectral type F8IV. The discrepancy between the location of the discontinuities of rotation and CaII emission flux and (Li) for stars with masses lower than 1.2 seems to reflect the sensitivity of these phenomena to the mass of the convective envelope. The drop in rotation, which results mostly from a magnetic braking, requires an increase in the mass of the convective envelope less than that required for the decrease in (Li). The location of the discontinuity in (Li) for stars with masses higher than 1.2 , in the same region of the discontinuities in rotation and CaII emission flux, may also be explained by the behavior of the deepening of the convective envelope. The more massive the star is, the earlier is the increase of the convective envelope. In contrast to the relationship between rotation and CaII flux, which is fairly linear, the relationship between lithium abundance and rotation shows no clear tendency toward linear behavior. Similarly, no clear linear trend is observed in the relationship between lithium abundance and CaII flux. In spite of these facts, subgiants with high lithium content also have high rotation and high CaII emission flux.

Luminosity calibration for OB stars from Hipparcos trigonometric parallaxes

Hipparcos trigonometric parallaxes and observational data for open clusters are used to determine the absolute magnitudes MV of O and B stars of various spectral subtypes and luminosity classes, including those with broadened lines and hydrogen emission lines. The same data are used to derive a relation between MV and the index β of the Stromgren photometric system. The resulting calibrations and the spectroscopic-parallax method are used to determine the distances to young open clusters.

Hipparcos trigonometric parallaxes and the distance scale for open star clusters

Hipparcos trigonometric parallaxes are used to estimate the distances to the maximum possible number of open star clusters (OSC); distance moduli are estimated for 45 clusters with maximum heliocentric distances of about 1000 pc. The latter value can serve as an estimate of the limit to which it still makes sense to use Hipparcos trigonometric parallaxes to determine the distances to small groups composed of 6–10 sufficiently bright stars. A systematic correction to the distance moduli of clusters from the homogeneous catalog of OSC parameters (Loktin et al. 1997, 2000) is estimated, which turns out to be independent of the cluster age.

The Distance scale and the rotation curve of young supergiants and open clusters

Abstract The Hipparcos trigonometric parallaxes of 188 blue (O-type and BO-A3 I-II) supergiants with published uvby and Hβ photometry are compared to the photomeric parallaxes of these stars based on the Mv absolute-magnitude calibration of Dambis (1990). The photometric distance scale is found to require only a minor correction −πHip = (1.03 ± 0.04)πPhot, i.e., r Hip = (0.97 ± 0.04)r Phot, which is corroborated by applying the statistical-parallax technique to a sample of 106 blue supergiants with published radial velocities and Hipparcos proper motions (r True = (0.98 ± 0.08)r Phot). The weighted mean distance-scale correction factor can thus be estimated at r True = (0.97 ± 0.03)r Phot, thereby constraining the LMC distance modulus to DM LMC = 18.36 ± 0.08 (standard error) ±0.07 (systematic error) and providing further evidence in favor of the so-called ‘short’ distance scale. An expanded sample consisting of 106 blue supergiants with corrected photometric distances, published radial velocities, and Hi...

An Empirical Procedure to Estimate Distances to Stellar Clusters

A most desirable feature of a standard candle to estimate astronomical distances is robustness against changes in metallicity and age. It is argued that the radii of main sequence stars with spectral types from solar to A0 show predictable changes with metallicity, and detectable changes with evolution. Such stars populate the solar neighborhood, and therefore benefit from measurements of angular diameters. Also, reliable determinations of their masses and radii are available from observations of eclipsing binaries. Three empirical relationships are defined and suggested for estimating distances to dwarfs from only BVK photometry. Comparison with HIPPARCOS trigonometric parallaxes shows that the method provides errors of about 15% for a particular star, which can be reduced to roughly 1.5% when applied to young clusters (age <~ 1-2 Gyr) with ~ 100 stars of the appropriate spectral types. If reddening is unknown, main sequence stars with effective temperatures close to 8000 K can constrain it, although an estimate of R=A(V)/E(B-V) is required.

Trigonometric parallaxes and a kinematically adjusted distance sale for OB associations

By directly comparing the photometric distances of Blaha and Humphreys (1989) (BH) to OB associations and field stars with the corresponding Hipparcos trigonometric parallaxes, we show that the BH distance scale is overestimated, on average, by 10–20%. This result is independently corroborated by applying the rigorous statistical-parallax method and its simplified analog (finding a kinematically adjusted rotation-curve solution from radial velocities and proper motions) to a sample of OB associations. These two methods lead us to conclude that the BH distance scale for OB associations should be shrunk, on average, by 11±6 and 24±10%, respectively. Kinematical parameters have been determined for the system of OB associations: u0 = 8.2 ± 1.3 km s−1, v0 = 11.9 ± 1.1 km s−1, w0 = 9.5 ± 0.9 km s−1, σu = 8.2 ± 1.1 km s−1, σv = 5.8 ± 0.8 km s−1, σw = 5.0 ± 0.8 km s−1, Ω0 = 29.1 ± 1.0 km s−1 kpc−1, Ω0′ = −4.57 ± 0.20 km s−1 kpc−2, and Ω0″ = 1.32 ± 0.14 km s−1 kpc−3. The distance scale for OB associations reduced by 20% matches the short Cepheid distance scale (Berdnikov and Efremov 1985; Sitnik and Mel’nik 1996). Our results are a further argument for the short distance scale in the Universe.

Structure and colour-magnitude diagrams of Scorpius OB2 based on kinematic modelling of Hipparcos data

All stars in a ‘moving group’ share the same space motion. The presence of such a coherent structure in velocity space can be used to derive (improved) estimates of the stellar parallaxes from the observed positions and proper motions. A Lund Observatory group (Dravins et al.) describes an elegant and sophisticated maximum likelihood procedure to do so using Hipparcos data. Their method determines the cluster centroid space motion, the internal velocity dispersion, which is assumed to be isotropic, and the individual model parallaxes for all member stars, implicitly using the assumption of a ‘compact’ cluster with a ‘small’ velocity dispersion. We implement the Lund procedure, and test it extensively using Monte Carlo simulations. We discuss the effects on the derived parallaxes of a ‘large’ velocity dispersion, as measured for physically extended, ‘loose’ OB associations. We also investigate the influence of an overall expanding motion, which is relevant to such unbound groups. We conclude that the method is robust against all systematic effects that we considered, except for the maximum likelihood estimate of the one-dimensional internal velocity dispersion σv, which is always underestimated. The model parallax accuracies are limited by the internal velocity dispersion for nearby groups (mean distance D≲50–150 pc, depending on Galactic longitude). We present an application to the nearby association Scorpius OB2, which consists of the three subgroups Upper Scorpius (mean distance 145 pc), Upper Centaurus Lupus (140 pc), and Lower Centaurus Crux (118 pc). Membership of these groups has recently been established by de Zeeuw et al. using Hipparcos data. The resulting model parallaxes are (1) statistically consistent with and (2) more precise by a factor of ∼2 than the Hipparcos trigonometric parallaxes; they (3) significantly narrow the locus of stars in the (B−V)0–MV0 colour–absolute magnitude diagram, and (4) define a single-star main sequence which is consistent with Mermilliod’s zero-age main-sequence calibration. We find, after bias correction based on Monte Carlo simulations, that σv≲1.0–1.5 km s−1 for all three subgroups; these values are confirmed by the statistics of the residual (μ⊥) proper motion components. Whereas, as a result of their consistency with the Hipparcos values, the model parallaxes do not improve significantly upon the mean association distances derived by de Zeeuw et al. from Hipparcos trigonometric parallaxes, they do resolve the parallax distribution, and thus the spatial structure, for Upper Centaurus Lupus and Lower Centaurus Crux.

Evolution of Population II stars

The current knowledge of the evolution of Population II stars, as observed in galactic halos and globular clusters, is outlined. The recent theoretical results provided by an improved physical understanding of the stars are reported, with a particular emphasis upon those stellar evolutionary phases which are the keystones of the interpretation of globular cluster stars. Within the up–to–date theoretical scenario, the luminosity of the turn–off stars and horizontal branch stars, which are of fundamental importance for distance and age determinations, turns out to be fainter and brighter, respectively, in comparison with previous theoretical computations. The predicted absolute magnitude \(M_V^{RR}\) of RR Lyrae stars is consistent with the bright values suggested from the long distance scale (Sandage 1993), but the slope of the relation between \(M_V^{RR}\) and metallicity ([Fe/H]) agrees with that suggested from the short distance scale (see, e.g., Carney et al. 1992, Clementini et al. 1995), at least with [Fe/H]\(\le\)-1.3. As to the globular cluster ages, the new computations provide younger ages (\(\sim\) 10 Gyr–13 Gyr), weakening the conflict with current cosmological estimates. The recent results derived from the fitting of HIPPARCOS parallaxes of field subdwarfs to the fiducial main sequence of globular clusters are consistent with the up–to–date theoretical models. However, the direct determinations of \(M_V^{RR}\), which are based on the HIPPARCOS proper motions and trigonometric parallaxes of field RR Lyrae stars, give fainter absolute magnitudes than those obtained from the improved evolutionary models. This seems to suggest that the problem of the globular cluster distance and age is still open.