A Data-driven Technique for Measuring Stellar Rotation

• Published in: The Astrophysical journal Vol. 875; no. 1; pp. 8 - 20
• Main Authors: Gilhool, Steven H., Blake, Cullen H.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10-04-2019; IOP Publishing
• Subjects: Accuracy; Angular momentum; Astrophysics; Estimates; Galactic evolution; High resolution; Line spectra; Mathematical models; methods: data analysis; methods: statistical; Parameter estimation; Sky surveys (astronomy); Stars; stars: fundamental parameters; stars: rotation; Stellar evolution; Stellar models; Stellar rotation; surveys; techniques: spectroscopic
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ab0a74

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, v sin i . Rather than directly measuring the broadening of spectral lines, we leverage the large information content of high-resolution spectral data to empirically estimate v sin i . 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 v sin i . This technique is computationally efficient and provides a means of rapidly estimating v sin i 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 v sin i up to 15 km s − 1 for 27,000 APOGEE spectra, in fractions of a second per spectrum. Our estimates agree with the APOGEE v sin i estimates to within 1.2 km s − 1 .