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At least 73 records · Page 4
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NASA NTRS2011

The Transitional Protoplanetary Disk Frequency as a Function of Age: Disk Evolution in the Coronet Cluster, Taurus, and Other 1--8 Myr-old Regions

We present Spitzer 3.6-24 micron photometry and spectroscopy for stars in the 1-3 Myr-old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. (2008). Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. (2008) to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters - IC 348, NGC 2362, and eta Cha -- to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks -- those with inner holes and those that are homologously depleted. The percentage of disks in the transitional phase increases from approx.15-20% at 1-2 Myr to > 50% at 5-8 Myr; the mean transitional disk lifetime is closer to approx. 1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. (2009) and Sicilia-Aguilar et al. (2009). In the Coronet Cluster and IC 348, transitional disks are more numerous for very low-mass M3--M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically-thick primordial disks is Mdisk approx. 0.001-0.003 M*. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full SED modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.

Currie, Thayne↗
NASA NTRS2012

Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk around PDS 70: Observations of the Disk

We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14 AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly resolvro for the first time, and the radius of the gap is approx 70 AU. Our data show that the geometric center of the disk shifts by approx 6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of SED fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit mass of companions at approx 30 to approx 50M(sub J) within the gap. Taking account of the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap.

Hashimoto, J.↗
NASA NTRS2013

Herschel - PACS Survey Of Protoplanetary Disks In Taurus - Auriga Observations Of [O I] And [C Ii], And Far-Infrared Continuum

The Herschel Space Observatory was used to observe approx. 120 pre-main-sequence stars in Taurus as part of the GASPS Open Time Key project. Photodetector Array Camera and Spectrometer was used to measure the continuum as well as several gas tracers such as [O I] 63 micron, [O I] 145 micron, [C II] 158, micron OH, H2O, and CO. The strongest line seen is [O I] at 63 micron. We find a clear correlation between the strength of the [O I] 63 micron line and the 63 micron continuum for disk sources. In outflow sources, the line emission can be up to 20 times stronger than in disk sources, suggesting that the line emission is dominated by the outflow. The tight correlation seen for disk sources suggests that the emission arises from the inner disk (<50 AU) and lower surface layers of the disk where the gas and dust are coupled. The [O I] 63 micron is fainter in transitional stars than in normal Class II disks. Simple spectral energy distribution models indicate that the dust responsible for the continuum emission is colder in these disks, leading to weaker line emission. [C II] 158 micron emission is only detected in strong outflow sources. The observed line ratios of [O I] 63 micron to [O I] 145 micron are in the regime where we are insensitive to the gas-to-dust ratio, neither can we discriminate between shock or photodissociation region emission. We detect no Class III object in [O I] 63 micron and only three in continuum, at least one of which is a candidate debris disk.

GASPS Open Time Key project↗
NASA NTRS2016

Calcium and Titanium Isotope Fractionation in CAIS: Tracers of Condensation and Inheritance in the Early Solar Protoplanetary Disk

The chemical and isotopic compositions of calcium-aluminum-rich inclusions (CAIs) can be used to understand the conditions present in the protoplantary disk where they formed. The isotopic compositions of these early-formed nebular materials are largely controlled by chemical volatility. The isotopic effects of evaporation/sublimation, which are well explained by both theory and experimental work, lead to enrichments of the heavy isotopes that are often exhibited by the moderately refractory elements Mg and Si. Less well understood are the isotopic effects of condensation, which limits our ability to determine whether a CAI is a primary condensate and/or retains any evidence of its primordial formation history.

Simon, J. I.↗
NASA NTRS2020

SCExAO/CHARIS High-contrast Imaging of Spirals and Darkening Features in the HD 34700 A Protoplanetary Disk

We present Subaru/SCExAO+Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) broadband (JHK-band) integral field spectroscopy of HD 34700 A. CHARIS data recover HD 34700 A's disk ring and confirm multiple spirals discovered by Monnier et al. We set limits on substellar companions of ∼12 MJup at 0.″3 (in the ring gap) and ∼5 M(Jup) at 0."75 (outside the ring). The data reveal darkening effects on the ring and spiral, although we do not identify the origin of each feature such as shadows or physical features related to the outer spirals. Geometric albedos converted from the surface brightness suggest a greater scale height and/or prominently abundant submicron dust at position angles between ∼45° and 90°. Spiral fitting resulted in very large pitch angles (∼30°–50°); a stellar flyby of HD 34700 B or infall from a possible envelope is perhaps a reasonable scenario to explain the large pitch angles.

Taichi Uyama↗
NASA NTRS2019

Grossite-Rich Refractory Inclusions in Carbonaceous Chondrites: Evidence for Early Generation of Different O-Isotope Reservoirs in the Protoplanetary Disk and O-Isotope Exchange During Fluid-Rock Interaction

The oxygen isotopic composition of the Sun inferred from the measurements of the solar wind returned by the Genesis spacecraft is O-16-enriched (△O-17 = -28.4±3.6‰) relative to the whole-rock O-isotope compositions of chondrites and achondrites, and chondrule phenocrysts, which all plot close to the terrestrial fractionation line (△O-17 ∼ ±5‰). Vast majority of refractory inclusions (CAIs and AOAs) in carbonaceous chondrites of petrologic types 2-3.0 are iso-topically uniform and have solar-like △O-17. In contrast, CAIs and AOAs in metamorphosed CV and CO chondrites are isotopically heterogeneous with melilite, anorthite, perovskite, Zr- and Sc-rich oxides and silicates, and occasionally Al, Ti-diopside being O-16-depleted relative to hibonite, spinel, Al-diopside, and forsterite. The timing of generation of different O-isotope reservoirs and the nature of O-isotope heterogeneity in refractory inclusions in CO3 and CV3 chondrites are poorly known. Grossite (CaAl4O7) is one of the first minerals predicted to condense from a gas of solar composition and therefore it could have recorded isotopic compositions of reservoirs during the earliest stages of the Solar System evolution. Here we report on O-isotope compositions of grossite-rich CAIs in CH3 and CO3 chondrites measured in situ with the UH Cameca ims-1280. For analytical procedures see [9].

A N Krot↗