Multiplicity of Massive stars in the Milky Way (M3W). I. Project description, UNWIND, application to GLS 11 448, and DIB catalog

Abstract

(ABRIDGED BUT NOT TOO FAR) Multiplicity is ubiquitous among massive stars and its understanding is constrained by the sample of well-determined orbits. The immediate goal of M3W is to significantly increase the number of massive multiple systems with well-determined orbits and masses. We will address issues such as multiplicity statistics, the mass function in clusters and the field, the properties of binaries with compact companions and gravitational-wave progenitors, the origin and characteristics of runaways and their 3-D motions, the use of apsidal motion as a probe of stellar interiors, and the mass discrepancy between different methods (evolutionary, spectroscopic, and Keplerian). In this first paper, we present the project; describe the data and tools that will be used, including the disentangling UNWIND tool; analyse the very massive twin binary system GLS 11 448; and briefly introduce some of the following papers of the series. We present a new orbit for GLS 11 448, using UNWIND to obtain for the first time disentangled spectra for the full 3820-11 000 $\mathring{A}$ range for an OB spectroscopic binary. We derive the stellar parameters, making new stellar lines available for the study of O stars. The Aa and Ab components of GLS 11 448, both classified as O3.5 II(f*), are the two most massive O stars ever detected according to the evolutionary masses of 70$\pm$10 M$_\odot$ and 76$\pm$11 M$_\odot$ determined in this paper. We also report the first-ever detection of the interstellar He I 10 830 triplet in absorption in an OB-star sightline. As a by-product of the ISM model derived for UNWIND using GLS 11 448 and five other standard stars, we present the most detailed diffuse-interstellar-band (DIB) library ever built, with a total of 631 DIBs in the 4000-17 100 $\mathring{A}$ range, of which 37 are fitted with multiple-Gaussian profiles and 119 had never been identified before.

Figures (11)

• Figure 1: Example of UNWIND output for the H$\alpha$ region of a GLS 11448.0 Aa,Ab spectroscopic epoch and the result of combining 77 epochs. The top spectra (green and blue) show the normalized output for the two components, shifted horizontally to the velocities of the epoch and upwards 0.1 continuum units, and diluted by their flux fractions. The bottom (orange and purple) spectra show the fitted telluric lines, specific to this epoch, and ISM spectrum, mostly DIBs and common to all epochs, in the two cases shifted downwards 0.1 units. The central spectra show the data (black) and fit (red) for this epoch, the fit being the sum of the green and blue spectra (minus one to leave the continuum fixed) multiplied by the orange and purple spectra.
• Figure 2: Phased radial velocity curves for GLS 11448.0 Aa and Ab.
• Figure 3: Disentangled Brackett (left) and Pfund (right) Heii series of GLS 11448.0 Aa (black) and Ab (red). The spectra are normalised, displaced in continuum units, and placed in the rest velocity frame of each component systemic velocity without taking into account wind infilling effects (hence, the small displacement in centroids towards the blue). Differences in S/N are caused by extinction increasing towards the blue and by the residuals of telluric-line subtraction (the most obvious ones being for Pf 5-8 and 5-10). The even-numbered Brackett series is not shown because of the proximity of the Hi Balmer series. The spectra have been degraded to $R=10000.0$ for display purposes.
• Figure 4: Disentangled blue-violet spectra of GLS 11448.0 Aa,Ab shifted to the stellar reference frame and degraded to the spectral classification resolution $R = 2500$. The two spectra are almost identical and there is no sign of the subtracted ISM. This is an update of Fig. 2 in Maizetal15a, where the S/N is higher but the spectra are not disentangled and the ISM is not subtracted.
• Figure 5: Section of the UNWIND extraction for GLS 11448.0 Aa (in the rest frame of the star determined from Table \ref{['orbitalparameters']}) with a significant portion of the Phillips C$_2$ (2,0) band. The black line is the star+ISM line (with the most prominent feature being the Hi Pa$\iota$ line) and the red line the fitted ISM, including the C$_2$ lines, DIBN8764, and DIBI8781. The vertical lines mark the expected position of the C$_2$ lines in the rest frame of the star, note the velocity displacement.