The STAR-MELT Python package for emission line analysis of YSOs

TL;DR

The STAR-MELT Python package enables detailed analysis of emission line variability in young stellar objects, providing insights into their accretion processes and inner disc structures from diverse archival and new spectral data.

Contribution

We developed STAR-MELT, a new Python tool that automates emission line analysis in YSOs, allowing for comprehensive variability studies and physical parameter estimation.

Findings

Confirmed a stable hot spot on EX Lupi linked to accretion

Correlated infall rates with low-temperature emission lines in GQ Lupi A

Analyzed rapid variability in CVSO109 indicating inner disc dynamics

Abstract

We introduce the STAR-MELT Python package that we developed to facilitate the analysis of time-resolved emission line spectroscopy of young stellar objects. STAR-MELT automatically extracts, identifies and fits emission lines. We summarise our analysis methods that utilises the time domain of high-resolution stellar spectra to investigate variability in the line profiles and corresponding emitting regions. This allows us to probe the innermost disc and accretion structures of YSOs. Local temperatures and densities can be determined using Boltzmann statistics, the Saha equation, and the Sobolev large velocity gradient approximation. STAR-MELT allows for new results to be obtained from archival data, as well as facilitating timely analysis of new data as it is obtained. We present the results of applying STAR-MELT to three YSOs, using spectra from UVES, XSHOOTER, FEROS, HARPS, and ESPaDOnS. We demonstrate what can be achieved for data with disparate time sampling, for stars with different inclinations and variability types. For EX Lupi, we confirm the presence of a localised and stable stellar-surface hot spot associated with the footprint of the accretion column. For GQ Lupi A, we find that the maximum infall rate from an accretion column is correlated with lines produced in the lowest temperatures. For CVSO109 we investigate the rapid temporal variability of a redshifted emission wing, indicative of rotating and infalling material in the inner disc. Our results show that STAR-MELT is a useful tool for such analysis, as well as other applications for emission lines.