257 research outputs found
NGC 6705 a young -enhanced Open Cluster from OCCASO data
The stellar [/Fe] abundance is sometimes used as a proxy for stellar
age, following standard chemical evolution models for the Galaxy, as seen by
different observational results. In this work we show that the Open Cluster
NGC6705/M11 has a significant -enhancement [/Fe] dex,
despite its young age (300 Myr), challenging the current paradigm. We use
high resolution (R) high signal-to-noise (70) spectra of 8 Red
Clump stars, acquired within the OCCASO survey. We determine very accurate
chemical abundances of several elements, using an equivalent width
methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain
[Si/Fe]=, [Mg/Fe]=, [O/Fe]=,
[Ca/Fe]= and [Ti/Fe]=. Our results place these
cluster within the group of young [/Fe]-enhanced field stars recently
found by several authors in the literature. The ages of our stars have an
uncertainty of around 50 Myr, much more precise than for field stars. By
integrating the cluster's orbit in several non-axisymmetric Galactic
potentials, we establish the M11's most likely birth radius to lie between
6.8-7.5 kpc from the Galactic center, not far from its current position. With
the robust Open Cluster age scale, our results prove that a moderate
[/Fe]-enhancement is no guarantee for a star to be old, and that not
all -enhanced stars can be explained with an evolved blue straggler
scenario. Based on our orbit calculations, we further argue against a Galactic
bar origin of M11.Comment: 10 pages, 6 figures, accepted in A&
One Star to Tag Them All (OSTTA): I. Radial velocities and chemical abundances for 20 poorly studied open clusters
Context: Open clusters are ideal laboratories to investigate a variety of
astrophysical topics, from the properties of the Galactic disc to stellar
evolution models. For this purpose, we need to know their chemical composition
in detail. Unfortunately, the number of systems with chemical abundances
determined from high resolution spectroscopy remains small. Aims: Our aim is to
increase the number of open clusters with radial velocities and chemical
abundances determined from high resolution spectroscopy by sampling a few stars
in clusters not studied previously. Methods: We obtained high resolution
spectra with the FIES spectrograph at NOT for 41 stars belonging to 20 open
clusters. These stars have high astrometric membership probabilities,
determined from the Gaia second data release. Results: We derived radial
velocities for all the observed stars, which were used to confirm their
membership to the corresponding clusters. For Gulliver\,37 we cannot be sure
the observed star is a real member. We derived atmospheric parameters for the
32 stars considered real cluster members. We discarded five stars because they
have very low gravity or atmospheric parameters were not properly constrained
due to low signal-to-noise ratio spectra. Therefore, detailed chemical
abundances were determined for 28 stars belonging to 17 clusters. For most of
them, this is the first chemical analysis available in the literature. Finally,
we compared the clusters in our sample to a large population of well studied
clusters. The studied systems follow the trends, both chemical and kinematical,
described by the majority of open clusters. Worth noticing that the three most
metal-poor studied clusters (NGC\,1027, NGC\,1750 and Trumpler 2) are enhanced
in Si but not in the other alpha-elements studied (Mg, Ca and Ti).Comment: 19 pages Accepted for publication on A&
Ultracool dwarfs in Gaia DR3
Aims. In this work we use the Gaia DR3 set of ultracool dwarf candidates and
complement the Gaia spectrophotometry with additional photometry in order to
characterise its global properties. This includes the inference of the
distances, their locus in the Gaia colour-absolute magnitude diagram and the
(biased through selection) luminosity function in the faint end of the Main
Sequence. We study the overall changes in the Gaia RP spectra as a function of
spectral type. We study the UCDs in binary systems, attempt to identify
low-mass members of nearby young associations, star forming regions and
clusters, and analyse their variability properties. Results. We detect 57
young, kinematically homogeneous groups some of which are identified as well
known star forming regions, associations and clusters of different ages. We
find that the primary members of 880 binary systems with a UCD belong mainly to
the thin and thick disk components of the Milky Way. We identify 1109 variable
UCDs using the variability tables in the Gaia archive, 728 of which belong to
the star forming regions defined by HMAC. We define two groups of variable UCDs
with extreme bright or faint outliers. Conclusions. The set of sources
identified as UCDs in the Gaia archive contains a wealth of information that
will require focused follow-up studies and observations. It will help to
advance our understanding of the nature of the faint end of the Main Sequence
and the stellar/substellar transition.Comment: Accepted by Astronomy and Astrophysics. 29 pages, 20 figures plus 3
appendice
Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa
BACKGROUND: A new investigation of the sedimentology and ichnology of the Early Jurassic Moyeni tracksite in Lesotho, southern Africa has yielded new insights into the behavior and locomotor dynamics of early dinosaurs. METHODOLOGY/PRINCIPAL FINDINGS: The tracksite is an ancient point bar preserving a heterogeneous substrate of varied consistency and inclination that includes a ripple-marked riverbed, a bar slope, and a stable algal-matted bar top surface. Several basal ornithischian dinosaurs and a single theropod dinosaur crossed its surface within days or perhaps weeks of one another, but responded to substrate heterogeneity differently. Whereas the theropod trackmaker accommodated sloping and slippery surfaces by gripping the substrate with its pedal claws, the basal ornithischian trackmakers adjusted to the terrain by changing between quadrupedal and bipedal stance, wide and narrow gauge limb support (abduction range = 31 degrees ), and plantigrade and digitigrade foot posture. CONCLUSIONS/SIGNIFICANCE: The locomotor adjustments coincide with changes in substrate consistency along the trackway and appear to reflect 'real time' responses to a complex terrain. It is proposed that these responses foreshadow important locomotor transformations characterizing the later evolution of the two main dinosaur lineages. Ornithischians, which shifted from bipedal to quadrupedal posture at least three times in their evolutionary history, are shown to have been capable of adopting both postures early in their evolutionary history. The substrate-gripping behavior demonstrated by the early theropod, in turn, is consistent with the hypothesized function of pedal claws in bird ancestors
Gaia Focused Product Release: A catalogue of sources around quasars to search for strongly lensed quasars
Context. Strongly lensed quasars are fundamental sources for cosmology. The
Gaia space mission covers the entire sky with the unprecedented resolution of
" in the optical, making it an ideal instrument to search for
gravitational lenses down to the limiting magnitude of 21. Nevertheless, the
previous Gaia Data Releases are known to be incomplete for small angular
separations such as those expected for most lenses. Aims. We present the Data
Processing and Analysis Consortium GravLens pipeline, which was built to
analyse all Gaia detections around quasars and to cluster them into sources,
thus producing a catalogue of secondary sources around each quasar. We analysed
the resulting catalogue to produce scores that indicate source configurations
that are compatible with strongly lensed quasars. Methods. GravLens uses the
DBSCAN unsupervised clustering algorithm to detect sources around quasars. The
resulting catalogue of multiplets is then analysed with several methods to
identify potential gravitational lenses. We developed and applied an outlier
scoring method, a comparison between the average BP and RP spectra of the
components, and we also used an extremely randomised tree algorithm. These
methods produce scores to identify the most probable configurations and to
establish a list of lens candidates. Results. We analysed the environment of 3
760 032 quasars. A total of 4 760 920 sources, including the quasars, were
found within 6" of the quasar positions. This list is given in the Gaia
archive. In 87\% of cases, the quasar remains a single source, and in 501 385
cases neighbouring sources were detected. We propose a list of 381 lensed
candidates, of which we identified 49 as the most promising. Beyond these
candidates, the associate tables in this Focused Product Release allow the
entire community to explore the unique Gaia data for strong lensing studies
further.Comment: 35 pages, 60 figures, accepted for publication by Astronomy and
Astrophysic
Gaia Focused Product Release: Radial velocity time series of long-period variables
The third Gaia Data Release (DR3) provided photometric time series of more
than 2 million long-period variable (LPV) candidates. Anticipating the
publication of full radial-velocity (RV) in DR4, this Focused Product Release
(FPR) provides RV time series for a selection of LPVs with high-quality
observations. We describe the production and content of the Gaia catalog of LPV
RV time series, and the methods used to compute variability parameters
published in the Gaia FPR. Starting from the DR3 LPVs catalog, we applied
filters to construct a sample of sources with high-quality RV measurements. We
modeled their RV and photometric time series to derive their periods and
amplitudes, and further refined the sample by requiring compatibility between
the RV period and at least one of the , , or
photometric periods. The catalog includes RV time series and variability
parameters for 9\,614 sources in the magnitude range , including a flagged top-quality subsample of 6\,093 stars
whose RV periods are fully compatible with the values derived from the ,
, and photometric time series. The RV time series
contain a mean of 24 measurements per source taken unevenly over a duration of
about three years. We identify the great most sources (88%) as genuine LPVs,
with about half of them showing a pulsation period and the other half
displaying a long secondary period. The remaining 12% consists of candidate
ellipsoidal binaries. Quality checks against RVs available in the literature
show excellent agreement. We provide illustrative examples and cautionary
remarks. The publication of RV time series for almost 10\,000 LPVs constitutes,
by far, the largest such database available to date in the literature. The
availability of simultaneous photometric measurements gives a unique added
value to the Gaia catalog (abridged)Comment: 36 pages, 38 figure
Gaia Data Release 2 Mapping the Milky Way disc kinematics
Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G(RVS) = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (sigma((omega) over bar)/(omega) over bar Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.Peer reviewe
Gaia Early Data Release 3 Acceleration of the Solar System from Gaia astrometry
Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions. Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar systembarycentre with respect to the rest frame of the Universe. Apart from being an important scientific result by itself, the acceleration measured in this way is a good quality indicator of the Gaia astrometric solution. Methods. Theeffect of the acceleration was obtained as a part of the general expansion of the vector field of proper motions in vector spherical harmonics (VSH). Various versions of the VSH fit and various subsets of the sources were tried and compared to get the most consistent result and a realistic estimate of its uncertainty. Additional tests with the Gaia astrometric solution were used to get a better idea of the possible systematic errors in the estimate. Results. Our best estimate of the acceleration based on Gaia EDR3 is (2.32 +/- 0.16) x 10(-10) m s(-2) (or 7.33 +/- 0.51 km s(-1) Myr-1) towards alpha = 269.1 degrees +/- 5.4 degrees, delta = -31.6 degrees +/- 4.1 degrees, corresponding to a proper motion amplitude of 5.05 +/- 0.35 mu as yr(-1). This is in good agreement with the acceleration expected from current models of the Galactic gravitational potential. We expect that future Gaia data releases will provide estimates of the acceleration with uncertainties substantially below 0.1 mu as yr(-1).Peer reviewe
Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G = 18.5
Stars and planetary system
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