arXiv subjects

C. Marois

Publications and source records attributed to C. Marois.

26 records · Page 2Linked to original sources

arXiv2005

TRIDENT: an Infrared Differential Imaging Camera Optimized for the Detection of Methanated Substellar Companions

A near-infrared camera in use at the Canada-France-Hawaii Telescope (CFHT) and at the 1.6-m telescope of the Observatoire du Mont-Megantic is described. The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector. Its main feature is to acquire three simultaneous images at three wavelengths across the methane absorption bandhead at 1.6 microns, enabling, in theory, an accurate subtraction of the stellar point spread function (PSF) and the detection of faint close methanated companions. The instrument has no coronagraph and features fast data acquisition, yielding high observing efficiency on bright stars. The performance of the instrument is described, and it is illustrated by laboratory tests and CFHT observations of the nearby stars GL526, Ups And and Chi And. TRIDENT can detect (6 sigma) a methanated companion with delta H = 9.5 at 0.5" separation from the star in one hour of observing time. Non-common path aberrations and amplitude modulation differences between the three optical paths are likely to be the limiting factors preventing further PSF attenuation. Instrument rotation and reference star subtraction improve the detection limit by a factor of 2 and 4 respectively. A PSF noise attenuation model is presented to estimate the non-common path wavefront difference effect on PSF subtraction performance.

astro-ph↗

arXiv2005

Can AB Dor C be a Tight Binary Brown Dwarf?

AB Dor C, a low-mass companion to the young star AB Dor A has recently been imaged. Direct detection and astrometric observations have been used to solve the AB Dor C orbit and obtain a dynamical mass estimate. Near-infrared magnitudes and effective temperatures from models have then been compared with observed values. Models and observations disagree at more than the 2 sigma level. This result prompts Close et al. 2005 to claim that models are overestimating young low-mass object luminosities by roughly a factor of two. This claim is based on the hypothesis that the detected source, AB Dor C, is a single object. Another possible interpretation of the data that was not considered is that AB Dor C is an unresolved binary brown dwarf. Considering that 21 brown dwarfs companions have been found to date around stars and that three of them are confirmed or potential brown dwarf binaries (Gl569Ba & Bb, GL564B & C and Indi Ba & Bb), this suggests that brown dwarf binaries may constitute a significant fraction (14% +/- 8%) of the brown dwarf population around stars. For these reasons, the possibility that AB Dor C is an unresolved binary brown dwarf deserves attention.

astro-ph↗

arXiv2004

La recherche de naines brunes et d'exoplanetes: developpement d'une technique d'imagerie multibande

The technique of simultaneous spectral differential imaging (SSDI) is used to image directly brown dwarfs and exoplanets around nearby stars. An analytical PSF model is first presented with numerical simulations to estimate the PSF noise attenuation performance. A three-wavelength infrared camera (TRIDENT) implementing the SSDI technique is then described. Results from a survey of 35 nearby stars carried out with TRIDENT at the Canada-France-Hawaii telescope are presented. Performance estimates show that a companion 9.5 magnitudes fainter than a star is detectable (6 sigma) at 0.5" separation. An analysis of the observations suggests that non-common path aberrations between TRIDENT optical channels are the limiting factor preventing further PSF noise attenuation. A new camera concept using a multi-wavelength detector featuring a microlens array combined with micro-filters is presented to overcome the non-common path aberration problem. Another imaging technique, differential angular imaging, is also discussed to obtain a reference PSF in each optical channel while observing a target. Finally, the accuracy of FFT-based image shifting, scaling and rotating algorithms is studied to show that a companion 10^9 times fainter than a star can theoretically be detected by those algorithms.

astro-ph↗

arXiv2004

Differential Imaging with a Multicolor Detector Assembly: A New ExoPlanet Finder Concept

Simultaneous spectral differential imaging is a high contrast technique by which subtraction of simultaneous images reduces noise from atmospheric speckles and optical aberrations. Small non-common wave front errors between channels can seriously degrade its performance. We present a new concept, a multicolor detector assembly (MCDA), which can eliminate this problem. The device consists of an infrared detector and a microlens array onto the flat side of which a checkerboard pattern of narrow-band micro-filters is deposited, each micro-filter coinciding with a microlens. Practical considerations for successful implementation of the technique are mentioned. Numerical simulations predict a noise attenuation of 10^-3 at 0.5" for a 10^5 seconds integration on a mH=5 star of Strehl ratio 0.9 taken with an 8-m telescope. This reaches a contrast of 10^-7 at an angular distance of 0.5" from the center of the star image.

astro-ph↗

arXiv2002

Effects of Quasi-Static Aberrations in Faint Companion Searches

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. The camera's main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, that enables a precise subtraction of the primary star PSF while keeping the companion signal. The main limitation is non-common path aberrations between the three optical paths that slightly decorrelate the PSFs. Two types of PSF calibrations are combined with the differential simultaneous imaging technique to further attenuate the PSF: reference star subtraction and instrument rotation to smooth aberrations. It is shown that a faint companion with a DeltaH of 10 magnitudes would be detected at 0.5 arcsec from the primary.

astro-ph↗

arXiv2002

TRIDENT: an infrared camera optimized for the detection of methanated substellar companions around nearby stars

A near-infrared (0.85-2.5 microns) camera in use at the Canada-France-Hawaii Telescope and at the 1.6m telescope of the Observatoire du Mont-Megantic is described. The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector. Its main feature is to acquire three simultaneous images at three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, enabling an accurate subtraction of the stellar point spread function (PSF) and the detection of faint close methanated companions. The instrument has no coronagraph and features a fast (1 MHz) data acquisition system without reset anomaly, yielding high observing efficiencies on bright stars. The performance of the instrument is described, and it is illustrated by CFHT images of the nearby star Ups And. TRIDENT can detect (3 sigma) a methanated companion with DeltaH=10 at 0.5 arcsec from the star in one hour of observing time. Non-common path aberrations between the three optical paths are the limiting factors preventing further PSF attenuation. Reference star subtraction and instrument rotation improve the detection limit by one order of magnitude.

astro-ph↗

arXiv2002

Differential Simultaneous Imaging and Faint Companions: TRIDENT First Results from CFHT

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. Its main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, that enables a precise subtraction of the primary star PSF while keeping the companion signal. Thirty-five stars have been observed in two observing missions, with no detection so far. It is shown that a faint companion with a DeltaH of 10 magnitudes would be detected at 0.5 arcsec from the primary.

astro-ph↗

arXiv2002

Searching for Faint Companions with the TRIDENT Differential Simultaneous Imaging Camera

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. Its main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, that enables a precise subtraction of the primary star PSF while keeping the companion signal. Gl229 and 55Cnc observations are presented to demonstrate TRIDENT subtraction performances. It is shown that a faint companion with a DeltaH of 10 magnitudes would be detected at 0.5 arcsec from the primary.

astro-ph↗