Radio spectral indices of the powering sources of outflows

Eight regions containing molecular or HH outflows (Mon R2E, S287, L1654, L4 83, PV Cephei, L1203, L1251A, and CB 247) have been observed with the VLA a t 6 cm, and a total of 55 sources have been detected above a 5 sigma level. By combining our observations at 6 cm with previous data obtained at 3.6 c m, we estimate the spectral indices of the sources in the fields. For 32 of the sources we discriminate the sign of the spectral index and thus, we ob tain information about the nature of the emission. For seven outflows (Mon R2E, S287-B, L1654, L483, PV Cephei, L1203, and L1251A) we found at least a central source with an spectral index consistent with thermal free-free em ission from thermal radio jets. Multiple sources, separated similar to 10 " , are found near the center of the Mon R2E, S287-B, L1654, and L1251A outfl ows. In the case of S287-B we found two sources that are valid candidates t o drive the S287-B molecular outflow and could be related to the outflow ex citation. Under the assumption that the observed emission arises from therm al radio jets, we discuss the mechanism responsible for the ionization and the constraints that introduces on their physical parameters, and we estima te that the flow of ionized material has to originate at a few AU from the exciting star. Most of the remaining, noncentral, sources are characterized by negative spectral indices (alpha < -0.1) and are probably nonthermal ba ckground objects unrelated to the studied star-forming regions.