Optimized Wide-Field Survey Telescope Using Adaptive Optics

We describe a new technique for ground-based telescopic surveys that can deliver a wide field of view and nearly diffraction-limited image quality. We discuss a very low cost, yet sensitive and efficient, concept to perform science previously considered from space. For ground-based telescopes with small D/r0 (aperture over turbulence cell diameter) a significant improvement in point source sensitivity can be achieved with tip-tilt correction only. However, the solid angle over which image motion is constant is typically less than an arcminute. To achieve tip-tilt correction over a larger field we propose to use a high order adaptive optics system where one pupil sub-aperture now corresponds to one isokinetic patch. The high order deformable mirror is conjugated to an atmospheric height where the tip-tilt "beams" separate from each other while the overall tip-tilt can be taken out with a tip-tilt secondary mirror conjugated to low height. One source per square arcminute with V ≤ 18^m is required for the determination of the image motion, allowing a sky coverage of more than 50%. The improvement over seeing limited observations is maximal at D/r_0 ≈ 4 with a S/N improvement of a factor of four. An inexpensive system with 500 actuators can correct a field of view of 0.4 × 0.4 deg^2. It is thus well-suited for searches of point sources, e.g. high-z SN Ia or other transient phenomena

Discovery of the Pre-Main Sequence Population of the Stellar Association LH 95 in the Large Magellanic Cloud with Hubble Space Telescope ACS Observations

We report the discovery of an extraordinary number of pre-main sequence (PMS) stars in the vicinity of the stellar association LH 95 in the Large Magellanic Cloud (LMC). Using the {\em Advanced Camera for Surveys} on-board the {\em Hubble} Space Telescope in wide-field mode we obtained deep high-resolution imaging of the main body of the association and of a nearby representative LMC background field. These observations allowed us to construct the color-magnitude diagram (CMD) of the association in unprecedented detail, and to decontaminate the CMD for the average LMC stellar population. The most significant result is the direct detection of a substantial population of PMS stars and their clustering properties with respect to the distribution of the higher mass members of the association. Although LH 95 represents a rather modest star forming region, our photometry, with a detection limit $V$ \lsim 28 mag, reveals in its vicinity more than 2,500 PMS stars with masses down to $\sim 0.3$ M{\solar}. Our observations offer, thus, a new perspective of a typical LMC association: The stellar content of LH 95 is found to extend from bright OB stars to faint red PMS stars, suggesting a fully populated Initial Mass Function (IMF) from the massive blue giants down to the sub-solar mass regime.Comment: Accepted for Publication in ApJ Letters - 4 Pages ApJ paper format - 3 figures in low-resolution/grayscal

The [Ne III]/[Ne II] line ratio in NGC 253

We present results of the mapping of the nucleus of the starburst galaxy NGC 253 and its immediate surroundings using the Infrared Spectrograph on board the Spitzer Space Telescope. The map is centered on the nucleus of the galaxy and spans the inner 800 × 688 pc^2. We perform a brief investigation of the implications of these measurement on the properties of the star formation in this region using theories developed to explain the deficiency of massive stars in starbursts

Optimized Wide-Field Survey Telescope Using Adaptive Optics

We describe a new technique for ground-based telescopic surveys that can deliver a wide field of view and nearly diffraction-limited image quality. We discuss a very low cost, yet sensitive and efficient, concept to perform science previously considered from space. For ground-based telescopes with small D/r0 (aperture over turbulence cell diameter) a significant improvement in point source sensitivity can be achieved with tip-tilt correction only. However, the solid angle over which image motion is constant is typically less than an arcminute. To achieve tip-tilt correction over a larger field we propose to use a high order adaptive optics system where one pupil sub-aperture now corresponds to one isokinetic patch. The high order deformable mirror is conjugated to an atmospheric height where the tip-tilt "beams" separate from each other while the overall tip-tilt can be taken out with a tip-tilt secondary mirror conjugated to low height. One source per square arcminute with V ≤ 18^m is required for the determination of the image motion, allowing a sky coverage of more than 50%. The improvement over seeing limited observations is maximal at D/r_0 ≈ 4 with a S/N improvement of a factor of four. An inexpensive system with 500 actuators can correct a field of view of 0.4 × 0.4 deg^2. It is thus well-suited for searches of point sources, e.g. high-z SN Ia or other transient phenomena

Towards Symbolic Model-Based Mutation Testing: Combining Reachability and Refinement Checking

Model-based mutation testing uses altered test models to derive test cases that are able to reveal whether a modelled fault has been implemented. This requires conformance checking between the original and the mutated model. This paper presents an approach for symbolic conformance checking of action systems, which are well-suited to specify reactive systems. We also consider nondeterminism in our models. Hence, we do not check for equivalence, but for refinement. We encode the transition relation as well as the conformance relation as a constraint satisfaction problem and use a constraint solver in our reachability and refinement checking algorithms. Explicit conformance checking techniques often face state space explosion. First experimental evaluations show that our approach has potential to outperform explicit conformance checkers.Comment: In Proceedings MBT 2012, arXiv:1202.582

Preliminary optical design for the common fore optics of METIS

METIS is the Mid-infrared E-ELT Imager and Spectrograph, which will provide outstanding observing capabilities, focusing on high angular and spectral resolution. It consists of two diffraction-limited imagers operating in the LM and NQ bands respectively and an IFU fed diffraction-limited high-resolution (R=100,000) LM band spectrograph. These science subsystems are preceded by the common fore optics (CFO), which provides the following essential functionalities: calibration, chopping, image de-rotation, thermal background and stray light reduction. We show the evolution of the CFO optical design from the conceptual design to the preliminary optical design, detail the optimization steps and discuss the necessary trade-offs