California Institute of Technology

About: California Institute of Technology is a education organization based out in Pasadena, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 57649 authors who have published 146691 publications receiving 8620287 citations. The organization is also known as: Caltech & Cal Tech.

Composite Quasar Spectra from the Sloan Digital Sky Survey

Abstract: We have created a variety of composite quasar spectra using a homogeneous data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The quasar sample spans a redshift range of 0.044 ≤ z ≤ 4.789 and an absolute r' magnitude range of -18.0 to -26.5. The input spectra cover an observed wavelength range of 3800–9200 A at a resolution of 1800. The median composite covers a rest-wavelength range from 800 to 8555 A and reaches a peak signal-to-noise ratio of over 300 per 1 A resolution element in the rest frame. We have identified over 80 emission-line features in the spectrum. Emission-line shifts relative to nominal laboratory wavelengths are seen for many of the ionic species. Peak shifts of the broad permitted and semiforbidden lines are strongly correlated with ionization energy, as previously suggested, but we find that the narrow forbidden lines are also shifted by amounts that are strongly correlated with ionization energy. The magnitude of the forbidden line shifts is 100 km s-1, compared with shifts of up to 550 km s-1 for some of the permitted and semiforbidden lines. At wavelengths longer than the Lyα emission, the continuum of the geometric mean composite is well fitted by two power laws, with a break at ≈5000 A. The frequency power-law index, αν, is -0.44 from ≈1300 to 5000 A and -2.45 redward of ≈5000 A. The abrupt change in slope can be accounted for partly by host-galaxy contamination at low redshift. Stellar absorption lines, including higher order Balmer lines, seen in the composites suggest that young or intermediate-age stars make a significant contribution to the light of the host galaxies. Most of the spectrum is populated by blended emission lines, especially in the range 1500–3500 A, which can make the estimation of quasar continua highly uncertain unless large ranges in wavelength are observed. An electronic table of the median quasar template is available.

THE NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY (NuSTAR) HIGH-ENERGY X-RAY MISSION

Abstract: The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to the peak epoch of galaxy assembly in the universe (at z ≾ 2) by surveying selected regions of the sky; (2) study the population of hard X-ray-emitting compact objects in the Galaxy by mapping the central regions of the Milky Way; (3) study the non-thermal radiation in young supernova remnants, both the hard X-ray continuum and the emission from the radioactive element ^(44)Ti; (4) observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets; and (5) observe line and continuum emission from core-collapse supernovae in the Local Group, and from nearby Type Ia events, to constrain explosion models. During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6° inclination orbit, the observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of 10 yr, we anticipate proposing a guest investigator program, to begin in late 2014.

Synthesis and Applications of RuCl2(CHR‘)(PR3)2: The Influence of the Alkylidene Moiety on Metathesis Activity

Abstract: The reactions of RuCl2(PPh3)3 with a number of diazoalkanes were surveyed, and alkylidene transfer to give RuCl2(CHR)(PPh3)2 (R = Me (1), Et (2)) and RuCl2(CH-p-C6H4X)(PPh3)2 (X = H (3), NMe2 (4), OMe (5), Me (6), F (7), Cl (8), NO2 (9)) was observed for alkyl diazoalkanes RCHN2 and various para-substituted aryl diazoalkanes p-C6H4XCHN2. Kinetic studies on the living ring-opening metathesis polymerization (ROMP) of norbornene using complexes 3−9 as catalysts have shown that initiation is in all cases faster than propagation (ki/kp = 9 for 3) and that the electronic effect of X on the metathesis activity of 3−9 is relatively small. Phosphine exchange in 3−9 with tricyclohexylphosphine leads to RuCl2(CH-p-C6H4X)(PCy3)2 10−16, which are efficient catalysts for ROMP of cyclooctene (PDI = 1.51−1.63) and 1,5-cyclooctadiene (PDI = 1.56−1.67). The crystal structure of RuCl2(CH-p-C6H4Cl)(PCy3)2 (15) indicated a distorted square-pyramidal geometry, in which the two phosphines are trans to each other, and the alkyli...

Solving Ordinary Differential Equations

Abstract: Initial-value ordinary differential equation solution via variable order Adams method (SIVA/DIVA) package is collection of subroutines for solution of nonstiff ordinary differential equations. There are versions for single-precision and double-precision arithmetic. Requires fewer evaluations of derivatives than other variable-order Adams predictor/ corrector methods. Option for direct integration of second-order equations makes integration of trajectory problems significantly more efficient. Written in FORTRAN 77.

Detection of $B$-Mode Polarization at Degree Angular Scales by BICEP2

Abstract: We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B -mode power spectrum around l∼80 . The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of ≈300 μK CMB s √ . BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes Q and U . In this paper we describe the observations, data reduction, maps, simulations, and results. We find an excess of B -mode power over the base lensed-ΛCDM expectation in the range 30 5σ . Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. Cross correlating against WMAP 23 GHz maps we find that Galactic synchrotron makes a negligible contribution to the observed signal. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power ∼(5–10)× smaller than the observed excess signal (with no significant cross-correlation with our maps). However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with 3σ significance and its spectral index is found to be consistent with that of the CMB, disfavoring dust at 1.7σ . The observed B -mode power spectrum is well fit by a lensed-ΛCDM+tensor theoretical model with tensor-to-scalar ratio r=0.20 +0.07 −0.05 , with r=0 disfavored at 7.0σ . Accounting for the contribution of foreground, dust will shift this value downward by an amount which will be better constrained with upcoming data sets