2019ApJ...875....8G

Measuring stellar rotational velocities is a powerful way to probe the many astrophysical phenomena that drive, or are driven by, the evolution of stellar angular momentum. In this paper, we present a novel data-driven approach to measuring the projected rotational velocity, vsini. Rather than directly measuring the broadening of spectral lines, we leverage the large information content of high-resolution spectral data to empirically estimate vsini. We adapt the framework laid down by The Cannon, which trains a generative model of the stellar flux as a function of wavelength using high-fidelity reference data, and can then produce estimates of stellar parameters and abundances for other stars directly from their spectra. Instead of modeling the flux as a function of wavelength, however, we model the first derivative of the spectra, as we expect the slopes of spectral lines to change as a function of vsini. This technique is computationally efficient and provides a means of rapidly estimating vsini for large numbers of stars in spectroscopic survey data. We analyze Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, constructing a model informed by high-fidelity stellar parameter estimates derived from high-resolution California Kepler Survey spectra of the same stars. We use the model to estimate vsini up to 15 kms^–1 for 27,000 APOGEE spectra, in fractions of a second per spectrum. Our estimates agree with the APOGEE vsini estimates to within 1.2 kms^–1.