The non-thermal radio jet in the NGC 2264 star forming region

Alfonso Trejo & Luis F. Rodríguez

Centro de Radioastronomía y Astrofísica - UNAM - Morelia, Michoacán, México. a.trejo; l.rodriguez@astrosmo.unam.mx.

ABSTRACTWe investigated the non-thermal radio jet in the NGC 2264 star forming region. The jet was discovered by Reipurth et al (2004), and it has a non-thermal spectrum and high polarization. We made new observations with the VLA in 2006 and compared with 1995 archival

data to search for proper motions and variability. We detect variability only in the core. The lack of variability and proper motions favors an extragalactic nature for this jet.

IntroductionReipurth et al. (2004) conducted a radio study from proto-stellar objects in several regions of star formation. They discovered a remarkably collimated radio jet in the NGC 2264 region (see figures 1 and 2). The overall extent for the jet is ~ 28 arcsec and is composed by eight knots. Reipurth et al. found that assuming that the jet was at a distance of 760 pc (in NGC 2264 region) and a knot’s velocity of 100 km/s, an ejection every 60 years was implied. This timescale is consistent with that of the knots found in other jets associated with young stellar objects. On the other hand, due to its non-thermal nature, the jet’s emission has a high degree of polarization, consistent with extragalactic jets.

ObservationsWe conducted an analysis of this radio jet, using VLA archive data (1990, 1995 and 2002 epochs). However these data did not result appropriate for a reliable search for proper motions and variability (they have different pointing centers , wavelengths and phase calibrators). In order to make a high precision comparison we made new VLA observations taken in the B configuration with 3.6 cm wavelength on 7 Sep 2006 (2006.68). These observations match the 1995.96 data. In this poster we present the comparison between these data taken with a separation of 10.72 years.

Fig. 2. Radio jet images, 1995.96 (top), 2006.68 (middle) and the residual image (bottom), showing the polarization vectors (1 arcsec corresponds to 100 %). The contours are -8,-4,4,8,16,32,64,128,256 times the rms noise (13.75, 14.79 and 20.29 microJy) and come from the I stokes map. The half contour of the synthesized beam was set to 0.86 X 0.86 arcsec, PA = 0, in order to make a reliable comparison,.

ResultsThe 1995.96 image was subtracted from the 2006.68 image. The lack of proper motions (less than 1.6 mas/year or 5.8 km/s if the jet were located in the NGC 2264 region) and variability (less than 3 %; see figure 2) favors an extragalactic nature for this jet. The bottom of figure 2 shows that only the core of the jet is variabie.

BibliographyReipurth et al. 2004, ApJ, 127, 1736Curiel et al. 1993, ApJ, 415, 191

Fig. 1. Image showing the optical emission of one part of the cone nebula (taken with ACS of the HST). The image also shows the approximately location and extend of the radio jet. It looks like the jet was emanating from the nebula.

ConclusionsWe searched for proper motions and variability in the NGC 2264 non-thermal radio jet. We concluded that it is an extragalactic jet, with variability only in the core.

ResultsThe total flux of the jet is ~ 11.3 mJy, and a polarization (up to ~30%) is consistent between both epochs.

1995.96

2006.68