124,965 research outputs found
A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star
No full textThis dataset includes selected portions of the JWST/MIRI spectrum of the J160532 disk analyzed in the paper by Tabone et al. (2023), to be published by Nature Astronomy. The original observational data are part of the Guaranteed Time Observation-MIRI programme ‘MIRI EC Protoplanetary and Debris Disks Survey’ (ID 1282) with number 47 and will become public on August 1st, 2023 on the MAST database https://archive.stsci.edu/. In addition, this release contains the best-fit slab models. Some basic information about the models can be found in the headers.
The dataset consists of two data files. The first file contains the continuum subtracted JWST/MIRI spectrum of J160532 in the 12.5-14.7 region shown in Fig. 1 (right panel) of Tabone et al. (2023) where C2H2 emission is seen as a broad bump and prominent narrower features. The best-fit slab models correspond to the highly optically thick C2H2 component I and the optically thinner C2H2 component II. The second file is the continuum subtracted JWST/MIRI spectrum in the 14.6-16.1 region shown in Fig. 2 of Tabone et al. (2023) where C6H6 (benzene), CO2, and C4H2 features are detected. The best-fit slab models for the three species are also provided. Fig. 1 (righ panel) and Fig. 2 of Tabone et al. (2023) can be reproduced using the two Python scripts
Constraining turbulence in protoplanetary discs using the gap contrast: an application to the DSHARP sample
No full textConstraining the strength of gas turbulence in protoplanetary discs is an
open problem that has relevant implications for the physics of gas accretion
and planet formation. In this work, we gauge the amount of turbulence in 6 of
the discs observed in the DSHARP programme by indirectly measuring the vertical
distribution of their dust component. We employ the differences in the gap
contrasts observed along the major and the minor axes due to projection
effects, and build a radiative transfer model to reproduce these features for
different values of the dust scale heights. We find that (a) the scale heights
that yield a better agreement with data are generally low ( AU at a
radial distance of AU), and in almost all cases we are only able to place
upper limits on their exact values; these conclusions imply (assuming an
average Stokes number of ) low turbulence levels of
; (b) for the 9 other systems we
considered out of the DSHARP sample, our method yields no significant
constraints on the disc vertical structure; we conclude that this is because
these discs have either a low inclination or gaps that are not deep enough.
Based on our analysis we provide an empirical criterion to assess whether a
given disc is suitable to measure the vertical scale height.Comment: Accepted for publication in MNRAS. 13 pages + appendix, 12 figure
Effect of MHD Wind-driven Disk Evolution on the Observed Sizes of Protoplanetary Disks
No full textAbstract
It is still unclear whether the evolution of protoplanetary disks, a key ingredient in the theory of planet formation, is driven by viscous turbulence or magnetic disk winds. As viscously evolving disks expand outward over time, the evolution of disk sizes is a discriminant test for studying disk evolution. However, it is unclear how the observed disk size changes over time if disk evolution is driven by magnetic disk winds. Combining the thermo-chemical code DALI with the analytical wind-driven disk-evolution model presented in Tabone et al., we study the time evolution of the observed gas outer radius as measured from CO rotational emission (R
CO,90%). The evolution of R
CO,90% is driven by the evolution of the disk mass, as the physical radius stays constant over time. For a constant α
DW
, an extension of the α Shakura–Sunyaev parameter to wind-driven accretion, R
CO,90% decreases linearly with time. Its initial size is set by the disk mass and the characteristic radius R
c,0, but only R
c,0 affects the evolution of R
CO,90%, with a larger R
c,0 resulting in a steeper decrease of R
CO,90%. For a time-dependent α
DW
, R
CO,90% stays approximately constant during most of the disk lifetime until R
CO,90% rapidly shrinks as the disk dissipates. The constant α
DW
models are able to reproduce the observed gas disk sizes in the ∼1–3 Myr old Lupus and ∼5–11 Myr old Upper Sco star-forming regions. However, they likely overpredict the gas disk size of younger (⪅0.7 Myr) disks
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Importance of source structure on complex organics emission III. Effect of disks around massive protostars
No full textComplex organic molecules are only detected toward a fraction of high-mass
protostars. The goal of this work is to investigate whether high-mass disks can
explain the lack of methanol emission from some massive protostellar systems.
We consider an envelope-only and an envelope-plus-disk model and use RADMC-3D
to calculate the methanol emission. High and low millimeter (mm) opacity dust
are considered for both models separately and the methanol abundance is
parameterized. Viscous heating is included due to the high accretion rates of
these objects in the disk. In contrast with low-mass protostars, the presence
of a disk does not significantly affect the temperature structure and methanol
emission. The shadowing effect of the disk is not as important for high-mass
objects and the disk mid-plane is hot because of viscous heating, which is
effective due to the high accretion rates. Consistent with observations of
infrared absorption lines toward high-mass protostars, we find a vertical
temperature inversion, i.e. higher temperatures in the disk mid-plane than the
disk surface, at radii < 50au for the models with L and
large mm opacity dust as long as the envelope mass is >550 M. The
large observed scatter in methanol emission from massive protostars can be
mostly explained toward lower luminosity objects with the envelope-plus-disk
models including low and high mm opacity dust. The methanol emission variation
toward sources with high luminosities cannot be explained by models with or
without a disk. However, the of these objects suggest that they could be
associated with hypercompact/ultracompact HII regions. Therefore, the low
methanol emission toward the high-luminosity sources can be explained by them
hosting an HII region where methanol is absent.Comment: 25 pages, 24 figures, Accepted for publication in A&
Creating Together: An Exploratory Research on Cartoon Design with Kindergarten Children
No full textThis research, following the participatory design tradition, explores the applicability of the cooperative inquiry approach to the design of a cartoon for young children. The research involved different design partners - researchers, authors of a cartoon production company and kindergarten children - during six design activity sessions carried out in a kindergarten setting. Through analysis of videotaped sessions, participants’ research journals, children’s interviews and questionnaires completed by the adults, the effectiveness of the cooperative inquiry approach for the elaboration of ideas for new cartoon episodes, the productiveness of the selected techniques and their benefits for both producer and children were verified. The research produced original stories for children to be transformed later into a quality cartoon that reflects the social interest and cultural experiences of the design partners
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
How Large Is a Disk—What Do Protoplanetary Disk Gas Sizes Really Mean?
No full textIt remains unclear what mechanism is driving the evolution of protoplanetary disks. Direct detection of the main candidates, either turbulence driven by magnetorotational instabilities or magnetohydrodynamical disk winds, has proven difficult, leaving the time evolution of the disk size as one of the most promising observables able to differentiate between these two mechanisms. But to do so successfully, we need to understand what the observed gas disk size actually traces. We studied the relation between R _CO,90% , the radius that encloses 90% of the ^12 CO flux, and R _c , the radius that encodes the physical disk size, in order to provide simple prescriptions for conversions between these two sizes. For an extensive grid of thermochemical models, we calculate R _CO,90% from synthetic observations and relate properties measured at this radius, such as the gas column density, to bulk disk properties, such as R _c and the disk mass M _disk . We found an empirical correlation between the gas column density at R _CO,90% and disk mass: . Using this correlation we derive an analytical prescription of R _CO,90% that only depends on R _c and M _disk . We derive R _c for disks in Lupus, Upper Sco, Taurus, and the DSHARP sample, finding that disks in the older Upper Sco region are significantly smaller (〈 R _c 〉 = 4.8 au) than disks in the younger Lupus and Taurus regions (〈 R _c 〉 = 19.8 and 20.9 au, respectively). This temporal decrease in R _c goes against predictions of both viscous and wind-driven evolution, but could be a sign of significant external photoevaporation truncating disks in Upper Sco
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