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Accueil > Séminaires > Archive des séminaires d’Utinam > 2013

Zhong Jing

M dwarfs classification in the LAMOST data

mardi 15 octobre 2013, 14h

salle de conférences de l’observatoire

Zhong Jing, Observatoire astronomique de Shangai, Académie des Sciences de Chine

Résumé :

We develop a template-fit method to automatically identify and classify late-type K and M dwarfs in spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). A search of the commissioning data, acquired in 2009-2010, yields the identification of 2,612 late-K and M dwarfs. The template fit method also provides spectral classification to half a subtype, classifies the stars along the dwarf-subdwarf (dM/sdM/esdM/usdM) metallicity sequence, and provides additional fine-scale metallicity/gravity information. The automated search and classification is performed using a set of cool star templates assembled from the Sloan Digital Sky Survey spectroscopic database. We show that the stars can be efficiently classified despite shortcomings in the LAMOST commissioning data which include bright sky lines in the red. In particular we find that the absolute and relative strengths of the critical TiO and CaH molecular bands around 7000 Å are cleanly measured, which provides accurate spectral typing from late-K to mid-M, and makes it possible to estimate metallicities in a way that is more efficient and reliable than with the use of spectral indices or spectral-index based parameters such as ζTiO/CaH . Most of the cool dwarfs observed by LAMOST are found to be metal-rich dwarfs (dM). However, we identify 52 metal-poor M subdwarfs (sdM), 5 very metal-poor extreme subdwarfs (esdM) and 1 probable super metal-poor ultrasubdwarf (usdM). A complete list of objects is provided. Proper motions are recovered from the SUPERBLINK and PPMXL catalogs ; a kinematics analysis shows that the mean velocity and standard deviation for the UVW components of velocity are : <U>=-3.7 km/s, σU =18.0 km/s ; <V>=-12.4 km/s,σV =23.2 km/s ; <W>=-7.1 km/s, σW =18.0 km/s. Only the W velocity component is consistent with other reported values. This may be because most of the stars in our sample are located in the direction of the Galactic anti-center, the influence of radial velocity uncertainty is minimum for the W velocity component