The Navy Precision Optical Interferometer (NPOI) has been recording astronomical observations for nearly two decades, at this point with hundreds of thousands of individual observations recorded to date for a total data volume of many terabytes. To make maximum use of the NPOI data it is necessary to organize them in an easily searchable manner and be able to extract essential diagnostic information from the data to allow users to quickly gauge data quality and suitability for a specific science investigation. This sets the motivation for creating a comprehensive database of observation metadata as well as, at least, reduced data products. The NPOI database is implemented in MySQL using standard database tools and interfaces. The use of standard database tools allows us to focus on top-level database and interface implementation and take advantage of standard features such as backup, remote access, mirroring, and complex queries which would otherwise be time-consuming to implement. A website was created in order to give scientists a user friendly interface for searching the database. It allows the user to select various metadata to search for and also allows them to decide how and what results are displayed. This streamlines the searches, making it easier and quicker for scientists to find the information they are looking for. The website has multiple browser and device support. In this paper we present the design of the NPOI database and website, and give examples of its use.
This paper describes two designs for beam combiners which measures all of the Stokes parameters. The first is the
combination of a optical polarimeter for a single telescope with a simple beam combiner. The second approach
forms 2N beams by splitting the light from each of the N telescopes into orthogonal, linear polarizations. Then,
those 2N beams are fed into a single, multi-beam combiner. We present optical designs for both systems. We
claim the second design is simpler and has the advantage of being easier to calibrate.
We present the results of the fifth Interferometric Imaging Beauty Contest. The contest consists in blind imaging of test data sets derived from model sources and distributed in the OIFITS format. Two scenarios of imaging with CHARA/MIRC-6T were offered for reconstruction: imaging a T Tauri disc and imaging a spotted red supergiant. There were eight different teams competing this time: Monnier with the software package MACIM; Hofmann, Schertl and Weigelt with IRS; Thiebaut and Soulez with MiRA ; Young with BSMEM; Mary and Vannier with MIROIRS; Millour and Vannier with independent BSMEM and MiRA entries; Rengaswamy with an original method; and Elias with the radio-astronomy package CASA. The contest model images, the data delivered to the contestants and the rules are described as well as the results of the image reconstruction obtained by each method. These results are discussed as well as the strengths and limitations of each algorithm.
Optical interferometry and polarimetry have separately provided new insights into stellar astronomy, especially
in the fields of fundamental parameters and atmospheric models. Optical interferometers will eventually add
full-Stokes polarization measuring capabilities, thus combining both techniques. In this paper, we: 1) list the
observables, calibration quantities, and data acquisition strategies for both limited and full optical interferometric
polarimetry (OIP); 2) describe the masking interferometer AMASING and its polarization measuring
enhancement called AMASING-POL; 3) show how a radio interferometry imaging package, CASA, can be used
for optical interferometry data reduction; and 4) present imaging simulations for Be stars.
PRIMA (Phase-Referenced Imaging and Microarcsecond Astrometry) is an ESO/VLTI instrument designed for
phase-referenced imaging and narrow-angle astrometry, dedicated to exoplanet detection. The astrometric datareduction
software (ADRS) is a key component of the system, calculating very precise (~ 10 μas) differential
angular separations projected on the sky. For an interferometer with a baseline of 100 m, this separation
corresponds to measuring the (differential) optical path difference with a precision of 5 - 15 nanometers. This
precision can only be achieved with careful calibration of the instrument, including effects that are irrelevant for
almost any other scientific application. PRIMA is currently being commissioned on Paranal, and we expect to obtain the first astrometric data in September 2010. These data will provide a new insight into the operation and calibration of the instrument.
PRIMA/PACMAN is scheduled for commissioning on Paranal in late 2008 as part of the VLTI. In this paper, we
discuss the important aspects of its astrometric data-reduction software. For example, the top-level requirements,
interfaces to existing ESO software, data types, data levels, and data flow among the recipes dictate the overall
design of any software package. In addition, the complexity of the PACMAN instrument, the long-term nature
of astrometric observations, and the need to improve algorithms as the understanding of the hardware improves,
impose additional requirements on the astrometric data-reduction software.
The PRIMA (Phase-Referenced Imaging and Microarcsecond Astrometry) instrument at ESO/VLTI is scheduled
for commissioning in late 2008. It is designed for phased-referenced imaging and narrow-angle astrometry. The
latter, which is the focus of this paper, may be used for exoplanet detection.
A key PRIMA subsystem consists of two fringe sensing units. They employ polarized and dispersive optics
to measure cross fluxes and differential phases in five narrow K band channels without the need of delay-line
dithering. The differential phases are used to correct the differential delays, which are the primary observables
used to determine relative proper motions, relative parallaxes, and planetary orbits. Real optical components
are imperfect, which means that systematics will appear in the differential phases.
In this paper, we 1) present a closed mathematical form for the differential phase, including small systematic
offsets and random errors; 2) perform Monte Carlo simulations to understand how the small systematic offsets
and random errors affect the differential phases; and 3) show that delay-line stepping can be used to eliminate
the effects of small systematic offsets and random errors.
PRIMA, the instrument for Phase-Referenced Imaging and Micro-arcsecond Astrometry at the VLTI, is currently being
developed at ESO. PRIMA will implement the dual-feed capability, at first for two UTs or ATs, to enable simultaneous
interferometric observations of two objects that are separated by up to 1 arcmin. PRIMA is designed to perform narrow-angle
astrometry in K-band with two ATs as well as phase-referenced aperture synthesis imaging with instruments like
Amber and Midi. In order to speed up the full implementation of the 10 microarcsec astrometric capability of the VLTI
and to carry out a large astrometric planet search program, a consortium lead by the Observatoire de Genève, Max
Planck Institute for Astronomy, and Landessternwarte Heidelberg, has built Differential Delay Lines for PRIMA and is
developing the astrometric observation preparation and data reduction software. When the facility becomes fully
operational in 2009, we will use PRIMA to carry out a systematic astrometric Exoplanet Search program, called ESPRI.
In this paper, we describe the narrow-angle astrometry measurement principle, give an overview of the ongoing hardand
software developments, and outline our anticipated astrometric exoplanet search program.
The Terrestrial Planet Finder Coronagraph (TPF-C) is a future NASA mission to search for earth-like planets around nearby stars. Detecting a planet that is almost 10 billion times fainter than its parent star is extremely difficult, and it has been shown that polarization effects can cause stellar leakage which threatens that sensitivity goal. Building on our earlier work, we now show the combination of basic polarization effects with a representative coronagraph masking system, the eighth order linear field mask and Lyot stop, results in adequate performance.
Due to the highly stringent requirements on planet-detecting nulling
interferometers, many approximations made for standard imaging systems are no longer valid. Analyses using scalar electric fields must be modified to employ vector (polarized) electric fields. In this paper, we present definitions of Stokes-related vectors, Mueller matrices, and the responses (scalar and vector) of single- and dual- Bracewell instruments. We study systematic errors due to instrumental polarization, discussing mismatched elliptically polarized arms, misaligned mirror trains, and beam non-uniformities. Also, we consider systematic errors due to interstellar polarization and polarized starspots. Last, we briefly discuss ancillary science projects that are possible with a space-based interferometer and polarimeter.
One of NASA's two planet-finding missions will be an optical coronagraph. Due to the stringent science requirements, i.e., detecting a planet that is more than a billion times fainter than its parent star, effects that normally do not enter into instrument design must now be considered. One such effect is polarization. This paper has several goals. First, we review scalar diffraction theory (PSFs and Strehl ratios) and extend it to include polarization. Second, we employ a systems-engineering approach to subdivide and categorize instrumental effects, ultimately concentrating on polarizing non-coronagraph components (mirrors). Third, we push the limits of Code-V commercial optical-engineering software to model the polarization behavior for on- and off- axis configurations, using protected-silver and bare-gold mirror coatings at four wavelengths. Last, we present a brief discussion of future tasks: easing polarization requirements, source polarization, and coronagraph masks and stops.
Over the past 25 years, classical optical interferometry (OIC) has become a mature discipline within astronomy. More recently, theoretical work has begun on optical interferometric polarimetry (OIP). Such analyses include adapting modern polarization mathematics from radio astronomy, modeling polarization effects in optical interferometers, and inventing observables with their corresponding output vectors. In this paper, I will demonstrate how OIP may be used to obtain significant results from relatively simple sources, such as
spherically symmetric stellar atmospheres, spotted stars, and scattering envelopes.
Data-reduction algorithms for nulling interferometers can be divided into two categories, model-fitting and imaging. We deal mostly with single-Bracewell instruments because of their simplicity, even though they suffer from “nuisance sources” such as stellar leakage and exo-zodiacal light. To simplify data reduction, we work with the Fourier compo-nents of the time series. Exo-zodiacal light dominates at low frequencies. In principle, it should be possible to model the exo-zodiacal light contribution and separate it from planets using data from a single observation. In practice, however, the uncertainty in the exact form of the exo-zodiacal cloud limits our ability to model and remove its contribution. The only unambiguous way to detect planets with a single Bracewell is to observe a system multiple times through its orbit, and look for month-to-month variations in the Fourier components. To calculate the planet parameters, we discuss a cor-relation technique based on Fourier components instead of time series, in conjunction with a linearized least-squares so-lution. Because the fringe pattern on the sky is wavelength dependent, observations over multiple bandpasses signifi-cantly increases the confidence in planet detection. These algorithms may be used with other types of nulling interfer-ometers. We briefly discuss their application to dual Bracewell data.
Polarization plays a significant role in nulling interferometry and should be considered early in the instrument design process. In this paper, I demonstrate that mirror trains with near-normal incidence angles increase the leakage into the central null more than other mirror trains for a given amount of misalignment perpendicular to the incidence plane. Also, throughput and polarization non-uniformity across a wave front will significantly increase the leakage. To simplify top-level modeling of this effect, I derive a "throughput/polarization" version of the Strehl ratio.
We describe the array metrology system of the Navy Prototype Optical Interferometer, a long-baseline interferometer whose purpose is to determine precise positions of bright stars and image the surfaces and circumstellar environments of stars and stellar systems. For the astrometric array of the NPOI to achieve its design goal of wide-angle astrometric precision of 1-3 milliarcseconds on 20 m baselines, an extensive laser metrology system is employed to measure the three-dimensional motions of those baselines with respect to an Earth-fixed reference system to an accuracy of approximately 100 nm. The array metrology system is described, along with its associated data analysis software, test results, and the application of those results to the analysis of astrometric data. It is shown that at the current stage of its development, the array metrology system is capable of monitoring the variations in the geometry of the astrometric array with micron-level precision.
In this paper, I discuss the need for optical interferometric polarimetry and demonstrate that it is possible with existing technology. Coherent averaging is required; it may be accomplished simply with the addition of a non-polarizing beam splitter after the beam combiner. I define three observables and their corresponding output vectors. One vector is identical to the normalized Stokes vector obtained from classical polarimetry, while the other two are related to the Stokes visibility vector. Calibration of the instrument requires only separate zero-spacing observations of calibrator stars on each of the individual arms - no interferometric measurements are necessary. For a large class of objects, it is possible to create images in all Stokes parameters with a single variable-length baseline.
The Navy Prototype Optical Interferometer (NPOI) has been routinely used since 1996 for observations of stellar diameters and limb darkening, and for the imaging of binary stars. Here, we present the first results of, and future goals for, wide-angle astrometric observations from the NPOI.
The USNO Astrometric Interferometer (USNOAI; the dedicated subarray of the Navy Prototype Optical Interferometer at Lowell Observatory, Flagstaff, AZ) is presently under construction and expected to begin limited operations in the spring of 1993. The main goal of the USNOAI observations is to provide a northern hemisphere catalog of approximately a thousand stars with positions known to a few mas. In order to meet this requirement, a baseline laser metrology system must be employed to measure the 3D motions of the baselines with an accuracy better than approximately equals 0.1 micrometers . The metrology scheme, as presently conceived, represents the largest and most complex high-resolution laser metrology system ever attempted.