NESSI and `Alopeke are two speckle imaging instruments for community use at the WIYN and Gemini-North telescopes. The two instruments were built at NASA ARC and include the capability for wide-field and traditional CCD imaging. Speckle interferometry utilizes extremely short exposures to produce interferograms from the turbulent atmosphere that are reconstructed into a diffraction-limited image, effectively giving space-based resolution from the ground. A primary role of these instruments is exoplanet validation for the Kepler, K2, TESS, and many RV programs. Contrast ratios of 6 or more magnitudes are easily obtained. The instrument uses two EMCCD cameras and two filter wheels to provide simultaneous dual-color observations in either narrowband or SDSS broadband filters to characterize detected companions. High resolution imaging enables the identification of blended binaries that contaminate many exoplanet detections, leading to incorrectly measured radii.
Speckle imaging produces diffraction-limited images from ground-based telescopes. Recent advancements in detectors such as electron-multiplying CCDs (EMCCDs), have spawned a resurgence of this technique, greatly improving sensitivity and observing efficiency. The high angular resolution provided by speckle imaging can discern blended binary system contamination and validate suspected exoplanets discovered by the Kepler and K2 transit surveys. High-resolution follow-up will also be required for upcoming missions including TESS. Multiplicity can be determined along with separation, position angle, photometry, and contrast ratio. In this way, speckle imaging can validate even small, rocky planets like TRAPPIST-1 and constrain exoplanet radii and density. Some of the developments leading to this technique will be discussed in conjunction with recent significant papers, ongoing speckle imaging programs, and prospects for the future.
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.
Two new instruments are currently being built for the Gemini-North and WIYN telescopes. They are based on the existing DSSI (Differential Speckle Survey Instrument), but the new dual-channel instruments will have both speckle and "wide-field" imaging capabilities. Nearly identical copies of the instrument will be installed as a public access permanent loan at the Gemini-N and WIYN telescopes. Many exoplanet targets will come from the NASA K2 and TESS missions. The faint limiting magnitude, for speckle observations, will remain around 16 to 17th magnitude depending on observing conditions, while wide-field, high speed imaging should be able to go to 21+. For Gemini, the instrument will be remotely operable from either the mid-level facility at Hale Pohaku or the remote operations base in Hilo.
The interferometric concept named ALOHA (Astronomical Light Optical Hybrid Analysis) offers an alternative for high resolution imaging in the mid-infrared domain by shifting the astronomical light to shorter wavelength where optical guided components from telecommunications are available and efficient. A prototype with two arms converting a signal from 1.55 μm to 630 nm is used to validate the concept in laboratory and on-sky. Thanks to collaboration with the CHARA team, photometric tests were achieved with a single arm of the interferometer and have allowed to predict instrument performance in its interferometric configuration in order to obtain first fringes in H band.
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.
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 K′−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.
We propose an exotic use of sum frequency generation process (SFG) to develop a new kind of high resolution interferometer for astronomical imaging. SFG is well known to be intrinsically a noiseless non linear process of upconversion which permits a wavelength shift. Thereby we propose to shift astronomical MIR and FIR radiation to shorter wavelength where optical fibers and optical components are available and efficient. In order to demonstrate the validity of this method for high resolution imaging, we plan to set up a two-arm upconversion interferometer on the CHARA telescope array (California). Each arm would include an upconversion stage at the focus of telescope. The success of such a project is obviously conditioned by the quality of nonlinear components (waveguided PPLN) in term of efficiency and noise biases. Moreover, coherence study requires the use of identical non linear components which implies manufacturing constraints. To ensure the feasibility of this project, several studies have been conducted. By implementing an upconversion interferometer in laboratory we have recently demonstrated our ability to analyze the coherence properties of a 1550nm signal at visible wavelength. We also have successfully converted astronomical light using one arm of this interferometer at the Hawaï observatory. It showed the capability of our instrument to astronomical observing conditions in photon counting regime. A preliminary mission at CHARA observatory allowed us to check the compatibility of our instrument with the environment onsite and expected photometric levels. From these data we estimate to be able to study the coherence of astronomical target at 1550nm using such an instrument.
FLUOR, which has been operational on CHARA since 2002, is an infrared fiber beam combiner. The telescope array will
soon be fitted with an adaptive optics system, which will enhance the interferometer performance. In this framework,
FLUOR has been entirely redeveloped and will be able to measure visibilities with higher accuracy and better sensitivity. The technical upgrades consist of improving some existing systems and developing new features. The bench, which is now remotely operable, primarily offers spectral dispersion (long fringes scanning), a more sensitive camera and a Fourier Transform Spectrometer mode. This paper presents the detailed opto-mechanical design of JouFLU (FLUOR rejuvenation), and the current instrument status.