Luminous [O III] and [N II] from Tidally Disrupted Horizontal Branch Stars

TL;DR

This paper models the emission lines from debris of a tidally disrupted horizontal branch star, predicting optical and UV spectra that can confirm the disruption scenario and estimate black hole mass.

Contribution

It introduces a model for emission lines from tidally disrupted horizontal branch stars and compares predictions with observations, providing a method to verify disruption events.

Findings

Bright optical emission lines are [N II] and [O III] at late times.

Model spectra match observations in a specific globular cluster.

Predicted UV lines can help confirm the disruption scenario.

Abstract

We model the emission lines generated in the photoionised debris of a tidally disrupted horizontal branch star. We find that at late times, the brightest optical emission lines are [N II] \lambda\lambda 6548,6583 and [O III] \lambda\lambda 4959,5007. Models of a red clump horizontal branch star undergoing mild disruption by a massive (50 -- 100 M_\sun) black hole yield an emission line spectrum that is in good agreement with that observed in the NGC 1399 globular cluster hosting the ultraluminous X-ray source CXOJ033831.8 - 352604. We make predictions for the UV emission line spectrum that can verify the tidal disruption scenario and constrain the mass of the BH.