منابع مشابه
The Detection of Silicate Emission from Quasars at 10 and 18 Microns
We report the spectroscopic detection of silicate emission at 10 and 18μm in five PG quasars, the first detection of these two features in galaxies outside the Local Group. This finding is consistent with the unification model for Active Galactic Nuclei (AGNs), which predicts that an AGN torus seen pole-on should show a silicate emission feature in the mid-infrared. The strengths of the detecte...
متن کاملVariability of Quasars at 10 Microns1 G. Neugebauer and K. Matthews
Twenty-Ðve low-redshift quasars have been monitored for several decades at Ðve nearand midinfrared wavelengths to detect rapid variations that would indicate that a nonthermal component was present in the ““ 10 km bump.ÏÏ Such variability has apparently been detected in several radio-loud quasars and in the radio-quiet quasar PG 1535]547. In addition, the structure function of PG 1226]023 shows...
متن کاملThe Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 Microns.
We present a study of Seyfert 1.5-2.0 galaxies observed at two epochs with the Hubble Space Telescope (HST) at 1.6 µm. We find that unresolved nuclear emission from nine of 14 nuclei varies at the level of 10%-40% on timescales of 0.7-14 months, depending upon the galaxy. A control sample of Seyfert galaxies lacking unresolved sources and galaxies lacking Seyfert nuclei show less than 3% instru...
متن کاملLong Term Variability of SDSS Quasars
We use a sample of 3791 quasars from the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR), and compare their photometry to historic plate material for the same set of quasars in order to study their variability properties. The time base-line we attain this way ranges from a few months to up to 50 years. In contrast to monitoring programs, where relatively few quasars are photometrically...
متن کاملOptical Monitoring of Quasars: I. Variability
We present an analysis of quasar variability from data collected during a photometric monitoring of 50 objects carried out at CNPq/Laboratório Nacional de Astrof́ısica, Brazil, between March 1993 and July 1996. A distinctive feature of this survey is its photometric accuracy, ∼ 0.02 V mag, achieved through differential photometry with CCD detectors, what allows the detection of faint levels of v...
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ژورنال
عنوان ژورنال: The Astronomical Journal
سال: 1999
ISSN: 0004-6256
DOI: 10.1086/300945