26 research outputs found
Evaporation Ages: a New Dating Method for Young Star Clusters
The ages of young star clusters are fundamental clocks to constrain the
formation and evolution of pre-main-sequence stars and their protoplanetary
disks and exoplanets. However, dating methods for very young clusters often
disagree, casting doubts on the accuracy of the derived ages. We propose a new
method to derive the kinematic age of star clusters based on the evaporation
ages of their stars. The method is validated and calibrated using hundreds of
clusters identified in a supernova-driven simulation of the interstellar medium
forming stars for approximately 40 Myr within a 250 pc region. We demonstrate
that the clusters' evaporation-age uncertainty can be as small as about 10% for
clusters with a large enough number of evaporated stars and small but realistic
observational errors. We have obtained evaporation ages for a pilot sample of
10 clusters, finding a good agreement with their published isochronal ages. The
evaporation ages will provide important constraints for modeling the
pre-main-sequence evolution of low-mass stars, as well as to investigate the
star-formation and gas-evaporation history of young clusters. These ages can be
more accurate than isochronal ages for very young clusters, for which
observations and models are more uncertain.Comment: 13 pages, 11 figures, 2 tables, submitted to A&A on Nov 14th, 202
The star formation history of Upper Scorpius and Ophiuchus
We aim to study spatial and kinematic substructures of the region encompassed
by Upper Scorpius and Ophiuchus star-forming regions, determining dynamical
traceback ages and studying the star formation history of the complex. We
identified seven different groups in this region. Four groups (nu Sco, beta
Sco, sigma Sco and delta Sco) are part of Upper Scorpius, two groups (rho Oph
and alpha Sco) are in Ophiuchus, and another group (pi Sco) is a nearby young
population. We found an age gradient from the rho Oph group (the youngest) to
the delta Sco group (<~5 Myr), showing that star formation was a sequential
process for the past 5 Myr. Our traceback analysis shows that Upper Scorpius
and rho Oph groups share a common origin. The closer group of pi Sco is
probably older, and the traceback analysis suggests that this group and the
alpha Sco group have a different origin, likely related to other associations
in the Sco-Cen complex. Our study shows that this region has a complex star
formation history that goes beyond the current formation scenario, likely a
result of stellar feedback from massive stars, supernovae explosions, and
dynamic interactions between stellar groups and the molecular gas. In
particular, we speculate that photo-ionisation from the massive delta Sco star
could have triggered star formation first in the beta Sco group and then in the
nu Sco group. The perturbations of stellar orbits due to stellar feedback and
dynamical interactions could also be responsible for the 1-3 Myr difference
that we found between dynamical traceback ages and isochronal ages.Comment: Accepted for publication in A&
The Corona Australis star formation complex is accelerating away from the Galactic plane
We study the kinematics of the recently discovered Corona Australis (CrA)
chain of clusters by examining the 3D space motion of its young stars using
Gaia DR3 and APOGEE-2 data. While we observe linear expansion between the
clusters in the Cartesian XY directions, the expansion along Z exhibits a
curved pattern. To our knowledge, this is the first time such a nonlinear
velocity-position relation has been observed for stellar clusters. We propose a
scenario to explain our findings, in which the observed gradient is caused by
stellar feedback, accelerating the gas away from the Galactic plane. A
traceback analysis confirms that the CrA star formation complex was located
near the central clusters of the Scorpius Centaurus (Sco-Cen) OB association
10-15 Myr ago. It contains massive stars and thus offers a natural source of
feedback. Based on the velocity of the youngest unbound CrA cluster, we
estimate that a median number of about two supernovae would have been
sufficient to inject the present-day kinetic energy of the CrA molecular cloud.
This number agrees with that of recent studies. The head-tail morphology of the
CrA molecular cloud further supports the proposed feedback scenario, in which a
feedback force pushed the primordial cloud from the Galactic north, leading to
the current separation of 100 pc from the center of Sco-Cen. The formation of
spatially and temporally well-defined star formation patterns, such as the CrA
chain of clusters, is likely a common process in massive star-forming regions.Comment: Accepted for publication as a Letter in Astronomy and Astrophysic
The cosmic DANCe of Perseus I: Membership, phase-space structure, mass, and energy distributions
Context. Star-forming regions are excellent benchmarks for testing and
validating theories of star formation and stellar evolution. The Perseus
star-forming region being one of the youngest (<10 Myr), closest (280-320 pc),
and most studied in the literature, is a fundamental benchmark. Aims. We aim to
study the membership, phase-space structure, mass, and energy (kinetic plus
potential) distribution of the Perseus star-forming region using public
catalogues (Gaia, APOGEE, 2MASS, PanSTARRS). Methods. We use Bayesian
methodologies accounting for extinction to identify the Perseus physical groups
in the phase-space, retrieve their candidate members, derive their properties
(age, mass, 3D positions, 3D velocities, and energy), and attempt to
reconstruct their origin. Results. We identify 1052 candidate members in seven
physical groups (one of them new) with ages between 3 and 10 Myr, dynamical
super-virial states, and large fractions of energetically unbound stars. Their
mass distributions are broadly compatible with that of Chabrier for masses >0.1
and do not show hints of over-abundance of low-mass stars in NGC1333
with respect to IC348. These groups' ages, spatial structure, and kinematics
are compatible with at least three generations of stars. Future work is still
needed to clarify if the formation of the youngest was triggered by the oldest.
Conclusions. The exquisite Gaia data complemented with public archives and
mined with comprehensive Bayesian methodologies allow us to identify 31% more
members than in previous studies, discover a new physical group (Gorgophone: 7
Myr, 191 members, and 145 ), and confirm that the spatial, kinematic,
and energy distributions of these groups support the hierarchical
star-formation scenario.Comment: Accepted for publication in Astronomy & Astrophysics, 29 pages, 22
Figures, 8 tables one of them electroni
NGC 6705 a young -enhanced Open Cluster from OCCASO data
The stellar [/Fe] abundance is sometimes used as a proxy for stellar
age, following standard chemical evolution models for the Galaxy, as seen by
different observational results. In this work we show that the Open Cluster
NGC6705/M11 has a significant -enhancement [/Fe] dex,
despite its young age (300 Myr), challenging the current paradigm. We use
high resolution (R) high signal-to-noise (70) spectra of 8 Red
Clump stars, acquired within the OCCASO survey. We determine very accurate
chemical abundances of several elements, using an equivalent width
methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain
[Si/Fe]=, [Mg/Fe]=, [O/Fe]=,
[Ca/Fe]= and [Ti/Fe]=. Our results place these
cluster within the group of young [/Fe]-enhanced field stars recently
found by several authors in the literature. The ages of our stars have an
uncertainty of around 50 Myr, much more precise than for field stars. By
integrating the cluster's orbit in several non-axisymmetric Galactic
potentials, we establish the M11's most likely birth radius to lie between
6.8-7.5 kpc from the Galactic center, not far from its current position. With
the robust Open Cluster age scale, our results prove that a moderate
[/Fe]-enhancement is no guarantee for a star to be old, and that not
all -enhanced stars can be explained with an evolved blue straggler
scenario. Based on our orbit calculations, we further argue against a Galactic
bar origin of M11.Comment: 10 pages, 6 figures, accepted in A&
IC 4665 DANCe I. Members, empirical isochrones, magnitude distributions, present-day system mass function, and spatial distribution
Context. The study of star formation is extremely challenging, due to the lack of complete and clean samples of young nearby clusters
and star-forming regions. The recent Gaia DR2 catalogue complemented with the deep ground-based COSMIC DANCe catalogue
o ers a new database of unprecedented accuracy to revisit the membership of clusters and star-forming regions. The 30 Myr open
cluster IC 4665 is one of the few well-known clusters of this age and it is an excellent target where evolutionary models can be tested
and planetary formation studied.
Aims. We provide a comprehensive membership analysis of IC 4665 and study the following properties: empirical isochrones, distance,
magnitude distribution, present-day system mass function, and spatial distribution.
Methods. We used the Gaia DR2 catalogue together with the DANCe catalogue to look for members via a probabilistic model of the
distribution of the observable quantities in both the cluster and background populations.
Results. We obtained a final list of 819 candidate members that cover a 12.4 magnitude range (7 < J < 19:4). We find that 50%
are new candidates, and we estimate a conservative contamination rate of 20%. This unique sample of members allows us to obtain
a present-day system mass function in the range of 0.02–6 M , which reveals a number of details not seen in previous studies. In
addition, we find that a spherically symmetric spatial distribution is favoured by our final list of members for this young open cluster.
Conclusions. Our membership analysis represents a significant increase in the quantity and quality (low contamination) with respect
to previous studies. It o ers an excellent opportunity to revisit other fundamental parameters such as age
Searching for debris discs in the 30 Myr open cluster IC 4665
Context. Debris discs orbiting young stars are key to understanding dust evolution and the planetary formation process. We take advantage of a recent membership analysis of the 30 Myr nearby open cluster IC 4665 based on the Gaia and DANCe surveys to revisit the disc population of this cluster.Aims. We aim to study the disc population of IC 4665 using Spitzer (MIPS and IRAC) and WISE photometry.Methods. We use several colour–colour diagrams with empirical photospheric sequences to detect the sources with an infrared excess. Independently, we also fit the spectral energy distribution (SED) of our debris-disc candidates with the Virtual Observatory SED analyser (VOSA) which is capable of automatically detecting infrared excesses and provides effective temperature estimates.Results. We find six candidate debris-disc host stars (five with MIPS and one with WISE), two of which are new candidates. We estimate a disc fraction of 24 ± 10% for the B–A stars, where our sample is expected to be complete. This is similar to what has been reported in other clusters of similar ages (Upper Centaurus Lupus, Lower Centaurus Crux, the β Pictoris moving group, and the Pleiades). For solar-type stars we find a disc fraction of 9 ± 9%, which is lower than that observed in regions with comparable ages.Conclusions. Our candidate debris-disc host stars are excellent targets to be studied with ALMA or the future James Webb Space Telescope (JWST)
Unravelling the luminosity distribution of IC 4665
The study of star formation is extremely challenging due to the lack of complete and low-contaminated samples of young, nearby, clusters and star forming regions. We aim at providing a membership analysis with a high completeness and low contamination of the young, nearby, open cluster IC4665. We apply modern Bayesian statistical tools to the recent Gaia DR2 catalogue to identify high probability members. We find a list of 543 members of IC4665 with membership probabilities >87%, 251 of which are new members. We compute the magnitude distribution of these sample which peaks at G˜10, equivalent to ˜0.25 M_⊙
Comprehensive study of IC4665
IC 4665 is one of the few well-known, young (30 Myr), open clusters in the solar neighbourhood. The relatively young age of this cluster provides a key anchor to study the stellar and planetary formation process. In addition it is a good target where to test evolutionary models. We aim to provide a comprehensive membership analysis of this open cluster which allows to study its properties (empirical isochrones, luminosity and mass functions, spatial distribution). We combine the Gaia DR2 catalogue together with the deep, ground based COSMIC DANCe catalogue to compute membership probabilities. We find 819 candidate members of IC 4665 with high membership probabilities, 50% of which are new members, and we estimate that 20% might be contaminants. This represents a signicant increase in the quantity and quality (higher completeness and low-contamination) with respect to previous studies. Our members include objects of sub-stellar masses which we will spectroscopically follow-up in order to do a spectral classication and search for possible companions