Red Giant stars in the Large Magellanic Cloud clusters

We present deep J,H,Ks photometry and accurate Color Magnitude Diagrams down to K ~18.5, for a sample of 13 globular clusters in the Large Magellanic Cloud. This data set combined with the previous sample of 6 clusters published by our group gives the opportunity to study the properties of giant stars in clusters with different ages (ranging from ~80 Myr up to ~3.5 Gyr). Quantitative estimates of star population ratios (by number and luminosity) in the Asymptotic Giant Branch, the Red Giant Branch and the He-clump, have been obtained and compared with theoretical models in the framework of probing the so-called phase transitions. The AGB contribution to the total luminosity starts to be significant at ~200 Myr and reaches its maximum at ~5-600 Myr, when the RGB Phase Transition is starting. At ~900 Myr the full developing of an extended and well populated RGB has been completed. Both the occurrence of the AGB and RGB Phase Transitions are sharp events, lasting a few hundreds Myr only. These empirical results agree very well with the theoretical predictions of simple stellar population models based on canonical tracks and the fuel-consumption approach.Comment: 32 pages, 11 figures, accepted to Ap

The Herbal Drug Melampyrum pratense

Melampyrum pratense L. (Koch) is used in traditional Austrian medicine for the treatment of different inflammation-related conditions. In this work, we show that the extracts of M. pratense stimulated peroxisome proliferator-activated receptors- (PPARs-)α and -γ that are well recognized for their anti-inflammatory activities. Furthermore, the extract inhibited the activation of the proinflammatory transcription factor NF-κB and induction of its target genes interleukin-8 (IL-8) and E-selectin in vitro. Bioassay-guided fractionation identified several active flavonoids and iridoids including melampyroside and mussaenoside and the phenolic compound lunularin that were identified in this species for the first time. The flavonoids apigenin and luteolin were distinguished as the main components accountable for the anti-inflammatory properties. Apigenin and luteolin effectively inhibited tumor necrosis factor α (TNF-α)-induced NF-κB-mediated transactivation of a luciferase reporter gene. Furthermore, the two compounds dose-dependently reduced IL-8 and E-selectin protein expression after stimulation with lipopolysaccharide (LPS) or TNF-α in endothelial cells (ECs). The iridoids melampyroside and mussaenoside prevented the elevation of E-selectin in LPS-stimulated ECs. Lunularin was found to reduce the protein levels of the proinflammatory mediators E-selectin and IL-8 in ECs in response to LPS. These data validate the ethnomedical use of M. pratense for the treatment of inflammatory conditions and point to the constituents accountable for its anti-inflammatory activity

The globular cluster system of NGC 1399. III. VLT spectroscopy and database

Radial velocities of 468 globular clusters around NGC 1399, the central galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The mean velocity uncertainty is 50 km s-1. This data sample is accurate and large enough to be used in studies of the mass distribution of NGC 1399 and the properties of its globular cluster system. Here we describe the observations and the reduction procedure, and we discuss the uncertainties of the resulting velocities. The complete sample of cluster velocities that is used in a dynamical study of NGC 1399 is tabulated. A subsample is compared with previously published values.Facultad de Ciencias Astronómicas y Geofísica

A Database of 2MASS Near-Infrared Colors of Magellanic Cloud Star Clusters

The (rest-frame) near-IR domain contains important stellar population diagnostics and is often used to estimate masses of galaxies at low as well as high redshifts. However, many stellar population models are still relatively poorly calibrated in this part of the spectrum. To allow an improvement of this calibration we present a new database of integrated near-infrared JHKs magnitudes for 75 star clusters in the Magellanic Clouds, using the 2-Micron All-Sky Survey (2MASS). The majority of the clusters in our sample have robust age and metallicity estimates from color-magnitude diagrams available in the literature, and populate a range of ages from 10 Myr to 15 Gyr and a range in [Fe/H] from -2.17 to +0.01 dex. A comparison with matched star clusters in the 2MASS Extended Source Catalog (XSC) reveals that the XSC only provides a good fit to the unresolved component of the cluster stellar population. We also compare our results with the often-cited single-channel JHK photometry of Persson and collaborators, and find significant differences, especially for their 30"-diameter apertures up to ~2.5 mag in the K-band, more than 1 mag in J-K, and up to 0.5 mag in H-K. Using simulations to center apertures based on maximum light throughput (as performed by Persson et al, we show that these differences can be attributed to near-IR-bright cluster stars (e.g., Carbon stars) located away from the true center of the star clusters. The wide age and metallicity coverage of our integrated JHKs photometry sample constitutes a fundamental dataset for testing population synthesis model predictions, and for direct comparison with near-IR observations of distant stellar populations.Comment: AJ August 2006 issue, 67 pages, 8 tables, 17 figure

The Chemical Enrichment History of the Large Magellanic Cloud

Ca II triplet spectroscopy has been used to derive stellar metallicities for individual stars in four LMC fields situated at galactocentric distances of 3\arcdeg, 5\arcdeg, 6\arcdeg\@ and 8\arcdeg\@ to the north of the Bar. Observed metallicity distributions show a well defined peak, with a tail toward low metallicities. The mean metallicity remains constant until 6\arcdeg\@ ([Fe/H]$\sim$-0.5 dex), while for the outermost field, at 8\arcdeg, the mean metallicity is substantially lower than in the rest of the disk ([Fe/H]$\sim$-0.8 dex). The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age--metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age--metallicity relationships for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk age--metallicity relationship is similar to that for clusters. However, the lack of objects with ages between 3 and 10 Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the age--metallicity relationship of the bar. Simple chemical evolution models have been used to reproduce the observed age--metallicity relationships with the purpose of investigating which mechanism has participated in the evolution of the disk and bar. We find that while the disk age--metallicity relationship is well reproduced by close-box models or models with a small degree of outflow, that of the bar is only reproduced by models with combination of infall and outflow.Comment: 45 pages, 10 figures, accepted for publication in Astronomical Journa

The globular cluster system of NGC 1399. III. VLT spectroscopy and database

Radial velocities of 468 globular clusters around NGC 1399, the central galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The mean velocity uncertainty is 50 km s-1. This data sample is accurate and large enough to be used in studies of the mass distribution of NGC 1399 and the properties of its globular cluster system. Here we describe the observations and the reduction procedure, and we discuss the uncertainties of the resulting velocities. The complete sample of cluster velocities that is used in a dynamical study of NGC 1399 is tabulated. A subsample is compared with previously published values.Facultad de Ciencias Astronómicas y Geofísica

The globular cluster NGC 1978 in the Large Magellanic Cloud

We have used deep high-resolution Hubble Space Telescope ACS observations to image the cluster NGC 1978 in the Large Magellanic Cloud. This high-quality photometric data set allowed us to confirm the high ellipticity (~0.30+-0.02) of this stellar system. The derived Color Magnitude Diagram allowed a detailed study of the main evolutionary sequences: in particular we have detected the so called Bump along the Red Giant Branch (at V_{555}=19.10+-0.10). This is the first detection of this feature in an intermediate-age cluster. Moreover the morphology of the evolutionary sequence and their population ratios have been compared with the expectations of different theoretical models (namely BaSTI, PEL and Padua) in order to quantify the effect of convective overshooting. The best agreement (both in terms of morphology and star counts) has been found the PEL (Pisa Evolutionary Library) isochrone with Z=0.008 (consistenly with the most recent determination of the cluster metallicity, [M/H]=-0.37 dex) and a mild overshooting efficiency (Lambda_{os}=0.1). By adopting this theoretical set an age of 1.9+-0.1 Gyr has been obtained.Comment: 26 pages, 8 figures, accepted to A

The Globular Cluster System of NGC 1399. II. Kinematics of a Large Sample of Globular Clusters

We study the kinematics and dynamics of the globular cluster system of NGC 1399, the central galaxy of the Fornax cluster. The observational data consists of medium resolution spectra, obtained at the Very Large Telescope. Our sample comprises 468 radial velocities in the magnitude range 20 < m_R < 23. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The radial range is 2 arcmin < r < 9 arcmin, corresponding to 11 kpc to 50 kpc of galactocentric distance. There is the possibility that unbound clusters and/or objects in the foreground contaminate the NGC 1399 cluster sample. Under strong error selection, practically no objects are found with velocities lower than 800 km/s or higher than 2000 km/s. Since the extreme velocities influence the velocity dispersion considerably, uncertainty regarding the exact value of the dispersion remains. Within the above velocity limits, we derive a projected velocity dispersion for the total sample of 274+-9 km/s which within the uncertainties remains constant over the entire radial range. Without any velocity restriction, it increases to 325 km/s. Blue and red clusters show different dispersions corresponding to their different surface density profiles. Spherical models point to a circular velocity of 415+-30$ km/s, assuming isotropy for the red clusters. This value is constant out to 40 kpc. The inferred dark halo potential can be well represented by a logarithmic potential. Also a halo of the NFW type fits well to the observations. Some mass profiles derived from X-ray analyses do not agree with a constant circular velocity within our radial range, irrespective of its exact value.Comment: 38 pages, 20 figures, accepted by A