arXiv subjects

Germano G. Sacco

Publications and source records attributed to Germano G. Sacco.

3 recordsLinked to original sources

arXiv2025

The Dynamics of the Milky Way: Unveiling the 6D Skeleton of Star Formation in the 2040s

The Milky Way (MW) is our unique laboratory to test star formation theories at the level of individual stars, serving as the Rosetta Stone to interpret extragalactic observations. The proposed White Paper focuses on the following key questions regarding the structure and evolution of the MW traced by young stellar populations: Q1. How do large-scale dynamical instabilities, like warps and vertical waves, drive the star formation of the Galactic thin disk? Q2. Do star-forming regions form stochastically, driven by local self-propagating feedback, or are they triggered by a common dynamical process acting on Galactic scales? Do internal feedback loops and external interactions tend to sustain or quench star formation in the MW? Q3. Are the clustered star-forming regions the only environments where stars form, or can stars also form in more diffuse structures such as the stellar strings?

astro-ph.IM↗

arXiv2019

A kinematically unbiased, all-sky search for nearby, young, low-mass stars

The past two decades have seen dramatic progress in our knowledge of the population of young stars of age $< 200\,$Myr that lie within $150\,$pc of the Sun. These nearby, young stars, most of which are found in loose, comoving groups, provide the opportunity to explore (among many other things) the dissolution of stellar clusters and their diffusion into the field star population. Here, we exploit the combination of astrometric and photometric data from {\it Gaia} and photometric data from GALEX (UV) and 2MASS (near-IR) in an attempt to identify additional nearby, young, late-type stars. Specifically, we present a sample of 146 GALEX UV-selected late-type (predominantly K-type) field stars with {\it Gaia}-based distances $< 125\,$pc (based on {\it Gaia} Data Release 1) that have isochronal ages $< 80\,$Myr even if equal-components binaries. We investigate the spectroscopic and kinematic properties of this sample. Despite their young isochronal ages, only $\sim 10$ per cent) of stars among this sample can be confidently associated with established nearby, young moving groups (MGs). These candidate MG members include 5 stars newly identified in this study. The vast majority of our sample of 146 nearby young star candidates have anomalous kinematics relative to the known MGs. These stars may hence represent a previously unrecognised population of young stars that has recently mixed into the older field star population. We discuss the implications and caveats of such a hypothesis---including the intriguing fact that, in addition to their non-young-star-like kinematics, the majority of the UV-selected, isochronally young field stars within $50\,$pc appear surprisingly X-ray faint.

astro-ph.SR↗

arXiv2015

The Gaia-ESO Survey: Catalogue of H$α$ emission stars

We discuss the properties of H$α$ emission stars across the sample of 22035 spectra from the Gaia-ESO Survey internal data release, observed with the GIRAFFE instrument and largely belonging to stars in young open clusters. Automated fits using two independent Gaussian profiles and a third component that accounts for the nebular emission allow us to discern distinct morphological types of H$α$ line profiles with the introduction of a simplified classification scheme. All in all we find 3765 stars with intrinsic emission and sort their spectra into eight distinct morphological categories: single--component emission, emission blend, sharp emission peaks, double emission, P-Cygni, inverted P-Cygni, self--absorption, and emission in absorption. We have more than one observation for 1430 stars in our sample, thus allowing a quantitative discussion of the degree of variability of H$α$ emission profiles, which is expected for young, active objects. We present a catalogue of stars with properties of their H$α$ emission line profiles, morphological classification, analysis of variability with time and the supplementary information from the SIMBAD, VizieR, and ADS databases. The records in SIMBAD indicate the presence of H$α$ emission for roughly 25% of all stars in our catalogue, while at least 305 of them have already been more thoroughly investigated according to the references in ADS. The most frequently identified morphological categories in our sample of spectra are emission blend (23%), emission in absorption (22%), and self--absorption (16%). Objects with repeated observations demonstrate that our classification into discrete categories is generally stable through time, but categories P-Cygni and self--absorption seem less stable, which is the consequence of discrete classification rules, as well as of the fundamental change in profile shape.

astro-ph.SR↗