High-contrast observations of brown dwarf companion HR 2562 B with the vector Apodizing Phase Plate coronagraph

The vector Apodizing Phase Plate (vAPP) is a class of pupil plane coronagraph that enables high-contrast imaging by modifying the Point Spread Function (PSF) to create a dark hole of deep flux suppression adjacent to the PSF core. Here, we recover the known brown dwarf HR 2562 B using a vAPP coronagraph, in conjunction with the Magellan Adaptive Optics (MagAO) system, at a signal-to-noise of S/N = 3.04 in the lesser studied L-band regime. The data contained a mix of field and pupil-stabilized observations, hence we explored three different processing techniques to extract the companion, including Flipped Differential Imaging (FDI), a newly devised Principal Component Analysis (PCA)-based method for vAPP data. Despite the partial field-stabilization, the companion is recovered sufficiently to measure a 3.94 mu m narrow-band contrast of (3.05 +/- 1.00) x 10(-4) (Delta m(3.94 mu m) = 8.79 +/- 0.36 mag). Combined with archival GPI and SPHERE observations, our atmospheric modelling indicates a spectral type at the L/T transition with mass M = 29 +/- 15 M-Jup, consistent with literature results. However, effective temperature and surface gravity vary significantly depending on the wavebands considered (1200 <= T-eff(K) <= 1700 and 4.0 <= log(g)(dex) <= 5.0), reflecting the challenges of modelling objects at the L/T transition. Observations between 2.4 and 3.2 mu m will be more effective in distinguishing cooler brown dwarfs due to the onset of absorption bands in this region. We explain that instrumental scattered light and wind-driven halo can be detrimental to FDI+PCA and thus must be sufficiently mitigated to use this processing technique. We thus demonstrate the potential of vAPP coronagraphs in the characterization of high-contrast substellar companions, even in sub-optimal conditions, and provide new complementary photometry of HR 2562 B.

Automated summary

The vAPP coronagraph is effective in high-contrast imaging by modifying the PSF to create a dark hole for deep flux suppression. In this study, the vAPP coronagraph was used to recover the brown dwarf HR 2562 B in the L-band, with successful extraction of the companion using different processing techniques. The atmospheric modeling of HR 2562 B indicates a spectral type at the L/T transition, with varying effective temperature and surface gravity depending on the wavebands considered.