Measuring diffuse interstellar bands with cool stars

Abstract

Context. Diffuse Stellar Bands (DIBs) are ubiquitous in stellar spectra. Traditionally, they have been studied through their extraction from hot (early-type) stars, because of their smooth continuum. In an era where there are several going-on or planned massive Galactic surveys using multi-object spectrographs, cool (late-type) stars constitute an appealing set of targets. However, from the technical point of view, the extraction of DIBs in their spectra is more challenging due to the complexity of the continuum. Aims. In this contribution we will provide the community with an improved set of stellar lines in the spectral regions associated to the strong DIBs at λ6196.0, λ6269.8, λ6283.8, and λ6379.3. These lines will allow for the creation of better stellar synthetic spectra, reproducing the background emission and a more accurate extraction of the magnitudes associated with a given DIB (e.g. equivalent width, radial velocity). Methods. The Sun and Arcturus were used as representative examples of dwarf and giant stars, respectively. A high quality spectrum for each of them was modeled using TURBOSPECTRUM and the VALD stellar line list. The oscillator strength log(g f ) and/or wavelength of specific lines were modified to create synthetic spectra where the residuals in both the Sun and Arcturus were minimized. Results. The TURBOSPECTRUM synthetic spectra based on the improved line lists reproduce the observed spectra for the Sun and Arcturus in the mentioned spectral ranges with greater accuracy. Residuals between the synthetic and observed spectra are always ∼ < 10%, much better than with previously existing options. The new line list has been tested with some characteristic spectra, from a variety of stars, including both giant and dwarf stars, and under different degrees of extinction. As it happened with the Sun and Arcturus residuals in the fits used to extract the DIB information are smaller when using synthetic spectra made with the updated line lists. Tables with the updated parameters are provided to the community.

Mapping diffuse interstellar bands in the local ISM on small scales via MUSE 3D spectroscopy

“…Several of the observable transitions of ISM species as well as DIBs fall into regions of strong sky contamination. Successful modeling of the stellar contributions and the telluric absorption is key to precision measurements of the often quite weak (in the mÅ range) equivalent widths (see, i.e., Puspitarini et al 2013 andLallement 2017). While studies based on high resolution spectra can aim at modeling telluric absorption lines individually, these absorption bands are not resolved by the MUSE spectrograph.…”

Developing Automated Spectral Analysis Tools for Interstellar Features Extractionto Support Construction of the 3D ISM Map

“…The tools must disentangle the stellar continuum and all features presented in the observed spectrum. In principle, the spectrum is fitted by a combination of polynomial function or synthetic stellar model, IS profile model, and telluric transmission model (see Puspitarini et al 2013, Puspitarini et al 2015, Monreal-Ibero & Lallement 2017).…”