Magnetic properties of the protostellar core IRAS 15398-3359

E Redaelli,P Caselli,F O Alves,F P Santos

doi:10.1051/0004-6361/201936271

E Redaelli, P Caselli + Show 2 more

Open Access

https://doi.org/10.1051/0004-6361/201936271

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Abstract

Context. Magnetic fields can significantly affect the star formation process. The theory of the magnetically driven collapse in a uniform field predicts that the contraction initially happens along the field lines. When the gravitational pull grows strong enough, the magnetic field lines pinch inwards, giving rise to a characteristic hourglass shape. Aims. We investigate the magnetic field structure of a young Class 0 object, IRAS 15398-3359, embedded in the Lupus I cloud. Previous observations at large scales have suggested that this source evolved in an highly magnetised environment. This object thus appears to be an ideal candidate to study the magnetically driven core collapse in the low-mass regime. Methods. We performed polarisation observations of IRAS 15398-3359 at 214 μm using the SOFIA telescope, thus tracing the linearly polarised thermal emission of cold dust. Results. Our data unveil a significant bend of the magnetic field lines from the gravitational pull. The magnetic field appears ordered and aligned with the large-scale B-field of the cloud and with the outflow direction. We estimate a magnetic field strength of B = 78 μG, which is expected to be accurate within a factor of two. The measured mass-to-flux parameter is λ = 0.95, indicating that the core is in a transcritical regime.

Highlights

Magnetic fields (B) are expected to play an important role in the star formation process, for instance providing a source of nonthermal pressure against the gravitational pull
We report our findings, which unveil an ordered magnetic field, which hints of pinching of the field lines resulting from the gravitational pull
Since the two datasets are sensitive to two different regimes, i.e. the optical data trace large cloud scale, whilst the Stratospheric Observatory for Infrared Astronomy (SOFIA) data are sensitive to the core scales, this means that the uniform magnetic field of the cloud has been inherited by the core and that the gravitational collapse was magnetically driven

Summary

Introduction

Magnetic fields (B) are expected to play an important role in the star formation process, for instance providing a source of nonthermal pressure against the gravitational pull (see e.g. McKee & Ostriker 2007). In low-mass star forming regions this feature has only been detected in 30% of young stellar objects in polarisation (9 sources out of 32; Hull & Zhang 2019), suggesting that this is not a universal picture. Out of these 9 detections only 2 show a clear hourglass shape, namely IRAS 4A (Girart et al 2006) and L1448 (Kwon et al 2018).

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Discussion

Conclusion