arXiv subjects

Pierre Darriulat

Publications and source records attributed to Pierre Darriulat.

11 recordsLinked to original sources

arXiv2026

Pulsations along the Asymptotic Giant Branch (AGB): a global view

In three preceding articles, we studied the relation between the light curves of Mira variables and their stellar properties. The analysis was restricted to a sample of stars offering high density and quality of observations in the visible, allowing for the definition of simple parameterizations of the light curves. Clear relations were revealed between the evolution of the stars along the AGB and parameters such as the width of the light pulse or the deviation of its ascending branch from a sine wave. However, the restriction to Mira variables was found to be a major drawback preventing a complete picture to be drawn. The present article overcomes this deficiency by reviewing a large sample of semi-regular and irregular variables. It gives evidence for two families of stars having different progenies. The first family enters the AGB already pulsating with amplitudes at the scale of one unit of magnitude. It keeps cooling down and expanding, while pulsating with increasing amplitudes and periods and decreasing width of the light pulse; its progeny is dominated by some of the Mira variables studied in the three preceding articles. The second family enters the AGB before displaying significant pulsations; some of its progeny may leave the AGB without entering the Thermally Pulsing Branch and experiencing strong TDU events; others may instead become Mira variables studied in the three preceding articles and pulsating with a broader light pulse. The possible transition of both families from oxygen-rich to carbon-rich is studied and described. Comments on the interpretation of these results in the context of current state-of-the-art knowledge are presented. While the stars of the first family tend to have larger initial masses than the stars of the second family, details of the properties of the convective envelope seem also to play a role in defining which families a star belongs to.

astro-ph.SR↗

arXiv2026

On the shape of the ascending branch of the light curves of Long Period Variables

The present article is written in the wake of a recently published study of the relation between the light curves of Long Period Variables and their evolution along the Asymptotic Giant Branch (AGB). It introduces a pair of new parameters that describe the shape of the ascending branches of such light curves. This parameterization reveals strong correlations with other parameters describing the evolution of the star on the AGB: periods, regularity and amplitudes of the oscillations, effective temperatures, mass loss rates, carbon and oxygen isotopic ratios, colour indices. It sheds new light on the occasional presence of humps on the ascending branches and on the distinction between stars that have not experienced strong Third Dredge Up (TDU) events and those that have as well as between oxygen-rich and carbon-rich stars. One of the new parameters, referred to as q, is particularly efficient at tracking the evolution of the star along the AGB. Globally, a simple picture can be drawn in the plane spanned by the period and by q. Yet, many details remain unexplained when looking at this picture in finer details. Overall, the results presented in the article help significantly with clarifying the complex set of observations that have been made in this domain and should inspire new considerations on their relation with the underlying physical mechanisms at stake inside the stars.

astro-ph.SR↗

arXiv2025

From the light curves of Long Period Variables to their evolution along the AGB

A sample of 116 Long Period Variables is studied with the aim to reveal relations between the properties of their light curves and of their evolution along the Asymptotic Giant Branch (AGB). Each light curve is carefully scrutinized and its properties are summarized in a set of five parameters. One of these, which measures the relative width of the light maxima and minima, is found to be particularly efficient at revealing significant correlations with the current state of the star on the AGB. The picture that had been sketched in an earlier work is clarified and new features are revealed. In particular, the evolution on the AGB of stars having not yet experienced a third dredge-up event is shown to go together with a closely related path followed by the light curve in the parameter space. Moreover, evidence is found for the existence of two different types of light curves for stars having experienced dredge-up events strong enough for their impact to be detectable. For some, probably associated with higher initial mass stars, the light maximum becomes broader as the star evolves along the AGB, while for others it becomes narrower. Interpretations are proposed, however often too speculative to be firmly ascertained: the results presented raise several unanswered questions and point to the need for new observations and analyses, suggesting that light curves still carry more messages and information than has been currently possible to decrypt.

astro-ph.SR↗

arXiv2022

Recent mass ejection from AGB star W Hya

We analyse archival ALMA (Atacama Large Millimeter/submillimeter Array) observations of two molecular line emissions, $^{12}$CO(3-2) and $^{29}$SiO(8-7), from oxygen-rich AGB (Asymptotic Giant Branch) star W Hya. Together with results of earlier VLT observations at visible and infrared wavelengths, our results suggest a two-component picture of the morpho-kinematics of the circumstellar envelope (CSE), one stable over time, at the scale of centuries, and the other variable, at the scale of years. The stable component consists of an approximately spherical shell of gas and dust expanding radially to a terminal velocity of $\sim$5 km s$^{-1}$ at a distance of $\sim$30 au from the star. It is found to display comparable features as seen in the CSE of R Dor, a star similar to W Hya. The variable component projects on the plane of the sky over a region confined to the neighbourhood of the star and elongated toward the north. Its very high density and sudden acceleration suggest an interpretation in terms of mass ejection initiated a few years ago. We discuss its properties in relation with earlier observations of dust formation in the same region. Our results offer a picture of the wind of W Hya that differs significantly from the picture that could be suggested by earlier analyses, giving evidence for a mass ejection that had been previously overlooked and underscoring new relations between the dust and gas emissions. They have an impact on the evidence published earlier for the presence of CO masers. They favour an interpretation in terms of convective cell ejections playing the main role in the generation of the nascent wind, the stable component of the CSE being seen as the result of many successive such events occurring in different directions at short time intervals.

astro-ph.SR↗

arXiv2021

ALMA Observations of W Hya: Impact of missing baselines

The lack of short baselines, referred to as short-spacing problem (SSP), is a well-known limitation of the performance of radio interferometers, causing a reduction of the detected flux from large scale source structures. The very large number of antennas operated in the Atacama Large Millimeter/sub-millimeter Array (ALMA) generates situations for which the impact of the SSP takes a complex form, not simply measurable by a single number, such as the maximal recoverable scale. In particular extended antenna configurations, complemented by a small group of closeby antennas at the centre of the array, may result in a double-humped baseline distribution with a significant gap between the two groups. In such cases one should adopt as effective maximal recoverable scale that associated with the extended array and use only the central array to recover missing flux, as one would do with single dish or ACA (Atacama Compact Array) observations. The impact of the missing baselines can be very important and may easily be underestimated, or even overlooked. The present study uses ALMA archival data of the $^{29}$SiO(8-7) line emission of AGB star W Hya as an illustration. A critical discussion of the reliability of the observations away from the star is presented together with comments of a broader scope. Properties of the circumstellar envelope of W Hya within $\sim$15 au from the star, many of which are not mentioned in the published literature, are briefly described and compared with R Dor, an AGB star having properties very similar to W Hya.

astro-ph.SR↗

arXiv2015

$^{12}$CO emission from the Red Rectangle

Observations of an unprecedented quality made by ALMA on the Red Rectangle of CO(3-2) and CO(6-5) emissions are analysed jointly with the aim of obtaining as simple as possible a description of the gas morphology and kinematics. Evidence is found for polar conical outflows and for a broad equatorial torus in rotation and expansion. Simple models of both are proposed. Comparing CO(6-5) and CO(3-2) emissions provides evidence for a strong temperature enhancement over the polar outflows. Continuum emission (dust) is seen to be enhanced in the equatorial region. Observed asymmetries are briefly discussed.

astro-ph.SR↗

arXiv2014

On the central symmetry of the circumstellar envelope of RS Cnc

We present a phenomenological study of CO(1-0) and CO(2-1) emission from the circumstellar envelope (CSE) of the Asymptotic Giant Branch (AGB) star RS\,Cnc. It reveals departures from central symmetry that turn out to be efficient tools for the exploration of some of the CSE properties. We use a wind model including a bipolar flow with a typical wind velocity of $\sim$8 km\,s$^{-1}$ decreasing to $\sim$2 km\,s$^{-1}$ near the equator to describe Doppler velocity spectral maps obtained by merging data collected at the IRAM Plateau de Bure Interferometer and Pico Veleta single dish radio telescope. Parameters describing the wind morphology and kinematics are obtained, together with the radial dependence of the gas temperature in the domain of the circumstellar envelope probed by the CO observations. Significant north-south central asymmetries are revealed by the analysis, which we quantify using a simple phenomenological description. The origin of such asymmetries is unclear.

astro-ph.SR↗

arXiv2012

Large-transverse-momentum processes: the ISR as a gluon collider

It is argued that, contrary to what is often said, large-transverse-momentum hadronic processes studied at the ISR have made a significant contribution to the understanding of the strong interaction and, in particular, to the development of quantum chromodynamics. In their unique role as a gluon collider the ISR have provided information that no other accelerator could have directly offered. They allowed one to probe high values of the centre-of-mass energy that were not available to fixed-target experiments. The latter, however, were more flexible and, together, they allowed for powerful explorations of the hadron structure and of the relevant dynamics in sectors such as inclusive particle production, direct photon production, and jet structure studies. It remains true that, rightly so, the ISR will be mostly remembered as the founders of a lineage that includes the proton-antiproton colliders and, today, the LHC.

physics.acc-ph↗

arXiv2012

Simulation of proton-induced and iron-induced extensive air showers at extreme energies

The development of extensive air showers at extreme energies is studied using a simulation model much simpler and cruder, but also more transparent and flexible, than existing sophisticated codes. Evidence for its satisfactory performance is presented. As an illustration, shower elongation rates are evaluated in the $10^{18}$ to $10^{20}$ eV region and compared with recently published data. Lateral distribution functions of both muons and electrons/photons are also briefly discussed. Reliable results are obtained in the comparison between proton-induced and iron-induced showers.

astro-ph.HE↗

arXiv2011

Three limits to the physical world

Three limits to the physical world (quantum physics, gravity and dark energy) are presented on a triangular diagram having as summits the Planck scale, the Universe and a neutrino-like object.

physics.pop-ph↗

arXiv2011

On a new method to analyse QSO spectra

A new method of analysis of QSO spectra, usually referred to as the "Thong method", has been recently presented and made use of in a number of publications. Several of these have been withdrawn because the authors have been convicted of plagiarism. However, there exists no publication showing that the method itself, which is an original contribution of the authors, is wrong. The purpose of the present note is to show that it is and that the results obtained when using it, including limits on the time variation of the fine structure constant many times smaller than published by other authors, must therefore be ignored and discarded.

astro-ph.CO↗