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Comparison of the empirical data of MILES spectral library against stellar theoretical models for stellar population modelling with variable alpha-enhancement

Grant number: 12/04953-0
Support type:Research Grants - Visiting Researcher Grant - International
Duration: August 10, 2012 - September 01, 2012
Field of knowledge:Physical Sciences and Mathematics - Astronomy - Stellar Astrophysics
Principal Investigator:Andre de Castro Milone
Grantee:Andre de Castro Milone
Visiting researcher: Anne Elizabeth Sansom
Visiting researcher institution: University of Central Lancashire (UCLAN), England
Home Institution: Instituto Nacional de Pesquisas Espaciais (INPE). Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brasil). São José dos Campos , SP, Brazil


This proposal requests funding for an important short-term scientific visit by Dr. Anne Sansom from the University of Central Lancashire (UCLan) in England (UK) to the Instituto Nacional de Pesquisas Espaciais at São José dos Campos (SP). This is in order to continue a collaboration with Dr. André Milone (INPE) under an international collaborative network involving other European institutions such as the Instituto de Astrofísica de Canarias and Universidad Autónoma de Madrid, both in Spain. Meetings are also scheduled with Dr. Beatriz Barbuy (IAG/USP) and Dr. Paula Coelho (NAT/Unicsul) who have wide expertise in the theoretical foundation of one area of our project. Dr. Sansom is an active researcher with a fixed post as Senior Lecturer at the Jeremiah Horrocks Institute (JHI) of UCLan. She is an expert on stellar population analysis and chemical evolution modelling of galaxies with a lot of published papers in these subjects and also owns deep skills on observational astronomic techniques at the optical and x-ray regions. She participates in several world wide astronomical consortia and also has other collaborators around UK and continental Europe. The applicants started their collaborative research when Dr. Milone did his post-doctoral stage at JHI/UCLan. They will hold discussions about, and continue working on, the comparison of empirical data of a stellar spectral library (world-widely known as MILES) against theoretical predictions of different sets of stellar models. This involves analyzing spectral line-strengths of relevant atomic and molecular features in the visible region (particularly in the blue) that are usually employed to recover the star formation history in galaxies. These comparisons will explore the dependence of those spectrum features on the Mg/Fe abundance ratio, which is the additional chemical information recently incorporated into the MILES database (Milone et al. 2011, MNRAS). The particular objectives over the planned visit are: (i) reveal and quantify the agreement and inconsistencies between MILES empirical spectra of stars and current model spectra for a range of stellar types and chemistries; and (ii) thus test the reliability of methods currently in use for stellar population analysis, using a large library of observational data to do this for the first time. One limitation of current semi-empirical simple stellar population (SSP) models is the use of stars whose atmospheres are not completely characterized in terms of element abundances. Typically, these models take the iron (Fe) as a metallicity tracer, but stellar spectra may change considerably if the abundance ratios between Fe and other metals depart from the scaled-solar mixture. Accounting for various element abundances, including alpha-elements (traced by magnesium, Mg) and iron peak elements (traced by Fe), will allow us to provide an empirical stellar library that is particularly useful for modelling spectral energy distributions of evolving stellar populations with different chemistries. In parallel, MILES is also being expanded through the inclusion of new stellar data set to improve the stars' distribution over the 4-D parameter space (Teff, log g, [Fe/H], [Mg/Fe]) (Milone et al. 2012, IAU S284). The knowledge gained will pave the way for the creation of a new generation of self-consistent semi-empirical SSP models assuming a variable alpha enhancement. Whilst models based on theoretical atmospheres allow one to generate spectra for stars in principle with any abundance ratio pattern, they are limited by incomplete data on line strengths from transitions in atoms and molecules. The empirical data can be used as a firm test of specific theoretical combinations. Therefore the two approaches are highly complementary. Our semi-empirical models will represent a benchmark for those theoretical SSP models as well as forming the building blocks for much more accurate analysis of stellar populations in galaxies than hitherto possible. (AU)

Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
SANSOM, A. E.; DE CASTRO MILONE, A.; VAZDEKIS, A.; SANCHEZ-BLAZQUEZ, P. Tests of model predictions for the responses of stellar spectra and absorption-line indices to element abundance variations. Monthly Notices of the Royal Astronomical Society, v. 435, n. 2, p. 952-974, OCT 2013. Web of Science Citations: 15.

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