Michiel R. Hogerheijde

Context . Herbig stars are intermediate mass pre-main sequence stars of 1.5 to ∼15 M _⊙ and are between low- and high-mass star formation. Despite the giant exoplanet occurrence rate peaking at intermediate mass stars, a systematic analysis of the complete known Herbig star and protoplanetary disk population is lacking. Aims . This work provides a catalog of all 243 known bona fide Herbig stars with clear infrared excess and in many cases accretion signatures within 1 kpc. It contains archival, recalibrated, and newly derived stellar parameters, accretion rate properties, and disk dust mass measurements. With these, we aim to examine the Herbig star relationship between the accretion rate and the stellar and disk dust mass, get an estimate for the completeness of our catalog, and obtain an estimate of the lifetime of a Herbig star. These relationships and disk dust masses are put into the context of T Tauri stars and the giant exoplanet population. Methods . We revised the stellar masses, radii, and ages using a Hertzsprung-Russell diagram, and computed new accretion rates for part of our sample. We derived dust masses for all targets using a combination of newly obtained millimeter photometry (60% of the targets) and literature values, from a combination of ALMA, ACA, SMA, and NOEMA data. Results . We find that 50% of Herbig dust disks are more massive than 10 M _⊕ , while this is only true for 20% and 5% of the T Tauri disks in Lupus and Upper Scorpius, respectively. Furthermore, the Herbig disk dust mass distribution is bimodal; it consists of a high and low disk mass population with a mean dust mass of 21 M _⊕ and 0.45 M _⊕ , respectively. We find that the catalog is near complete for within 300 pc, however, this decreases to 24% out to 1 kpc. We also find a decreasing Herbig lifetime with increasing stellar mass of the form t = 12 × M _⋆ ^−1.4 Myr. The bulk of the Herbig disks are above the T Tauri accretion rate-disk mass relationship, and we observe a flat relation for Herbig disks due to objects with short disk lifetimes, caused by a combination of low disk masses and high accretion rates. Furthermore, we find the peak of the occurrence rate of massive (>10 M _⊕ ) disks to occur at ∼1–2 M _⊙ stars, which coincides with the peak in occurrence rate of giant exoplanets. For higher stellar masses, the disk dust mass decreases again. Conclusions . This catalog characterizes intermediate mass star formation, and links massive disks to the occurrence rate of giant exoplanets. The scarcity of Herbig stars with low accretion rates (−8 M _⊙ yr ⁻¹ ) or disk masses (≲1 M _⊕ ), combined with the lack of disk dust mass age dependence, suggests that the observed Herbig star population represents the surviving disk-hosting phase in late intermediate mass star formation. We attribute this survival to deep dust traps, late-infall replenishment, or a combination of the two.

The planet-forming disk of HD 142527 is known for its azimuthally asymmetric dust trap, shadows, and spiral arms. In this work we used new observations of the Atacama Large Millimeter/submillimeter Array to investigate the molecular composition and to determine the ongoing chemical processes and the origin of its asymmetric molecular emission, and to infer possible effects of dust continuum obscuration. The observations cover a wide variety of molecular species over a large frequency range, enlarging the known molecular inventory of this system. Strikingly, the emission of H ₂ CO, CN, and C ₂ H is dominated by spiral-like features peaking in the southern region of the disk, opposite to the large dust trap, while no relation is found between the observed asymmetries and the shadows seen in the scattered light due to the misaligned inner disk. We attribute these features to low-density, late infalling, atomic carbon-rich material that locally increases the C/O ratio and, subsequently, facilitates the gas-phase formation of these species. Azimuthal offsets between the peak emission of H ₂ CO and that of CN and C ₂ H are possibly due to a delay of a few hundred years in the gas-phase formation of H ₂ CO. As opposed to the emission of H ₂ CO, CN, and C ₂ H, the emission of C ¹⁷ O and the HCO ⁺ J =1–0 transition is aligned with the large dust trap, likely due to an azimuthal increase in the surface density. Differences between the two observed C ¹⁷ O transitions may be due to dust obscuration effects. These effects are not expected to affect molecular emission at 3 mm, given the lower optical depth of the dust trap. The four observed transitions of CS display different azimuthal extents and strengths, with the lines with lower upper-level energies appearing more ring-like. An analysis of the ¹³ CO brightness temperature yields no significant temperature variations across the disk’s azimuth. Therefore, we propose that the observed CS transitions trace two different reservoirs: a cold reservoir that resides on a Keplerian orbit and a second, hotter reservoir of CS that is facilitated by the infalling material and resides in a higher atmospheric layer of the disk. A single weak transition of SO is observed, which may be explained by weak shocks induced by the spirals observed in the scattered light that liberate sulphur. Future higher-resolution, multi-line observations of species such as H ₂ CO, CS, CN, and C ₂ H are needed to investigate the role and importance of late infalling material in setting the chemical composition of planet-forming disks.

Context . Circumstellar discs, and especially their inner regions, which cover ranges from less than 1 au to a few au, are the birthplaces of terrestrial planets. The inner regions are thought to be as diverse in structure as the well-observed outer regions probed by ALMA. Aims . By combining data and results from previous studies using the VLTI/PIONIER and VLTI/GRAVITY instruments with new, multi-epoch VLTI/MATISSE observations, we aim to provide a comprehensive picture of the structure of the inner regions of the circumstellar disc around the F-type Herbig Ae/Be star HD 142527 A, the primary of a binary star system. Methods . We modelled the multi-wavelength interferometric data using a parametrised, geometrically thin disc model, allowing for azimuthal asymmetry, and exploring a first-order disc modulation and an off-centre Gaussian component. Results . We find time-variable structures in the N -band observables, which we reproduce with time-dependent models. This variability manifests as azimuthally asymmetric emission, evidenced by strong, non-zero closure phases in the N -band data. Fits to individual epochs of the N -band observations yield better χ ² _r values than fits to all epochs simultaneously. This suggests substantial changes in the geometry of the inner disc emission from ∼1 au up to a few astronomical-unit scales from one year to the next. Moreover, our models produce a very close-in inner disc rim R _rim ≈ 0.1 au. Altogether, we find a very complex, substantially non-point symmetric and temporally variable disc ( r _out ≲ 6 au) around the primary. Conclusions . The very close-in inner rim indicates the presence of material within the typical wall-like sublimation radius, R _{rim,literature} ≈ 0.3 au. The complex, temporally variable inner-disc geometry is likely affected, or even caused by, the close passage (∼5 au) and short orbit ( P ≈ 24 yr) of the companion HD 142527 B.

Aims. Studying protostellar objects in their earliest stages, particularly during the Class 0 phase, provides key insight into the beginnings of planet formation and dust evolution. Disentangling the various components, such as the envelope, outflow, and nascent disk, to characterize and understand these young systems, however, is particularly challenging. High spatial and spectral resolution observations of molecular line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) are therefore crucial for probing their complex environments. Methods. We present high-resolution (∼30 au) ALMA observations at 1.3 mm of the Class 0 protostellar system IRAS4A2. We analyzed the gas emission surrounding this young source, tracing it from the extended outflow to the most compact inner region and identifying emission lines using the spectral analysis tool CASSIS. Results. We detect large, well-traced outflows in HCN (3–2), H ₂ CO (2 ₁₂ –1 ₁₁ ), and HCO ⁺ (3–2), along with numerous complex organic molecules (COMs) such as C ₂ H ₃ CN, CH ₂ (OH)CHO, CH ₃ OCHO, and CH ₃ C ¹⁵ N that trace central, more compact regions. These molecules span upper-energy levels (E _u ) ranging from 20 to 487 K and have excitation temperatures between 100 and 300 K. Using moment maps, we analyzed the kinematics and spatial distributions of the molecular emission, revealing a wide range of spatial scales, from compact structures within the IRAS4A2 core at ∼8 au in radius, to extended ∼5000 au outflow emission. Specifically, we find that CH ₃ CDO and CH ₃ OCHO could both be good tracers of the disk, possibly tracing its rotation. Lines of OCS (22–21), SO ₂ (13 _{3 11} –13 _{2 12} ), HCN, H ₂ CO, and HCO ⁺ , which have lower upper-level energies, show more extended structures around IRAS4A2, likely tracing the envelope, disk, accretion shocks, the base of an outflow, and the outflow itself. Some of these molecular lines exhibit signatures consistent with Keplerian rotation, indicating a central protostellar mass of approximately 0.2 M _⊙ . Conclusions. Most COMs appear to trace distinct inner regions near the central protostar, while other molecules like OCS, SO ₂ , HCN, and H ₂ CO trace more extended structures, such as the envelope or outflows. The kinematics, emission patterns, and position-velocity diagrams suggest that individual molecules trace multiple components simultaneously, making it challenging to disentangle their true origins. Altogether, these findings highlight the complex spatial distribution within the IRAS4A2 system.

Protoplanetary disk evolution can be deeply influenced by the UV radiation emitted by neighboring massive stars (mainly of spectral types O and B). We show that the process of external photoevaporation, which causes an outside-in depletion of disk material due to environmental UV radiation, can lead to a significant decrease in disk size, disk mass, and lifetime even at moderate irradiation levels (1–10 G₀). In this work, we investigate the role of external photoevaporation in shaping the masses and sizes of the 10 AGE-PRO disks in the Upper Scorpius (Upper Sco) region, which we estimate to be subject to far-ultraviolet (FUV) fluxes ranging between ∼2 and ∼12 G₀, on average. We compare the disk masses and sizes resulting from 1D numerical viscous evolution simulations, in which the effect of external photoevaporation is included, to the values retrieved from the AGE-PRO observations. While the pure viscous framework fails in adequately explaining the observed disk properties in Upper Sco, with the inclusion of external photoevaporation, we can successfully reproduce gas disk sizes for seven out of 10 sources within a factor <2, when the initial disk mass is 1%–10% of the stellar mass. We emphasize the importance of accounting for the environmental irradiation when comparing star-forming regions of different ages, even when moderate FUV irradiation fields are experienced, as in the case of Upper Sco.

The architecture of planetary systems depends on the evolution of the disks in which they form. In this work, we develop a population synthesis approach to interpret the Atacama Large Millimeter/submillimeter Array survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO) measurements of disk gas mass and size considering two scenarios: turbulence-driven evolution with photoevaporative winds and MHD wind-driven evolution. A systematic method is proposed to constrain the distribution of disk parameters from the disk fractions, accretion rates, disk gas masses, and CO gas sizes. We find that turbulence-driven accretion with initially compact disks (R ₀ ≃ 5–20 au), low mass-loss rates, and relatively long viscous timescales (t _ν,0 ≃ 0.4–3 Myr or α _SS ≃ 2–4 × 10⁻⁴) can reproduce the disk fractions and gas sizes. However, the distribution of apparent disk lifetimes defined as the M D / M ̇ * ratio is severely overestimated by turbulence-driven models. On the other hand, MHD wind-driven accretion can reproduce the bulk properties of disk populations from Ophiuchus to Upper Scorpius assuming compact disks with an initial magnetization of about β ≃ 10⁵ (α _DW ≃ 0.5–1 × 10⁻³) and a magnetic field that declines with time. More studies are needed to confirm the low masses found by AGE-PRO, notably for compact disks that question turbulence-driven accretion. The constrained synthetic disk populations can now be used for realistic planet population models to interpret the properties of planetary systems on a statistical basis.

The evolution of the gas mass of planet-forming disks around young stars is crucial for our understanding of planet formation, yet it has proven hard to constrain observationally, due both to the difficulties of measuring gas masses and the lack of a homogeneous sample. Here we present a large grid of thermochemical models that we use to measure protoplanetary gas disk masses of AGE-PRO, the Atacama Large Millimeter/submillimeter Array survey of Gas Evolution in PROtoplanetary disks. AGE-PRO covers a sample of 30 disks around similar spectral type (M3-K6) stars with ages between 0.1 and 10 Myr. Our approach is to simultaneously fit observations of CO isotopologues and N₂H⁺, a complementary molecule produced when CO freezes out. We find that the median gas mass of the three regions decreases over time, from 7 . 0 − 2.6 + 4.4 × 1 0 − 3 M ⊙ in Ophiuchus (≲1 Myr) to 9 . 4 − 3.4 + 5.4 × 1 0 − 4 M ⊙ for Lupus (∼1–3 Myr) and 6 . 8 − 2.8 + 5.1 × 1 0 − 4 M ⊙ for Upper Sco (∼2–6 Myr), with ∼1 dex scatter in gas mass in each region. We note that the gas mass distributions for Lupus and Upper Sco look very similar, which could be due to survivorship bias for the latter. The median bulk CO abundance in the CO emitting layer is found to be a factor ∼10 lower than the interstellar medium value but does not significantly change between Lupus and Upper Sco. From Lupus to Upper Sco, the median gas-to-dust mass ratio increases by a factor ∼3 from ∼40 to ∼120, suggesting efficient inward pebble drift and/or the formation of planetesimals.

The Atacama Large Millimeter/submillimeter Array (ALMA) large program AGE-PRO explores protoplanetary disk evolution by studying gas and dust across various ages. This work focuses on 10 evolved disks in Upper Scorpius, observed in dust continuum emission, CO and its isotopologues, and N₂H⁺ with ALMA Bands 6 and 7. Disk radii, from the radial location enclosing 68% of the flux, are comparable to those in the younger Lupus region for both gas and dust tracers. However, solid masses are about an order of magnitude below those in Lupus and Ophiuchus, while the dust spectral index suggests some level of dust evolution. These empirical findings align with a combination of radial drift, dust trapping, and grain growth into larger bodies. A moderate correlation between CO and continuum fluxes suggests a link between gas and dust content, through the increased scatter compared to younger regions, possibly due to age variations, gas-to-dust ratio differences, or CO depletion. Additionally, the correlation between C¹⁸O and N₂H⁺ fluxes observed in Lupus persists in Upper Scorpius, indicating a relatively stable CO gas abundance over the Class II stage of disk evolution. In conclusion, the AGE-PRO survey of Upper Scorpius disks reveals intriguing trends in disk evolution. The findings point toward potential gas evolution and the presence of dust traps in these older disks. Future high-resolution observations are needed to confirm these possibilities and further refine our understanding of disk evolution and planet formation in older environments.

We present Band 6 and Band 7 observations of 10 Lupus disks around M3-K6 stars from the Atacama Large Millimeter/submillimeter Array survey of Gas Evolution in PROtoplanetary disks (AGE-PRO) Large Program. In addition to continuum emission in both bands, our Band 6 setup covers the ¹²CO, ¹³CO, and C¹⁸O J = 2–1 lines, while our Band 7 setup covers the N₂H⁺ J = 3–2 line. All of our sources are detected in ¹²CO and ¹³CO; seven out of ten are detected in C¹⁸O; and three are detected in N₂H⁺. We find strong correlations between the CO isotopologue line fluxes and the continuum flux densities. With the exception of one disk, we also identify a strong correlation between the C¹⁸O J = 2–1 and N₂H⁺ J = 3–2 fluxes, indicating similar CO abundances across this sample. For the two sources with well-resolved continuum and ¹²CO J = 2–1 images, we find that their gas-to-dust size ratio is consistent with the median value of ∼2 inferred from a larger sample of Lupus disks. We derive dust disk masses from continuum flux densities. We estimate gas disk masses by comparing C¹⁸O J = 2–1 line fluxes with those predicted by the limited grid of self-consistent disk models of M. Ruaud et al. A comparison of these mass estimates with those derived by L. Trapman et al., using a combination of CO isotopologue and N₂H⁺ line emission, shows that the masses are consistent with each other. Some discrepancies appear for small and faint disks, but they are still within the uncertainties. Both methods find gas disk masses increase with dust disk masses, and gas-to-dust mass ratios are between 10 and 100 in the AGE-PRO Lupus sample.

We present the Atacama Large Millimeter/submillimeter Array Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO), a large program of the ALMA. AGE-PRO aims to systematically trace the evolution of gas disk mass and size throughout the lifetime of protoplanetary disks. It uses a carefully selected sample of 30 disks around M3-K6 stars in three nearby star-forming regions: Ophiuchus (0.5–1 Myr), Lupus (1–3 Myr), and Upper Sco (2–6 Myr). Assuming the three regions had similar initial conditions and evolutionary paths, we find the median gas disk mass appears to decrease with age. Ophiuchus disks have the highest median gas mass (6 M _Jup), while the Lupus and Upper Sco disks have significantly lower median masses (0.68 and 0.44 M _Jup, respectively). Notably, the gas and dust disk masses appear to evolve on different timescales. This is evidenced by the median gas-to-dust mass ratio, which decreases from 122 in the youngest disks (1 Myr disks by an order of magnitude. Here, we discuss the program’s motivation, survey design, sample selection, observation and data calibration processes, and highlight the initial results.