165 research outputs found
Analytic solution of Chemical Evolution Models with Type Ia SNe
Context: In the last years, a significant number of works have focused on
finding analytic solutions for the chemical enrichment models of galactic
systems, including the Milky Way. Some of these solutions, however, cannot
account for the enrichment produced by Type Ia SNe due to the presence of the
delay time distributions (DTDs) in the models.
Aims: We present a new analytic solution for the chemical evolution model of
the Galaxy. This solution can be used with different prescriptions of the DTD,
including the single and double degenerate scenarios, and allows the inclusion
of an arbitrary number of pristine gas infalls.
Methods: We integrate the chemical evolution model by extending the
instantaneous recycling approximation with the contribution of Type Ia SNe. For
those DTDs that lead to non-analytic integrals, we describe them as a
superposition of Gaussian, exponential and 1/t functions using a restricted
least-squares fitting method.
Results: We obtain the exact solution for a chemical model with Type Ia SNe
widely used in previous works. This solution can reproduce the expected
chemical evolution of the alpha and iron-peak elements in less computing time
than numerical integration methods. We compare the pattern in the [Si/Fe] vs.
[Fe/H] plane observed by APOGEE DR17 with that predicted by the model. We find
the low alpha sequence can be explained by a delayed gas infall. We exploit the
applicability of our solution by modelling the chemical evolution of a
simulated Milky Way-like galaxy from its star formation history. The
implementation of our solution is released as a python package.
Conclusions: Our solution constitutes a promising tool for the Galactic
Archaeology and is able to model the observed trends in alpha element
abundances versus [Fe/H] in the solar neighbourhood. We infer the chemical
information of a simulated galaxy modelled without Chemistry.Comment: Accepted for publication in A&A. 22 pages, 16 figures. ChEAP code
available at https://bitbucket.org/pedroap/cheap/src/master
Beyond the two-infall model I. Indications for a recent gas infall with Gaia DR3 chemical abundances
The recent Gaia Data Release 3 (DR3) represents an unparalleled revolution in
Galactic Archaeology, providing us with numerous radial velocities chemical
abundances for millions of stars, with all-sky coverage. We present a new
chemical evolution model for the Galactic disc components (high- and low-
sequence stars) designed to reproduce the new abundance ratios
provided by the GSP-spec module for the Gaia DR3 and also constrained by the
detailed star formation histories for both the thick and thin disc stars
inferred from previous Gaia releases. Sophisticated modeling based on previous
Gaia releases has found evidence for narrow episodes of enhanced SF inferred in
recent time. Additionally, Gaia DR3 highlighted the presence of young (massive)
low- disc stars which show evidence of a recent chemical impoverishment
in several elements. Hence, in this study, we compare Gaia DR3 chemical
abundances with the predictions of a three-infall chemical evolution model for
the high- and low- components. The proposed three-infall chemical
evolution model nicely reproduces the main features of the abundance ratio
[X/Fe] versus [M/H] (X=Mg, Si, Ca, Ti, ) of Gaia DR3 stars in different
age bins for the considered elements. Moreover, the most recent gas
infall - which started 2.7 Gyr ago - allows us to predict well the Gaia
DR3 young population which has experienced a recent chemical impoverishment.Comment: Accepted for publication in Astronomy and Astrophysics (A&A), 17
pages, 16 figure
The chemical signature of the Galactic spiral arms revealed by Gaia DR3
Taking advantage of the recent Gaia Data Release 3 (DR3), we map chemical
inhomogeneities in the Milky Way's disc out to a distance of 4 kpc from
the Sun, using different samples of bright giant stars. The samples are
selected using effective temperatures and surface gravities from the GSP-Spec
module, and are expected to trace stellar populations of different typical age.
The cool (old) giants exhibit a relatively smooth radial metallicity gradient
with an azimuthal dependence. Binning in Galactic azimuth , the slope
gradually varies from [M/H] dex kpc at to dex kpc at . On the
other hand, the relatively hotter (and younger) stars present remarkable
inhomogeneities, apparent as three (possibly four) metal-rich elongated
features in correspondence of the spiral arms' locations in the Galactic disc.
When projected onto Galactic radius, those features manifest themselves as
statistically significant bumps on top of the observed radial metallicity
gradients with amplitudes up to dex, making the assumption of
a linear radial decrease not applicable to this sample. The strong correlation
between the spiral structure of the Galaxy and the observed chemical pattern in
the young sample indicates that the spiral arms might be at the origin for the
detected chemical inhomogeneities. In this scenario, the spiral arms would
leave in the younger stars a strong signature, which progressively disappears
when cooler (and older) giants are considered.Comment: 9 pages, 6 figures. Accepted for publication in A&A Letter
The cerium content of the Milky Way as revealed by Gaia DR3 GSP-Spec abundances
The recent Gaia Third Data Release contains a homogeneous analysis of
millions of high-quality Radial Velocity Spectrometer (RVS) stellar spectra by
the GSP-Spec module. This lead to the estimation of millions of individual
chemical abundances and allows us to chemically map the Milky Way. Among the
published GSP-Spec abundances, three heavy-elements produced by
neutron-captures in stellar interiors can be found: Ce, Zr and Nd. We use a
sample of about 30,000 LTE Ce abundances, selected after applying different
combinations of GSP-Spec flags. Thanks to the Gaia DR3 astrometric data and
radial velocities, we explore the cerium content in the Milky Way and, in
particular, in its halo and disc components. The high quality of the Ce
GSP-Spec abundances is quantified thanks to literature comparisons. We found a
rather flat [Ce/Fe] versus [M/H] trend. We also found a flat radial gradient in
the disc derived from field stars and, independently, from about 50 open
clusters, in agreement with previous studies. The [Ce/Fe] vertical gradient has
also been estimated. We also report an increasing [Ce/Ca] vs [Ca/H] in the
disc, illustrating the late contribution of AGB with respect to SN II. Our
cerium abundances in the disc, including the young massive population, are well
reproduced by a new three-infall chemical evolution model. Among the halo
population, the M 4 globular cluster is found to be enriched in cerium.
Moreover, eleven stars with cerium abundances belonging to the Thamnos, Helmi
Stream and Gaia-Sausage-Enceladus accreted systems were identified from
chemo-dynamical diagnostics. We found that the Helmi Stream could be slightly
underabundant in cerium, compared to the two other systems. This work
illustrates the high quality of the GSP-Spec chemical abundances, that
significantly contributes to unveil the heavy elements evolution history of the
Milky Way.Comment: 15 pages, 10 figures, submitted to A&
Solid confirmation of the broad DIB around 864.8 nm using stacked GaiaâRVS spectra
Context. Studies of the correlation between different diffuse interstellar bands (DIBs) are important for exploring their origins. However, the GaiaâRVS spectral window between 846 and 870 nm contains few DIBs, the strong DIB at 862 nm being the only convincingly confirmed one. /
Aims. Here we attempt to confirm the existence of a broad DIB around 864.8 nm and estimate its characteristics using the stacked GaiaâRVS spectra of a large number of stars. We study the correlations between the two DIBs at 862 nm (λ862) and 864.8 nm (λ864.8), as well as the interstellar extinction. /
Methods. We obtained spectra of the interstellar medium (ISM) absorption by subtracting the stellar components using templates constructed from real spectra at high Galactic latitudes with low extinctions. We then stacked the ISM spectra in Galactic coordinates (â,ââb) â pixelized by the HEALPix scheme â to measure the DIBs. The stacked spectrum is modeled by the profiles of the two DIBs, Gaussian for λ862 and Lorentzian for λ864.8, and a linear continuum. We report the fitted central depth (CD), central wavelength, equivalent width (EW), and their uncertainties for the two DIBs. /
Results. We obtain 8458 stacked spectra in total, of which 1103 (13%) have reliable fitting results after applying numerous conservative filters. This work is the first of its kind to fit and measure λ862 and λ864.8 simultaneously in cool-star spectra. Based on these measurements, we find that the EWs and CDs of λ862 and λ864.8 are well correlated with each other, with Pearson coefficients (rp) of 0.78 and 0.87, respectively. The full width at half maximum (FWHM) of λ864.8 is estimated as 1.62â
屉
0.33 nm which compares to 0.55â
屉
0.06 nm for λ862. We also measure the vacuum rest-frame wavelength of λ864.8 to be λ0â=â864.53â
屉
0.14 nm, smaller than previous estimates. /
Conclusions. We find solid confirmation of the existence of the DIB around 864.8 nm based on an exploration of its correlation with λ862 and estimation of its FWHM. The DIB λ864.8 is very broad and shallow. That at λ862 correlates better with E(BPâ
ââ
RP) than λ864.8. The profiles of the two DIBs could strongly overlap with each other, which contributes to the skew of the λ862 profile
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
Anti-PF4 immunothrombosis without proximate heparin or adenovirus vector vaccine exposure.
Platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies and anti-PF4 antibodies cause heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombocytopenia and thrombosis (VITT), respectively. Diagnostic and treatment considerations differ somewhat between HIT and VITT. We identified patients with thrombocytopenia and thrombosis without proximate heparin exposure or adenovirus-based vaccination who tested strongly positive by PF4/polyanion enzyme-immunoassays and negative/weakly positive by heparin-induced platelet activation (HIPA) test but strongly positive by PF4-induced platelet activation (PIPA) test (ie, VITT-like profile). We tested these patients by a standard chemiluminescence assay that detects anti-PF4/heparin antibodies found in HIT (HemosIL AcuStar HIT-IgG(PF4-H)) as well as a novel chemiluminescence assay for anti-PF4 antibodies found in VITT. Representative control sera included an exploratory anti-PF4 antibody-positive but HIPA-negative/weak cohort obtained before 2020 (n = 188). We identified 9 patients with a clinical-pathological profile of a VITT-like disorder in the absence of proximate heparin or vaccination, with a high frequency of stroke (arterial, n = 3; cerebral venous sinus thrombosis, n = 4), thrombocytopenia (median platelet count nadir, 49 Ă 109/L), and hypercoagulability (greatly elevated D-dimer levels). VITT-like serological features included strong reactivity by PIPA (aggregation <10 minutes in 9/9 sera) and positive testing in the novel anti-PF4 chemiluminescence assay (3/9 also tested positive in the anti-PF4/heparin chemiluminescence assay). Our exploratory cohort identified 13 additional patient sera obtained before 2020 with VITT-like anti-PF4 antibodies. Platelet-activating VITT-like anti-PF4 antibodies should be considered in patients with thrombocytopenia, thrombosis, and very high D-dimer levels, even without a proximate exposure to heparin or adenovirus vector vaccines
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
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
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
- âŠ