926 research outputs found
Seismology of Procyon A: determination of mode frequencies, amplitudes, lifetimes, and granulation noise
The F5 IV-V star Procyon A (aCMi) was observed in January 2001 by means of
the high resolution spectrograph SARG operating with the TNG 3.5m Italian
telescope (Telescopio Nazionale Galileo) at Canary Islands, exploiting the
iodine cell technique. The time-series of about 950 spectra carried out during
6 observation nights and a preliminary data analysis were presented in Claudi
et al. 2005. These measurements showed a significant excess of power between
0.5 and 1.5 mHz, with ~ 1 m/s peak amplitude. Here we present a more detailed
analysis of the time-series, based on both radial velocity and line equivalent
width analyses. From the power spectrum we found a typical p-mode frequency
comb-like structure, identified with a good margin of certainty 11 frequencies
in the interval 0.5-1400 mHz of modes with l=0,1,2 and 7< n < 22, and
determined large and small frequency separations, Dn = 55.90 \pm 0.08 muHz and
dnu_02=7.1 \pm 1.3 muHz, respectively. The mean amplitude per mode (l=0,1) at
peak power results to be 0.45 \pm 0.07 m/s, twice larger than the solar one,
and the mode lifetime 2 \pm 0.4 d, that indicates a non-coherent, stochastic
source of mode excitation. Line equivalent width measurements do not show a
significant excess of power in the examined spectral region but allowed us to
infer an upper limit to the granulation noise.Comment: 10 pages, 15 figures, 4 tables. Accepted for publication in A&
Precision limits of the twin-beam multiband URSULA
URSULA is a multiband astronomical photoelectric photometer which minimizes errors introduced by the presence of the atmosphere. It operates with two identical channels, one for the star to be measured and the other for a reference star. After a technical description of the present version of the apparatus, some measurements of stellar sources of different brightness, and in different atmospheric conditions are presented. These measurements, based on observations made with the 91 cm Cassegrain telescope of the Catania Astrophysical Observatory, are used to check the photometer accuracy and compare its performance with that of standard photometers
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Crust-mantle interaction inferred from the petrology and Sr-Nd-Pb isotope geochemistry of Eocene arc lavas from the Kahrizak Mountains, north-Central Iran
The Eocene volcanic rocks from the Kahrizak Mountains in north-central Iran are part of the Urumieh-Dokhtar magmatic arc, which runs parallel to the Main Zagros Thrust segment of the Neo-Tethys suture. These volcanic rocks, similar to those from eastern Pontides and northern Anatolia, Turkey, were mainly produced during the Eocene magmatic flare-up associated with the Arabia-Eurasia convergence. The rock suite includes basalt, trachyandesite/andesite and trachydacite/rhyolite lavas and pyroclastic deposits that evolved compositionally from calc-alkalic to shoshonitic. Their normalized trace element concentration patterns are moderately enriched in light rare earth element and depleted in high field-strength elements (HFSE; e.g., Nb, Ta, Ti). They have narrow ranges of initial Pb isotopic ratios and ^(143)Nd/^(144)Nd_i, but highly variable ^(87)Sr/^(86)Sr_i. The new analyses indicate that the parental magmas of the volcanic rocks were derived from a mantle source that had been enriched by fluids released from a subducted oceanic slab. The fluids introduced significant amounts of large ion lithophile elements, but negligible HFSE to the source. The parental magmas underwent fractional crystallization and assimilation of upper crustal materials to produce the range of volcanic rocks. Integration of new analyses with regional data suggests that the Eocene volcanic rocks from north-central Iran, together with ~coeval volcanic rocks in eastern Pontides and northern Anatolia, were most probably derived from a lithospheric mantle source that had been previously metasomatized by fluids derived from a subducted slab before and during the Arabia-Eurasia collision
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The boundary between the Central Asian Orogenic belt and Tethyan tectonic domain deduced from Pb isotopic data
The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA) I: The Sample and the Spectra
We introduce Project MEGaSaURA: The Magellan Evolution of Galaxies
Spectroscopic and Ultraviolet Reference Atlas. MEGaSaURA comprises
medium-resolution, rest-frame ultraviolet spectroscopy of N=15 bright
gravitationally lensed galaxies at redshifts of 1.68z3.6, obtained with
the MagE spectrograph on the Magellan telescopes. The spectra cover the
observed-frame wavelength range \AA ; the average
spectral resolving power is R=3300. The median spectrum has a signal-to-noise
ratio of per resolution element at 5000 \AA . As such, the MEGaSaURA
spectra have superior signal-to-noise-ratio and wavelength coverage compared to
what COS/HST provides for starburst galaxies in the local universe. This paper
describes the sample, the observations, and the data reduction. We compare the
measured redshifts for the stars, the ionized gas as traced by nebular lines,
and the neutral gas as traced by absorption lines; we find the expected bulk
outflow of the neutral gas, and no systemic offset between the redshifts
measured from nebular lines and the redshifts measured from the stellar
continuum. We provide the MEGaSaURA spectra to the astronomical community
through a data release.Comment: Resubmitted to AAS Journals. Data release will accompany journal
publication. v2 addresses minor comments from refere
Tuning Fullerene Intercalation in a Poly (thiophene) derivative by Controlling the Polymer Degree of Self-Organisation
Controlling the nanoscale arrangement in polymer-fullerene organic solar cells is of paramount importance to boost the performance of such promising class of photovoltaic diodes. In this work, we use a pseudo-bilayer system made of poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), to acquire a more complete understanding of the diffusion and intercalation of the fullerene-derivative within the polymer layer. By exploiting morphological and structural characterisation techniques, we observe that if we increase the film solidification time the polymer develops a higher crystalline order, and, as a result, it does not allow fullerene molecules to intercalate between the polymer side-chains. Gaining insight into the detailed fullerene intercalation mechanism is important for the development of organic photovoltaic diodes (PVDs)
Oceanic Zircon Records Extreme Fractional Crystallization of MORB to Rhyolite on the Alarcon Rise Mid-Ocean Ridge
The first known occurrence of rhyolite along the submarine segments of the mid-ocean ridge (MOR) system was discovered on Alarcon Rise, the northernmost segment of the East Pacific Rise (EPR), by the Monterey Bay Aquarium Research Institute in 2012. Zircon trace element and Hf and O isotope patterns indicate that the rhyolite formed by extreme crystal fractionation of primary mid-ocean ridge basalt (MORB) sourced from normal to enriched MOR mantle with little to no addition of continental lithosphere or hydrated oceanic crust. A large range in zircon ϵHf spanning 11 ϵ units is comparable to the range of whole rock ϵHf from the entire EPR. This variability is comparable to continental granitoids that develop over long periods of time from multiple sources. Zircon geochronology from Alarcon Rise suggests that at least 20 kyr was needed for rhyolite petrogenesis. Grain-scale textural discontinuities and trace element trends from zircon cores and rims are consistent with crystal fractionation from a MORB magma with possible perturbations associated with mixing or replenishment events. Comparison of whole rock and zircon oxygen isotopes with modeled fractionation and zircon-melt patterns suggests that, after they formed, rhyolite magmas entrained hydrated mafic crust from conduit walls during ascent and/or were hydrated by seawater in the vent during eruption. These data do not support a model where rhyolites formed directly from partial melts of hydrated oceanic crust or do they require assimilation of such crust during fractional crystallization, both models being commonly invoked for the formation of oceanic plagiogranites and dacites. A spatial association of highly evolved lavas (rhyolites) with an increased number of fault scarps on the northern Alarcon Rise might suggest that low magma flux for ∼20 kyr facilitated extended magma residence necessary to generate rhyolite from MORB
Lens Model and Time Delay Predictions for the Sextuply Lensed Quasar SDSS J2222+2745
SDSS J2222+2745 is a galaxy cluster at z=0.49, strongly lensing a quasar at
z=2.805 into six widely separated images. In recent HST imaging of the field,
we identify additional multiply lensed galaxies, and confirm the sixth quasar
image that was identified by Dahle et al. (2013). We used the Gemini North
telescope to measure a spectroscopic redshift of z=4.56 of one of the secondary
lensed galaxies. These data are used to refine the lens model of SDSS
J2222+2745, compute the time delay and magnifications of the lensed quasar
images, and reconstruct the source image of the quasar host and a second lensed
galaxy at z=2.3. This second galaxy also appears in absorption in our Gemini
spectra of the lensed quasar, at a projected distance of 34 kpc. Our model is
in agreement with the recent time delay measurements of Dahle et al. (2015),
who found tAB=47.7+/-6.0 days and tAC=-722+/-24 days. We use the observed time
delays to further constrain the model, and find that the model-predicted time
delays of the three faint images of the quasar are tAD=502+/-68 days,
tAE=611+/-75 days, and tAF=415+/-72 days. We have initiated a follow-up
campaign to measure these time delays with Gemini North. Finally, we present
initial results from an X-ray monitoring program with Swift, indicating the
presence of hard X-ray emission from the lensed quasar, as well as extended
X-ray emission from the cluster itself, which is consistent with the lensing
mass measurement and the cluster velocity dispersion.Comment: 16 pages, 11 figures; submitted to Ap
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