The CHARA Array, operated by Georgia State University, is located at Mount Wilson Observatory just north of Los Angeles in California. The CHARA consortium includes many groups, including LIESA in Paris, Observatoire de la Cote d’Azur, the University of Michigan, Sydney University, the Australian National University, the NASA Exoplanet Science Institute, and most recently the University of Exeter. The CHARA Array is a six-element optical/NIR interferometer, and for the time being at least, has the largest operational baselines in the world. In this paper we will give a brief introduction to the array infrastructure with a focus on our Adaptive Optics program, and then discuss current funding as well as opportunities of funding in the near future.
We describe a back-end Adaptive Optics system for the CHARA Array called Lab-AO intended to compensate for non-common path errors between the AO system at the telescopes and the final beam combining area some hundreds of meters away. The system is an on-axis, very small field of view, low order system that will work on star light if enough is present, or will make use of a blue light beacon sent from the telescope towards the laboratory if not enough star light is available. The first of six of these system has been installed and has recently been tested on the sky. Another five will be built for the remaining telescopes later this year.
The CHARA array is an optical interferometer with six 1-meter diameter telescopes, providing baselines from 33 to 331 meters. With sub-milliarcsecond angular resolution, its versatile visible and near infrared combiners offer a unique angle of studying nearby stellar systems by spatially resolving their detailed structures. To improve the sensitivity and scientific throughput, the CHARA array was funded by NSF-ATI in 2011 to install adaptive optics (AO) systems on all six telescopes. The initial grant covers Phase I of the AO systems, which includes on-telescope Wavefront Sensors (WFS) and non-common-path (NCP) error correction. Meanwhile we are seeking funding for Phase II which will add large Deformable Mirrors on telescopes to close the full AO loop. The corrections of NCP error and static aberrations in the optical system beyond the WFS are described in the second paper of this series. This paper describes the design of the common-path optical system and the on-telescope WFS, and shows the on-sky commissioning results.
This discussion, the first of three describing how the CHARA Array came to be, focuses on the establishment of the Center for High Angular Resolution Astronomy at Georgia State University, our site selection saga, and some apparently brilliant decisions stumbled into. The technical and scientific achievements of the CHARA Array to date are far more than just an argument for perseverance. CHARA's success stands upon audacity, risk taking, luck, and, above all else, a core team of wonderfully talented and dedicated individuals who made it all turn out well.
The CHARA Array has been a PI led, low budget, and low manpower operation, and has followed a fairly unconventional path in its development. In this, the third paper of a series of three, we discuss some of the engineering and design decisions made along the way, some right and some wrong, with a focus on the choice between in-house development and the purchase of pre-built, or sub-contracted, subsystems. Along with these issues we will also address a few parts of the system that we might have done differently given our current knowledge, and those that somehow turned out very well.
The reviewers of our first NSF proposal asked us to prepare a more ambitious plan, and we did. When it was funded, the scope of the resources made available was far below the scope of the project. What to do? The only way to proceed within budget was to eliminate the entire professional engineering component of the proposal team, and we did so. This left the CHARA staff and a few consultants. The story of building the CHARA Array is largely the story of how to build a facility and instrument with no engineers, no managers, and no meetings. How was this possible?
We initiated a multi-technique campaign to understand the physics and properties of the massive binary system MWC 314. Our observations included optical high-resolution spectroscopy and Johnson photometry, nearinfrared spectrophotometry, and <i>K′</i>−band long-baseline interferometry with the CHARA Array. Our results place strong constraints on the spectroscopic orbit, along with reasonable observations of the phase-locked photometric variability. Our interferometry, with input from the spectrophotometry, provides information on the geometry of the system that appears to consist of a primary star filling its Roche Lobe and loosing mass both onto a hidden companion and through the outer Lagrangian point, feeding a circumbinary disk. While the multi-faceted observing program is allowing us to place some constraints on the system, there is also a possibility that the outflow seen by CHARA is actually a jet and not a circumbinary disk.
The CHARA Array is a six telescope optical/IR interferometer run by the Center for High Angular Resolution
Astronomy of Georgia State University and is located at Mount Wilson Observatory just to the north of Los Angeles
California. The CHARA Array has the largest operational baselines in the world and has been in regular use for
scientific observations since 2004. In 2011 we received funding from the NSF to begin work on Adaptive Optics for our
six telescopes. Phase I of this project, fully funded by the NSF grant, consists of designing and building wavefront
sensors for each telescope that will also serve as tip/tilt detectors. Having tip/tilt at the telescopes, instead of in the
laboratory, will add several magnitudes of sensitivity to this system. Phase I also includes a slow wavefront sensor in the
laboratory to measure non-common path errors and small deformable mirrors in the laboratory to remove static and
slowly changing aberrations. Phase II of the project will allow us to place high-speed deformable mirrors at the
telescopes thereby enabling full closed loop operation. We are currently seeking funding for Phase II. This paper will
describe the scientific rational and design of the system and give the current status of the project.
In this paper, we review the current performance of the VEGA/CHARA visible spectrograph and make a review of
the most recent astrophysical results. The science programs take benefit of the exceptional angular resolution, the
unique spectral resolution and one of the main features of CHARA: Infrared and Visible parallel operation. We
also discuss recent developments concerning the tools for the preparation of observations and important features
of the data reduction software. A short discussion of the future developments will complete the presentation,
directed towards new detectors and possible new beam combination scheme for improved sensitivity and imaging
Rotation plays a crucial role in the shaping and evolution of a star. Widely incorporated into early and late-stage stellar models, rotational effects remain poorly understood in main-sequence stars, mainly due to the absence of observations challenging contemporary models. The Precision Astronomical Visible Observations (PAVO) instrument, located at the Center for High Angular Resolution Astronomy (CHARA) array, provides the highest angular resolution yet achieved (0.3 mas) for stars V=8 magnitude and brighter. We describe instrumental techniques and advances implemented in PAVO@CHARA to observe heavily resolved targets and yield well calibrated closure phases which are key milestones on the pathway to delivery of the first-ever image in the visible of fast-rotating main-sequence star.
The CHARA Array is a six telescope optical/IR interferometer run by the Center for High Angular Resolution
Astronomy of Georgia State University and is located at Mount Wilson Observatory just to the north of Los
Angeles California. The CHARA Array has the largest operational baselines in the world and has been in regular
use for scientific observations since 2004. Our most sensitive beam combiner capable of measuring closure phases
is the CLassic Interferometry with Multiple Baselines beam combiner known as CLIMB. In this paper we discuss
the design and layout of CLIMB with a particular focus on the data analysis methodology. This analysis is
presented in a very general form and will have applications in many other beam combiners. We also present
examples of on sky data showing the precision and stability of both amplitude and closure phase measurements.
The CHARA Array is a six-telescope optical/IR interferometer managed by the Center for High Angular Resolution
Astronomy of Georgia State University and located at Mount Wilson Observatory in the San Gabriel Mountains
overlooking Pasadena, California. The CHARA Array has the longest operational baselines in the world and has been in
regular use for scientific observations since 2005. In this paper we give an update of instrumentation improvements,
primarily focused on the beam combiner activity. The CHARA Array supports seven beam combiners: CHARA
CLASSIC, a two-way high-sensitivity K/H/J band system; CLIMB, a three-way K/H/J open-air combiner; FLUOR, a
two-way K-band high-precision system; MIRC, a four/six-way H/K-band imaging system; CHAMP, a six-way K-band
fringe tracker; VEGA, a four-way visible light high spectral resolution system; and PAVO, a three-way visible light high
sensitivity system. We also present an overview of science results obtained over the last few years, including some recent imaging results.
The efficiency of the CHARA Array has proven satisfactory for a wide variety of scientific programs enabled by the
first-generation beam combination and detector systems. With multi-beam combination and more ambitious scientific
goals, improvements in throughput and efficiency will be highly leveraged. Engineering data from several years of
nightly operations are used to infer atmospheric characteristics and raw instrumental visibility in both classic optical and
single-mode fiber beam combiners. This information is the basis for estimates of potential gains that could be afforded
by the implementation of adaptive optics. In addition to the very important partial compensation for higher order
atmosphere-induced wavefront errors, the benefits include reduction of static and quasi-static aberrations, reduction of
residual tilt error, compensation for differential atmospheric refraction, and reduction of diffractive beam propagation
losses, each leading to improved flux throughput and instrumental visibility, and to associated gains in operability and
This paper presents the current status of the VEGA (Visible spEctroGraph and polArimeter) instrument installed
at the coherent focus of the CHARA Array, Mount Wilson CA. Installed in september 2007, the first science
programs have started during summer 2008 and first science results are now published. Dedicated to high angular (0.3mas) and high spectral (R=30000) astrophysical studies, VEGA main objectives are the study of circumstellar environments of hot active stars or interactive binary systems and a large palette of new programs dedicated to fundamental stellar parameters. We will present successively the main characteristics of the instrument and its current performances in the CHARA environment, a short summary of two science programs and finally we will develop some studies showing the potential and difficulties of the 3 telescopes mode of VEGA/CHARA.
This paper presents the first empirical measurement of the <i>K</i><sup>1</sup>-band effective wavelength and bandwidth of the
CHARA Classic beam combiner on the CHARA Array. Prior to this work, the accepted effective wavelength
value used for CHARA Classic data (2.1501μm) came from a model of the system; it was not derived from
measurements done on the system directly. We employ two data collection methods for our observations: using
the Optical Path Length Equalizer (OPLE) cart to scan through the interference fringes and using the dither
mirror to scan through the fringes. The two observational methods yield similar effective wavelength measurements
(2.141±0.003μm with the OPLE cart and 2.136±0.002μm with the dither mirror). Both of these results are lower than the previously adopted effective wavelength value, but by less than 0.7%. The bandwidth values
measured by the two methods differ from each other by almost 5% (0.334 ± 0.002μm with the OPLE cart and
0.351±0.003μm with the dither mirror). Our results establish the first estimate of the uncertainty in the effective
wavelength and bandwidth.
We present the procedure used to optically align the CHARA telescopes. We show that the beam quality,
delivered by the CHARA telescopes E1, E2 and W2, is significantly better now than in 2008. RMS wavefront
error is about 200 nm. The astigmatism observed in W1 is more likely due to a combination of a mechanical
problem in the mounting and misalignment. We present wavefront quality results from four telescopes. Further
beam quality improvements can be expected when the second part of the alignment procedure (tuning) will be
carried out later this year.
Two identical three-way beam combiners have been installed at the CHARA Array. The new setup is an extension of the
two-beam pupil plain combiner, which has been in use thus far. Using the new beam combiners we can now obtain
phase closure data in H, K or J band on two sets of three telescopes. A new optical design has been implemented to
image the six outputs of the combiners onto six separate pixels in the infrared detector array. The new optical
arrangement provides reduced background and spatial filtering. The magnitude limit of this beam combiner has reached
7.8 in K magnitude mainly as a result of better image quality by the new infrared camera optics.
The CHARA Array is a six-telescope optical/IR interferometer operated by the Center for High Angular Resolution
Astronomy of Georgia State University and is located at Mount Wilson Observatory just to the north of Los Angeles
California. The CHARA Array has the largest operational baselines in the world and has been in regular use for scientific
observations since 2004. In this paper we give an update of instrumentation improvements, primarily focused on the
beam combiner activity. The CHARA Array supports seven beam combiners: CHARA CLASSIC, a two-way high
sensitivity K/H/J band system; CLIMB, a three-way K/H/J open air combiner, FLUOR, a two-way K band high
precision system; MIRC, a four/six-way H/K band imaging system; CHAMP, a six way K band fringe tracker; VEGA, a
four way visible light high spectral resolution system; and PAVO, a three-way visible light high sensitivity system. The
paper will conclude with a review of science results obtained over the last few years, including our most recent imaging results.
The efficiency of the CHARA Array has proven satisfactory for the scientific programs enabled by the first-generation
beam combination and detector systems. With multi-beam combination and more ambitious scientific goals,
improvements in throughput and efficiency will be highly leveraged. Engineering data from several years of nightly
operations are used to infer atmospheric characteristics and raw instrumental visibility in both classic optical and single-
mode fiber beam combiners. This information is the basis for estimates of potential gains that could be afforded by the
implementation of adaptive optics. This includes reduction of static and quasi-static aberrations, reduction of residual
tilt error, compensation for differential atmospheric refraction, reduction of diffractive beam propagation losses, each
leading to improved flux throughput and instrumental visibility, and to associated gains in operability and scientific
The CHARA Array is a six telescope optical/IR interferometer run by the Center for High Angular Resolution
Astronomy of Georgia State University (GSU) and is located at Mount Wilson Observatory just to the north of Los
Angeles, California. The CHARA Array has the largest operational baselines in the world and has been in regular use for
scientific observations since 2004. In this paper we give an update of instrumentation improvements, primarily focused
on the beam combiner activity. The CHARA Array supports seven beam combiners: CHARA CLASSIC, a two way
high sensitivity K/H band system; CLIMB, an upgrade to CLASSIC that includes closure phase measurements; FLUOR,
a two way K band high precision system; MIRC, a six way H/K band imaging system; CHAMP, a six way K band fringe
tracker; VEGA, a 4 way visible light high spectral resolution system; and PAVO, a 3 way visible light high sensitivity
system. The paper will conclude with a brief review of some science results obtained over the last few years.
The Precision Astronomical Visible Observations (PAVO) beam combiner is a new concept in visible beam
combination, recently commissioned at the CHARA array. By creating spatially-modulated fringes in a pupil
plane and then dispersing with an integral field unit, PAVO utilizes the full multi-r0 aperture of the CHARA
array over a standard 50% (630-950nm) bandwidth. In addition, minimal optimized spatial filtering ensures
calibration that is in principle as good as using single-mode fibers. We describe the design of and initial results
from the PAVO instrument.
The VEGA spectrograph and polarimeter has been recently integrated on the visible beams of the CHARA
Array. With a spectral resolution up to 35000 and thanks to operation at visible wavelengths, VEGA brings
unique capabilities in terms of spatial and spectral resolution to the CHARA Array. We will present the main
characteristics of VEGA on CHARA, some results concerning the performance and a preliminary analysis of the
first science run.
We report the first scientific results from the Michigan Infrared Combiner (MIRC), including the first resolved
image of a main-sequence star besides the Sun. Using the CHARA Array, MIRC was able to clearly resolve the
well-known elongation of Altair's photosphere due to centrifugal distortion, and was also able to unambiguously
image the effect of gravity darkening. In this report, we also show preliminary images of the interacting binary
β Lyr and give an update of MIRC performance.
We describe a project for the installation of a visible focal instrument at the CHARA Array, named VEGA for Visible spEctroGraph and polArimeter. This new instrument will further open the visible domain and offer both spectral and polarimetric capabilities at the CHARA Array. It will create a new and unique scientific niche for the CHARA Array, especially in the context of international competition. The combination of the visible domain and high spectral resolution mode combined with a good sensitivity will allow VEGA/CHARA to carve out a new piece of observational phase space and compliment many existing or planned near-infrared interferometers. VEGA will help make CHARA the interferometer with the largest spectral and spatial resolution worldwide.
Extrasolar planetary systems are assumed as a sample to exhibit random orbital inclinations. The chance exists that a few of the 152 extrasolar planetary systems known to date may have face-on orbits for which the sin <i>i</i> factor will make a stellar-mass companion mimic a planetary-mass object. Such systems may thus harbor a late spectral type stellar companion instead of planets. Using Georgia State University's CHARA Array, we are undertaking an observing program on accessible extrasolar planetary systems that is expected to be completed in 2007. This effort will assist in culling the exoplanet list of some very low-inclination stellar interlopers that may be present. We will also determine the diameters of the central stars in an effort to refine our knowledge of the evolutionary status of the host stars.
A new CCD based tip/tilt detection system was installed in the CHARA array on August 21, 2005. The new system can serve six telescopes simultaneously and is sensitive to a wavelength as long as 1 μm. The tip/tilt camera is based on an E2V CCD39-01, a small (80×80) back illuminated frame transfer device with a pixel size of 24×24 μm<sup>2</sup>. The measured read-out noise and conversion gain of the camera is 6.4 e<sup>-</sup> at 384 kpx s<sup>-1</sup> and 1.1 e<sup>-</sup>/ADU, respectively at a temperature of -30 C°. Nine quad-pixel channels have been created on the CCD in a 10×10 pixel sub-array close to one of the read out amplifiers. Vignetting on the quad-pixel channels is negligible. Crosstalk between adjacent channels has been eliminated. The image scale on the CCD is 3.46 arcsecs/pixel. The limiting magnitude is expected to be V=12 at 20 ms integration time under good seeing conditions.
The Michigan Infrared Combiner (MIRC) has been designed for two primary goals: 1) imaging with all six CHARA telescopes simultaneously in the near-infrared, 2) direct detection of "hot Jupiter" exoplanets using precision closure phases. In September 2005, MIRC was commissioned on-sky at the CHARA Array on Mt. Wilson, CA, successfully combining light from 4 telescopes simultaneously. After a brief overview of MIRC features and design philosophy, we provide detailed description of key components and present results of laboratory tests. Lastly, we present first results from the commissioning run, focusing on engineering performance. We also present remarkable on-sky closure phase results from the first night of recorded data with the best-ever demonstrated closure phase stability and precision (ΔΦ = 0.03 degrees).
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%.
The use of high-resolution techniques for detecting binary and multiple star systems, such as speckle interferometry, and extensive spectroscopic survey efforts have led to the discovery of stellar systems over a broad range of orbital periods. However, there remains a gap between these two techniques, wherein neither is sensitive to detection of companions. Thus, it is possible that some nearby stars may have companions that have been overlooked. Using the longest baselines of the CHARA Array (~275-330 m), we are examining 158 nearby F and G dwarfs previously included in speckle interferometry and radial velocity surveys. Included in this sample are previously unresolved double- and single-lined spectroscopic binaries that show separated fringe packets measured on two nearly perpendicular baselines to determine true position angle and angular separation. Specifically, we are exploring the spectroscopic sample of Duquennoy and Mayor and include selected systems from the CHARA Catalog of Orbital Elements of Spectroscopic Binaries that have predicted separations that fall in this gap. In addition to the search for new companions, we will attempt to use astrometric data to determine orbital inclination in conjunction with previously determined spectroscopic orbits for accurate mass determination. We intend to utilize the Array to more fully explore the undersampled regime of approximately 5-50 mas to characterize the completeness of the multiplicity in the stellar neighborhood.
Observational modes in which simultaneous high spatial and spectral information are recovered, without the complexity and expense of a dispersed detection system, have been discussed for some time. Sometimes called Double Fourier/Spatio-Spectral Interferometry (DFSSI), these methods fuse the concepts of Fourier Transform Spectrometry with high spatial resolution interferometry. The basic underlying principle comes from the idea that different spectral components, yielding different fringe frequencies, can be separated out in the fringe spectrum for individual study. However in practice, seeing fluctuations have the effect of shifting and blurring together the fringe frequencies making it difficult to isolate discrete spectral components. DFSSI has not been widely exploited in astronomical interferometry, due in part to such considerations. Here we propose a closely-related, although distinct technique which is the analog of DFSSI implemented in the spatial (delay) space rather than the time (frequency) domain. We propose the name Double-Fourier Spatio-Spectral Decoding to distinguish it from the latter. The technique relies on careful calibration of the fringe envelope shape, which is a function of the shape of the overall bandpass of the interferometer. We show that for astrophysical systems with interesting variations in spatial structure for neighboring spectral regions (such as stars with emission-line winds) that it is possible to untangle separate spatial and spectral components without a multi-channel dispersed fringe detector. The principle has been demonstrated successfully with observations of the prototype emission-line object P Cygni
at the CHARA array.
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 a brief update on the status of this facility along with summaries of the first scientific results from the Array.
Using the FLUOR beam-combiner installed at the CHARA Array (Mt. Wilson, CA), we have obtained highprecision visibility measurements of Vega, one of the prototypic debris-disk stars, known to be surrounded by a large amount of cold dust in a ring-like structure at 80-100 AU. The combination of short and long baselines has allowed us to separately resolve the stellar photosphere and the close environment of the star (less than 8 AU). Our observations show a significant deficit in square visibility at short baselines with respect to the expected visibility of a simple UD stellar model (Δ<i>V</i><sup>2</sup> equal or equivalent to 2%), suggesting the presence of an extended source of emission around Vega. The sparse (u, v) plane coverage does not allow the discrimination between a point source and an extended circumstellar emission as the source of the extended emission. However, we show that the presence of a point-like source within the FLUOR field-of-view (1" in radius, i.e., 7.8 AU at the distance of Vega) is highly unlikely. The excess emission is most likely due to the presence of hot circumstellar dust in the inner part of Vega's debris disk, with a flux ratio of 1.29 plus or minus 0.19% between the integrated dust emission and the stellar photosphere. Complementing this result with archival photometric data in the near- and mid-infrared and taking into account a realistic photospheric model for the rapidly rotating Vega, we derive the expected physical properties of the circumstellar dust by modelling its Spectral Energy Distribution. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations.
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.
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 (r<sub>0</sub> ≈ 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.
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.
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.
In this paper we describe the telescope optics, manufacturing tolerances and the geometric alignment procedure of the CHARA telescopes. We also report on our efforts to test and refine the alignment of the telescopes by implementing the curvature sensing method. The results of the first experiments on telescope W1 show that we can get consistent results with this method. We also found a slight distortion caused by the lateral support of the primary mirror.
The fibered beam combiner FLUOR, which has provided high accuracy
visibility measurements on the IOTA interferometer, is being moved to
the CHARA array which provides five 1m telescopes on baselines ranging from 35 to 330m. The combination CHARA/FLUOR makes it possible for the first time to achieve sub-milliarcsecond resolution in the K band, with a dynamic range of 100 or more.
We explore the scientific potential of CHARA/FLUOR, most notably in the domains of high contrast binaries and the characterization of Cepheid pulsations, and present some of the anticipated developements.
A remote operations center for Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Array is in the final stages of implementation on the university campus in Atlanta, GA. Several technological considerations were incorporated into the overall design including a secure network infrastructure with an acceptable end-to-end latency, a control room replete with appropriate computing and projection systems, an efficient client-server model, and a data archival system. Although independent of the local weather, remote operations have practical considerations, such as routine preparations requiring on-site personnel and the observation of astronomical targets with celestial coordinates appropriate to the Local Sidereal Time (LST) and U-V plane coverage of the array.
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.
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 CHARA Array consists of six 1-meter telescopes. The telescopes are at fixed positions laid out in a Y-shaped pattern, where the longest available baseline is 330 meters. The resolving power of this interferometric array operating at visible and short infrared wavelengths is better than one milli-arcsecond. The current infrared beam combination system is capable of combining the light from any two of the six telescopes in the array. With the existing infrared beam combination and detection system, we routinely observe in K and H band, where our magnitude limit is 6.
A unique set of instrument enclosures was implemented as part of an interferometric array now in place atop Mt. Wilson, California. These enclosures were designed in response to project criteria set forth in the planning phases of a new project by the Center for High Angular Resolution Astronomy at Georgia State University. The array is intended for high resolution imaging at optical and infrared wavelengths and is comprised of six 1-m diameter telescopes arranged in a Y-shaped configuration with a maximum baseline of approximately 350 m.
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 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.
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.
During 1996 and 1997 more than 20 nights observing time have been used by, or allocated to, the CHARPA group at Georgia State University using the Mount Wilson Institute Adaptive Optics mounted on the Hooker 100 inch telescope on Mt. Wilson. Several scientific programs are being pursued including: differential photometry of binary stars; a search for faint companions of local solar type stars; attempts to image dust shells around YSOs; and experiments involving the combination of non-redundant aperture masking interferometry and adaptive optics. We have learned, and continue to learn, a great deal about the problems associated with, and methods of calibration of, adaptive optics images, especially in the area of accurate photometric measurements. So far, more than 30 binary systems have been measured in multiple filters and several previously unknown faint companions to local stars have been identified.
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.
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.