287 research outputs found
Axisymmetric Three-Integral Models for Galaxies
We describe an improved, practical method for constructing galaxy models that
match an arbitrary set of observational constraints, without prior assumptions
about the phase-space distribution function (DF). Our method is an extension of
Schwarzschild's orbit superposition technique. As in Schwarzschild's original
implementation, we compute a representative library of orbits in a given
potential. We then project each orbit onto the space of observables, consisting
of position on the sky and line-of-sight velocity, while properly taking into
account seeing convolution and pixel binning. We find the combination of orbits
that produces a dynamical model that best fits the observed photometry and
kinematics of the galaxy. A key new element of this work is the ability to
predict and match to the data the full line-of-sight velocity profile shapes. A
dark component (such as a black hole and/or a dark halo) can easily be included
in the models.
We have tested our method, by using it to reconstruct the properties of a
two-integral model built with independent software. The test model is
reproduced satisfactorily, either with the regular orbits, or with the
two-integral components. This paper mainly deals with the technical aspects of
the method, while applications to the galaxies M32 and NGC 4342 are described
elsewhere (van der Marel et al., Cretton & van den Bosch). (abridged)Comment: minor changes, accepted for publication in the Astrophysical Journal
Supplement
Shear and Ellipticity in Gravitational Lenses
Galaxies modeled as singular isothermal ellipsoids with an axis ratio
distribution similar to the observed axis ratio distribution of E and S0
galaxies are statistically consistent with both the observed numbers of
two-image and four-image lenses and the inferred ellipticities of individual
lenses. However, no four-image lens is well fit by the model (typical
), the axis ratio of the model can be significantly
different from that of the observed lens galaxy, and the major axes of the
model and the galaxy may be slightly misaligned. We found that models with a
second, independent, external shear axis could fit the data well (typical
), while adding the same number of extra parameters to
the radial mass distribution does not produce such a dramatic improvement in
the fit. An independent shear axis can be produced by misalignments between the
luminous galaxy and its dark matter halo, or by external shear perturbations
due to galaxies and clusters correlated with the primary lens or along the line
of sight. We estimate that the external shear perturbations have no significant
effect on the expected numbers of two-image and four-image lenses, but that
they can be important perturbations in individual lens models. However, the
amplitudes of the external shears required to produce the good fits are larger
than our estimates for typical external shear perturbations (10-15% shear
instead of 1-3% shear) suggesting that the origin of the extra angular
structure must be intrinsic to the primary lens galaxy in most cases.Comment: 38 pages, 9 figures, submitted to Ap
Gaia Early Data Release 3: Summary of the contents and survey properties
ABSTRACT: Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2.
Aims. A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results.
Methods. The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity.
Results. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (GBP ? GRP) colour are also available. The passbands for G, GBP, and GRP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Conclusions. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30-40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, GBP, and GRP is valid over the entire magnitude and colour range, with no systematics above the 1% levelThe Gaia mission and data processing have financially been supported by ; the Spanish Ministry of Economy (MINECO/FEDER, UE) through grants ESP2016-80079-C2-1-R, ESP2016-80079-C2-2-R, RTI2018-095076-B-C21, RTI2018-095076-B-C22, BES-2016-078499, and BES-2017-083126 and the Juan de la Cierva formaciĂłn 2015 grant FJCI-2015-2671, the Spanish Ministry of Education, Culture, and Sports through grant FPU16/03827, the Spanish Ministry of Science and Innovation (MICINN) through grant
AYA2017-89841P for project âEstudio de las propiedades de los fĂłsiles estelares en el entorno del Grupo Localâ and through grant TIN2015-65316-P for project
âComputaciĂłn de Altas Prestaciones VII
<i>Gaia</i> Data Release 1. Summary of the astrometric, photometric, and survey properties
Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7.
Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release.
Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue.
Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues â a realisation of the Tycho-Gaia Astrometric Solution (TGAS) â and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of âŒ3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yrâ1 for the proper motions. A systematic component of âŒ0.3 mas should be added to the parallax uncertainties. For the subset of âŒ94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yrâ1. For the secondary astrometric data set, the typical uncertainty of the positions is âŒ10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to âŒ0.03 mag over the magnitude range 5 to 20.7.
Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data
A method for selecting M dwarfs with an increased likelihood of unresolved ultracool companionship
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [N. J, Cook, et al, 'A method for selecting M dwarfs with an increased likelihood of unresolved ultracool companionship', MNRAS, Vol. 457(2): 2192-2208, February 2016] is available online at: https://doi.org/10.1093/mnras/stw061. Published by Oxford University Press on behalf of the Royal Astronomical Society.Locating ultracool companions to M dwarfs is important for constraining low-mass formation models, the measurement of substellar dynamical masses and radii, and for testing ultracool evolutionary models. We present an optimized method for identifying M dwarfs which may have unresolved ultracool companions. We construct a catalogue of 440 694 M dwarf candidates, from Wide-Field Infrared Survey Explorer, Two Micron All-Sky Survey and Sloan Digital Sky Survey, based on optical- and near-infrared colours and reduced proper motion. With strict reddening, photometric and quality constraints we isolate a subsample of 36 898 M dwarfs and search for possible mid-infrared M dwarf + ultracool dwarf candidates by comparing M dwarfs which have similar optical/near-infrared colours (chosen for their sensitivity to effective temperature and metallicity). We present 1082 M dwarf + ultracool dwarf candidates for follow-up. Using simulated ultracool dwarf companions to M dwarfs, we estimate that the occurrence of unresolved ultracool companions amongst our M dwarf + ultracool dwarf candidates should be at least four times the average for our full M dwarf catalogue. We discuss possible contamination and bias and predict yields of candidates based on our simulations.Peer reviewe
The design and performance of the Gaia photometric system
The European Gaia astrometry mission is due for launch in 2011. Gaia will rely on the proven principles of the ESA Hipparcos mission to create an all-sky survey of about one billion stars throughout our Galaxy and beyond, by observing all objects down to 20 mag. Through its massive measurement of stellar distances, motions and multicolour photometry, it will provide fundamental data necessary for unravelling the structure, formation and evolution of the Galaxy. This paper presents the design and performance of the broad- and medium-band set of photometric filters adopted as the baseline for Gaia. The 19 selected passbands (extending from the UV to the far-red), the criteria and the methodology on which this choice has been based are discussed in detail. We analyse the photometric capabilities for characterizing the luminosity, temperature, gravity and chemical composition of stars. We also discuss the automatic determination of these physical parameters for the large number of observations involved, for objects located throughout the entire Hertzsprung-Russell diagram. Finally, the capability of the photometric system (PS) to deal with the main Gaia science case is outline
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) Ă 10â10 m sâ2 (or 7.33 ±0.51 km sâ1 Myrâ1) towards α = 269.1° ± 5.4°, ÎŽ = â31.6° ± 4.1°, corresponding to a proper motion amplitude of 5.05 ±0.35 ÎŒas yrâ1. 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 ÎŒas yrâ1. Movie is only available at https://www.aanda.or
Gaia Early Data Release 3. Summary of the contents and survey properties
Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Aims: A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results. Methods: The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity. Results: Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (GBP â GRP) colour are also available. The passbands for G, GBP, and GRP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Conclusions: Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30-40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, GBP, and GRP is valid over the entire magnitude and colour range, with no systematics above the 1% leve
Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
We present an all-sky catalog of 2970 nearby ( pc), bright
() M- or late K-type dwarf stars, 86% of which have been confirmed by
spectroscopy. This catalog will be useful for searches for Earth-size and
possibly Earth-like planets by future space-based transit missions and
ground-based infrared Doppler radial velocity surveys. Stars were selected from
the SUPERBLINK proper motion catalog according to absolute magnitudes, spectra,
or a combination of reduced proper motions and photometric colors. From our
spectra we determined gravity-sensitive indices, and identified and removed
0.2% of these as interloping hotter or evolved stars. Thirteen percent of the
stars exhibit H-alpha emission, an indication of stellar magnetic activity and
possible youth. The mean metallicity is [Fe/H] = -0.07 with a standard
deviation of 0.22 dex, similar to nearby solar-type stars. We determined
stellar effective temperatures by least-squares fitting of spectra to model
predictions calibrated by fits to stars with established bolometric
temperatures, and estimated radii, luminosities, and masses using empirical
relations. Six percent of stars with images from integral field spectra are
resolved doubles. We inferred the planet population around M dwarfs using
data and applied this to our catalog to predict detections by future
exoplanet surveys.Comment: Accepted to MNRAS 22 figures, 3 tables, 2 electronic tables.
Electronic tables are available as links on this pag
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
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