arXiv subjects

Andrew Sellek

Publications and source records attributed to Andrew Sellek.

6 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↗

arXiv2025

The past, present and future of observations of externally irradiated disks

Recent years have seen a surge of interest in the community studying the effect of ultraviolet radiation environment, predominantly set by OB stars, on protoplanetary disc evolution and planet formation. This is important because a significant fraction of planetary systems, potentially including our own, formed in close proximity to OB stars. This is a rapidly developing field, with a broad range of observations across many regions recently obtained or recently scheduled. In this paper, stimulated by a series of workshops on the topic, we take stock of the current and upcoming observations. We discuss how the community can build on this recent success with future observations to make progress in answering the big questions of the field, with the broad goal of disentangling how external photoevaporation contributes to shaping the observed (exo)planet population. Both existing and future instruments offer numerous opportunities to make progress towards this goal.

astro-ph.SR↗

arXiv2025

MINDS. JWST-MIRI Observations of a Spatially Resolved Atomic Jet and Polychromatic Molecular Wind Toward SY Cha

The removal of angular momentum from protostellar systems drives accretion onto the central star and may drive the dispersal of the protoplanetary disk. Winds and jets can contribute to removing angular momentum from the disk, though the dominant process remain unclear. To date, observational studies of resolved disk winds have mostly targeted highly inclined disks. We report the detection of extended H2 and [Ne II] emission toward the young stellar object SY Cha with the JWST Mid-InfraRed Instrument Medium Resolution Spectrometer (MIRI-MRS). This is one of the first polychromatic detections of extended H2 toward a moderately inclined, i=51.1 degrees, Class II source. We measure the semi-opening angle of the H2 emission as well as build a rotation diagram to determine the H2 excitation temperature and abundance. We find a wide semi-opening angle, high temperature, and low column density for the H2 emission, all of which are characteristic of a disk wind. We derive a molecular wind mass loss rate of 3+-2e-9 Msun/yr, which is high compared to the previously derived stellar accretion rate of 6.6e-10 Msun/yr. This suggests either that the stellar accretion and the disk wind are driven by different mechanisms or that accretion onto the star is highly variable. These observations demonstrate MIRI-MRS's utility in expanding studies of resolved disk winds beyond edge-on sources.

astro-ph.SR↗

arXiv2025

MINDS. The influence of outer dust disc structure on the volatile delivery to the inner disc

ALMA has revealed that the millimetre dust structures of protoplanetary discs are extremely diverse. It has been proposed that the strength of H$_2$O emission in the inner disc particularly depends on the influx of icy pebbles from the outer disc, a process that would correlate with the outer dust disc radius, and that could be prevented by pressure bumps. This work aims to assess the influence of pressure bumps on the inner disc's molecular reservoirs. Using JWST's MIRI/MRS, we compared the observational emission properties of H$_2$O, HCN, C$_2$H$_2$, and CO$_2$ with the outer dust disc structure from ALMA observations, in eight discs with confirmed gaps in ALMA observations, and two discs with gaps of tens of astronomical units in width, around stars with $M_\star \geq 0.45M_{\odot}$. We used new visibility plane fits of the ALMA data to determine the outer dust disc radius and identify substructures in the discs. We find that the presence of a dust gap does not necessarily result in weak H$_2$O emission. Furthermore, the relative lack of colder H$_2$O-emission seems to go hand in hand with elevated emission from carbon-bearing species. The discs with cavities and extremely wide gaps appear to behave as a somewhat separate group, with stronger cold H$_2$O emission and weak warm H$_2$O emission. We conclude that fully blocking radial dust drift from the outer disc seems difficult to achieve. However, there does seem to be a dichotomy between discs that show a strong cold H$_2$O excess and ones that show strong emission from HCN and C$_2$H$_2$. Better constraints on the influence of the outer dust disc structure and inner disc composition require more information on substructure formation timescales and disc ages, along with the importance of trapping of volatiles like CO and CO$_2$ into more strongly bound ices like H$_2$O and chemical transformation of CO into less volatile species.

astro-ph.EP↗

arXiv2024

JWST captures a sudden stellar outburst and inner disk wall destruction

We present JWST/MIRI observations of T~Cha, a highly variable ($ΔV \sim$3-5\,mag) accreting Sun-like star surrounded by a disk with a large ($\sim 15$\,au) dust gap. We find that the JWST mid-infrared spectrum is signiticantly different from the {\it Spitzer} spectrum obtained 17 years before, where the emission at short wavelengths ($5-10 μm$) has decreased by $\sim 2/3$ while at longer wavelengths ($15-25 μm$) it increased by up to a factor of $\sim 3$. This 'seesaw' behavior is contemporary with a fairly constant higher optical emission captured by the All Sky Automated Survey. By analyzing and modelling both SEDs, we propose that JWST caught the star during an outburst that destructed the asymmetric inner disk wall responsible for the high optical variability and lower $15-25$\,micron\ emission during the {\it Spitzer} time. The dust mass lost during this outburst is estimated to be comparable ($\sim 1/5$) to the upper limit of the total micron-sized dust mass in the inner disk of T~Cha now. Monitoring this system during possible future outbursts and more observations of its quiescent state will reveal if the inner disk can be replenished or will continue to be depleted and vanish.

astro-ph.EP↗

arXiv2024

JWST MIRI/MRS Observations of T Cha: Discovery of a Spatially Resolved Disk Wind

Understanding when and how circumstellar disks disperse is crucial to constrain planet formation and migration. Thermal winds powered by high-energy stellar photons have long been theorized to drive disk dispersal. However, evidence for these winds is currently based only on small (~3-6 km/s) blue-shifts in [Ne II] 12.81 um lines, which does not exclude MHD winds. We report JWST MIRI MRS spectro-imaging of T Cha, a disk with a large dust gap (~30 au in radius) and blue-shifted [Ne II] emission. We detect four forbidden noble gas lines, [Ar II], [Ar III], [Ne II], and [Ne III], of which [Ar III] is the first detection in any protoplanetary disk. We use line flux ratios to constrain the energy of the ionizing photons and find that Argon is ionized by EUV whereas Neon is most likely ionized by X-rays. After performing continuum and Point Spread Function (PSF) subtraction on the IFU cube, we discover a spatial extension in the [Ne II] emission off the disk continuum emission. This is the first spatially resolved [Ne II] disk wind emission. The mostly ionic spectrum of T Cha, in combination with the extended [Ne II] emission, points to an evolved stage for any inner MHD wind and is consistent with the existence of an outer thermal wind ionized and driven by high-energy stellar photons. This work acts as a pathfinder for future observations aiming at investigating disk dispersal using JWST.

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