A Profile Analysis of Raman-scattered O VI Bands at 6825 \AA\ and 7082 \AA\ in Sanduleak's Star

TL;DR

This paper models the Raman-scattered O VI bands in Sanduleak's star, revealing complex profiles and a detailed structure of the emission regions, with implications for the star's neutral hydrogen column density.

Contribution

It provides the first detailed profile analysis and modeling of Raman O VI bands in Sanduleak's star, including high-resolution spectra and Monte Carlo simulations.

Findings

Raman 6825 Å band shows a broad profile with a red bump.

Raman 7082 Å band exhibits a triple-peak profile.

Neutral hydrogen column density estimated at ~1×10^{23} cm^{-2}.

Abstract

We present a detailed modeling of the two broad bands observed at 6825 \AA\ and 7082 \AA\ in Sanduleak's star, a controversial object in the Large Magellanic Cloud. These bands are known to originate from Raman-scattering of O VI $\lambda\lambda$ 1032 and 1038 photons with atomic hydrogen and are only observed in bona fide symbiotic stars. Our high-resolution spectrum obtained with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph at the Magellan-Clay Telescope reveals, quite surprisingly, that the profiles of the two bands look very different: while the Raman 6825 \AA\ band shows a single broad profile with a redward extended bump, the Raman 7082 \AA\ band exhibits a distinct triple-peak profile. Our model suggests that the O VI emission nebula can be decomposed into a red, blue and central emission regions from an accretion disk, a bipolar outflow and a further compact, optically thick region. We also perform Monte Carlo simulations with the aim of fitting the observed flux ratio $F(6825)/F(7082) \sim 4.5$, which indicate that the neutral region in Sanduleak's star is characterized by the column density $N_{HI} \sim 1 \times 10^{23} {\rm\ cm^{-2}}$.