29 research outputs found
Reconnaissance of the HR 8799 exosolar system. II. Astrometry and orbital motion
This is the final version of the article. Available from the American Astronomical Society / IOP Publishing via the DOI in this record.We present an analysis of the orbital motion of the four substellar objects orbiting HR 8799. Our study relies on the published astrometric history of this system augmented with an epoch obtained with the Project 1640 coronagraph with an integral field spectrograph (IFS) installed at the Palomar Hale telescope. We first focus on the intricacies associated with astrometric estimation using the combination of an extreme adaptive optics system (PALM-3000), a coronagraph, and an IFS. We introduce two new algorithms. The first one retrieves the stellar focal plane position when the star is occulted by a coronagraphic stop. The second one yields precise astrometric and spectrophotometric estimates of faint point sources even when they are initially buried in the speckle noise. The second part of our paper is devoted to studying orbital motion in this system. In order to complement the orbital architectures discussed in the literature, we determine an ensemble of likely Keplerian orbits for HR 8799bcde, using a Bayesian analysis with maximally vague priors regarding the overall configuration of the system. Although the astrometric history is currently too scarce to formally rule out coplanarity, HR 8799d appears to be misaligned with respect to the most likely planes of HR 8799bce orbits. This misalignment is sufficient to question the strictly coplanar assumption made by various authors when identifying a Laplace resonance as a potential architecture. Finally, we establish a high likelihood that HR 8799de have dynamical masses below 13 MJup, using a loose dynamical survival argument based on geometric close encounters. We illustrate how future dynamical analyses will further constrain dynamical masses in the entire system
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When you want it done right now: Experience from programming hard real time systems in Xenomai for the Magdalena Ridge Observatory interferometer
Xenomai is a hard real-time operating system suitable for many low-latency tasks encountered in astronomical instruments. It is open source, has microsecond-level response time and coexists with the Linux kernel, thereby facilitating the execution of hard real time code on Linux systems. This presentation presents experience coding systems with Xenomai for the Magdalena Ridge Observatory Interferometer. Firstly an overview of Xenomai is given, focusing on how it achieves hard real time performance and how it can be used to interact with hardware using Linux-like device drivers. Secondly, a generic outline of the development process is given, including the mindset needed, general pitfalls to be avoided, and strategies that can be employed depending on how open the hardware and any existing source code is. Two specific case studies from the Magdalena Ridge Observatory are then presented: Firstly, the fast tip-tilt system, which must read out a 32x32 subframe from an EMCCD camera, determine a stellar image centroid and send a correction voltage to a tip-tilt mirror at up to 1kHz. Secondly, the MROI delay line metrology system, which must read laser metrology position data for ten delay line trolleys and send correction voltages to their cat’s eyes at 5kHz. Finally, some future challenges to development with Xenomai and other hard real time operating systems are discussed: processors with functionality such as system management interrupts that are beyond operating system control, and the trend towards buffered or closed interfaces between computers and hardware.Grant from New Mexico Tech, a university in the United States of America. The ultimate source is the US Air Force Research Labs. It is in the process of being imported into Simplectic
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Deployment of beam alignment hardware at the magdalena ridge observatory interferometer
The first unit telescope of Ridge Observatory Interferometer is integrated on the array and starlight has been observed in the Beam Combining Area for the first time. From the telescope, the beam travels in vacuum over a path of >50m, including a beam relay system and delay line. This feat was made possible by a prototype version of the Automated Alignment System that we are developing for minimising fringe visibility loss due to misalignment. We present results of on-site validation of UTLIS, a reference light source at the unit telescope acting as a proxy for starlight, and BEASST, a Shack-Hartmann sensor that simultaneously detects beam angle and position