This article reports the advances on the development of mid-infrared integrated optics for stellar interferometry. The devices are fabricated by laser writing techniques on chalcogenide glasses. Laboratory characterizaton is reported and analyzed.
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-proce
ssing techniques to detect faint companions to stars at small separations. We have focused on I-band direct imaging of the previously detected brown dwarf binary HD130948BC,attempting to spatially resolve the L2+L2 benchmark system. We used the Lucky-Imaging instrument FastCam at the 2.5-m Nordic Telescope to obtain quasi diffraction-limited images of HD130948 with ~0.1 resolution.In order to improve the detectability of the faint binary in the vicinity of a bright (I=5.19 pm 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 dominates. We detect for the first time the BD binary HD130948BC in the optical band I with a SNR~9 at 2.561pm 0.007 (46.5 AU) from HD130948A and confirm in two independent dataset 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 that predict a separation below the NOT resolution.We reach at this distance a contrast of dI = 11.30 pm 0.11, and estimate a combined magnitude for this binary to I = 16.49 pm 0.11 and a I-J colour 3.29 pm 0.13. At 1, we reach a detectability 10.5 mag fainter than the primary after image post-processing. We obtain on-sky validation of a technique based on speckle imaging and wavelet-transform processing,which improves the high contrast capabilities of speckle imaging.The I-J colour measured for the BD companion is slightly bluer, but still consistent with what typically found for L2 dwarfs(~3.4-3.6).
In this paper, we present an original observational approach, which combines, for the first time, traditional speckle imaging with image post-processing to obtain in the optical domain diffraction-limited images with high contrast (1e-5) within 0.5 t
o 2 arcseconds around a bright star. The post-processing step is based on wavelet filtering an has analogy with edge enhancement and high-pass filtering. Our I-band on-sky results with the 2.5-m Nordic Telescope (NOT) and the lucky imaging instrument FASTCAM show that we are able to detect L-type brown dwarf companions around a solar-type star with a contrast DI~12 at 2 and with no use of any coronographic capability, which greatly simplifies the instrumental and hardware approach. This object has been detected from the ground in J and H bands so far only with AO-assisted 8-10 m class telescopes (Gemini, Keck), although more recently detected with small-class telescopes in the K band. Discussing the advantage and disadvantage of the optical regime for the detection of faint intrinsic fluxes close to bright stars, we develop some perspectives for other fields, including the study of dense cores in globular clusters. To the best of our knowledge this is the first time that high contrast considerations are included in optical speckle imaging approach.
Aims: In the context of space interferometry missions devoted to the search of exo-Earths, this paper investigates the capabilities of new single mode conductive waveguides at providing modal filtering in an infrared and monochromatic nulling experim
ent; Methods: A Michelson laser interferometer with a co-axial beam combination scheme at 10.6 microns is used. After introducing a Pi phase shift using a translating mirror, dynamic and static measurements of the nulling ratio are performed in the two cases where modal filtering is implemented and suppressed. No additional active control of the wavefront errors is involved. Results: We achieve on average a statistical nulling ratio of 2.5e-4 with a 1-sigma upper limit of 6e-4, while a best null of 5.6e-5 is obtained in static mode. At the moment, the impact of external vibrations limits our ability to maintain the null to 10 to 20 seconds.; Conclusions: A positive effect of SM conductive waveguide on modal filtering has been observed in this study. Further improvement of the null should be possible with proper mechanical isolation of the setup.
