A Spectrophotometric Method to Determine the Inclination of Class I Objects

A new method which enables us to estimate the inclination of Class I youngstellar objects is proposed. Since Class I objects are not sphericallysymmetric, it is likely that the observed feature is sensitive to theinclination of the system. Thus, we construct a protostar model by carefullytreating two-dimensional (2D) radiative transfer and radiative equilibrium. Weshow from the present 2D numerical simulations that the emergent luminosityL_SED,which is the frequency integration of spectral energy distribution (SED),depends strongly on the inclination of the system i, whereas the peak flux isinsensitive to i. Based on this result, we introduce a novel indicator f_L,which is the ratio of L_SED to the peak flux, as a good measure for theinclination. By using f_L, we can determine the inclination regardless of theother physical parameters. The inclination would be determined by f_L withinthe accuracy of +- 5 degree, if the opening angle of bipolar outflows isspecified by any other procedure. Since this spectrophotometric method iseasier than a geometrical method or a full SED fitting method, this methodcould be a powerful tool to investigate the feature of protostars statisticallywith observational data which will be provided by future missions, such asSIRTF, ASTRO-F, and ALMA.Comment: 14 pages, 9 figures, accepted by Ap