Few Skewed Disks Found in First Closure‐Phase Survey of Herbig Ae/Be Stars

Using the 3-telescope IOTA interferometer on Mt. Hopkins, we report resultsfrom the first near-infrared (lambda=1.65 mu) closure-phase survey of YoungStellar Objects (YSOs). These closure phases allow us to unambiguously detectdepartures from centrosymmetry (i.e., skew) in the emission pattern from YSOdisks on the scale of ~4 milliarcseconds, expected from generic ``flared disk''models. Six of fourteen targets showed small, yet statistically-significant,non-zero closure phases, with largest values from the young binary system MWC361-A and the (pre-main sequence?) Be star HD 45677. Our observations are quitesensitive to the vertical structure of the inner disk and we confront thepredictions of the ``puffed-up inner wall'' models of Dullemond, Dominik, andNatta (DDN). Our data support disks models with curved inner rims because theexpected emission appear symmetrically-distributed around the star over a widerange of inclination angles. In contrast, our results are incompatible with themodels possessing vertical inner walls because they predict extreme skewness(i.e., large closure phases) from the near-IR disk emission that is not seen inour data. In addition, we also present the discovery of mysterious H-band``halos'' (~5-10% of light on scales 0.01-0.50 arcsec) around a few objects, apreliminary ``parametric imaging'' study for HD 45677, and the firstastrometric orbit for the young binary MWC 361-A.Comment: Accepted for publication in Astrophysical Journa