A dichotomy in group II Herbig disks: ALMA gas disk height measurements show both shadowed large vertically extended disks and compact flat disks

Herbig stars can be classified into group I and group II depending on the shape of the far-IR excess from the spectral energy distribution. This separation may be evolutionary and related to the vertical structure of these disks. We aim to determine the emission height of Herbig disks and compare the resulting vertical extent of both groups. ALMA Band 6 observations of 12CO emission lines at sufficient velocity and spatial resolution of eight Herbig disks (four group I and four group II sources) are used to determine the emission heights from the channel maps via geometrical methods developed in other works. We find that all group I disks are vertically extended with a height to radius ratio of at least 0.25, and for three of the disks the gas emission profile can be traced out to 200-500 au. The group II disks are divided between MWC 480 and HD 163296 which have similar emission height profiles as the group I disks, and AK Sco and HD 142666 which are very flat (not exceeding a height of 10 au) and more compact (<200 au in size). The brightness temperatures show no differences between the disks when the luminosity of the host star is accounted for. Our findings agree with previous work suggesting that group I disks are vertically extended and that group II disks are either large and self-shadowed or compact. Both MWC 480 and HD 163296 could be precursors of group I disks, which we see now before a cavity has formed that would allow irradiation of the outer parts of the disk. The very flat disks AK Sco and HD 142666 could be due to significant settling because of the advanced age of these disks (~20 instead of <10 Myr). These large differences in vertical structures are not reflected in the spectral energy distributions of these disks. More and deeper observations at higher spatial and velocity resolution are necessary to further characterize the Herbig sub-groups.Comment: Accepted for publication in Astronomy and Astrophysics. 8 pages, 4 figures, plus appendice

Directly tracing the vertical stratification of molecules in protoplanetary disks

We aim to directly trace the vertical location of the emitting surface of multiple molecular tracers in protoplanetary disks. Our sample of disks includes Elias 2-27, WaOph 6 and the sources targeted by the MAPS ALMA Large Program. The set of molecules studied include CO isotopologues in various transitions, HCN, CN, H2CO, HCO+, C2H and c-C3H2. The vertical emitting region is determined directly from the channel maps, implementing accurate masking of the channel emission to recover the vertical location of the emission surface even at large radial distances from the star and for low-SNR lines. The vertical location of the emitting layer is obtained for 4-10 lines in each disk. IM Lup, HD163296 and MWC 480 12CO and 13CO show vertical modulations, which are coincident with dust gaps and kinematical perturbations. We also present estimates of the gas pressure scale height in the disks from the MAPS sample. Compared to physical-chemical models we find good agreement with the vertical location of CO isotopologues. In HD 163296 CN and HCN trace a similar intermediate layer, for the other disks, the UV flux tracers and the vertical profiles of HCN and C2H are lower than predicted in theoretical models. HCN and H2CO show a highly structured vertical profile, possibly indicative of different formation pathways. It is possible to trace the vertical locations of multiple molecular species that trace a wide variety of physical and chemical disk properties. The distribution of CO isotopologues are found at a wide range of vertical heights $z/r =$ 0.5-0.05. Other molecular lines are mostly found at $z/r \leq$0.15. The vertical layering of molecules is in agreement with theory in some systems, but not in all, therefore dedicated chemical-physical models are needed to further study and understand the emission surfaces.Comment: Accepted for publication in A&A. 29 pages, 28 figure

Vertically extended and asymmetric CN emission in the Elias 2-27 protoplanetary disk

Elias 2-27 is a young star that hosts an extended, bright and inclined disk of dust and gas. The inclination and extreme flaring of the disk make Elias 2-27 an ideal target to study the vertical distribution of molecules, particularly CN. We directly trace the emission of CN in Elias 2-27 and compare it to previously published CO isotopologue data. CN $N = 3-2$ emission is analyzed in two different transitions $J = 7/2 - 5/2$ and $J = 5/2 - 3/2$, for which we detect two hyperfine group transitions. The vertical location of CN emission is traced directly from the channel maps, following geometrical methods that have been previously used to analyze the CO emission of Elias 2-27. Analytical models are used to parametrize the vertical profile of each molecule and study the extent of each tracer, additionally we compute radial profiles of column density and optical depth. We show that the vertical location of CN and CO isotopologues in Elias 2-27 is layered and consistent with predictions from thermochemical models. A north/south asymmetry in the radial extent of CN is detected and we find that the CN emission is mostly optically thin and constrained vertically to a thin slab at $z/r \sim$0.5. A column density of 10$^{14}$\,cm$^{-2}$ is measured in the inner disk which for the north side decreases to 10$^{12}$\,cm$^{-2}$ and for the south side to 10$^{13}$\,cm$^{-2}$ in the outer regions. In Elias 2-27, CN traces a vertically elevated region above the midplane, very similar to that traced by $^{12}$CO. The inferred CN properties are consistent with thermo-chemical disk models, in which CN formation is initiated by the reaction of N with UV-pumped H$_2$. The observed north/south asymmetry may be caused by either ongoing infall or by a warped inner disk. This study highlights the importance of tracing the vertical location of various molecules to constrain the disk physical conditions.Comment: Accepted for publication in A&A, 19 pages, 14 figure

Vertically extended and asymmetric CN emission in the Elias 2-27 protoplanetary disk

Stars and planetary systemsInterstellar matter and star formatio

Gas temperature structure across transition disk cavities

[Abridged] Most disks observed at high angular resolution show substructures. Knowledge about the gas surface density and temperature is essential to understand these. The aim of this work is to constrain the gas temperature and surface density in two transition disks: LkCa15 and HD 169142. We use new ALMA observations of the $^{13}$CO $J=6-5$ transition together with archival $J=2-1$ data of $^{12}$CO, $^{13}$CO and C$^{18}$O to observationally constrain the gas temperature and surface density. Furthermore, we use the thermochemical code DALI to model the temperature and density structure of a typical transition disk. The $6-5/2-1$ line ratio in LkCa15 constrains the gas temperature in the emitting layers inside the dust cavity to be up to 65 K, warmer than in the outer disk at 20-30 K. For the HD 169142, the peak brightness temperature constrains the gas in the dust cavity of HD 169142 to be 170 K, whereas that in the outer disk is only 100 K. Models also show that a more luminous central star, a lower abundance of PAHs and the absence of a dusty inner disk increase the temperature of the emitting layers and hence the line ratio in the gas cavity. The gas column density in the LkCa15 dust cavity drops by a factor >2 compared to the outer disk, with an additional drop of an order of magnitude inside the gas cavity at 10 AU. In the case of HD 169142, the gas column density drops by a factor of 200$-$500 inside the gas cavity, which could be due to a massive companion of several M$_{\mathrm{J}}$. The broad dust-depleted gas region from 10-68 AU for LkCa15 may imply several lower mass planets. This work demonstrates that knowledge of the gas temperature is important to determine the gas surface density and thus whether planets, and if so what kind of planets, are the most likely carving the dust cavities.Comment: Accepted for publication in Astronomy and astrophysic

Angular momentum transport via gravitational instability in the Elias 2-27 disc

Gravitational instability is thought to be one of the main drivers of angular momentum transport in young protoplanetary discs. The disc around Elias 2−27 offers a unique example of gravitational instability at work. It is young and massive, displaying two prominent spiral arms in dust continuum emission and global non-axisymmetric kinematic signatures in molecular line data. In this work, we used archival ALMA observations of 13CO line emission to measure the efficiency of angular momentum transport in the Elias 2−27 system through the kinematic signatures generated by gravitational instability, known as “GI wiggles”. Assuming the angular momentum is transported by the observed spiral structure and leveraging previously-derived dynamical disc mass measurements, the amount of angular momentum transport we found corresponds to an α-viscosity of α = 0.038 ± 0.018. This value implies an accretion rate onto the central star of log10 Ṁ⋆ = −6.99 ± 0.17 M⊙ yr−1, which reproduces the one observed value of log10 Ṁ⋆,obs = −7.2 ± 0.5 M⊙ yr−1 very well. The excellent agreement we have found serves as further proof that gravitational instability is the main driver of angular momentum transport acting in this system.</jats:p

Gas temperature structure across transition disk cavities

Galaxie

Spiral Arms and a Massive Dust Disk with Non-Keplerian Kinematics: Possible Evidence for Gravitational Instability in the Disk of Elias 2-27

International audienceTo determine the origin of the spiral structure observed in the dust continuum emission of Elias 2-27 we analyze multiwavelength continuum ALMA data with a resolution of ~0"2 (~23 au) at 0.89, 1.3, and 3.3 mm. We also study the kinematics of the disk with 13CO and C18O ALMA observations in the J = 3-2 transition. The spiral arm morphology is recovered at all wavelengths in the dust continuum observations, where we measure contrast and spectral index variations along the spiral arms and detect subtle dust-trapping signatures. We determine that the emission from the midplane is cold and interpret the optical depth results as signatures of a disk mass higher than previous constraints. From the gas data, we search for deviations from Keplerian motion and trace the morphology of the emitting surfaces and the velocity profiles. We find an azimuthally varying emission layer height in the system, large-scale emission surrounding the disk, and strong perturbations in the channel maps, colocated with the spirals. Additionally, we develop multigrain dust and gas hydrodynamical simulations of a gravitationally unstable disk and compare them to the observations. Given the large-scale emission and highly perturbed gas structure, together with the comparison of continuum observations to theoretical predictions, we propose infall-triggered gravitational instabilities as the origin for the observed spiral structure

Anales de Edafología y Agrobiología Tomo 30 Número 5-6

Fixation of molybdenum by soils in aqueous media at different temperatures, by S. Lal, S. K. De and R. K. Shukla.-- Azufre en suelo. Efecto de la adición de SO. l. Experiencias con macetas, por E. Esteban. M. Gómez y E. Hinojosa.-- Algunos aspectos de la distribución y formas del hierro en los suelos, por J. L. Olmedo.-- Contenido, distribución y formas del hierro en suelos de Andalucía occidental. l. Condiciones ambientales y descripción de perfiles, por J. Olmedo y G. Paneque.-- Contenido, distribución y formas del hierro en suelos de Andalucía occidental. II Características químicas de los suelos, por G. Paneque y J. Olmedo.-- Alteración hidrotermal de arenisca y ofita, por J. lñíguez Herrero.-- Determinación indirecta de fósforo en plantas por espectrofotometría de absorción atómica, por T. González Carreño y F. Duque Macías.-- Estudio sobre fertilización 'de comunidades pratenses seminaturales. IV. Interacciones N-P, N-K, P-K, por J. M. Gómez Gutiérrez.-- Contribución al estudio del Rotlehm, por J. Gallardo y J. Rodríguez Sanchidrián.-- Constitución y propiedades de la materia húmica de una tierra negra andaluza, por F. Martín Martínez, Díaz Barrientos y F. González García.-- El nitrógeno en dos fracciones de la materia húmica de una tierra negra andaluza, por F. Martín Martínez, E. Díaz Barrientos y F. González García.-- Influencia del sulfato sódico sobre el desarrollo y asimilación de elementos en el rabanito redondo escarlata, por Ma P. Sánchez Conde.-- Condiciones de formación y evolución de los suelos de Tenerife, por E. Fernández Caldas y A. Guerra Delgado.-- Notas.-- Reunión plenaria del Patronato Alonso de Herrera.-- Nuevo Presidente y Vicepresidente del Patronato Alonso de Herrera.-- Designación de representantes del Patronato en el Consejo Ejecutivo.-- VIII Simposio Internacional de Agroquímica sobre La energía nuclear en agricultura.-- Reunión del Grupo de Trabajo Internacional de Fertilidad de Suelos en Ljubljana (Yugoslavia).-- Reunión sobre estructura y propiedades de superficie de los minerales de arcilla.-- Visita y conferencias del Dr. Farmer.-- Visita y conferencias del Prof. Dandy.-- Creación de nuevos laboratorios en el Centro de Edafología y Biología Aplicada del Segura.-- Memoria del Congreso Mundial sobre Hidropónicos 1969.-- Jornadas sobre electrodos selectivos de iones.-- Instituto Nacional de Racionalización del Trabajo.-- Convocatoria de premios del C. S. l. C.-- Premios a los doctores Hernando y Cadahía.-- La Real Sociedad de Historia Natural cumple cien años.-- Curso de Biología Vegetal.-- El profesor Heywood, de la Universidad de Reading, en el Centro Pirenaico de Biología Experimental.-- Real Academia de Farmacia. Concurso científico para 1971.-- BibliografíaPeer reviewe