Dynamical ages of the young local associations with Gaia

Abstract

Context. The Young Local Associations (YLAs) constitute an excellent sample for the study of a variety of astrophysical topics, especially the star formation process in low-density environments. Data from the Gaia mission allows us to undertake studies of the YLAs with unprecedented accuracy. Aims. We determine the dynamical age and place of birth of a set of associations in a uniform and dynamically consistent manner. There are nine YLAs in our sample Chamaeleontis, TW Hydrae, β Pictoris, Octans, Tucana-Horologium, Columba, Carina, Argus, and AB Doradus. Methods. We designed a method for deriving the dynamical age of the YLAs based on the orbital integration. The method involves a strategy to account for the effect of observational errors. We tested the method using mock YLAs. Finally, we applied it to our set of nine YLAs with astrometry from the first Gaia data release and complementary on-ground radial velocities from the literature. Results. Our orbital analysis yields a first estimate of the dynamical age of 3 +9 −0 Myr, 13 +7 −0 Myr, and 5 +23 −0 Myr for Chamaeleontis, β Pictoris, and Tucana-Horologium, respectively. For four other associations (Octans, Columba, Carina, and Argus), we provide a lower limit for the dynamical age. Our rigorous error treatment indicates that TW Hydrae and AB Doradus deserve further study. Conclusions. The dynamical ages that we obtain are compatible spectroscopic and isochrone fitting ages obtained elsewhere. From the orbital analysis, we suggest a scenario for these YLAs where there were two episodes of star formation: one ∼ 40 Myr ago in the first quadrant that gave birth to Chamaeleontis, TW Hydrae, and β Pictoris, and another 5 − 15 Myr ago close to the Sun that formed Tucana-Horologium, Columba, and Carina. Future Gaia data will provide the necessary accuracy to improve the present results, especially for the controversial age determinations, and additional evidence for the proposed scenario once a complete census of YLAs and better membership can be obtained.

Birth Sites of Young Stellar Associations and Recent Star Formation in a Flocculent Corrugated Disk

“…To the associations listed by Gagné et al (2018a) we add the Argus association, but with measurements from the BANYAN analysis using the members and measurements by and a recently discovered ≈ 62 Myr old stellar association, µ Tau (Gagné et al 2020). We have checked that the results of the BANYAN analyses by Gagné et al (2018a) are consistent with the mean position and velocity measurements by other recent works (Binks et al 2015;Riedel et al 2017;Miret-Roig et al 2018).…”

“…We focus here on what we can learn from integrating the orbits of recent compilations of young stellar associations and star formation regions (e.g., Gagné et al 2018a). Backwards orbit integration has been used to the estimate kinematics of stellar associations by finding when their stellar members were likely to have been in proximity (de la Reza et al 2006;Miret-Roig et al 2018;Crundall et al 2019). Here we do not try to estimate kinematic ages, rather we search for patterns in the history of recent star formation near the Sun.…”

Dynamical traceback age of theβPictoris moving group

“…We consider the same 3D Milky Way potential as in Miret-Roig et al (2018) to integrate the equations of motion. This model is based on the Allen & Santillan (1991) potential which consists Table 4.…”

“…Following the example of other studies (e.g. Fernández et al 2008;Ducourant et al 2014;Mamajek & Bell 2014;Riedel et al 2017b;Miret-Roig et al 2018), we define the dynamical age as the time at which the members of the association were most concentrated in space. The algorithm to measure the degree of concentration, hereafter the size of the association, is of uttermost importance and different strategies to compute the size have been used in the literature.…”

“…We see that the vertical component does not provide useful information for constraining the age of the association, while the two components in the Galactic plane have a minimum at a similar time. In this panel we highlighted the azimuthal component (S η ) which is the size estimator we used in Miret-Roig et al (2018).…”