119 research outputs found
CN rings in full protoplanetary disks around young stars as probes of disk structure
Bright ring-like structure emission of the CN molecule has been observed in
protoplanetary disks. We investigate whether such structures are due to the
morphology of the disk itself or if they are instead an intrinsic feature of CN
emission. With the intention of using CN as a diagnostic, we also address to
which physical and chemical parameters CN is most sensitive. A set of disk
models were run for different stellar spectra, masses, and physical structures
via the 2D thermochemical code DALI. An updated chemical network that accounts
for the most relevant CN reactions was adopted. Ring-shaped emission is found
to be a common feature of all adopted models; the highest abundance is found in
the upper outer regions of the disk, and the column density peaks at 30-100 AU
for T Tauri stars with standard accretion rates. Higher mass disks generally
show brighter CN. Higher UV fields, such as those appropriate for T Tauri stars
with high accretion rates or for Herbig Ae stars or for higher disk flaring,
generally result in brighter and larger rings. These trends are due to the main
formation paths of CN, which all start with vibrationally excited H2*
molecules, that are produced through far ultraviolet (FUV) pumping of H2. The
model results compare well with observed disk-integrated CN fluxes and the
observed location of the CN ring for the TW Hya disk. CN rings are produced
naturally in protoplanetary disks and do not require a specific underlying disk
structure such as a dust cavity or gap. The strong link between FUV flux and CN
emission can provide critical information regarding the vertical structure of
the disk and the distribution of dust grains which affects the UV penetration,
and could help to break some degeneracies in the SED fitting. In contrast with
C2H or c-C3H2, the CN flux is not very sensitive to carbon and oxygen
depletion.Comment: New version of paper, correcting too high H2 excitation rates and
consequently too high CN column densities. Qualitative conclusions of the
paper remain unchanged. Quantitatively, the CN column densities are an order
of magnitude lower whereas fluxes decrease by a factor of 3-4. Rings are
larger by up to a factor of 2. 13 pages, 19 figures, accepted for publication
in A&
Not so smooth after all: resolving dust and gas structures in protoplanetary disks
A large diversity of exoplanetary systems has been found, but it is still unclear what drives this diversity. Planets are formed in disks around young stars, but the sensitivity and resolution of pre-ALMA data have allowed only a handful of disks to be characterized. ALMA has opened up the possibility to survey hundreds of disks in both the gas and dust, and to also spatially resolve them. The most recent observations of protoplanetary disks in the (sub-)mm emission and in optical/near-infrared scattered light have revealed complex structures such as spirals, rings, gaps and vortices. Planets are often invoked as an explanation, but their number and location are degenerate, and the same system can be often explained by more than one scenario. In this thesis, the origin of these gas and dust structures both through dust observations and through chemical modelling of the gas emission is studied, and the link between the structures observed in the different tracers is investigated.These studies are critical to understand if substructures in disks are the signpost of ongoing planet formation and will ultimately also tell whether and how the variety of structures observed is linked to the diversity in the exoplanetary systemsâ properties.Galaxie
The cool core state of Planck SZ-selected clusters versus X-ray selected samples: evidence for cool core bias
We characterized the population of galaxy clusters detected with the SZ
effect with Planck, by measuring the cool core state of the objects in a
well-defined subsample of the Planck catalogue. We used as indicator the
concentration parameter Santos et al. (2008). The fraction of cool core
clusters is and does not show significant indications of
evolution in the redshift range covered by our sample. We compare the
distribution of the concentration parameter in the Planck sample with the one
of the X-ray selected sample MACS (Mann & Ebeling, 2011): the distributions are
significantly different and the cool core fraction in MACS is much higher (). Since X-ray selected samples are known to be biased towards cool
cores due to the presence of their prominent surface brightness peak, we
simulated the impact of the "cool core bias" following Eckert et al. (2011). We
found that it plays a large role in the difference between the fractions of
cool cores in the two samples. We examined other selection effects that could
in principle bias SZ-surveys against cool cores but we found that their impact
is not sufficient to explain the difference between Planck and MACS. The
population of X-ray under-luminous objects, which are found in SZ-surveys but
missing in X-ray samples (Planck Collaboration 2016), could possibly contribute
to the difference, as we found most of them to be non cool cores, but this
hypothesis deserves further investigation.Comment: Accepted for publication in MNRA
An Inner Disk in the Large Gap of the Transition Disk SR 24S
We report new Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 3
observations at 2.75 mm of the TD around SR 24S with an angular resolution of
0.11'' 0.09'' and a peak signal-to-noise ratio of . We
detect an inner disk and a mostly symmetric ring-like structure that peaks at
0.32'', that is 37 au at a distance of 114.4 pc. The full
width at half maximum of this ring is 28 au. We analyze the observed
structures by fitting the dust continuum visibilities using different models
for the intensity profile, and compare with previous ALMA observations of the
same disk at 0.45 mm and 1.30 mm. We qualitatively compare the results of these
fits with theoretical predictions of different scenarios for the formation of a
cavity or large gap. The comparison of the dust continuum structure between
different ALMA bands indicates that photoevaporation and dead zone can be
excluded as leading mechanisms for the cavity formation in SR 24S disk, leaving
the planet scenario (single or multiple planets) as the most plausible
mechanism. We compared the 2.75 mm emission with published (sub-)centimeter
data and find that the inner disk is likely tracing dust thermal emission. This
implies that any companion in the system should allow dust to move inwards
throughout the gap and replenish the inner disk. In the case of one single
planet, this puts strong constraints on the mass of the potential planet inside
the cavity and the disk viscosity of about 5 and
, respectively
Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, Nâ). Semi-forbidden C II] λ2325 and UV-fluorescent Hâ emission were also measured to constrain inner disk populations of Câș and vibrationally excited H2. We find a significant positive correlation between 14 ÎŒm HCN emission and fluxes from the FUV continuum and C II] λ2325, consistent with model predictions requiring Nâ photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-Hâ emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer
ALMA Observations of the Young Substellar Binary System 2M1207
We present ALMA observations of the 2M1207 system, a young binary made of a
brown dwarf with a planetary-mass companion at a projected separation of about
40 au. We detect emission from dust continuum at 0.89 mm and from the rotational transition of CO from a very compact disk around the young brown
dwarf. The small radius found for this brown dwarf disk may be due to
truncation from the tidal interaction with the planetary-mass companion. Under
the assumption of optically thin dust emission, we estimated a dust mass of 0.1
for the 2M1207A disk, and a 3 upper limit of for dust surrounding 2M1207b, which is the tightest upper
limit obtained so far for the mass of dust particles surrounding a young
planetary-mass companion. We discuss the impact of this and other
non-detections of young planetary-mass companions for models of planet
formation, which predict the presence of circum-planetary material surrounding
these objects.Comment: 10 pages, 6 figures, accepted for publication in A
Evidence for a massive dust-trapping vortex connected to spirals: Multi-wavelength analysis of the HD 135344B protoplanetary disk
Spiral arms, rings and large scale asymmetries are structures observed in
high resolution observations of protoplanetary disks, and it appears that some
of the disks showing spiral arms in scattered light also show asymmetries in
millimeter-sized dust. HD~135344B is one of these disks. Planets are invoked as
the origin of these structures, but no planet has been observed so far. We
investigate the nature of the asymmetric structure in the HD~135344B disk in
order to understand the origin of the spirals and of the asymmetry seen in this
disk. Ultimately, we aim at understanding whether or not one or more planets
are needed to explain such structures. We present new ALMA sub-0.1" resolution
observations in Band 3 and 4. The high spatial resolution allows us to
characterize the mm-dust morphology of the disk. The low optical depth of
continuum emission probes the bulk of the dust in vortex. Moreover, we combine
the new observations with archival data to perform a multi-wavelength analysis
and to obtain information about the dust distribution and properties inside the
asymmetry. We resolve the asymmetric disk into a symmetric ring + asymmetric
crescent, and observe that: (1) the spectral index strongly decreases at the
center of the vortex, consistent with the presence of large grains; (2) for the
first time, an azimuthal shift of the peak of the vortex with wavelength is
observed; (3) the azimuthal width of the vortex decreases at longer
wavelengths, as expected for dust traps. These features allow to confirm the
nature of the asymmetry as a vortex. Finally a lower limit to the total mass of
the vortex is . Considering the uncertainties involved in
this estimate, it is possible that the actual mass of the vortex is higher and
possibly within the required values () to launch
spiral arms similar to those observed in scattered light.P.P. acknowledges support by NASA through Hubble Fellowship grant HST-HF2-51380.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. M.B. acknowledges funding from ANR of France under contract number ANR-16-CE31-0013 (Planet Forming disks). M.T. has been supported by the DISCSIM project, grant agreement 341137 funded by the European Research Council under ERC-2013-ADG. Astrochemistry in Leiden is supported by the European Union A-ERC grant 291141 CHEMPLAN, by the Netherlands Research School for Astronomy (NOVA), and by a Royal Netherlands Academy of Arts and Sciences (KNAW) professor prize
Probing UV-Sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in
surface layers of disks around young stars. In an effort to understand the
relationship between photocatalyzing UV radiation fields and gas emission
observed at infrared and sub-mm wavelengths, we present an analysis of new and
archival HST, Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus
cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to
measure LyA and FUV continuum fluxes reaching the disk surface, which are
responsible for dissociating relevant molecular species (e.g. HCN, N2).
Semi-forbidden C II] 2325 and UV-fluorescent H2 emission were also measured to
constrain inner disk populations of C+ and vibrationally excited H2. We find a
significant positive correlation between 14 micron HCN emission and fluxes from
the FUV continuum and C II] 2325, consistent with model predictions requiring
N2 photodissociation and carbon ionization to trigger the main CN/HCN formation
pathways. We also report significant negative correlations between sub-mm CN
emission and both C II] and FUV continuum fluxes, implying that CN is also more
readily dissociated in disks with stronger FUV irradiation. No clear
relationships are detected between either CN or HCN and LyA or UV-H2 emission.
This is attributed to the spatial stratification of the various molecular
species, which span several vertical layers and radii across the inner and
outer disk. We expect that future observations with JWST will build on this
work by enabling more sensitive IR surveys than were possible with Spitzer.Comment: Accepted for publication in A
Chronic bronchitis without airflow obstruction, asthma and rhinitis are differently associated with cardiovascular risk factors and diseases
Cardiovascular and respiratory diseases can frequently coexist. Understanding their link may improve disease management. We aimed at assessing the associations of chronic bronchitis (CB), asthma and rhinitis with cardiovascular diseases and risk factors in the general population
Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, Nâ). Semi-forbidden C II] λ2325 and UV-fluorescent Hâ emission were also measured to constrain inner disk populations of Câș and vibrationally excited H2. We find a significant positive correlation between 14 ÎŒm HCN emission and fluxes from the FUV continuum and C II] λ2325, consistent with model predictions requiring Nâ photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-Hâ emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer
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