Simultaneous J-, H-, K- and L-band spectroscopic observations of galactic Be stars. I. IR atlas

Abstract

It is already accepted that Be stars are surrounded by circumstellar envelopes, which are mostly compatible with a disc geometry in Keplerian rotation. We aim to obtain a more complete characterisation of the properties of the circumstellar environment of Be stars that helps to constrain the theoretical models of the Be phenomenon. We present near-infrared, medium-resolution spectra of a sample of galactic Be stars with different spectral subtypes and luminosity classes. We measure different parameters of the hydrogen recombination lines from the Paschen, Brackett, Pfund, and Humphreys series, and use them to diagnose physical conditions in the circumstellar environment. We analysed the equivalent-width (EW) ratio between Br$\alpha$ and Br$\gamma$ lines and different diagrams of flux ratios. We also identify lines from He I, C I, N I, O I, Na I, Mg I, Mg II, Si I, Fe I, and Fe II. Analysing the EW measurements of particular He I, Mg II, Fe I, Fe II and O I lines, we find that for some lines they correlate with the spectral type of the star. Particularly, the emission of the O I~$\lambda 1.3168\mu$m line decreases towards the later spectral types. We present an atlas of 22 Be stars, that covers a wide infrared (IR) spectral range with quasi-simultaneous observations. From a detailed analysis, we define new complementary criteria to Mennickent's classification of Be stars according to their disc opacity. Some objects in our sample present compact thick envelopes, while in others the envelope is extended and optically thin. The correlation between the full widths at half maximum (FWHM) and the peak separation ($\Delta \mathrm{V}$) versus $V\sin i$ for the Br10, Br$\delta$, and Hu14 lines reveals that the broadening mechanism is rotational. The Ly$\beta$ fluorescence is a key mechanism to explain the intensity of the emission of Mg II and O I lines.

27 pages, 14 figures. Accepted for publication in A&A

References in corpus (7)

• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• A brief introductory guide to TLUSTY and SYNSPEC
• High-resolution, H band Spectroscopy of Be Stars with SDSS-III/APOGEE: I. New Be Stars, Line Identifications, and Line Profiles
• L-band spectra of 13 outbursting Be stars
• Spectral classification of B stars: The empirical sequence using SDSS-IV/APOGEE near-IR data
• Be and Bn stars: Balmer discontinuity and stellar-class relationship
• Intriguing detection of ${}^{12}$CO molecular emission in a classical Be star

Cited by in corpus (1)

• A survey for variable young stars with small telescopes: VI -- Analysis of the outbursting Be stars NSW284, Gaia19eyy, and VES263