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 post-processing 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).
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 2011
- DOI:
- 10.1051/0004-6361/201014358
- arXiv:
- arXiv:1009.5670
- Bibcode:
- 2011A&A...526A.144L
- Keywords:
-
- instrumentation: high angular resolution;
- methods: observational;
- techniques: image processing;
- binaries: close;
- brown dwarfs;
- circumstellar matter;
- Astrophysics - Instrumentation and Methods for Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- accepted in A\&