Lucky Spectroscopy, an equivalent technique to Lucky Imaging

Spatially resolved spectroscopy of massive close visual binaries using the William Herschel Telescope

¹ Centro de Astrobiología, CSIC-INTA, Campus ESAC, Camino bajo del castillo s/n, 28692 Vill. de la Cañada, Madrid, Spain
e-mail: jmaiz@cab.inta-csic.es
² Departamento de Física y Astronomía, Universidad de La Serena, Av. Cisternas, 1200 Norte La Serena, Chile
³ Instituto de Astrofísica de Canarias, 38 200 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, 38 205 La Laguna, Tenerife Spain
⁵ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁶ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Escuela Politécnica Superior, Universidad de Alicante, Carretera San Vicente del Raspeig s/n, 03690 San Vicente del Raspeig, Alicante, Spain

Received: 23 February 2018
Accepted: 6 April 2018

Abstract

Context. Many massive stars have nearby companions whose presence hamper their characterization through spectroscopy.

Aims. We want to obtain spatially resolved spectroscopy of close massive visual binaries to derive their spectral types.

Methods. We obtained a large number of short long-slit spectroscopic exposures of five close binaries under good seeing conditions. We selected those with the best characteristics, extracted the spectra using multiple-profile fitting, and combined the results to derive spatially separated spectra.

Results. We demonstrate the usefulness of Lucky Spectroscopy by presenting the spatially resolved spectra of the components of each system, in two cases with separations of only ~0.′′3. Those are δ Ori Aa+Ab (resolved in the optical for the first time) and σ Ori AaAb+B (first time ever resolved). We also spatially resolve 15 Mon AaAb+B, ζ Ori AaAb+B (both previously resolved with GOSSS, the Galactic O-Star Spectroscopic Survey), and η Ori AaAb+B, a system with two spectroscopic B+B binaries and a fifth visual component. The systems have in common that they are composed of an inner pair of slow rotators orbited by one or more fast rotators, a characteristic that could have consequences for the theories of massive star formation.