We have obtained high resolution orbital data with the CHARA Array for the bright star 12 Persei, a resolved double-lined spectroscopic
binary, an example of a Separated Fringe Packet Binary. We describe the data reduction process involved. By using a technique we have developed of 'side-lobe verniering', we can obtain an improved precision in separation of up to 25 micro-arcsec along a given baseline. For this object we find a semi-major axis 0.3 of Barlow, Scarfe, and Fekel (1998) [BSF], but with an increased inclination angle. The revised masses are therefore almost 6% greater than those of BSF. The overall accuracy in the masses is about 1.3%, now primarily limited by the spectroscopically determined radial velocities. The precision of the masses due to the interferometrically derived "visual" orbit alone is only about 0.2%. We expect that improved RVs and improved absolute calibration can bring down the mass errors to below 1%.
Georgia State University's Center for High Angular Resolution Astronomy (CHARA) operates a multi-telescope, long-baseline, optical/infrared interferometric array on Mt. Wilson, California. We present an update on the status of this facility along with a sample of preliminary results from current scientific programs.
During the 2001 observing season, the CHARA Array was in regular operation for a combined program of science, technical development, test, and commissioning. Interferometric science operations were carried out on baselines up to 330 meters -- the maximum available in the six-telescope array. This poster gives sample results obtained with the approximately north-south telescope pair designated S1-E1. At operating wavelengths in the K band, the 330 m baseline is well suited to diameter determinations for angular diameters in the range 0.6 - 1.2 milliarcseconds. This is a good
range for study of a wide range of hot stars. In this poster, angular
diameters for a set of A,B and F stars are compared to results derived from other sources. These confirm CHARA performance in the range 3-10% in visibility. The normal stars follow a normal spectral type - surface brightness relation, and a classical Be star deviates from the norm by an amount consistent with its apparent colors.
The Center for High Angular Resolution Astronomy (CHARA) has constructed an array of six alt-az telescopes at Mount Wilson Observatory in southern California. Together with the central beam combining facility, the telescopes operate as an optical/near-infrared interferometer with a maximum baseline of 330 meters. Due to practicality and cost constraints, some of the long path delay required for path length compensation occurs out of vacuum. A
consequence is a spectrally dispersed beam along the optical axis which decreases fringe contrast. To combat this visibility loss, wedges of glass are placed in the beam to chromatically equalize path lengths. Each set of glass wedges is called a Longitudinal Dispersion Compensator (LDC).
The design and fabrication phases for the LDC systems are described. Beginning with the material selection process, a glass with similar dispersive qualities to air within the observing bandwidths was selected. Next was the optomechanical design which included custom engineered optical mounts for the glass wedges, high precision translation stages for automated thickness variation and calibration adjustments. Following this, the hardware driver, software controls, and the user interface were written. Finally, the LDC components were assembled, integrated into the Beam Synthesis Facility, and
tested. The quantified results are presented and demonstrate an improvement to the interferometric measurements.
Individually resolved packets produced by scans from the CHARA Interferometer Array for binary stars can be analyzed in terms of the astrometry of the binary without using visibilities. We considered various methods for finding the locations of the packets, including autocorrelation and Shift-and-Add, but our best results were obtained from a method of direct packet fitting.
This method was put to use in analyzing two data sets each for the stars 12 Persei and Beta Arietis respectively. These data were taken between Nov 6 and 15, 2001 with the CHARA Array 330 m E1-S1 baseline. Some 460 to 830 scans were taken in both directions with the auxiliary PZT, and seeing conditions were fair to poor for these runs (r0 ≈ 7 cm).
This procedure yielded a projected separation for each data set, with an intrinsic accuracy of 0.15 - 0.3 mas. This represents an order of magnitude improvement over speckle interferometry techniques. The orbits were refined by a maximum likelihood technique. In the case of 12 Per the semimajor axis obtained was α = 53.53 mas, compared with the previous orbit of 53.38 mas, a small increase of 0.27%, which implies a mass increase of 0.8%, an insignificant change for this well-established orbit. For Beta Arietis, we find that α = 35.62 versus the previous orbit's value of 36.00 mas. This is a 1.0% decrease, resulting in a mass decrease of 3.0% for this system.
Georgia State University's Center for High Angular Resolution Astronomy (CHARA) operates a multi-telescope, long-baseline, optical/infrared interferometric array on Mt. Wilson, California. Since its inception, one of the primary scientific goals for the CHARA Array has been the resolution of spectroscopic binary stars, which offer tremendous potential for the determination of fundamental parameters for stars (masses, luminosities, radii and effective temperatures). A new bibliographic catalog of spectroscopic binary orbits, including a calculated estimate of the anticipated angular separation of the components, has been produced as an input catalog in planning observations with the Array. We briefly describe that catalog, which will be made available to the community on the Internet, prior to discussing observations obtained with our 330-m baseline during the fall of 2001 of the double-lined spectroscopic systems β Aur and β Tri. We also describe the initial results of an inspection of the extrasolar planetary system υ And.
The CHARA Array is a six element optical and near infrared interferometer built by Georgia State University on Mount Wilson in California. It is currently operating in the K and H bands and has the largest baseline (330 m) in operation of any similar instrument in the world. We expect to begin I band operations in 2002. We will present an update of the status of the instrumentation in the Array and set out our plans for the near term expansion of the system.
Georgia State University's Center for High Angular Resolution Astronomy (CHARA) is building an interferometric array of telescopes for high resolution imaging at optical and infrared wavelengths. The `CHARA Array' consists of six 1-m diameter telescopes arranged in a Y-shaped configuration with a maximum baseline of approximately 350 m. Construction of the facility will be completed during 2000, and the project will enter a phase in which beam combination subsystems will be brought on line concurrently with initial scientific investigations. This paper provides an update on recent progress, including our reaching the significant milestone of `first fringes' in November 1999. An extensive collection of project technical reports and images are available at our website.
The CHARA array achieved first fringes late last year and is currently being expanded on Mount Wilson CA. This presentation is a follow on from the overview given by Hal McAlister and will give more technical detail on the optical systems, with a focus on the telescopes, the delay lines, the control system, and the beam combining scheme. Combining more than three beams is not a simple problem with no obvious best solution, and we have by no means locked ourselves into a particular design. Preliminary designs will be shown, the first beam combiner will also be discussed along with our plans for future development.
The CHARA Array employs vacuum light pipes between the telescopes and the beam combination area. The complex terrain of the Mt. Wilson site poses interesting problems, with light pipes both underground and suspended up to 10 meters above ground. Telescope to beam-combination distances are up to about 180 meters. The support scheme and alignment strategy will be described.
The Center for High Angular Resolution Astronomy (CHARA) at Georgia State University is building an
interferometric array of telescopes for high resolution imaging at optical and infrared wavelengths. The "CHARA Array" will initially consist offive 1-rn diameter telescopes arranged in a Y-shaped configuration with a maximum baseline of approximately 350 m. The facility is being constructed on Mt. Wilson, near Pasadena, California, a site noted for stable atmospheric conditions that often gives rise to exceptional image quality. The Array will be capable of submilliarcsecond imaging and will be devoted to a broad program of science aimed at fundamental stellar astrophysics in the visible and the astrophysics of young stellar objects in the infrared (2.2μm) spectral regions. This project is being funded in approximately 50/50% shares by Georgia State University and the National Science Foundation. The CHARA Array is expected to become operational during 1999. This paper presents a project status report. An extensive collection of project reports and images are available at our website (http://www.chara.gsu.edu).
The telescope requirements of optical interferometry are somewhat different from conventional astronomy. The need for multiple units (in the CHARA case initially five, eventually seven) accentuates the importance of cost control, and at the same time provides opportunity for cost savings by careful procurement and production practices. Modern ideas about telescope enclosures offer significantly reduced dome seeing, but it is difficult to capture these benefits at low cost. The CHARA group has followed a series of design and bid procedures intended to optimize the costperformance of the telescope+enclosures. These have led to a compact but massive telescope design, blending modern and classical features, an unusual mirror blank selection process (directly ompeting several mirror blank technologies) , and a novel telescope enclosure concept which allows a continuous trade between wind protection and natural ventilation. This contribution will review and motivate the design decisions and show the resulting equipment and facilities.
The Center for High Angular Resolution Astronomy (CHARA) at Georgia State University is building an interferometric array of telescopes for high resolution imaging at optical and infrared wavelengths. The 'CHARA Array' will initially consist of five 1-m diameter telescopes arranged in a Y-shaped configuration with a maximum baseline of approximately 350 m. The facility will be located on Mt. Wilson, near Pasadena, California, a site noted for its stable atmoshperic conditions that often gives rise to exceptional image quality. The Array will be capable of submilliarcsecond imaging and will be devoted to a broad program of science aimed at fundamental stellar astrophysics in the visible and the astrophysics of young stellar objects in the infrared (2.2 micrometers ) spectral regions. This project has been supported by the National Sceince Foundation through Phase A feasibility and Phase B preliminary design stages, and NSF awarded 5.6 million dollars towards the construction of the facility in October 1994. Georgia State University is committed to providing an additional 5.8 million dollars in construction funds. The CHARA Array is expected to be operational late this decade. This paper will provide a summary overview of the project.
The CHARA array is an optical and IR imaging array of seven 1-m aperture telescopes with a Y-shaped configuration contained within a 400-m diameter circle. The facility will be capable of submilliarcsecond imaging and will be devoted to a broad program of science aimed at fundamental stellar astrophysics in the visible and the astrophysics of young stellar objects in the infrared spectral regions. The concept for the array has been carried through Phase A feasibility and Phase B preliminary design stages with funding provided by the National Science Foundation. This paper will provide a progress report on the status of the project.
With the advent of speckle interferometry and similar techniques, it has been possible to obtain orbital data, and, thereby, masses for a number of binary stars which were higherto unresolvable. For the full astrophysical exploitation of this benefit, it then becomes essential to obtain photometric and spectrophotometric information on these systems. Photometry can often be secured by extensions of the basic speckle resolution technique, and several solutions have been proposed for the problem of obtaining uncontaminated spectra of the normally blended stellar components such as objective prism speckle spectroscopy and wideband projection speckle spectroscopy, and passive interspectroscopy. We present here further practical development of the methods suggested in Paper I and the results of some observational tests of the technique.
The problem of designing a beam combiner that involves more than two or three beams is complex and by no means solved. No such system has been built to date. The CHARA Array will require a beam combining system that can cope with up the seven beams with a number of spectral channels. The design of a beam combiner is probably driven more by the available technology than any theoretical constraints. Many tradeoffs between ease of manufacture and required integration time are involved. A design solution for CHARA will be presented that will incorporate spatial fringe encoding and forming fringes in the image plane.
A feasibility study of a multiple telescope array for high-spatial-resolution astronomy has been completed, and an initial design concept has been defined. The array (referred to as the CHARA array for Georgia State University's Center for High Angular Resolution Astronomy) would consist of seven 1-m-aperture telescopes in a VLA-type configuration contained within a circle of 400-m-diameter to provide a limiting resolution of 0.3 milliarcsec for stellar angular diameter measurements or 0.1 mas for binary-star measurements. The initial scientific program will be directed at the imaging of stars to determine stellar radii, masses, temperatures, distances, and surface morphology. The array is also intended to provide the means of developing techniques for the very-high-resolution imaging of a large class of objects with geometries far more complicated than those of stars and star systems.
"Interspectroscopy" le a method of ol,taining the separated spectra of binary (or multiple) stars too close to be resolved by conventional techniques. The method is "passive" because, like speckle interferometry, the atmosphere provides a series of random phase variations, and no control system is used to maintain phase. Results in terms of spectral purity are given for several cases in both the pupil and image planes. It is shown that significant spectral separation can occur. We briefly discuss planned observations with a fiber-fed pulse-counting spectrograph at the 1.9-m DDO telescope.
Algorithms for reconstruction of isoplanically blurred point source pairs are considerably simpler and faster than full-blown image reconstruction techniques. Traditional autocorrelation approaches suffer from a 180 degree ambiguity, however, and only yield order of magnitude estimates for brightness ratios. A new asymmetric algorithm is here presented: the "Directed Vector Autocorrelation" (DVA), which is a rapid alternative to vector autocorrelation. Together with the 'Fork algorithm", a directional filter for estimating brightness ratios, the DVA algorithm has been used to resolve ambiguous orbits and produce differential color photometry for several binary stars.
We describe a new spectroscopic facility based upon a novel Multi- Telescope Telescope (MTT) and a fiber
optic fed spectrograph. The MTT is an inexpensive one meter light collecting telescope, whose "primary" mirror
consists of nine commercially made amateur-size (33.3 cm) telescope mirrors. Each mirror of the MTT will focus
light into a separate optical fiber, thus avoiding the light loss associated with the dead space in conventional fiber
bundles. Throughput is further enhanced by low mirror obscuration and having only one reflection from the high
reflectivity coatings available for smaller mirrors. The telescope is thus equivalent to about a 1.3-m conventional
telescope for spectroscopy. The optical fibers will feed an off-plane Ebert-Fastie spectrograph with a COD detector.
We conservatively estimate an overall optical efficiency of about 2.7% (4.4% without a slit at somewhat lower
resolution), which corresponds to a limitirg magnitude of 9.4 for 1000 sec exposure, SNR=100, and a resolution of
By using a combination of an innovative structure, a control system, some existing materials, and donated
shop time we can reduce the material cost of the telescope, spectrograph, and detector to about *35K to $55K,
depending on the detector. The MTT and spectrograph will be installed at the newly commissioned Georgia State
University Hard Labor Creek Observatory and will be used for spectroscopic observations of binaries and nonradial
pulsations in Be stars.