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Published July 2012 | Published
Journal Article Open

Probing the time variability of five Fe low broad absorption-line quasars


We study the time variability of five Fe low-ionization broad absorption line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2-m telescope at IUCAA Girawali Observatory (IGO) spanning an interval of up to 10 years. We report a dramatic variation in the Al iii and Fe iii fine-structure lines in the spectra of SDSS J221511.93−004549.9 (z_em ∼ 1.478). However, there is no such strong variability shown by the C iv absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe iii absorption being stronger than Fe ii and (iii) the apparent ratio of Fe iii UV 48 to Fe iii UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe iii fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between 2000 and 2008. Using the template-fitting techniques, we show that the apparent inversion of the strength of ultraviolet lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to a change in the ionization state of the gas or due to the transverse motion of this absorbing gas. The shortest variability time-scale of Al iii line gives a lower limit on the electron density of the absorbing gas as n_e ≥ 1.1×10^4 cm^(−3). The remaining four FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93−004549.9 shows significant (≥0.2 mag) variability.

Additional Information

© 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Accepted 2012 April 12. Received 2012 April 6; in original form 2012 January 10. We wish to acknowledge the IUCAA/IGO staff for their support during our observations and Maria-Jose Maureira for help with MagE observations. We also thank Dr DiPompeo for sharing VLT/FORS data with us and the anonymous referee for useful suggestions. MV gratefully acknowledges the University Grants Commission, India, for financial support through the RFSMS scheme and IUCAA for hospitality, where most of this work was done. RS and PP gratefully acknowledge support from the Indo-French Centre for the Promotion of Advanced Research (Centre Franco-Indien pour la promotion de la recherche avancée) under Project N.4304-2. This paper uses archival data based on observations carried out at the European Southern Observatory (ESO) under programmes 267.B-5698 and 71.B-0121.

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