arXiv subjects

Laurens B. F. M. Waters

Publications and source records attributed to Laurens B. F. M. Waters.

4 recordsLinked to original sources

arXiv2026

MINDS: Intertwined evolution of dust and gas in large planet-forming disks. A diversity driven by halted pebble drift?

(Abridged) We aim to investigate the inner regions of large and massive disks orbiting T Tauri stars, thought to be progenitors of systems with wide-orbit planets and possible cases of halted pebble drift. We analyze the MIRI spectra of three disks from the MINDS program: V1094 Sco, DL Tau, and IM Lup. The spectra reveal a striking diversity. V1094 Sco and DL Tau exhibit the highest C$_2$H$_2$/H$_2$O flux ratio in the MINDS sample of T Tauri disks. In V1094 Sco, even cold C$_4$H$_2$ is seen. In contrast, the IM Lup spectrum is dominated by O-bearing species. No one-to-one correspondence is found between the gas in the outer disk, as traced by the C$_2$H/C$^{18}$O flux ratio, and that of the inner disk as traced by the C$_2$H$_2$/H$_2$O flux ratio. To explain these results, we propose a scenario based on a toy model of halted pebble drift. We show that a volatile C/O ratio close to unity and low C and O abundances in inner disks arise only if: (1) ~95$\%$ of the icy grains are blocked in the outer disk, (2) the outer disk is chemically evolved, and (3) the gas in the outer disk has had time to reach the inner disk. DL Tau and perhaps V1094 Sco would be the rare examples for which all these conditions are met. Therefore, a high C$_2$H$_2$/H$_2$O flux ratio in pebble-rich disks would have a different origin than proposed for very-low mass stars, for which fast drift of O-rich pebbles would eventually leave a C-rich inner disk. We also show for the first time that the disks with high C$_2$H$_2$/H$_2$O flux ratio exhibit a prominent silica dust component, a result found in four disks published so far (V1094 Sco, DL Tau, CY Tau, DoAr 33). We propose that the reformation of dust at the sublimation front of silicates in a gas with super-solar (but below unity) C/O ratio leads to a silica stoichiometry (SiO$_2$). In turn, silica is a promising diagnostic of the C/O ratio in the inner disks.

astro-ph.EP↗

arXiv2026

Three outstanding physical questions for K2-18 b and other temperate sub-Neptunes

Recent transmission spectra of the temperate sub-Neptune K2-18 b obtained with JWST have attracted significant attention. Debates have quickly arisen over the interpretation of the spectral data, particularly the recent MIRI observation where dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) are claimed. Here we revisit K2-18 b as a case study to examine several key questions that are also broadly relevant to the temperate sub-Neptune population: i) Can the low water abundance be reconciled with water clouds driven by orbital eccentricity? ii) Are the observed and non-observed atmospheric compositions mutually consistent? iii) Is it kinetically possible to produce DMS under sub-Neptune conditions? To address these questions, we couple climate and photochemical models to obtain self-consistent climate-photochemistry states for K2-18 b with a moderate orbital eccentricity of 0.2, as suggested by radial-velocity measurements. In addition, we present new laboratory measurements of DMS and DMDS infrared opacities by HFML-FELIX and compile updated C$_2$H$_6$ (ethane) opacities that include weak overtone bands. Our results support the interpretation of a sub-Neptune scenario without invoking DMS, and we do not find strong evidence for a water-rich interior.

astro-ph.EP↗

arXiv2021

Thermal imaging of dust hiding the black hole in the Active Galaxy NGC 1068

In the widely accepted 'Unified Model' solution of the classification puzzle of Active Galactic Nuclei, the orientation of a dusty accretion torus around the central black hole dominates their appearance. In 'type-1' systems, the bright nucleus is visible at the centre of a face-on torus. In 'type-2' systems the thick, nearly edge-on torus hides the central engine. Later studies suggested evolutionary effects and added dusty clumps and polar winds but left the basic picture intact. However, recent high-resolution images of the archetypal type-2 galaxy NGC 1068 suggested a more radical revision. They displayed a ring-like emission feature which the authors advocated to be hot dust surrounding the black hole at the radius where the radiation from the central engine evaporates the dust. That ring is too thin and too far tilted from edge-on to hide the central engine, and ad hoc foreground extinction is needed to explain the type-2 classification. These images quickly generated reinterpretations of the type 1-2 dichotomy. Here we present new multi-band mid-infrared images of NGC1068 that detail the dust temperature distribution and reaffirm the original model. Combined with radio data, our maps locate the central engine below the previously reported ring and obscured by a thick, nearly edge-on disk, as predicted by the Unified Model. We also identify emission from polar flows and absorbing dust that is mineralogically distinct from that towards the Milky Way centre.

astro-ph.GA↗

arXiv2011

The Intermediate-mass Young Stellar Object 08576nr292: Discovery of a disk-jet system

We present observations of the embedded massive young stellar object (YSO) candidate 08576nr292, obtained with X-shooter and SINFONI on the ESO Very Large Telescope (VLT). The flux-calibrated, medium-resolution X-shooter spectrum (300 - 2500 nm) includes over 300 emission lines, but no (photospheric) absorption lines and is consistent with a reddened disk spectrum. Among the emission lines are three hydrogen series and helium lines, both permitted and forbidden metal lines, and CO first-overtone emission. A representative sample of lines with different morphologies is presented. The H alpha and Ca II triplet lines are very strong, with profiles indicative of outflow and - possibly - infall, usually observed in accreting stars. These lines include a blue-shifted absorption component at ~ -125 km/s. The He I and metal-line profiles are double-peaked, with a likely origin in a circumstellar disk. The forbidden lines, associated with outflow, have a single blue-shifted emission component centered at -125 km/s, coinciding with the absorption components in H alpha and Ca II. SINFONI H- and K-band integral-field spectroscopy of the cluster environment demonstrates that the [Fe II] emission is produced by a jet originating at the location of 08576nr292. Because the spectral type of the central object cannot be determined, its mass remains uncertain. We argue that 08576nr292 is an intermediate-mass YSO with a high accretion rate Mdot_acc ~ 10^-5 - 10^-6 Msun/yr. These observations demonstrate the potential of X-shooter and SINFONI to study in great detail an accretion disk-jet system, rarely seen around the more massive YSOs.

astro-ph.SR↗