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High-resolution studies of M dwarfs

Sara M. B. Lindgren
Uppsala University

M dwarfs constitute 70% of the stars in the local Galaxy and are becoming attractive targets in the search for Earth-sized planets and planets within the habitable zone. With our research we aim to extend the current understanding of planet formation theory and explore the planet host metallicity correlation for these cooler hosts. Unlike their solar-type counterparts, the metallicity of M dwarf is difficult to determine. Their low surface temperature results in plenty of diatomic and triatomic molecules in the photospheric layers. Especially in the optical, these molecules give rise to a forest of millions of weak lines leaving almost no unblended atomic lines, making continuum placement and accurate spectroscopy nearly impossible. Previous studies of M dwarfs have therefore established different metallicity calibrations using photometric colors or spectral indices. But these methods exclude the possibility of detailed chemical analysis. In our work we use the fact that high-resolution spectrographs have opened up a new window for investigating M dwarfs. In the infrared the number of molecular transitions is greatly reduced, reducing the amount of blends with atomic lines and allowing an accurate continuum placement. This enabled us to use similar methods as is standard for warmer solar-like stars, and determine the overall metallicity though synthetic spectral fitting.
In the first part of our work we used high-resolution spectra taken in the J band (1100-1400nm) with the CRIRES spectrograph, VLT, to verify our method internally and externally by analyzing both components in several M+FGK binaries. In the second part of this study we will analyze 20 single M dwarfs to achieve a good coverage of Teff and metallicity, where our sample cover subtypes M0-M6 and estimated metallicites ranging from +0.8 to -0.8 dex. With this data we aim to derive the to-date most accurate relationship between photometric colors and metallicity for M dwarfs.

2015 November 04, 13:30

Centro de AstrofÝsica da Universidade do Porto (Auditorium)
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Instituto de Astrof├şsica e Ci├¬ncias do Espa├žo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda├ž├úo para a Ci├¬ncia e a Tecnologia
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