Discovery of Variable Hydrogen Balmer Absorption Lines with Inverse Decrement in PG 1411+442

We present new optical spectra of the well-known broad absorption line (BAL) quasar PG 1411+442, using the DBSP spectrograph at the Palomar 200 inch telescope in 2014 and 2017 and the YFOSC spectrograph at the Lijiang 2.4 m telescope in 2015. A blueshifted narrow absorption line system is clearly re...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2017-07, Vol.843 (1), p.L14
Main Authors: Shi, Xi-Heng, Pan, Xiang, Zhang, Shao-Hua, Sun, Lu-Ming, Wang, Jian-Guo, Ji, Tuo, Yang, Chen-Wei, Liu, Bo, Jiang, Ning, Zhou, Hong-Yan
Format: Article
Language:English
Subjects:
ABSORPTION
ACCRETION DISKS
accretion, accretion disks
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BALMER LINES
Balmer series
Centroids
Helium
HYDROGEN
Hydrogen storage
OSCILLATOR STRENGTHS
OSCILLATORS
Outflow
PHOTOIONIZATION
QUASARS
quasars: absorption lines
quasars: individual (PG 1411+442)
RESOLUTION
Space telescopes
SPECTRA
TELESCOPES
VELOCITY
WAVELENGTHS
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Summary:We present new optical spectra of the well-known broad absorption line (BAL) quasar PG 1411+442, using the DBSP spectrograph at the Palomar 200 inch telescope in 2014 and 2017 and the YFOSC spectrograph at the Lijiang 2.4 m telescope in 2015. A blueshifted narrow absorption line system is clearly revealed in 2014 and 2015 consisting of hydrogen Balmer series and metastable He i lines. The velocity of these lines is similar to the centroid velocity of the UV BALs, suggesting that both originate from the outflow. The Balmer lines vary significantly between the two observations and vanished in 2017. They were also absent in the archived spectra obtained before 2001. The variation is thought to be driven by photoionization change. Besides, the absorption lines show inversed Balmer decrement, i.e., the apparent optical depths of higher-order Balmer absorption lines are larger than those of lower-order lines, which is inconsistent with the oscillator strengths of the transitions. We suggest that such anomalous line ratios can be naturally explained by the thermal structure of a background accretion disk, which allows the obscured part of the disk to contribute differently to the continuum flux at different wavelengths. High-resolution spectroscopic and photometric monitoring would be very useful to probe the structure of the accretion disk as well as the geometry and physical conditions of the outflow.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/aa725e