679 research outputs found
CHARA/MIRC observations of two M supergiants in Perseus OB1: temperature, Bayesian modeling, and compressed sensing imaging
Two red supergiants of the Per OB1 association, RS Per and T Per, have been
observed in H band using the MIRC instrument at the CHARA array. The data show
clear evidence of departure from circular symmetry. We present here new
techniques specially developed to analyze such cases, based on state-of-the-art
statistical frameworks. The stellar surfaces are first modeled as limb-darkened
discs based on SATLAS models that fit both MIRC interferometric data and
publicly available spectrophotometric data. Bayesian model selection is then
used to determine the most probable number of spots. The effective surface
temperatures are also determined and give further support to the recently
derived hotter temperature scales of red su- pergiants. The stellar surfaces
are reconstructed by our model-independent imaging code SQUEEZE, making use of
its novel regularizer based on Compressed Sensing theory. We find excellent
agreement between the model-selection results and the reconstructions. Our
results provide evidence for the presence of near-infrared spots representing
about 3-5% of the stellar flux
Confronting Standard Models of Proto--Planetary Disks With New Mid--Infrared Sizes from the Keck Interferometer
We present near and mid-infrared interferometric observations made with the
Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the
IRTF of 11 well known young stellar objects, several observed for the first
time in these spectral and spatial resolution regimes. With AU-level spatial
resolution, we first establish characteristic sizes of the infrared emission
using a simple geometrical model consisting of a hot inner rim and mid-infrared
disk emission. We find a high degree of correlation between the stellar
luminosity and the mid-infrared disk sizes after using near-infrared data to
remove the contribution from the inner rim. We then use a semi-analytical
physical model to also find that the very widely used "star + inner dust rim +
flared disk" class of models strongly fails to reproduce the SED and
spatially-resolved mid-infrared data simultaneously; specifically a more
compact source of mid-infrared emission is required than results from the
standard flared disk model. We explore the viability of a modification to the
model whereby a second dust rim containing smaller dust grains is added, and
find that the two-rim model leads to significantly improved fits in most cases.
This complexity is largely missed when carrying out SED modelling alone,
although detailed silicate feature fitting by McClure et al. 2013 recently came
to a similar conclusion. As has been suggested recently by Menu et al. 2015,
the difficulty in predicting mid-infrared sizes from the SED alone might hint
at "transition disk"-like gaps in the inner AU; however, the relatively high
correlation found in our mid-infrared disk size vs. stellar luminosity relation
favors layered disk morphologies and points to missing disk model ingredients
instead
What is epistemic blame?
PostprintPeer reviewe
Probing the Inner Disk Emission of the Herbig Ae Stars HD 163296 and HD 190073
The physical processes occurring within the inner few astronomical units of
proto-planetary disks surrounding Herbig Ae stars are crucial to setting the
environment in which the outer planet-forming disk evolves and put critical
constraints on the processes of accretion and planet migration. We present the
most complete published sample of high angular resolution H- and K-band
observations of the stars HD 163296 and HD 190073, including 30 previously
unpublished nights of observations of the former and 45 nights of the latter
with the CHARA long-baseline interferometer, in addition to archival VLTI data.
We confirm previous observations suggesting significant near-infrared emission
originates within the putative dust evaporation front of HD 163296 and show
this is the case for HD 190073 as well. The H- and K-band sizes are the same
within for HD 163296 and within for HD 190073. The
radial surface brightness profiles for both disks are remarkably Gaussian-like
with little or no sign of the sharp edge expected for a dust evaporation front.
Coupled with spectral energy distribution analysis, our direct measurements of
the stellar flux component at H and K bands suggest that HD 190073 is much
younger (<400 kyr) and more massive (~5.6 M) than previously thought,
mainly as a consequence of the new Gaia distance (891 pc).Comment: 19 pages, 6 figure
Polarized disk emission from Herbig AE/BE stars observed using Gemini planet imager: HD 144432, HD 150193, HD 163296, and HD 169142
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.In order to look for signs of on-going planet formation in young disks, we carried out the first J-band polarized emission imaging of the Herbig Ae/Be stars HD 150193, HD 163296, and HD 169142 using
the Gemini Planet Imager (GPI), along with new H band observations of HD 144432. We confirm the complex âdouble ringâ structure for the nearly face-on system HD 169142 first seen in H-band, finding
the outer ring to be substantially redder than the inner one in polarized intensity. Using radiative transfer modeling, we developed a physical model that explains the full spectral energy distribution (SED) and J- and H-band surface brightness profiles, suggesting that the diâ”erential color of the two rings could come from reddened starlight traversing the inner wall and may not require diâ”erences in grain properties. In addition, we clearly detect an elongated, oâ”-center ring in HD 163296 (MWC 275), locating the scattering surface to be 18 AU above the midplane at a radial distance of 77 AU, cospatial with a ring seen at 1.3mm by ALMA linked to the CO snow line. Lastly, we report a weak tentative detection of scattered light for HD 150193 (MWC 863) and a non-detection for HD 144432; the stellar companion known for each of these targets has likely disrupted the material in the outer disk of the primary star. For HD 163296 and HD 169142, the prominent outer rings we detect could be evidence for giant planet formation in the outer disk or a manifestation of large-scale dust growth processes possibly related to snow-line chemistry.Exeterâs STFC Consolidated Grant (ST/J001627/1). SK acknowledges support from an STFC Rutherford Fellowship
(ST/J004030/1) and a European Research Council (ERC) Starting Grant (Grant agreement No 639889).
This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of
the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology,
funded by the National Aeronautics and Space Administration and the National Science Foundation. Based on
observations obtained at the Gemini Observatory (programs GS-2014A-SV-412, GS-2015A-Q-49), which is operated
by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on
behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council
(Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologa e Innovacin Productiva (Argentina), and Ministrio da
Cincia, Tecnologia e Inovao (Brazil)
FU Orionis disk outburst: evidence for a gravitational instability scenario triggered in a magnetically dead zone
Context: FUors outbursts are a crucial stage of accretion in young stars.
However a complete mechanism at the origin of the outburst still remains
missing. Aims: We aim at constraining the instability mechanism in FU Orionis
star itself, by directly probing the size and the evolution in time of the
outburst region with near-infrared interferometry, and to confront it to
physical models of this region. Methods: FU Orionis has been a regular target
of near-infrared interferometry. In this paper, we analyze more than 20 years
of interferometric observations to perform a temporal monitoring of the region
of the outburst, and compare it to the spatial structure deduced from 1D MHD
simulations. Results: We measure from the interferometric observations that the
size variation of the outburst region is compatible with a constant or slightly
decreasing size over time in the H and K band. The temporal variation and the
mean sizes are consistently reproduced by our 1D MHD simulations. We find that
the most compatible scenario is a model of an outburst occurring in a
magnetically layered disk, where a Magneto-Rotational Instability (MRI) is
triggered by a Gravitational Instability (GI) at the outer edge of a dead-zone.
The scenario of a pure Thermal Instability (TI) fails to reproduce our
interferometric sizes since it can only be sustained in a very compact zone of
the disk <0.1 AU. The scenario of MRI-GI could be compatible with an external
perturbation enhancing the GI, such as tidal interactions with a stellar
companion, or a planet at the outer edge of the dead-zone. Conclusions: The
layered disk model driven by MRI turbulence is favored to interpret the spatial
structure and temporal evolution of FU Orionis outburst region. Understanding
this phase gives a crucial link between the early phase of disk evolution and
the process of planet formation in the first inner AUs.Comment: Accepted for publication in A&
Rationality as the Rule of Reason
The demands of rationality are linked both to our subjective normative perspective (given that rationality is a person-level concept) and to objective reasons or favoring relations (given that rationality is non-contingently authoritative for us). In this paper, I propose a new way of reconciling the tension between these two aspects: roughly, what rationality requires of us is having the attitudes that correspond to our take on reasons in the light of our evidence, but only if it is competent. I show how this view can account for structural rationality on the assumption that intentions and beliefs as such involve competent perceptions of downstream reasons, and explore various implications of the account
ASIC-E4: Interplay of Beta-Amyloid, Synaptic Density and Neuroinflammation in Cognitively Normal Volunteers With Three Levels of Genetic Risk for Late-Onset Alzheimer's Disease â Study Protocol and Baseline Characteristics
Background: Detailed characterization of early pathophysiological changes in preclinical Alzheimer's disease (AD) is necessary to enable development of correctly targeted and timed disease-modifying treatments. ASIC-E4 study (âBeta-Amyloid, Synaptic loss, Inflammation and Cognition in healthy APOE Δ4 carriersâ) combines state-of-the-art neuroimaging and fluid-based biomarker measurements to study the early interplay of three key pathological features of AD, i.e., beta-amyloid (AÎČ) deposition, neuroinflammation and synaptic dysfunction and loss in cognitively normal volunteers with three different levels of genetic (APOE-related) risk for late-onset AD. Objective: Here, our objective is to describe the study design, used protocols and baseline demographics of the ASIC-E4 study. Methods/Design: ASIC-E4 is a prospective observational multimodal imaging study performed in Turku PET Centre in collaboration with University of Gothenburg. Cognitively normal 60â75-year-old-individuals with known APOE Δ4/Δ4 genotype were recruited via local Auria Biobank (Turku, Finland). Recruitment of the project has been completed in July 2020 and 63 individuals were enrolled to three study groups (Group 1: APOE Δ4/Δ4, N = 19; Group 2: APOE Δ4/Δ3, N = 22; Group 3: APOE Δ3/Δ3, N = 22). At baseline, all participants will undergo positron emission tomography imaging with tracers targeted against AÎČ deposition (11C-PIB), activated glia (11C-PK11195) and synaptic vesicle glycoprotein 2A (11C-UCB-J), two brain magnetic resonance imaging scans, and extensive cognitive testing. In addition, blood samples are collected for various laboratory measurements and blood biomarker analysis and cerebrospinal fluid samples are collected from a subset of participants based on additional voluntary informed consent. To evaluate the predictive value of the early neuroimaging findings, neuropsychological evaluation and blood biomarker measurements will be repeated after a 4-year follow-up period. Discussion: Results of the ASIC-E4 project will bridge the gap related to limited knowledge of the synaptic and inflammatory changes and their association with each other and AÎČ in âat-riskâ individuals. Thorough in vivo characterization of the biomarker profiles in this population will produce valuable information for diagnostic purposes and future drug development, where the field has already started to look beyond AÎČ
Confronting Standard Models of ProtoâPlanetary Disks With New MidâInfrared Sizes from the Keck Interferometer
This is the final version of the article. Available from American Astronomical Society via the DOI in this record.The accepted author manuscript is in ORE at http://hdl.handle.net/10871/21611We present near- and mid-infrared (MIR) interferometric observations made with the Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the infrared telescope facilities (IRTFs) of 11 well-known young stellar objects, several of which were observed for the first time in these spectral and spatial resolution regimes. With au-level spatial resolution, we first establish characteristic sizes of the infrared emission using a simple geometrical model consisting of a hot inner rim and MIR disk emission. We find a high degree of correlation between the stellar luminosity and the MIR disk sizes after using near-infrared data to remove the contribution from the inner rim. We then use a semi-analytical physical model to also find that the very widely used "star + inner dust rim + flared disk" class of models strongly fails to reproduce the spectral energy distribution (SED) and spatially resolved MIR data simultaneously; specifically a more compact source of MIR emission is required than results from the standard flared disk model. We explore the viability of a modification to the model whereby a second dust rim containing smaller dust grains is added, and find that the 2-rim model leads to significantly improved fits in most cases. This complexity is largely missed when carrying out SED modeling alone, although detailed silicate feature fitting by McClure et al. recently came to a similar conclusion. As has been suggested recently by Menu et al., the difficulty in predicting MIR sizes from the SED alone might hint at "transition disk"-like gaps in the inner au; however, the relatively high correlation found in our MIR disk size versus stellar luminosity relation favors layered disk morphologies and points to missing disk model ingredients instead.M.S. was supported by NASA ADAP grant NNX09AC73G. R.W.R. was supported by the IR&D program of The Aerospace Corporation
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