The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGNs) can be investigated by analyzing the temporal response of the torus's infrared (IR) dust emission to ...variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths (≤4.5 m). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of ∼3, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberation mapping. However, overall, the models predict radii at 2.2 m that are typically a factor of ∼2 larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.
The acceptorless dehydrogenative coupling (ADC) of primary alcohols to esters by diazabutadiene-coordinated ruthenium compounds is reported. Treatment of cis-Ru(dmso)4Cl2 in acetone at 56 °C with ...different 1,4-diazabutadienes p-XC6H4N=C(H)(H)C=NC6H4X-p; X = H, CH3, OCH3, and Cl; abbreviated as DAB-X, gives trans-Ruκ2-N,N-DAB-X2Cl2 as the kinetic product of substitution. Heating these products in o-xylene at 144 °C gives the thermodynamically favored cis-Ruκ2-N,N-DAB-X2Cl2 isomers. Electronic structure calculations confirm the greater stability of the cis diastereomer. The molecular structures for each pair of geometric isomers have been determined by X-ray diffraction analyses. Cyclic voltammetry experiments on the complexes show an oxidative response and a reductive response within 0.50 to 0.93 V and −0.76 to −1.24 V vs. SCE respectively. The cis-Ruκ2-N,N-DAB-X2Cl2 complexes function as catalyst precursors for the acceptorless dehydrogenative coupling of primary alcohols to H2 and homo- and cross-coupled esters. When 1,4-butanediol and 1,5-pentanediol are employed as substrates, lactones and hydroxyaldehydes are produced as the major dehydrogenation products, while secondary alcohols afforded ketones in excellent yields. The mechanism for the dehydrogenation of benzyl alcohol to benzyl benzoate and H2 using cis-Ruκ2-N,N-DAB-H2Cl2 (cis-1) as a catalyst precursor was investigated by DFT calculations. The data support a catalytic cycle that involves the four-coordinate species Ruκ2-N,N-DAB-Hκ1-N-DAB-H(κ1-OCH2Ph) whose protonated κ1-diazabutadiene moiety functions as a chemically non-innocent ligand that facilitates a β-hydrogen elimination from the κ1-O-benzoxide ligand to give the corresponding hydride HRuκ2-N,N-DAB-Hκ1-N-DAB-H(κ2-O,C-benzaldehyde). H2 production follows a Noyori-type elimination to give (H2)Ruκ2-N,N-DAB-Hκ1-N-DAB-H(κ1-O-benzaldehyde) as an intermediate in the catalytic cycle.
The obscuring circumnuclear torus of dusty molecular gas is one of the major components of active galactic nuclei (AGN). The torus can be studied by analyzing the time response of its infrared (IR) ...dust emission to variations in the AGN continuum luminosity, a technique known as reverberation mapping. The IR response is the convolution of the AGN ultraviolet/optical light curve with a transfer function that contains information about the size, geometry, and structure of the torus. Here, we describe a new computer model that simulates the reverberation response of a clumpy torus. Given an input optical light curve, the code computes the emission of a 3D ensemble of dust clouds as a function of time at selected IR wavelengths, taking into account light travel delays. We present simulated dust emission responses at 3.6, 4.5, and 30 m that explore the effects of various geometrical and structural properties, dust cloud orientation, and anisotropy of the illuminating radiation field. We also briefly explore the effects of cloud shadowing (clouds are shielded from the AGN continuum source). Example synthetic light curves have also been generated, using the observed optical light curve of the Seyfert 1 galaxy NGC 6418 as input. The torus response is strongly wavelength-dependent, due to the gradient in cloud surface temperature within the torus, and because the cloud emission is strongly anisotropic at shorter wavelengths. Anisotropic illumination of the torus also significantly modifies the torus response, reducing the lag between the IR and optical variations.
This paper describes the data release of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey conducted between 2005 and 2007. Light curves, spectra, classifications, and ancillary data are ...presented for 10,258 variable and transient sources discovered through repeat ugriz imaging of SDSS Stripe 82, a 300 deg2 area along the celestial equator. This data release is comprised of all transient sources brighter than r 22.5 mag with no history of variability prior to 2004. Dedicated spectroscopic observations were performed on a subset of 889 transients, as well as spectra for thousands of transient host galaxies using the SDSS-III BOSS spectrographs. Photometric classifications are provided for the candidates with good multi-color light curves that were not observed spectroscopically, using host galaxy redshift information when available. From these observations, 4607 transients are either spectroscopically confirmed, or likely to be, supernovae, making this the largest sample of supernova candidates ever compiled. We present a new method for SN host-galaxy identification and derive host-galaxy properties including stellar masses, star formation rates, and the average stellar population ages from our SDSS multi-band photometry. We derive SALT2 distance moduli for a total of 1364 SN Ia with spectroscopic redshifts as well as photometric redshifts for a further 624 purely photometric SN Ia candidates. Using the spectroscopically confirmed subset of the three-year SDSS-II SN Ia sample and assuming a flat ΛCDM cosmology, we determine M = 0.315 0.093 (statistical error only) and detect a non-zero cosmological constant at 5.7 .
Upon reaction with Ru(PPh3)2(CO)2Cl2, N‐(naphthyl)‐4‐R‐salicylaldimines (R = OCH3, H, Cl; H2L1–H2L3) and 2‐hydroxy‐N‐(naphthyl)naphthaldimine (H2L4) readily undergo cycloruthenation by C–H bond ...activation at the peri position to afford complexes of the type Ru(PPh3)2(L)(CO) (L = L1–L4). The crystal structures of the Ru(PPh3)2(L)(CO) (L = L1, L2, L4) complexes were determined and the structure of Ru(PPh3)2(L3)(CO) optimized by DFT calculations. The thermodynamics for the reaction of Ru(PPh3)2(CO)2Cl2 with H2L2 to give Ru(PPh3)2(L2)(CO) were determined. All the complexes show intense absorptions in the visible and UV regions, which have been analyzed by TDDFT calculations. Cyclic voltammetry of the four cycloruthenated complexes showed two oxidations within the range 0.50–1.35 V versus SCE and a reduction at around –1.75 V versus SCE. The Ru(PPh3)2(L)(CO) (L = L1–L4) complexes were found to efficiently catalyze the transfer hydrogenation of carbonyl compounds.
N‐(Naphthyl)‐4‐R‐salicylaldimines (R = OCH3, H, Cl; H2L1–H2L3) and 2‐hydroxy‐N‐(naphthyl)naphthaldimine (H2L4) react with Ru(PPh3)2(CO)2Cl2, undergoing C–H bond activation at the peri position, to afford complexes of the type Ru(PPh3)2(L)(CO) (L = L1–L4), which can efficiently catalyze the transfer hydrogenation of carbonyl compounds.
Reactions of Fe2(CO)6(μ-pdt) (pdt = SCH2CH2CH2S) with aminodiphosphines Ph2PN(R)PPh2 (R = allyl, (i)Pr, (i)Bu, p-tolyl, H) have been carried out under different conditions. At room temperature in ...MeCN with added Me3NO·2H2O, dibasal chelate complexes Fe2(CO)4{κ(2)-Ph2PN(R)PPh2}(μ-pdt) are formed, while in refluxing toluene bridge isomers Fe2(CO)4{μ-Ph2PN(R)PPh2}(μ-pdt) are the major products. Separate studies have shown that chelate complexes convert to the bridge isomers at higher temperatures. Two pairs of bridge and chelate isomers (R = allyl, (i)Pr) have been crystallographically characterised together with Fe2(CO)4{μ-Ph2PN(H)PPh2}(μ-pdt). Chelate complexes adopt the dibasal diphosphine arrangement in the solid state and exhibit very small P-Fe-P bite-angles, while the bridge complexes adopt the expected cisoid dibasal geometry. Density functional calculations have been carried out on the chelate and bridge isomers of the model compound Fe2(CO)4{Ph2PN(Me)PPh2}(μ-pdt) and reveal that the bridge isomer is thermodynamically favourable relative to the chelate isomers that are isoenergetic. The HOMO in each of the three isomers exhibits significant metal-metal bonding character, supporting a site-specific protonation of the iron-iron bond upon treatment with acid. Addition of HBF4·Et2O to the Fe2(CO)4{κ(2)-Ph2PN(allyl)PPh2}(μ-pdt) results in the clean formation of the corresponding dibasal hydride complex Fe2(CO)4{κ(2)-Ph2PN(allyl)PPh2}(μ-H)(μ-pdt)BF4, with spectroscopic measurements revealing the intermediate formation of a basal-apical isomer. A crystallographic study reveals that there are only very small metric changes upon protonation. In contrast, the bridge isomers react more slowly to form unstable species that cannot be isolated. Electrochemical and electrocatalysis studies have been carried out on the isomers of Fe2(CO)4{Ph2PN(allyl)PPh2}(μ-pdt). Electron accession is predicted to occur at an orbital that is anti-bonding with respect to the two metal centres based on the DFT calculations. The LUMO in the isomeric model compounds is similar in nature and is best described as an antibonding Fe-Fe interaction that contains differing amounts of aryl π* contributions from the ancillary PNP ligand. The proton reduction catalysis observed under electrochemical conditions at ca. -1.55 V is discussed as a function of the initial isomer and a mechanism that involves an initial protonation step involving the iron-iron bond. The measured CV currents were higher at this potential for the chelating complex, indicating faster turnover. Digital simulations showed that the faster rate of catalysis of the chelating complex can be traced to its greater propensity for protonation. This supports the theory that asymmetric distribution of electron density along the iron-iron bond leads to faster catalysis for models of the Fe-Fe hydrogenase active site.
TASS Mark IV Photometric Survey of the Northern Sky Droege, Thomas F.; Richmond, Michael W.; Sallman, Michael P. ...
Publications of the Astronomical Society of the Pacific,
12/2006, Volume:
118, Issue:
850
Journal Article
Peer reviewed
Open access
The Amateur Sky Survey (TASS) is a loose confederation of amateur and professional astronomers. We describe the design and construction of our Mark IV systems, a set of wide‐field telescopes with CCD ...cameras that take simultaneous images in theVandI
Cpassbands. We explain our observational procedures and the pipeline that processes and reduces the images into lists of stellar positions and magnitudes. We have compiled a large database of measurements for stars in the northern celestial hemisphere withV‐band magnitudes in the range
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. This paper describes data taken over the 4 year period beginning in 2001 November. One of our results is a catalog of repeated measurements on the Johnson‐Cousins system for over 4.3 million stars.
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