Ultraviolet observations by the IUE of 31 clusters of the Large Magellanic Cloud

Cassatella, A.; Barbero, Javier; Geyer, E. H.

doi:10.1086/191192

Cited by 28 publications

(53 citation statements)

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“…We use IUE observations (Cassatella et al 1987) of 10 GCs in the Large Magellanic Cloud (LMC), which have independent age and metallicity determinations (Table 3). Ages and metallicities were obtained from different sources.…”

Section: Globular Cluster Templatesmentioning

confidence: 99%

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Absorption line indices in theUV

Maraston¹,

Colmenárez

Bender

et al. 2008

A&A

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Aims. Stellar absorption lines in the optical (e.g. the Lick system) have been extensively studied and constitute an important stellar population diagnostic for galaxies in the local universe and up to moderate redshifts. Proceeding towards higher look-back times, galaxies are younger and the ultraviolet becomes the relevant spectral region where the dominant stellar populations shine. A comprehensive study of ultraviolet absorption lines of stellar population models is however still lacking. With this in mind, we study absorption line indices in the far and mid-ultraviolet in order to determine age and metallicity indicators for UV-bright stellar populations in the local universe as well as at high redshift. Methods. We explore empirical and theoretical spectral libraries and use evolutionary population synthesis to compute synthetic line indices of stellar population models. From the empirical side, we exploit the IUE-low resolution library of stellar spectra and system of absorption lines, from which we derive analytical functions (fitting functions) describing the strength of stellar line indices as a function of gravity, temperature and metallicity. The fitting functions are entered into an evolutionary population synthesis code in order to compute the integrated line indices of stellar populations models. The same line indices are also directly evaluated on theoretical spectral energy distributions of stellar population models based on Kurucz high-resolution synthetic spectra, In order to select indices that can be used as age and/or metallicity indicators for distant galaxies and globular clusters, we compare the models to data of template globular clusters from the Magellanic Clouds with independently known ages and metallicities. Results. We provide synthetic line indices in the wavelength range ∼1200 Å to ∼3000 Å for stellar populations of various ages and metallicities.This adds several new indices to the already well-studied CIV and SiIV absorptions. Based on the comparison with globular cluster data, we select a set of 11 indices blueward of the 2000 Å rest-frame that allows us to recover well the ages and the metallicities of the clusters. These indices are ideal to study ages and metallicities of young galaxies at high redshift. We also provide the synthetic high-resolution stellar population SEDs.

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Section: Globular Cluster Templatesmentioning

confidence: 99%

“…These values are given in Tables B.1 Mackey & Gilmore (2003); 10 colour excess from: Cassatella et al (1987), with the exception of NGC 2011;…”

Section: Globular Cluster Templatesmentioning

confidence: 99%

Absorption line indices in theUV

Maraston¹,

Colmenárez

Bender

et al. 2008

A&A

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“…E(B − V) values for this cluster are similar to NGC 1818: ground based data indicate 0.05 ≤ E(B − V) ≤ 0.10 (Persson et al 1983;Cassatella et al 1987 (IUE spectroscopy); Meurer et al 1990;Grebel 1997 (isochrone fit)), while HST data and the extinction map from BH82 suggest 0.03 ≤ E(B − V) ≤ 0.05 (Hunter et al 1997;Castro et al 2001;Javiel et al 2005).…”

Section: Ngc 1818mentioning

confidence: 61%

Physical parameters of rich LMC clusters from modeling of deep HST colour–magnitude diagrams

Kerber¹,

Santiago²

2005

A&A

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Abstract.We present the analysis of deep colour-magnitude diagrams (CMDs) of five rich LMC clusters. The data were obtained with HST/WFPC2 in the F555W (∼V) and F814W (∼I) filters, reaching V 555 ∼ 25. The sample of clusters is composed of NGC 1805 and NGC 1818, the youngest ones (τ < 100 Myr), NGC 1831 and NGC 1868, of intermediate-age (400 < τ < 1000 Myr), and Hodge 14, the oldest (τ > 1200 Myr). We discuss and apply a statistical method for correcting the CMD for sampling incompleteness and field star contamination. Efficient use of the CMD data was made by means of direct comparisons of the observed to model CMDs. The CMD modeling process generates a synthetic Main Sequence (MS), where we introduce as model inputs the information about age, chemical composition, present day mass function (PDMF), fraction of unresolved binaries, distance modulus and light extinction. The photometric uncertainties were empirically determined from the data and incorporated into the model as well. Statistical techniques of CMD comparisons using 1 and 2 dimensions are presented and applied as an objective method to assess the compatibility between model and data CMDs. By modeling the CMDs from the central region we infer the metallicity (Z), the intrinsic distance modulus ((m− M) 0 ) and the reddening value (E(B− V)) for each cluster. We also determined the age for the clusters with τ > 400 Myr. By means of two-dimensional CMD comparisons we Taking into account the uncertainties, these values are in accordance with the ones obtained applying the one-dimensional CMD analysis, adding reliability to these determinations.

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“…The spectrum is extracted from the International Ultraviolet Explorer ( IUE ) archive. The intrinsic flux of the spectrum is obtained using the extinction law described in Cassatella, Barbero & Geyer (1987). The fundamental parameters of the cluster adopted for the comparison are an age of 0.2 Gyr and Z = 0.004 (Vallenari et al 1991).…”

Section: Interpretation Of Cluster Spectramentioning

confidence: 99%

Simple stellar population models including blue stragglers

Xin

Deng

Grijs

et al. 2010

Monthly Notices of the Royal Astronomical Society

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Observations show that nearly all star clusters and stellar populations contain blue straggler stars (BSs). BSs in a cluster can significantly enhance the integrated spectrum of the host population, preferentially at short wavelengths, and render it much bluer in photometric colours. Current theoretical simple stellar population (SSP) models constructed within the traditional framework of single and binary stellar evolution cannot fully account for the impact of these objects on the integrated spectral properties of stellar populations. Using conventional SSP models without taking into account BS contributions may significantly underestimate a cluster's age and/or metallicity, simply because one has to balance the observed bluer colours (or a bluer spectrum) with a younger age and/or a lower metallicity. Therefore, inclusion of BS contributions in SSP models is an important and necessary improvement for population synthesis and its applications. Here, we present a new set of SSP models, which include BS contributions based on our analysis of individual star clusters. The models cover the wavelength range from 91~{\AA} to 160~$\mu$m, ages from 0.1 to 20 Gyr and metallicities $Z=0.0004, 0.004, 0.008, 0.02$ (solar) and 0.05. We use the observed integrated spectra of several Magellanic Cloud star clusters to cross-check and validate our models. The results show that the age predictions from our models are closer to those from isochrone fitting in the clusters' colour-magnitude diagrams compared to age predictions based on standard SSP models.Comment: 16 pages, 15 figures, 4 tables, accepted for publication in MNRA

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Ultraviolet observations by the IUE of 31 clusters of the Large Magellanic Cloud

Cited by 28 publications

References 0 publications

Absorption line indices in theUV

Absorption line indices in theUV

Physical parameters of rich LMC clusters from modeling of deep HST colour–magnitude diagrams

Simple stellar population models including blue stragglers

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