The Giant Magellan Telescope is proceeding with design, fabrication, and site construction. Of the seven 8.4 m diameter mirror segments required for the primary mirror, two have been completed and placed in storage, a third has been polished to specification, three more have been cast and are in various stages of fabrication, and glass is in hand to cast the final segment. The telescope structure is nearing final design review and the start of fabrication. Residence buildings and other facilities needed to support construction at the Las Campanas site in Chile are complete. Hard rock excavation of the foundations for the enclosure and telescope pier is complete. The enclosure is in final design. The first off-axis adaptive secondary mirror is being fabricated, and a primary mirror cell has been fabricated and is under test. Two adaptive optics and phasing testbeds are being fabricated for risk reduction testing and component qualification. Our fabrication and construction schedule is being revised in response to evolving programmatic factors, including the US-ELT initiative, which received the top ranking in the National Academies’ ASTRO2020 Decadal Survey.
We describe the development status of the first-generation science instruments for the Giant Magellan Telescope (GMT). The first-generation suite includes two infrared and two visible light spectrographs that together will deliver from wide-band imaging to R~200,000 spectroscopy at wavelengths from 0.3 to 5 µm. All four instruments are designed for use with diffraction limited or ground-layer adaptive optics modes. G-CLEF, a visible light echelle designed for broad scientific use and for precision radial velocity measurements, is in fabrication. The other three (GMACS, a wide field multi-object spectrograph; GMTNIRS, a near- to thermal-infrared echelle spectrograph utilizing silicon immersion gratings; and GMTIFS, a near-infrared imager and integral field spectrograph) are in Preliminary Design. The first-generation suite also includes a robotic fiber-feed system called MANIFEST, which enables spectroscopy over the 20 arcmin field of view of the telescope with custom fibers for G-CLEF, GMACS, and GMTNIRS. An additional facility instrument, GMagAO-X, is being developed to provide high-contrast imaging at visible and near-infrared wavelengths and is in Preliminary Design. We also discuss the visible and infrared cameras (called ComCam and AOTC, respectively) that will be used for alignment, verification, and commissioning of the active and adaptive optics modes of the telescope and enable early science activities.
This paper describes the deployment of the GMT-Consortium Large Earth Finder (G-CLEF) at the Clay telescope, one of the two Magellan telescopes, in late 2025, moving to the GMT in 2030. G-CLEF is a fiber-fed, ultra-high stability optical band echelle spectrograph designed for extremely precise stellar radial velocity measurement. On the Magellan Clay telescope, G-CLEF will take spectra with resolution up to ~300,000, fully resolving molecular spectral features and opening totally new discovery space for exoplanet atmosphere composition studies. G@M will also be coupled to the Magellan extreme adaptive optics facility, MagAO-X which will allow it to spatially resolve several exoplanets from their host stars. We provide a system description of the G@M instrument as it will be configured at Magellan. A top-level review of optomechanics, electronics and control systems follows, as well as a description of several risk-reduction exercises the team has undertaken.
With more than a decade of design work behind them, the instrumentation program of each of the three Extremely Large Telescope (ELT)-class telescopes is now ready to lock-in the set of capabilities it will be able to offer to their respective community at first light. The Giant Magellan Telescope, the Thirty Meter Telescope, and the European Southern Observatory’s ELT have each followed a formal instrumentation prioritization process with input from the astronomical community, which resulted in extensive and complementary suites of instruments that will be divided into two generations. We present this process as well as the general scientific characteristics of every instrument currently being developed for the three observatories. We also present how these instruments will fit the operation models of the observatories.
The Giant Magellan Telescope project is proceeding with design, fabrication, and site construction. The first two 8.4m primary mirror segments have been completed and placed in storage, three segments are in various stages of grinding and polishing, the sixth segment is in the initial stages of casting, and glass is in hand to cast the seventh segment. An industry contract is in place to complete the design and proceed with fabrication of the telescope structure. Residence buildings and other facilities at the Las Campanas site in Chile are complete. Hard rock excavation of the foundations for the enclosure and telescope pier is complete. Preliminary design of the enclosure has been completed and final design is underway. Seismic isolation system bearings have been tested. A primary mirror segment test cell that will be used to qualify control system components and software is being fabricated. Prototyping continues in several areas, including on-telescope wavefront sensing and control elements, telescope laser metrology, and a subscale Adaptive Secondary Mirror (ASM). Adaptive optics and phasing testbeds are under development. Construction activities were delayed by the global coronavirus pandemic, but work has now resumed.
In the advanced design, construction, and commissioning phases of GMTO project, the critical role of systems engineering is tracking and managing expected observatory performance and ensuring that the scientific goals of the Giant Magellan Telescope (GMT) are met. GMTO’s approach to this role is defining Key Performance Parameters (KPPs) to measure technical performance. A set of KPPs have been established to assess the performance of the telescope through construction and Assembly, Integration, Verification, and Commissioning (AIVC). Each KPP has a threshold value representing the minimum acceptable performance, and an objective value representing the desired operational performance. KPPs are used to prioritize maturation plans for technologies and novel system-level design strategies. The KPPs directly characterize the performance of the telescope by ensuring focal plane (image), exit pupil (wavefront) and light collecting capabilities of the telescope. The paper demonstrates that the chosen KPPs properly represent key science capabilities, as image size, sensitivity, photometric, and astrometric accuracy. It is also shown how detailed error budgets link the KPPs to component technical specifications that in turn are closely monitored by simulations. Integrated modeling is crucial for the performance-based systems engineering approach of defining and then evaluating the objective and threshold levels for the KPPs. As described in other GMTO paper at this conference, contributions from individual subsystems and components are modeled to determine their effect on system performance. We describe how GMTO has implemented KPPs and is now using them to guide and coordinate technical development.
MANIFEST is a multi-object fibre positioner for the Giant Magellan Telescope that uses ‘Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeing-limited instruments, GMACS and GCLEF, offers access to: larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via multiple integral-field-units; increased spectral resolution using image-slicers; the capability for simultaneous observations with multiple instruments; the possibility of a gravity-invariant spectrograph mounting; the potential for OH suppression via fiber systems in the near-infrared; and the versatility of adding new instruments in the future. We have now completed the pre-concept phase for MANIFEST. This phase has focused on developing the science case and requirements, further developing high risk aspects of the instrument design, designing the opto-mechanical interfaces to the GMACS and GCLEF instruments, and detailing the interfaces to the GMT.
The presence of large amounts of dust in the habitable zones of nearby stars is a significant obstacle for future exo-Earth imaging missions. We executed the HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey to determine the typical amount of such exozodiacal dust around a sample of nearby main sequence stars. The majority of the data have been analyzed and we present here an update of our ongoing work. Nulling interferometry in N band was used to suppress the bright stellar light and to detect faint, extended circumstellar dust emission. We present an overview of the latest results from our ongoing work. We find seven new N band excesses in addition to the high confidence confirmation of three that were previously known. We find the first detections around Sun-like stars and around stars without previously known circumstellar dust. Our overall detection rate is 23%. The inferred occurrence rate is comparable for early type and Sun-like stars, but decreases from 71+11 -20% for stars with previously detected mid- to far-infrared excess to 11+9 -4% for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal luminosity function of the dust, we find upper limits on the median dust level around all stars without previously known mid to far infrared excess of 11.5 zodis at 95% confidence level. The corresponding upper limit for Sun-like stars is 16 zodis. An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a corresponding limit of 7.5 zodis. We provide important new insights into the occurrence rate and typical levels of habitable zone dust around main sequence stars. Exploiting the full range of capabilities of the LBTI provides a critical opportunity for the detailed characterization of a sample of exozodiacal dust disks to understand the origin, distribution, and properties of the dust.
MANIFEST is a multi-object fibre facility for the Giant Magellan Telescope that uses ‘Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeinglimited instruments, offers access to larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via integral-field-units; image-slicers; and in some cases higher spatial and spectral resolution. The TAIPAN instrument on the UK Schmidt Telescope is now close to science verification which will demonstrate the feasibility of the Starbug concept. We are now moving into the conceptual development phase for MANIFEST, with a focus on developing interfaces for the telescope and for the instruments.
The Planet Formation Imager (PFI) is a near- and mid-infrared interferometer project with the driving science goal of imaging directly the key stages of planet formation, including the young proto-planets themselves. Here, we will present an update on the work of the Science Working Group (SWG), including new simulations of dust structures during the assembly phase of planet formation and quantitative detection efficiencies for accreting and non-accreting young exoplanets as a function of mass and age. We use these results to motivate two reference PFI designs consisting of a) twelve 3m telescopes with a maximum baseline of 1.2km focused on young exoplanet imaging and b) twelve 8m telescopes optimized for a wider range of young exoplanets and protoplanetary disk imaging out to the 150K H2O ice line. Armed with 4 x 8m telescopes, the ESO/VLTI can already detect young exoplanets in principle and projects such as MATISSE, Hi-5 and Heimdallr are important PFI pathfinders to make this possible. We also discuss the state of technology development needed to make PFI more affordable, including progress towards new designs for inexpensive, small field-of-view, large aperture telescopes and prospects for Cubesat-based space interferometry.
The Giant Magellan Telescope project is proceeding with design, fabrication, and site construction. The first of the seven required 8.4-m primary mirror segments is completed and in storage, three segments are in various stages of grinding and polishing, and the fifth segment has been cast. Industry contracts are underway to complete the design of the telescope structure. Residence buildings and other facilities needed to support construction at the Las Campanas site in Chile are complete. Hard rock excavation is imminent in preparation for the pouring of concrete for the telescope pier and other foundations. Computational fluid dynamics analysis is informing the design of the telescope enclosure, and further construction work packages are being readied for tender. Seismic design considerations have resulted in the incorporation of a seismic isolation system into the telescope pier, as well as modifications to the primary mirror support system. Designs for the fast-steering and adaptive secondary mirrors, science instruments, and other subsystems are maturing. Prototyping is underway in various aspects, including on-sky testing of wavefront sensing and control elements, and the telescope metrology system. Our fabrication and construction schedule calls for engineering first light with a subset of primary mirror segments in late 2023, with buildout to the full configuration occurring in stages, paced by the availability of primary mirror segments and other components.
NASA has funded a project called the Hunt for Observable Signatures of Terrestrial Systems (HOSTS) to survey nearby solar type stars to determine the amount of warm zodiacal dust in their habitable zones. The goal is not only to determine the luminosity distribution function but also to know which individual stars have the least amount of zodiacal dust. It is important to have this information for future missions that directly image exoplanets as this dust is the main source of astrophysical noise for them. The HOSTS project utilizes the Large Binocular Telescope Interferometer (LBTI), which consists of two 8.4-m apertures separated by a 14.4-m baseline on Mt. Graham, Arizona. The LBTI operates in a nulling mode in the mid-infrared spectral window (8-13 μm), in which light from the two telescopes is coherently combined with a 180 degree phase shift between them, producing a dark fringe at the location of the target star. In doing so the starlight is greatly reduced, increasing the contrast, analogous to a coronagraph operating at shorter wavelengths. The LBTI is a unique instrument, having only three warm reflections before the starlight reaches cold mirrors, giving it the best photometric sensitivity of any interferometer operating in the mid-infrared. It also has a superb Adaptive Optics (AO) system giving it Strehl ratios greater than 98% at 10 μm. In 2014 into early 2015 LBTI was undergoing commissioning. The HOSTS project team passed its Operational Readiness Review (ORR) in April 2015. The team recently published papers on the target sample, modeling of the nulled disk images, and initial results such as the detection of warm dust around η Corvi. Recently a paper was published on the data pipeline and on-sky performance. An additional paper is in preparation on β Leo. We will discuss the scientific and programmatic context for the LBTI project, and we will report recent progress, new results, and plans for the science verification phase that started in February 2016, and for the survey.
The Large Binocular Telescope Interferometer (LBTI) is a high spatial resolution instrument developed for coherent imaging and nulling interferometry using the 14.4 m baseline of the 2×8.4 m LBT. The unique telescope design, comprising of the dual apertures on a common elevation-azimuth mount, enables a broad use of observing modes. The full system is comprised of dual adaptive optics systems, a near-infrared phasing camera, a 1-5 μm camera (called LMIRCam), and an 8-13 μm camera (called NOMIC). The key program for LBTI is the Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS), a survey using nulling interferometry to constrain the typical brightness from exozodiacal dust around nearby stars. Additional observations focus on the detection and characterization of giant planets in the thermal infrared, high spatial resolution imaging of complex scenes such as Jupiter's moon, Io, planets forming in transition disks, and the structure of active Galactic Nuclei (AGN). Several instrumental upgrades are currently underway to improve and expand the capabilities of LBTI. These include: Improving the performance and limiting magnitude of the parallel adaptive optics systems; quadrupling the field of view of LMIRcam (increasing to 20"x20"); adding an integral field spectrometry mode; and implementing a new algorithm for path length correction that accounts for dispersion due to atmospheric water vapor. We present the current architecture and performance of LBTI, as well as an overview of the upgrades.
The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to ~100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs.
The characterization of exozodiacal light emission is both important for the understanding of planetary systems evolution
and for the preparation of future space missions aiming to characterize low mass planets in the habitable zone of nearby
main sequence stars. The Large Binocular Telescope Interferometer (LBTI) exozodi survey aims at providing a ten-fold
improvement over current state of the art, measuring dust emission levels down to a typical accuracy of ~12 zodis per star,
for a representative ensemble of ~30+ high priority targets. Such measurements promise to yield a final accuracy of about
2 zodis on the median exozodi level of the targets sample. Reaching a 1 σ measurement uncertainty of 12 zodis per star
corresponds to measuring interferometric cancellation (“null”) levels, i.e visibilities at the few 100 ppm uncertainty level.
We discuss here the challenges posed by making such high accuracy mid-infrared visibility measurements from the ground
and present the methodology we developed for achieving current best levels of 500 ppm or so. We also discuss current
limitations and plans for enhanced exozodi observations over the next few years at LBTI.
The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 microns). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the new sensing approach that has been developed at the LBT to measure and monitor the optical path length fluctuations due to dry air and water vapor separately. After reviewing the current performance of the system for dry air seeing compensation, we present simultaneous H-, K-, and N-band observations that illustrate the feasibility of our feedforward approach to stabilize the path length fluctuations seen by the LBTI nuller.
The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for highsensitivity, high-contrast, and high-resolution infrared (1.5-13 μm) imaging of nearby planetary systems. To carry out a wide range of high-spatial resolution observations, it can combine the two AO-corrected 8.4-m apertures of the LBT in various ways including direct (non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging, non-redundant aperture masking, and nulling interferometry. It also has broadband, narrowband, and spectrally dispersed capabilities. In this paper, we review the performance of these modes in terms of exoplanet science capabilities and describe recent instrumental milestones such as first-light Fizeau images (with the angular resolution of an equivalent 22.8-m telescope) and deep interferometric nulling observations.
The Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS) program on the Large Binocular Telescope Interferometer (LBTI) will survey nearby stars for faint exozodiacal dust (exozodi). This warm circumstellar dust, analogous to the interplanetary dust found in the vicinity of the Earth in our own system, is produced in comet breakups and asteroid collisions. Emission and/or scattered light from the exozodi will be the major source of astrophysical noise for a future space telescope aimed at direct imaging and spectroscopy of terrestrial planets (exo- Earths) around nearby stars. About 20% of nearby field stars have cold dust coming from planetesimals at large distances from the stars (Eiroa et al. 2013, A&A, 555, A11; Siercho et al. 2014, ApJ, 785, 33). Much less is known about exozodi; current detection limits for individual stars are at best ~ 500 times our solar system's level (aka. 500 zodi). LBTI-HOSTS will be the first survey capable of measuring exozodi at the 10 zodi level (3σ). Detections of warm dust will also reveal new information about planetary system architectures and evolution. We will describe the motivation for the survey and progress on target selection, not only the actual stars likely to be observed by such a mission but also those whose observation will enable sensible extrapolations for stars that will not be observed with LBTI. We briefly describe the detection of the debris disk around η Crv, which is the first scientific result from the LBTI coming from the commissioning of the instrument in December 2013, shortly after the first time the fringes were stabilized.
The Large Binocular Telescope Interferometer is a NASA-funded nulling and imaging instrument designed to coherently combine the two 8.4-m primary mirrors of the LBT for high-sensitivity, high-contrast, and highresolution infrared imaging (1.5-13 μm). PHASECam is LBTI's near-infrared camera used to measure tip-tilt and phase variations between the two AO-corrected apertures and provide high-angular resolution observations. We report on the status of the system and describe its on-sky performance measured during the first semester of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope and the light-gathering power of single 11.8-meter mirror, the co-phased LBT can be considered to be a forerunner of the next-generation extremely large telescopes (ELT).
With a null precision of a few 10-4 at all azimuth angles inside a field-of-view extending from 35 to 275 mas, the
Palomar Fiber Nuller (PFN) is able to explore angular scales intermediate between those accessed by coronagraphic
imaging and by long baseline interferometry. We first briefly summarize the recent performance improvements of the
PFN (sensitivity, azimuthal coverage, duty cycle efficiency on-sky) over the 2011-2014 time period. Then we report on
recent K-band observations of the young pre-main sequence star AB Aurigae obtained with the PFN. It is shown that a
mean astrophysical null of 1.52% was detected around AB Aur at all probed azimuthal angles, and this inside a field-of-view
corresponding to projected separations between 5 and 40 AU. In addition, we also report a slight ±0.2% modulation
in addition to this average null level. The isotropic astrophysical null is indicative of circumstellar emission dominated
by an azimuthally extended source, possibly a halo or one or more rings of dust. The modest azimuthal variation may be
explained by some skewness or anisotropy of the spatially-extended source, e.g. with an elliptical or spiral geometry, or
clumping, but it could also be due to the presence of a point-source located at a separation of ~120 mas (17AU) and
carrying ~6*10-3 of the stellar flux.
The Fiber Linked Unit for Optical Recombination (FLUOR) is a precision interferometric beam combiner operating at the CHARA Array on Mt. Wilson, CA. It has recently been upgraded as part of a mission known as “Jouvence of FLUOR” or JouFLU. As part of this program JouFLU has new mechanic stages and optical payloads, new alignment systems, and new command/control software. Furthermore, new capabilities have been implemented such as a Fourier Transform Spectrograph (FTS) mode and spectral dispersion mode. These upgrades provide new capabilities to JouFLU as well as improving statistical precision and increasing observing efficiency. With these new systems, measurements of interferometric visibility to the level of 0.1% precision are expected on targets as faint as 6th magnitude in the K band. Here we detail the upgrades of JouFLU and report on its current status.
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its ~130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope’s overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L’ (3.8 μm), as opposed to the shorter wavelength near-infrared bands (1-2.4 μm) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent (~0.1-1 Gyr) stars. LEECH’s contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5μm in preparation for JWST.
In the course of our VLTI young stellar object PIONIER imaging program, we have identified a strong visibility chromatic dependency that appeared in certain sources. This effect, rising value of visibilities with decreasing wavelengths over one base, is also present in previous published and archival AMBER data. For Herbig AeBe stars, the H band is generally located at the transition between the star and the disk predominance in flux for Herbig AeBe stars. We believe that this phenomenon is responsible for the visibility rise effect. We present a method to correct the visibilities from this effect in order to allow "gray" image reconstruction software, like Mira, to be used. In parallel we probe the interest of carrying an image reconstruction in each spectral channel and then combine them to obtain the final broadband one. As an illustration we apply these imaging methods to MWC158, a (possibly Herbig) B[e] star intensively observed with PIONIER. Finally, we compare our result with a parametric model fitted onto the data.
The visitor instrument PIONIER provides VLTI with improved imaging capabilities and sensitivity. The in-
strument started routinely delivering scientic data in November 2010, that is less than 12 months after being
approved by the ESO Science and Technical Committee. We recall the challenges that had to be tackled to design, built and commission PIONIER. We summarize the typical performances and some astrophysical results obtained so far. We conclude this paper by summarizing lessons learned.
The CHARA-Michigan Phasetracker (CHAMP) successfully tracks fringes in 4-telescope and 6-telescope modes when observing high-visibility targets. We have found that our primary targets (Young Stellar Objects) have unexpectedly low visibility fringes (<20%) for most baselines at CHARA, generally below our tracking thresholds. We have undertaken an upgrade cycle in 2011-2012 to re-optimize CHAMP to allow group-delay tracking on the faintest fringes possible. We describe our multi-pronged strategy using special dicroics, new piezo scanners, and our first attempts to explore CHARA J-band made possible by using special metrology-blocking laser filters. CHAMP can now be used with all the combiners at CHARA.
We report here on some of the major astronomical observations obtained by the Keck Interferometer Nuller (KIN), the
high dynamic range instrument recombining the Keck Telescopes at wavelengths of 8 to 13 microns. A few science
targets were observed during the commissioning phase (2004-2007). These early observations aimed at demonstrating
the KIN’s ability to spatially resolve and characterize circumstellar dust emission around a variety of targets, ranging
from evolved stars to young debris disks. Science operations started then in 2008 with the more demanding KIN exozodi key science programs, augmented by observations of YSOs and hot debris disks between 2009 and 2011. The last
KIN observations were gathered in 2011B, and the interpretation of some of the results depicted here is still preliminary
(exo-zodi survey) or pending (complicated behavior observed in YSOs). We discuss in particular the initial results of the
KIN’s exo-zodi observations, which targeted a total of 40 nearby main sequence single stars. We look for trends in this
sample, searching for possible correlations between the measured KIN excesses and basic stellar properties such as
spectral type or the presence of dust inferred from separate observations.
The Keck Interferometer (KI) combines the two 10m diameter Keck telescopes providing milliarcsecond angular
resolution. KI has unique observing capabilities such as sensitive K-band V2, L-band V2 and N-band nulling modes. The
instrument improvements and status of the Keck Interferometer since the 2010 SPIE meeting are summarized. We
discuss the current capabilities of the KI, operational improvements, and the science from the KI during the past two
years. We will conclude with a brief note on the closure of the KI facility. Details of dual field phase referencing
developments and nulling science results are presented elsewhere at this conference.
Cophasing six telescopes from the CHARA array, the CHARA-Michigan Phasetracker (CHAMP) and Michigan
Infrared Combiner (MIRC) are pushing the frontiers of infrared long-baseline interferometric imaging in key
scientific areas such as star- and planet-formation. Here we review our concepts and recent improvements on
the CHAMP and MIRC control interfaces, which establish the communication to the real-time data recording
& fringe tracking code, provide essential performance diagnostics, and assist the observer in the alignment and
flux optimization procedure. For fringe detection and tracking with MIRC, we have developed a novel matrix
approach, which provides predictions for the fringe positions based on cross-fringe information.
Ground-baseed long baselinne interferomeeters have lonng been limiteed in sensitiviity by the shoort integration periods imposed by atmospheric tuurbulence. Thee first observaation fainter thhan this limit wwas performedd on January 222, 2011 when the Keck Interferommeter observedd a K=11.5 taarget, about onne magnitude fainter than iits K=10.3 limmit. This observation wwas made posssible by the Duual Field Phase Referencing instrument of the ASTRA pproject: simultaaneously measuring thhe real-time efffects of the atmmosphere on a nearby bright guide star, andd correcting foor it on the fainnt target, integration tiime longer thaan the turbulennce time scale are made possible. As a preelude to this ddemonstration, we first present the implementatioon of Dual FField Phase RReferencing onn the interferoometer. We tthen detail itss on-sky performance focusing on tthe accuracy oof the turbulennce correction, and on the reesulting fringe contrast stabiility. We conclude witth a presentatioon of early resuults obtained wwith Laser Guidde Star AO andd the interferommeter.
We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain
very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring
closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the
object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star
around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s)
dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the
PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first
observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique.
ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the existing Keck Interferometer
which aims at providing new self-phase referencing (high spectral resolution observation of YSOs), dual-field
phase referencing (sensitive AGN observations), and astrometric (known exoplanetary systems characterization
and galactic center general relativity in strong field regime) capabilities. With the first high spectral resolution
mode now offered to the community, this contribution focuses on the progress of the dual field and astrometric modes.
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide phase referencing and astrometric
observations at the Keck Interferometer, leading to enhanced sensitivity and the ability to monitor
orbits at an accuracy level of 30-100 microarcseconds. Here we discuss recent scientific results from ASTRA,
and describe new scientific programs that will begin in 2010-2011. We begin with results from the "self phase
referencing" (SPR) mode of ASTRA, which uses continuum light to correct atmospheric phase variations and
produce a phase-stabilized channel for spectroscopy. We have observed a number of protoplanetary disks using
SPR and a grism providing a spectral dispersion of ~ 2000. In our data we spatially resolve emission from dust
as well as gas. Hydrogen line emission is spectrally resolved, allowing differential phase measurements across the
emission line that constrain the relative centroids of different velocity components at the 10 microarcsecond level.
In the upcoming year, we will begin dual-field phase referencing (DFPR) measurements of the Galactic Center
and a number of exoplanet systems. These observations will, in part, serve as precursors to astrometric monitoring
of stellar orbits in the Galactic Center and stellar wobbles of exoplanet host stars. We describe the design
of several scientific investigations capitalizing on the upcoming phase-referencing and astrometric capabilities of ASTRA.
Recently, the Keck interferometer was upgraded to do self-phase-referencing (SPR) assisted K-band spectroscopy at R ~ 2000. This means, combining a spectral resolution of 150 km/s with an angular resolution of 2.7 mas, while maintaining
high sensitiviy. This SPR mode operates two fringe trackers in parallel, and explores several infrastructural requirements
for off-axis phase-referencing, as currently being implemented as the KI-ASTRA project. The technology of self-phasereferencing
opens the way to reach very high spectral resolution in near-infrared interferometry. We present the scientific
capabilities of the KI-SPR mode in detail, at the example of observations of the Be-star 48 Lib. Several spectral lines of the
cirumstellar disk are resolved. We describe the first detection of Pfund-lines in an interferometric spectrum of a Be star, in
addition to Br γ. The differential phase signal can be used to (i) distinguish circum-stellar line emission from the star, (ii) to directly measure line asymmetries tracing an asymetric gas density distribution, (iii) to reach a differential, astrometric
precision beyond single-telescope limits sufficient for studying the radial disk structure. Our data support the existence of
a radius-dependent disk density perturbation, typically used to explain slow variations of Be-disk hydrogen line profiles.
The Keck Interferometer combines the two 10 m Keck telescopes as a long baseline interferometer. It is funded by
NASA as a joint development among the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the NASA
Exoplanet Science Institute. In February 2008, the 10 um nulling mode began a 32 night observing program with three
key science teams to perform a survey of nearby stars for exozodiacal dust. This program has recently concluded, and
has been followed by nuller observing on a variety of science topics through the standard proposal process. We provide a
review and update of the nuller implementation, and describe the data reduction process, including the calibration
approach. We then review the technical performance of the instrument based on the full key science data set, including
sensitivity and systematic errors. We also provide some summary data on atmospheric effects applicable to the cophasing approach.
In this paper, we present the results of three different studies of the Fomalhaut debris disk with infrared interferometry.
First, VLTI/AMBER measurements are used to determine the position angle of the slightly oblate
rapidly rotating photosphere by means of differential phase measurements across the Br-gamma photospheric
line. This measurement allows us to confirm that the debris disk is located in the equatorial plane of its host
star. Second, we use VLTI/VINCI to search for resolved near-infrared emission around the stellar photosphere,
which would correspond to the presence of large amounts of hot dust grains located between the sublimation
radius and the habitable zone. Our observations reveal a small excess of 0.88%±0.12% in K band relative to the
photospheric flux. Finally, we use the Keck Interferometer Nuller in order to derive additional constraints on the
nature of the resolved infrared emission. Our observations suggest a marginal detection of a circumstellar excess
at 10 μm, which we use together with the VINCI detection to model the circumstellar emission. Preliminary results from this modeling effort are discussed.
KEYWORDS: Stars, Interferometers, Calibration, K band, L band, Interferometry, Nulling interferometry, Visibility, Active galactic nuclei, Data modeling
The addition of new observational capabilities and continued sensitivity improvements have allowed observations
with the Keck Interferometer to encompass new areas of astrophysics and expanded significantly the available sample size in areas which had been the focus of previous work. The technical details of the instrument techniques (including nulling, L-band and increased spectral resolution) are covered in other contributions to this conference. Here, we will highlight the astrophsyics enabled by these instruments including: a summary of the NASA Exo-zodical Dust Survey Key Project, observations across a range of dust temperatures with K and L-band measurements and faint target studies of active galactic nuclei and young stellar disks.
Based on the success of four-telescope imaging with the Michigan Infrared Combiner (MIRC) on the CHARA
Array, our Michigan-based group will now upgrade our system to combine all six CHARA telescope simultaneously.
In order to make this observationally efficient, we have had to improve a number of subsystems and
commission new ones, including the new CHAMP fringe tracker, the introduction of photometric channels, the
upgrading of the realtime operating systems, and the obvious hardware and software upgrades of the control
system and the data pipeline. Here we will discuss the advantages of six-telescope operation, outline our upgrade
plans and discuss our current progress.
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to
see its first fringes in 2010. It combines four ATs or four UTs
using a pairwise ABCD integrated optics combiner that can also be
used in scanning mode. It provides low spectral resolution in H and K band. PIONIER is designed for
imaging with a specific emphasis on fast fringe recording to allow
closure-phases and visibilities to be precisely measured. In
this work we provide the detailed description of the instrument and
present its updated status.
The Keck Interferometer (KI) combines the two 10m diameter Keck telescopes providing milliarcsecond angular
resolution. KI has unique observing capabilities such as sensitive K-band V2, L-band V2 and N-band nulling operations. The instrument status of the Keck Interferometer since the last SPIE meeting in 2008 is summarized. We discuss the
performance of new visibility observing capabilities including L-band and self-phase referencing modes. A simultaneous
dual-beam-combiner mode in the K and L-band has been demonstrated, nearly doubling operational efficiency for bright
targets. Operational improvements including simplified reliable operations with reduced personnel resources are
highlighted. We conclude with a brief review of the current and future developmental activities of KI. Details of ASTRA
developments, nulling performance and science results are presented elsewhere at this conference.
A working group on interferometry data standards has been established within IAU Commission 54 (Optical/
Infrared Interferometry). The working group includes members representing the major optical interferometry
projects worldwide, and aims to enhance existing standards and develop new ones to satisfy the broad interests
of the optical interferometry community. We present the initial work of the group to enhance the OIFITS data
exchange standard, and outline the software packages and libraries now available which implement the standard.
Using the sub-milli-arcsecond resolution of the CHARA interferometer array and
combining light with the 2-telescope combiner CHARA Classic, we have detected
strong near-infrared (NIR) emission interior to the dust-sublimation radius of
Herbig Ae stars MWC275 and AB Aur. The large contribution of this emission
component, which we argue to be hot gas, to the total NIR spectral energy distribution
(SED) is not predicted by current models of the dust evaporation front,
indicating that the NIR disk is more complicated than expected. Furthermore,
we demonstrate that the structure of the evaporation front in MWC275 is time
variable, making single epoch, large uv coverage observations critical to decoding
front geometry. With the commissioning of CHARA Michigan Phase Tracker
in the summer of 2008, the Michigan Infrared Combiner (a 6 telescope combiner
at CHARA) will become an ideal instrument for studying the evaporation
front, achieving the required sensitivities to begin the first "true" interferometric
imaging of the gas-dust transition region in young stellar objects (YSOs).
Here, we summarize results on the evaporation front structure obtained with
CHARA Classic and describe future prospects with CHARA MIRC in elucidating
morphology of the gas-dust transition region.
The CHARA Michigan Phase-tracker (CHAMP) is a real-time fringe tracker for the CHARA Array, a six-telescope
long baseline optical interferometer on Mount Wilson, California. CHAMP has been optimized for
tracking sensitivity at J, H, or K bands and is not meant as a science instrument itself. This ultimately results
in maximum sensitivity for all the science beam combiners that benefit from stabilized fringes. CHAMP was
designed, built, and tested in the laboratory at the University of Michigan and will be delivered to the CHARA
Array in 2008. We present the final design of CHAMP, highlighting some its key characteristics, including a novel
post-combination transport and imaging system. We also discuss testing and validation studies and present first
closed-loop operation in the laboratory.
The Keck Interferometer combines the two 10 m Keck telescopes as a long baseline interferometer, funded by
NASA, as a joint development among the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the
Michelson Science Center. Since 2004, it has offered an H- and K-band fringe visibility mode through the Keck
TAC process. Recently this mode has been upgraded with the addition of a grism for higher spectral resolution.
The 10 um nulling mode, for which first nulling data were collected in 2005, completed the bulk of its engineering
development in 2007. At the end of 2007, three teams were chosen in response to a nuller key science call to
perform a survey of nearby stars for exozodiacal dust. This key science observation program began in Feb. 2008.
Under NSF funding, Keck Observatory is leading development of ASTRA, a project to add dual-star capability for
high sensitivity observations and dual-star astrometry. We review recent activity at the Keck Interferometer, with an
emphasis on the nuller development.
The Keck Interferometer combines the two 10m diameter Keck telescopes for near-infrared fringe visibility, and mid-infrared
nulling observations. We report on recent progress with an emphasis on new visibility observing capabilities,
operations improvements for visibility and nulling, and on recent visibility science. New visibility observing capabilities
include a grism spectrometer for higher spectral resolution. Recent improvements include a new AO output dichroic for
increased infrared light throughput, and the installation of new wave-front controllers on both Keck telescopes. We also
report on recent visibility results in several areas including (1) young stars and their circumstellar disks, (2) pre-main
sequence star masses, and (3) Circumstellar environment of evolved stars. Details on nuller instrument and nuller science
results, and the ASTRA phase referencing and astrometry upgrade, are presented in more detail elsewhere in this
conference.
The infrared optical telescope array (IOTA), one of the most productive interferometers in term of science and
new technologies was decommissioned in summer 2006. We discuss the testing of a low-resolution spectrograph
coupled with the IOTA-3T integrated-optics beam combiner and some of the scientific results obtained from this
instrument.
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.
The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a spacecraft-borne nulling
interferometer for high-resolution astronomy and the direct detection of exoplanets and assay of their
environments and atmospheres. FKSI is a high angular resolution system operating in the near to mid-infrared
spectral region and is a scientific and technological pathfinder to the Darwin and Terrestrial Planet
Finder (TPF) missions. The instrument is configured with an optical system consisting, depending on
configuration, of two 0.5 - 1.0 m telescopes on a 12.5 - 20 m boom feeding a symmetric, dual Mach-
Zehnder beam combiner. We report on progress on our nulling testbed including the design of an optical
pathlength null-tracking control system and development of a testing regime for hollow-core fiber
waveguides proposed for use in wavefront cleanup. We also report results of integrated simulation studies
of the planet detection performance of FKSI and results from an in-depth control system and residual
optical pathlength jitter analysis.
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 present the design for a near-infrared (JHK) fringe tracker to be used at the CHARA Array, a long baseline optical interferometer located at Mount Wilson Observatory. The CHARA Michigan Phase-tracker (CHAMP) is being fabricated and tested at the University of Michigan and will be transported to the CHARA Array for general use. CHAMP is separate from the science combiners and can therefore be optimized for fringe tracking. It will modulate around fringe center by 1-2λ at up to 500 Hz and calculate phase offsets in real-time using a modified 'ABCD' method . Six pair-wise Mach-Zehnder combiners will phase the entire Array. We give an overview of the optical layout and discuss our design strategy. Components such as the path-length modulators, low-OH fiber transport system, 1024x1024 HAWAII-1 detector, and control computer are discussed.
We present a brief review of recent scientific and technical advances at the Infrared Optical Telescope Array (IOTA). IOTA is a long-baseline interferometer located atop Mount Hopkins, Arizona. Recent work has emphasized the use of the three-telescope interferometer completed in 2002. We report on results obtained on a range of scientific targets, including AGB stars, Herbig AeBe Stars, binary stars, and the recent outburst of the recurrent nova RS Oph. We report the completion of a new spectrometer which allows visibility measurements at several high spectral resolution channels simultaneously. Finally, it is our sad duty to report that IOTA will be closed this year.
In this paper we report on progress at the Keck Interferometer since the 2004 SPIE meeting with an emphasis on the operations improvements for visibility science.
The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for an imaging and nulling interferometer for the near infrared to mid-infrared spectral region (3-8 microns). FKSI is a scientific and technological pathfinder to TPF/DARWIN as well as SPIRIT, SPECS, and SAFIR. It will also be a high angular resolution system complementary to JWST. There are four key scientific issues the FKSI mission is designed to address. First, we plan to characterize the atmospheres of the known extra-solar giant planets. Second, we will explore the morphology of debris disks to look for resonant structures to find and characterize extrasolar planets. Third, we will observe young stellar systems to understand their evolution and planet forming potential, and study circumstellar material around a variety of stellar types to better understand their evolutionary state. Finally, we plan to measure detailed structures inside active galactic nuclei. We report results of simulation studies of the imaging capabilities of the FKSI with various configurations of two to five telescopes including the effects of thermal noise and local and exozodiacal dust emission. We also report preliminary results from our symmetric Mach-Zehnder nulling testbed.
We present the design of the Michigan Infra-Red Combiner (MIRC). MIRC
is planned for deployment at the Georgia State University CHARA array
to simultaneously combine all six telescope beams in an image-plane
combiner. The novel design incorporates spatial-filtering with
single-mode fiber optics, a synthetic (densified) pupil, and a
low-resolution spectrometer to allow good calibration and efficient
aperture synthesis imaging in the near-infrared. In addition, the
focalization and spectrometer optics can accommodate an integrated
optics component with minimal re-alignment. The MIRC concept can be
scaled-up for interferometer arrays with more telescopes.
We describe the fringe-packet tracking software installed at the infrared optical telescope array (IOTA). Three independently developed fringe-packet tracking algorithms can be used to equalise the optical path lengths at the interferometer. We compare the performance of these three algorithms and show results obtained tracking fringes for three independent baselines on the sky.
The visibility science mode of the Keck Interferometer fully transitioned into operations with the successful completion of its operational readiness review in April 2004. The goal of this paper is to describe this science mode and the operations structure that supports it.
The Antarctic Planet Interferometer is a concept for an instrument designed to detect and characterize extrasolar planets by exploiting the unique potential of the best accessible site on earth for thermal infrared interferometry. High-precision interferometric techniques under development for extrasolar planet detection and characterization (differential phase, nulling and astrometry) all benefit substantially from the slow, low-altitude turbulence, low water vapor content, and low temperature found on the Antarctic plateau. At the best of these locations, such as the Concordia base being developed at Dome C, an interferometer with two-meter diameter class apertures has the potential to deliver unique science for a variety of topics, including extrasolar planets, active galactic nuclei, young stellar objects, and protoplanetary disks.
Closure-phase science and technology are dominant features of the recent activity at IOTA.
Our science projects include imaging several spectroscopic binary stars, imaging YSOs including Herbig AeBe stars, detecting asymmetries in a large sample of Mira stars, and measuring water shells around Miras.
Many technology projects were pursued in order to make these science observations possible. These include installation of a third-generation integrated-optics 3-beam combiner (IONIC), completion of the real-time control system software, installation of fringe-packet tracking software, use of narrow sub-H band filters, validation of
the phase-closure operation, development of CPLD control of the science camera (PICNIC) and star-tracker camera (LLiST), installation of a new star-tracker camera, expansion of the observing facility, and installation of new semi-automated optical alignment tools.
The Fourier-Kelvin Stellar Interferometer (FKSI) is a mission concept for a nulling interferometer for the near-to-mid-infrared spectral region (3-8µm). FKSI is conceived as a scientific and technological precursor to TPF. The scientific emphasis of the mission is on the evolution of protostellar systems, from just after the collapse of the precursor molecular cloud core, through the formation of the disk surrounding the protostar, the formation of planets in the disk, and eventual dispersal of the disk material. FKSI will answer key questions about extrasolar planets:
Σ What are the characteristics of the known extrasolar giant planets?
Σ What are the characteristics of the extrasolar zodiacal clouds around nearby stars?
Σ Are there giant planets around classes of stars other than those already studied?
We present preliminary results of a detailed design study of the FKSI. Using a nulling interferometer configuration, the optical system consists of two 0.5m telescopes on a 12.5m boom feeding a Mach-Zender beam combiner with a fiber wavefront error reducer to produce a 0.01% null of the central starlight. With this system, planets around nearby stars can be detected and characterized using a combination of spectral and spatial resolution.
We are working towards imaging the surfaces and circumstellar envelopes of Mira stars in the near-infrared, using the IOTA interferometer and the IONIC integrated-optics 3-beam combiner. In order to study atmospheric structures of these stars, we installed 3 narrow-band filters that subdivide H-band into 3 roughly equal-width sub-bands - a central one for continuum, and 2 adjacent ones to sample Mira star's (mostly water) absorption-bands. We present here our characterization of the IOTA 3-Telescope interferometer for closure-phase measurements with broad and narrow-band filters in the H atmospheric window. This includes characterizing the stability, chromaticity, and polarization effects of the present IOTA optics with the IONIC beam-combiner, and characterizing the accuracy of our closure phase measurements.
The design and scientific objectives of a near infrared channeled spectrometer planned at the IOTA interferometer are discussed. The spectrometer has the flexibility to reconfigure easily for conventional broadband operations in addition to multi-channel mode. This instrument makes use of the existing PICNIC camera at the IOTA in order to be cost efficient. The spectrometer has been designed specifically for studying Mira stars. However, it will find its application in other areas of astrophysical interests such as studies of circumstellar disks around young stars and binary stars.
Several scientific topics linked to the observation of extended structures around astrophysical sources (dust torus around AGN, disks around young stars, envelopes around AGBs) require imaging capability with milli-arcsecond spatial resolution. The current VLTI instruments, AMBER and MIDI, will provide in the coming months the
required high angular resolution, yet without actual imaging. As a rule of thumb, the image quality accessible with an optical interferometer is directly related to the number of telescopes used simultaneously: the more the apertures, the better and the faster the reconstruction of the image. We propose an instrument concept to
achieve interferometric combination of N telescopes (4 ≤ N ≤ 8) thanks to planar optics technology: 4 x 8-m telescopes in the short term and/or 8 x 1.8-m telescopes in the long term. The foreseen image reconstruction quality in the visible and/or in the near infrared will be equivalent to the one achieved with millimeter radio interferometers. Achievable spatial resolution will be better than the one foreseen with ALMA. This instrument would be able to acquire routinely 1 mas resolution images. A 13 to 20 magnitude sensitivity in spectral ranges from 0.6 to 2.5 μm is expected depending on the choice of the phase referencing guide source. High dynamic range, even on faint objects, is achievable thanks to the high accuracy provided by integrated optics
for visibility amplitude and phase measurements. Based on recent validations of integrated optics presented here an imaging instrument concept can be proposed. The results obtained using the VLTI facilities give a demonstration of the potential of the proposed technique.
Single-mode fibers have been used in the near-infrared to dramatically reduce calibration error for long-baseline interferometry. We have begun an effort to apply the advantages of spatial filtering at visible wavelengths for precision measurements of pulsating Cepheids using the IOTA interferometer. Rather than employing photometric taps to calibrate fluctuating coupling efficiency, we are using an "asymmetric" coupler which allows this calibration to be done without losing photons. The Single-Mode Asymmetric Recombination Technique (SMART) experiment has finished lab-testing, and has been installed at IOTA for full commissioning in Summer 2002. We report the results of lab characterization and first sky tests, as well as first fringes on a star using a visible-wavelength single-mode coupler. With both lab and sky experience using unpolarized light, we have found that circular silica fibers are quite practical for precision interferometric measurements. We conclude that circular fibers (as opposed to polarization maintaining fibers) have an undeserved poor reputation and that birefringence effects pose no significant difficulty.
We present observations of the symbiotic star CH Cyg with a new JHK-band beam combiner mounted to the IOTA interferometer. The new beam combiner consists of an anamorphic cylindrical lens system and a grism, and allows the simultaneous recording of spectrally dispersed J-, H- and K-band Michelson interferograms. The observations of CH Cyg were conducted on 5, 6, 8 and 11 June 2001 using baselines of 17m to 25m. From the interferograms of CH Cyg, J-, H-, and K-band visibility functions can be determined. Uniform-disk fits to the visibilities give, e.g., stellar diameters of (7.8 ± 0.6) mas and (8.7 ± 0.8) mas in H and K, respectively. Angular stellar filter radii and Rosseland radii are derived from the measured visibilities by fitting theoretical center-to-limb intensity variations (CLVs) of Mira star models. The available HIPPARCOS parallax of CH Cyg allows us to determine linear radii. For example, on the basis of the K-band visibility, Rosseland radii in the range of 214 to 243 solar radii can be derived utilizing CLVs of different fundamental mode Mira models as fit functions. These radii agree well within the error bars with the corresponding theoretical model Rosseland radii of 230 to 282 solar radii. Models of first overtone pulsators are not in good agreement with the observations. The wavelength dependence of the stellar diameter can be well studied by using visibility ratios V(λ1)/V(λ2) since ratios of visibilities of different spectral channels can be measured with higher precision than absolute visibilities. We found that the 2.03 μm uniform disk diameter of CH Cyg is approximately 1.1
times larger than the 2.15 μm and 2.26 μm uniform-disk diameter.
As the number of optical interferometers increase, multi-facility observations become both feasible and scientifically interesting. For
imaging of complex sources, the capability of increasing (u,v) coverage by using multiple arrays may be necessary for accurately interpreting the fringe visibility and closure phase data. Toward this end, coordinated observations with the IOTA interferometer and Keck aperture masking have been carried out to test techniques for synthesizing images using data from heterogeneous arrays with sparse (u,v) coverage. In particular, we will focus on how the image prior in the Maximum Entropy Method can be used to efficiently incorporate very high spatial frequency information with "low-resolution" data for imaging the generic prototype "Star + Dust Shell" image morphology. Preliminary results using real data for a few dusty
evolved stars are presented.
New beam combination techniques, using two and three telescopes, have been the focus of activity at IOTA during the past two years since our last update. In particular, we have added a third telescope, made closure-phase measurements, demonstrated two- and three-beam combination with integrated optics combiners, demonstrated two-beam combination with an asymmetric coupler, and made simultaneous JHK visibility measurements with an image-plane combiner.
We report the first long-baseline interferometric observations of R CrB. The observations were carried out at the Infrared Optical Telescope Array (IOTA), using our new JHK beam combiner which enables us to record fringes simultaneously in the J-, H-, and K-bands. The circumstellar envelope of R CrB is resolved at a baseline of 21 m, and the K-band visibility is derived to be 0.61 ± 0.03 along a position angle of about 170 degrees. The visibility obtained with IOTA, as well as speckle visibilities with baselines up to 6 m and the spectral energy distribution (SED), are fitted with 2-component models consisting of the central star and an optically thin dust shell. The K-band visibilities predicted by the models are about 10% smaller than the visibility obtained with IOTA. However, given the simplifications adopted in our models and the complex nature of the object, this can be regarded as rough agreement. As a hypothesis to explain the small discrepancy, we propose that there might be a group of newly formed dust clouds, which might appear as a third visibility component.
The IOTA (Infrared Optical Telescope Array) has been routinely
operating with two-telescopes since 1994, a mode destined to become
obsolete following its recent conversion to a three-telescope
array. In two-telescope mode, the IOTA has made numerous
scientific and technical contributions, see e.g. our list of
publications at http://cfa-www.harvard.edu/cfa/oir/IOTA/PUBLI/publications.html.
We present preliminary results on three different topics using recent
data from the two-telescope IOTA: (1) measurements of Mira star
diameters simultaneously in three different near-infrared spectral
bands, (2) measurement of the characteristic size and shape of the
source of near-infared emission in the x-ray binary system CI Cam, and (3) aperture synthesis of the Carbon star V Hydrae combining data from the IOTA and from aperture masking at the Keck-I telescope.
Our new IOTA JHK-band beam combiner allows the simultaneous recording of spectrally dispersed J-, H- and K-band Michelson interferograms. In this paper we present our IOTA observations of the Mira star T Cep with this beam combiner (observations in June 2001; four baselines in the range of 14 m to 27 m). The beam combiner optics consists of an anamorphic cylindrical lens system and a prism. From the interferograms of T Cep we derive the visibilities and the J-, H-, and K-band uniform-disk diameters of 14.0 ± 0.6 mas, 13.7 ± 0.6 mas and 15.0 ± 0.6 mas, respectively. Angular stellar filter radii and Rosseland radii are derived from the measured visibilities by fitting theoretical center-to-limb intensity variations (CLVs) of different Mira star models. The available HIPPARCOS parallax (4.76 ± 0.75 mas) of T Cep allows us to determine linear radii. For example, from the K-band visibility we derive a Rosseland radius of 329-50/+70 solar radii if we use the CLVs of the M-models as fit functions. This radius is in good agreement with the theoretical M-model Rosseland radius of 315 solar radii. The comparison of measured stellar parameters (e.g. diameters, effective temperature, visibility shape) with theoretical parameters indicates whether any of the models is a fair representation of T Cep.
The ratios of visibilities of different spectral channels can be measured with higher precision than absolute visibilities. Therefore, we use the visibility ratios V(λ1)/V(λ2) to investigate the wavelength dependence of the stellar diameter. We find that the 2.03 μm uniform-disk diameter of T Cep is about 1.26 times larger than the 2.26 μm uniform-disk diameter.
We report here the first visibility and closure-phase measurements done with the IONIC instrument at the IOTA interferometer. The IONIC
instrument is presented and preliminary analysis of the results
discussed. Future improvements of IONIC are envisioned.
We describe the new control system for the PICNIC near-infrared camera and the visible star tracker, implemented at the IOTA interferometer, based on the ALTERA Complex Programmable Logic Device (CPLD) technology. These digital components provide an adaptive interface between the control system and the cameras used at IOTA, allowing flexibility when connecting very different devices. In particular the clocking and processing circuits used for the PICNIC camera can be changed in milliseconds during normal operation. The camera can then switch between full quadrant readout mode used for alignment and diagnostics, and a N pixel readout mode used for science operation.
We have conducted the first systematic study of Herbig Ae/Be stars using the technique of long baseline stellar interferometry. The Infrared Optical Telescope Array resolves the source of the near-infrared excess flux characteristic of these systems in 11 of the 15 stars observed. A close companion to MWC 361-A (18 mas separation) has been detected interferometrically for the first time. The visibility data has been interpreted within the context of four models which represent the range of plausible representations for the brightness of the excess emission: a Gaussian distribution, a narrow uniform ring, an accretion disk, and an infrared companion. We find that the large sizes measured by the interferometer, 0.5 - 5.9 AU, essentially invalidate accretion disk models that had been previously used to explain the spectroscopic observations. Although a unique model can not be determined for each source due to limited spatial frequency coverage, the observed symmetry of the sources favors, for the ensemble of the data, models in which the circumstellar dust is distributed in spherical envelopes.
We present K-band observations of five Mira stars with the IOTA interferometer. The interferograms were obtained with the FLUOR fiber optics beam combiner which provides high- accuracy visibility measurements in spite of time-variable atmospheric conditions. For the Mira stars X Oph, R Aql, RU Her, R Ser, and V CrB we derived the uniform-disk diameters 11.7 mas, 10.9 mas, 8.4 mas, 8.1 mas, and 7.9 mas (+/- 0.3 mas), respectively. Simultaneous photometric observations yielded the bolometric fluxes. The derived angular Rosseland radii and the bolometric fluxes allowed the determination of effective temperatures. For instance, the effective temperature of R Aql was determined to be 3072 K +/- 161 K. A Rosseland radius for R Aql of 250 R. +/- 63 R. was derived from the angular Rosseland radius of 5.5 mas +/- 0.2 mas and the HIPPARCOS parallax of 4.73 mas +/- 1.19 mas. The observations were compared with theoretical Mira star models (D/P model Rosseland radius equals 255 R.; measured R Aql Rosseland radius equals 250 R. +/- 63 R.).
The third telescope project to enable phase-closure observations at the IOTA interferometer is well underway, and is anticipated to be completed later this year. For this project, we present the main technical improvements which we have already made or expect to make, including a new VxWorks control system, improved star acquisition cameras, improved siderostat and primary mirror supports, five-axis control of the telescope secondary mirrors, automated control of the long delay line, trihedral retroreflectors, three-beam combination, the PICNIC camera, and fringe packet tracking.
Following a previous successful study, we present new and more complete interferometric observations of FU Orionis. The combination of both IOTA (Infrared and Optical Telescope Array, Mt. Hopkins, AZ) and PTI (Palomar Testbed Interferometer, Palomar Observatory, CA) interferometers allowed an increase in (u, v) coverage and H and K bands measurements. We confirm the presence of a resolved structure around FU Ori that can be interpreted in terms of accretion disk. However, we find significant differences between our results and standard accretion disks models. In particular the temperature power law is best explained if two different radial regimes are used. Moreover, a clear visibility oscillation trend at 110 m is well fitted with a binary (or hot spot) model. This may have important implications on accretion disk models for such objects.
We summarize the characteristics and performance of a recent instrument for the detection of interference fringes in the near IR at the IR Optical Telescope Array (IOTA). The instrument had its first test run and saw 'first fringes' in Spring 1997, and has been regularly used since by several groups at the IOTA for a variety of high resolution investigations in the near IR. We present preliminary results from our group's campaign to study Mira variables and the circumstellar environments of Herbig AeBe stars.
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