Other
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...183.3206s&link_type=abstract
American Astronomical Society, 183rd AAS Meeting, #32.06; Bulletin of the American Astronomical Society, Vol. 25, p.1341
Other
Scientific paper
We propose that the CO first overtone emission detected in YSOs originates in a centrifugally driven disk-wind where the level population of CO is dominated by non-LTE effects. Using a revised set of collisional cross sections, we show that there is no need to invoke an LTE level population to account for the observed fluxes and line ratios. We use the disk-wind models presented by Safier (1993; ApJ 408, 115), and compute for the four lowest Delta v=2 transitions the emergent intensities and line profiles. In contrast to previous work by other authors, the thermal structure of the emitting region is not freely specified to match the data, but is computed self-consistently once the wind's mass outflow rate, the stellar parameters (M_*, R_*, and T_*), and the wind dynamical parameters (ratio of magnetic flux to mass flux and the initial angle between the magnetic field and the disk surface) are specified. These winds are endowed with a robust heating mechanism, ambipolar diffusion heating, which keeps the wind hot (T_wind ~ a few thousand K) at large distances (several AU) from the central star. We compute the abundance of CO in the wind using a simplified chemical network that includes the destruction and formation of H_2 and the destruction of CO by endothermic reactions with H atoms. In addition, we do not assume that the populations of the vibrational levels of CO are in LTE (as assumed by other workers in the field), but carry a full NLTE calculation which includes IR radiative pumping and the ``surprisal'' cross sections for collisional excitation. The agreement of our results with the observed fluxes and line profiles for the v=2-> 0 and v=3-> 1 transitions is excellent, but because we compute the level population for only the lowest six vibrational levels, the computed fluxes for the v=4-> 2 and higher transitions do not match the data. A better fit to these transitions requires the inclusion of many more vibrational levels in the model molecule. We have under way calculations which include at least the lowest ten vibrational levels of the ground electronic state of CO.
Konigl Arieh
Martín Samuel
Safier Pedro N.
No associations
LandOfFree
A Non-LTE Model for the Origin of the CO First Overtone Band Emission in Young Stellar Objects. does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A Non-LTE Model for the Origin of the CO First Overtone Band Emission in Young Stellar Objects., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Non-LTE Model for the Origin of the CO First Overtone Band Emission in Young Stellar Objects. will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-778431