Free-floating planets (FFPs) are the lightest products of star formation and they carry important information on the initial conditions of the environment in which they were formed. They were first ...discovered in the 2000 s but still few of them have been identified and confirmed due to observational challenges. This is a review of the last advances in the detection of these objects and the understanding of their origin. Several studies indicate that the observed fraction of FFPs outnumbers the prediction of turbulent fragmentation and suggest that many were formed in planetary systems that were later abandoned. The JWST will certainly constitute a new step further in the detection and characterisation of FFPs. To interpret these new observations, precise ages for the nearby star-forming regions in which they were formed will be necessary.
VISIONS: the VISTA Star Formation Atlas Meingast, Stefan; Alves, João; Bouy, Hervé ...
Astronomy and astrophysics (Berlin),
05/2023, Letnik:
673
Journal Article
Recenzirano
Odprti dostop
VISIONS is an ESO public survey of five nearby (
d
< 500 pc) star-forming molecular cloud complexes that are canonically associated with the constellations of Chamaeleon, Corona Australis, Lupus, ...Ophiuchus, and Orion. The survey was carried out with the Visible and Infrared Survey Telescope for Astronomy (VISTA), using the VISTA Infrared Camera (VIRCAM), and collected data in the near-infrared passbands
J
(1.25 μm), H (1.65 μm), and
K
S
(2.15 μm). With a total on-sky exposure time of 49.4h VISIONS covers an area of 650 deg
2
, it is designed to build an infrared legacy archive with a structure and content similar to the Two Micron All Sky Survey (2MASS) for the screened star-forming regions. Taking place between April 2017 and March 2022, the observations yielded approximately 1.15 million images, which comprise 19 TB of raw data. The observations undertaken within the survey are grouped into three different subsurveys. First, the wide subsurvey comprises shallow, large-scale observations and it has revisited the star-forming complexes six times over the course of its execution. Second, the deep subsurvey of dedicated high-sensitivity observations has collected data on areas with the largest amounts of dust extinction. Third, the control subsurvey includes observations of areas of low-to-negligible dust extinction. Using this strategy, the VISIONS observation program offers multi-epoch position measurements, with the ability to access deeply embedded objects, and it provides a baseline for statistical comparisons and sample completeness – all at the same time. In particular, VISIONS is designed to measure the proper motions of point sources, with a precision of 1 mas yr
−1
or better, when complemented with data from the VISTA Hemisphere Survey (VHS). In this way, VISIONS can provide proper motions of complete ensembles of embedded and low-mass objects, including sources inaccessible to the optical ESA
Gaia
mission. VISIONS will enable the community to address a variety of research topics from a more informed perspective, including the 3D distribution and motion of embedded stars and the nearby interstellar medium, the identification and characterization of young stellar objects, the formation and evolution of embedded stellar clusters and their initial mass function, as well as the characteristics of interstellar dust and the reddening law.
ABSTRACT
The Tucana-Horologium association is one of the closest young stellar groups to the Sun and despite the close proximity its age is still debated in the literature. We take advantage of the ...state-of-the-art astrometry delivered by the third data release of the Gaia space mission combined with precise radial velocity measurements obtained from high-resolution spectroscopy to investigate the dynamical age of the association. We perform an extensive traceback analysis using a combination of different samples of cluster members, metrics to evaluate the minimum size of the association in the past and models for the galactic potential to integrate the stellar orbits back in time. The dynamical age of $38.5^{+1.6}_{-8.0}$ Myr that we derive in this paper is consistent with the various age estimates obtained from isochrone fitting in the literature (30–50 Myr) and reconciles, for the first time, the dynamical age of the Tucana-Horologium association with the age obtained from lithium depletion (∼40 Myr). Our results are independent from stellar models and represent one more step towards constructing a self-consistent age scale for the young stellar groups of the Solar neighbourhood based on the 3D space motion of the stars.
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.
Tycho's Supernova: The View from Gaia Ruiz-Lapuente, Pilar; González Hernández, Jonay I.; Mor, Roger ...
The Astrophysical journal,
01/2019, Letnik:
870, Številka:
2
Journal Article
Recenzirano
Odprti dostop
SN 1572 (Tycho Brahe's supernova) clearly belongs to the Ia (thermonuclear) type. It was produced by the explosion of a white dwarf (WD) in a binary system. Its remnant has been the first of this ...type to be explored in search of a possible surviving companion, the mass donor that brought the WD to the point of explosion. A high peculiar motion with respect to the stars at the same location in the Galaxy, mainly due to the orbital velocity at the time of the explosion, is a basic criterion for the detection of such companions. Radial velocities from the spectra of the stars close to the geometrical center of Tycho's supernova remnant, plus proper motions of the same stars, obtained by astrometry with the Hubble Space Telescope (HST), have been used so far. In addition, a detailed chemical analysis of the atmospheres of a sample of candidate stars had been made. However, the distances to the stars remained uncertain. Now, the Second Gaia Data Release (DR2) provides unprecedented accurate distances, and new proper motions for the stars can be compared with those obtained from the HST. We consider the Galactic orbits that the candidate stars to the SN companion would have in the future. We do this to explore any kinematic peculiarity. We also locate a representative sample of candidate stars in the Toomre diagram. Using the new data, we re-evaluate the status of the candidates suggested thus far, as well as the larger sample of the stars seen in the central region of the remnant.
We reconstructed the star formation history of the Sco-Cen OB association using a novel high-resolution age map of the region. We developed an approach to produce robust ages for Sco-Cen’s recently ...identified 37 stellar clusters using the
SigMA
algorithm. The Sco-Cen star formation timeline reveals four periods of enhanced star formation activity, or bursts, remarkably separated by about 5 Myr. Of these, the second burst, which occurred about 15 million years ago, is by far the dominant one, and most of Sco-Cen’s stars and clusters were in place by the end of this burst. The formation of stars and clusters in Sco-Cen is correlated but not linearly, implying that more stars were formed per cluster during the peak of the star formation rate. Most of the clusters that are large enough to have supernova precursors were formed during the second burst around 15 Myr ago. Star and cluster formation activity has been continuously declining since then. We have clear evidence that Sco-Cen formed from the inside out and that it contains 100-pc long chains of contiguous clusters exhibiting well-defined age gradients, from massive older clusters to smaller young clusters. These observables suggest an important role for feedback in forming about half of Sco-Cen stars, although follow-up work is needed to quantify this statement. Finally, we confirm that the Upper-Sco age controversy discussed in the literature during the last decades is solved: the nine clusters previously lumped together as Upper-Sco, a benchmark region for planet formation studies, exhibit a wide range of ages from 3 to 19 Myr.
Age is one of the most fundamental parameters of stars, yet it is one of the hardest to determine as it requires modelling various aspects of stellar formation and evolution. When we compare the ages ...derived from isochronal and dynamical traceback methods for six young stellar associations, we find a systematic discrepancy. Specifically, dynamical traceback ages are consistently younger by an average of \(\langle\Delta_{\rm Age}\rangle = 5.5 \pm 1.1\) Myr. We rule out measurement errors as the cause of the age mismatch and propose that \(\Delta_{\rm Age}\) indicates the time a young star remains bound to its parental cloud before moving away from its siblings. In this framework, the dynamical traceback "clock" starts when a stellar cluster or association begins to expand after expelling most of the gas, while the isochronal "clock" starts earlier when most stars form. The difference between these two age-dating techniques is a powerful tool to constraint evolutionary models, as isochronal ages cannot be younger than dynamical traceback ages. Measuring the \(\Delta_{\rm Age}\) accurately and understanding its variations across different environments will provide further information on the impact of local conditions and stellar feedback on the formation and dispersal of stellar clusters.
Free-floating planets (FFPs) are the lightest products of star formation and they carry important information on the initial conditions of the environment in which they were formed. They were first ...discovered in the 2000s but still few of them have been identified and confirmed due to observational challenges. This is a review of the last advances in the detection of these objects and the understanding of their origin. Several studies indicate that the observed fraction of FFPs outnumbers the prediction of turbulent fragmentation and suggest that many were formed in planetary systems that were later abandoned. The JWST will certainly constitute a new step further in the detection and characterisation of FFPs. To interpret these new observations, precise ages for the nearby star-forming regions in which they were formed will be necessary.
PDF
