Title: Comprehensive characterisation of L subdwarfs

  Speaker: 张曾华 (Instituto de Astrofisica de Canarias) 

　Time: Aug. 24(Wednesday) 13:00 

　Place: Room 701

  Abstract:  
L subdwarfs are metal-poor counterpart of L dwarfs in the Galactic halo and thick disk. Only about 40 L subdwarfs reported in the literatures. I have conducted a search for L subdwarf candidates within the UKIDSS and SDSS. 34 of my candidates were confirmed as L subdwarfs spectroscopically at optical and/or near infrared wavelengths with VLT, GTC and Magallen. I examined the spectral types and metallicity subclasses classification of known L subdwarfs, and established a new classification scheme of L subdwarfs. I estimate temperatures and metallicities of 22 late type M and L subdwarfs by comparing their spectra to BT-Settl models. I find that L subdwarfs have temperatures between 1500 K and 2700 K, which are higher than similarly-typed L dwarfs by around 100-400 K depending on different subclasses and subtypes. I constrained the metallicity ranges of subclasses of M, L and T subdwarfs. I also discussed the spectral type and absolute magnitude relationships for L and T subdwarfs. Then I will briefly introduce two of my observational programme on L subdwarfs. I followed up 18 L subdwarfs with X-shooter on the VLT for more detailed model comparison and radial velocity measurements. I am leading a 3-years programme to measure parallaxes of 20 L subdwarfs with the 10.4m GTC telescope (comparing only 6 L subdwarfs have parallaxes in the literature). This programme is involving 123 hours of GTC time, and completing in a year.  

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