391 research outputs found
Unveiling the Structure of Pre-Transitional Disks
In the past few years, several disks with inner holes that are empty of small
dust grains have been detected and are known as transitional disks. Recently,
Spitzer has identified a new class of "pre-transitional disks" with gaps; these
objects have an optically thick inner disk separated from an optically thick
outer disk by an optically thin disk gap. A near-infrared spectrum provided the
first confirmation of a gap in the pre-transitional disk of LkCa 15 by
verifying that the near-infrared excess emission in this object was due to an
optically thick inner disk. Here we investigate the difference between the
nature of the inner regions of transitional and pre-transitional disks using
the same veiling-based technique to extract the near-infrared excess emission
above the stellar photosphere. We show that the near-infrared excess emission
of the previously identified pre-transitional disks of LkCa 15 and UX Tau A in
Taurus as well as the newly identified pre-transitional disk of ROX 44 in
Ophiuchus can be fit with an inner disk wall located at the dust destruction
radius. We also model the broad-band SEDs of these objects, taking into account
the effect of shadowing by the inner disk on the outer disk, considering the
finite size of the star. The near-infrared excess continua of these three
pre-transitional disks, which can be explained by optically thick inner disks,
are significantly different from that of the transitional disks of GM Aur,
whose near-infrared excess continuum can be reproduced by emission from
sub-micron-sized optically thin dust, and DM Tau, whose near-infrared spectrum
is consistent with a disk hole that is relatively free of small dust. The
structure of pre-transitional disks may be a sign of young planets forming in
these disks and future studies of pre-transitional disks will provide
constraints to aid in theoretical modeling of planet formation.Comment: Accepted for publication in ApJ on May 10, 2010; 29 page
Ophiolite-Related Ultramafic Rocks (Serpentinites) in the Caribbean Region : a Review of their Occurrence, Composition, Origin, Emplacement and Ni-Laterite Soil Formation
Ultramafic rocks, mainly serpentinized peridotites of mantle origin, are mostly associated with the ophiolites of Mesozoic age that occur in belts along three of the margins of the Caribbean plate. The most extensive exposures are in Cuba. The ultramafic-mafic association (ophiolites) were formed and emplaced in several different tectonic environments. Mineralogical studies of the ultramafic rocks and the chemistry of the associated mafic rocks indicate that most of the ultramafic-mafic associations in both the northern and southern margins of the plate were formed in arc-related environments. There is little mantle peridotite exposed in the ophiolitic associations of the west coast of Central America, in the south Caribbean in Curacao and in the Andean belts in Colombia. In these occurrences the chemistry and age of the mafic rocks indicates that this association is mainly part of the 89 Ma Caribbean plateau province. The age of the mantle peridotites and associated ophiolites is probably mainly late Jurassic or Early Cretaceous. Emplacement of the ophiolites possibly began in the Early Cretaceous in Hispaniola and Puerto Rico, but most emplacement took place in the Late Cretaceous to Eocene (e.g. Cuba). Along the northern South America plate margin, in the Caribbean mountain belt, emplacement was by major thrusting and probably was not completed until the Oligocene or even the early Miocene. Caribbean mantle peridotites, before serpentinization, were mainly harzburgites, but dunites and lherzolites are also present. In detail, the mineralogical and chemical composition varies even within one ultramafic body, reflecting melting processes and peridotite/melt interaction in the upper mantle. At least for the northern Caribbean, uplift (postemplacement tectonics) exposed the ultramafic massifs as a land surface to effective laterization in the beginning of the Miocene. Tectonic factors, determining the uplift, exposing the peridotites to weathering varied. In the northern Caribbean, in Guatemala, Jamaica, and Hispaniola, uplift occurred as a result of transpresional movement along pre-existing major faults. In Cuba, uplift occurred on a regional scale, determined by isostatic adjustment. In the south Caribbean, uplift of the Cordillera de la Costa and Serrania del Interior exposing the peridotites, also appears to be related to strike-slip movement along the El Pilar fault system. In the Caribbean, Ni-laterite deposits are currently being mined in the central Dominican Republic, eastern Cuba, northern Venezuela and northwest Colombia. Although apparently formed over ultramafic rocks of similar composition and under similar climatic conditions, the composition of the lateritic soils varies. Factors that probably determined these differences in laterite composition are geomorphology, topography, drainage and tectonics. According to the mineralogy of principal ore-bearing phases, Dominican Ni-laterite deposits are classified as the hydrous silicate-type. The main Ni-bearing minerals are hydrated Mg-Ni silicates (serpentine and "garnierite") occurring deeper in the profile (saprolite horizon). In contrast, in the deposits of eastern Cuba, the Ni and Co occurs mainly in the limonite zone composed of Fe hydroxides and oxides as the dominant mineralogy in the upper part of the profile, and are classified as the oxide-type
Disk Imaging Survey of Chemistry with SMA: II. Southern Sky Protoplanetary Disk Data and Full Sample Statistics
This is the second in a series of papers based on data from DISCS, a
Submillimeter Array observing program aimed at spatially and spectrally
resolving the chemical composition of 12 protoplanetary disks. We present data
on six Southern sky sources - IM Lup, SAO 206462 (HD 135344b), HD 142527, AS
209, AS 205 and V4046 Sgr - which complement the six sources in the Taurus star
forming region reported previously. CO 2-1 and HCO+ 3-2 emission are detected
and resolved in all disks and show velocity patterns consistent with Keplerian
rotation. Where detected, the emission from DCO+ 3-2, N2H+ 3-2, H2CO 3-2 and
4-3,HCN 3-2 and CN 2-1 are also generally spatially resolved. The detection
rates are highest toward the M and K stars, while the F star SAO 206462 has
only weak CN and HCN emission, and H2CO alone is detected toward HD 142527.
These findings together with the statistics from the previous Taurus disks,
support the hypothesis that high detection rates of many small molecules depend
on the presence of a cold and protected disk midplane, which is less common
around F and A stars compared to M and K stars. Disk-averaged variations in the
proposed radiation tracer CN/HCN are found to be small, despite two orders of
magnitude range of spectral types and accretion rates. In contrast, the
resolved images suggest that the CN/HCN emission ratio varies with disk radius
in at least two of the systems. There are no clear observational differences in
the disk chemistry between the classical/full T Tauri disks and transitional
disks. Furthermore, the observed line emission does not depend on measured
accretion luminosities or the number of infrared lines detected, which suggests
that the chemistry outside of 100 AU is not coupled to the physical processes
that drive the chemistry in the innermost few AU.Comment: accepted for publication in ApJ, 41 pages including 7 figure
Ophiolite-Related Ultramafic Rocks (Serpentinites) in the Caribbean Region: A Review of their Occurrence, Composition, Origin, Emplacement and Ni-Laterite Soil Formation
Ultramafic rocks, mainly serpentinized peridotites of mantle origin, are mostly associated with the ophiolites of Mesozoic age that occur in belts along three of the margins of the Caribbean plate. The most extensive exposures are in Cuba. The ultramafic-mafic association (ophiolites) were formed and emplaced in several different tectonic environments. Mineralogical studies of the ultramafic rocks and the chemistry of the associated mafic rocks indicate that most of the ultramafic-mafic associations in both the northern and southern margins of the plate were formed in arc-related environments. There is little mantle peridotite exposed in the ophiolitic associations of the west coast of Central America, in the south Caribbean in Curacao and in the Andean belts in Colombia. In these occurrences the chemistry and age of the mafic rocks indicates that this association is mainly part of the 89 Ma Caribbean plateau province. The age of the mantle peridotites and associated ophiolites is probably mainly late Jurassic or Early Cretaceous. Emplacement of the ophiolites possibly began in the Early Cretaceous in Hispaniola and Puerto Rico, but most emplacement took place in the Late Cretaceous to Eocene (e.g. Cuba). Along the northern South America plate margin, in the Caribbean mountain belt, emplacement was by major thrusting and probably was not completed until the Oligocene or even the early Miocene. Caribbean mantle peridotites, before serpentinization, were mainly harzburgites, but dunites and lherzolites are also present. In detail, the mineralogical and chemical composition varies even within one ultramafic body, reflecting melting processes and peridotite/melt interaction in the upper mantle. At least for the northern Caribbean, uplift (postemplacement tectonics) exposed the ultramafic massifs as a land surface to effective laterization in the beginning of the Miocene. Tectonic factors, determining the uplift, exposing the peridotites to weathering varied. In the northern Caribbean, in Guatemala, Jamaica, and Hispaniola, uplift occurred as a result of transpresional movement along pre-existing major faults. In Cuba, uplift occurred on a regional scale, determined by isostatic adjustment. In the south Caribbean, uplift of the Cordillera de la Costa and Serrania del Interior exposing the peridotites, also appears to be related to strike-slip movement along the El Pilar fault system. In the Caribbean, Ni-laterite deposits are currently being mined in the central Dominican Republic, eastern Cuba, northern Venezuela and northwest Colombia. Although apparently formed over ultramafic rocks of similar composition and under similar climatic conditions, the composition of the lateritic soils varies. Factors that probably determined these differences in laterite composition are geomorphology, topography, drainage and tectonics. According to the mineralogy of principal ore-bearing phases, Dominican Ni-laterite deposits are classified as the hydrous silicate-type. The main Ni-bearing minerals are hydrated Mg-Ni silicates (serpentine and “garnierite”) occurring deeper in the profile (saprolite horizon). In contrast, in the deposits of eastern Cuba, the Ni and Co occurs mainly in the limonite zone composed of Fe hydroxides and oxides as the dominant mineralogy in the upper part of the profile, and are classified as the oxide-type
Predictors of photic phenomena with a trifocal IOL
© 2021 Espaillat et al. This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution - Non Commercial (unported, v3.0) License.Aim: To assess predictive factors associated with glares and halos in patients undergoing cataract surgery with PanOptix trifocal IOL implantation.
Methods: Single-center retrospective study. One hundred and forty eyes from 70 patients with cataract were bilaterally implanted with a trifocal PanOptix aspherical diffractive lens between 2017 and 2019 and followed-up for six months. All patients were evaluated for refraction, corneal topography, and aberrometry pre- and post-operatively. Patients were assessed at 1 day, 6 days, 1 and 6 months after surgery. One and six months post-operatively patients were asked to complete a satisfaction questionnaire that included photic phenomena assessment. Main outcome measures were photic phenomena at 1 and 6 months of follow-up. Predictors of photic phenomena at 1 and 6 months were also analyzed.
Results: A higher corneal coma was associated with more mild halos at 6 months with no association regarding other degrees of severity. The lower the age the higher the glare or halos, the higher the lens thickness and the lower the anterior chamber depth or chord μ the less halos at 1 month. A significant proportion of patients had more none/mild compared to moderate/severe glare and halos both at 1 and 6 months post-operatively. Baseline BCVA was the only predictor of halos at 1 month and glare and halos at 6 months post-surgery.
Conclusion: On multivariate regression analyses, the only predictor of photic phenomena was baseline visual acuity, suggesting that patients that have a better visual acuity before surgery are more demanding regarding visual outcomes after surgery.info:eu-repo/semantics/publishedVersio
Herschel evidence for disk flattening or gas depletion in transitional disks
Transitional disks are protoplanetary disks characterized by reduced near-
and mid-infrared emission with respect to full disks. This characteristic
spectral energy distribution indicates the presence of an optically thin inner
cavity within the dust disk believed to mark the disappearance of the
primordial massive disk. We present new Herschel Space Observatory PACS spectra
of [OI] 63 micron for 21 transitional disks. Our survey complements the larger
Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by
quadrupling the number of transitional disks observed with PACS at this
wavelength. [OI] 63 micron traces material in the outer regions of the disk,
beyond the inner cavity of most transitional disks. We find that transitional
disks have [OI] 63 micron line luminosities two times fainter than their full
disk counterparts. We self consistently determine various stellar properties
(e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk
dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we
find no correlations that can explain the lower [OI] 63 micron line
luminosities in transitional disks. Using a grid of thermo-chemical
protoplanetary disk models, we conclude that either transitional disks are less
flared than full disks or they possess lower gas-to-dust ratios due to a
depletion of gas mass. This result suggests that transitional disks are more
evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table
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