Douglas L. Miller

An imaging survey for extrasolar planets around 45 close, young stars with the simultaneous differential imager at the very large telescope and MMT

Wepresent theresultsof asurveyof 45young(P250Myr), close(P50pc) starswiththeSimultaneous Differential Imager (SDI) implemented at the VLT and the MMT for the direct detection of extrasolar planets. As part of the survey, we observed 54 objects, consisting of 45 close, young stars; two more distant ( 2 � which behaved consistently like a real object. From our survey null result,we can rule out (with 93% confidence) a model planet population where N(a) / constant out to a distance of 45 AU.

Large Binocular Telescope Adaptive Optics System: new achievements and perspectives in adaptive optics

The Large Binocular Telescope (LBT) is a unique telescope featuring two co-mounted optical trains with 8.4m primary mirrors. The telescope Adaptive Optics (AO) system uses two innovative key components, namely an adaptive secondary mirror with 672 actuators and a high-order pyramid wave-front sensor. During the on-sky commissioning such a system reached performances never achieved before on large ground-based optical telescopes. Images with 40mas resolution and Strehl Ratios higher than 80% have been acquired in H band (1.6 μm). Such images showed a contrast as high as 10-4. Based on these results, we compare the performances offered by a Natural Guide Star (NGS) system upgraded with the state-of-the-art technology and those delivered by existing Laser Guide Star (LGS) systems. The comparison, in terms of sky coverage and performances, suggests rethinking the current role ascribed to NGS and LGS in the next generation of AO systems for the 8-10 meter class telescopes and Extremely Large Telescopes (ELTs).

MMT adaptive secondary: first AO closed-loop results

The adaptive secondary for the MMT is the first mirror of its kind. It was designed to allow the application of wavefront corrections (including tip-tilt) directly at the secondary mirror location. Among the advantages of such a choice for adaptive optics operation are higher throughput, lower emissivity, and simpler optical setup. Furthermore, this specific implementation provides capabilities that are not found in most correctors including internal position feedback, large stroke (to allow chopping) and provision for absolute position calibration. The mirror has now been used at the MMT during several runs where it has performed reliably. In this paper we discuss the mirror operation and AO performance achieved during these runs in which the adaptive secondary has been operating in conjunction with a Shack-Hartmann wavefront sensor as part of the MMT adaptive optics system. In particular we mention a residual mirror position error due to wind buffeting and other errors of ≈ 15 nm rms surface and a stable closed loop operation with a 0dB point of the error transfer function in the range 20-30 Hz limited mainly by the wavefront sensor maximum frame rate. Because of the location of the adaptive secondary with respect to the wavefront sensor camera, reimaging optics are required in order to perform the optical interaction matrix measurements needed to run the AO loop. This optical setup has been used in the lab but not replicated at the telescope so far. We will discuss the effects of the lack of such an internal calibration on the AO loop performances and a possible alternative to the lab calibration technique that uses directly light from sky objects.

Supernova absolute-magnitude distributions

The Asiago Supernova Catalogue and the Nearby Galaxies Catalog are used to study the absolute-magnitude distributions of supernovae. SNe Ia that appear to be subluminous are in highly inclined disk galaxies, which implies that the apparent dispersion in SN Ia absolute magnitudes is dominated by interstellar extinction in the parent galaxies, and, thus, that SNe Ia are good intrinsic standard candles (sigma below 0.4 mag). An upper limit to the difference between SNe Ib and SNe Ia in the B band is 1.87 mag, but the bolometric difference is smaller. Due to a large intrinsic range in peak absolute magnitude (about 6 mag), the observed sample of SNe II is severely influenced by selection effects; intrinsically faint SNe II (M/B/greater than about -17 for H0 = 75 km/s per Mpc) are much more common than intrinsically bright ones. 45 refs.

MMT-AO: two years of operation with the first adaptive secondary

The Multiple Mirror Telescope (MMT) adaptive optics system (MMT-AO) has been operated in a campaign mode for the last two years. In total seven runs, each lasting about two weeks, have been carried out. During these observational runs a large amount of data have been collected. These data allow us to draw some preliminary conclusions about the overall system performances. In this paper we discuss in detail the achieved performances of the MMT-AO system which is equipped with the first adaptive secondary ever developed. The performances are examined both in terms of number of corrected modes and control bandwidth achieved. We also discuss our attempts to improve the system calibration. This is done by modulating the internal slope offsets while the system is operating in closed loop on the sky.

MMT/AO 5 μm Imaging Constraints on the Existence of Giant Planets Orbiting Fomalhaut at ~13-40 AU

A candidate3MJup extrasolar planet was recently imaged by Kalas et al. usingHubble Space Telescope/Advanced Camera for Surveys and Keck II at 12. �� 7 (96 AU) separation from the nearby (d = 7.7 pc) young (∼200 Myr) A2V star Fomalhaut. Here, we report results from M-band (4.8 μm) imaging of Fomalhaut on 2006 December 5 using the Clio IR imager on the 6.5 m MMT with the adaptive secondary mirror. Our images are sensitive to giant planets at orbital radii comparable to the outer solar system (∼10–40 AU). Comparing our 5σ M-band photometric limits to theoretical evolutionary tracks for substellar objects, our results rule out the existence of planets with masses >2 MJup from ∼13 to 40 AU and objects >13 MJup from ∼ 8t o 40 AU.

Lessons learned from the first adaptive secondary mirror

The adaptive optics system for the 6.5 m MMT, based on a deformable secondary mirror, has been on the sky now for three commissioning runs totalling approximately 30 nights. The mirror has begun to demonstrate uniquely clean point-spread functions, high photon efficiency, and very low background in the thermal infrared. In this paper we review the lessons learned from the first few months of operation. Broadly, the hardware works well, and we are learning how procedures related to operation, system error recovery, and safety should be implemented in software. Experience with the MMT system is now guiding the design of the second and third adaptive secondaries, being built for the Large Binocular Telescope. In this context, we discuss the general requirements for retrofitting an adaptive secondary to an existing large telescope. Finally, we describe how the new technology can support the design of adaptive optics for 30-cm class telescopes, with particular attention to ground-layer adaptive optics (GLAO), where conjugation as close as possible to the turbulence is important.

Use of field aberrations in the alignment of the Large Binocular Telescope optics

It is now well-known that measurement of field-aberration, and in particular the asymmetric field-astigmatism, is required to break the degeneracy of tip-induced and de-centre-induced aberration that exists when only on-axis misalignment aberrations are considered. This paper discusses the application of the measurement of field-aberrations to the alignment of LBT optics. This application ranges from the use of wide field out-of-focus images to determine corrector tip for the red and blue prime-focus correctors, to the use of data acquired by off-axis Shack-Hartman wavefront sensors to actively reposition the hexapod-mounted primary and secondary mirrors so as to simultaneously remove both de-centre and tip/tilt such that the only remaining field-astigmatism has rotational symmetry about the centre of the detector. Also introduced is a novel method to calculate the misalignment aberrations based on an extension of the plate-diagram analysis. It is shown that this method is readily applicable to the calculation of misalignment aberrations for systems of three-or-more powered mirrors, with almost no more computational difficulty than that of the two-mirror case. Results are discussed, as well as work in progress in this area.

Living with adaptive secondary mirrors 365/7/24

The Large Binocular Telescope has two adaptive secondary mirrors which are used for regular observing in both seeinglimited mode and for diffraction-limited mode unlike the adaptive secondaries at the MMT and Magellan telescopes which are swapped in for diffraction-limited observing only. The LBTO secondary mirrors have been in routine operation for ~ 4 years for the first and for ~ 2 years for the second. We review the operational history of these units and discuss the various failure modes unique to adaptive secondaries as compared with rigid secondaries for seeing-limited observing and more conventional adaptive optics systems for diffraction-limited observing.

Scientific results from the MMT Natural Guide Star Adaptive Optics system

The Natural Guide Star Adaptive Optics (NGS AO) system for the MMT Observatory is currently the only AO system in the world that uses a deformable secondary mirror to provide wavefront correction. This approach has unique advantages in terms of optical simplicity, high throughput and low emissivity. Here we present selected scientific results from the past year and a half of operation. Research with the AO system ranges from small scale structure around planetary nebulae, low mass stellar systems in the near IR, through to nulling interferometry in the mid infra-red.