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تسجيل مستخدم جديدOptical spectral variability of PG QSOs
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In previous studies we have shown that the optical variability of quasars increases, on average, with redshift. We explained this dependance in terms of a hardening of the spectrum during bright phases, coupled with the increase of the rest-frame frequency for increasing redshift. We re-analize now these correlations on the basis of new light curves of PG quasars, recently published by the Wise Observatory group.
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A new analysis of the variability of the spectral slope of PG QSOs has been performed, on the basis of recent literature data in the B and R photometric bands. Preliminary results confirm our previous findings concerning the increase of variability w
ith the rest-frame observing frequency. We also find a correlation of the spectral slope with luminosity, consistent with temperature changes of an emitting black body.
For some samples, it has been shown that spectra of QSOs with low redshift are bluer during their brighter phases. For the FIRST bright QSO sample, we assemble their spectra from SDSS DR7 to investigate variability between the spectra from White et a
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A spectral principal component analysis (SPCA) of a sample of 87 PG QSOs at $z < 0.5$ is presented for their mid-infrared spectra from Spitzer Space Telescope. We have derived the first five eigenspectra, which account for 85.2% of the mid-infrared s
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It is found that feii emission contributes significantly to the optical and ultraviolet spectra of most active galactic nuclei. The origin of the optical/UV feii emission is still a question open to debate. The variability of feii would give clues to
this origin. Using 7.5 yr spectroscopic monitoring data of one Palomer-Green (PG) quasi-stellar object (QSO), PG 1700+518, with strong optical feii emission, we obtain the light curves of the continuum lv, feii, the broad component of hb, and the narrow component of hb by the spectral decomposition. Through the interpolation cross-correlation method, we calculate the time lags for light curves of feii, the total hb, the broad component of hb, and the narrow component of hb with respect to the continuum light curve. We find that the feii time lag in PG1700+518 is $209^{+100}_{-147}$ days, and the hb time lag cannot be determined. Assuming that feii and hb emission regions follow the virial relation between the time lag and the FWHM for the hb and feii emission lines, we can derive that the hb time lag is $148^{+72}_{-104}$ days. The hb time lag calculated from the empirical luminosity--size relation is 222 days, which is consistent with our measured feii time lag. Considering the optical feii contribution, PG 1700+518 shares the same characteristic on the spectral slope variability as other 15 PG QSOs in our previous work, i.e., harder spectrum during brighter phase.
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