Context.
Stars tend to form in clusters, but many escape their birth clusters very early. Identifying the escaped members of clusters can inform us about the dissolution of star clusters, but also ...about the stellar dynamics in the galaxy. Methods capable of finding escaped stars from many clusters are required to fully exploit the large amounts of data in the
Gaia
era.
Aims.
We present a new method of identifying escaped members of nearby clusters and apply it to ten young clusters.
Methods.
We assumed the escaped stars were close to the cluster in the past and performed traceback computations based on the
Gaia
DR3 radial velocity subsample. For each individual star, our method produces a probability estimate that it is an escaped member of a cluster, and for each cluster it also estimates the field star contamination rate of the identified fugitives.
Results.
Our method is capable of finding fugitives that have escaped from their cluster in the last few ten million years. In many cases the fugitives form an elongated structure that covers a large volume.
Conclusions.
The results presented here show that traceback computations using
Gaia
DR3 data can identify stars that have recently escaped their cluster. Our method will be even more useful when applied to future
Gaia
data releases that contain more radial velocity measurements.
Aims. We analyze the surroundings of HD 97300, one of two intermediate-mass stars in the Chamaeleon I star-forming region. The star is known to be surrounded by a conspicuous ring of polycyclic ...aromatic hydrocarbons (PAHs). Methods. We present infrared images taken with Herschel and Spitzer using 11 different broad-band filters between 3.6 μm and 500 μm. We compare the morphology of the emission using cuts along different position angles. We construct spectral energy distributions, which we compare to different dust models, and calculate dust temperatures. We also derive opacity maps and analyze the density structure of the environment of HD 97300. Results. We find that HD 97300 has no infrared excess at or below 24 μm, confirming its zero-age main-sequence nature. The morphology of the ring is very similar between 3.6 μm and 24 μm. The emission at these wavelengths is dominated by either PAH features or PAH continuum. At longer wavelengths, only the northwestern part of the ring is visible. A fit to the 100–500 μm observations suggests that the emission is due to relatively warm ( ≈ 26 K) dust. The temperature gradually decreases with increasing distance from the ring. We find a general decrease in the density from north to south, and an approximate 10% density increase in the northeastern part of the ring. Conclusions. Our results are consistent with the theory that the ring around HD 97300 is essentially a bubble blown into the surrounding interstellar matter and heated by the star.
We investigate the long-term optical–infrared variability of SV Cep and explain it in the context of an existing UX Ori (UXOR) model. A 25-month monitoring programme was completed with the Infrared ...Space Observatory in the 3.3–100 μm wavelength range. Following a careful data reduction, the infrared light curves were correlated with the variations of SV Cep in the V band. A remarkable correlation was found between the optical and the far-infrared light curves. In the mid-infrared regime, the amplitude of variations is lower, with a hint for a weak anti-correlation with the optical changes. In order to interpret the observations, we modelled the spectral energy distribution of SV Cep assuming a self-shadowed disc with a puffed-up inner rim, using a two-dimensional radiative transfer code. We found that modifying the height of the inner rim, the wavelength dependence of the long-term optical–infrared variations is well reproduced, except the mid-infrared domain. The origin of variation of the rim height might be fluctuation in the accretion rate in the outer disc. In order to model the mid-infrared behaviour, we tested adding an optically thin envelope to the system, but this model failed to explain the far-infrared variability. Infrared variability is a powerful tool to discriminate between models of the circumstellar environment. The proposed mechanism of variable rim height may not be restricted to UXOR stars, but might be a general characteristic of intermediate-mass young stars.
Context.
Tidal tails of star clusters are commonly understood to be populated symmetrically. Recently, the analysis of
Gaia
data revealed large asymmetries between the leading and trailing tidal tail ...arms of the four open star clusters Hyades, Praesepe, Coma Berenices, and NGC 752.
Aims.
As the evaporation of stars from star clusters into the tidal tails is a stochastic process, the degree of stochastic asymmetry is quantified in this work.
Methods.
For each star cluster, 1000 configurations of test particles were integrated in the combined potential of a Plummer sphere and the Galactic tidal field over the lifetime of the particular star cluster. For each of the four star clusters, the distribution function of the stochastic asymmetry was determined and compared with the observed asymmetry.
Results.
The probabilities for a stochastic origin of the observed asymmetry of the four star clusters are ≈1.7
σ
for Praesepe, ≈2.4
σ
for Coma Berenices, ≈6.7
σ
for Hyades, and ≈1.6
σ
for NGC 752.
Conclusions.
In the case of Praesepe, Coma Berenices, and NGC 752, the observed asymmetry can be interpreted as a stochastic evaporation event. However, for the formation of the asymmetric tidal tails of the Hyades, additional dynamical processes beyond a pure statistical evaporation effect are required.
The ESA space astrometry mission Gaia will measure the positions, parallaxes and proper motions of the 1 billion brightest stars on the sky. Expected accuracies are in the 7–25 μas range down to 15 ...mag and sub-mas accuracies at the faint limit (20 mag). The astrometric data are complemented by low-resolution spectrophotometric data in the 330–1000 nm wavelength range and, for the brighter stars, radial velocity measurements. The scientific case covers an extremely wide range of topics in galactic and stellar astrophysics, solar system and exoplanet science, as well as the establishment of a very accurate, dense and faint optical reference frame. With a planned launch around 2012 and an (extended) operational lifetime of 6 years, final results are expected around 2021. We give a brief overview of the science goals of Gaia, the overall project organisation, expected performance, and some key technical features and challenges.
Gaia Data Release 2 Cropper, M.; Katz, D.; Sartoretti, P. ...
Astronomy and astrophysics (Berlin),
8/2018, Letnik:
616
Journal Article, Web Resource
Recenzirano
Odprti dostop
This paper presents the specification, design, and development of the Radial Velocity Spectrometer (RVS) on the European Space Agency’s
Gaia
mission. Starting with the rationale for the full six ...dimensions of phase space in the dynamical modelling of the Galaxy, the scientific goals and derived top-level instrument requirements are discussed, leading to a brief description of the initial concepts for the instrument. The main part of the paper is a description of the flight RVS, considering the optical design, the focal plane, the detection and acquisition chain, and the as-built performance drivers and critical technical areas. After presenting the pre-launch performance predictions, the paper concludes with the post-launch developments and mitigation strategies, together with a summary of the in-flight performance at the end of commissioning.
We have mapped the dark cloud L183 in the far-infrared at 100 μm and 200 μm with the ISOPHOT photometer aboard the ISO satellite. The observations make it possible for the first time to study the ...distribution and properties of the large dust grains in L183 without confusion from smaller grains. The observations show clear colour temperature variations which are likely to be caused by changes in the emission properties of the dust particles. In the cloud core the far-infrared colour temperature drops below 12 K. The data allow a new determination of the cloud mass and the mass distribution based on dust emission. The estimated mass within a radius of 10′ from the cloud centre is 25 $M_{\odot}$. We have mapped the cloud in several molecular lines including DCO+(2–1) and H13CO+(1–0). These species are believed to be tracers of cold and dense molecular material and we detect a strong anticorrelation between the DCO+ emission and the dust colour temperatures. In particular, the DCO+(2–1) emission is not detected towards the maximum of the 100 μm emission where the colour temperature rises above 15 K. The H13CO+ emission follows closely the DCO+ distribution but CO isotopes show strong emission even towards the 100 μm peak. Detailed comparison of the DCO+ and C18O maps shows sharp variations in the relative intensities of the species. Morphologically the 200 μm dust emission traces the distribution of dense molecular material as seen e.g. in C18O lines. A comparison with dust column density shows, however, that C18O is depleted by a factor of ~1.5 in the cloud core. We present results of R- and B-band starcounts. The extinction is much better correlated with the 200$~\mu$m than with the 100 μm emission. Based on the 200 μm correlation at low extinction values we deduce a value of ~17m for the visual extinction towards the cloud centre where no background stars are observed anymore.
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