three metallicity classes (Table \[tab\_MplusTeff\_sdM:table\_param\]) fitting the full SEDs (Tables \[tab\_MplusTeff\_sdM:table\_best\_fits\_FF\] and \[tab\_MplusTeff\_sdM:table\_best\_fits\_FL\]). The T$_{\rm eff}$ range from $\sim$3800K for the earlier M subdwarfs down to $\sim$2600K for the latest spectral types. We can hardly distinguish the three classes in the T$_{\rm eff}$ vs. spectral type diagram shown in Fig. \[fig\_MplusTeff\_sdM:plot\_SpT\_Teff\] within the error bars of 100K set by the steps available in the models. We overplotted the temperature scale of field M dwarfs (solid black line in Fig. \[fig\_MplusTeff\_sdM:plot\_SpT\_Teff\])from the latest relation of @rajpurohit13, whose trend is comparable to earlier studies within error bars [@bessell91; @leggett96; @leggett00a; @testi09a]. Dwarfs with spectral types earlier than M2 are indistinguishable in the temperature parameter space. Overall, the temperatures of metal-poor M dwarfs are similar to those of solar-type M dwarfs with an offset of 200$\pm$100K towards warmer temperatures. They follow a linear trend with some spectral types being off by 100K or 200K, which may be due to the error on the spectral classification or binarity which is mainly based on a spectral index measuring the strength of the CaH and TiO bands in the optical [@lepine07c].

We note that the temperature scale of the line fitting option tends to infer lower 