The Age, Metallicity and Alpha-Element Abundance of GGCs from SSP models

[0705.4511 astro-ph] The Age, Metallicity and Alpha-Element Abundance …

The Age, Metallicity and Alpha-Element Abundance of Galactic Globular Clusters
from Single Stellar Population Models

Authors: Jon T. Mendel (Swinburne University), Robert N. Proctor (Swinburne), Duncan A. Forbes (Swinburne) (Submitted on 31 May 2007 (v1), last revised 31 May 2007 (this version, v2))

(…) Here we present age, metallicity and alpha-element abundance measurements for 48 Galactic globular clusters (GCs) as determined from integrated spectra using Lick indices and SSP models from Thomas, Maraston & Korn, Lee & Worthey and Vazdekis et al. By comparing our new measurements to independent determinations we are able to assess the ability of these SSPs to derive consistent results — a key requirement before application to heterogeneous stellar populations like galaxies(…).

22 pages, 19 figures, accepted for publication in MNRAS

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The RR Lyrae period–K-luminosity relation for globular clusters: an observational approach

New Paper :: Variable Stars

Monthly Notices of the Royal Astronomical Society
“Online Early”
doi:10.1111/j.1365-2966.2006.10962.x

A. Sollima,  C. Cacciari and E. Valenti
“The RR Lyrae period–K-luminosity relation for globular clusters: an observational approach”

Abstract:
The period–metallicity–K-band luminosity (PL_K) relation for RR Lyrae stars in 15 Galactic globular clusters and in the Large Magellanic Cloud (LMC) globular cluster Reticulum has been derived. It is based on accurate near-infrared (K) photometry combined with Two-Micron All-Sky Survey (2MASS) and other literature data. The PL_K relation has been calibrated and compared with the previous empirical and theoretical determinations in literature. The zero point of the absolute calibration has been obtained from the K magnitude of RR Lyr whose distance modulus has been measured via trigonometric parallax with Hubble Space Telescope (HST). Using this relation, we obtain a distance modulus to the LMC of (m − M)₀ = 18.54 ± 0.15 mag, in good agreement with recent determinations based on the analysis of Cepheid variable stars.

Link to the MNRAS website
(access restriction applies for the full article)

CCD photometry of the globular cluster M2…

M2 (NGC7089) :: New paper available

Monthly Notices of the Royal Astronomical Society
Online Early Issue

C. Lázaro, A. Arellano Ferro, M. J. Arévalo, D. M. Bramich, S. Giridhar, E. Poretti
CCD photometry of the globular cluster M2: RR Lyrae physical parameters and new variables

We report the results of CCD V and R photometry of the RR Lyrae stars in M2. The periodicities of most variables are revised and new ephemerides are calculated. Light-curve decomposition of the RR Lyrae stars was carried out and the corresponding mean physical parameters [Fe/H] = −1.47, T_eff = 6276 K, log L = 1.63 L and M_V = 0.71 from nine RRab and [Fe/H] = −1.61, M = 0.54 M, T_eff = 7215 K, log L = 1.74 L and M_V = 0.71 from two RRc stars were calculated. A comparison of the radii obtained from the above luminosity and temperature with predicted radii from non-linear convective models is discussed. The estimated mean distance to the cluster is 10.49 ± 0.15 kpc. These results place M2 correctly in the general globular cluster sequences for Oosterhoff type, mass, luminosity and temperature, all as a function of the metallicity. Mean relationships for M, log L/L, T_eff and M_V as a function of [Fe/H] for a family of globular clusters are offered. These trends are consistent with evolutionary and structural notions on the horizontal branch. Eight new variables are reported.

Link to MNRAS website

The period-luminosity relation for type II Cepheids in GCs

New paper:

Matsunaga, Noriyuki et al.

The period-luminosity relation for type II Cepheids in globular clusters

We report the result of our near-infrared observations (JHK_s) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well-defined period-luminosity relation at each wavelength. Two type II Cepheids in NGC 6441 also obey the relation if we assume the horizontal branch stars in NGC 6441 are as bright as those in metal-poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster (…)

Publication: Monthly Notices of the Royal Astronomical Society, Online Early

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