In the course of our VLTI young stellar object PIONIER imaging program, we have identified a strong visibility chromatic dependency that appeared in certain sources. This effect, rising value of visibilities with decreasing wavelengths over one base, is also present in previous published and archival AMBER data. For Herbig AeBe stars, the H band is generally located at the transition between the star and the disk predominance in flux for Herbig AeBe stars. We believe that this phenomenon is responsible for the visibility rise effect. We present a method to correct the visibilities from this effect in order to allow "gray" image reconstruction software, like Mira, to be used. In parallel we probe the interest of carrying an image reconstruction in each spectral channel and then combine them to obtain the final broadband one. As an illustration we apply these imaging methods to MWC158, a (possibly Herbig) B[e] star intensively observed with PIONIER. Finally, we compare our result with a parametric model fitted onto the data.
The visitor instrument PIONIER provides VLTI with improved imaging capabilities and sensitivity. The in-
strument started routinely delivering scientic data in November 2010, that is less than 12 months after being
approved by the ESO Science and Technical Committee. We recall the challenges that had to be tackled to design, built and commission PIONIER. We summarize the typical performances and some astrophysical results obtained so far. We conclude this paper by summarizing lessons learned.
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to
see its first fringes in 2010. It combines four ATs or four UTs
using a pairwise ABCD integrated optics combiner that can also be
used in scanning mode. It provides low spectral resolution in H and K band. PIONIER is designed for
imaging with a specific emphasis on fast fringe recording to allow
closure-phases and visibilities to be precisely measured. In
this work we provide the detailed description of the instrument and
present its updated status.
The science objectives of VITRUV is to investigate the morphology of compact astrophysical objects in optical wavelengths like the environment of AGN, star forming regions, stellar surfaces. This instrument will take full advantage of the VLTI site with 4 very large telescopes and 4 auxiliary telescopes. The instrument concept is to built aperture synthesis images like the millimeter-wave radiointerferometer of the IRAM Plateau de Bure. VITRUV coupled to the VLTI will have similar and even better resolution than ALMA. The astrophysical specifications although not yet finalized will be a temporal resolution of the order of 1 day, spectral resolution from 100 to 30,000, image dynamic from 100 to 1,000, a field of view of 1 arcsec for an initial wavlength coverage from 1 to 2.5 microns that could be extended from 0.5 to 5 microns. The technology that is contemplated at this stage is integrated optics.
In this poster, we examine the science potential of an 800 meter interferometer such as the OHANA Array. The working assumptions are a K = 12 limiting magnitude, a 0.5 milliarcsecond resolution at K band, and a small (diffraction limit of individual telescope) field of view. The science cases described herein are by no means exhaustive and perhaps not even the ones that will eventually be carried out, but serve to illustrate the potential of the array. We expect that operation of the array will be proposal driven, so the actual science will come from the Mauna Kea communities. Our philosophy is that any measurement that can be made at a dedicated interferometer facility should not be a strong driver for OHANA. Therefore the science areas discussed in the poster focus on very high angular resolution measurements of faint sources. In some cases, science which can be addressed with simpler or dedicated facilities at an exploratory level can be carried to a significant new capability with OHANA. A limitng magnitude of 12 was obtained by simple computations, but first tests on the sky with the injection module (See adjacent poster on Phase I) will help narrow down this figure. At such sensitivity, Cepheid pulsations can be studied in considerable detail for a wide range of stellar parameters, leading to enhanced confidence in the accuracy of their use for distance measurement with minimal extrapolation or inferrence. The disk/star interaction zone in young stellar objects can be resolved with unprecedented detail for a range of masses and ages, providing direct information about the jet formation region, accretion rates and disk conditions. The broad line region of active galactic nuclei can be studied in a large number of sources of differing characteristics, testing specific models for AGN nuclear structure. For OHANA Phase III, a dual-star phase tracking capability is planned. With the resulting increased sensitivity, direct brown dwarf diameter measurement will provide a strong check on evolution models. Microlensing events could be resolved and provide unique new information about the lensing and the lensed objects.
OHANA will be a near-infrared long-baseline interferometer. It will be located at the summit of Mauna Kea and will link, by fiber optics, the existing telescopes equipped with adaptive optics into a giant interferometer. OHANA will have baselines up to 4 times longer than VLTI's. The improved resolution will be complementary to VLTI's and will be very well suited to study the star formation processes. Indeed, measuring and understanding the circumstellar environment of young stellar objects (YSOs), especially their accretion disk, is the key to understand the formation of planetary systems. Up to an age of about 10 million years, these disks are thought to be rich enough in dust and gas to host planet formation in their central regions. But this affirmation relies solely on an extrapolation of measurements and models of the outer, tenuous and cold parts of disks where planets cannot form because the measured density is too low. One can therefore rightly wonder how realistic these extrapolations to the central regions are and how secure is the claim that planets are forming around the young solar-like T Tauri stars. The disks' central region, located within a few stellar radii from the center, will become observable by OHANA. In this contribution we will show that OHANA will allow to measure and understand the structure of the accretion disk and differentiate between different models: equatorial vs. magnetospheric accretion; magnetized vs. standard disks, etc. These observations are fundamental to understand the link between the accretion process and the outflow/jet phenomenon frequently observed in these stars.
We present optical linear polarimetry of 9 ultra cool field
dwarfs. The linear polarisation of each L dwarf we measured is
less than 0.2 percent. Three dwarfs have polarisations compatible with zero, two are marginal detections, and three have significant polarisation. Due to their small distance, an insterstellar origin for the detected polarisation can be safely ruled out. Our detections confirm that dust is present in the atmosphere of these L dwarfs and that the scattering geometry is not symmetric.
Rethinking the efficient use of 4m-class telescopes in the dawning era of larger facilities is a timely but challenging debate. The extensive use of PUEO for imaging (and now spectroscopy) has kept CFHT at the forefront of scientific research with adaptive optics since its commissioning in 1996. Even though larger facilities are now starting to think about ways to implement high order AO systems, we believe the medium size of the CFHT and the excellent quality of the site on Mauna Kea is a perfect combination to reach the highest performances with a high order AO system.
The fields of application of high order adaptive optics are exciting: They include extremely high contrast imaging and coronography in the near-infrared and diffraction-limited imaging in the optical, with the corresponding gain in angular resolution. In this paper we present a quick description of a few specific astrophysical problems that would benefit from an upgraded AO system at the Canada-France-Hawaii Telescope.
More technical details about the upgrade of PUEO are presented by Lai et al. and Cuillandre et al. in these proceedings, see papers 4839-78 and 4839-31.
Rethinking the efficient use of 4m-class telescopes in the dawning era of larger facilities is a timely but challenging debate. The extensive use of PUEO for imaging (and now spectroscopy) has kept CFHT at the forefront of scientific research with adaptive optics since its commissioning in 1996. Even though larger facilities are now starting to think about ways of implementing high order AO systems, we believe the medium size of the CFHT and the excellent quality of our site on Mauna Kea is a perfect combination to reach the highest performances with a high order AO system.
The fields of application of high order adaptive optics are exciting: They include extremely high contrast imaging and coronography in the near-infrared and diffraction-limited imaging in the optical, with the corresponding gain in angular resolution. Specific science examples are described in and adjacent paper (Menard et al, these proceedings (4839-133)), and planned instrumentation in the form of four quadrant coronograph or existing dual (or triple) wavelength imagers (such as TRIDENT) would benefit tremendously from >90% Strehl ratios in the K band.
Simulations of a high order (104 electrodes) curvature system have been performed and produce the required performance and are presented in an adjacent paper (Lai & Craven-Bartle, (4860-28)). Technologically, the system is quite simple and re-uses most of the opto-mechanics of the existing PUEO. Deformable mirrors and real time computers are well within existing (and commercially available) specifications. An innovative solution of using a dedicated low read noise CCD camera (specifically for curvature systems) overcomes the potential cost drawbacks of using avalanche photo-diodes (APDs). This detector is described in detail in an adjacent paper (Cuillandre et al, these proceedings (4839-31)).
Until now, only avalanche photodiodes (APD) have been used as the detectors in curvature wavefront sensors in astronomy. This is due to the strict requirements of very short integration time and very low readout noise. In 1999, Beletic et al. invented a new CCD design which should achieve the same performance as APDs but with higher reliability and lower cost. In addition, this CCD has higher quantum efficiency than APD modules and larger dynamic range, eliminating the need for neutral density filters on bright objects. The CCD was designed and fabricated by MIT Lincoln Laboratory in collaboration with ESO and IfA. R. Dorn extensively tested the CCD in laboratory at ESO and proved that it achieves the predicted performance. CFHT is currently implementing this CCD on PUEO, CFHT’s Adaptive Optics system, to assess its performance for the first time in real conditions on the sky for a direct comparison with the current 19 APD detector system. In this article we present the current implementation scheme and discuss the upgrade we foresee for PUEO NUI, a 104-element high-order curvature AO system envisaged to replace the current AO system at Canada-France-Hawaii Telescope.
We utilized AO to discover a moon around asteroid 45 Eugenia by use of the PUEO AO facility at CFHT. With PUEO we performed a search for asteroidal satellites among two dozen asteroids, achieving moderate Strehl ratios (35%) and FWHM of about 0.12' at H band. During this survey, we detected a faint close companion to 45 Eugenia. The satellite was 6.14 magnitudes (at 1.65 micrometer) fainter and located at most 0.75' from Eugenia. Without the ability of AO to sharpen the contrast and increase the resolution to 0.1', the detection of this companion would have been impossible with ground-based telescopes. The companion was found to be in a 1200 km circular orbit with a period of 4.7 days. We discovered that the bulk density of the large (215 km) asteroid 45 Eugenia is a surprisingly low 1.2 g/cm3. This has lead to the exciting possibilities that either this main belt asteroid is a burned out comet or has a hollow 'rubble-pile' structure.
Young Stellar Objects (YSOs) are the builders of worlds. During its infancy, a star transforms ordinary interstellar dust particles into astronomical gold: planets to say the process is complex, and largely unknown to data. Yet, violent and spectacular events of mass ejection are witnessed, disks in keplerian rotation are detected, multiple stars dancing around each other are found. These are as many traces of the stellar and planet formation process. The high angular resolution provided by adaptive optics, and the related gain in sensitivity, have allowed major breakthrough discoveries to be made in each of these specific fields and our understanding of the various physical processes involved in the formation of a star has leaped forward tremendously over the last few years. In the following, meant as a report of the progress made recently in star formation due to adaptive optics, we will describe new results obtained at optical and near- infrared wavelengths, in imaging and spectroscopic modes. Our images of accretion disks and ionized stellar jets permit direct measurements of many physical parameters and shed light into the physics of the accretion and ejection processes. Although the accretion/ejection process so fundamental to star formation is usually studied around single objects, most of young stars form as part of multiple systems. We also present our findings on how the fraction of stars in binary systems evolves with age. The implications of these results on the conditions under which these stars must have formed are discussed.
The design of adaptive optics system requires astrophysically driven requirements and specifications. We present here the study performed to help specifying and designing the ESO Nasmyth Adaptive Optics System of the VLT.