Dynamical orbital classification of selected N-rich stars with Gaia Data Release 2 astrometry

Abstract

We have used the galaxy modelling algorithm gravpot16, to explore the most probable orbital elements of a sample of 64 selected N-rich stars across the Milky Way. We use the newly measured proper motions from Gaia Data Release 2 with existing line-of-sight velocities from the second generation of the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) and spectrophotometric distance estimations from starhorse. We adopted a set of high-resolution particle simulations evolved in the same steady-state Galactic potential model with a bar, in order to identify the groups of N-rich stars that have a high probability of belonging to the bulge/bar, disc and stellar halo component. We find that the vast majority of the N-rich stars show typically maximum height from the Galactic plane below 3 kpc, and develop eccentric orbits (e > 0.5), which means that these stars appear to have bulge/bar-like and/or halo-like orbits. We also show that ∼66 per cent of the selected N-rich stars currently reside in the inner Galaxy inside the corotation radius, whilst ∼ 14 per cent are in halo-like orbits. Among the N-rich stars in the inner Galaxy, ∼ 27 per cent share orbital properties in the boundary between bulge/bar and disc, depending on the bar pattern speeds. Our dynamical analysis also indicates that some of the N-rich stars are likely to be halo interlopers, which suggests that halo contamination is not insignificant within the bulge area.

Jurassic: A chemically anomalous structure in the Galactic halo

“…This potential fits the structural and dynamical parameters of the Galaxy, based on recent knowledge of our MW. For each star, we computed an ensemble of orbits by assuming three different values for the angular velocity of the bar, Ω bar = 33, 43, and 53 km s −1 kpc −1 , with a bar mass of 1.1 × 10 10 M , and a present-day angle orientation of 20 • , in the same manner as in Fernández-Trincado et al (2020a). To model the uncertainty distributions, we sampled one million orbits using a simple Monte Carlo approach assuming Gaussian distributions for the input parameters (heliocentric distances, radial velocities, and proper motions), with 1σ equal to the errors of the input parameters as listed in Table A.1.…”

“…In this convention, the Sun's orbital velocity vector is 11.1, 12.24, 7.25] km s −1 (Brunthaler et al 2011). The model has been rescaled to the Sun's Galactocentric distance, 8 kpc, and a local rotation velocity of V LSR = 244.5 km s −1 (Fernández-Trincado et al 2020a).…”

The search for extratidal star candidates around Galactic globular clusters NGC 2808, NGC 6266, and NGC 6397 with Gaia DR2 astrometry

“…To get a general picture about their specific extra-tidal features, we computed the orbits of each cluster. To this purpose, we used the GravPot16 code 6 , which employs a physical and realistic (as far as possible) "boxy/peanut" bar model of the Galaxy along with other stellar components (see, e.g., Fernández-Trincado et al 2020c). For this study, we have caried out a backwards integration (until 3 Gyr) of an ensemble (one million simulations per cluster) for orbits of each cluster by adopting the same galactic configurations and a Monte Carlo approach, as described in Fernández-Trincado et al (2020c).…”

“…The plot is divided into three different regions corresponding to disk population, stellar halo and bulge/bar population (see Fig. 3 in Fernández-Trincado et al 2020c). The position of the cluster in this diagram gives us the membership probability corresponding to each Galactic component.…”

The enigmatic globular cluster UKS 1 obscured by the bulge: H-band discovery of nitrogen-enhanced stars

“…Globular clusters (GCs) are generally considered one of the key probes for revealing vital information about the mass-assembly history of the Milky Way (Khoperskov et al 2018;Minniti et al 2018;Massari et al 2019;Fernández-Trincado et al 2020;Hanke et al 2020). In the dawning era of the Gaia mission (Gaia Collaboration 2018), it has been possible to provide useful information on the fundamental parameters (see, e.g.…”