 Subjects -> SCIENCES: COMPREHENSIVE WORKS (Total: 374 journals)
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- Le séisme de Mila du 07/08/2020 (Nord-Est algérien) : essai
d’interprétation de l’activité sismique et des effets induits au
niveau de la colline d’El Kherba
Abstract: La vulnérabilité du site de la ville de Mila aux mouvements de masse est une contrainte majeure devant son développement urbain. Son héritage morphologique explique largement sa dynamique actuelle. Les grandes coulées quaternaires, issues du démantèlement du flanc nord de Marechau, ont dévié l’oued Mila vers l’ouest pour s’enfoncer sous forme d’arc de cercle et dégager la colline d’El Kherba. La massivité de cette dernière a permis l’installation d’une série de ravins (paléo-vallons) parallèles, inégalement creusés. Faute de soutirage efficace, ces derniers ont été comblés. La surface de contact entre la roche en place et le matériau de comblement est restée une semelle de glissement potentielle. Aussi, la fréquence et l’intensité des séismes (probablement en partie induits) sont loin d’être négligeables. En effet, après l’envahissement du site par une urbanisation rapide et massive, les effets induits des derniers séismes ont été probablement amplifiés d’où les dégâts observés. The vulnerability of the site of the city of Mila to mass movements is a major constraint to its urban development. Its morphological heritage largely explains its current dynamics. The large Quaternary flows, resulting from the dismantling of the northern flank of Marechau, have deviated the wadi Mila westwards to sink in the form of an arc and clear the hill of El Kherba. The massiveness of the latter allowed the development of a series of parallel gullies (paleo valleys), unevenly dug. Due to the lack of effective extraction, these gullies were filled in by erosion waste material. The contact surface between the bedrock and the fill material remained a potential failure surface. The frequency and intensity of the (probably partly induced) earthquakes are far from negligible. Indeed, after the invasion of the site by a rapid and massive urbanization, the induced effects of the last earthquakes were probably amplified, hence the damage observed.
PubDate: Thu, 21 Sep 2023 00:00:00 +020
- Sociolinguistic Aspects of the Speech Act of Greeting in Persian and
English
Abstract: This paper has been DELETED
PubDate: Thu, 27 Jul 2023 00:00:00 +020
- The holoparasitic Orobanchaceae of Tlemcen region (north-western Algeria):
diversity, distribution and host range
Abstract: The knowledge of the holoparasitic Orobanchaceae of Tlemcen region is updated through surveys based on eleven years of fieldwork, analysis and revision of bibliographic information and consultation of the main Herbaria related to the studied area. The detailed distribution in geographical units of the 20 taxa, belonging to the four genera: Boulardia, Cistanche, Orobanche and Phelipanche have been provided, together with habitat description and host plants. We also highlight the presence of taxa with marked chorological interest, rarely cited on the territory, such as O. alba, O. gracilis, O. hederae, P. portoilicitana and P. reuteriana. Note that the species: Cistanche violacea, Orobanche calendulae, Orobanche caryophyllacea, Orobanche reticulata, and Phelipanche cernuahave not been found in the Tlemcen area so far, so we will consider them as conflicting species to be searched.
PubDate: Sun, 25 Jun 2023 00:00:00 +020
- The SALT survey of chemically-peculiar hot subdwarfs
Abstract: The Southern African Large Telescope (SALT) has surveyed a sample of 300 chemically-peculiar hot subdwarfs with a view to explore evolutionary pathways and connections between a large variety of stars. Observations have been obtained for the entire sample at intermediate resolution to provide classifications and atmosphere parameters, and a smaller sample at high resolution to permit detailed chemical abundance analyses. The first has provided a substantial sample of extremely helium-rich sdO stars, but has also led to significant discoveries of hot white dwarfs, pre-white dwarfs, heavy-metal subdwarfs and extreme helium stars. This paper provides an overview of the current status of the project.
PubDate: Thu, 25 May 2023 00:00:00 +020
- The origin of subdwarf B stars
Abstract: The origin of subdwarf B stars (sdBs) is unclear. Different formation channels are proposed including: close-binary evolution, helium-mixing on the red giant branch and the hot flasher scenario. Circumstantial evidence exists that sdBs can result from single star evolution in high metallicity populations. We investigate this possibility by using membership in the thin, thick disk and halo populations as a metallicity indicator. Radial velocity measurements were com-bined with Gaia proper motions to calculate space motions in the Galaxy. Galactic orbits and population memberships were derived. Preliminary results indicate more sdBs are members of the thin disk (86 sdBs) than of thick disk and halo (28 sdBs). Apparently single sdBs are found among all three populations. We look into the temperature distributions of the different types and discuss implication for formation scenarios.
PubDate: Tue, 23 May 2023 00:00:00 +020
- Eclipse Timing Variations Observed in PCEB Systems
Abstract: Post-common Envelope Eclipsing Binary (PCEB) systems with a white or sub-dwarf primary and a low-mass secondary are ideal systems to study Eclipse Timing Variations (ETVs) due to their relatively small total masses which make it easy to detect gravitationally bound, yet unseen, additional bodies even within planetary limits on long-period orbits. With the addition of the recent discovery of two planetary-mass bodies in the sdB + dM binary Kepler-451 system, the number of circumbinary planets in PCEBs approaches 30 now. However, some of these systems turned out to be dynamically unstable with the suggested planetary parameters. As more observations accumulate over time, there have been significant changes in both the number of suggested planets and their parameters. These necessitate a look back to the ETV analyses of these systems with new and more precise data spanning longer baselines. Within this contribution, we review the systems hosting substellar bodies suggested from the light-time effect they are claimed to be causing. We list the general problems encountered during the ETV analyses and the interpretation of the results, and comment on their possible solutions. We cal-culate and present the potentials of supporting evidence from astrometry, radial velocity, and transit observations as well as tests through dynamical stability analyses and magnetic activity assumptions.
PubDate: Tue, 23 May 2023 00:00:00 +020
- The fastest hot subdwarfs revisited
Abstract: Hyper-velocity stars (HVS) are enigmatic objects because they are travelling so fast that they escape from the Galaxy. Among hot subdwarfs, only one such star is known, the He-sdO US 708. The Hyper-MUCHFUSS collaboration provided additional HVS candidates. Here we revisit the fastest candidates including US 708 by analysing optical spectra and spectral energy distributions using a new grid of tailored model atmospheres and report preliminary results. The sample is dominated by H-rich subdwarfs and their distribution in the Kiel diagram appears to be bimodal for the sdB stars but otherwise fits canonical evolutionary models well. Gaia’s proper motion measurements allowed a precise kinematic investigation to be made. It turns out that all previously proposed HVS candidates are actually bound to the Galaxy, except US 708. The original candidate sample turns out to belong to an extreme halo population. The scarcity of available observations of US 708 calls for space-based UV and IR photometry as well as high precision radial velocity measurements.
PubDate: Tue, 23 May 2023 00:00:00 +020
- New Hot Subdwarf Variables from Gaia eDR3
Abstract: We present a search for new variable hot subdwarfs from Gaia eDR3 using the Zwicky Transient Facility DR9 and the 2.1 m Otto Struve Telescope at McDonald Observatory. We report the discovery of 22 HW Vir binaries, 24 reflection effect binaries, and 14 ellipsoidally modulated systems. Candidate selection for our high-speed observations was based on object location on the Gaia color-magnitude diagram and on intrinsic variability, which we estimate from the Gaia G flux uncertainties. Notable discoveries include a candidate 72 min period sdB+WD binary and two short period HW Vir binaries with periods around 67 min and 79 min, which includes the shortest-period eclipsing sdB+dM/BD discovered to date.
PubDate: Tue, 23 May 2023 00:00:00 +020
- sdO and peculiar X-ray emissions
Abstract: Some Be stars exhibit a bright and extremely hard X-ray emission, whose origin is debated. In this context, it has been advocated that stripped helium-star sdO companions could play a significant role. Using high quality datasets, we examined (1) the binarity of these peculiar Be stars and (2) the X-ray emission of known Be+sdO systems. In this contribution, we present the result of these two studies and assess their impact on the proposed scenario. Certaines étoiles de type Be présentent une émission en rayons X brillante et très dure, d’origine débattue. Il a notamment été proposé que des compagnons sdO pouvaient jouent un rôle majeur dans la génération de cette émission. Grâce à des donnés inédites de grande qualité, nous avons étudié (1) la binarité de ces étoiles Be particulières et (2) l’émission en rayons X de systèmes Be+sdO. Cette contribution présente les résultats de ces deux recherches et leur impact sur le scénario proposé.
PubDate: Tue, 23 May 2023 00:00:00 +020
- A grid of Non-LTE line-blanketed atmosphere structures and synthetic
spectra for subdwarfs
Abstract: We present an update of the grid of detailed atmosphere models and homogeneous synthetic spectra for hot, high-gravity subdwarf stars. High-resolution spectra and synthetic photometry were calculated in the wavelength range 1,000 Å – 10,000 Å using Non-LTE extensively line-blanketed atmosphere structures. Nous prèsentons une mise à jour de la grille des modèles d’atmosphère détaillés et des spectres synthétiques homogénes pour les étoiles sous-naines chaudes de haute gravité. Les spectres haute résolution et la photométrie synthétique ont été calculés dans la gamme de longueurs d’onde 1.000 Å - 10.000 Å à l’aide de structures atmosphériques non-LTE entiérement recouvertes de lignes.
PubDate: Tue, 23 May 2023 00:00:00 +020
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