# Photoionization-driven Absorption Lines Variability in Balmer Absorption Line Quasar LBQS 1206+1052

## TL;DR

This study analyzes absorption line variability in quasar LBQS 1206+1052, demonstrating that changes are driven by photoionization effects rather than gas movement, with detailed density and distance estimates for different absorbing components.

## Contribution

It provides the first detailed evidence that absorption line variability in this quasar is driven by photoionization, with specific physical parameters derived from spectral analysis and simulations.

## Key findings

- Absorption line strengths vary without velocity changes.
- Variability is caused by ionization state changes, not gas movement.
- Absorbing gas densities and distances are estimated for two components.

## Abstract

In this paper we present an analysis of absorption line variability in mini-BAL quasar LBQS 1206+1052. The SDSS spectrum demonstrates that the absorption troughs can be divided into two components of blueshift velocities of $\sim$700 km s$^{-1}$ and $\sim$1400 km s$^{-1}$ relative to the quasar rest-frame. The former component shows rare Balmer absorption, which is an indicator of high density absorbing gas, thus the quasar is worth follow-up spectroscopic observations. Our follow-up optical and near-infrared spectra using MMT, YFOSC, TripleSpec and DBSP reveal that the strengths of the absorption lines vary for both of the two components, while the velocities do not change. We reproduce all of the spectral data by assuming that only the ionization state of the absorbing gas is variable and that all other physical properties are invariable. The variation of ionization is consistent with the variation of optical continuum from the V-band light-curve. Additionally, we can not interpret the data by assuming that the variability is due to a movement of the absorbing gas. Therefore, our analysis strongly indicates that the absorption line variability in LBQS 1206+1052 is photoionization-driven. As shown from photo-ionization simulations, the absorbing gas with blueshift velocity of $\sim$700 km s$^{-1}$ has a density in the range of $10^9$ to $10^{10}$ cm$^{-3}$ and a distance of $\sim$1 pc, and the gas with blueshift velocity of $\sim$1400 km s$^{-1}$ has a density of $10^3$ cm$^{-3}$ and a distance of $\sim$1 kpc.