VELOCE III. Reconstructing Radial Velocity Curves of Classical Cepheids

TL;DR

This paper introduces a new framework for reconstructing radial velocity curves of classical Cepheids from sparse data, enabling precise measurements of their velocities and amplitudes for large spectroscopic surveys, and identifying spectroscopic binaries.

Contribution

The novel framework allows accurate RV curve reconstruction from minimal data, improving efficiency and enabling large-scale kinematic studies of Cepheids in surveys.

Findings

Achieves $v_\gamma$ accuracy within 20-30 m/s

Determines $P2P$ amplitudes within ~2% from few observations

Identifies new spectroscopic binaries in LMC and SMC

Abstract

We present a novel framework for accurately reconstructing radial velocity (RV) curves of classical Cepheids (Cepheids) from sparsely sampled time-series data suitable for application in large spectroscopic surveys. The framework provides a set of priors for the principal components of RV curves established based on high-precision measurements from the VELOCE project; template RV curves of Cepheids can be readily extracted from our results. We demonstrate the ability of our framework to estimate unbiased pulsation average velocities, $v_\gamma$, to within $20-30$m/s, and peak-to-peak amplitudes, $P2P$, to within $\sim 2\%$. Subsampling the initial data set, we show that $v_\gamma$ and $P2P$ can be determined to within $\sim 0.35$ km/s and $\sim 6-7\%$, respectively, from as few as three observations. We fitted existing time-series RV data of Cepheids in the LMC and SMC using this framework and obtained typical RMSE of $0.5-2.0$ km/s. The typical total uncertainty on $v_\gamma$ achieved for the SMC Cepheids is $\sim 0.85$ km/s, providing sensitivity to spectroscopic binaries (SB). We identified 8 SB1 systems; two and one of which are new detections in the LMC and SMC, respectively. This yields a single-lined SB fraction of $\sim 25\%$ and $29\%$ in the two galaxies, similar to the Milky Way's SB fraction of $29\%$ established as part of VELOCE. Despite their relatively small number, LMC Cepheids reproduce the known line-of-sight component of the LMC's large-scale rotation, which differs in the extremes by more than $80$km/s. The kinematics of the SMC are more complex and not sufficiently sampled by the available Cepheids. Our framework is designed to yield accurate $v_\gamma$ and $P2P$ of Cepheids observed by large spectroscopic surveys, such as 4MOST, SDSS-V, and others, and will unlock new insights into the kinematics and multiplicity of evolved intermediate-mass stellar populations.