“Protostars” are stars a few million years old, which are still accreting gas and contracting for their own gravity, and whose nucleus has not reached yet the temperature and pressure necessary for the onset of thermonuclear reactions. The youngest protostars are still surrounded by a protoplanetary disk of gas and dust (class II protostars) or even by an accreting envelope
The study of the X-ray emission from stars provides an unmatched view of those energetic phenomena occurring in stars. In massive stars (O and early B stars), soft X-ray photons (less energetic than about 1 keV) are emitted from shocks in stellar winds. More energetic photons (the hard X-ray emission) is due to colliding stellar winds in binary systems or
di Mario Giuseppe Guarcello ( segui mguarce) Lo studio dell’emissione di raggi X dalle stelle offre molte diagnostiche di fenomeni stellari ad alta energia. Nelle stelle massive (di classe spettrale O le B più calde) raggi X “soffici” (con energia generalmente minore di 1keV, corrispondente a temperature minori di 10 milioni di gradi) sono emessi in shock nei
