tokens: photometry listed in Table 1 alone, the range of quoted spectral types translates to a reddening of E ( B V ) 0.09mag. Combining this estimate along with the two previous independent reddening estimates from Section 2 , we adopt a mean reddening estimate of E ( B V ) 0.070.02 and V band extinction of A V 0.240.07mag. Adopting the mean distance to the Ori OB1a from Hernndez etal. ( 2005 ) as representative for PDS110, we can now calculate stellar parameters like absolute magnitude ( M V = 2.540.11), apparent bolometric magnitude ( m bol = 10.140.08), absolute bolometric magnitude ( M bol = 2.520.11), luminosity (log(L/L ) = 0.890.05 dex) and radius ( R = 2.230.18R ). Interpolating between the pre-MS isochrones from Siess, Dufour Forestini ( 2000 ), the stellar mass is 1.6M and its age of 11Myr, consistent with the rest of Ori OB1a. 4.2 SED disc model To model the SED of PDS 110, we used the self-consistent irradiated, accretion disc models of DAlessio etal. ( 2006 ) to create a model grid using the stellar parameters of PDS 110 in Table 2 . We adopted a dust sublimation temperature of 1400K to set the inner radius of the disc. We included outer disc radii of 50, 150 and 300au, viscosity parameters () of 0.01, 0.001 and 0.0001 and dust settling parameters (; i.e. the dust-to-gas mass ratio in the upper disc layers relative to the standard dust-to-gas mass ratio) of 1.0, 0.5, 0.1, 0.01, 0.001 and 0.0001. The minimum grain size in the disc atmosphere was held fixed at 0.005 m while we varied the maximum grain size between 0.25, 1.0 and 2.0m to reproduce the 10 m silicate emission feature. The inclination angle was fixed at 60. Table 2. Determined Stellar Parameters for PDS 110. Based on the -squared values, the best-fitting model has a max = 0.25 m , = 0.5, = 0.01 and an outer radius of 300au. Uncertainties are beyond the scope of this analysis. This disc model has a mass of 0.006 using equation (38) in DAlessio etal. ( 1999 ). While there are no millimeter data available to provide spatial constraints, a large outer radius of 300au is consistent with the significant MIR and FIR excess of this object given that the strength of the disc emission is related to the disc mass, which, in turn, depends on radius (DAlessio etal. 1999 ). We also note that = 0.5 corresponds to a relatively flared disc. Here, we measure a disc height at 2 of 0.3au. 4.3 Photometry Some out-of-eclipse variability is seen with peak-to-peak amplitudes on the order of 3percent. From the measured v sin( i ) (64kms 1 ), we would naively estimate a P rot of 1.7d. However, searches with lomb-scargle periodograms (Press Rybicki 1989 ) on both the entire data set and shorter segments do not detect any coherent period of variation attributable to rotation, with the signals dominated by day- and month-aliases from the ground-based surveys. This suggests that variations are stochastic or quasi-periodic, as has been seen for T-Tauri stars before (Rucinski etal. 2008 ; Siwak etal. 2011 ).
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