Toward a 3D kinetic tomography of Taurus clouds. I. Linking neutral potassium and dust

Abstract

Context. Gaia parallaxes and photometric measurements open a three-dimensional (3D) era for the Milky Way, including its interstellar (IS) matter. Three-dimensional Galactic dust distributions are constructed in various ways, based on Gaia data and photometric or spectroscopic surveys. Aims. The assignment of radial motions to IS dust structures seen in 3D, or 3D kinetic tomography, would be a valuable tool allowing one to connect the structures to emission lines of the associated gas, which are now measured at increasingly higher spectral and angular resolutions, and rich in information on physical and chemical processes. To this end, one of the potential techniques is to establish a link between dust clouds and Doppler velocities of absorption lines imprinted in stellar spectra by the gas associated with the dust. This requires a relatively close correlation between the absorber column and the dust opacity. We have investigated the link between the strength of interstellar K I absorption and the opacity of the dust in front of stars in the Taurus area, and we have tested the feasibility of assigning velocities to 3D dust clouds on the basis of K I absorption data. Methods. We have obtained high spectral resolution and high signal-to-noise spectra of 58 early-type stars in the direction of the Taurus, Perseus, and California molecular clouds. We have developed a new, dual interstellar and telluric profile-fitting technique to extract the interstellar K I λλ 7665, 7699 Å absorption lines from stellar spectra and applied it to the new data and to archived spectra of 58 additional targets. In parallel, we have updated 3D dust maps reconstructed through the inversion of individual stellar light extinctions. To do so, we supplemented the catalog of extinction estimates based on Gaia and 2MASS photometry with recently published extinction catalogs based on stellar spectroscopic surveys. We used the 3D map and the set of velocity components seen in absorption to assign radial velocities to the dust clouds distributed along their paths in the most consistent way. Results. We illustrate our profile-fitting technique and present the K I velocity structure of the dense ISM along the paths to all targets. As a validation test of the dust map, we show comparisons between distances to several reconstructed clouds with recent distance assignments based on different techniques. Target star extinctions estimated by integration in the 3D map are compared with their K I 7699 Å absorptions and the degree of correlation is found comparable to the one between the same K I line and the total hydrogen column for stars distributed over the sky that are part of a published high resolution survey. We show images of the updated dust distribution in a series of vertical planes in the Galactic longitude interval 150–182.5° and our estimated assignments of radial velocities to the opaque regions. Most clearly defined K I absorptions may be assigned to a dense dust cloud between the Sun and the target star. It appeared relatively straightforward to find a velocity pattern consistent will all absorptions and ensuring coherence between adjacent lines of sight, at the exception of a few weak lines. We compare our results with recent determinations of the velocities of several clouds and find good agreement. These results demonstrate that the extinction-K I relationship is tight enough to allow one to link the radial velocity of the K I lines to the dust clouds seen in 3D and that their combination may be a valuable tool in building a 3D kinetic structure of the dense ISM. We discuss limitations and perspectives for this technique.

A catalogue of white dwarfs in Gaia EDR3

“…The hierarchical inversion is using extinction catalogues from Sanders & Das (2018) and Queiroz et al (2020) that are based on major spectroscopic surveys, and, during the inversion, the map presented in Lallement et al (2019), which is based on photometry from Gaia and the Two Micron All-Sky Survey (2MASS), is used as a prior distribution and as a final solution in regions of space devoid of spectroscopic survey targets. A more detailed description of this type of data combination, for Sanders & Das (2018) data solely, can be found in Ivanova et al (2021). This 4 × 4 × 0.8 kpc 3 new map (X, Y axes in the plane and Z-axis along Galactic poles) is particularly well suited for nearby stellar sources such as white dwarfs, because spectroscopic surveys are generally targeting brighter, closer stars.…”

Discovery of a thin lithium plateau among metal-poor red giant branch stars

“…The T eff values were derived adopting the (BP − RP) 0 -T eff transformation from Mucciarelli et al (2021). Colour excesses were estimated from integration within 3D extinction maps (Ivanova et al 2021) except for the star HE0401-0138, for which we adopted the value from Schlafly & Finkbeiner (2011). For very distant halo stars that fall outside the maps, we used the upper limits based on dust emission from Planck Collaboration Int.…”

Discovery of a thin lithium plateau among metal-poor red giant branch stars

“…T eff have been derived adopting the (BP − RP) 0 -T eff transformation by Mucciarelli, Bellazzini & Massari (2021). Colour excesses are estimated from integration within 3D extinction maps (Ivanova et al 2021) but for the star HE0401-0138, for which we adopted the value by Schlafly & Finkbeiner (2011). For very distant halo stars falling out of the maps, we used the upper limits based on dust emission from Planck Collaboration et al ( 2016), in all cases very close to the value achieved at the map boundary.…”