Infrared Astronomical Satellite (IRAS) Scientific Data Analysis System

The Jet Propulsion Laboratory's Scientific Data Analysis System will process Infrared Astronomical Satellite data and produce a catalog of perhaps a million infrared sources in the sky, as well as other vital information for astronomical research

Infrared Astronomical Satellite (IRAS) Scientific Data Analysis System

The Jet Propulsion Laboratory's Scientific Data Analysis System will process Infrared Astronomical Satellite data and produce a catalog of perhaps a million infrared sources in the sky, as well as other vital information for astronomical research

Mode-selective coupling of coherent phonons to the Bi2212 electronic band structure

Cuprate superconductors host a multitude of low-energy optical phonons. Using time- and angle-resolved photoemission spectroscopy, we study coherent phonons in Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+\delta}$. Sub-meV modulations of the electronic band structure are observed at frequencies of $3.94\pm 0.01$ and $5.59\pm 0.06$ THz. For the dominant mode at 3.94 THz, the amplitude of the band energy oscillation weakly increases as a function of momentum away from the node. Theoretical calculations allow identifying the observed modes as CuO$_{2}$-derived $A_{1g}$ phonons. The Bi- and Sr-derived $A_{1g}$ modes which dominate Raman spectra in the relevant frequency range are absent in our measurements. This highlights the mode-selectivity for phonons coupled to the near-Fermi-level electrons, which originate from CuO$_{2}$ planes and dictate thermodynamic properties.Comment: 7 pages, 3 figure

Near-threshold high-order harmonic spectroscopy with aligned molecules

We study high-order harmonic generation in aligned molecules close to the ionization threshold. Two distinct contributions to the harmonic signal are observed, which show very different responses to molecular alignment and ellipticity of the driving field. We perform a classical electron trajectory analysis, taking into account the significant influence of the Coulomb potential on the strong-field-driven electron dynamics. The two contributions are related to primary ionization and excitation processes, offering a deeper understanding of the origin of high harmonics near the ionization threshold. This work shows that high harmonic spectroscopy can be extended to the near-threshold spectral range, which is in general spectroscopically rich.Comment: 4 pages, 4 figure

The near-infrared variability of a sample of optically selected quasars

A complete sample of 108 optically selected quasars, the Palomar-Green quasars, has been studied at near-infrared wavelengths over an average time base of about 6 yr; in some cases the time base extends to 20 yr. The measurements show that about half the quasars have a high probability of having varied, but that half show little evidence of variability, in sharp contrast to published studies indicating that most quasars vary on comparable timescales at optical wavelengths. The maximum amplitude of variation is less than 1 mag and generally near 0.5 mag. During variations, the near-infrared colors are almost constant. The more luminous quasars show a smaller mean probability of having varied in the time frame of the study than the less-luminous quasars. The majority of the quasars with flat radio spectra have a high probability of having varied. Among those quasars that have a high probability of having varied, the rate is fairly independent of the time interval between the observations after the first year. The quasar 3C 273 shows definite variations at 10.1 µm which preclude the emission being thermal emission from heated dust grains for that quasar. The observations of the other quasars cannot be used to differentiate uniquely between thermal and nonthermal emission mechanisms

Infrared photometry of the nebulosity around quasars

Measurements of the nebulosity around quasars have been carried out in the near-infrared. The colors of the host galaxies found in these observations are consistent with those of normal galaxies. The luminosities are also similar to those of normal galaxies but are slightly brighter than average

A 2.2-µm search for variable galactic plane radio sources

A search for infrared counterparts of some of the variable galactic plane radio sources identified by Gregory and Taylor has yielded two detections. Of these, one is of the star LSI + 61°303, already identified by Gregory et al. as the counterpart of GT 0236 + 610, while the other, GT 2100 + 468, appears to be a heavily obscured object which may be either galactic or extragalactic