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Student cleans up archival data and uncovers two stellar cocoons

While investigating 16 years of images of young stars from a retired astronomical camera, Leiden master's student Sam de Regt discovered that two of those stars were still enveloped in birth clouds. Never before has anyone captured these two stars in so much detail. He publishes his data-cleaning method and the new images of the two stars in the journal Astronomy & Astrophysics.

When Sam de Regt (Leiden University, the Netherlands) attended lectures of Matthew Kenworthy (Leiden University) and Christian Ginski (now University of Galway, Ireland), he thought it would be interesting to research the so-called PDI method for his master's thesis. PDI stands for Polarimetric Differential Imaging. This method allows astronomers to distinguish between the extremely bright, unpolarised light from a star and the faint, polarised light reflected from dust particles located in a disk around the star. In such dust disks, planets can be formed.

Normally, the faint light from the dust disk is overwhelmed by the overpowering light from the associated star. Dust disks are therefore difficult to see. By using the PDI method to effectively filter out unpolarised light, you can make the dust disks visible.

How does it work? Polarised light

Light that comes directly from a source, such as a star, is unaffected. As a result, the light waves vibrate in all possible directions. This is called unpolarized light. When light passes through something, like a disk of dust and gas in this case, the light is "scattered" by these particles. The light waves then vibrate in a specific preferred direction. This is polarised light.

Stars were already secretely captured

Ginski and Kenworthy suggested to De Regt to reanalyse archival images from the NACO instrument. That instrument was located on the Very Large Telescope in Chile from 2003 to 2019 and contains data from 57 young stars.

After cleaning up the images, De Regt saw dust disks around twenty known stars. To his surprise, in addition to those 20, two other stars were found to contain dust structures in these observations: YLW 16A and Elia 2-21. These protostars are located some 360 light years towards the constellation Ophiuchus (known as the serpent-bearer). The stars were already known, but now they have also been depicted in imagery on this archival data.

The NACO archive contains data on 57 young stars. Twenty stars had known dust disks or substructures. Master's student Sam de Regt (Leiden University, the Netherlands) discovered two new images of YLW 16A and Elia 2-21 (bottom left and bottom center), while cleaning up the archive. (c) ESO/VLT/NACO, De Regt et al.

Cleaned-up data openly accessible

‘I find it super cool that we have made two new images of these stellar cocoons,’ says De Regt. ‘Furthermore, it is of course great that, thanks to the standard procedure we developed, the data have been reduced and are openly accessible via a Zenodo archive.’ Thesis supervisor Matthew Kenworthy adds: ‘This allows other astronomers to carry out research with these data, breathing new life into it. It's a good example of the Open Science principle.’

PhD-research into exoplanets

‘The fact that Sam managed to achieve this in a few months is fantastic,’ says graduation supervisor Christian Ginski. ‘We don't often witness such productivity.’ De Regt is now a PhD student at Leiden University. He studies how the formation of exoplanets leaves imprints in their atmospheres.

Scientific paper and cleaned data archive

Polarimetric Differential Imaging with VLT/NACO. A comprehensive PDI pipeline for NACO data (PIPPIN). By: S. de Regt, C. Ginski, M.A. Kenworthy, C. Caceres, A. Garufi, T.M. Gledhill, A.S. Hales, N. Huelamo, Á. Kóspál, M.A. Millar-Blanchaer, S. Pérez & M.R. Schreiber. Accepted for publication in Astronomy & Astrophysics. [original (when published) | preprint (pdf) | Zenodo archive]

The original press release can be found on astronomie.nl

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