arXiv subjects

T. T. Thai

Publications and source records attributed to T. T. Thai.

At least 19 recordsLinked to original sources

arXiv2026

Euclid Quick Data Release (Q1). AstroVink: A vision transformer approach to find strong gravitational lens systems

We present AstroVink, a vision transformer classifier designed for automated identification of strong lens candidates in Euclid imaging. We build upon the DINOv2 encoder, fine tuned to distinguish between lens and non-lens galaxies. Our base model, trained on simulated strong lens systems and labelled non lenses, recovers 88 of the 110 lens candidates within the top 500 ranked candidates, corresponding to an inspection efficiency of one lens per 5.7 inspected objects in our test set. After the Q1 data release, which yielded about 500 lens candidates, we retrained the model using high confidence lens candidates and new negatives, initially flagged as potential lenses by other classifiers but rejected during visual inspection. The retrained network further improves performance, achieving recovery of all 110 systems within the same ranking and reducing the inspection effort to one lens per 4.5 inspected objects, demonstrating that incorporating real examples significantly enhances model generalisation. An analysis of training subsets revealed that the inclusion of realistic negative examples played a key role in this improvement. Finally, we applied the retrained model to the Q1 original selection of 1.08M targets, followed by a new round of Space Warps citizen science inspection and expert vetting, where we identified a total of eight Grade A and 26 Grade B new lens candidates. These results demonstrate that transformer based architectures can recover strong lens candidates with high efficiency in real Euclid data, while substantially reducing the number of candidates requiring visual inspection.

astro-ph.IM↗

arXiv2026

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine F -- Bright and low-redshift strong lenses

We present 72 additional galaxy-galaxy strong lenses that complement the sample discovered in the Euclid Quick Release 1 data (63.1 deg^2) of the Strong Lens Discovery Engine (SLDE) papers A-E. It is shown that previous pre-selection of potential lenses, which excluded objects from the Gaia catalogue, led to missing several bright and low-redshift strong lenses, adding more than 10% new strong lens candidates compared to the previous search. In total, the catalogue includes 38 "grade A" (confident) and 34 "grade B" (probable) candidates. These lenses are identified through a combination of two independent searches for bright nearby objects: one based on machine-learning models followed by expert visual inspection, and the other based solely on expert visual inspection, targeting objects not included in the initial machine-learning selection (a limitation identified only after extensive visual inspection). With these additional strong lens candidates, we augment the expected number of high-confidence candidates in the Euclid Wide Survey from previous forecasts to 120000. Detailed semi-automated lens modelling confirms at least 41 systems out of 72, a fraction consistent with that found in SLDE A (315 out of 488). These include: multiple edge-on disc lenses; sources with arcs near the lens centre; "red sources"; and an edge-on disk galaxy lensing a galaxy merger, producing two sets of lensed features, an Einstein ring and a doubly imaged component. The median redshift of these systems is $Δ$ z ~ 0.3 lower than that of the SLDE A sample.

astro-ph.GA↗

arXiv2026

Euclid preparation. Far-infrared predictions for Euclid galaxy catalogues: cluster, protocluster, and field

The MAMBO mock galaxy catalogue, based on the Millennium Simulation with empirically assigned galaxy properties, provides predictions of FIR fluxes and physical parameters of Euclid-detectable galaxies. Predicted FIR flux distributions confirm that only the brightest Euclid sources will be detectable in existing FIR surveys. We employ stacking to measure the mean dust properties as a function of stellar mass and redshift. We find dust temperatures and infrared luminosities increase with redshift across all mass bins, while dust masses remain roughly constant. FIR number counts from MAMBO show overall good agreement with observations, and the total infrared luminosity function reproduces published estimates across most redshift ranges, extending to z~10. Comparing the Euclid Wide and Deep Surveys, we find that the EDS recovers the total IRLF to fainter luminosities and higher redshifts (up to z~6 in $I_E$), although its detectability falls below 80% at z>4, whereas the EWS becomes strongly incomplete beyond z~2. We also examine the dependence of the IRLF on environment. Schechter fits indicate that the faint-end slope $α$ flattens with redshift for cluster and protocluster galaxies, while remaining approximately constant for field populations. Imposing additional detection limits from Herschel-PACS and SPIRE shows that only the most luminous ($L_{IR}$ > $10^{12.5}$ $L_{\odot}$) galaxies remain detectable at z~4, but the limited MAMBO area (3.14$deg^2$) is inadequate for statistically robust (>3$σ$) constraints. Survey areas at least 30 times larger are required. Overall, the MAMBO FIR extension reproduces key number count and IRLF trends, provides realistic predictions for FIR-detected Euclid galaxies, and highlights the importance of synergies with current and future FIR/sub-mm facilities to probe environmental dependence with sufficient depth and area.

astro-ph.GA↗

arXiv2026

Accurate spectroscopic redshift estimation using non-negative matrix factorization: application to MUSE spectra

Accurate and automated galaxy redshift determination is essential for maximizing the scientific return of spectroscopic surveys. In this paper, we propose a data-driven method to address this challenge. The method first learns a rest-frame representation of galaxy spectra using Non-negative Matrix Factorization (NMF). The method then reconstructs new spectra using this representation at different trial redshifts, and identifies the correct redshift by selecting the one that minimizes the reconstruction error. We apply our method to galaxy spectra from the Multi Unit Spectroscopic Explorer (MUSE), covering redshifts from 0 to 6.7. Our method achieves an overall success rate of 93.7%. We further demonstrate two applications: (i) the separation between true and false sources, and (ii) the detection of blended sources from one-dimensional spectra. Our results demonstrate that NMF-based representations provide a powerful and physically motivated framework for redshift estimation in current and future large spectroscopic surveys.

astro-ph.IM↗

arXiv2025

Parametric strong lensing model of the galaxy cluster Abell 2390 from Euclid and MUSE observations

We present a new high precision parametric strong lensing total mass reconstruction of the Euclid Early Release Observations (ERO) galaxy cluster Abell 2390, at redshift z = 0.231. We include in this analysis 35 multiple images from 13 background sources, of which 25 are spectroscopically confirmed thanks to observations from the MUSE, spanning a redshift range from z = 0.535 to z = 4.877. After fully reanalysing the MUSE spectroscopy, we combine it with archival spectroscopic catalogues allowing us to select 65 secure cluster members. This sample is further complemented with 114 photometric member galaxies, identified within the Euclid VIS and NISP imaging down to magnitude H = 23. We also measure the stellar velocity dispersions for 22 cluster members, in order to calibrate the Faber-Jackson relation and hence the scaling relations for the subhalo mass components. We test and compare 11 total mass parametrisations of the galaxy cluster with increasing complexity. To do so, we employ the new parametric strong lensing modelling code Gravity.jl. Our best fit total mass parametrisation is characterised by a single large scale halo, 179 subhalo components, and an external shear term. The reference model yields a mean scatter between the model predicted and observed positions of the multiple images of 0.32 arcseconds. We are able to quantify the systematics arising from our modelling choices by taking advantage of all the different explored total mass parametrisations. When our results are compared with those from other lensing studies, we notice an overall agreement in the reconstructed cluster total mass profile in the outermost strong lensing regime: the discrepancy in the innermost region of the cluster (few kiloparsec from the brightest cluster galaxy, where few or no strong lensing features are observed) could possibly be ascribed to the different data and modelling choices.

astro-ph.CO↗

arXiv2025

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine C: Finding lenses with machine learning

Strong gravitational lensing has the potential to provide a powerful probe of astrophysics and cosmology, but fewer than 1000 strong lenses have been confirmed so far. With a 0.16'' resolution covering a third of the sky, the Euclid telescope will revolutionise the identification of strong lenses, with 170 000 lenses forecasted to be discovered amongst the 1.5 billion galaxies it will observe. We present an analysis of the performance of five machine-learning models at finding strong gravitational lenses in the quick release of Euclid data (Q1) covering 63 deg2. The models have been validated by citizen scientists and expert visual inspection. We focus on the best-performing network: a fine-tuned version of the Zoobot pretrained model originally trained to classify galaxy morphologies in heterogeneous astronomical imaging surveys. Of the one million Q1 objects that Zoobot was tasked to find strong lenses within, the top 1000 ranked objects contain 122 grade A lenses (almost-certain lenses) and 41 grade B lenses (probable lenses). A deeper search with the five networks combined with visual inspection yielded 250 (247) grade A (B) lenses, of which 224 (182) are ranked in the top 20 000 by Zoobot. When extrapolated to the full Euclid survey, the highest ranked one million images will contain 75 000 grade A or B strong gravitational lenses.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1): The Strong Lensing Discovery Engine A -- System overview and lens catalogue

We present a catalogue of 497 galaxy-galaxy strong lenses in the Euclid Quick Release 1 data (63 deg$^2$). In the initial 0.45\% of Euclid's surveys, we double the total number of known lens candidates with space-based imaging. Our catalogue includes 250 grade A candidates, the vast majority of which (243) were previously unpublished. Euclid's resolution reveals rare lens configurations of scientific value including double-source-plane lenses, edge-on lenses, complete Einstein rings, and quadruply-imaged lenses. We resolve lenses with small Einstein radii ($θ_{\rm E} < 1''$) in large numbers for the first time. These lenses are found through an initial sweep by deep learning models, followed by Space Warps citizen scientist inspection, expert vetting, and system-by-system modelling. Our search approach scales straightforwardly to Euclid Data Release 1 and, without changes, would yield approximately 7000 high-confidence (grade A or B) lens candidates by late 2026. Further extrapolating to the complete Euclid Wide Survey implies a likely yield of over 100000 high-confidence candidates, transforming strong lensing science.

astro-ph.GA↗

arXiv2025

Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine E -- Ensemble classification of strong gravitational lenses: lessons for Data Release 1

The Euclid Wide Survey (EWS) is expected to identify of order $100\,000$ galaxy-galaxy strong lenses across $14\,000$deg$^2$. The Euclid Quick Data Release (Q1) of $63.1$deg$^2$ Euclid images provides an excellent opportunity to test our lens-finding ability, and to verify the anticipated lens frequency in the EWS. Following the Q1 data release, eight machine learning networks from five teams were applied to approximately one million images. This was followed by a citizen science inspection of a subset of around $100\,000$ images, of which $65\%$ received high network scores, with the remainder randomly selected. The top scoring outputs were inspected by experts to establish confident (grade A), likely (grade B), possible (grade C), and unlikely lenses. In this paper we combine the citizen science and machine learning classifiers into an ensemble, demonstrating that a combined approach can produce a purer and more complete sample than the original individual classifiers. Using the expert-graded subset as ground truth, we find that this ensemble can provide a purity of $52\pm2\%$ (grade A/B lenses) with $50\%$ completeness (for context, due to the rarity of lenses a random classifier would have a purity of $0.05\%$). We discuss future lessons for the first major Euclid data release (DR1), where the big-data challenges will become more significant and will require analysing more than $\sim300$ million galaxies, and thus time investment of both experts and citizens must be carefully managed.

astro-ph.GA↗

arXiv2025

Euclid: Finding strong gravitational lenses in the Early Release Observations using convolutional neural networks

The Early Release Observations (ERO) from Euclid have detected several new galaxy-galaxy strong gravitational lenses, with the all-sky survey expected to find 170,000 new systems, greatly enhancing studies of dark matter, dark energy, and constraints on the cosmological parameters. As a first step, visual inspection of all galaxies in one of the ERO fields (Perseus) was carried out to identify candidate strong lensing systems and compared to the predictions from Convolutional Neural Networks (CNNs). However, the entire ERO data set is too large for expert visual inspection. In this paper, we therefore extend the CNN analysis to the whole ERO data set, using different CNN architectures and methodologies. Using five CNN architectures, we identified 8,469 strong gravitational lens candidates from IE-band cutouts of 13 Euclid ERO fields, narrowing them to 97 through visual inspection, including 14 grade A and 31 grade B candidates. We present the spectroscopic confirmation of a strong gravitational lensing candidate, EUCLJ081705.61+702348.8. The foreground lensing galaxy, an early-type system at redshift z = 0.335, and the background source, a star-forming galaxy at redshift z = 1.475 with [O II] emission, are both identified. Lens modeling using the Euclid strong lens modeling pipeline reveals two distinct arcs in a lensing configuration, with an Einstein radius of 1.18 \pm 0.03 arcseconds, confirming the lensing nature of the system. These findings highlight the importance of a broad CNN search to efficiently reduce candidates, followed by visual inspection to eliminate false positives and achieve a high-purity sample of strong lenses in Euclid.

astro-ph.GA↗

arXiv2024

EP Aquarii: a new picture of the circumstellar envelope

New analyses of earlier ALMA observations of oxygen-rich AGB star EP Aquarii are presented, which contribute major progress to our understanding of the morpho-kinematics of the circumstellar envelope (CSE). The birth of the equatorial density enhancement (EDE) is shown to occur very close to the star where evidence for rotation has been obtained. High Doppler velocity wings are seen to consist of two components, the front end of the global wind, reaching above $\pm$12 km s$^{-1}$, and an effective line broadening, confined within 200 mas from the centre of the star, reaching above $\pm$20 km s$^{-1}$ and interpreted as caused by the pattern of shock waves resulting from the interaction between stellar pulsation and convective cell granulation. Close to the star, episodic and lumpy mass ejections are observed, and their interaction with the gas of the nascent EDE, first rotating and later slowly expanding, is seen to play an important role in the development of the wind and the evolution of its radial velocity from 8-10 km s$^{-1}$ on the polar symmetry axis to $\sim$2 km s$^{-1}$ at the equator. It implies a very complex morpho-kinematics, which prevents making reliable interpretations with reasonable confidence. In particular, it sheds serious doubts on an earlier interpretation implying the presence of a white dwarf companion orbiting the star at an angular distance of $\sim$0.4 arcsec from its centre and currently west of it.

astro-ph.SR↗

arXiv2024

Galaxy main sequence and properties of low-mass Lyman-alpha Emitters towards reionisation viewed by VLT/MUSE and JWST/NIRCam

Faint, star-forming galaxies likely play a dominant role in cosmic reionisation. Strides have been made in recent years to characterise these populations at high redshifts ($z>3$). Now for the first time, with JWST photometry beyond 1$\,μm$ in the rest frame, we can derive accurate stellar masses and position these galaxies on the galaxy main sequence. We seek to assess the place of 96 individual Lyman-alpha emitters (LAEs) selected behind the A2744 lensing cluster with MUSE spectroscopy on the galaxy main sequence. We also compare derived stellar masses to Lyman-alpha luminosities and equivalent widths to better quantify the relationship between the Lyman-alpha emission and the host galaxy. These 96 LAEs lie in the redshift range $2.9<z<6.7$, and their range of masses extends down to $10^6\,\mathrm{M_{\odot}}$ (over half with $\mathrm{M_{\star}}<10^8\,\mathrm{M_{\odot}}$). We use the JWST/NIRCam and HST photometric catalogs from the UNCOVER project, giving us excellent wavelength coverage from $450\,\mathrm{nm}$ to $4.5\,μm$. We find a main sequence relation for these low mass LAEs of the form: $\mathrm{log\,SFR}=(0.88\pm0.07 - 0.030\pm0.027\times t)\,\mathrm{log\,M_{\star}} - ( 6.31\pm0.41 - 0.08\pm0.37\times t)$. This is in approximate agreement with best-fits of previous collated studies, however, with a steeper slope and a higher normalisation. This indicates that low-mass LAEs towards the epoch of reionisation lie above typical literature main sequence relations derived at lower redshift and higher masses. Additionally, comparing our results to UV-selected samples, we see that while low-mass LAEs lie above these typical main sequence relations, they are likely not singular in this respect at these masses and redshifts. While low-mass galaxies have been shown to play a significant role in cosmic reionisation, our results point to no special position for LAEs in this regard.

astro-ph.GA↗

arXiv2024

Linking UV spectral properties of MUSE Ly-alpha emitters at z>3 to Lyman continuum escape

The physical conditions giving rise to high escape fractions of ionizing radiation (LyC $f_{\rm{esc}}$) in star-forming galaxies - most likely protagonists of cosmic reionization - are not yet fully understood. Using the VLT/MUSE observations of ~1400 Ly$α$ emitters at 2.9 < z < 6.7, we compare stacked rest-frame UV spectra of candidates for LyC leakers and non-leakers selected based on their Ly$α$ profiles. We find that the stacks of potential LyC leakers, i.e. galaxies with narrow, symmetric Ly$α$ profiles with small peak separation, generally show (i) strong nebular OIII]1666, [SiIII]1883, and [CIII]1907+CIII]1909 emission, indicating a high-ionization state of the interstellar medium (ISM); (ii) high equivalent widths of HeII1640 (~1-3 A), suggesting the presence of hard ionizing radiation fields; (iii) SiII*1533 emission, revealing substantial amounts of neutral hydrogen off the line of sight; (iv) high CIV1548,1550 to [CIII]1907+CIII]1909 ratios (CIV/CIII] > 0.75), signalling the presence of low column density channels in the ISM. In contrast, the stacks with broad, asymmetric Ly$α$ profiles with large peak separation show weak nebular emission lines, low HeII1640 equivalent widths (<1 A), and low CIV/CIII] (<0.25), implying low-ionization states and high-neutral hydrogen column densities. Our results suggest that CIV/CIII] might be sensitive to the physical conditions that govern LyC photon escape, providing a promising tool for identification of ionizing sources among star-forming galaxies in the epoch of reionization.

astro-ph.GA↗

arXiv2023

On the nascent wind of nearby oxygen-rich AGB stars: a brief review

The commonly accepted mechanism governing the formation of the nascent wind in oxygen-rich AGB stars combines an initial boost above the photosphere, given by shock waves resulting from stellar pulsations and convective cell granulation, with a subsequent acceleration fuelled by the radiation pressure of the star on dust grains. We use six nearby stars, for which detailed studies of visible and infrared observations at the VLT and millimetre observations at ALMA are available, to assess the extent to which the validity of this picture is currently corroborated. We show that while providing a very useful guide to current research and having received general support and suffered no contradiction, it still requires many additional observations to be reliably validated. In particular, observations of the highest possible angular resolution at both millimetre and visible/infrared wavelengths, performed in conjunction with measurements of the light curve, are necessary to tell apart the respective roles played by convection and stellar pulsations. The observed concurrence of high variability near the photosphere with persistence over decades, or even centuries, of the global anisotropy displayed by the CSE need to be understood. New observations of the close neighbourhood of the star are required to elucidate the mechanism that governs rotation, in particular in the cases of R Dor, L2 Pup and EP Aqr. We argue that the presence of stellar or planetary companions does not seriously impact the formation of the nascent wind and only modifies its subsequent evolution.

astro-ph.SR↗

arXiv2022

Evidence for episodic and patchy mass ejection in the circumstellar envelope of AGB star R Leonis

The morpho-kinematics of the circumstellar envelope of oxygen-rich AGB star R Leonis is probed using ALMA (Atacama Large Millimeter/submillimeter Array) observations of the emission of molecular lines, including in particular CO(2-1) and $^{29}$SiO(5-4). Evidence is found for an episode of enhanced mass loss, a few centuries ago, that produced a broad expanding shell of mean radius $\sim$6 arcsec and mean radial expansion velocity $\sim$5.5 km s$^{-1}$ . Detailed scrutiny of its structure, as displayed by the emission of the CO(2-1) line, reveals strong inhomogeneity and patchy morphology. Evidence is also found, in particular from the morpho-kinematics of the emission of SiO, SO and SO$_2$ lines probing the close neighbourhood of the star, for distinct gas outflows covering broad solid angles in the south-eastern, south-western and north-western quadrants, suggesting significant contribution of the convective cell granulation in defining the pattern of mass ejection. A study of relative molecular abundances in these outflows suggests that a Local Thermal Equilibrium (LTE) description applies approximately beyond $\sim$10 stellar radii from the centre of the star but not at the smaller angular separations where the SO and SO$_2$ molecules are found to be confined. Near the stellar disc, masers of the vibrationally excited SiO lines are found to probe north-western parts of a layer of hot gas, consistent with the earlier observation of an asymmetric expanding shell within 1-2 stellar radii from the centre of the star. Globally, a picture dominated by episodic and patchy mass ejections is found to prevail.

astro-ph.SR↗

arXiv2022

Contributions of rotation, expansion and line broadening to the morpho-kinematics of the inner CSE of oxygen-rich AGB star R Hya

We use archival ALMA observations of the CO(2-1) and SiO(5-4) molecular line emissions of AGB star R Hya to illustrate the relative contributions of rotation, expansion and line broadening to the morphology and kinematics of the circumstellar envelope (CSE) within some ~70 au (~0.5 arcsec) from the centre of the star. We give evidence for rotation and important line broadening to dominate the inner region, within ~14 au (~100 mas) from the centre of the star. The former is about an axis that projects a few degrees west of north and has a projected rotation velocity of a few km/s. The latter occurs within some 7-14 au (50-100 mas) from the centre of the star, the line width reaching two to three times its value outside this region. We suggest that it is caused by shocks induced by stellar pulsations and convective cell granulation. We show the importance of properly accounting for the observed line broadening when discussing rotation and evaluating the radial dependence of the rotation velocity.

astro-ph.SR↗

arXiv2022

Mira Ceti, atypical archetype

With the aim of unraveling the complexity of the morpho-kinematics of the circumstellar envelope (CSE) of Mira Ceti, we review, extend and in some cases revisit ALMA millimeter observations of the emission of the SiO(5-4) and CO(3-2) molecular lines. In addition, we present a detailed analysis of the optically thin $^{13}$CO(3-2) emission, which provides several important new results. In agreement with observations at infrared and visible wavelengths, we give evidence for confinement and probably rotation of a dense gas volume within $\sim$50 au from the star and for a large SiO line-width within $\sim$15 au. We show that the mass loss process is episodic and takes the form of clumps having a very low SiO/CO abundance ratio compared with similar oxygen-rich long period variables, probably a result of depletion on dust grains and photo-dissociation. We evaluate the mass loss rate associated with the main clumps and compare it with values obtained from single dish observations. We argue that the SiO emission observed in the south-western quadrant is not related to the mechanism of generation of the nascent wind but to a mass ejection that occurred eleven years before the observations. We remark that Mira Ceti is not a good archetype in terms of its wind: models aiming at describing the very complex gas-dust chemistry in action in the CSE of oxygen-rich AGB stars may find it difficult to account for its peculiar features, small variations in the parameters deciding when and where mass loss can proceed significantly.

astro-ph.SR↗

arXiv2022

The Lensed Lyman-Alpha MUSE Arcs Sample (LLAMAS) : I. Characterisation of extended Lyman-alpha haloes and spatial offsets

We present the Lensed Lyman-Alpha MUSE Arcs Sample (LLAMAS) selected from MUSE and HST observations of 17 lensing clusters. The sample consists of 603 continuum-faint (-23<M_UV<-14) lensed Lyman-alpha emitters (producing 959 images) with spectroscopic redshifts between 2.9 and 6.7. Combining the power of cluster magnification with 3D spectroscopic observations, we are able to reveal the resolved morphological properties of 268 Lyman-alpha emitters. We use a forward modelling approach to model both Lyman-alpha and rest-frame UV continuum emission profiles in the source plane and measure spatial extent, ellipticity and spatial offsets between UV and Lyman-alpha emission. We find a significant correlation between UV continuum and Lyman-alpha spatial extent. Our characterization of the Lyman-alpha haloes indicates that the halo size is linked to the physical properties of the host galaxy (SFR, Lyman-alpha EW and Lyman-alpha line FWHM). We find that 48% of Lyman-alpha haloes are best-fitted by an elliptical emission distribution with a median axis ratio of q=0.48. We observe that 60% of galaxies detected both in UV and Lyman-alpha emission show a significant spatial offset (Delta). We measure a median offset of Delta= 0.58 \pm 0.14 kpc for the entire sample. By comparing the spatial offset values with the size of the UV component, we show that 40% of the offsets could be due to star-forming sub-structures in the UV component, while the larger offsets are more likely due to larger distance processes such as scattering effects inside the circumgalactic medium or emission from faint satellites or merging galaxies. Comparisons with a zoom-in radiative hydrodynamics simulation of a typical Lyman-alpha emitting galaxy show a good agreement with LLAMAS galaxies and indicate that bright star-formation clumps and satellite galaxies could produce a similar spatial offsets distribution. (abridged)

astro-ph.GA↗

arXiv2021

Morpho-kinematics of the wind of AGB star L$_2$ Pup

Single dish observations of AGB star L$_2$ Pup have revealed exceptionally low mass loss rate and expansion velocity, challenging interpretations in terms of standard wind models. Recent VLT and ALMA observations have drawn a detailed picture of the circumstellar envelope within $\sim$20 au from the centre of the star: a nearly edge-on rotating disc of gas and dust, probably hosting a planetary companion near the star. However, these observations provide no direct information on the wind escaping the gravity of the star. The present article uses ALMA observations of the $^{12,13}$CO(3-2), $^{29}$SiO(8-7), $^{12}$CO(2-1) and $^{28}$SiO(5-4) line emissions to shed new light on this issue. It shows the apparent normality of L$_2$ Pup in terms of the formation of the nascent wind, with important line broadening within 4 au from the centre of the star, but no evidence for a wind flowing along the disc axis. At larger distances, up to some 200 au from the centre of the star, the wind morpho-kinematics is dominated by a disc, or equatorial enhancement, expanding isotropically and radially with a velocity not exceeding some 5 km s$^{-1}$ , inclined in the north-west/south-east direction with respect to the plane of the sky. In addition, outflows of lower density are observed on both sides of the disc, covering large solid angles about the disc axis, contributing about half the flux of the disc. Such morphology is at strong variance with the expectation of a pair of back-to-back outflows collimated by the central gas-and-dust disc.

astro-ph.SR↗