The analysis is focused on the ability of galactic open clusters to trace the spiral arms, based on the recent data releases from Gaia. For this, a simple 1D description of the motion of spiral arms ...and clusters is introduced. As next step, results are verified using a widely accepted kinematic model of the motion in spiral galaxies. As expected, both approaches show that open clusters older than about 100 Myr are bad tracers of spiral arms. The younger clusters (ideally < 30 Myr) should be used instead. This agrees with the most recent observational evidence. The latest maps of the diffuse interstellar bands are compared with the spiral structure of the Milky Way and the Antennae Galaxies. The idea of these bands being useful for studying a galactic structure cannot be supported based on the current data.
ABSTRACT
With the use of the data from archives, we studied the correlations between the equivalent widths of four diffuse interstellar bands (4430, 5780, 5797, 6284 $\mathring{\rm A}$) and ...properties of the target stars (colour excess values, distances, and Galactic coordinates). Many different plots of the diffuse interstellar bands and their maps were produced and further analysed. There appears to be a structure in the plot of equivalent widths of 5780 $\mathring{\rm A}$ DIB (and 6284 $\mathring{\rm A}$ DIB) against the Galactic x-coordinate. The structure is well defined below ∼ 150 m$\mathring{\rm A}$ and within |x| < 250 pc, peaking around x = 170 pc. We argue that the origin of this structure is not a statistical fluctuation. Splitting the data in the Galactic longitude into several subregions improve or lower the well-known linear relation between the equivalent widths and the colour excess, which was expected. However, some of the lines of sight display drastically different behaviour. The region within 150° < l < 200° shows scatter in the correlation plots with the colour excess for all of the four bands with correlation coefficients R < 0.58. We suspect that the variation of physical conditions in the nearby molecular clouds could be responsible. Finally, the area 250° < l < 300° displays (from the statistical point of view) significantly lower values of equivalent widths than the other regions – this tells us that there is either a significant underabundance of carriers (when compared with the other regions) or that this has to be a result of an observational bias.
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.
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.
We outline the impact of a small two-band UV-photometry satellite mission on the field of stellar physics, magnetospheres of stars, binaries, stellar clusters, interstellar matter, and exoplanets. On ...specific examples of different types of stars and stellar systems, we discuss particular requirements for such a satellite mission in terms of specific mission parameters such as bandpass, precision, cadence, and mission duration. We show that such a mission may provide crucial data not only for hot stars that emit most of their light in UV, but also for cool stars, where UV traces their activity. This is important, for instance, for exoplanetary studies, because the level of stellar activity influences habitability. While the main asset of the two-band UV mission rests in time-domain astronomy, an example of open clusters proves that such a mission would be important also for the study of stellar populations. Properties of the interstellar dust are best explored when combining optical and IR information with observations in UV.
It is well known that dust absorbs UV radiation efficiently. Consequently, we outline how such a UV mission can be used to detect eclipses of sufficiently hot stars by various dusty objects and study disks, rings, clouds, disintegrating exoplanets or exoasteroids. Furthermore, UV radiation can be used to study the cooling of neutron stars providing information about the extreme states of matter in the interiors of neutron stars and used for mapping heated spots on their surfaces.
Very precise observational data are needed for studying the stellar cluster parameters (distance, reddening, age, metallicity) and cluster internal kinematics. In turn, these give us an insight into ...the properties of our Galaxy, for example, by giving us the ability to trace Galactic spiral structure, star formation rates and metallicity gradients. We investigated the available Gaia DR2 catalogue of 1229 open clusters and studied cluster distances, sizes and membership distributions in the 3D space. An appropriate analysis of the parallaxto-distance transformation problem is presented in the context of getting distances toward open clusters and estimating their sizes. Based on our investigation of the Gaia DR2 data we argue that, within 2 kpc, the inverse-parallax method gives comparable results (distances and sizes) as the Bayesian approach based on the exponentially decreasing volume density prior. Both of these methods show very similar dependence of the line-of-sight elongation of clusters (needle-like shapes resulting from the parallax uncertainties) on the distance. We also looked at a measure of elongations of the studied clusters and find the maximum distance of 665 pc at which a spherical fit still contains about half of the stellar population of a cluster. It follows from these results that the 3D structure of an open cluster cannot be properly studied beyond about 500 pc when using any of mentioned standard transformations of parallaxes to distances.
With the use of the data from archives, we studied the correlations between the equivalent widths of four diffuse interstellar bands (4430\(Å\), 5780\(Å\), 5797\(Å\), 6284\(Å\)) and properties of the ...target stars (colour excess values, distances and Galactic coordinates). Many different plots of the diffuse interstellar bands and their maps were produced and further analysed. There appears to be a structure in the plot of equivalent widths of 5780\(Å\) DIB (and 6284\(Å\) DIB) against the Galactic \(x\)-coordinate. The structure is well defined below \(\sim150\) m\(Å\) and within \(|x|<250\) pc, peaking around \(x=170\) pc. We argue that the origin of this structure is not a statistical fluctuation. Splitting the data in the Galactic longitude into several subregions improves or lowers the well known linear relation between the equivalent widths and the colour excess, which was expected. However, some of the lines of sight display drastically different behaviour. The region within \(150^\circ<l<200^\circ\) shows scatter in the correlation plots with the colour excess for all of the four bands with correlation coefficients \(\textrm{R}<0.58\). We suspect that the variation of physical conditions in the nearby molecular clouds could be responsible. Finally, the area \(250^\circ<l<300^\circ\) displays (from the statistical point of view) significantly lower values of equivalent widths than the other regions -- this tells us that there is either a significant underabundance of carriers (when compared with the other regions) or that this has to be a result of an observational bias.
This paper discusses the B{\"o}hm-Vitense gap, a gap in the colours of stars
that occurs when the atmosphere changes from radiative to convective in deep
layers. We are using different algorithms for ...detecting gaps in
colour-magnitude diagrams (CMDs), including the k-nearest neighbours (k-NN) and
UniDip algorithms. We propose using a combination of the k-NN algorithm and the
UniDip algorithm and manual verification to identify gaps unlikely to be of a
statistical origin. Using the $Gaia$ photometric system, i.e. $BP-RP$, we took
the data of 130 star clusters and searched for gaps in the ranges of 0.40 to
0.47\,mag, and 0.56 to 0.60\,mag, respectively. We analysed all data
statistically and identified the gaps in the individual clusters. Finally, we
applied the kernel density estimator to see how the gaps are distributed.
This paper discusses the B{\"o}hm-Vitense gap, a gap in the colours of stars that occurs when the atmosphere changes from radiative to convective in deep layers. We are using different algorithms for ...detecting gaps in colour-magnitude diagrams (CMDs), including the k-nearest neighbours (k-NN) and UniDip algorithms. We propose using a combination of the k-NN algorithm and the UniDip algorithm and manual verification to identify gaps unlikely to be of a statistical origin. Using the \(Gaia\) photometric system, i.e. \(BP-RP\), we took the data of 130 star clusters and searched for gaps in the ranges of 0.40 to 0.47\,mag, and 0.56 to 0.60\,mag, respectively. We analysed all data statistically and identified the gaps in the individual clusters. Finally, we applied the kernel density estimator to see how the gaps are distributed.
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