English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

It is found that \feii emission contributes significantly to the optical andultraviolet spectra of most active galactic nuclei. The origin of theoptical/UV \feii emission is still a question open to debate. The variabilityof \feii would give clues to this origin. Using 7.5 yr spectroscopic monitoringdata of one Palomer-Green (PG) quasi-stellar object (QSO), PG 1700+518, withstrong 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 thespectral decomposition. Through the interpolation cross-correlation method, wecalculate the time lags for light curves of \feii, the total \hb, the broadcomponent of \hb, and the narrow component of \hb with respect to the continuumlight curve. We find that the \feii time lag in PG1700+518 is$209^{+100}_{-147}$ days, and the \hb time lag cannot be determined. Assumingthat \feii and \hb emission regions follow the virial relation between the timelag 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 theempirical luminosity--size relation is 222 days, which is consistent with ourmeasured \feii time lag. Considering the optical \feii contribution, PG1700+518 shares the same characteristic on the spectral slope variability asother 15 PG QSOs in our previous work, i.e., harder spectrum during brighterphase.

The variability of optical \feii emission in PG QSO 1700+518