Unidentified Features in the Ultraviolet Spectrum of X Per

TL;DR

This study uses high-resolution ultraviolet spectra to identify two likely interstellar absorption features in the sightline towards X Per, contributing to the understanding of unknown interstellar phenomena.

Contribution

It reports the detection of two new unidentified interstellar features in ultraviolet spectra, distinguishing them from instrumental noise and discussing potential carriers.

Findings

Two unidentified features detected with >3% depth of continuum

Features are likely of interstellar origin, not instrumental noise

Discussion on possible carriers and future research directions

Abstract

High-resolution ultraviolet spectra from the Space Telescope Imaging Spectrograph (STIS) were used to search for unidentified interstellar absorption features in the well studied sightline towards X Per (HD 24534). The significance of features detected was determined from Gaussian fits to the data, as well as the features' persistence in multiple observations. Fixed pattern noise characteristics were studied in STIS echelle data to distinguish between interstellar and instrumental features. We report the detection of two unidentified features that stand out from the more common fixed pattern noise features. Both features have depths of > 3% of the continuum level making them very likely of interstellar origin. Lastly, we comment on possible carriers, and discuss future prospects for studying these and perhaps other unidentified lines in larger samples of sightlines.