Context.
The discovery of giant planets orbiting very low mass stars (VLMS) and the recent observed substructures in disks around VLMS is challenging planet formation models. Specifically, radial ...drift of dust particles is a catastrophic barrier in these disks, which prevents the formation of planetesimals and therefore planets.
Aims.
We aim to estimate if structures, such as cavities, rings, and gaps, are common in disks around VLMS and to test models of structure formation in these disks. We also aim to compare the radial extent of the gas and dust emission in disks around VLMS, which can give us insight about radial drift.
Methods.
We studied six disks around VLMS in the Taurus star-forming region using ALMA Band 7 (~340 GHz) at a resolution of ~0.1″. The targets were selected because of their high disk dust content in their stellar mass regime.
Results.
Our observations resolve the disk dust continuum in all disks. In addition, we detect the
12
CO (
J
= 3−2) emission line in all targets and
13
CO (
J
= 3−2) in five of the six sources. The angular resolution allows the detection of dust substructures in three out of the six disks, which we studied by using UV-modeling. Central cavities are observed in the disks around stars MHO 6 (M 5.0) and CIDA 1 (M 4.5), while we have a tentative detection of a multi-ringed disk around J0433. We estimate that a planet mass of ~0.1
M
Jup
or ~0.4
M
Saturn
is required for a single planet to create the first gap in J0433. For the cavities of MHO 6 and CIDA 1, a Saturn-mass planet (~0.3
M
Jup
) is required. The other three disks with no observed structures are the most compact and faintest in our sample, with the radius enclosing 90% of the continuum emission varying between ~13 and 21 au. The emission of
12
CO and
13
CO is more extended than the dust continuum emission in all disks of our sample. When using the
12
CO emission to determine the gas disk extension
R
gas
, the ratio of
R
gas
∕
R
dust
in our sample varies from 2.3 to 6.0. One of the disks in our sample, CIDA 7, has the largest
R
gas
∕
R
dust
ratio observed so far, which is consistent with models of radial drift being very efficient around VLMS in the absence of substructures.
Conclusions.
Given our limited angular resolution, substructures were only directly detected in the most extended disks, which represent 50% of our sample, and there are hints of unresolved structured emission in one of the bright smooth sources. Our observations do not exclude giant planet formation on the substructures observed. A comparison of the size and luminosity of VLMS disks with their counterparts around higher mass stars shows that they follow a similar relation.
The frequency of Earth-sized planets in habitable zones appears to be higher around M-dwarfs, making these systems exciting laboratories to investigate planet formation. Observations of ...protoplanetary disks around very low-mass stars and brown dwarfs remain challenging and little is known about their properties. The disk around CIDA 1 (~0.1–0.2
M
⊙
) is one of the very few known disks that host a large cavity (20 au radius in size) around a very low-mass star. We present new ALMA observations at Band 7 (0.9 mm) and Band 4 (2.1 mm) of CIDA 1 with a resolution of ~0.05″ × 0.034″. These new ALMA observations reveal a very bright and unresolved inner disk, a shallow spectral index of the dust emission (~2), and a complex morphology of a ring located at 20 au. We also present X-shooter (VLT) observations that confirm the high accretion rate of CIDA 1 of
Ṁ
acc
= 1.4 × 10
−8
M
⊙
yr
−1
. This high value of
Ṁ
acc
, the observed inner disk, and the large cavity of 20 au exclude models of photo-evaporation to explain the observed cavity. When comparing these observations with models that combine planet–disk interaction, dust evolution, and radiative transfer, we exclude planets more massive than 0.5
M
Jup
as the potential origin of the large cavity because with these it is difficult to maintain a long-lived and bright inner disk. Even in this planet mass regime, an additional physical process may be needed to stop the particles from migrating inwards and to maintain a bright inner disk on timescales of millions of years. Such mechanisms include a trap formed by a very close-in extra planet or the inner edge of a dead zone. The low spectral index of the disk around CIDA 1 is difficult to explain and challenges our current dust evolution models, in particular processes like fragmentation, growth, and diffusion of particles inside pressure bumps.
New ALMA observations of protoplanetary disks allow us to probe planet formation in other planetary systems, giving us new constraints on planet formation processes. Meanwhile, studies of our own ...Solar System rely on constraints derived in a completely different way. However, it is still unclear what features the Solar System protoplanetary disk could have produced during its gas phase. By running 2D isothermal hydro-simulations used as inputs for a dust evolution model, we derive synthetic images at millimeter wavelengths using the radiative transfer code RADMC3D. We find that the embedded multiple giant planets strongly perturb the radial gas velocities of the disk. These velocity perturbations create traffic jams in the dust, producing over-densities different from the ones created by pressure traps and located away from the planets’ positions in the disk. By deriving the images at
λ
= 1.3 mm from these dust distributions, we show that very high resolution observations are needed to distinguish the most important features expected in the inner part (<15 AU) of the disk. The traffic jams, observable with a high resolution, further blur the link between the number of gaps and rings in disks and the number of embedded planets. We additionally show that a system capable of producing eccentric planets by scattering events that match the eccentricity distributions in observed exoplanets does not automatically produce bright outer rings at large radii in the disk. This means that high resolution observations of disks of various sizes are needed to distinguish between different giant planet formation scenarios during the disk phase, where the giants form either in the outer regions of the disks or in the inner regions. In the second scenario, the disks do not present planet-related features at large radii. Finally, we find that, even when the dust temperature is determined self-consistently, the dust masses derived observationally might be off by up to a factor of ten compared to the dust contained in our simulations due to the creation of optically thick regions. Our study clearly shows that in addition to the constraints from exoplanets and the Solar System, ALMA has the power to constrain different stages of planet formation already during the first few million years, which corresponds to the gas disk phase.
Context.
Exoplanetary research has provided us with exciting discoveries of planets around very low-mass (VLM) stars (0.08
M
⊙
≲
M
*
≲ 0.3
M
⊙
; e.g., TRAPPIST-1 and Proxima Centauri). However, ...current theoretical models still strive to explain planet formation in these conditions and do not predict the development of giant planets. Recent high-resolution observations from the Atacama Large Millimeter/submillimeter Array (ALMA) of the disk around CIDA 1, a VLM star in Taurus, show substructures that hint at the presence of a massive planet.
Aims.
We aim to reproduce the dust ring of CIDA 1, observed in the dust continuum emission in ALMA Band 7 (0.9 mm) and Band 4 (2.1 mm), along with its
12
CO (
J
= 3−2) and
13
CO (
J
= 3−2) channel maps, assuming the structures are shaped by the interaction of the disk with a massive planet. We seek to retrieve the mass and position of the putative planet, through a global simulation that assesses planet-disk interactions to quantitatively reproduce protoplanetary disk observations of both dust and gas emission in a self-consistent way.
Methods.
Using a set of hydrodynamical simulations, we model a protoplanetary disk that hosts an embedded planet with a starting mass of between 0.1 and 4.0
M
Jup
and initially located at a distance of between 9 and 11 au from the central star. We compute the dust and gas emission using radiative transfer simulations, and, finally, we obtain the synthetic observations, treating the images as the actual ALMA observations.
Results.
Our models indicate that a planet with a minimum mass of ~1.4
M
Jup
orbiting at a distance of ~9−10 au can explain the morphology and location of the observed dust ring in Band 7 and Band 4. We match the flux of the dust emission observation with a dust-to-gas mass ratio in the disk of ~10
−2
. We are able to reproduce the low spectral index (~2) observed where the dust ring is detected, with a ~40−50% fraction of optically thick emission. Assuming a
12
CO abundance of 5 × 10
−5
and a
13
CO abundance 70 times lower, our synthetic images reproduce the morphology of the
12
CO (
J
= 3−2) and
13
CO (
J
=
3−2) observed channel maps where the cloud absorption allowed a detection. From our simulations, we estimate that a stellar mass
M
*
= 0.2
M
⊙
and a systemic velocity
v
sys
= 6.25 km s
−1
are needed to reproduce the gas rotation as retrieved from molecular line observations. Applying an empirical relation between planet mass and gap width in the dust, we predict a maximum planet mass of ~4−8
M
Jup
.
Conclusions.
Our results suggest the presence of a massive planet orbiting CIDA 1, thus challenging our understanding of planet formation around VLM stars.
Most studies on human immunity to malaria have focused on the roles of immunoglobulin G (IgG), whereas the roles of IgM remain undefined. Analyzing multiple human cohorts to assess the dynamics of ...malaria-specific IgM during experimentally induced and naturally acquired malaria, we identified IgM activity against blood-stage parasites. We found that merozoite-specific IgM appears rapidly in
infection and is prominent during malaria in children and adults with lifetime exposure, together with IgG. Unexpectedly, IgM persisted for extended periods of time; we found no difference in decay of merozoite-specific IgM over time compared to that of IgG. IgM blocked merozoite invasion of red blood cells in a complement-dependent manner. IgM was also associated with significantly reduced risk of clinical malaria in a longitudinal cohort of children. These findings suggest that merozoite-specific IgM is an important functional and long-lived antibody response targeting blood-stage malaria parasites that contributes to malaria immunity.
Abstract
Young, low-mass brown dwarfs orbiting early-type stars, with low mass ratios (
q
≲ 0.01), appear to be intrinsically rare and present a formation dilemma: could a handful of these objects be ...the highest-mass outcomes of “planetary” formation channels (bottom up within a protoplanetary disk), or are they more representative of the lowest-mass “failed binaries” (formed via disk fragmentation or core fragmentation)? Additionally, their orbits can yield model-independent dynamical masses, and when paired with wide wavelength coverage and accurate system age estimates, can constrain evolutionary models in a regime where the models have a wide dispersion depending on the initial conditions. We present new interferometric observations of the 16 Myr substellar companion HD 136164 Ab (HIP 75056 Ab) made with the Very Large Telescope Interferometer (VLTI)/GRAVITY and an updated orbit fit including proper motion measurements from the Hipparcos–Gaia Catalog of Accelerations. We estimate a dynamical mass of 35 ± 10
M
J
(
q
∼ 0.02), making HD 136164 Ab the youngest substellar companion with a dynamical mass estimate. The new mass and newly constrained orbital eccentricity (
e
= 0.44 ± 0.03) and separation (22.5 ± 1 au) could indicate that the companion formed via the low-mass tail of the initial mass function. Our atmospheric fit to a
SPHINX
M-dwarf model grid suggests a subsolar C/O ratio of 0.45 and 3 × solar metallicity, which could indicate formation in a circumstellar disk via disk fragmentation. Either way, the revised mass estimate likely excludes bottom-up formation via core accretion in a circumstellar disk. HD 136164 Ab joins a select group of young substellar objects with dynamical mass estimates; epoch astrometry from future Gaia data releases will constrain the dynamical mass of this crucial object further.
Aims. L 98-59 (TIC 307210830, TOI-175) is a nearby M3 dwarf around which TESS revealed three small transiting planets (0.80, 1.35, 1.57 Earth radii) in a compact configuration with orbital periods ...shorter than 7.5 days. Here we aim to measure the masses of the known transiting planets in this system using precise radial velocity (RV) measurements taken with the HARPS spectrograph. Methods. We considered both trained and untrained Gaussian process regression models of stellar activity, which are modeled simultaneously with the planetary signals. Our RV analysis was then supplemented with dynamical simulations to provide strong constraints on the planets’ orbital eccentricities by requiring long-term stability. Results. We measure the planet masses of the two outermost planets to be 2.42 ± 0.35 and 2.31 ± 0.46 Earth masses, which confirms the bulk terrestrial composition of the former and eludes to a significant radius fraction in an extended gaseous envelope for the latter. We are able to place an upper limit on the mass of the smallest, innermost planet of <1.01 Earth masses with 95% confidence. Our RV plus dynamical stability analysis places strong constraints on the orbital eccentricities and reveals that each planet’s orbit likely has e < 0.1. Conclusions. L 98-59 is likely a compact system of two rocky planets plus a third outer planet with a lower bulk density possibly indicative of the planet having retained a modest atmosphere. The system offers a unique laboratory for studies of planet formation, dynamical stability, and comparative atmospheric planetology as the two outer planets are attractive targets for atmospheric characterization through transmission spectroscopy. Continued RV monitoring will help refine the characterization of the innermost planet and potentially reveal additional planets in the system at wider separations.
Context.
In recent years high-angular-resolution observations have revealed that circumstellar discs appear in a variety of shapes with diverse substructures being ubiquitous. This has given rise to ...the question of whether these substructures are triggered by planet–disc interactions. Besides direct imaging, one of the most promising methods to distinguish between different disc-shaping mechanisms is to study the kinematics of the gas disc. In particular, the deviations of the rotation profile from Keplerian velocity can be used to probe perturbations in the gas pressure profile that may be caused by embedded (proto-) planets.
Aims.
In this paper we aim to analyse the gas brightness temperature and kinematics of the transitional disc around the intermediate-mass star CQ Tau in order to resolve and characterise substructure in the gas caused by possible perturbers.
Methods.
For our analysis we used spatially resolved ALMA observations of the three CO isotopologues
12
CO,
13
CO, and C
18
O (
J
= 2−1) from the disc around CQ Tau. We further extracted robust line centroids for each channel map and fitted a number of Keplerian disc models to the velocity field.
Results.
The gas kinematics of the CQ Tau disc present non-Keplerian features, showing bent and twisted iso-velocity curves in
12
CO and
13
CO. Significant spiral structures are detected between ~10 and 180 au in both the brightness temperature and the rotation velocity of
12
CO after subtraction of an azimuthally symmetric model, which may be tracing planet–disc interactions with an embedded planet or low-mass companion. We identify three spirals, two in the brightness temperature and one in the velocity residuals, spanning a large azimuth and radial extent. The brightness temperature spirals are morphologically connected to spirals observed in near-infrared scattered light in the same disc, indicating a common origin. Together with the observed large dust and gas cavity, these spiral structures support the hypothesis of a massive embedded companion in the CQ Tau disc.
Aims.
L 98-59 (TIC 307210830, TOI-175) is a nearby M3 dwarf around which TESS revealed three small transiting planets (0.80, 1.35, 1.57 Earth radii) in a compact configuration with orbital periods ...shorter than 7.5 days. Here we aim to measure the masses of the known transiting planets in this system using precise radial velocity (RV) measurements taken with the HARPS spectrograph.
Methods.
We considered both trained and untrained Gaussian process regression models of stellar activity, which are modeled simultaneously with the planetary signals. Our RV analysis was then supplemented with dynamical simulations to provide strong constraints on the planets’ orbital eccentricities by requiring long-term stability.
Results.
We measure the planet masses of the two outermost planets to be 2.42 ± 0.35 and 2.31 ± 0.46 Earth masses, which confirms the bulk terrestrial composition of the former and eludes to a significant radius fraction in an extended gaseous envelope for the latter. We are able to place an upper limit on the mass of the smallest, innermost planet of <1.01 Earth masses with 95% confidence. Our RV plus dynamical stability analysis places strong constraints on the orbital eccentricities and reveals that each planet’s orbit likely has
e
< 0.1.
Conclusions.
L 98-59 is likely a compact system of two rocky planets plus a third outer planet with a lower bulk density possibly indicative of the planet having retained a modest atmosphere. The system offers a unique laboratory for studies of planet formation, dynamical stability, and comparative atmospheric planetology as the two outer planets are attractive targets for atmospheric characterization through transmission spectroscopy. Continued RV monitoring will help refine the characterization of the innermost planet and potentially reveal additional planets in the system at wider separations.
Planets that are forming around young stars are expected to leave clear imprints in the distribution of the gas and dust of their parental protoplanetary disks. In this paper, we present new ...scattered light and millimeter observations of the protoplanetary disk around LkH
α
330, using SPHERE/VLT and ALMA, respectively. The scattered-light SPHERE observations reveal an asymmetric ring at around 45 au from the star in addition to two spiral arms with similar radial launching points at around 90 au. The millimeter observations from ALMA (resolution of 0.06″ × 0.04″) mainly show an asymmetric ring located at 110 au from the star. In addition to this asymmetry, there are two faint symmetric rings at 60 au and 200 au. The
12
CO,
13
CO, and C
18
O lines seem to be less abundant in the inner disk (these observations have a resolution of 0.16″ × 0.11″). The
13
CO peaks at a location similar to the inner ring observed with SPHERE, suggesting that this line is optically thick and traces variations of disk temperature instead of gas surface-density variations, while the C
18
O peaks slightly further away at around 60 au. We compare our observations with hydrodynamical simulations that include gas and dust evolution, and conclude that a 10
M
Jup
mass planet at 60 au and in an eccentric orbit (
e
= 0.1) can qualitatively explain most of the observed structures. A planet in a circular orbit leads to a much narrower concentration in the millimeter emission, while a planet in a more eccentric orbit leads to a very eccentric cavity as well. In addition, the outer spiral arm launched by the planet changes its pitch angle along the spiral due to the eccentricity and when it interacts with the vortex, potentially appearing in observations as two distinct spirals. Our observations and models show that LkH
α
330 is an interesting target to search for (eccentric-) planets while they are still embedded in their parental disk, making it an excellent candidate for studies on planet-disk interaction.
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