A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts
Link to papers: Baburaj et al. 2025, 2026a, 2026c, all published in the Astronomical Journal
Most directly imaged planet host stars are poorly characterized in terms of their abundances, primarily due to their very high rotation velocities (\(v\sin{i}>10~\rm km/s\)), and some even in excess of \(100~\rm km/s\). Such high velocities can cause significant rotational broadening in these stars and lead to blending of adjacent spectral absorption lines, making spectral characterizationa challenging. However, decoding the formation and evolution pathways of these directly imaged planets requires abundance measurements for both the planets and their host stars. A slew of ongoing projects involving both ground-based and space-based instruments have led to measurements of elemental abundance ratios, primarily the carbon-to-oxygen (C/O) ratio , for the companions. My work aims to measure the abundance of 16 elements (C, O, Na, Mg, Si, S, K, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y), as well as certain abundance ratios (C/O, but also carbon-to-sulfur: C/S and oxygen-to-sulfur: O/S ratios) for directly imaged planet host stars.
I have led a survey on the detailed characterization of these stars using Lick/APF-Levy and Gemini-South/GHOST. The fastest rotator I have been able to analyze using these methods is the multi-planetary system host star \(\beta\) Pictoris (\(v\sin{i}\sim120~\rm km/s\)), 60 times faster than our Sun (\(v\sin{i}\sim2~\rm km/s\)). Other fast-rotating imaged planet hosts I have characterized using these methods include HR 8799, 51 Eridani, AF Leporis, and YSES 1. My work shows that assumption of solar abundances for the hosts while benchmarking planetary abundances can lead to incorrect formation inferences.