ALMA and VLA observations of the HD 141569 system

Abstract

We present VLA 9 mm (33 GHz) and archival ALMA 2.9 mm (103 GHz) observations of the HD 141569 system. The VLA observations achieve a resolution of 0.25 arcsec (~28 au) and a sensitivity of 4.7 μJy beam-1. We find (1) a 52 ± 5 μJy point source at the location of HD141569A that shows potential variability, (2) the detected flux is contained within the SEDinferred central clearing of the disc meaning the spectral index of the dust disc is steeper than previously inferred, and (3) the M dwarf companions are also detected and variable. Previous lower resolution VLA observations (semester 14A) found a higher flux density, interpreted as solely dust emission. When combined with ALMA observations, the VLA 14A observations suggested the spectral index, and grain size distribution of HD 141569's disc was shallow and an outlier among debris systems. Using archival ALMA observations of HD 141569 at 0.87 and 2.9 mm, we find a dust spectral index of αmm = 1.81 ± 0.20. The VLA 16A flux corresponds to a brightness temperature of ~5 × 106 K, suggesting strong non-disc emission is affecting the inferred grain properties. The VLA 16A flux density of the M2V companion HD 141569B is 149 ± 9 μJy, corresponding to a brightness temperature of ~2 × 108 K and suggesting significant stellar variability when compared to the VLA14A observations, which are smaller by a factor of ~6.