4 research outputs found

    Light-Induced Structural Change in Iridium Complexes Studied by Electron Spin Resonance

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    Iridium-based compounds are materials of great interest in the production of highly efficient organic light emitting diodes and several other applications. However, these organometallic compounds present relative low stability due to photodegradation processes still not well understood. In this work we investigated paramagnetic states induced by UV photoexcitation on iridium­(III) bis­[(4,6-fluorophenyl)-pyridinato-N,C2′]­picolinate (FIrpic) and iridium­(III)-tris­(2-phenylpyridine) (Ir­(ppy)<sub>3</sub>) complexes dispersed in different polymeric matrices by electron spin resonance (ESR). Photogenerated charged states with relatively strong hyperfine interactions were observed and attributed to matrix/complex charge-transfer processes. Measurements of the signal amplitude decay after photoexcitation interruption were performed as a function of temperature. The photoinduced centers are thermally activated with energy barrier between 0.3 and 0.6 eV. Electronic structure calculations suggest that the signals observed by ESR are associated with metastable negatively charged Ir complexes distorted structures

    An Ultraviolet Spectrum of the Tidal Disruption Flare ASASSN-14li

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    We present a Hubble Space Telescope STIS spectrum of ASASSN-14li, the first rest-frame UV spectrum of a tidal disruption flare (TDF). The underlying continuum is well fit by a blackbody with TUV=3.5×104T_{\mathrm{UV}} = 3.5 \times 10^{4} K, an order of magnitude smaller than the temperature inferred from X-ray spectra (and significantly more precise than previous efforts based on optical and near-UV photometry). Super-imposed on this blue continuum, we detect three classes of features: narrow absorption from the Milky Way (probably a High-Velocity Cloud), and narrow absorption and broad (FWHM ≈2000\approx 2000-8000 km s−1^{-1}) emission lines at/near the systemic host velocity. The absorption lines are blueshifted with respect to the emission lines by Δv=−(250\Delta v = -(250-400) km s−1^{-1}. Together with the lack of common low-ionization features (Mg II, Fe II), we argue these arise from the same absorbing material responsible for the low-velocity outflow discovered at X-ray wavelengths. The broad nuclear emission lines display a remarkable abundance pattern: N III], N IV], He II are quite prominent, while the common quasar emission lines of C III] and Mg II are weak or entirely absent. Detailed modeling of this spectrum will help elucidate fundamental questions regarding the nature of the emission process(es) at work in TDFs, while future UV spectroscopy of ASASSN-14li would help to confirm (or refute) the previously proposed connection between TDFs and "N-rich" quasars

    THE MOST LUMINOUS GALAXIES DISCOVERED BY WISE

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    We present 20 Wide-field Infrared Survey Explorer (WISE)-selected galaxies with bolometric luminosities Lbol > 1014 LO;, including five with infrared luminosities LIR ≡ L(rest 8-1000 μm) > 1014 LO. These "extremely luminous infrared galaxies," or ELIRGs, were discovered using the "W1W2-dropout" selection criteria which requires marginal or non-detections at 3.4 and 4.6 μm (W1 and W2, respectively) but strong detections at 12 and 22 μm in the WISE survey. Their spectral energy distributions are dominated by emission at rest-frame 4-10 μm, suggesting that hot dust with Td ∼ 450 K is responsible for the high luminosities. These galaxies are likely powered by highly obscured active galactic nuclei (AGNs), and there is no evidence suggesting these systems are beamed or lensed. We compare this WISE-selected sample with 116 optically selected quasars that reach the same Lbol level, corresponding to the most luminous unobscured quasars in the literature. We find that the rest-frame 5.8 and 7.8 μm luminosities of the WISE-selected ELIRGs can be 30%-80% higher than that of the unobscured quasars. The existence of AGNs with Lbol > 1014 L at z > 3 suggests that these supermassive black holes are born with large mass, or have very rapid mass assembly. For black hole seed masses ∼103 MO, either sustained super-Eddington accretion is needed, or the radiative efficiency must be <15%, implying a black hole with slow spin, possibly due to chaotic accretion
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