  Context. Being the most numerous and oldest stars in the galaxy, M dwarfs are
objects of great interest for exoplanet searches. The presence of molecules in
their atmosphere complicates our understanding of their atmospheric properties.
But great advances have recently been made in the modeling of M dwarfs due to
the revision of solar abundances. Aims. We aim to determine stellar parameters
of M dwarfs using high resolution spectra (R = 90 000) simultaneously in the
visible and the near-infrared. The high resolution spectra and broad wavelength
coverage provide an unique opportunity to understand the onset of dust and
cloud formation at cool temperatures. Furthermore, this study will help in
understanding the physical processes which occur in a cool atmospheres,
particularly, the redistribution of energy from the optical to the
near-infrared. Methods. The stellar parameters of M dwarfs in our sample have
been determined by comparing the high resolution spectra both in the optical
and in the near-infrared simultaneously observed by CARMENES with the synthetic
spectra obtained from the BT-Settl model atmosphere. The detailed spectral
synthesis of these observed spectra both in the optical and in the
near-infrared helps to understand the missing continuum opacity. Results. For
the first time, we derive fundamental stellar parameters of M dwarfs using the
high resolution optical and near-infrared spectra simultaneously. We determine
Teff , log g and [M/H] for 292 M dwarfs of spectral type M0 to M9, where the
formation of dust and clouds are important. The derived Teff for the sample
ranges from 2300 to 4000 K, values of log g ranges from 4.5 geq log g leq 5.5
and the resulting metallicity ranges from -0.5 geq [M/H] leq +0.5. We have also
explored the possible differences in Teff , log g and [M/H] by comparing them
with other studies of the same sample of M dwarfs.
