High-contrast optical imaging of companions: the case of the brown dwarf binary HD 130948 BC

Abstract

Context. High-contrast imaging at optical wavelengths is limited by the modest correction of conventional near-IR optimized AO systems. We take advantage of new fast and low-readout-noise detectors to explore the potential of fast imaging coupled to postprocessing techniques to detect faint companions of stars at small angular separations. Aims. We have focused on I-band direct imaging of the previously detected brown dwarf binary HD 130948 BC, attempting to spatially resolve the L2+L2 system considered as a benchmark for the determination of substellar objects dynamical masses. Methods. We used the lucky-imaging instrument FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited images of HD 130948 with ∼0.1 resolution. In order to improve the detectability of the faint binary in the vicinity of a bright (I = 5.19 ± 0.03) solar-type star, we implemented a post-processing technique based on wavelet transform filtering of the image, which allows us to strongly enhance the presence of point-like sources in regions where the primary halo generally dominates. Results. We detect for the first time the binary brown dwarf HD 130948 BC in the optical band I with a SNR ∼ 9 at 2.561 ± 0.007 (46.5 AU) from HD 130948 A and confirm in two independent datasets (2008 May 29 and July 25) that the object is real, as opposed to time-varying residual speckles. We do not resolve the binary, which can be explained by astrometric results posterior to our observations, which predict a separation below the telescope resolution. We reach a contrast of ΔI = 11.30 ± 0.11 at this distance, and estimate a combined magnitude for this binary I = 16.49 ± 0.11 and a I − J color of 3.29 ± 0.13. At 1 , we reach a detectability 10.5 mag fainter than the primary after image post-processing. Conclusions. We obtain on-sky validation of a technique based on speckle imaging and wavelet-transform post-processing, which improves the high-contrast capabilities of speckle imaging. The I − J color measured for the BD companion is slightly bluer, but still consistent with what is typically found for L2 dwarfs (∼3.4-3.6).

HADES RV program with HARPS-N at the TNG GJ 3998: An early M-dwarf hosting a system of super-Earths

“…FastCam is an optical imager with a low noise EMCCD camera which allows to obtain speckle-featuring not saturated images at a fast frame rate, see Labadie et al (2011).…”

Laboratory and telescope demonstration of the TP3-WFS for the adaptive optics segment of AOLI

“…However, this technique suffers from two important limitations. First, resolutions similar to the HST can only be achieved in telescopes with sizes below 2.5m (Femenía et al 2011;Labadie et al 2011). Second, most of the images are discarded, meaning that only relatively bright targets can be observed.…”

Commissioning and first observations with Wide FastCam at the Telescopio Carlos Sánchez

“…Since the develop of FastCam, the high optical spatial resolution group at the IAC has worked with EMCCDs, developing new instruments, such as AOLI (see Velasco et al [3,2015] and Mackay et al [4,2014]), and producing many very valuable science results (e.g. Velasco et al [5,2016], Femenía et al [6,2011] and Labadie et al [7,2011]). As a needed complement of these observations, along the years a huge amount of laboratory and telescope hours have been devoted to characterize the EMCCD detectors in use by these instruments.…”