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arXiv · 1511.04086

Ubiquitous Time Variability of Integrated Stellar Populations

Charlie Conroy·Pieter van Dokkum·Jieun Choi
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Abstract

Long period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to ~1000d and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long period variables in a population is directly related to their lifetime, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not been previously taken into account when modeling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long period variable stars, and report the ubiquitous detection of this expected `pixel shimmer' in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviors, including linearly rising and falling curves, semi-periodic curves, and sudden increases or decreases in the flux level. The observed variation of 0.1-1% is very well matched to the predictions of our models. The data provide a strong and novel constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long period variables in M87 is shorter by approximately 30% compared to predictions from the latest stellar evolution models.

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Charlie Conroy, Pieter van Dokkum, Jieun Choi. 2015-11-12. Ubiquitous Time Variability of Integrated Stellar Populations. https://doi.org/10.1038/nature15731

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