Characterizing the IYJ Excess Continuum Emission in T Tauri Stars

We present the first characterization of the excess continuum emission of accreting T Tauri stars between optical and near-infrared wavelengths. With nearly simultaneous spectra from 0.48 to 2.4 microns acquired with HIRES and NIRSPEC on Keck and SpeX on the IRTF, we find significant excess continuum emission throughout this region, including the I, Y, and J bands, which are usually thought to diagnose primarily photospheric emission. The IYJ excess correlates with the excess in the V band, attributed to accretion shocks in the photosphere, and the excess in the K band, attributed to dust in the inner disk near the dust sublimation radius, but it is too large to be an extension of the excess from these sources. The spectrum of the excess emission is broad and featureless, suggestive of blackbody radiation with a temperature between 2200 and 5000 K. The luminosity of the IYJ excess is comparable to the accretion luminosity inferred from modeling the blue and ultraviolet excess emission and may require reassessment of disk accretion rates. The source of the IYJ excess is unclear. In stars of low accretion rate, the size of the emitting region is consistent with cooler material surrounding small hot accretion spots in the photosphere. However, for stars with high accretion rates, the projected area is comparable to or exceeds that of the stellar surface. We suggest that at least some of the IYJ excess emission arises in the dust-free gas inside the dust sublimation radius in the disk.Comment: Accepted to ApJ, 31 pages, 21 figure

A Taxonomy of Internet Appliances

The world is evolving from one in which almost all access to the Internet comes from personal computers (PCs) to one in which so-called Internet appliances (IAs) will make up a greater share of end-user equipment. Today's PC is a general-purpose, highly configurable and extensible device ? an "intelligent end-node" of the sort the Internet's designers had in mind. As such, it allows users much freedom of choice (such as which service provider to use, which Web sites to visit, and which new software to download) in exchange for dealing with associated complexity. An IA is a device connected to the Internet, but beyond that there is little consensus on functionality and target markets. There is, however, general agreement that it reduces the level of complexity seen by the user. A variety of approaches to reducing complexity are being pursued. These fall on a spectrum from totally fixing the function of devices, to automating the configuration of more general purpose systems. In the middle are devices whose functions appear more or less fixed to the user, but which retain some limited capability for upgrade through their Internet connection

Benjamin F. Smith Correspondence

Entry is a typed letter on Writers Press Association stationery from William J. Hartford to the Kennebec Public Library, presenting a booklet of an interview with Smith

ALMA Discovery of a Disk around the Planetary-Mass Companion Sr 12 C

We report an Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum detection of the accretion disk around SR 12 c, an ∼11 M Jup planetary-mass companion (PMC) orbiting its host binary at 980 au. This is the first submillimeter detection of a circumplanetary disk around a wide PMC. The disk has a flux density of 127 ± 14 μJy and is not resolved by the ∼0.″1 beam, so the dust disk radius is likely less than 5 au and can be much smaller if the dust continuum is optically thick. If, however, the dust emission is optically thin, then the SR 12 c disk has a comparable dust mass to the circumplanetary disk around PDS 70 c but is about five times lower than that of the ∼12 M Jup free-floating OTS 44. This suggests that disks around bound and unbound planetary-mass objects can span a wide range of masses. The gas mass estimated with an accretion rate of 10-11 M ⊙ yr-1 implies a gas-to-dust ratio higher than 100. If cloud absorption is not significant, a nondetection of 12CO(3-2) implies a compact gas disk around SR 12 c. Future sensitive observations may detect more PMC disks at 0.88 mm flux densities of ≲ 100 μJy

Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk

We show that grains have grown to ~mm size (sand sized) or larger in the terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3 Myr old binary star KH 15D. We also argue that the reflected light in the system reaches us by back scattering off the far side of the same ring whose near side causes the obscuration.Comment: 22 pages, 5 figures. To be published in Nature, March 13, 2008. Contains a Supplemen

Adjustment of global precipitation data for enhanced hydrologic modeling of tropical Andean watersheds

Global gridded precipitation is an essential driving input for hydrologic models to simulate runoff dynamics in large river basins. However, the data often fail to adequately represent precipitation variability in mountainous regions due to orographic effects and sparse and highly uncertain gauge data. Water balance simulations in tropical montane regions covered by cloud forests are especially challenging because of the additional water input from cloud water interception. The ISI-MIP2 hydrologic model ensemble encountered these problems for Andean sub-basins of the Upper Amazon Basin, where all models significantly underestimated observed runoff. In this paper, we propose simple yet plausible ways to adjust global precipitation data provided by WFDEI, the WATCH Forcing Data methodology applied to ERA-Interim reanalysis, for tropical montane watersheds. The modifications were based on plausible reasoning and freely available tropics-wide data: (i) a high-resolution climatology of the Tropical Rainfall Measuring Mission (TRMM) and (ii) the percentage of tropical montane cloud forest cover. Using the modified precipitation data, runoff predictions significantly improved for all hydrologic models considered. The precipitation adjustment methods presented here have the potential to enhance other global precipitation products for hydrologic model applications in the Upper Amazon Basin as well as in other tropical montane watersheds

Muscarinic cholinergic hyperactivity in schizophrenia : relationship to positive and negative symptoms

Based on the implication of increased muscarinic ACh activity in the production of negative symptoms, the association of decreasing cholinergic activity with positive symptoms, and the covariance of positive and negative symptoms in the psychotic phase of schizophrenia, a model of (DA) dopaminergic/(ACh) cholinergic interactions in schizophrenia was recently formulated. It suggests that DA/ACh balance is of central importance in schizophrenic pathophysiology and that muscarinic ACh activity increases in an attempt to maintain this balance in the face of increasing DA activity that occurs in the psychotic phase of the illness. The model further suggests that the muscarinic system exerts a damping influence on the emergence of positive symptoms associated with DA hyperactivity, but that this compensatory increase in muscarinic activity is accompanied by an intensification of negative symptoms. In the present study, we tested two important postulates of this model. We tested the prediction that muscarinic activity is increased in schizophrenia by comparing the effect of biperiden, an antimuscarinic M-1 agent, on REM latency in 12 drug-free schizophrenic inpatients and matched normal controls. We found that biperiden caused a smaller increase in REM latency in schizophrenic patients, suggesting that muscarinic activity is increased in schizophrenia. We tested the prediction that an anticholinergic agent would increase positive symptoms and decrease negative symptoms by studying the effect of 8 mg of biperiden/day for 2 days on positive and negative symptoms (assessed by the BPRS) in 30 medication-free schizophrenic inpatients. Biperiden produced a significant increase in positive symptoms (t = 6.36, DF = 29, P t = -2.05, DF = 29, P < 0.05). These findings suggest that central muscarinic activity is increased in the psychotic phase of schizophrenia and is relevant to the expression of positive and negative symptoms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29522/1/0000609.pd

Near-Infrared Spectroscopy of TW Hya: A Revised Spectral Type and Comparison with Magnetospheric Accretion Models

We present high signal-to-noise, moderate spectral resolution (R ~ 2000-2500) near-infrared (0.8-5.0 micron) spectroscopy of the nearby T Tauri star TW Hya. By comparing the spectrum and the equivalent widths of several atomic and molecular features with those for stars in the IRTF near-infrared library, we revise the spectral type to M2.5V, which is later than usually adopted (K7V). This implies a substantially cooler stellar temperature than previously assumed. Comparison with various pre-main sequence models suggests that TW Hya is only ~3 Myr old; much younger than the usually adopted 8 - 10 Myr. Analysis of the relative strengths of the H lines seen in the spectrum yields estimates for the temperature and density of the emitting region of T_e > 7500 K and n_e ~ 10^{12} - 10^{13} cm^{-3}. The thickness of the emitting region is 10^2 - 10^4 km and the covering fraction is f_\ast ~ 0.04. Our derived physical parameter values agree with the predictions of the magnetospheric accretion scenario. The highest signal-to-noise H lines have profiles that indicate multiple emission components. We derive an excess spectrum (above that of the M2.5V template) that peaks in the H band. Although our derived veiling values, ~ 0.1, agree with previous estimates, the excess spectrum does not match that of current models in which this flux is generated by an inner optically thin disk. We suggest that the excess flux spectrum instead reflects the differences in atmospheric opacity, gravity, and age between TW Hya and older, higher gravity field M2.5 dwarfs.Comment: 43 pages, 12 figures; accepted for publication in Ap