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Kastner J.H.,Chester rlson Center For Imaging Science | Qi C.,Harvard - Smithsonian Center for Astrophysics | Gorti U.,Search for Extraterrestrial Intelligence Institute | Gorti U.,NASA | And 7 more authors.
Astrophysical Journal | Year: 2015

We have used the Submillimeter Array to image, at ∼1.″5 resolution, C2H emission from the circumstellar disk orbiting the nearby (D = 54 pc), ∼8 Myr-old, ∼0.8 classical T Tauri star TW Hya. The SMA imaging reveals that the C2H emission exhibits a ring-like morphology. Based on a model in which the C2H column density follows a truncated radial power-law distribution, we find that the inner edge of the ring lies at ∼45 AU, and that the ring extends to at least ∼120 AU. Comparison with previous (single-dish) observations of C2H emission indicates that the C2H molecules are subthermally excited and, hence, that the emission arises from the relatively warm ( K), tenuous ( cm-3) upper atmosphere of the disk. Based on these results and comparisons of the SMA C2H map with previous submillimeter and scattered-light imaging, we propose that the C2H emission most likely traces particularly efficient photo-destruction of small grains and/or photodesorption and photodissociation of hydrocarbons derived from grain ice mantles in the surface layers of the outer disk. The presence of a C2H ring in the TW Hya disk hence likely serves as a marker of dust grain processing and radial and vertical grain size segregation within the disk. © 2015. The American Astronomical Society. All rights reserved. Source


Mzinyane T.D.,University of KwaZulu - Natal | Van Aardt J.,Chester rlson Center For Imaging Science | Ahmed F.,University of South Africa
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing | Year: 2015

This study assessed the suitability of chlorophyll, nitrogen, and water content, derived from leaf-level spectroradiometer data, for estimating volume of Eucalyptus clones in KwaZulu-Natal, South Africa. Volume was derived from field measurements of diameter at breast height (dbh) and tree height. Chlorophyll, nitrogen, and water related indices were used to estimate merchantable volume of Eucalyptus clones. Analysis of variance (ANOVA) was used to assess whether significant differences could be detected amongst index values within the plots or compartments, based on different age groups, clones, and site qualities. Cross validation and model selection based on adjusted R2 and low Mallows' Cp were utilized in the development of volume models. The strength of the correlations for all clones combined was found to be much lower than the individual relationships for E. grandis and E. saligna. ANOVA results indicated that volume was significantly (P < 0.05) influenced by age, site quality, and the clone in question. Models developed using stepwise approach without ancillary data, such as age and site index, had low adjusted R2 values (0.47 ≥ R2 ≥ 0.72) and high root-mean-square error (RMSE) values compared to models that included ancillary data (0.81 ≥ R2 ≥ 0.90). Partial least square regression models exhibited higher R2(0.92 ≥ R2 ≥ 0.96) and lower RMSE and Mallows' Cp. These results suggest that spectral measurements of chlorophyll, nitrogen, and water content have potential as independent variables to assist in the estimation of merchantable volume of Eucalyptus clones. This has important implications since results can be extended to airborne data and regional assessments. © 2015 IEEE. Source


Kastner J.H.,Chester rlson Center For Imaging Science | Qi C.,Harvard - Smithsonian Center for Astrophysics | Gorti U.,Search for Extraterrestrial Intelligence Institute | Gorti U.,NASA | And 7 more authors.
Astrophysical Journal | Year: 2015

We have used the Submillimeter Array to image, at ∼1.″5 resolution, C2H emission from the circumstellar disk orbiting the nearby (D = 54 pc), ∼8 Myr-old, ∼0.8 classical T Tauri star TW Hya. The SMA imaging reveals that the C2H emission exhibits a ring-like morphology. Based on a model in which the C2H column density follows a truncated radial power-law distribution, we find that the inner edge of the ring lies at ∼45 AU, and that the ring extends to at least ∼120 AU. Comparison with previous (single-dish) observations of C2H emission indicates that the C2H molecules are subthermally excited and, hence, that the emission arises from the relatively warm ( K), tenuous ( cm-3) upper atmosphere of the disk. Based on these results and comparisons of the SMA C2H map with previous submillimeter and scattered-light imaging, we propose that the C2H emission most likely traces particularly efficient photo-destruction of small grains and/or photodesorption and photodissociation of hydrocarbons derived from grain ice mantles in the surface layers of the outer disk. The presence of a C2H ring in the TW Hya disk hence likely serves as a marker of dust grain processing and radial and vertical grain size segregation within the disk. © 2015. The American Astronomical Society. All rights reserved. Source


Hamer S.L.,Durham University | Hamer S.L.,Paris Observatory | Edge A.C.,Durham University | Swinbank A.M.,Durham University | And 15 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present multifrequency observations of the radio galaxy Hydra-A (3C218) located in the core of a massive, X-ray luminous galaxy cluster. Integral field unit spectroscopy is used to trace the kinematics of the ionized and warm molecular hydrogen which are consistent with an ~5 kpc rotating disc. Broad, double-peaked lines of CO(2-1), [C II] 157 μm and [O I] 63 μmare detected. We estimate the mass of the cold gas within the disc to be Mgas=2.3±0.3×109M⊙. These observations demonstrate that the complex line profiles found in the cold atomic and molecular gas are related to the rotating disc or ring of gas. Finally, a Hubble Space Telescope image of the galaxy shows that this gas disc contains a substantial mass of dust. The large gas mass, star formation rate and kinematics are consistent with the levels of gas cooling from the intracluster medium (ICM). We conclude that the cold gas originates from the continual quiescent accumulation of cooled ICM gas. The rotation is in a plane perpendicular to the projected orientation of the radio jets and ICM cavities hinting at a possible connection between the kpc-scale cooling gas and the accretion of material on to the black hole. We discuss the implications of these observations for models of cold accretion, AGN feedback and cooling flows. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


David F.,Monash University | James S.D.,University of Edinburgh | Marek J.K.,Royal Observatory Greenwich | Michael J.I.B.,Monash University | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present deep Hubble Space Telescope (HST)/Wide-Field Planetary Camera 2 (WFPC2), rest-frame U images of 17L quasars at z-1 and 2 (V and I bands, respectively), designed to explore the host galaxies.We fit the images with simple axisymmetric galaxy models, including a point source, in order to separate nuclear and host-galaxy emission. We successfully model all of the host galax es, with luminosities stable to within 0.3 mag. Combining with our earlier Near Infrared Camera and Multi-Object Spectrometer rest-frame optical study of the same sample, we provide the first rest-frame U - V colours for a sample of quasar host galaxies. While the optical luminosities of theirhost galaxies indicate that they are drawn purely from the most massive (L) early-type galaxy population, their colours are systematically bluer than those of comparably massive galaxies at t e same redshift. The host galaxies of the radioloud quasars (RLQs) in our sample are more luminousthan their radio-quiet quasar (RQQ) counterparts at each epoch, but have indistinguishable colours, confirming that the RLQs are drawn from only the most massive galaxies (1011-1012M even at z - 2), while the RQQs are slightly less massive (1011M). This is consistent with the well-known anticorrelation between radio-loudness and accretion rate. Using simple stellar population 'frosting' models, we estimate mean star formation rates of 350M yr-1 for the RLQs and 100M yr-1 forthe RQQs at z - 2. By z - 1, these rates have fallen to 150M yr-1 for the RLQs and 50M yr-1 for the RQQs.We conclude that while the host galaxies are extremely massive, they remain actively star forming at, or close to, the epoch of the quasar ©2012 The Authors. Source

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