2,781 research outputs found
A Hipparcos census of the nearby OB associations
A comprehensive census of the stellar content of the nearby OB associations
is presented, based on Hipparcos positions, proper motions, and parallaxes.
Moving groups are identified by combining de Bruijne's refurbished convergent
point method with the `Spaghetti method' of Hoogerwerf & Aguilar. Monte Carlo
simulations are used to estimate the expected number of interloper field stars.
Astrometric members are listed for 12 young stellar groups, out to a distance
of ~650 pc. These are the 3 subgroups Upper Scorpius, Upper Centaurus Lupus and
Lower Centaurus Crux of Sco OB2, as well as Vel OB2, Tr 10, Col 121, Per OB2,
alpha Persei (Per OB3), Cas-Tau, Lac OB1, Cep OB2, and a new group designated
as Cep OB6. The selection procedure corrects the list of previously known
astrometric and photometric B- and A-type members, and identifies many new
members, including a significant number of F stars, as well as evolved stars,
e.g., the Wolf-Rayet stars gamma^2 Vel (Vel OB2) and EZ CMa (Col 121), and the
classical Cepheid delta Cep in Cep OB6. In the nearest associations the
later-type members include T Tauri objects and other pre-main sequence stars.
Astrometric evidence for moving groups in the fields of R CrA, CMa OB1, Mon
OB1, Ori OB1, Cam OB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is
inconclusive, due to their large distance or unfavorable kinematics.
The mean distances of the well-established groups are systematically smaller
than previous estimates. The mean motions display a systematic pattern, which
is discussed in relation to the Gould Belt. Six of the 12 detected moving
groups do not appear in the classical list of nearby OB associations. The
number of unbound young stellar groups in the Solar neighbourhood may be
significantly larger than thought previously.Comment: 51 pages, 30 PostScript figures, 6 tables in PostScript format,
default LaTeX using psfig.sty; accepted for publication in the Astronomical
Journal, scheduled for January 1999 issue. Abbreviated abstrac
OB Associations
Since the previous (1990) edition of this meeting enormous progress in the
field of OB associations has been made. Data from X-ray satellites have greatly
advanced the study of the low-mass stellar content of associations, while
astrometric data from the Hipparcos satellite allow for a characterization of
the higher-mass content of associations with unprecedented accuracy. We review
recent work on the OB associations located within 1.5 kpc from the Sun, discuss
the Hipparcos results at length, and point out directions for future research.Comment: To appear in The Physics of Star Formation and Early Stellar
Evolution II, eds C.J. Lada & N. Kylafis (Kluwer Academic), 30 pages, 9
EPS-figures, LaTeX using crckapb.sty, epsfig.sty, amssymb.st
Dark matter in elliptical galaxies
We present measurements of the shape of the stellar line-of-sight velocity
distribution out to two effective radii along the major axes of the four
elliptical galaxies NGC 2434, 2663, 3706, and 5018. The velocity dispersion
profiles are flat or decline gently with radius. We compare the data to the
predictions of f=f(E,L_z) axisymmetric models with and without dark matter.
Strong tangential anisotropy is ruled out at large radii. We conclude from our
measurements that massive dark halos must be present in three of the four
galaxies, while for the fourth galaxy (NGC 2663) the case is inconclusive.Comment: 15 pages, uuencoded compressed PostScript, includes 3 figure
Mapping young stellar populations towards Orion with Gaia DR1
We use the first data release of the Gaia mission to explore the three
dimensional arrangement and the age ordering of the many stellar groups towards
the Orion OB association, aiming at a new classification and characterization
of the stellar population. We make use of the parallaxes and proper motions
provided in the Tycho Gaia Astrometric Solution (TGAS) sub-set of the Gaia
catalogue, and of the combination of Gaia and 2MASS photometry. In TGAS we find
evidence for the presence of a young population, at a parallax , loosely distributed around some known clusters: 25 Ori,
Ori and Ori, and NGC 1980 ( Ori). The low mass
counterpart of this population is visible in the color-magnitude diagrams
constructed by combining Gaia and 2MASS photometry. We study the density
distribution of the young sources in the sky. We find the same groups as in
TGAS, and also some other density enhancements that might be related to the
recently discovered Orion X group, the Orion dust ring, and to the
Ori complex. We estimate the ages of this population and we infer the presence
of an age gradient going from 25 Ori (13-15 Myr) to the ONC (1-2 Myr). We
confirm this age ordering by repeating the Bayesian fit using the Pan-STARRS1
data. The estimated ages towards the NGC 1980 cluster span a broad range of
values. This can either be due to the presence of two populations coming from
two different episodes of star formation or to a large spread along the line of
sight of the same population. Our results form the first step towards using the
Gaia data to unravel the complex star formation history of the Orion region in
terms of the different star formation episodes, their duration, and their
effects on the surrounding interstellar medium.Comment: 17 pages, 17 figure
The ESO Spectroscopic facility
We present the concept of a novel facility dedicated to massively-multiplexed
spectroscopy. The telescope has a very wide field Cassegrain focus optimised
for fibre feeding. With a Field of View (FoV) of 2.5 degrees diameter and a
11.4m pupil, it will be the largest etendue telescope. The large focal plane
can easily host up to 16.000 fibres. In addition, a gravity invariant focus for
the central 10 arc-minutes is available to host a giant integral field unit
(IFU). The 3 lenses corrector includes an ADC, and has good performance in the
360-1300 nm wavelength range. The top level science requirements were developed
by a dedicated ESO working group, and one of the primary cases is high
resolution spectroscopy of GAIA stars and, in general, how our Galaxy formed
and evolves. The facility will therefore be equipped with both, high and low
resolution spectrographs. We stress the importance of developing the telescope
and instrument designs simultaneously. The most relevant R\&D aspect is also
briefly discussed.Comment: 6 pages 4 figures , presented at IAU Symposium 334 "rediscovering our
galaxy
Treating diabetic complications; from large randomized clinical trials to precision medicine
In the last decades, many large randomized controlled trials have been conducted to assess the efficacy and safety of new interventions for the treatment of diabetic kidney disease (DKD). Unfortunately, these trials failed to demonstrate additional kidney or cardiovascular protection. One of the explanations for the failure of these trials appears to be the large variation in drug response between individual patients. All trials to date tested a drug which was targeted to a large heterogeneous population assuming that every individual will show a similar beneficial respond to the drug. Post hoc analyses from the past clinical trials, however, suggest that individual patients show a marked variation in drug response. This highlights the need to personalize treatment taking proper account of the characteristics and preferences of individual patients. Transitioning to a personalized therapy approach will have implications for clinical trial designs, drug registration and its use in clinical practice. Successful implementation of personalized medicine thus requires engagement of multiple stakeholders including academic community, pharmaceutical industry, regulatory agencies, health policy makers, physicians and patients. This supplement of Diabetes Obesity and Metabolism provides a summary on the state-of-the-art of personalized medicine in diabetic kidney disease from the views of various stakeholders
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