arXiv subjects

A. Lancon

Publications and source records attributed to A. Lancon.

26 records · Page 2Linked to original sources

arXiv2000

Post-Starburst Populations Near and Far - The Potential of Near-IR Spectroscopy

The efficient use of near-IR data in studies of external stellar populations depends on our ability to recognize the nature of the predominant sources of light, and to interprete these findings in terms of age and metallicity. Here we focus on elderly post-starburst populations, with ages of 0.1-1 Gyr. New models confirm that they are indeed expected to display specific spectral signatures in the near-IR, due to variable M stars of the asymptotic giant branch and to carbon stars. The signatures depend on age and metallicity. We summarize the status of current quantitative predictions and emphasize the importance of an empirical calibration of the spectral synthesis models.

astro-ph↗

arXiv2000

Can We Date Starbursts?

Age dating starbursts is an exercise with many caveats. We attempt to summarise a discussion session that was lead along a rather optimistic guideline: the aim was to highlight that current age estimates, despite undeniable uncertainties, do provide constraints on the physics of starbursts. In many cases, better starburst theories will be needed before the improvement of empirical timelines becomes crucial.

astro-ph↗

arXiv2000

Asymptotic Giant Branch Stars in Interacting Galaxy Globular Clusters

We present new modelling of the spectrophotometric properties of intermediate age stellar populations in the near-infrared (NIR). We take into account the evolutionary and spectroscopic properties of the Asymptotic Giant Branch (AGB) stars which dominate the integrated NIR emission of those populations. The predictions of spectrophotometric narrow-band molecular indices require the use of an effective temperature -- colour (or spectrum) calibration for AGB stars; synthetic indices show a strong dependence upon this calibration. Preliminary results of NIR observations of a supermassive 500 Myr old stellar cluster in the prototypical merger remnant NGC 7252 are presented. The spectra are indeed consistent with intermediate age models dominated by light from AGB stars, a significant fraction of which may be carbon rich. Implications for the stellar inputs used in the modelling of intermediate age stellar populations and their NIR emission are discussed.

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arXiv1999

Optical and near-infrared spectrophotometric properties of Long Period Variables and other luminous red stars

Based on a new and large sample of optical and near-infrared spectra obtained at the Mount Stromlo and Siding Spring Observatories (Lancon & Wood 1998; Lancon & Wood, in preparation), spectrophotometric properties of cool oxygen- and carbon-rich Long Period Variables and supergiants are presented. Temperatures of oxygen-rich stars are assigned by comparison with synthetic spectra computed from up-to-date oxygen-rich model atmosphere grids. The existence of reliable optical and near-infrared temperature indicators is investigated. A narrow relation between the bolometric correction BC(I) and the broad-band colour I-J is obtained for oxygen-rich cool stars. The ability of specific near-infrared indices to separate luminosity classes, atmospheric chemistry or variability subtypes is discussed. Some comments are also given on extinction effects, water band strengths in Long Period Variables and the evaluation of 12CO/13CO ratio in red giants.

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arXiv1999

The usage of the Asymptotic Giant Branch Star Features As Age Indicators in Post-Starburst Galaxies

We investigate techniques that can be used to determine ages of recently star forming regions during the phase dominated in the near-IR by the asymptotic giant branch stars (10^8-10^9 yrs). In particular, we present selected near-IR spectroscopic features that identify the contribution of O-rich and C-rich AGB variable stars to the integrated spectra of post-starbursts. The observational strategy based on those features is presented. We discuss the robustness of our selected features in constraining the ages of the post-starburst population depending on its physical environment and on underlying evolved populations. The interplay between the integrated features of populations and the stellar parameters is discussed.

astro-ph↗

arXiv1999

A Stellar Library for Evolutionary Synthesis Modeling Including Variable AGB Stars

A self-consistent spectrophotometric modelling of intermediate age post-starburst requires accurate stellar ingredients taking into account a principal feature of the stars dominating the near-IR emission during this phase: the variability of the AGB stars. A new library of stellar spectra based on averages of the empirical spectra of variable AGB stars is presented. This library is designed for convenient use in the population synthesis models. We discuss meaningful ways to compute these averages, and the non-trivial connection with the theoretical stellar parameters. Our library covers the near infrared wavelength range between 0.5 micron and 2.5 micron and exhibits fundamental differences when compared to the standard libraries using only static giants.

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arXiv1999

How to search for AGB stars in the near-IR post-starburst spectra

Based on evolutionary spectral synthesis models explicitly including the spectra of variable AGB stars, we select near-IR features that dentify the strong O-rich or C-rich AGB contributions to the near-IR light of post-starburst populations. AGB temperature scales and lifetimes remain major sources of uncertainties. We discuss applications and suggest massive post-starburst clusters as prime targets for observational tests.

astro-ph↗

arXiv1998

A critical look at the role of AGB stars in stellar population synthesis

Asymptotic giant branch stars are essential contributors to the near and mid-IR emission of intermediate age (0.1-1Gyr old) stellar populations. Detecting this light sets constraints on the star formation history in galaxies and, conversely, the search for AGB signatures in well studied populations will help us reduce some of the still large uncertainties in AGB models. This paper reviews how AGB stars are currently included in population synthesis models and which spectral features can be used to identify their emission in galaxy light; targets for observational tests are suggested, and some observational and theoretical difficulties are discussed.

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