63 research outputs found
A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Radial velocities of early-type stars in the Perseus OB2 association
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Origin of the Local Bubble
We present a new unbiased search for OB associations in the Solar neighbourhood
which have hosted the progenitor stars of the core collapse supernovae responsible for the
Local Bubble in the interstellar gas. For this purpose we have analyzed a volume complete
set (with a diameter of 400 pc) of B stars drawn from the Hipparcos catalogue and the Arivel
data base, from which candidate members were selected by a kinematical criterion. After
careful dereddening the star colours we have constructed a colour-magnitude diagram and
confirmed that the Upper Scorpius, Upper Centaurus Lupus, and Lower Centaurus Crux
subgroups of the Sco OB2 association are the youngest nearby OB associations. We dated
their ages with theoretical isochrones in the range of 20â30 Myr, in agreement with previous
work. We have traced backwards in time the paths of the stars and found that they entered
the volume of the present bubble at 10 to 15 Myr ago. We argue that the Local Bubble began
to form then and estimate that 14 to 20 supernovae have exploded since. The implied energy
input into the ambient medium can be shown to be sufficient to excavate a bubble of the
presently observed size
Low-mass pre--main-sequence stars in the Magellanic Clouds
[Abridged] The stellar Initial Mass Function (IMF) suggests that sub-solar
stars form in very large numbers. Most attractive places for catching low-mass
star formation in the act are young stellar clusters and associations, still
(half-)embedded in star-forming regions. The low-mass stars in such regions are
still in their pre--main-sequence (PMS) evolutionary phase. The peculiar nature
of these objects and the contamination of their samples by the evolved
populations of the Galactic disk impose demanding observational techniques for
the detection of complete numbers of PMS stars in the Milky Way. The Magellanic
Clouds, the companion galaxies to our own, demonstrate an exceptional star
formation activity. The low extinction and stellar field contamination in
star-forming regions of these galaxies imply a more efficient detection of
low-mass PMS stars than in the Milky Way, but their distance from us make the
application of special detection techniques unfeasible. Nonetheless, imaging
with the Hubble Space Telescope yield the discovery of solar and sub-solar PMS
stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of
such objects are identified as the low-mass stellar content of their
star-forming regions, changing completely our picture of young stellar systems
outside the Milky Way, and extending the extragalactic stellar IMF below the
persisting threshold of a few solar masses. This review presents the recent
developments in the investigation of PMS stars in the Magellanic Clouds, with
special focus on the limitations by single-epoch photometry that can only be
circumvented by the detailed study of the observable behavior of these stars in
the color-magnitude diagram. The achieved characterization of the low-mass PMS
stars in the Magellanic Clouds allowed thus a more comprehensive understanding
of the star formation process in our neighboring galaxies.Comment: Review paper, 26 pages (in LaTeX style for Springer journals), 4
figures. Accepted for publication in Space Science Review
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Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)
Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 ÎŒas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution
Gaia Early Data Release 3: acceleration of the solar system from Gaia astrometry
Stars and planetary system
Gaia early data release 3: summary of the contents and survey properties (Corrigendum)
ERRATUMThis article is an erratum for:[https://doi.org/10.1051/0004-6361/202039657]âââââââInstrumentatio
Gaia Early Data Release 3: the Gaia catalogue of nearby stars
Stars and planetary system
Gaia Data Release 3: reflectance spectra of Solar System small bodies
Stars and planetary system
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