92 research outputs found
A new interpretation of the period-luminosity sequences of long-period variables
Period-luminosity (PL) sequences of long period variables (LPVs) are commonly
interpreted as different pulsation modes, but there is disagreement on the
modal assignment. Here, we re-examine the observed PL sequences in the Large
Magellanic Cloud, including the sequence of long secondary periods (LSPs), and
their associated pulsation modes. Firstly, we theoretically model the sequences
using linear, radial, non-adiabatic pulsation models and a population synthesis
model of the LMC red giants. Then, we use a semi-empirical approach to assign
modes to the pulsation sequences by exploiting observed multi-mode pulsators.
As a result of the combined approaches, we consistently find that sequences B
and C both correspond to first overtone pulsation, although there
are some fundamental mode pulsators at low luminosities on both sequences. The
masses of these fundamental mode pulsators are larger at a given luminosity
than the mass of the first overtone pulsators. These two sequences B and
C are separated by a small period interval in which large amplitude
pulsation in a long secondary period (sequence D variability) occurs, meaning
that the first overtone pulsation is not seen as the primary mode of pulsation.
Observationally, this leads to the splitting of the first overtone pulsation
sequence into the two observed sequences B and C. Our two
independent examinations also show that sequences A, A and C
correspond to third overtone, second overtone and fundamental mode pulsation,
respectively.Comment: 10 pages, 7 figures, accepted for publication in Ap
Modelling Long-Period Variables -- II. Fundamental mode pulsation in the nonlinear regime
Long-period variability in luminous red giants has several promising
applications, all of which require models able to accurately predict pulsation
periods. Linear pulsation models have proven successful in reproducing the
observed periods of overtone modes in evolved red giants, but they fail to
accurately predict their fundamental mode periods. Here, we use a 1D
hydrodynamic code to investigate the long-period variability of M-type
asymptotic giant branch stars in the nonlinear regime. We examine the period
and stability of low-order radial pulsation modes as a function of mass and
radius, and find overtone mode periods in complete agreement with predictions
from linear pulsation models. In contrast, nonlinear models predict an earlier
onset of dominant fundamental mode pulsation, and shorter periods at large
radii. Both features lead to a substantially better agreement with
observations, that we verify against OGLE and Gaia data for the Magellanic
Clouds. We provide simple analytic relations describing the nonlinear
fundamental mode period-mass-radius relation. Differences with respect to
linear predictions originate from the readjustment of the envelope structure
induced by large-amplitude pulsation. We investigate the impact of turbulent
viscosity on linear and nonlinear pulsation, and probe possible effects of
varying metallicity and carbon abundance.Comment: 18 pages, 17 figures; accepted for publication in MNRA
Identification of a set of KSRP target transcripts upregulated by PI3K-AKT signaling
BACKGROUND: KSRP is a AU-rich element (ARE) binding protein that causes decay of select sets of transcripts in different cell types. We have recently described that phosphatidylinositol 3-kinase/AKT (PI3K-AKT) activation induces stabilization and accumulation of the labile β-catenin mRNA through an impairment of KSRP function. RESULTS: Aim of this study was to identify additional KSRP targets whose stability and steady-state levels are enhanced by PI3K-AKT activation. First, through microarray analyses of the AU-rich transcriptome in pituitary αT3-1 cells, we identified 34 ARE-containing transcripts upregulated in cells expressing a constitutively active form of AKT1. In parallel, by an affinity chromatography-based technique followed by microarray analyses, 12 mRNAs target of KSRP, additional to β-catenin, were identified. Among them, seven mRNAs were upregulated in cells expressing activated AKT1. Both steady-state levels and stability of these new KSRP targets were consistently increased by either KSRP knock-down or PI3K-AKT activation. CONCLUSION: Our study identified a set of transcripts that are targets of KSRP and whose expression is increased by PI3K-AKT activation. These mRNAs encode RNA binding proteins, signaling molecules and a replication-independent histone. The increased expression of these gene products upon PI3K-AKT activation could play a role in the cellular events initiated by this signaling pathway
Determining stellar parameters of asteroseismic targets: Going beyond the use of scaling relations
Asteroseismic parameters allow us to measure the basic stellar properties of field giants observed far across the Galaxy. Most of such determinations are, up to now, based on simple scaling relations involving the large-frequency separation, \u394\u3bd, and the frequency of maximum power, \u3bdmax. In this work, we implement \u394\u3bd and the period spacing, \u394P, computed along detailed grids of stellar evolutionary tracks, into stellar isochrones and hence in a Bayesian method of parameter estimation. Tests with synthetic data reveal that masses and ages can be determined with typical precision of 5 and 19 per cent, respectively, provided precise seismic parameters are available. Adding independent on the stellar luminosity, these values can decrease down to 3 and 10 per cent, respectively. The application of these methods to NGC 6819 giants produces a mean age in agreement with those derived from isochrone fitting, and no evidence of systematic differences between RGB and RC stars. The age dispersion of NGC 6819 stars, however, is larger than expected, with at least part of the spread ascribable to stars that underwent mass-transfer events
The first comprehensive Milky Way stellar mock catalogue for the Chinese Space Station Telescope Survey Camera
The Chinese Space Station Telescope (CSST) is a cutting-edge two-meter astronomical space telescope currently under construction. Its primary Survey Camera (SC) is designed to conduct large-area imaging sky surveys using a sophisticated seven-band photometric system. The resulting data will provide unprecedented data for studying the structure and stellar populations of the Milky Way. To support the CSST development and scientific projects related to its survey data, we generate the first comprehensive Milky Way stellar mock catalogue for the CSST SC photometric system using the TRILEGAL stellar population synthesis tool. The catalogue includes approximately 12.6 billion stars, covering a wide range of stellar parameters, photometry, astrometry, and kinematics, with magnitude reaching down to g=27.5 mag in the AB magnitude system. The catalogue represents our benchmark understanding of the stellar populations in the Milky Way, enabling a direct comparison with the future CSST survey data. Particularly, it sheds light on faint stars that are hidden from current sky surveys. Our crowding limit analysis based on this catalogue provides compelling evidence for the extension of the CSST Optical Survey (OS) to cover low Galactic latitude regions. The strategic extension of the CSST-OS coverage, combined with this comprehensive mock catalogue, will enable transformative science with the CSST
Dissecting the <i>Gaia </i>HR diagram – II. The vertical structure of the star formation history across the solar cylinder
Starting from the Gaia DR3 HR diagram, we derive the star formation history (SFH) as a function of distance from the Galactic plane within a cylinder centred on the Sun with a 200 pc radius and spanning 1.3 kpc above and below the Galaxy’s midplane. We quantify both the concentration of the more recent star formation in the Galactic plane, and the age-related increase in the scale height of the Galactic disc stellar component, which is well-described by power laws with indices ranging from 1/2 to 2/3. The vertically-integrated star formation rate falls from (1.147 ± 0.039) × 10−8 M☉ yr−1 pc−2 at earlier times down to (6.2 ± 3.0) × 10−9 M☉ yr−1 pc−2 at present times, but we find a significant peak of star formation in the 2–3 Gyr age bin. The total mass of stars formed per unit area over time is 118.7 ± 6.2 M☉ pc−2, which is nearly twice the present stellar mass derived from kinematics within 1 kpc from the Galactic plane, implying a high degree of matter recycling in successive generations of stars. The method is then modified by adopting an age-dependent correlation between the SFH across the different slices, which results in less noisy and more symmetrical results without significantly changing the previously mentioned quantities. This appears to be a promising way to improve SFH recovery in external galaxies
Dissecting the Gaia HR diagram II. The vertical structure of the star formation history across the Solar Cylinder
Starting from the Gaia DR3 HR diagram, we derive the star formation history
(SFH) as a function of distance from the Galactic Plane within a cylinder
centred on the Sun with a 200~pc radius and spanning 1.3~kpc above and below
the Galaxy's midplane. We quantify both the concentration of the more recent
star formation in the Galactic Plane, and the age-related increase in the scale
height of the Galactic Disc stellar component, which is well-described by
power-laws with indices ranging from to . The vertically-integrated
star formation rate falls from at earlier times down to at
present times, but we find a significant peak of star formation in the 2 to 3
Gyr age bin. The total mass of stars formed per unit area over time is , which is nearly twice the present
stellar mass derived from kinematics within 1~kpc from the Galactic Plane,
implying a high degree of matter recycling in successive generations of stars.
The method is then modified by adopting an age-dependent correlation between
the SFH across the different slices, which results in less noisy and more
symmetrical results without significantly changing the previously mentioned
quantities. This appears to be a promising way to improve SFH recovery in
external galaxies.Comment: Accepted for publication in MNRA
Dissecting the Gaia HR diagram II. The vertical structure of the star formation history across the Solar Cylinder
Starting from the Gaia DR3 HR diagram, we derive the star formation history (SFH) as a function of distance from the Galactic Plane within a cylinder centred on the Sun with a 200 pc radius and spanning 1.3 kpc above and below the Galaxy's midplane. We quantify both the concentration of the more recent star formation in the Galactic Plane, and the age-related increase in the scale height of the Galactic Disc stellar component, which is well-described by power-laws with indices ranging from 1/2 to 2/3. The vertically-integrated star formation rate falls from (1.147 ± 0.039) × 10-8 M⊙yr-1pc-2 at earlier times down to (6.2 ± 3.0) × 10-9 M⊙yr-1pc-2 at present times, but we find a significant peak of star formation in the 2 to 3 Gyr age bin. The total mass of stars formed per unit area over time is 118.7 ± 6.2 M⊙pc-2, which is nearly twice the present stellar mass derived from kinematics within 1 kpc from the Galactic Plane, implying a high degree of matter recycling in successive generations of stars. The method is then modified by adopting an age-dependent correlation between the SFH across the different slices, which results in less noisy and more symmetrical results without significantly changing the previously mentioned quantities. This appears to be a promising way to improve SFH recovery in external galaxies
RNY-derived small RNAs as a signature of coronary artery disease
International audienceBackgroundData from next generation sequencing technologies uncovered the existence of many classes of small RNAs. Recent studies reported that small RNAs are released by cells and can be detected in the blood. In this report, we aimed to discover the occurrence of novel circulating small RNAs in coronary artery disease (CAD).MethodsWe used high-throughput sequencing of small RNAs from human and mouse apoptotic primary macrophages, and analyzed the data by empirical Bayes moderated t-statistics to assess differential expression and the Benjamini and Hochberg method to control the false discovery rate. Results were then confirmed by Northern blot and RT-qPCR in foam cells and in two animal models for atherosclerosis, namely ApoE −/− and Ldlr −/− mouse lines. Quantitative RT-PCR to detect identified small RNAs, the RNY-derived small RNAs, was performed using sera of 263 patients with CAD compared to 514 matched healthy controls; the Student t-test was applied to statistically assess differences. Associations of small RNAs with clinical characteristics and biological markers were tested using Spearman’s rank correlations, while multivariate logistic regressions were performed to test the statistical association of small RNA levels with CAD.ResultsHere, we report that, in macrophages stimulated with pro-apoptotic or pro-atherogenic stimuli, the Ro-associated non-coding RNAs, called RNYs or Y-RNAs, are processed into small RNAs (~24–34 nt) referred to as small-RNYs (s-RNYs), including s-RNY1-5p processed from RNY1. A significant upregulation of s-RNY expression was found in aortic arches and blood plasma from ApoE −/− and Ldlr −/− mice and in serum from CAD patients (P <0.001). Biostatistical analysis revealed a positive association of s-RNY1-5p with hs-CRP and ApoB levels; however, no statistical interaction was found between either of these two markers and s-RNY1-5p in relation to the CAD status. Levels of s-RNY1-5p were also independent from statin and fibrate therapies.ConclusionOur results position the s-RNY1-5p as a relevant novel independent diagnostic biomarker for atherosclerosis-related diseases. Measurement of circulating s-RNY expression would be a valuable companion diagnostic to monitor foam cell apoptosis during atherosclerosis pathogenesis and to evaluate patient’s responsiveness to future therapeutic strategies aiming to attenuate apoptosis in foam cells in advanced atherosclerotic lesions
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