Lennart M. Böhm

Publications

First-author work below; a full, continuously updated record is available via ADS / SciX and in the downloadable CV.

First-author publications

APEX survey of interstellar HCl: ³⁵Cl/³⁷Cl isotopic ratios in dense cores and outflows

Lennart M. Böhm, Arshia M. Jacob, Friedrich Wyrowski, Karl M. Menten, Katharina Immer, Ashley T. Barnes

PublishedAstronomy & Astrophysics, 705, A802026
Plot of the H35Cl/H37Cl isotopic ratio against Galactocentric radius for 28 high-mass star-forming regions, showing a decreasing trend with increasing distance from the Galactic centre.

A systematic survey of hydrogen chloride (HCl) toward 28 high-mass star-forming regions, observed with the SEPIA660 receiver on the APEX 12 m telescope. H³⁵Cl is detected in every source, and the ³⁵Cl/³⁷Cl isotopic ratio is measured across a wide range of Galactocentric radii.

The ratios trace a gradient consistent with Galactic chemical-evolution models, in which the two chlorine isotopes are built up at different rates as the Galaxy ages and enriches. Several sources with strong molecular outflows show ratios that diverge from this trend, pointing to local chemical or excitation effects distinct from the Galactic-scale pattern – the starting point for the explosive-outflow follow-up described on the Research page.

I surveyed 28 massive star-forming regions for a molecule called hydrogen chloride, using a radio telescope in Chile, and found it in every single one. Comparing two slightly different versions of chlorine in each source traced a pattern that matches how the Galaxy's chemistry has built up over billions of years. A handful of sources broke that pattern – the first clue leading to the explosive-outflow story described on the Research page.

I looked for a certain kind of gas in 28 different star-forming clouds, and found it in every one. By comparing two slightly different versions of one of its atoms, I could tell how the Galaxy's chemistry has changed over a very, very long time. A few clouds looked strange – and that turned out to be a clue about stellar explosions, which you can read about on the Research page.

DOIarXiv:2511.21813ADS / SciXPDF

MACNIFY I. Parsec-scale accretion in the W33 Main hub-filament system

Lennart M. Böhm, Katharina Immer, Ashley T. Barnes, Alexia Anguera-Gonzalez, Farideh Mazoochi, Álvaro Sánchez-Monge, James S. Urquhart, Taehwa Yoo, Qizhou Zhang

Submitted – in review2026
Three-panel map of peak ammonia brightness in NH3 (1,1), (2,2) and (3,3) across the W33 Main filaments, with the filament spine traced through numbered clumps and zoomed insets of the central hub showing compact emission and absorption spectra.
Peak NH₃ (1,1)–(3,3) brightness across the W33 Main filaments, with the north/centre/south spine used for the position–velocity cuts below.
Position-velocity cuts along the northern, central, and southern segments of the W33 Main filament spine, showing the velocity offset of ammonia emission as a function of position along each segment.
Velocity structure along the filament spine (north/centre/south) – the smooth, continuous velocity offset traces how the two filaments stay kinematically connected into the hub.

The first paper in the MACNIFY series investigates whether the parsec-scale filaments feeding the W33 Main hub-filament system remain kinematically connected into the central hub, where massive-star feedback is already active. Using Very Large Array NH₃ (1,1)–(7,7) observations complemented by Green Bank Telescope short-spacing data, the two dominant filaments are traced from a few parsecs out to the hub and characterised through their velocity structure and physical conditions.

The first paper in the MACNIFY series asks whether two long streams of gas feeding a young, massive star-forming region called W33 Main stay smoothly connected all the way into its crowded, feedback-active centre. Using a radio telescope that sees the glow of ammonia gas, together with a second telescope's wide-field data, the two main gas streams are traced from several light-years out down into the hub and their motion is mapped along the way.

This study watches two long rivers of gas, stretching for trillions of kilometres, flow into a busy star nursery called W33 Main. Using radio dishes that can see a particular glowing gas, it checks whether those rivers stay connected all the way to the crowded centre, or break apart before they get there.

Selected co-authored work

Cracking open the "dragon egg": ALMA 1.3 mm observations of a compact, young high-mass core candidate at 30 mas resolution

A. T. Barnes, J. D. Henshaw, Á. Sánchez-Monge, P. Caselli, I. Jiménez-Serra, J. E. Pineda, K. Immer, M. De Simone, R. J. Parker, F. Fontani, E. Redaelli, S. N. Longmore, L. Böhm, Q. Zhang, C. Y. Law, G. Cosentino, J. C. Tan

Submitted – in review2026

High-resolution ALMA 1.3 mm observations resolving a compact, young high-mass prestellar core candidate (“the dragon egg”) down to roughly 30 milliarcsecond (≈175 AU) scales, revealing a compact central component with a steep temperature gradient and no detected outflow or hot-core signatures – consistent with the earliest stage of a protostellar “seed” forming within a larger cold reservoir.

Using the ALMA telescope array at extremely high resolution, we zoomed into one of the youngest, most compact clumps of gas resolved at this scale yet – nicknamed the 'dragon egg' – and found a dense, cold centre with none of the usual signs of a star already forming inside. That makes it one of the best candidates yet for catching a massive star right at the very first moment of its birth.

We used a very powerful set of telescopes to zoom in super close on a tiny, dense little blob of gas nicknamed the 'dragon egg.' It looks cold and quiet, with no baby star glowing inside yet – which might mean we're looking at a giant star right before it's even born.

arXiv:2610.07138ADS / SciXPDF