The characterization of dust properties in the interstellar medium ( ISM ) is key for understanding the physics and chemistry of star formation .
Mass estimates are crucial to determine gravitational collapse conditions for the birth of new stellar objects in molecular clouds .
However , most of these estimates rely on dust models that need further observational constraints to capture the relevant parameters variations depending on the local environment : from clouds to prestellar and protostellar cores .

We present results of a new study of dust emissivity changes based on millimeter ( mm ) continuum data obtained with the NIKA camera at the IRAM-30m telescope .
Observing dust emission at 1.15 mm and 2 mm allows us to constrain the dust emissivity index , \beta , in the Rayleigh-Jeans tail of the dust spectral energy distribution ( SED ) far from its peak emission , where the contribution of other parameters ( i.e .
dust temperature ) is more important .
Focusing on the Taurus molecular cloud , one of the most famous low-mass star-forming regions in the Gould Belt , we analyze the emission properties of several distinct objects in the B213 filament .
This sub-parsec size region is of particular interest since it is characterized by the presence of a collection of evolutionary stages of early star formation : three prestellar cores , two Class-0/I protostellar cores and one Class-II object .
We are therefore able to compare dust properties among a sequence of sources that likely derive from the same parent filament .

By means of the ratio of the two NIKA channel-maps , we show that in the Rayleigh-Jeans approximation , \beta _ { RJ } varies among the objects : it decreases from prestellar cores ( \beta _ { RJ } \sim 2 ) to protostellar cores ( \beta _ { RJ } \sim 1 ) and the Class-II object ( \beta _ { RJ } \sim 0 ) .
For one prestellar and two protostellar cores , we produce a robust study using available Herschel data to constrain the dust temperature of the sources .
By using the Abel transform inversion technique we get accurate radial temperature profiles that allow us to obtain radial \beta profiles .
We find systematic spatial variations of \beta in the protostellar cores that is not observed in the prestellar core .
While in the former case \beta decreases toward the center ( with \beta varying between 1 and 2 ) , in the latter it remains constant ( \beta = 2.4 \pm 0.3 ) .
Moreover , the dust emissivity index appears anticorrelated with the dust temperature .
We discuss the implication of these results in terms of dust grain evolution between pre- and protostellar cores .