Gyr Age Research Articles

HAT-P-14b: A 2.2MJEXOPLANET TRANSITING A BRIGHT F STAR

We report the discovery of HAT-P-14b, a fairly massive transiting extrasolar planet orbiting the moderately bright star GSC 3086-00152 (V = 9.98), with a period of P = 4.627669 +/- 0.000005 days. The transit is close to grazing (impact parameter 0.891 +0.007/-0.008) and has a duration of 0.0912 +/- 0.0017 days, with a reference epoch of mid transit of Tc = 2454875.28938 +/- 0.00047 (BJD). The orbit is slightly eccentric (e = 0.107 +/- 0.013), and the orientation is such that occultations are unlikely to occur. The host star is a slightly evolved mid-F dwarf with a mass of 1.386 +/- 0.045 M(Sun), a radius of 1.468 +/- 0.054 R(Sun) effective temperature 6600 +/- 90 K, and a slightly metal-rich composition corresponding to [Fe/H] = +0.11 +/- 0.08. The planet has a mass of 2.232 +/- 0.059 M(Jup) and a radius of 1.150 +/- 0.052 R(Jup), implying a mean density of 1.82 +/- 0.24 g/cm3. Its radius is well reproduced by theoretical models for the 1.3 Gyr age of the system if the planet has a heavy-element fraction of about 50 M(Earth) (7% of its total mass). The brightness, near-grazing orientation, and other properties of HAT-P-14 make it a favorable transiting system to look for changes in the orbital elements or transit timing variations induced by a possible second planet, and also to place meaningful constraints on the presence of sub-Earth mass or Earth mass exomoons, by monitoring it for transit duration variations.

Quiescent and flaring X-ray emission from the nearby M/T dwarf binary SCR 1845-6357

We investigate an XMM-Newton observation of SCR 1845-6357, a nearby, ultracool M8.5/T5.5 dwarf binary. The binary is unresolved in the XMM detectors, however the X-ray emission is very likely from the M8.5 dwarf. We compare its flaring emission to those of similar very low mass stars and additionally present an XMM observation of the M8 dwarf VB 10. We detect quasi-quiescent X-ray emission from SCR 1845-6357 at soft X-ray energies in the 0.2-2.0 keV band, as well as a strong flare with a count rate increase of a factor of 30 and a duration of only 10 minutes. The quasi-quiescent X-ray luminosity of log L_x = 26.2 erg/s and the corresponding activity level of log L_x/L_bol = -3.8 point to a fairly active star. Coronal temperatures of up to 5 MK and frequent minor variability support this picture. During the flare, that is accompanied by a significant brightening in the near-UV, plasma temperatures of 25-30 MK are observed and an X-ray luminosity of L_x= 8 x 10^27 erg/s is reached. SCR 1845-6357 is a nearby, very low mass star that emits X-rays at detectable levels in quasi-quiescence, implying the existence of a corona. The high activity level, coronal temperatures and the observed large flare point to a rather active star, despite its estimated age of a few Gyr.

CHEMODYNAMICS OF COMPACT STELLAR SYSTEMS IN NGC 5128: HOW SIMILAR ARE GLOBULAR CLUSTERS, ULTRA-COMPACT DWARFS, AND DWARF GALAXIES?

Velocity dispersion measurements are presented for luminous GCs in NGC 5128 derived from high-res. UVES spectra. The measurements are made with the pPXF code that parametrically recovers line-of-sight velocity dispersions. Combining the measured velocity dispersions with surface photometry and structural parameter data from HST enables both dynamical masses and M/L ratios to be derived. The fundamental plane relations of these clusters are investigated in order to fill the apparent gap between the relations of Local Group GCs and more massive early-type galaxies. It is found that the properties of these massive stellar systems match those of nuclear clusters in dwarf elliptical galaxies and UCDs better than those of Local Group GCs, and that all objects share similarly old (>8 Gyr) ages, suggesting a possible link between the formation and evolution of dE,Ns, UCDs and massive GCs. We find a very steep correlation between dynamical (M/L) ratio and dynamical mass of the form (M/L)_dyn ~ M_dyn^(0.24+/-0.02) above M_dyn = 2x10^6 Msol. Formation scenarios are investigated with a chemical abundance analysis using absorption line strengths calibrated to the Lick/IDS index system. The results lend support to two scenarios contained within a single general formation scheme. Old, massive, super-solar [alpha/Fe] systems are formed on short (<100 Myr) timescales through the merging of single-collapse GCs which themselves are formed within single, giant molecular clouds. More intermediate- and old-aged (~3-10 Gyr), solar- to sub-solar [alpha/Fe] systems are formed on much longer (~Gyr) timescales through the stripping of dE,Ns in the 10^13-10^15 Msol potential wells of massive galaxies and galaxy clusters.

On the kinematic age of brown dwarfs: radial velocities and space motions of 43 nearby L dwarfs

We present radial velocity measurements of a sample of L0-L8 dwarfs observed with VLT/UVES and Keck/HIRES. We combine these measurements with distance and proper motion from the literature to determine space motions for 43 of our targets. We identify nine candidate members of young moving groups, which have ages of 50-600 Myr according to their space motion. From the total velocity dispersion of the 43 L dwarfs, we calculate a kinematic age of ~5 Gyr for our sample. This age is significantly higher than the ~3 Gyr age known for late M dwarfs in the solar neighbourhood. We find that the distributions of the U and V velocity components of our sample are clearly non-Gaussian, placing the age estimate inferred from the full space motion vector into question. The W-component exhibits a distribution more consistent with a normal distribution, and from W alone we derive an age of ~3 Gyr, which is the same age found for late-M dwarf samples. Our brightness-limited sample is probably contaminated by a number of outliers that predominantly bias the U and V velocity components. The origin of the outliers remain unclear, but we suggest that these brown dwarfs may have gained their high velocities by means of ejection from multiple systems during their formation.

PERIODIC RADIO AND Hα EMISSION FROM THE L DWARF BINARY 2MASSW J0746425+200032: EXPLORING THE MAGNETIC FIELD TOPOLOGY AND RADIUS OF AN L DWARF

[Abridged] We present an 8.5-hour simultaneous radio, X-ray, UV, and optical observation of the L dwarf binary 2MASSW J0746+20. We detect strong radio emission, dominated by short-duration periodic pulses at 4.86 GHz with P=124.32+/-0.11 min. The stability of the pulse profiles and arrival times demonstrates that they are due to the rotational modulation of a B~1.7 kG magnetic field. A quiescent non-variable component is also detected, likely due to emission from a uniform large-scale field. The H-alpha emission exhibits identical periodicity, but unlike the radio pulses it varies sinusoidally and is offset by exactly 1/4 of a phase. The sinusoidal variations require chromospheric emission from a large-scale field structure, with the radio pulses likely emanating from the magnetic poles. While both light curves can be explained by a rotating mis-aligned magnetic field, the 1/4 phase lag rules out a symmetric dipole topology since it would result in a phase lag of 1/2 (poloidal field) or zero (toroidal field). We therefore conclude that either (i) the field is dominated by a quadrupole configuration, which can naturally explain the 1/4 phase lag; or (ii) the H-alpha and/or radio emission regions are not trivially aligned with the field. Regardless of the field topology, we use the measured period along with the known rotation velocity (vsini=27 km/s), and the binary orbital inclination (i=142 deg), to derive a radius for the primary star of 0.078+/-0.010 R_sun. This is the first measurement of the radius of an L dwarf, and along with a mass of 0.085+/-0.010 M_sun it provides a constraint on the mass-radius relation below 0.1 M_sun. We find that the radius is about 30% smaller than expected from theoretical models, even for an age of a few Gyr.

THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION

We present results from an adaptive optics survey for substellar and stellar companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3 Myr-3 Gyr age range with distances of 10-190 pc. Results from the survey include the discovery of two dwarf companions (HD 49197B and HD 203030B), 24 new stellar binaries, and a triple system. We infer that the frequency of 0.012-0.072 M_☉ dwarfs in 28-1590 AU orbits around young solar analogs is 3.2^(+3.1)_(–2.7%) (2σ limits). The result demonstrates that the deficiency of substellar companions at wide orbital separations from Sun-like stars is less pronounced than in the radial velocity brown dwarf desert. We infer that the mass distribution of companions in 28-1590 AU orbits around solar-mass stars follows a continuous dN/dM_(2)∝ M^(–0.4)_2 relation over the 0.01-1.0 M_☉ secondary mass range. While this functional form is similar to that for isolated objects less than 0.1 M_☉ , over the entire 0.01-1.0 M_☉ range, the mass functions of companions and of isolated objects differ significantly. Based on this conclusion and on similar results from other direct imaging and radial velocity companion surveys in the literature, we argue that the companion mass function follows the same universal form over the entire range between 0 and 1590 AU in orbital semimajor axis and ≈ 0.01-20 M_☉ in companion mass. In this context, the relative dearth of substellar versus stellar secondaries at all orbital separations arises naturally from the inferred form of the companion mass function.

Asiago eclipsing binaries program

The orbit and physical parameters of the previously unsolved double-lined eclipsing binary V570 Per, discovered by the Hipparcos satellite, were derived using high-resolution Echelle spectroscopy and B,V photoelectric photometry. The metallicity from χ 2 analysis of the spectra is (M/H) =+ 0.02 ± 0.03, and reddening from interstellar NaI and KI absorption lines is EB−V = 0.023 ± 0.007. V570 Per is a well-detached system, with shallow eclipses (due to low orbital inclination) and no sign of chromospheric activity. The two components have masses of 1.449 ± 0.006 and 1.350 ± 0.006 Mand spectral types F3 and F5, respectively. They are both still within the main sequence band (T1 = 6842 ± 25 K, T2 = 6562 ± 25 K from χ 2 analysis, R1 = 1.523 ± 0.030, R2 = 1.388 ± 0.019 R� derived by forcing the orbital solution to conform to the spectroscopic light ratio) and are dynamically relaxed to co-rotation with the orbital motion (Vrot,1,2 sini = 40 and 36 (±1) km s −1 ). The distance to V570 Per obtained from the orbital solution is 123 ± 2p c, in excellent agreement with the revised Hipparcos distance of 123 ± 11 pc. The observed properties of V570 Per components were compared to available families of stellar evolutionary tracks and, in particular, to BaSTI models computed on purpose for exactly the observed masses and varied chemical compositions. This system is interesting since both components have their masses in the range where the efficiency of convective core overshooting has to decrease with the total mass as a consequence of the decreasing size of the convective core during the central H-burning stage. Our numerical simulations show that, in order to match all empirical constraints, a small but not null overshooting is required, with efficiencies of λOV = 0.14 and 0.11 for the 1.449 and 1.350 Mcomponents, respectively. This confirms the finding of Paper II on the similar system V505 Per. At the ≈0.8 Gyr age of the system, the element diffusion has reduced the surface metallicity of the models from the initial (M/H) =+ 0.17 to (M/H) =+ 0.02, in perfect agreement with the spectroscopically derived (M/H) =+ 0.02 ± 0.03 value.

Diverse young stellar populations in the intermediate-redshift radio galaxies 3C 213.1 and 3C 459: implications for the evolution of the host galaxies

We present European Southern Observatory Very Large Telescope (ESO VLT) and William Herschel Telescope (WHT) spectroscopic observations of two powerful radio galaxies at intermediate redshifts (3C 213.1 and 3C 459), obtained with the aim of establishing the nature and evolutionary status of the host galaxies. Spectral synthesis modelling has been used to demonstrate that young stellar populations (YSP) make a major contribution to the integrated optical light in both sources, contributing at least 37 and 80 per cent of the integrated B-band light in 3C 213.1 and 3C 459, respectively. While in the case of 3C 213.1 the YSP has an intermediate age (0.4–0.8 Gyr) and comprises 3–30 per cent of the total stellar mass, adequate fits to the spectra of 3C 459 require a combination of younger (<0.1 Gyr) and intermediate (0.2–1.2 Gyr) age YSP components that together comprise 5–100 per cent of the total stellar mass. Both the optical and far-IR properties of 3C 459 are consistent with its status as an ultraluminous infrared galaxy (ULIRG), and a scenario in which the observed radio source has been triggered close to the peak of star formation activity in a major gas-rich merger. On the other hand, in 3C 213.1 it is likely that the radio source has been triggered (or re-triggered) a significant period after the starburst peak, and the far-IR luminosity of the source is substantially lower. Following correction for the contributions of the YSP, the absolute magnitudes of the host galaxies of both sources are relatively modest (≤2L*), thus demonstrating that powerful radio activity is not always associated with the most massive and luminous elliptical galaxies. These results serve to emphasize that the radio source population is diverse, in terms of both the host galaxy properties and the triggering mechanism(s) for the radio source activity.

The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy

As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. The distance and reddening to M54 are revised using both isochrone and main-sequence fitting to (m - M)0 = 17.27 and E(B - V) = 0.15. Preliminary assessment finds the M54+Sgr field to be dominated by the old metal-poor populations of Sgr and the globular cluster. Multiple turnoffs indicate the presence of at least two intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H] = -0.4 to -0.6. We also clearly show, for the first time, a prominent, ~2.3 Gyr old Sgr population of near-solar abundance. A trace population of even younger (~0.1-0.8 Gyr old), more metal-rich ([Fe/H] ~ 0.6) stars is also indicated. The Sgr age-metallicity relation is consistent with a closed-box model and multiple (4-5) star formation bursts over the entire life of the satellite, including the time since Sgr began disrupting.

Keck HIRES Spectroscopy of Four Candidate Solar Twins

We use high signal-to-noise ratio, high-resolution Keck HIRES spectroscopy of four solar twin candidates (HIP 71813, 76114, 77718, and 78399) pulled from our Hipparcos-based Ca II H and K survey to carry out parameter and abundance analyses of these objects. Our spectroscopic Teff estimates are ~100 K hotter than the photometric scale of the recent Geneva-Copenhagen survey; several lines of evidence suggest the photometric temperatures are too cool at solar Teff. At the same time, our abundances for the three solar twin candidates included in the Geneva-Copenhagen survey are in outstanding agreement with the photometric metallicities; there is no sign of the anomalously low photometric metallicities derived for some late-G UMa group and Hyades dwarfs. A first radial velocity determination is made for HIP 78399 and UVW kinematics derived for all stars. HIP 71813 appears to be a kinematic member of the Wolf 630 moving group (a structure apparently reidentified in a recent analysis of late-type Hipparcos stars), but its metallicity is 0.1 dex higher than the most recent estimate of this group's metallicity. While certainly solar-type stars, HIP 76114 and 77718 are a few percent less massive, significantly older, and metal-poor compared to the Sun; they are neither good solar twin candidates nor solar analogs providing a look at the Sun at some other point in its evolution. HIP 71813 appears to be an excellent solar analog of ~8 Gyr age. Our results for HIP 78399 suggest the promise of this star as a solar twin may be equivalent to the closest ever solar twin, HR 6060; follow-up study of this star is encouraged.

GU Bootis: A New 0.6M⊙Detached Eclipsing Binary

We have found a new low-mass, double-lined, detached eclipsing binary, GU Boo, among a sample of new variables from the ROTSE-I database. The binary has an orbital period of 0.488728 ± 0.000002 days and estimated apparent magnitudes Vrotse 13.7 and I 11.8. Our analysis of the light and radial velocity curves of the system yields individual masses and radii of M1 = 0.610 ± 0.007 M☉, M2 = 0.599 ± 0.006 M☉, R1 = 0.623 ± 0.016 R☉, and R2 = 0.620 ± 0.020 R☉. The stars in GU Boo are therefore very similar to the components of the eclipsing binary YY Gem. For this study we have adopted a mean effective temperature for the binary of Teff = 3870 ± 130 K. Based on its space velocities we suggest that GU Boo is a main-sequence binary, possibly with an age of several Gyr. The metallicity of the binary is not well constrained at this point, but we speculate that it should not be very different from solar. We have compared the physical parameters of GU Boo with current low-mass stellar models, accounting for uncertainties in age and metallicity by considering a wide range of values for those parameters. Our comparisons reveal that all the models underestimate the radii of the components of GU Boo by at least 10%-15%. This result is in agreement with the recent studies of YY Gem and CU Cnc.

The Chandra Deep Field–North Survey. XVII. Evolution of Magnetic Activity in Old Late‐Type Stars

The extremely sensitive Chandra Deep Field–North (CDF-N) pencil-beam X-ray survey is used to identify and characterize the X-ray emission from old high-latitude main-sequence Galactic stars. Our principal goal is to investigate the expected long-term decay of magnetic activity of late-type stars due to the gradual spin-down of stellar rotation from a magnetized stellar wind. Thirteen X-ray sources are associated with late-type stars; 11 of these constitute a well-defined sample for statistical analysis. This sample consists of two G, two K0–K4, and seven M2–M5 stars with median V-band magnitude around 19 and median distance around 300 pc. X-ray luminosities are typically logLX ’ 27 ergs s � 1 but are substantially higher in two cases. The combination of large-amplitude variations on timescales of hours and plasma temperatures around 5–30 MK indicates that the observed X-ray emission is dominated by magnetic reconnection flares rather than quiescent coronal emission. These X-ray properties are quantitatively similar to those seen in the active contemporary Sun. The CDF-N stellar sample is compared to simulations based on convolution of X-ray luminosity functions (XLFs) with the known spatial distribution of old-disk stars. The model indicates that the CDF-N stars are the most magnetically active old-disk stars. A substantial decline in X-ray luminosities over the 1 Gyr < t < 11 Gyr age interval is required: 39 rather than 11 stars should have been detected if the XLF does not evolve over this time interval. This is a clear demonstration that the coronal and flaring components of stellar magnetic activity—and presumably the interior magnetic dynamos responsible for the reconnecting fields at the stellar surface—exhibit long-term decay over the age of the Galactic disk. The model that best fits the magnitudes, spectral types, and X-ray luminosities of the sample has LX / t � 2 ergs s � 1 , which is faster than the t � 1 decay rate predicted from widely accepted rotational spin-down rates and X-ray–activity relations. Subject headingg stars: activity — stars: coronae — stars: late-type — stars: magnetic fields — X-rays: stars

Formation, migration, and stability of extrasolar planetary systems

This paper presents recent results concerning the planet formation, planet migration, and the long term stability of planetary systems. Most stars are found in binary systems and binary companions can disrupt both planet formation and stability. We first consider the effects of outer binary companions on the late stages of terrestrial planet formation and show how planet formation depends on the binary periastron. We then consider migration mechanisms for giant planets. In this case, planet scattering produces the full range of orbital eccentricities, but is less effective in moving planets inward (decreasing their semi-major axes). Disk torques are effective at moving planets inward, but not at increasing the eccentricities. We explore a scenario in which disk torques act in concert with planet scattering to provide the full range of orbital elements observed in extrasolar planetary systems. Finally, we consider the longer term stability of Earth-like planets in binary systems; we find that nearly 50 percent of binaries allow for Earth-like planets to remain stable over the current (4.6 Gyr) age of our solar system.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Asiago eclipsing binaries program

The orbit and physical parameters of the previously unsolved eclipsing binary V432 Aur, discovered by Hipparcos, have been derived with errors better than 1% from extensive Echelle spectroscopy and B, V photometry. Synthetic spectral analysis of both components has been performed, yielding Teff and in close agreement with the orbital solution, a metallicity [ ] = -0.6 and rotational synchronization for both components. Direct comparison on the theoretical plane with the Padova evolutionary tracks and isochrones for the masses of the two components (1.22 and 1.08 ) provides a perfect match and a 3.75 Gyr age. The more massive and cooler component is approaching the base of the giant branch and displays a probable pulsation activity with an amplitude of = 0.075 mag and Δrad.vel. = 1.5 km s-1. With a Teff = 6080 K it falls to the red of the nearby instability strip populated by δ Sct and γ Dor types of pulsating variables. Orbital modeling reveals a large and bright surface spot on it. The pulsations activity and the large spot(s) suggest the presence of macro-turbulent motions in its atmosphere. They reflect in a line broadening that at cursory inspection could be taken as indication of a rotation faster than synchronization, something obviously odd for an old, expanding star.

Dynamical Stability of Earth‐like Planetary Orbits in Binary Systems

ABSTRACTThis paper explores the stability of an Earth‐like planet orbiting a solar‐mass star in the presence of an outer‐lying intermediate‐mass companion. The overall goal is to estimate the fraction of binary systems that allow Earth‐like planets to remain stable over long timescales. We numerically determine the planet’s ejection time τej over a range of companion masses (MC = 0.001–0.5 M⊙), orbital eccentricities ϵ, and semimajor axes a. This suite of ∼40,000 numerical experiments suggests that the most important variables are the companion’s mass MC and periastron distance Rmin = a(1 - ϵ) to the primary star. At fixed MC, the ejection time is a steeply increasing function of Rmin over the range of parameter space considered here (although the ejection time has a distribution of values for a given Rmin). Most of the integration times are limited to 10 Myr, but a small set of integrations extend to 500 Myr. For each companion mass, we find fitting formulae that approximate the mean ejection time as a function of Rmin. These functions can then be extrapolated to longer timescales. By combining the numerically determined ejection times with the observed distributions of orbital parameters for binary systems, we estimate that (at least) 50% of binaries allow an Earth‐like planet to remain stable over the 4.6 Gyr age of our solar system.

A Dynamical Fossil in the Ursa Minor Dwarf Spheroidal Galaxy

The nearby Ursa Minor dwarf spheroidal (UMi dSph) is one of the most dark matter-dominated galaxies known, with a central mass-to-light ratio M/L ~ 70. Somewhat anomalously, it appears to contain morphological substructure in the form of a second peak in the stellar number density. It is often argued that this substructure must be transient, because it could not survive for the ~12 Gyr age of the system, given the crossing time implied by UMi's 8.8 km s-1 internal velocity dispersion. In this Letter, however, we present evidence that the substructure has a cold kinematical signature and argue that UMi's clumpiness could indeed be a primordial artefact. Using numerical simulations, we demonstrate that substructure is incompatible with the cusped dark matter halos predicted by the prevailing cold dark matter (CDM) paradigm but is consistent with an unbound stellar cluster sloshing back and forth within the nearly harmonic potential of a cored dark matter halo. Thus, CDM appears to disagree with observation at the least massive, most dark matter-dominated end of the galaxy mass spectrum.

Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs

Trigonometric parallax determinations are presented for 28 late-type dwarfs and brown dwarfs, including eight M dwarfs with spectral types between M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8, and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz*) and/or near-IR wavelengths (JHK) is presented for these objects and for 24 additional late-type dwarfs. Supplemented with astrometry and photometry from the literature, including 10 L and two T dwarfs with parallaxes established by association with bright, usually Hipparcos primaries, this material forms the basis for studying various color-color and color?absolute magnitude relations. The I-J color is a good predictor of absolute magnitude for late M and L dwarfs. MJ becomes monotonically fainter with I-J color and with spectral type through late L dwarfs, then brightens for early T dwarfs. The combination of z*JK colors alone can be used to classify late M, early L, and T dwarfs accurately, as well as to predict their absolute magnitudes, but is less effective at untangling the scatter among mid- and late L dwarfs. The mean tangential velocity of these objects is found to be slightly less than that for dM stars in the solar neighborhood, consistent with a sample with a mean age of several Gyr. Using colors to estimate bolometric corrections and models to estimate stellar radii, effective temperatures are derived. The latest L dwarfs are found to have Teff ~ 1360 K.

A new, cleaner colour-magnitude diagram for the metal-rich globular cluster NGC 6528

Using two epochs of HST/WFPC2 images of the metal-rich globular cluster NGC 6528 we derive the proper motions of the stars and use them to separate the stars belonging to NGC 6528 from those of the Galactic bulge. The stellar sequences in the resulting colour-magnitude diagram for the cluster are significantly better determined than in previously published data. From comparison of the colour-magnitude diagram with the fiducial line for NGC 6553 from Zoccali et al. ([CITE]) we conclude that the two globular clusters have the same age. Further, using α-enhanced stellar isochrones, NGC 6528 is found to have an age of Gyr. This fitting of isochrones also give that the cluster is 7.2 kpc away from us. From the measured velocities both the proper motion of the cluster and the velocity dispersion in the Galactic bulge are found. NGC 6528 is found to have a proper motion relative to the Galactic bulge of = 0.006 and = 0.044 arcsec per century. Using stars with ~14 (i.e. the red giant branch and horizontal branch) we find, for the Galactic bulge, and arcsec per century. This give , consistent both with previous proper motion studies of K giants in the Galactic bulge as well as with predictions by models of the kinematics of bulge stars.

Age Estimates for Globular Clusters in NGC 1399

We present high signal-to-noise Keck spectra for 10 globular clusters associated with the giant Fornax elliptical NGC 1399, and compare measured line indices with current stellar population models. Our data convincingly demonstrate, for the first time, that at least some of the clusters in a giant elliptical galaxy have super-solar abundance ratios, similar to the host galaxy. From Hbeta line-strengths the majority of clusters have ages of ~11 Gyrs (within 2sigma), which is similar to the luminosity-weighted stellar age of NGC 1399. Two of the clusters (which also reveal enhanced abundance ratios) show significantly higher Hbeta values than the others. It remains unclear whether this is due to young (~2 Gyr) ages, or extremely old (> 15 Gyr) ages with a warm blue horizontal branch. However a conflict with current cosmological parameters is avoided if the young age is favored. Either alternative indicates a complicated age distribution among the metal-rich clusters and sets interesting constraints on their chemical enrichment at late epochs.

Geochemical evidence for terrestrial ecosystems 2.6 billion years ago.

Microorganisms have flourished in the oceans since at least 3.8 billion years (3.8 Gyr) ago, but it is not at present clear when they first colonized the land. Organic matter in some Au/U-rich conglomerates and ancient soils of 2.3-2.7 Gyr age has been suggested as remnants of terrestrial organisms. Some 2.7-Gyr-old stromatolites have also been suggested as structures created by terrestrial organisms. However, it has been disputed whether this organic matter is indigenous or exogenic, and whether these stromatolites formed in marine or fresh water. Consequently, the oldest undisputed remnants of terrestrial organisms are currently the 1.2-Gyr-old microfossils from Arizona, USA. Unusually carbonaceous ancient soils--palaeosols--have been found in the Mpumalanga Province (Eastern Transvaal) of South Africa. Here we report the occurrences, elemental ratios (C, H, N, P) and isotopic compositions of this organic matter and its host rocks. These data show that the organic matter very probably represents remnants of microbial mats that developed on the soil surface between 2.6 and 2.7 Gyr ago. This places the development of terrestrial biomass more than 1.4 billion years earlier than previously reported.