iiinova — where your digital self keeps evolving

Andrew Sellek @andrewsellek.bsky.social · 01/09/2026

New academic year, new postdoc position!

Andrew Sellek @andrewsellek.bsky.social · 15/10/2025

Interestingly, a linear extrapolation from Cycles 1-4 (increasing about 400 proposals a Cycle) would also put us somewhere in the middle (2756) of the estimates shown!

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Andrew Sellek @andrewsellek.bsky.social · 15/10/2025

Ah, interesting to know for the future! Alas we can't see dates for those but there must be a much longer early tail than we thought.

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Andrew Sellek @andrewsellek.bsky.social · 15/10/2025

I've been trying this in Leiden too - but this looks like much more sophisticated analysis! We were working off of a start of 9549 since PID 9548 was awarded DDT time...

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Andrew Sellek @andrewsellek.bsky.social · 15/10/2025

With just under 12 hours to go, here's how JWST Cycle 5 proposal submissions are progressing according to our sampling of the star and planet formation people here in Leiden! We're well past the 1000 mark for the year (and 10,000 across all years!) now, but where will we end up?

The image shows a plot of the ID number of proposals submitted to JWST with the date of submission plotted from left to right. Each is marked as a green triangle and together they form an upwards curve showing roughly exponential growth. A horizontal yellow line below the data shows the minimum start point based on previously accepted proposals.

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Andrew Sellek @andrewsellek.bsky.social · 26/08/2025

Wow, what a great image! Congrats to Richelle! With last week's 2MJ1612 it seems like accreting protoplanets are like buses: we wait 7 years since PDS70 and now two come along at once!

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Reposted by Andrew Sellek

Sierra Grant @sierragrant.bsky.social · 07/08/2025

Another MINDS JWST paper! We explore the stark transition from H2O-dominated spectra in Sun-like systems to the carbon-rich chemistry seen for low-mass objects. We don't know exactly what is driving this trend, but we explore the possibilities that may be acting in concert. arxiv.org/pdf/2508.04692

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Reposted by Andrew Sellek

Sierra Grant @sierragrant.bsky.social · 05/08/2025

New MINDS paper from Nicolas Kurtovic, focused on binary systems. Spectra, extended emission, variability, multi-observatory analysis -- there's something for everyone! arxiv.org/pdf/2508.02576

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Andrew Sellek @andrewsellek.bsky.social · 12/05/2025

I'm surprised no one here has mentioned the new A&A page limit. I can only expect that what would have been large monolithic papers will be broken up, further boosting the number. It may also increase quality and brevity, making each review less demanding, but I'll be curious to see how it plays out

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Andrew Sellek @andrewsellek.bsky.social · 02/05/2025

Based on a recent workshop series, hosted by Giovanni Rosotti, @cfmanara.bsky.social, Tom Haworth, and Megan Reiter, we summarised in @ojastro.bsky.social the latest results on a growing topic in protoplanetary discs - the role of external irradiation - and how we hope to answer the open questions:

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Reposted by Andrew Sellek

Nienke van der Marel @nienkemarel.bsky.social · 26/03/2025

Super proud of my PhD student Osmar who discovered that the so-called 'compact disks' around young stars are REALLY REALLY small! Look at the full sample of Lupus disks, observed at 30 mas resolution with ALMA.

astronomie.nl

Protoplanetary discs are much smaller than previously thought

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Andrew Sellek @andrewsellek.bsky.social · 11/03/2025

Thanks for being the one ray of sunshine in my otherwise gloomy inbox of rejection!

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Andrew Sellek @andrewsellek.bsky.social · 18/02/2025

Never underestimate how hard this dilemma is to navigate... I spent around 3-4 months looking for the bug in our code a couple of years ago before finally deciding it was a real effect.

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Andrew Sellek @andrewsellek.bsky.social · 11/02/2025

Of course, there was the time we forgot to ask them out their names on them and had the fun puzzle to try to match up more than 50 pairs, having to resort to forensic analysis of how they drew hands, feet etc etc if the picture had changed a lot.

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Andrew Sellek @andrewsellek.bsky.social · 11/02/2025

Nice to see that some of our favourites are still on the website! chaosscience.org.uk/sponsors/#tr... It was always an evening highlight to look at these back at the campsite and see what else changed (many fewer adjectives like "mad" and "evil", more "useful" or "anyone can be a scientist"!).

chaosscience.org.uk

Sponsors – CHaOS

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Reposted by Andrew Sellek

Dr Jared Jeyaretnam ⚛️🧪 @jaredjeya.github.io · 11/02/2025

I used to do science outreach with a group called CHaOS (see link!). We’d often ask kids to draw a scientist at the start and end of our sessions. They’d often go from drawing an Einstein-esque mad scientist, to someone who looked at lot like themselves (or perhaps one of us) 😊 #AcademicChatter

chaosscience.org.uk

CHaOS – Hands-On Science

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Andrew Sellek @andrewsellek.bsky.social · 31/01/2025

Ahh got it, thanks! Is there a reason there would only be an outflow from one source then? The discs look roughly equally bright on ALMA continuum? Presumably we can't get a good handle on their relative masses for such young sources though that know if that contributes...

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Andrew Sellek @andrewsellek.bsky.social · 31/01/2025

Nice work by Isaac! I bookmarked it on arXiv this morning to have a closer look later, but what line is tracing the outflows here? Is that a streamer feeding Aa and is it connected to the outflow?

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Reposted by Andrew Sellek

Ilaria Pascucci @pascucci.bsky.social · 21/01/2025

Congrats to my student Chengyan Xie 🎉 for his work analyzing Spitzer+JWST data on T Cha! 🌟 He uncovered dramatic changes in the star’s disk—inner disk eroding in an outburst, reshaping IR emission. This object deserves follow-up! 🪐✨ #JWST iopscience.iop.org/article/10.3...

iopscience.iop.org

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Andrew Sellek @andrewsellek.bsky.social · 18/12/2024

the isotopologues probe deeper in the disc, providing a truer picture of how much CO2 there is and if it is enhanced. But higher resolution images are needed to confirm if this is due to drift or can be explained with an as yet unresolved cavity. 4/4 @sierragrant.bsky.social @theschwarz.bsky.social

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Andrew Sellek @andrewsellek.bsky.social · 18/12/2024

However the strong CO2 is particularly exciting, because we see not only CO2 itself but potentially two of its isotopologues - 13CO2 and CO18O (more tenatively) - where one of the atoms has been replaced by a rarer isotope. The shapes and relative strengths of the emission features imply that... 3/4

The spectrum of CX Tau between 13.5 and 17.5 micron, with the continuum variations subtracted to provide a flat baseline, shown in black. The spectrum shows various spikes due to emission from different molcules, overlaid in different colours are the spectra of different molecules with properties that allow them to match these patterns. In the centre is a strong triangular feature from CO2, overlaid in green, while insets show emission attributed to 13CO2 and CO18O.

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Andrew Sellek @andrewsellek.bsky.social · 18/12/2024

Marissa found that CX Tau is an example of the discs with weak water but strong CO2. The weakness of the water is more or less in line with what one expects for given the disc's low accretion rate, though there is still evidence for cold water strong emission which may be connected to drift. 2/4

A zoom in on the spectrum around 23.9 microns showing a set of four water lines. CX Tau, in black, is compared to a disc with strong water,, DR Tau, in blue, showing that both show that the first and third lines are brighter than the other two, a pattern which indicates the presence of cold water.

A plot showing that the luminosity of the water lines for a sample of discs from the literature (grey points) is correlated with the luminosity produced by accreting material. CX Tau, indicated with a blue star, sits in line with this trend on the very left of the figure at low accretion luminosity and water line luminosity.

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Andrew Sellek @andrewsellek.bsky.social · 18/12/2024

The latest protoplanetary disk study by the MINDS collaboration using JWST-MIRI is out now! arxiv.org/abs/2412.127... Led by Leiden PhD student Marissa Vlasblom, it focusses on CX Tau, a disk for which the dust emission is much more compact than gas, suggesting dust grains have drifted inwards. 1/4

The spectrum of CX Tau showing how bright the disc emission is as a function of infrared wavelength. The disc gets brighter going from shorter wavelengths on the left to longer wavelenghts on the right, with a large bump at 10 micron due to Silicate dust grains. On top of the smooth continuum are a few weak lines, the most prominent ones being due to atoms such as HI and Ne or CO2. Inset panels show zoom-ins that demonstrate the presence of weak water features.

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Reposted by Andrew Sellek

Nienke van der Marel @nienkemarel.bsky.social · 12/12/2024

JWST MIRI has revealed that disks around very low-mass stars are hydrocarbon-rich but water-poor in the inner disk (Aditya Arabhavi). Result of dust traps? What are the implications for planets forming here? #NOVA25

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Andrew Sellek @andrewsellek.bsky.social · 11/12/2024

JWST mostly sees warm gas in the inner regions if protoplanetary discs. These discs are where planets form and the inner regions are especially important for rocky planets like Earth. So with such data we hope to learn what the building blocks of Earthlike planets are made of - how much water etc?

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Andrew Sellek @andrewsellek.bsky.social · 11/12/2024

...(no resolved structure) and closest to models with no gap or a gap fairly close in and GW Lup has a ring at ~70au (from memory) and is closest to models with a gap at 30-60au (but not too far). But the difference is slight and the models are not tuned in M* or gap depth which may also play a role

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Andrew Sellek @andrewsellek.bsky.social · 11/12/2024

Thanks, Sierk! I would be of course cautious about trusting absolute values as our 1D estimates can't really account for how the molecules might be photodissociated differently, but hopefully the trends stand somewhat. But for the C-rich discs that come closest, CX Tau is extremely compact...

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Andrew Sellek @andrewsellek.bsky.social · 11/12/2024

The natural follow up being "How intensive are the simulations you need to run to keep yourselves warm?"?

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Andrew Sellek @andrewsellek.bsky.social · 05/12/2024

The location and shape of the continuum variations can acually tell us which silicate minerals most likely make up the dust. As far as I know, that hasn't been calculated in detail yet for GW Lup or DR Tau, but see Jang et al. 2024 for a exploration of dust in the PDS70 disc arxiv.org/abs/2408.16367

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Andrew Sellek @andrewsellek.bsky.social · 05/12/2024

However, the dust emits too: the 2 disc spectra that I showed for reference had had the dust emission (which is a smooth underlying variation) subtracted. This is the raw spectrum of GW Lup from Grant et al. 2023, where you can see the same line features atop the larger scale continuum variations.

The spectrum of the protoplanetary disc GW Lup showing its brightness (flux) as a function of wavelength. The flux generally increases from left-to-right, going towards longer wavelengths. There is a broad, flat-topped bump situated at 10 micron. On top of the wider variations are sharp spikes corresponding to emission lines of atoms and molecules.

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Andrew Sellek @andrewsellek.bsky.social · 05/12/2024

Great question! To transport the ices we just need them to be frozen onto materials which are more resistant to sublimation, but most loosely we could mean any solids. In our models we assumed dust is some mix of silicates (essentially rocks) and carbonaceous material (possibly similar to graphite).

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

Thankfully, the dust does not alter the ratio of CO2/H2O that could be seen, which always closely follows the true mass ratio. So comparing the two molecules could be the best way to test when radial drift is playing a role in inner disc compositions and at what stage of evolution the disc is. 6/6

A plot with 3 rows and 2 columns showing how the masses of H2O and CO2 in vapour form (left), and the visible column densities (right) change over time. Each plot shows the evolution for 8 discs, one in grey with no dust trap, and 7 in blue with dust trapped outside a gap at succesively closer distances from the star with increasingly blue colours. The vapour masses initially rise and then fall; the vapour mass ratio initially falls, then rises again, before returning to its initial value. The traps generally lower the vapour mass of H2O and CO2, but raise the ratio of CO2/H2O. The column densites show a different evolution, which is an almost entirely flat line for the H2O but similar to the vapour mass for the CO2 or the CO2/H2O column density ratio. Overplotted as circular points in red/orange/yellow shades are data from different discs observed with JWST.

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

But what can we actually see with JWST? It becomes a little complicated because the drift naturally supplies dust which might help to obscure some of the molecules we seek to observe! In the worst case scenario (labelled Scenario 1 in the figure) we would see no enhancement in the water at all! 5/6

Two side-by-side panels of a plot showing how the column density relates to the vapour mass for water (left) and CO2 (right). Each panel shows three scenarios in purple, red and gold. Notably, the purple Scenario 1 is an almost completely flat line for water. All other lines show a pattern of moving towards the (lower) right, then sharply upwards, and then declining more gradually to the lower left.

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

Perhaps counterintuively, the biggest effect is if the trap is quite far from the star, since it lets a lot of CO2 through but ultimately still cuts off the replenishment of the H2O. This is quite similar to what is seen for GW Lup, which has a dust ring at 10s of au! 4/6

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

The delivery of CO2 happens slightly later and lasts longer: it is more volatile than H2O so sublimates further out in the disc and so takes longer to accrete onto the star. If radial drift is interrupted, e.g. by dust traps, H2O disappears more quickly and the disc becomes relatively CO2-rich. 3/6

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

Dust grains in discs undergo an inward migration process known as radial drift .This has been argued to lead to enhancements of H2O as the dust grains are coated in ice which they release when they reach the warm inner disc. The dust will also carry CO2 ice, and should therefore enhance CO2 too. 2/6

A plot showing how the enhancement in mass in vapour form of different molecules - H2O (blue), CO2 (green), CH4 (olive) - changes over 5 Myr of disc evolution. Each molecule shows an increase from its initial value to a peak, followed by a decline. Water peaks the sharply early-on with a very high enhancement. the earliest, while CO2 peaks later, lower and with a broader peak. CH4 has the latest, lowest and broadest peak.

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

It's paper day! arxiv.org/abs/2412.01895 JWST is studying the molecular contents of the inner regions of protoplanetary discs in unprecented detail, and they turn out to be very varied. Some discs, eg DR Tau, are dominated by emission from water, others, eg GW Lup, are dominated by CO2. But why? 1/6

Two panels showing the JWST Spectrum of DR Tau (a protoplanetary disc) and its decomposition into different molecules as a function of wavelength, from Temmink et al. (2024a). The spectrum shows many sharp spikes corresponding to bright emission lines of water, with some broader underlying variations. Models of emission of different molecules are plotted in different colours at the bottom and their sum as the shaded red region at the top, which is overlaid on the data in black.

Two plots showing the JWST Spectrum of GW Lup (a protoplanetary disc) and its decomposition into different molecules as a function of wavelength, from Grant et al. (2023). The clearest feature is a broad triangular shaped bump at ~15 micron resulting from CO2, with some fainter surrounding spikes mostly due to water or CO2. Models of emission of different molecules are plotted in different colours at the bottom and their sum as the shaded red region at the top, which is overlaid on the data in black.

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Andrew Sellek @andrewsellek.bsky.social · 04/12/2024

Long rumoured to be the handiwork of @marievandesande.bsky.social, I have now had this confirmed off the record by a source very close to Marie.

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Andrew Sellek @andrewsellek.bsky.social · 10/09/2024

Best of luck in the new position!

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