arXiv subjects

M. Kama

Publications and source records attributed to M. Kama.

At least 19 recordsLinked to original sources

arXiv2026

Ariel stellar characterisation IV. Fundamental parameters of 18 hot stars in the Ariel mission candidate sample

The characterisation of exoplanetary systems depends on the accurate determination of host star parameters. The Ariel mission will probe the atmospheres of a statistically significant sample of exoplanets, and so requires a precise characterisation of the stellar properties well before its launch in 2029. The homogeneous determination of stellar parameters for Ariel will enable both the optimisation of the final target list and set roots for a reliable interpretation of the formation and evolution of planetary systems. Such a homogeneous characterisation has thus far only been carried out for the cool (\teff\ $\lesssim 7000\,$K) host stars among the Ariel target candidates. We present a uniform determination of fundamental stellar parameters for 18 hot stars in the Tier 1 candidate list of the Ariel mission candidate sample. We adopted an iterative spectro-trigonometric approach optimised for high-temperature stars. High-resolution spectra were analysed using the \textsc{zeeman} code with $\chi^2$ minimisation, combining model fits to metal and Balmer lines. Surface gravity was refined using photometry-based radii and masses from stellar evolutionary tracks. We derived effective temperatures, surface gravities, projected rotational velocities, microturbulent velocities, overall metallicities, iron abundances, stellar masses, and radii for our sample of $18$ hot stars. Our results were validated against a set of benchmark stars previously presented in the literature. The derived parameters provide an internally consistent basis for studying the link between stellar properties and planetary characteristics in intermediate-mass stars. Building on our previous work on FGK host stars, we show that correlations between stellar mass, metallicity, and planetary radii also extend to early-type stars, and stellar properties influence the architecture of multi-planet systems.

astro-ph.SR↗

arXiv2025

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake. How do Planetary Systems Form?

The detection and characterization of protoplanets in protoplanetary disks around young stars is emerging as a transformative field that will redefine our understanding of how planetary systems form. While current facilities have revealed the diversity of mature exoplanets and the complex structures of disks, we still lack the crucial observational link between them: a statistically meaningful census of planets caught in the act of formation. This white paper argues that such a breakthrough requires access to the nearest and most informative star-forming regions, roughly half of which are poorly accessible or entirely unreachable from Cerro Armazones. Although the ELT alone will strongly impact our knowledge of planet formation, its location prevents Europe from fully exploiting the necessary parameter space. A 30-40 m telescope in the northern hemisphere is therefore essential for obtaining diffraction-limited imaging of protoplanets and disks across the entire sky, enabling robust demographics, exploiting synergies with ngVLA, Gaia, and other facilities covering the north, and ensuring that Europe remains at the forefront of the planet-formation revolution in the coming decades.

astro-ph.IM↗

arXiv2025

Investigating Circumstellar Atomic Radiation-driven Dynamics

The interactions between stars and their orbiting planets, driven by forces such as stellar radiation and gravity, play an essential role in shaping exoplanetary atmospheres and gas-rich debris discs. One way to look into the composition of these environments is to observe how they can contaminate the stellar photospheres. For that, we examine how stellar radiation pressure and gravity influence atomic species and analyse their effects across various stellar effective temperatures. Using the radiative-to-gravitational force ratio, we determined the atomic movement direction and assessed the velocity boost imparted to neutral atoms escaping from exoplanet atmospheres or debris discs. Incorporating the solar far ultraviolet/extreme ultraviolet spectrum to address flux discrepancies in the {\sc{atlas9}} model, we find that radiation affects atoms differently according to their ionisation state, with highly ionised species less affected by stellar radiation. Our results conclude that the stars most suitable for observing stellar contamination are those between 6,500 and 8,000 K, with neutral noble gases and ionised iron-peak elements as the most likely contaminants.

astro-ph.EP↗

arXiv2024

Vertical and radial distribution of atomic carbon in HD 163296

In protoplanetary disks, atomic carbon is expected to originate from the PDR at the disk surface where CO is dissociated by UV photons coming from the stellar, or external interstellar, radiation field. Even though atomic carbon has been detected in several protoplanetary disks, there is a lack of spatially resolved observations of it. For HD 163296 protoplanetary disk, we aim to obtain both radial and vertical structure of [CI]$={^3}{P_1} - {^3}{P_0}$ line emission and perform the first direct comparison of this tracer with optically thick line emission $^{12}$CO $J=2-1$. We used archival ALMA data for [CI]$={^3}{P_1} - {^3}{P_0}$ and previously published ${^{12}}$ CO $J=2-1$ data in HD 163296. Through the software of disksurf we extracted the vertical structure, meanwhile radial profiles were obtained directly from imaging. Brand new DALI modelling was employed to perform direct comparison to the data. We found that these tracers are collocated radially but not vertically, where $^{12}$CO $J=2-1$ emission is, on average, located at higher altitudes, as it is also the case for other tracers in the same disk. Due to this difference in vertical height of the emission, the optically thick $^{12}$CO $J=2-1$ emission line appears to trace the highest altitudes, despite the expected formation mechanism of [CI] in the disk. The latter phenomena may be due to efficient mixing of the upper layers of the disk, or UV photons penetrating deeper than we expected.

astro-ph.EP↗

arXiv2022

Relation between metallicities and spectral energy distributions of Herbig Ae/Be stars. A potential link with planet formation

(Abridged) The stellar metallicity, [M/H], may have important implications for planet formation. In particular, Kama et al. proposed that the deficit of refractory elements in the surfaces of some Herbig Ae/Be stars (HAeBes) may be linked to the presence of disk cavities likely caused by Jovian planets that trap the metal-rich content. This work aims to provide a robust test on the previous proposal by analyzing the largest sample of HAeBes with homogeneously derived [M/H] values, stellar, and circumstellar properties. [M/H] values of 67 HAeBes were derived based on observed spectra and Kurucz synthetic models. Statistical analyses were carried out aiming to test the potential relation between [M/H] and the group I sources from the spectral energy distribution (SED) classification by Meeus et al., associated to the presence of cavities potentially carved by giant planets. Our study robustly confirms that group I sources tend to have a lower [M/H] than that of group II HAeBes. A similar analysis involving SED-based transitional disks does not reveal such a relation, indicating that not all processes capable of creating dust holes have an effect on the stellar abundances. We also show that the observed [M/H] differences are not driven by environmental effects. Finally, group I sources tend to have stronger (sub-) mm continuum emission presumably related to the presence of giant planets. Indeed, literature results indicate that disk substructures probably associated to their presence are up to ten times more frequent in group I HAeBes. We provide indirect evidences suggesting that giant planets are more frequent around group I/low [M/H] stars than around the rest of the HAeBes. However, the direct test requires multiple detections of forming planets in their disks, so far limited to the candidate around the metal depleted ([M/H] = -0.35 +- 0.25) group I HAeBe star AB Aur.

astro-ph.SR↗

arXiv2022

Tracing pebble drift and trapping using radial carbon depletion profiles in protoplanetary disks

The composition of planets may be largely determined by the chemical processing and accretion of icy pebbles in protoplanetary disks. Recent observations of protoplanetary disks hint at wide-spread depletion of gaseous carbon. The missing volatile carbon is likely frozen in CO and/or CO$_2$ ice on grains and locked into the disk through pebble trapping in pressure bumps or planetesimals. We present the results of the first successful ACA (Atacama Compact Array) [C I] $J$ = 1-0 mini-survey of seven protoplanetary disks. Using tailored azimuthally symmetric DALI (Dust And LInes) thermo-chemical disk models, supported by the [C I] $J$ = 1-0 and resolved CO isotopologue data, we determine the system-averaged elemental volatile carbon abundance in the outer disk of three sources. Six out of seven sources are detected in [C I] $J$ = 1-0 with ACA, four of which show a distinct disk component. Based on the modeling we find severe cold gaseous carbon depletion in the outer disk of DL Tau and moderate depletion in the outer disks of DR Tau and DO Tau. Combining the outer and inner disk carbon abundances, we demonstrate definitive evidence for radial drift in the disk of DL Tau, where the existence of multiple dust rings points to either short lived or leaky dust traps. We find dust locking in the compact and smooth disks of DO Tau and DR Tau, hinting at unresolved dust substructure. Comparing our results with stars of different ages and luminosities, we identify an observational evolutionary trend in gaseous carbon depletion that is consistent with dynamical models of CO depletion processes. Transport efficiency of solids in protoplanetary disks can significantly differ from what we expect based on the current resolved substructure in the continuum observations. This has important implications for our understanding of the impact of radial drift and pebble accretion on planetary compositions.

astro-ph.EP↗

arXiv2020

Rapid CO gas dispersal from NO Lup's class III circumstellar disc

We observed the K7 class III star NO Lup in an ALMA survey of the 1-3 Myr Lupus association and detected circumstellar dust and CO gas. Here we show that the J = 3-2 CO emission is both spectrally and spatially resolved, with a broad velocity width ${\sim}19$kms$^{-1}$ for its resolved size ${\sim}1''$ (${\sim}130$ au). We model the gas emission as a Keplerian disc, finding consistency, but only with a central mass of ${\sim}11M_{\odot}$, which is implausible given its spectral type and X-Shooter spectrum. A good fit to the data can also be found by modelling the CO emission as outflowing gas with a radial velocity ${\sim}22$kms$^{-1}$. We interpret NO Lup's CO emission as the first imaged class III circumstellar disc with outflowing gas. We conclude that the CO is continually replenished, but cannot say if this is from the break-up of icy planetesimals or from the last remnants of the protoplanetary disc. We suggest further work to explore the origin of this CO, and its higher than expected velocity in comparison to photoevaporative models.

astro-ph.EP↗

arXiv2020

ALMA Survey of Lupus Class III Stars: Early Planetesimal Belt Formation and Rapid Disk Dispersal

Class III stars are those in star forming regions without large non-photospheric infrared emission, suggesting recent dispersal of their protoplanetary disks. We observed 30 class III stars in the 1-3 Myr Lupus region with ALMA at ${\sim}856μ$m, resulting in 4 detections that we attribute to circumstellar dust. Inferred dust masses are $0.036{-}0.093M_\oplus$, ${\sim}1$ order of magnitude lower than any previous measurements; one disk is resolved with radius ${\sim}80$ au. Two class II sources in the field of view were also detected, and 11 other sources, consistent with sub-mm galaxy number counts. Stacking non-detections yields a marginal detection with mean dust mass ${\sim}0.0048M_\oplus$. We searched for gas emission from the CO J=3-2 line, and present its detection to NO Lup inferring a gas mass ($4.9 {\pm} 1.1$) ${\times}10^{-5} M_\oplus$ and gas-to-dust ratio $1.0{\pm}0.4$. Combining our survey with class II sources shows a gap in the disk mass distribution from $0.09{-}2M_\oplus$ for ${>}0.7M_\odot$ Lupus stars, evidence of rapid dispersal of mm-sized dust from protoplanetary disks. The class III disk mass distribution is consistent with a population model of planetesimal belts that go on to replenish the debris disks seen around main sequence stars. This suggests that planetesimal belt formation does not require long-lived protoplanetary disks, i.e., planetesimals form within ${\sim}$2 Myr. While all 4 class III disks are consistent with collisional replenishment, for two the gas and/or mid-IR emission could indicate primordial circumstellar material in the final stages of protoplanetary disk dispersal. Two class III stars without sub-mm detections exhibit hot emission that could arise from ongoing planet formation processes inside ${\sim}1$ au.

astro-ph.EP↗

arXiv2020

Measuring the atomic composition of planetary building blocks

Volatile molecules are critical to terrestrial planetary habitability, yet difficult to observe directly where planets form at the midplanes of protoplanetary disks. It is unclear whether the inner 1 AU of disks are volatile-poor or if this region is resupplied with ice-rich dust from colder disk regions. Dust traps at radial pressure maxima bounding disk gaps can cut off the inner disk from such volatile reservoirs. However, the trap retention efficiency and atomic composition of trapped dust have not been measured. We present a new technique to measure the absolute atomic abundances in gas accreting onto T Tauri stars and infer the bulk atomic composition and distribution of midplane solids retained in the disk around the young star TW Hya. We identify line emission from gas-phase material inside the dust sublimation rim of TW Hya. Gaussian decomposition of the strongest H Paschen lines isolates the inner disk hydrogen emission. We measure several key elemental abundances, relative to hydrogen, using a chemical photoionization model and infer dust retention in the disk. With a 1D transport model, we determine approximate radial locations and retention efficiencies of dust traps for different elements. Volatile and refractory elements are depleted from TW Hya's hot gas by factors of ~10^2 and up to 10^5, respectively. Dust traps beyond the CO and N2 snowline cumulatively sequester 96% of the total dust, while the trap at 2 AU retains 3% of the initial dust mass. The high depletions of Si, Mg, and Ca are explained by a third trap at 0.3 AU. TW Hya has a significant volatile reservoir rich in C- and N-ices in its outer ring structure. However, the lack of C resupply may leave the terrestrial planet-forming region dry and carbon-poor. Any planets that form within the silicate dust trap at 0.3 AU may resemble Earth in terms of the degree of their volatile depletion.

astro-ph.EP↗

arXiv2020

Searching for a cometary belt around Trappist-1 with ALMA

Low mass stars might offer today the best opportunities to detect and characterise planetary systems, especially those harbouring close-in low mass temperate planets. Among those stars, TRAPPIST-1 is exceptional since it has seven Earth-sized planets, of which three could sustain liquid water on their surfaces. Here we present new and deep ALMA observations of TRAPPIST-1 to look for an exo-Kuiper belt which can provide clues about the formation and architecture of this system. Our observations at 0.88 mm did not detect dust emission, but can place an upper limit of 23$μ$Jy if the belt is smaller than 4 au, and 0.15 mJy if resolved and 100 au in radius. These limits correspond to low dust masses of $\sim10^{-5}-10^{-2}$ $M_\oplus$, which are expected after 8 Gyr of collisional evolution unless the system was born with a $>20$ $M_\oplus$ belt of 100 km-sized planetesimals beyond 40 au or suffered a dynamical instability. This $20$ $M_\oplus$ mass upper limit is comparable to the combined mass in TRAPPIST-1 planets, thus it is possible that most of the available solid mass in this system was used to form the known planets. A similar analysis of the ALMA data on Proxima Cen leads us to conclude that a belt born with a mass $\gtrsim1$ $M_\oplus$ in 100 km-sized planetesimals could explain its putative outer belt at 30 au. We recommend that future characterisations of debris discs around low mass stars should focus on nearby and young systems if possible.

astro-ph.EP↗

arXiv2019

Mass constraints for 15 protoplanetary disks from HD 1-0

Hydrogen deuteride (HD) rotational line emission can provide reliable protoplanetary disk gas mass measurements, but it is difficult to observe and detections have been limited to three T-Tauri disks. No new data have been available since the \emph{Herschel} Space Observatory mission ended in 2013. We set out to obtain new disk gas mass constraints by analysing upper limits on HD 1-0 emission in \emph{Herschel}/PACS archival data from the DIGIT key programme. With a focus on the Herbig Ae/Be disks, whose stars are more luminous than T Tauris, we determine upper limits for HD in data previosly analysed for its line detections. Their significance is studied with a grid of models run with the DALI physical-chemical code, customised to include deuterium chemistry. Nearly all the disks are constrained to $M_{\rm gas}\leq0.1\,$M$_{\odot}$, ruling out global gravitational instability. A strong constraint is obtained for the HD 163296 disk mass, $M_{\rm gas} \leq 0.067\,$M$_{\odot}$, implying $Δ_{\rm g/d}\leq100$. This HD-based mass limit is towards the low end of CO-based mass estimates for the disk, highlighting the large uncertainty in using only CO and suggesting that gas-phase CO depletion in HD 163296 is at most a factor of a few. The $M_{\rm gas}$ limits for HD 163296 and HD 100546, both bright disks with massive candidate protoplanetary systems, suggest disk-to-planet mass conversion efficiencies of $M_{\rm p}/(M_{\rm gas} + M_{\rm p})\approx10$ to $40\,$% for present-day values. Near-future observations with SOFIA/HIRMES will be able to detect HD in the brightest Herbig~Ae/Be disks within $150\,$pc with $\approx10\,$h integration time.

astro-ph.EP↗

arXiv2019

ALMA and NACO observations towards the young exoring transit system J1407 (V1400 Cen)

Our aim was to directly detect the thermal emission of the putative exoring system responsible for the complex deep transits observed in the light curve for the young Sco-Cen star 1SWASP J140747.93-394542.6 (V1400 Cen, hereafter J1407), confirming it as the occulter seen in May 2007, and to determine its orbital parameters with respect to the star. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe the field centred on J1407 in the 340 GHz (Band 7) continuum in order to determine the flux and astrometric location of the ring system relative to the star. We used the VLT/NACO camera to observe the J1407 system in March 2019 and to search for the central planetary mass object at thermal infrared wavelengths. We detect no point source at the expected location of J1407, and derive an upper limit $3σ$ level of $57.6~μ\rm{Jy}$. There is a point source detected at an angular separation consistent with the expected location for a free-floating ring system that occulted J1407 in May 2007, with a flux of $89~μ\rm{Jy}$ consistent with optically thin dust surrounding a massive substellar companion. At 3.8 microns with the NACO camera, we detect the star J1407 but no other additional point sources within 1.3 arcseconds of the star, with a lower bound on the sensitivity of $6M_{Jup}$ at the location of the ALMA source, and down to $4M_{Jup}$ in the sky background limit. The ALMA upper limit at the location of J1407 implies that a hypothesised bound ring system is composed of dust smaller than $1\rm{~mm}$ in size, implying a young ring structure. The detected ALMA source has multiple interpretations, including: (i) it is an unbound substellar object surrounded by warm dust in Sco-Cen with an upper mass limit of $6M_{Jup}$, or (ii) it is a background galaxy.

astro-ph.EP↗

arXiv2018

SOLIS IV. Hydrocarbons in the OMC-2 FIR 4 region, a probe of energetic particle irradiation of the region

We report new interferometric images of cyclopropenylidene, c-C$_3$H$_2$, towards the young protocluster OMC-2 FIR\,4. The observations were performed at 82 and 85 GHz with the NOrthern Extended Millimeter Array (NOEMA) as part of the project Seeds Of Life In Space (SOLIS). In addition, IRAM-30m data observations were used to investigate the physical structure of OMC-2 FIR\,4. We find that the c-C$_3$H$_2$ gas emits from the same region where previous SOLIS observations showed bright HC$_5$N emission. From a non-LTE analysis of the IRAM-30m data, the c-C$_3$H$_2$ gas has an average temperature of $\sim$40K, a H$_2$ density of $\sim$3$\times$10$^{5}$~cm$^{-3}$, and a c-C$_3$H$_2$ abundance relative to H$_2$ of ($7\pm1$)$\times$10$^{-12}$. In addition, the NOEMA observations provide no sign of significant c-C$_3$H$_2$ excitation temperature gradients across the region (about 3-4 beams), with T$_{ex}$ in the range 8$\pm$3 up to 16$\pm$7K. We thus infer that our observations are inconsistent with a physical interaction of the OMC-2 FIR\,4 envelope with the outflow arising from OMC-2 FIR\,3, as claimed by previous studies. The comparison of the measured c-C$_3$H$_2$ abundance with the predictions from an astrochemical PDR model indicates that OMC-2 FIR\,4 is irradiated by a FUV field $\sim$1000 times larger than the interstellar one, and by a flux of ionising particles $\sim$4000 times larger than the canonical value of $1\times10^{-17}$~s$^{-1}$ from the Galaxy cosmic rays, which is consistent with our previous HC$_5$N observations. This provides an important and independent confirmation of other studies that one or more sources inside the OMC-2 FIR\,4 region emit energetic ($\geq10$~MeV) particles.

astro-ph.GA↗

arXiv2018

Interstellar bromine abundance is consistent with cometary ices from Rosetta

Cometary ices are formed during star and planet formation, and their molecular and elemental makeup can be related to the early solar system via the study of inter- and protostellar material. The first cometary abundance of the halogen element bromine (Br) was recently made available by the Rosetta mission. Its abundance in protostellar gas is thus far unconstrained, however. We set out to place the first observational constraints on the interstellar gas-phase abundance of bromine (Br). We further aim to compare the protostellar Br abundance with that measured by Rosetta in the ices of comet 67P/Churyumov-Gerasimenko. Archival Herschel data of Orion KL, Sgr B2(N), and NGC 6334I are examined for the presence of HBr and HBr$^{+}$ emission or absorption lines. A chemical network for modelling HBr in protostellar molecular gas is compiled to aid in the interpretation. HBr and HBr$^{+}$ were not detected towards any of our targets. However, in the Orion KL Hot Core, our upper limit on HBr/H$_{2}$O is a factor of ten below the ratio measured in comet 67P. This result is consistent with the chemical network prediction that HBr is not a dominant gas-phase Br carrier. Cometary HBr is likely predominantly formed in icy grain mantles which lock up nearly all elemental Br.

astro-ph.GA↗

arXiv2017

Observing the linked depletion of dust and CO gas at 0.1-10 au in disks of intermediate-mass stars

We report on the discovery of correlations between dust and CO gas tracers of the 0.1-10 au region in planet-forming disks around young intermediate-mass stars. The abundance of refractory elements on stellar photospheres decreases as the location of hot CO gas emission recedes to larger disk radii, and as the near-infrared excess emission from hot dust in the inner disk decreases. The linked behavior between these observables demonstrates that the recession of infrared CO emission to larger disk radii traces an inner disk region where dust is being depleted. We also find that Herbig disk cavities have either low (~ 5-10 %) or high (~ 20-35 %) near-infrared excess, a dichotomy that has not been captured by the classic definition of "pre-transitional" disks.

astro-ph.EP↗

arXiv2017

The onset of energetic particle irradiation in Class 0 protostars

The early stages of low-mass star formation are likely to be subject to intense ionization by protostellar energetic MeV particles. As a result, the surrounding gas is enriched in molecular ions, such as HCO$^{+}$ and N$_{2}$H$^{+}$. Nonetheless, this phenomenon remains poorly understood for Class 0 objects. Recently, based on Herschel observations taken as part of the key program Chemical HErschel Surveys of Star forming regions (CHESS), a very low HCO$^{+}$/N$_{2}$H$^{+}$ abundance ratio of about 3-4, has been reported toward the protocluster OMC-2 FIR4. This finding suggests a cosmic-ray ionization rate in excess of 10$^{-14}$ s$^{-1}$, much higher than the canonical value of $ζ$ = 3$\times$10$^{-17}$ s$^{-1}$ (value expected in quiescent dense clouds). To assess the specificity of OMC-2 FIR4, we have extended this study to a sample of sources in low- and intermediate mass. More specifically, we seek to measure the HCO$^{+}$/N$_2$H$^{+}$ abundance ratio from high energy lines (J $\ge$ 6) toward this source sample in order to infer the flux of energetic particles in the warm and dense gas surrounding the protostars. We use observations performed with the Heterodyne Instrument for the FarInfrared spectrometer on board the Herschel Space Observatory toward a sample of 9 protostars. We report HCO$^{+}$/N$_2$H$^{+}$ abundance ratios in the range of 5 up to 73 toward our source sample. The large error bars do not allow us to conclude whether OMC-2~FIR4 is a peculiar source. Nonetheless, an important result is that the measured HCO$^{+}$/N$_2$H$^{+}$ ratio does not vary with the source luminosity. At the present time, OMC-2 FIR4 remains the only source where a high flux of energetic particles is clearly evident. More sensitive and higher angular resolution observations are required to further investigate this process.

astro-ph.GA↗

arXiv2017

Neutron Star Planets: Atmospheric processes and habitability

Of the roughly 3000 neutron stars known, only a handful have sub-stellar companions. The most famous of these are the low-mass planets around the millisecond pulsar B1257+12. New evidence indicates that observational biases could still hide a wide variety of planetary systems around most neutron stars. We consider the environment and physical processes relevant to neutron star planets, in particular the effect of X-ray irradiation and the relativistic pulsar wind on the planetary atmosphere. We discuss the survival time of planet atmospheres and the planetary surface conditions around different classes of neutron stars, and define a neutron star habitable zone. Depending on as-yet poorly constrained aspects of the pulsar wind, both Super-Earths around B1257+12 could lie within its habitable zone.

astro-ph.EP↗

arXiv2016

A "Rosetta Stone" for protoplanetary disks: The synergy of multi-wavelength observations

The recent progress in instrumentation and telescope development has brought us different ways to observe protoplanetary disks, including interferometers, space missions, adaptive optics, polarimetry, and time- and spectrally-resolved data. While the new facilities have changed the way we can tackle the existing open problems in disk structure and evolution, there is a substantial lack of interconnection between different observing techniques and their user communities. Here, we explore the complementarity of some of the state-of-the-art observing techniques, and how they can be brought together in a collective effort to understand how disks evolve and disperse at the time of planet formation. This paper was born at the "Protoplanetary Discussions" meeting in Edinburgh, 2016. Its goal is to clarify where multi-wavelength observations of disks converge in unveiling disk structure and evolution, and where they diverge and challenge our current understanding. We discuss caveats that should be considered when linking results from different observations, or when drawing conclusions based on limited datasets (in terms of wavelength or sample). We focus on disk properties that are currently being revolutionized by multi-wavelength observations. Specifically: the inner disk radius, holes and gaps and their link to large-scale disk structures, the disk mass, and the accretion rate. We discuss how the links between them, as well as the apparent contradictions, can help us to disentangle the disk physics and to learn about disk evolution.

astro-ph.SR↗