arXiv subjects

Lionel Siess

Publications and source records attributed to Lionel Siess.

At least 19 recordsLinked to original sources

arXiv2026

On the formation of subdwarf B stars via engulfment of substellar companions

The canonical scenario for the formation of subdwarf B (sdB) stars involves the ejection of the progenitor's envelope near the tip of the Red Giant Branch (RGB), concurrent with the onset of core He-burning. While binary interactions are known to dominate sdB formation, the origin of apparently single sdB stars remains uncertain. We investigate the conditions under which a sdB progenitor can eject its envelope through the engulfment of a substellar companion, using an energy balance approach. We further estimate the fraction of sdB stars that could form via this channel. We simulate the orbital evolution of substellar companions during the subgiant and RGB phases to determine the onset of engulfment and calculate the energy released during inspiral within the stellar envelope. By comparing this energy with the envelope binding energy and exploring different efficiencies for its deposition, we identify the conditions required for envelope ejection. We then combine these results with the observed population of substellar companions to estimate the occurrence rate of sdB formation. The engulfment of substellar objects can lead to envelope ejection within a limited region of the mass-semi-major axis parameter space, whose extent depend on the host star's properties and energy transfer efficiency. The minimum companion mass required for ejection increases with decreasing efficiency and increasing stellar mass. As a result, the frequency of envelope ejection is strongly influenced by the distribution of substellar companions, particularly by the paucity of objects in the brown-dwarf desert. Low-mass brown dwarfs and massive planets are viable candidates for explaining the existence of apparently single sdB stars. Our results define the region of parameter space where this mechanism is energetically possible and provide a guide for future multidimensional hydrodynamical simulations.

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arXiv2026

Dust Formation in Common Envelope Binary Interactions -- III. Lightcurves

Luminous red novae are transient events thought to arise from common envelope binary interactions. In this paper, we perform post-processing light-curve calculations for two, 3D hydrodynamic simulations of common envelope events. These simulations model interactions between 1.7 $M_\odot$ and 3.7 $M_\odot$ asymptotic giant branch stars and a 0.6 $M_\odot$ compact companion, including dust nucleation. In both our simulations, which are carried out for 44 years under adiabatic conditions, we observe a bright, hot peak lasting $3-5$ years, primarily due to the expansion of the photosphere before and during inspiral. Additional peaks can be seen appearing at different times and for different viewing angles, due to the asymmetry of the interaction. Dust forms about $1-3$ years after the beginning of the simulated interaction and shortly afterwards we witness a sharp decline in the bolometric luminosity, followed by a partial recovery and a plateau with an effective temperature of $\sim$400 K. The dust photosphere reaches a size of $\sim$250 au by the end of the simulations, but we predict that between 100 and 200 years, the dust will become optically thin at visible wavelengths, revealing an inner, warmer photosphere. The lightcurves obtained have two, well-quantified, but large uncertainties: insufficient surface resolution primarily affecting the first 1-2 years of the simulated lightcurves and the adiabatic assumption that affects primarily the later years. We finally contextualise our simulations within a group of observed luminous red nova transients, drawing particular attention to the outburst of OGLE-2002-BLG-360 and AT 2025abao, which are the closest match to our simulation.

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arXiv2026

The chemical fingerprint of the Gaia BH3 system. Evidence for early cluster enrichment from the analysis of 51 elements

The Gaia BH3 system hosts the most massive known stellar-origin black hole and a low-mass metal-poor companion whose chemical composition may constrain early explosive nucleosynthesis processes. We investigate the chemical abundances of the companion in order to constrain the formation of this remarkable system. We perform a detailed analysis of high-resolution ESO-UVES spectra of the companion. 51 elements from lithium to uranium were investigated through spectral synthesis, including 15 treated in NLTE. We compare the resulting pattern to r-process enriched stars, to nucleosynthesis models and to stars of the ED-2 stream. The abundance pattern of the BH3 companion is consistent with that of r-I stars and is well reproduced by a combination of core-collapse supernova yields and an r-process component. The chemical patterns of four ED-2 stars closely match that of the companion especially when a dilution is taken into account. The present analysis provides the most detailed chemical characterisation of a metal-poor star associated with a stellar-mass black hole. The chemical similarity with ED-2 stars argue against local pollution across the binary system. The abundances instead reflect early spatially inhomogeneous enrichment of the progenitor cluster.

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arXiv2026

Evolving Low- and Intermediate-Mass Binaries: Departures from Classical Theory

This review explores the physical mechanisms driving the evolution of low- and intermediate-mass binary star systems, with particular emphasis on emerging mechanisms that challenge classical paradigms. We begin by describing the principal formation channels and orbital properties of binary systems. A critical reassessment of the Roche lobe formalism is presented, focusing on systems with eccentric orbits and asynchronous rotation, where deviations from traditional approximations become significant. We then review current theoretical models of mass and angular momentum exchange via Roche-lobe overflow, incorporating results from recent hydrodynamical simulations of wind accretion. The review also reports advances in tidal dissipation theory. Finally, we explore mechanisms capable of sustaining or exciting orbital eccentricity, including perturbations induced by mass transfer and interactions with circumbinary disks. These discussions aim to outline underexplored facets of binary evolution, offering new perspectives for theoretical and observational studies.

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arXiv2025

Weakened inspirals -- I: High mass ratio common envelope interactions in RGB stars

The common envelope (CE) interaction between an expanding giant star and a compact companion typically leads to a rapid orbital decay, ending in either a merger or the formation of a close binary. However, the existence of post-red giant and post-asymptotic giant branch binaries with separations of 100 to 800 Rsun challenges this standard picture, as these systems appear to have experienced strong interactions without undergoing a classic CE inspiral. In this work, we investigate the effect of high mass ratio, q = M2/M1, on the CE inspiral using three-dimensional hydrodynamical simulations performed with the smoothed particle hydrodynamics code PHANTOM. The primary is a 0.88 Msun, 90 Rsun red giant branch star, while the companion masses span q = 0.68 to 1.5. Higher mass ratios lead to wider post-CE separations, with a maximum of approximately 40 Rsun. The pre-CE mass transfer phase is longer for larger companion masses, and for q greater than or equal to 1 the inspiral becomes significantly more stable, broadly consistent with analytical expectations. This phase is not fully converged with respect to numerical resolution, and higher resolution simulations are expected to further increase its duration and stability. Although higher q systems show enhanced mass loss through the L2 and L3 Lagrange points, we find that circumbinary discs are more likely to form from fallback of bound envelope material. Fallback times are short, of order a few hundred years, and fallback radii lie well outside the binary, between 0.5 and 5 au, where discs are expected to spread efficiently through viscous torques. While high mass ratio systems produce wider post-interaction separations, these remain smaller than those observed. In contrast, fallback-formed discs have properties consistent with observed circumbinary discs.

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arXiv2025

Evidence for the Keplerian orbit of a close companion around a giant star

Close companions influence stellar evolution through tidal interactions, mass transfer, and mass loss effects. While such companions are detected around young stellar objects, main-sequence stars, red giants, and compact objects, direct observational evidence of close-in companions around asymptotic giant branch (AGB) stars has remained elusive. Here, we present (sub)millimeter time-domain imaging spectroscopy revealing the Keplerian motion of a close-in companion around the AGB star pi1 Gruis. The companion, slightly more massive than the AGB star, is likely a main-sequence star. Unlike more evolved stars with companions at comparable distances, pi1 Gru's companion follows a circular orbit, suggesting an eccentricity-generating mechanism late- or post-AGB. Our analysis suggests that model-predicted circularization rates may be underestimated. Our results highlight the potential of multi-epoch (sub)millimeter interferometry in detecting the Keplerian motion of close companions to giant stars and open avenues for our understanding of tidal interaction physics and binary evolution.

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arXiv2025

Eppur si eclissa: Eccentric low-mass companions and time-in-dust selection explain long secondary periods

[abbreviated] Long Secondary Periods (LSPs) are observed in about one third of pulsating red giants yet remain unexplained. Four key observational constraints anchor the discussion: (i) a roughly 30 percent occurrence rate in semi-regular variable AGB stars (SRVs), with a much lower rate or absence in regularly pulsating Mira-type AGB stars (Miras), (ii) about 50 percent of LSP stars show a secondary mid-infrared minimum, (iii) Keplerian fits to radial-velocity curves favor argument of periastron greater than 180 degrees, and (iv) the radial-velocity to light-curve phase lag clusters around minus 90 degrees. We test whether a close-in, eccentric, low-mass companion that spends only part of its orbit within the giant's dust-formation zone can match all four empirical constraints. Guided by observed radial-velocity amplitudes and periods of about 500 to 1500 days, we adopt companion masses of 0.08 to 0.25 solar masses, orbital separations of 1.5 to 3 AU, eccentricities up to 0.6, and dust condensation radii of about 2.5 to 3 AU for SRVs (larger for Miras via scaling with luminosity). We compute the fraction of the orbit spent outside the condensation radius and apply line-of-sight criteria for detectability. We test the first three empirical constraints analytically, then model the phase offset using three-dimensional hydrodynamical simulations. Our scenario explains the observed excess of systems with argument of periastron greater than 180 degrees and yields LSP detectability of about 27 percent for SRVs and about 2.5 percent for Miras, with a conditional secondary mid-infrared eclipse fraction of about 44 percent. The hydrodynamical models place the optical-depth maximum downstream of the companion near apastron and then shift it forward by roughly 90 to 225 degrees later in the orbit, consistent with the observed radial-velocity to light-curve offsets.

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arXiv2025

Technetium-rich M Stars: Prime diagnostics of recent third dredge-up events on the Asymptotic Giant Branch

Context. Technetium (Tc)-rich M-type stars have been known for over 45 years. However, the origin of Tc in these stars, particularly its detection without the concomitant detection of other s-process elements, typically produced during the asymptotic giant branch (AGB) s-process nucleosynthesis, remains poorly understood. Technetium was first identified in the spectra of S-type stars (which exhibit prominent ZrO bands) in 1952. The simultaneous enrichment of both Zr and Tc is well understood within the framework of s-process nucleosynthesis, which occurs during the AGB phase. However, despite being known for 45 years, Tc-rich M stars remain an enigma, as M-type stars are typically not enriched in heavy elements. Aims. This study aims at analyzing high-resolution spectra of a large sample of M-type stars to examine their spectral characteristics, and to compare their spectral properties with those of Tc-rich S-type stars in an attempt to understand the origin of their difference. Methods. We define a robust classification scheme to assign M stars to the Tc-rich or Tc-poor class. We compute nucleosynthesis models to trace the evolution of Zr and Tc abundances across successive thermal pulses during the AGB phase. We further analyze spectral indices measuring the depth of the TiO and ZrO bands as well as the wavelength of the Tc blend on both synthetic and observed spectra. Results. The Tc lines in Tc-rich M stars are similar to those in S stars. However, Tc-rich M stars exhibit stronger TiO bands than S stars while displaying similarly strong ZrO bands. Spectral synthesis, together with location in the HR diagram and spatial properties suggest that Tc-rich M stars may have slightly lower metallicity and lower masses than Tc-rich S stars.

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arXiv2025

Impact of a binary companion in AGB outflows on CO spectral lines

In the late stage of their evolution, low- to intermediate-mass stars pass through the asymptotic giant branch (AGB) phase, characterised by strong mass loss through dust driven winds. High angular resolution observations reveal that these winds harbour strong deviations from spherical symmetry, such as spirals and arcs, believed to be caused by hidden (sub-)stellar companions. Much more often, one observes spectral lines, where the presence of a companion is less clear. We study the impact of a binary companion on low-J CO spectral lines of AGB star outflows. By varying the orbital separation and wind velocity, we aim to find line shapes characteristic of more complex binary-induced morphologies. We generated a grid of nine 3D models of a mass-losing AGB star using the smoothed particle hydrodynamics code Phantom, with three values for both the outflow velocity and orbital separation. Utilising the radiative transfer code Magritte, we created synthetic spectral lines for the low rotational transitions of CO at different inclinations and position angles. Our simulations show a variety of morphologies, always with a pronounced spiral structure arising in the orbital plane, but with varying shapes in the meridional plane, and different degrees of global flattening. We find that the CO line profiles can deviate strongly from the parabolic or flat-topped profiles expected from spherically symmetric outflows. A variety of line shapes emerge, with two peaks near the terminal velocity, and a central bump near the central velocity being the most pronounced. In specific cases, the spectral lines can appear parabolic, hiding the presence of a binary companion. We find the CO spectral lines can serve as a binary diagnostic. The influence of the companion on the line can however also go easily unnoticed, as the features can be concealed by the beam profile and the noise of the observations.

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arXiv2025

Synthesis of actinides and short-lived radionuclides during i-process nucleosynthesis in AGB stars

A complex interplay between mixing and nucleosynthesis is at work in asymptotic giant branch (AGB) stars. In addition to the slow neutron capture process (s-process), the intermediate neutron capture process (i-process) can develop during protons ingestion events (PIEs). In this paper, after quickly reviewing the different modes of production of heavy elements in AGB stars that were identified so far, we investigate the synthesis of actinides and other short-lived radioactive nuclei (SLRs, $^{60}$Fe, $^{107}$Pd, $^{126}$Sn, $^{129}$I, $^{135}$Cs and $^{182}$Hf) during i-process nucleosynthesis. AGB stellar models with initial masses $1 \leq M_{\rm ini}/M_{\odot} \leq 3$, metallicities $-3 \leq $ [Fe/H] $ \leq 0$ and different overshoot strengths were computed with the stellar evolution code STAREVOL. During PIEs, a nuclear network of 1160 isotopes is used and coupled to the transport equations. We found that AGB models with [Fe/H] $<-2$ can synthesize actinides with sometimes abundances greater than solar. The $^{60}$Fe yield scales with the initial metallicity while the $^{107}$Pd, $^{126}$Sn, $^{129}$I, $^{135}$Cs and $^{182}$Hf yields follow a similar pattern as a function of metallicity, with a production peak at [Fe/H] $\simeq -1.3$. At [Fe/H] $<-1$, the fraction of odd Ba isotopes $f_{\rm Ba,odd}$ is predicted to vary between 0.6 and 0.8 depending on the initial mass and metallicity. Nuclear uncertainties on our $1 M_{\odot}$, [Fe/H] $=-2.5$ model lead to $f_{\rm Ba,odd}$ ranging between 0.27 and 0.76, which is clearly above the s-process value. AGB stars experiencing PIEs appear to be potential producers of actinides and SLRs, particularly at low metallicity (except for $^{60}$Fe). Galactic chemical evolution modeling are required to assess their possible contribution to the galactic enrichment.

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arXiv2024

SPH modelling of AGB wind morphology in hierarchical triple systems \& comparison to observation of R Aql

Asymmetric 3D structures are observed in the outflows of evolved low- and intermediate-mass stars, and are believed to be shaped through the interaction of companions that are hidden within the dense wind. We investigate how triple systems can shape the outflow of AGB stars. We focus on coplanar systems in a hierarchical, stable orbit, consisting of an AGB star with one relatively close companion, and one at large orbital separation. We model a grid of hierarchical triple systems including a wind-launching AGB star, with the smoothed-particle-hydrodynamic Phantom code. We vary the outer companion mass, the AGB wind velocity and the orbital eccentricities to study the impact of these parameters on the wind morphology. Further, we investigate if the outflow of the AGB star R Aql could be shaped by a triple system, by post-processing one of our triple models with a radiative transfer routine, and comparing this to data of the ALMA ATOMIUM programme. The characteristic wind structures resulting from a hierarchical triple system are the following. A large two-edged spiral wake results behind the outer companion star. This structure lies on top of the spiral structure formed by the close binary, which is affected by the orbital motion around the system centre-of-mass. This dense inner spiral pattern interacts with, and strongly impacts, the spiral wake of the outer companion, resulting in a waved-pattern on the outer edge of this spiral wake. From the comparison of our models to the observations of R Aql, we conclude that this circumstellar environment might be shaped by a similar system as the ones modelled in this work, but an elaborate study of the observational data is needed to determine better the orbital parameters and characteristics of the central system.

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arXiv2024

Dust formation in common envelope binary interactions -- II: 3D simulations with self-consistent dust formation

We performed numerical simulations of the common envelope (CE) interaction between thermally-pulsing asymptotic giant branch (AGB) stars of 1.7~\Msun and 3.7~\Msun, respectively, and a 0.6~\Msun compact companion. We use tabulated equations of state to take into account recombination energy. For the first time, formation and growth of dust is calculated explicitly, using a carbon dust nucleation network with a C/O abundance ratio of 2.5 (by number). The first dust grains appear within $\sim$1--3~yrs after the onset of the CE, forming an optically thick shell at $\sim$10--20~au, growing in thickness and radius to values of $\sim$400--500~au over $\sim$40~yrs, with temperatures around 400~K. Most dust is formed in unbound material, having little effect on mass ejection or orbital evolution. By the end of the simulations, the total dust yield is $\sim8.4\times10^{-3}$~\Msun and $\sim2.2\times10^{-2}$~\Msun for the CE with a 1.7~\Msun and a 3.7~\Msun AGB star, respectively, corresponding to a nucleation efficiency close to 100\%, if no dust destruction mechanism is considered. Despite comparable dust yields to single AGB stars, \textit{in CE ejections the dust forms a thousand times faster, over tens of years as opposed to tens of thousands of years}. This rapid dust formation may account for the shift in the infrared of the spectral energy distribution of some optical transients known as luminous red novae. Simulated dusty CEs support the idea that extreme carbon stars and "water fountains" may be objects observed after a CE event.

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arXiv2024

Impact of HI cooling and study of accretion disks in AGB wind-companion smoothed particle hydrodynamic simulations

High-resolution observations reveal that the outflows of evolved low- and intermediate-mass stars harbour complex morphological structures that are linked to the presence of one or multiple companions. Hydrodynamical simulations provide a way to study the impact of a companion on the shaping of the AGB outflow. Using smoothed particle hydrodynamic (SPH) simulations of a mass losing AGB star with a binary companion, we study the impact of including HI atomic line cooling on the flow morphology and on the properties of accretion disks that form around the companion. We perform high-resolution 3D SPH simulations of the interaction of a solar-mass companion with the outflow of an AGB star using different wind velocities and eccentricities. We compare the models properties computed with and without the inclusion of HI cooling. The inclusion of HI cooling produces a large decrease in the temperature up to one order of magnitude in the region closely surrounding the companion star. As a consequence, morphological irregularities and relatively energetic outflows that were obtained without HI cooling no longer appear. In case of an eccentric orbit and low wind velocity, the morphologies are still highly asymmetric, but the same structures recur at every orbital period, making the morphology more regular. Flared accretion disks with a (sub)-Keplerian velocity profile form around the companion in all models, provided the accretion radius is small enough. The disks have radial sizes ranging from about 0.4 to 0.9 au. For the considered wind velocities, mass accretion onto the companion is up to 2 times higher than predicted by the BHL rate, and ranges between 0.04-0.21 times the AGB wind mass loss rate. The lower the wind velocity at the location of the companion, the larger and the more massive the disk, and the higher the mass accretion efficiency.

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arXiv2024

Dust formation during the interaction of binary stars by common envelope

We performed numerical simulations of the common envelope (CE) interaction between two intermediate-mass asymptotic giant branch (AGB) stars and their low-mass companions. For the first time, formation and growth of dust in the envelope is calculated explicitly. We find that the first dust grains appear as early as $\sim$1-3 yrs after the onset of the CE, and are smaller than grains formed later. As the simulations progress, a high-opacity dusty shell forms, resulting in the CE photosphere being up to an order of magnitude larger than it would be without the inclusion of dust. At the end of the simulations, the total dust yield is $0.0082~M_{\odot}$ ($0.022~M_{\odot}$) for a CE with a $1.7~M_{\odot}$ ($3.7~M_{\odot}$) AGB star. Dust formation does not substantially lead to more mass unbinding or substantially alter the orbital evolution.

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arXiv2024

Dust Formation in Common Envelope Binary Interaction -- I: 3D Simulations Using the Bowen Approximation

We carried out 3D smoothed particle hydrodynamics simulations of the common envelope binary interaction using the approximation of Bowen to calculate the dust opacity in order to investigate the resulting dust-driven accelerations. We have simulated two types of binary star: a 1.7 and a 3.7 $M_{\odot}$ thermally-pulsating, asymptotic giant branch stars with a 0.6 $M_{\odot}$ companion. We carried out simulations using both an ideal gas and a tabulated equations of state, with the latter considering the recombination energy of the envelope. We found that the dust-driven wind leads to a relatively small increase in the unbound gas, with the effect being smaller for the tabulated equation of state simulations and for the more massive primary. Dust acceleration does contribute to envelope expansion with only a slightly elongated morphology, if we believe the results from the tabulated equation of state as more reliable. The Bowen opacities in the outer envelopes of the two models, at late times, are large enough that the photosphere of the post-inspiral object is about ten times larger compared to the same without accounting for the dust opacities. As such, the prediction of the appearance of the transient would change substantially if dust is included.

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arXiv2023

Experimentally constrained $^{165,166}\text{Ho}(n,γ)$ rates and implications for the $s$ process

The $γ$-ray strength function and the nuclear level density of $^{167}$Ho have been extracted using the Oslo method from a $^{164}\text{Dy}(α,pγ)^{167}$Ho experiment carried out at the Oslo Cyclotron Laboratory. The level density displays a shape that is compatible with %can be approximated with the constant temperature model in the quasicontinuum, while the strength function shows structures indicating the presence of both a scissors and a pygmy dipole resonance. Using our present results as well as data from a previous $^{163}\text{Dy}(α,pγ)^{166}$Ho experiment, the $^{165}\text{Ho}(n,γ)$ and $^{166}\text{Ho}(n,γ)$ MACS uncertainties have been constrained. The possible influence of the low-lying, long-lived 6~keV isomer $^{166}$Ho in the $s$ process is investigated in the context of a 2~$M_\odot$, [Fe/H]=-0.5 AGB star. We show that the newly obtained $^{165}\text{Ho}(n,γ)$ MACS affects the final $^{165}$Ho abundance, while the $^{166}\text{Ho}(n,γ)$ MACS only impacts the enrichment of $^{166,167}$Er to a limited degree due to the relatively rapid $β$ decay of the thermalized $^{166}$Ho at typical $s$-process temperatures.

nucl-ex↗

arXiv2023

3D simulations of AGB stellar winds -- II. Ray-tracer implementation and impact of radiation on the outflow morphology

Stars with an initial mass below ~ 8 Msun evolve through the asymptotic giant branch (AGB) phase, during which they develop strong stellar winds. Recent observations have revealed significant morphological complexities in their outflows, most likely caused by a companion. We study the impact of the radiation force on such companion-perturbed AGB outflows. We present the implementation of a ray tracer for radiative transfer in smoothed particle hydrodynamics (SPH) and compared four different descriptions of radiative transfer: the free-wind, the geometrical, the Lucy, and the attenuation approximation. For both low and high mass-loss rates, the velocity profile of the outflow is modified when going from the free-wind to the geometrical approximation, also resulting in a different morphology. In the case of a low mass-loss rate, the effect of the Lucy and attenuation approximation is negligible due to the low densities but morphological differences appear in the high mass-loss rate regime. By comparing the radiative equilibrium temperature and radiation force to full 3D radiative transfer, we show that the Lucy approximation works best. Although, close to the companion, artificial heating occurs and it fails to simulate the shadow cast by the companion. The attenuation approximation produces a lower equilibrium temperature and weaker radiation force, but it produces the shadow cast by the companion. From the predictions of the 3D radiative transfer, we also conclude that a radially directed radiation force is a reasonable assumption. The radiation force thus plays a critical role in dust-driven AGB winds, impacting the velocity profile and morphological structures. For low mass-loss rates, the geometrical approximation suffices, while high mass-loss rates require a more rigorous method, where the Lucy approximation provides the most accurate results although not accounting for all effects.

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arXiv2022

X-Shooter Survey of Young Intermediate Mass Stars -- I. Stellar Characterization and Disc Evolution

Intermediate mass stars (IMSs) represent the link between low-mass and high-mass stars and cover a key mass range for giant planet formation. In this paper, we present a spectroscopic survey of 241 young IMS candidates with IR-excess, the most complete unbiased sample to date within 300 pc. We combined VLT/X-Shooter spectra with BVR photometric observations and Gaia DR3 distances to estimate fundamental stellar parameters such as Teff, mass, radius, age, and luminosity. We further selected those stars within the intermediate mass range 1.5 <= Mstar/Msun <= 3.5 and discarded old contaminants. We used 2MASS and WISE photometry to study the IR-excesses of the sample, finding 92 previously unidentified stars with IR-excess. We classified this sample into 'protoplanetary', 'hybrid candidates' and 'debris' discs based on their observed fractional excess at 12microns, finding a new population of 17 hybrid disc candidates. We studied inner disc dispersal timescales for λ < 10μm and found very different trends for IMSs and low mass stars (LMSs). IMSs show excesses dropping fast during the first 6 Myrs independently of the wavelength, while LMSs show consistently lower fractions of excess at the shortest wavelengths and increasingly higher fractions for longer wavelengths, with slower dispersal rates. In conclusion, this study demonstrates empirically that IMSs dissipate their inner discs very differently than LMSs, providing a possible explanation for the lack of short period planets around IMSs.

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