134 research outputs found
Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the delta Scuti stars rho Pup and DX Cet
High-resolution spectroscopy is a powerful tool to study the dynamical
structure of pulsating stars atmosphere. We aim at comparing the line asymmetry
and velocity of the two delta Sct stars rho Pup and DX Cet with previous
spectroscopic data obtained on classical Cepheids and beta Cep stars. We
obtained, analysed and discuss HARPS high-resolution spectra of rho Pup and DX
Cet. We derived the same physical quantities as used in previous studies, which
are the first-moment radial velocities and the bi-Gaussian spectral line
asymmetries. The identification of f=7.098 (1/d) as a fundamental radial mode
and the very accurate Hipparcos parallax promote rho Pup as the best standard
candle to test the period-luminosity relations of delta Sct stars. The action
of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle
variations in the radial velocity measurements of rho Pup. Using the
spectral-line asymmetry method, we also found the centre-of-mass velocities of
rho Pup and DX Cet, V_gamma = 47.49 +/- 0.07 km/s and V_gamma = 25.75 +/- 0.06
km/s, respectively. By comparing our results with previous HARPS observations
of classical Cepheids and beta Cep stars, we confirm the linear relation
between the atmospheric velocity gradient and the amplitude of the radial
velocity curve, but only for amplitudes larger than 22.5 km/s. For lower values
of the velocity amplitude (i.e., < 22.5 km/s), our data on rho Pup seem to
indicate that the velocity gradient is null, but this result needs to be
confirmed with additional data. We derived the Baade-Wesselink projection
factor p = 1.36 +/- 0.02 for rho Pup and p = 1.39 +/- 0.02 for DX Cet. We
successfully extended the period-projection factor relation from classical
Cepheids to delta Scuti stars.Comment: Accepted for publication in A&A (in press
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A revised chronostratigraphic framework for International Ocean Discovery Program Expedition 355 sites in Laxmi Basin, eastern Arabian Sea
AbstractInternational Ocean Discovery Program Expedition 355 drilled Sites U1456 and U1457 in Laxmi Basin (eastern Arabian Sea) to document the impact of the South Asian monsoon on weathering and erosion of the Himalaya. We revised the chronostratigraphic framework for these sites using a combination of biostratigraphy, magnetostratigraphy and strontium isotope stratigraphy. The sedimentary section at the two sites is similar and we divided it into six units bounded by unconformities or emplaced as a mass-transport deposit (MTD). Unit 1 underlies the MTD, and is of earlyâmiddle Miocene age at Site U1456 and early Paleocene age at Site U1457. An unconformity (U1) created by emplacement of the MTD (unit 2) during the late Miocene Epoch (at c. 9.83â9.69 Ma) separates units 1 and 2 and is identified by a marked change in lithology. Unit 3 consists of hemipelagic sediment with thin interbeds of graded sandstone of late Miocene age, separated from unit 4 by a second unconformity (U2) of 0.5â0.9 Myr duration. Unit 4 consists of upper Miocene interbedded mudstone and sandstone and hemipelagic chalk deposited between c. 8 and 6 Ma. A c. 1.4â1.6 Myr hiatus (U3) encompasses the MioceneâPliocene boundary and separates unit 4 from unit 5. Unit 5 includes upper Pliocene â lower Pleistocene siliciclastic sediment that is separated from unit 6 by a c. 0.45 Myr hiatus (U4) in the lower Pleistocene sediments. Unit 6 includes a thick package of rapidly deposited Pleistocene sand and mud overlain by predominantly hemipelagic sediment deposited since c. 1.2 Ma
Preliminary orbital elements of six visual binary stars
International audiencePreliminary new orbital elements were computed for the visual binary stars A 1 - ADS 1345, A 2629 - ADS 3610, BU 560 - ADS 4371, STF 3115 - ADS 4376, STF 1426 AB - ADS 7730 and STF 2437 - ADS 11956. Using Straizys and Kuriliene's data, we derived new formulae for computing dynamical parallaxes for luminosity classes IV and V. The values found for those systems are in agreement with the {Hipparcos} parallaxes and the corresponding systemic masses are consistent with the spectral types
Speckle observations with PISCO in Merate - II. Astrometric measurements of visual binaries in 2004
International audienceWe present relative astrometric measurements of visual binaries taken during the second semester of 2004 with the Pupil Interferometry Speckle camera and Coronagraph (PISCO) at the 1-m Zeiss telescope of the Brera Astronomical Observatory, in Merate, Italy. We performed 207 new observations of 194 objects with angular separations in the range 0.1-4.0 arcsec and an accuracy better than ~0.01 arcsec. Our sample contains orbital couples as well as binaries whose motion is still uncertain. Our purpose is to improve the accuracy of the orbits and constrain the masses of the components. Those measurements show that the orbit of ADS 15115 needs to be revised; we propose a new orbit for this object
Time intervals to assess active and capable faults for engineering practices in Italy
The time span necessary to define a fault as âactive and capableâ can mainly be derived from the framework of
the regulations and the literature produced since the 1970s on risk estimation in engineering planning of
strategic buildings. Within this framework, two different lines of thought can be determined, which have
mainly developed in the USA. On the one side, there is a tendency to produce ânarrowâ chronological
definitions. This is particularly evident in the regulatory acts for the planning of nuclear reactors. The much
more effective second line of thought anchors the chronological definitions of the terms âactiveâ and,
therefore âcapableâ, to the concept of âseismotectonic domainâ. As the domains are different in different
regions of the World, the chronological definition cannot be univocal; i.e., different criteria are needed to
define fault activity, which will depend on the characteristics of the local tectonic domain and of the related
recurrence times of fault activation. Current research on active tectonics indicates that methodological
aspects can also condition the chronological choice to define fault activity. Indeed, this practice implies the
use of earth science methods, the applications of which can be inherently limited. For example, limits and
constraints might be related to the availability of datable sediments and landforms that can be used to define
the recent fault kinematic history. For the Italian territory, we consider two main tectonic domains: (a) the
compressive domain along the southern margin of the Alpine chain and the northern and northeastern
margins of the Apennines, which is characterised by the activity of blind thrusts and reverse faults; and (b)
the extensional domain of the Apennines and the Calabria region, which is often manifest through the activity
of seismogenic normal and normal-oblique faults. In case (a), the general geomorphic and subsurficial
evidence of recent activity suggests that a reverse blind fault or a blind thrust should be considered active and
potentially capable if showing evidence of activity during the Quaternary (i.e., over the last 2.6 Myr), unless
information is available that documents its inactivity since at least the Last Glacial Maximum (LGM) (ca. 20 ka).
The choice of the LGM period as the minimum age necessary to define fault inactivity is related to practical
aspects (the diffusion of the LGM deposits and landforms) and to the evidence that ca. 20 kyr to assess fault
inactivity precautionarily includes a number of seismic cycles. In the extensional domains of the Apennines
and Calabria region, the general geological setting suggests that the present tectonic regime has been active
since the beginning of the Middle Pleistocene. Therefore, we propose that a normal fault in the Italian
extensional domain should be considered active and capable if it displays evidence of activation in the last 0.8 Myr,
unless it is sealed by deposits or landforms not younger than the LGM. The choice of the LGM as the minimum
age to ascertain fault inactivity follows the same criteria described for the compressive tectonic domain
Speckle observations with PISCO in Merate - III. Astrometric measurements of visual binaries in 2005 and scale calibration with a grating mask
International audienceWe present relative astrometric measurements of visual binaries made during the first semester of 2005, with the Pupil Interferometry Speckle Camera and Coronagraph (PISCO) at the 102-cm Zeiss telescope of the Brera Astronomical Observatory, in Merate. We performed 214 new observations of 192 objects, with angular separations in the range 0.2-4.3arcsec, and with an average accuracy of 0.01arcsec. Most of the position angles could be determined without the usual 180° ambiguity, and their mean error is . Our sample contains orbital couples as well as binaries whose motion is still uncertain. The purpose of this long-term programme is to improve the accuracy of the orbits and constrain the masses of the components. For the first time with PISCO, the astrometric calibration was made with a grating mask mounted at the entrance of the telescope. The advantage of this procedure is to provide a reliable and fully independent scale determination. We have found two possible new triple systems: ADS 7871 and KUI 15. We propose a preliminary orbit for ADS 4208
Speckle observations with PISCO in Merate - V. Astrometric measurements of visual binaries in 2006
International audienceWe present relative astrometric measurements of visual binaries made during the first semester of 2006, with the Pupil Interferometry Speckle camera and COronagraph at the 102-cm Zeiss telescope of the Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 217 new measurements of 194 objects, with angular separations in the range 0.1-4.2arcsec, and an average accuracy of 0.01arcsec. The mean error on the position angles is 0.5°. About half of those angles could be determined without the usual 180° ambiguity by the application of triple-correlation techniques. We also present a revised orbit for ADS 277 for which the previously published orbit resulted in a large residual from our measurements
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