SPHERE view of Wolf-Rayet 104

A Soulain,A Matter,A Sevin,M Carle,P Martinez,A La Camera,T Moulin,M Carbillet,A Roux,F Millour,Y Magnard,H Avenhaus,B Lopez,M Langlois,E Lagadec,L Abe,J Ramos,A Lamberts,J Milli

doi:10.1051/0004-6361/201832817

Abstract

Context. WR104 is an emblematic dusty Wolf-Rayet star and the prototypical member of a sub-group hosting spirals that are mainly observable with high-angular resolution techniques. Previous aperture masking observations showed that WR104 is likely to be an interacting binary star at the end of its life. However, several aspects of the system are still unknown. This includes the opening angle of the spiral, the dust formation locus, and the link between the central binary star and a candidate companion star detected with the Hubble Space Telescope (HST) at 1′′. Aims. Our aim was to directly image the dusty spiral or “pinwheel” structure around WR104 for the first time and determine its physical properties at large spatial scales. We also wanted to address the characteristics of the candidate companion detected by the HST. Methods. For this purpose, we used SPHERE and VISIR at the Very Large Telescope to image the system in the near- and mid-infrared, respectively. Both instruments furnished an excellent view of the system at the highest angular resolution a single, ground-based telescope can provide. Based on these direct images, we then used analytical and radiative transfer models to determine several physical properties of the system. Results. Employing a different technique than previously used, our new images have allowed us to confirm the presence of the dust pinwheel around the central star. We have also detected up to five revolutions of the spiral pattern of WR104 in the K band for the first time. The circumstellar dust extends up to 2 arcsec from the central binary star in the N band, corresponding to the past 20 yr of mass loss. Moreover, we found no clear evidence of a shadow of the first spiral coil onto the subsequent ones, which likely points to a dusty environment less massive than inferred in previous studies. We have also confirmed that the stellar candidate companion previously detected by the HST is gravitationally bound to WR104 and herein provide information about its nature and orbital elements.

Highlights

The study of massive stars is important for many aspects of stellar evolution and cosmic enrichment
After 20 yr of observations based on reconstructed images from the aperture-masking technique and Fourier plane sampling, we present the first direct images of the WR104 system obtained with the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument at the Very Large Telescope (VLT) in Chile
With direct imaging using the SPHERE and VLT Imager and Spectrometer for mid-InfraRed (VISIR) instruments on the VLT, we have confirmed the spiral structure of the WR104 system for the first time

Summary

Introduction

The study of massive stars is important for many aspects of stellar evolution and cosmic enrichment. A significant fraction of massive stars are part of in binary systems. The stellar components of these binaries are good candidates to generate gravitational waves by the merging of the resulting black holes or neutron stars. Wolf-Rayet (WR) stars are hot stars with broad emission lines These lines originate from a strong and optically thick wind, which is driven by radiation pressure and reaches a velocity of up to a thousand kilometers per second. This supersonic wind of WR stars exerts a major influence on the immediate surroundings of the star

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Discussion

Conclusion