A new technique for monitoring the water vapor in the atmosphere

In the correction of satellite Doppler data for tropospheric effects the precipitable water vapor (PWV) is inferred at the tracking site. The technique depends on: (1) an ephemeris for the satellite; (2) an analytic model for the refraction range effect that is good to a few centimeters; (3) Doppler data with noise level below 10 centimeters; and (4) a surface pressure/temperature measurement at the tracking site. The PWV is a by product of the computation necessary to correct the Doppler data for tropospheric effects. A formulation of the refraction integral minimizes the necessity for explicit water vapor, temperature and pressure profiles

WL 17: A Young Embedded Transition Disk

We present the highest spatial resolution ALMA observations to date of the Class I protostar WL 17 in the $\rho$ Ophiuchus L1688 molecular cloud complex, which show that it has a 12 AU hole in the center of its disk. We consider whether WL 17 is actually a Class II disk being extincted by foreground material, but find that such models do not provide a good fit to the broadband SED and also require such high extinction that it would presumably arise from dense material close to the source such as a remnant envelope. Self-consistent models of a disk embedded in a rotating collapsing envelope can nicely reproduce both the ALMA 3 mm observations and the broadband SED of WL 17. This suggests that WL 17 is a disk in the early stages of its formation, and yet even at this young age the inner disk has been depleted. Although there are multiple pathways for such a hole to be created in a disk, if this hole were produced by the formation of planets it could place constraints on the timescale for the growth of planetesimals in protoplanetary disks.Comment: 7 pages, 3 figures, 2 tables, accepted for publication in ApJ

Protoplanetary Disks in the Orion Nebula Cluster: Gas Disk Morphologies and Kinematics as seen with ALMA

We present Atacama Large Millimeter Array CO(3$-$2) and HCO$^+$(4$-$3) observations covering the central $1\rlap{.}'5$$\times$$1\rlap{.}'5$ region of the Orion Nebula Cluster (ONC). The unprecedented level of sensitivity ($\sim$0.1 mJy beam$^{-1}$) and angular resolution ($\sim$$0\rlap{.}''09 \approx 35$ AU) of these line observations enable us to search for gas-disk detections towards the known positions of submillimeter-detected dust disks in this region. We detect 23 disks in gas: 17 in CO(3$-$2), 17 in HCO$^+$(4$-$3), and 11 in both lines. Depending on where the sources are located in the ONC, we see the line detections in emission, in absorption against the warm background, or in both emission and absorption. We spectrally resolve the gas with $0.5$ km s$^{-1}$ channels, and find that the kinematics of most sources are consistent with Keplerian rotation. We measure the distribution of gas-disk sizes and find typical radii of $\sim$50-200 AU. As such, gas disks in the ONC are compact in comparison with the gas disks seen in low-density star-forming regions. Gas sizes are universally larger than the dust sizes. However, the gas and dust sizes are not strongly correlated. We find a positive correlation between gas size and distance from the massive star $\theta^1$ Ori C, indicating that disks in the ONC are influenced by photoionization. Finally, we use the observed kinematics of the detected gas lines to model Keplerian rotation and infer the masses of the central pre-main-sequence stars. Our dynamically-derived stellar masses are not consistent with the spectroscopically-derived masses, and we discuss possible reasons for this discrepancy.Comment: 42 pages, 31 figure

Coping with speaker-related variation via abstract phonemic categories

Listeners can cope with considerable variation in the way that different speakers talk. We argue here that they can do so because of a process of phonological abstraction in the speech-recognition system. We review evidence that listeners adjust the bounds of phonemic categories after only very limited exposure to a deviant realisation of a given phoneme. This learning can be talker-specific and is stable over time; further, the learning generalizes to previously unheard words containing the deviant phoneme. Together these results suggest that the learning involves adjustment of prelexical phonemic representations which mediate between the speech signal and the mental lexicon during word recognition. We argue that such an abstraction process is inconsistent with claims made by some recent models of language processing that the mental lexicon consists solely of multiple detailed traces of acoustic episodes. Simulations with a purely episodic model without functional prelexical abstraction confirm that such a model cannot account for the evidence on lexical generalization of perceptual learning. We conclude that abstract phonemic categories form a necessary part of lexical access, and that the ability to store talker-specific knowledge about those categories provides listeners with the means to deal with cross-talker variation

Spatially and Spectrally Resolved Hydrogen Gas within 0.1 AU of T Tauri and Herbig Ae/Be Stars

We present near-infrared observations of T Tauri and Herbig Ae/Be stars with a spatial resolution of a few milli-arcseconds and a spectral resolution of ~2000. Our observations spatially resolve gas and dust in the inner regions of protoplanetary disks, and spectrally resolve broad-linewidth emission from the Brackett gamma transition of hydrogen gas. We use the technique of spectro-astrometry to determine centroids of different velocity components of this gaseous emission at a precision orders of magnitude better than the angular resolution. In all sources, we find the gaseous emission to be more compact than or distributed on similar spatial scales to the dust emission. We attempt to fit the data with models including both dust and Brackett gamma-emitting gas, and we consider both disk and infall/outflow morphologies for the gaseous matter. In most cases where we can distinguish between these two models, the data show a preference for infall/outflow models. In all cases, our data appear consistent with the presence of some gas at stellocentric radii of ~0.01 AU. Our findings support the hypothesis that Brackett gamma emission generally traces magnetospherically driven accretion and/or outflows in young star/disk systems.Comment: 48 pages, including 17 figures. Accepted for publication by Ap

A VLA Survey For Faint Compact Radio Sources in the Orion Nebula Cluster

We present Karl G. Janksy Very Large Array (VLA) 1.3 cm, 3.6 cm, and 6 cm continuum maps of compact radio sources in the Orion Nebular Cluster. We mosaicked 34 square arcminutes at 1.3 cm, 70 square arcminutes at 3.6 cm and 109 square arcminutes at 6 cm, containing 778 near-infrared detected YSOs and 190 HST-identified proplyds (with significant overlap between those characterizations). We detected radio emission from 175 compact radio sources in the ONC, including 26 sources that were detected for the first time at these wavelengths. For each detected source we fit a simple free-free and dust emission model to characterize the radio emission. We extrapolate the free-free emission spectrum model for each source to ALMA bands to illustrate how these measurements could be used to correctly measure protoplanetary disk dust masses from sub-millimeter flux measurements. Finally, we compare the fluxes measured in this survey with previously measured fluxes for our targets, as well as four separate epochs of 1.3 cm data, to search for and quantify variability of our sources.Comment: 13 pages, 6 figures, 4 tables, ApJ, in pres