Herbig Ae Star Research Articles

Volatile composition of the HD 169142 disk and its embedded planet

Abstract The composition of a planet’s atmosphere is intricately linked to the chemical makeup of the protoplanetary disk in which it formed. Determining the elemental abundances from key volatiles within disks is therefore essential for establishing connections between the composition of disks and planets. The disk around the Herbig Ae star HD 169142 is a compelling target for such a study due to its molecule-rich nature and the presence of a newly-forming planet between two prominent dust rings. In this work, we probe the chemistry of the HD 169142 disk at small spatial scales, drawing links between the composition of the disk and the planet-accreted gas. Using thermochemical models and archival data, we constrain the elemental abundances of volatile carbon, oxygen, and sulfur. Carbon and oxygen are only moderately depleted from the gas phase relative to their interstellar abundances, with the inner ~60 au appearing enriched in volatile oxygen. The C/O ratio is approximately solar within the inner disk (~0.5) and rises above this in the outer disk (>0.5), as expected across the H2O snowline. The gas-phase sulfur abundance is depleted by a factor of ~1000, consistent with a number of other protoplanetary disks. Interestingly, the observed SiS emission near the HD 169142 b protoplanet vastly exceeds chemical model predictions, supporting previous hypotheses suggesting its origin in shocked gas or a localised outflow. We contextualise our findings in terms of the potential atmospheric composition of the embedded planet, and highlight the utility of sulfur-bearing molecules as probes of protoplanetary disk chemistry.

Detection of Dimethyl Ether in the Central Region of the MWC 480 Protoplanetary Disk

Characterizing the chemistry of complex organic molecules (COMs) at the epoch of planet formation provides insights into the chemical evolution of the interstellar medium (ISM) and the origin of organic materials in our solar system. We report a detection of dimethyl ether (CH3OCH3) in the disk around the Herbig Ae star MWC 480 with sensitive Atacama Large Millimeter/submillimeter Array observations. This is the first detection of CH3OCH3 in a nontransitional Class II disk. The spatially unresolved, compact (≲25 au in radius) nature, broad line width (∼30 km s−1), and high excitation temperature (∼200 K) indicate the sublimation of COMs in the warm inner disk. Despite the detection of CH3OCH3, methanol (CH3OH), the most abundant COM in the ISM, has not been detected, from which we constrain the column density ratio of CH3OCH3/CH3OH ≳ 7. This high ratio may indicate the reprocessing of COMs during the disk phase, as well as the effect of the physical structure in the inner disk. We also find that this ratio is higher than in COM-rich transition disks recently discovered. This may indicate that in the full disk of MWC 480, COMs have experienced substantial chemical reprocessing in the innermost region, while the COM emission in the transition disks predominantly traces the inherited ice sublimating at the dust cavity edge located at larger radii (≳20 au).

Sulfur monoxide (SO) as a shock tracer in protoplanetary disks: Case of AB Aurigae

Context. Sulfur monoxide (SO) is known to be a good shock tracer in molecular clouds and protostar environments, but its abundance is difficult to reproduce, even with state-of-the-art astrochemical models. Aims. We investigate the properties of the observed SO emission in the protoplanetary disk of AB Auriga, a Herbig Ae star of 2.4 M⊙ in mass, located at 156 pc. The AB Aur system is unique because it exhibits a dust trap and at least one young putative planet orbiting at about 30 au from the central star. Methods. We reduced ALMA archival data (projects 2019.1.00579.S, 2021.1.00690.S, and 2021.1.01216.S) and analyzed the three detected SO lines (SO 65 − 54, 67 − 56 and 56 − 45). We also used C17O and C18O 2–1 data to complement the interpretation of the SO data. Results. For the three SO lines, the maximum SO emission in the ring is not located in the dust trap. Moreover, the inner radius of the SO ring is significantly larger than the CO emission inner radius, ∼160 au versus ∼90 au. The SO emission traces gas located in part beyond the dust ring. This emission likely originates from shocks at the interface of the outer spirals, observed in CO and scattered light emission, as well as those in the molecular and dust ring. Also, SO is detected within the cavity, at a radius of ∼20 − 30 au and with a rotation velocity compatible with the protoplanet P1. We speculate that this SO emission originates from accretion shocks onto the circumplanetary disk of the putative protoplanet P1. Conclusions. These observations confirm that SO is a good tracer of shocks in protoplanetary disks and could serve as a powerful new tool for detecting embedded (proto)planets.

Gas Dynamics in the Herbig Ae Star HD 163296 in 2024

We observed the Herbig Ae star HD 163296 over 9 nights in 2024. On 4 of the nights, the He i line at 1.083 μm exhibited a profile rarely seen in the star. Rather than the typical P Cygni profile indicating a net gas outflow, the profile consisted of a deep absorption line with weak emission peaks on either side. These seem to be consistent with either an outflowing bipolar jet, a circular ring of gas orbiting close to the star, and/or accretion columns connecting the inner disk to the star. Given the history of the ejection of Herbi-Haro object in the star’s bipolar jets, these observations should coincide with the very beginning of the ejection event. Coordinated observations with multiple observing techniques over the next decade are warranted.

Searching for Protoplanets around MWC 758 and MWC 480 in Br-γ Using Kernel Phase and SCExAO/CHARIS

Discovering new actively accreting protoplanets is crucial to answering open questions about planet formation. However, identifying such planets at orbital distances where they are expected to be abundant is extremely challenging, both due to the technical requirements and large distances to star-forming regions. Here we use the kernel phase interferometry (KPI) technique to search for companions around the ∼6 and ∼8 Myr old Herbig Ae stars MWC 758 and MWC 480. KPI is a data analysis technique that is sensitive to moderate asymmetries, arising from, e.g., a circumstellar disk or companions with contrasts of up to 6–8 mag, at separations down to and even below the classical Rayleigh diffraction limit (∼1.2λ/D). Using the high-spectral-resolution K-band mode of the SCExAO/CHARIS integral field spectrograph, we search for both excess Br-γ line emission and continuum emission from companions around MWC 480 and MWC 758. We are able to set limits on the presence of rapidly accreting protoplanets and brown dwarfs between 4 and 16 au, well interior to those of previous studies. In Br-γ, we set limits on excess line emission equivalent to accretion rates ranging from 10−5Mj2.yr−1 to 10−6Mj2.yr−1 . Our achievable contrasts demonstrate that KPI using SCExAO/CHARIS is a promising technique to search for giant accreting protoplanets at smaller separations compared to conventional imaging.

MINDS: The JWST MIRI Mid-INfrared Disk Survey

The study of protoplanetary disks has become increasingly important with the Kepler satellite finding that exoplanets are ubiquitous around stars in our galaxy and the discovery of enormous diversity in planetary system architectures and planet properties. High-resolution near-IR and ALMA images show strong evidence for ongoing planet formation in young disks. The JWST MIRI mid-INfrared Disk Survey (MINDS) aims to (1) investigate the chemical inventory in the terrestrial planet-forming zone across stellar spectral type, (2) follow the gas evolution into the disk dispersal stage, and (3) study the structure of protoplanetary and debris disks in the thermal mid-IR. The MINDS survey will thus build a bridge between the chemical inventory of disks and the properties of exoplanets. The survey comprises 52 targets (Herbig Ae stars, T Tauri stars, very low-mass stars and young debris disks). We primarily obtain MIRI/MRS spectra with high signal-to-noise ratio (∼100–500) covering the complete wavelength range from 4.9 to 27.9 μm. For a handful of selected targets we also obtain NIRSpec IFU high resolution spectroscopy (2.87–5.27 μm). We will search for signposts of planet formation in thermal emission of micron-sized dust—information complementary to near-IR scattered light emission from small dust grains and emission from large dust in the submillimeter wavelength domain. We will also study the spatial structure of disks in three key systems that have shown signposts for planet formation, TW Hya and HD 169142 using the MIRI coronagraph at 15.5 μm and 10.65 μm respectively and PDS 70 using NIRCam imaging in the 1.87 μm narrow and the 4.8 μm medium band filter. We provide here an overview of the MINDS survey and showcase the power of the new JWST mid-IR molecular spectroscopy with the TW Hya disk spectrum where we report the detection of the molecular ion CH3+ and the robust confirmation of HCO+ earlier detected with Spitzer.

Radial and Vertical Constraints on the Icy Origin of H2CO in the HD 163296 Protoplanetary Disk

H2CO is a small organic molecule widely detected in protoplanetary disks. As a precursor to grain-surface formation of CH3OH, H2CO is considered an important precursor of O-bearing organic molecules that are locked in ices. Still, since gas-phase reactions can also form H2CO, there remains an open question on the channels by which organics form in disks, and how much the grain versus the gas pathways impact the overall organic reservoir. We present spectrally and spatially resolved Atacama Large Millimeter/submillimeter Array observations of several ortho- and para-H2CO transitions toward the bright protoplanetary disk around the Herbig Ae star HD 163296. We derive column density, excitation temperature, and ortho-to-para ratio (OPR) radial profiles for H2CO, as well as disk-averaged values of N T ∼ 4 × 1012 cm−2, T ex ∼ 20 K, and OPR ∼ 2.7, respectively. We empirically determine the vertical structure of the emission, finding vertical heights of z/r ∼ 0.1. From the profiles, we find a relatively constant OPR ∼ 2.7 with radius, but still consistent with 3.0 among the uncertainties, a secondary increase of N T in the outer disk, and low T ex values that decrease with disk radius. Our resulting radial, vertical, and OPR constraints suggest an increased UV penetration beyond the dust millimeter edge, consistent with an icy origin but also with cold gas-phase chemistry. This Herbig disk contrasts previous results for the T Tauri disk, TW Hya, which had a larger contribution from cold gas-phase chemistry. More observations of other sources are needed to disentangle the dominant formation pathway of H2CO in protoplanetary disks.

Deep Paβ Imaging of the Candidate Accreting Protoplanet AB Aur b

Giant planets grow by accreting gas through circumplanetary disks, but little is known about the timescale and mechanisms involved in the planet-assembly process because few accreting protoplanets have been discovered. Recent visible and infrared imaging revealed a potential accreting protoplanet within the transition disk around the young intermediate-mass Herbig Ae star, AB Aurigae (AB Aur). Additional imaging in Hα probed for accretion and found agreement between the line-to-continuum flux ratio of the star and companion, raising the possibility that the emission source could be a compact disk feature seen in scattered starlight. We present new deep Keck/NIRC2 high-contrast imaging of AB Aur to characterize emission in Paβ, another accretion tracer less subject to extinction. Our narrow band observations reach a 5σ contrast of 9.6 mag at 0.″6, but we do not detect significant emission at the expected location of the companion, nor from other any other source in the system. Our upper limit on Paβ emission suggests that if AB Aur b is a protoplanet, it is not heavily accreting or accretion is stochastic and was weak during the observations.

An ALMA Molecular Inventory of Warm Herbig Ae Disks. I. Molecular Rings, Asymmetries, and Complexity in the HD 100546 Disk

Observations of disks with the Atacama Large Millimeter/submillimeter Array (ALMA) allow us to map the chemical makeup of nearby protoplanetary disks with unprecedented spatial resolution and sensitivity. The typical outer Class II disk observed with ALMA is one with an elevated C/O ratio and a lack of oxygen-bearing complex organic molecules, but there are now some interesting exceptions: three transition disks around Herbig Ae stars all show oxygen-rich gas traced via the unique detections of the molecules SO and CH3OH. We present the first results of an ALMA line survey at ≈337–357 GHz of such disks and focus this paper on the first Herbig Ae disk to exhibit this chemical signature—HD 100546. In these data, we detect 19 different molecules including NO, SO2, and CH3OCHO (methyl formate). We also make the first tentative detections of H213CO and 34SO in protoplanetary disks. Multiple molecular species are detected in rings, which are, surprisingly, all peaking just beyond the underlying millimeter continuum ring at ≈200 au. This result demonstrates a clear connection between the large dust distribution and the chemistry in this flat disk. We discuss the physical and/or chemical origin of these substructures in relation to ongoing planet formation in the HD 100546 disk. We also investigate how similar and/or different this molecular makeup of this disk is to other chemically well-characterized Herbig Ae disks. The line-rich data we present motivate the need for more ALMA line surveys to probe the observable chemistry in Herbig Ae systems, which offer unique insight into the composition of disks ices, including complex organic molecules.

Mid-infrared evidence for iron-rich dust in the multi-ringed inner disk of HD 144432

Context. Rocky planets form by the concentration of solid particles in the inner few au regions of planet-forming disks. Their chemical composition reflects the materials in the disk available in the solid phase at the time the planets were forming. Studying the dust before it gets incorporated in planets provides a valuable diagnostic for the material composition. Aims. We aim to constrain the structure and dust composition of the inner disk of the young Herbig Ae star HD 144432, using an extensive set of infrared interferometric data taken by the Very Large Telescope Interferometer (VLTI), combining PIONIER, GRAVITY, and MATISSE observations. Methods. We introduced a new physical disk model, TGMdust, to image the interferometric data, and to fit the disk structure and dust composition. We also performed equilibrium condensation calculations with GGchem to assess the hidden diversity of minerals occurring in a planet-forming disk such as HD 144432. Results. Our best-fit model has three disk zones with ring-like structures at 0.15, 1.3, and 4.1 au. Assuming that the dark regions in the disk at ~0.9 au and at ~3 au are gaps opened by planets, we estimate the masses of the putative gap-opening planets to be around a Jupiter mass. We find evidence for an optically thin emission (τ < 0.4) from the inner two disk zones (r < 4 au) at λ > 3 µm. Our silicate compositional fits confirm radial mineralogy gradients, as for the mass fraction of crystalline silicates we get around 61% in the innermost zone (r < 1.3 au), mostly from enstatite, while only ~20% in the outer two zones. To identify the dust component responsible for the infrared continuum emission, we explore two cases for the dust composition, one with a silicate+iron mixture and the other with a silicate+carbon one. We find that the iron-rich model provides a better fit to the spectral energy distribution. Our GGchem calculations also support an iron-rich and carbon-poor dust composition in the warm disk regions (r < 5 au, T > 300 K). Conclusions. We propose that in the warm inner regions (r < 5 au) of typical planet-forming disks, most if not all carbon is in the gas phase, while iron and iron sulfide grains are major constituents of the solid mixture along with forsterite and enstatite. Our analysis demonstrates the need for detailed studies of the dust in inner disks with new mid-infrared instruments such as MATISSE and JWST/MIRI.

Modelling UX Ori star eclipses based on spectral observations with the Nordic Optical Telescope − I. RR Tau

ABSTRACT Based on observations obtained with the Nordic Optical Telescope (NOT) we investigate the spectral variability of the Herbig Ae star RR Tau. This star belongs to the UX Ori family, characterized by very deep fadings caused by the screening of the star with opaque fragments (clouds) of the protoplanetary discs. At the moments of such minima one observes strong spectral variability due to the fact that the dust cloud occults, for an observer, not only the star but also a part of the region where the emission spectrum originates. We calculated a series of obscuration models to interpret the observed variability of the H α line parameters. We consider two main obscuration scenarios: (1) the dust screen rises vertically above the circumstellar disc, and (2) the screen intersects the line-of-sight moving azimuthally with the disc. In both cases, the model of the emission region consists of a compact magnetosphere and a magnetocentrifugal disc wind. Comparison with observations shows that the first scenario explains well the variability of the radiation flux, the equivalent width, as well as the asymmetry of the H α line during eclipses, while the second scenario explains them only partly. This permits us to suggest that in the case of RR Tau, the main causes of the eclipses are either a structured disc wind, or the charged dust lifted along the field lines of the poloidal component of the magnetic field of the circumstellar disc.

A Survey of Herbig Ae/Be Multiplicity

Although the majority of Herbig Ae/Be (HAEBE) stars are likely multiple systems, relatively few multiples have been identified. We aim to create a statistically significant survey of HAEBE multiplicity as a function of stellar mass, to shed light on mixed-mass star formation. Two independent adaptive optics IR imaging surveys were conducted, between 1993 and 2007. A total of 143 stars were observed, including 126 HAEBE stars. These surveys are significantly more sensitive than previous imaging work and, combined with accurate distance and proper-motion data from GAIA Data Release 3, provide a broad survey of intermediate-mass multiplicity. We perform a statistical probability analysis to identify the likely physical companions, and analyze multiepoch observations for common proper motions. We find 250 stellar detections around 88 sample stars. Of these, 70 systems are likely multiple systems, and 42 companions around 29 systems are reported here for the first time. Correcting for completeness, we find a multiplicity fraction of 54%. Multiples are found randomly across all spectral types, but high-order multiples are more common among the hottest stars. Statistically likely companions are found at distances of up to several thousand astronomical units and ΔK magnitudes ranging from <0.1 to ∼9, although companions with ΔK < 1.5 are rare. Companions around Herbig Ae stars tend to be closer than those around Herbig Be stars. We confirm 24 proper-motion companions in 21 systems, including roughly half of the statistically very likely companions; however, many proper-motion results are inconclusive.

Identification and Parameter Determination of F-type Herbig Stars from LAMOST DR8

We identify 20 F-type Herbig stars and provide a list of 22 pre-main-sequence candidates from LAMOST DR8. The effective temperature, distance, extinction, stellar luminosity, mass, age, and radius are derived for each Herbig star based on optical spectra, photometry, Gaia EDR3 parallaxes, and pre-main-sequence evolutionary tracks. According to spectral energy distribution, 19 F-type Herbig stars belong to Class II YSOs, and one belongs to the flat-spectrum class. Four have Spitzer IRS spectra, of which three show extremely weak polycyclic aromatic hydrocarbon emissions, and three with both amorphous and crystalline silicate emissions share similar parameters and are at the same evolutionary stage. We detect a solar-nearby outbursting EXor Herbig star J034344.48+314309.3, a possible precursor of a Herbig Ae star. Intense emission lines of H i, He i, O i, Na i, and Ca ii originating from the rapid accretion during the outbursts are detected in its optical spectra, and silicate emission features are detected in its infrared spectrum. We also conduct a statistical analysis of the disk properties of all known Herbig stars using the defined infrared spectral indices ( and ). The proportion of Herbig stars with moderate infrared excesses decreases as effective temperature increases. The majority of the precursors (F, G, or K type) have moderate infrared excesses. Hotter Herbig stars tend to have a larger proportion with large infrared excesses. The trends may be due to the fact that hotter stars have larger areas of re-emitting dust, although there is some scatter due to the particularities of each disk.

AB Aur, a Rosetta stone for studies of planet formation

Context. The sulfur abundance is poorly known in most environments. Yet, deriving the sulfur abundance is key to understanding the evolution of the chemistry from molecular clouds to planetary atmospheres. We present observations of H2S 110–101 at 168.763 GHz toward the Herbig Ae star AB Aur. Aims. We aim to study the abundance of sulfuretted species toward AB Aur and to constrain how different species and phases contribute to the sulfur budget. Methods. We present new NOrthern Extended Millimeter Array (NOEMA) interferometric observations of the continuum and H2S 110–101 line at 168.763 GHz toward AB Aur. We derived radial and azimuthal profiles and used them to compare the geometrical distribution of different species in the disk. Assuming local thermodynamical equilibrium (LTE), we derived column density and abundance maps for H2S, and we further used Nautilus to produce a more detailed model of the chemical abundances at different heights over the mid-plane at a distance of r = 200 au. Results. We have resolved H2S emission in the AB Aur protoplanetary disk. The emission comes from a ring extending from 0.67″ (~109 au) to 1.69″ (~275 au). Assuming T = 30 K, nH = 109 cm−3, and an ortho-to-para ratio of three, we derived a column density of (2.3 ± 0.5) × 1013 cm−2. Under simple assumptions, we derived an abundance of (3.1 ± 0.8) × 10−10 with respect to H nuclei, which we compare with Nautilus models to deepen our understanding of the sulfur chemistry in protoplanetary disks. Chemical models indicate that H2S is an important sulfur carrier in the solid and gas phase. We also find an important transition at a height of ~12 au, where the sulfur budget moves from being dominated by ice species to being dominated by gas species. Conclusions. We confirm that present-day models still struggle to simultaneously reproduce the observed column densities of the different sulfuretted species, and the observed abundances are still orders of magnitude away from the cosmic sulfur abundance. Studying sulfuretted species in detail in the different phases of the interstellar medium is key to solving the issue.

H2O distribution in the disc of HD 100546 and HD 163296: the role of dust dynamics and planet–disc interaction

Water plays a fundamental role in the formation of planets and their atmospheres. Far-infrared observations with the Herschel Space Observatory revealed a surprisingly low abundance of cold-water reservoirs in protoplanetary discs. On the other hand, a handful of discs show emission of hot water transitions excited at temperatures above a few hundred Kelvin. In particular, the protoplanetary discs around the Herbig Ae stars HD 100546 and HD 163296 show opposite trends in terms of cold versus hot water emission: in the first case, the ground-state transitions are detected and the high-J lines are undetected, while the trend is opposite in HD 163296. As the different transitions arise from different regions of the disc, it is possible to address the overall distribution of water molecules throughout the disc. We performed a detailed spectral analysis using the thermo-chemical model DALI. We find that HD 163296 is characterised by a water-rich (abundance ≳10−5) hot inner disc (within the snow line) and a water-poor (&lt;10−10) outer disc: the relative abundance of water molecules in the hot inner region may be due to the thermal desorption of icy grains that have migrated inward. Remarkably, the size of the H2O emitting region corresponds to a narrow dust gap visible in the millmeter continuum at r = 10 au observed with the Atacama Large Milµmetre Array (ALMA). This spatial coincidence may be due to pebble growth at the border of the snow line. The low-J lines detected in HD 100546 instead imply an abundance of a few 10−9 in the cold outer disc (&gt;40 au). The emitting region of the cold H2O transitions is spatially coincident with that of the H2O ice previously seen in the near-infrared. Notably, milµmetre observations with ALMA reveal the presence of a large dust gap between nearly 40 and 150 au, likely opened by a massive embedded protoplanet. In both discs, we find that the warm molecular layer in the outer region (beyond the snow line) is highly depleted of water molecules, implying an oxygen-poor chemical composition of the gas. We speculate that gas-phase oxygen in the outer disc is readily depleted and its distribution in the disc is tightly coupled to the dynamics of the dust grains.

The morphology of the HD 163296 jet as a window on its planetary system

Context. HD 163296 is a Herbig Ae star which drives a bipolar knotty jet with a total length of ~6000 au. Strong evidence exists that the disk of HD 163296 harbors planets. Studies have shown that the presence of companions around jet-driving stars could affect the morphology of the jets. This includes a ‘wiggling’ of the jet axis and a periodicity in the positions of the jet knots. Aims. In this study we investigate the morphology (including the jet width and axis position) and proper motions of the HD 163296 jets, and use our results to better understand the whole system. Methods. This study is based on optical integral-field spectroscopy observations obtained with VLT/MUSE in 2017. Using spectro-images and position velocity diagrams extracted from the MUSE data cube, we investigated the number and positions of the jet knots. A comparison was made to X-shooter data collected in 2012 and the knot proper motions were estimated. The jet width and jet axis position with distance from the star were studied from the extracted spectro-images. This was done using Gaussian fitting to spatial profiles of the jet emission extracted perpendicular to the position angle of the jet. The centroid of the fit is taken as the position of the jet axis. Results. We observe the merging of knots and identify two previously undetected knots. We find proper motions that are broadly in agreement with previous studies. The jet width increases with distance from the source and we measure an opening angle of ~5° and 2.5° for the red and blue lobes, respectively. Measurements of the jet axis position, derived from Gaussian centroids of transverse intensity profiles, reveal a similar pattern of deviation in all forbidden emission lines along the first 20 arcsec of the jets. This result is interpreted as being due to asymmetric shocks and not due to a wiggling of the jet axis. Conclusions. The number of new knots detected and their positions challenge the 16-yr knot ejection periodicity proposed in prior studies, arguing for a more complicated jet system than was previously assumed. We use the non-detection of a jet axis wiggling to rule out companions with a mass &gt;0.1 M⊙ and orbits between 1 au and 35 au. Any object inferred at these distances using other methods must be a brown dwarf or planet, otherwise it would have impacted the jet axis position. Both the precession and orbital motion scenarios are considered. Overall it is concluded that it is difficult to detect planets with orbits &gt;1 au through a study of the jet axis.

Photometric Behavior of the Herbig Ae Star VX Cas in the Near-Infrared and Optical Ranges of the Spectrum

Photometric Behavior of the Herbig Ae Star VX Cas in the Near-Infrared and Optical Ranges of the Spectrum

Scattering and sublimation: a multiscale view of µm-sized dust in the inclined disc of HD 145718

ABSTRACT We present multi-instrument observations of the disc around the Herbig Ae star, HD 145718, employing geometric and Monte Carlo radiative transfer models to explore the disc orientation, the vertical and radial extent of the near-infrared (NIR) scattering surface, and the properties of the dust in the disc surface and sublimation rim. The disc appears inclined at 67–71°, with position angle, PA = −1.0 to 0.6°, consistent with previous estimates. The NIR scattering surface extends out to ${\sim}75\,$ au and we infer an aspect ratio, hscat(r)/r ∼ 0.24 in J band; ∼0.22 in H band. Our Gemini Planet Imager images and VLTI + CHARA NIR interferometry suggest that the disc surface layers are populated by grains ≳λ/2π in size, indicating these grains are aerodynamically supported against settling and/or the density of smaller grains is relatively low. We demonstrate that our geometric analysis provides a reasonable assessment of the height of the NIR scattering surface at the outer edge of the disc and, if the inclination can be independently constrained, has the potential to probe the flaring exponent of the scattering surface in similarly inclined (i ≳ 70°) discs. In re-evaluating HD 145718’s stellar properties, we found that the object’s dimming events – previously characterized as UX Or and dipper variability – are consistent with dust occultation by grains larger, on average, than found in the ISM. This occulting dust likely originates close to the inferred dust sublimation radius at $0.17\,$ au.

AB Aur: A Rosetta stone for planet formation theories

AB Aur is a Herbig Ae star that hosts a well-known protoplanetary disk that depicts a plethora of features that can be attributed to the presence of a forming planet, such as a large inner cavity, a dust trap, and spiral arms. We present NOEMA observations of molecular species towards this transition disk around AB Aur, including CO, 13CO, C18O, HCN, HCO+, SO, H2CO, and H2S. These observations reveal complex chemistry with strong chemical differentiation and the presence of a cavity-crossing filament.

Searching for Magnetospheres around Herbig Ae/Be Stars

We describe four different approaches for the detection of magnetospheric accretion among Herbig Ae/Be stars with accretion disks. Studies of several unique objects have been carried out. One of the objects is the Herbig Ae star HD 101412 with a comparatively strong magnetic field. The second is the early-type Herbig B6e star HD 259431. The existence of a magnetosphere in these objects was not recognized earlier. In both cases, a periodicity in the variation of some line parameters, originating near the region of the disk/star interaction, has been found. The third object is the young binary system HD 104237, hosting a Herbig Ae star and a T Tauri star. Based on the discovery of periodic variations of equivalent widths of atmospheric lines in the spectrum of the primary, we have concluded that the surface of the star is spotted. Comparing our result with an earlier one, we argue that these spots can be connected with the infall of material from the disk onto the stellar surface through a magnetosphere. The fourth example is the Herbig Ae/Be star HD 37806. Signatures of magnetospheric accretion in this object have been identified using a different method. They were inferred from the short-term variability of the He i λ5876 line profile forming in the region of the disk/star interaction.