The Navy Precision Optical Interferometer (NPOI) is currently undergoing a fundamental renaissance in its functionality and capabilities. Operationally, its fast delay line (FDL) infrastructure is completing its upgrade from a VME/VxWorks foundation to a modern PC/RTLinux core. The Classic beam combiner is being upgraded with the New Classic FPGA-based backend, and the VISION beam combiner has been upgraded over this past summer with low-noise EMCCD cameras, resulting in substantial gains in sensitivity. Building on those infrastructure improvements, substantial upgrades are also in progress. Three 1-meter PlaneWave CDK1000 telescopes are being delivered to the site, along with their relocatable enclosure-transporters, and stations are being commissioned for those telescopes with baselines ranging from 8 meters to 432 meters. Baseline-wavelength bootstrapping will be implemented on the facility back-end with a near-infrared beam combiner under development. Collectively, these improvements mark substantial progress in taking the facility towards realizing its full intrinsic potential.
High-resolution broadband spectroscopy at near-infrared (NIR) wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar, with the TEDI interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec NIR echelle spectrograph. These are the first multidelay EDI demonstrations on starlight. We demonstrated very high (10×) resolution boost and dramatic (20× or more) robustness to point spread function wavelength drifts in the native spectrograph. Data analysis, results, and instrument noise are described in a companion paper (part 1). This part 2 describes theoretical photon limited and readout noise limited behaviors, using simulated spectra and instrument model with noise added at the detector. We show that a single interferometer delay can be used to reduce the high frequency noise at the original resolution (1× boost case), and that except for delays much smaller than the native response peak half width, the fringing and nonfringing noises act uncorrelated and add in quadrature. This is due to the frequency shifting of the noise due to the heterodyning effect. We find a sum rule for the noise variance for multiple delays. The multiple delay EDI using a Gaussian distribution of exposure times has noise-to-signal ratio for photon-limited noise similar to a classical spectrograph with reduced slitwidth and reduced flux, proportional to the square root of resolution boost achieved, but without the focal spot limitation and pixel spacing Nyquist limitations. At low boost (∼1×) EDI has ∼1.4× smaller noise than conventional, and at >10× boost, EDI has ∼1.4× larger noise than conventional. Readout noise is minimized by the use of three or four steps instead of 10 of TEDI. Net noise grows as step phases change from symmetrical arrangement with wavenumber across the band. For three (or four) steps, we calculate a multiplicative bandwidth of 1.8:1 (2.3:1), sufficient to handle the visible band (400 to 700 nm, 1.8:1) and most of TripleSpec (2.6:1).
The TOU robotic, compact very high resolution optical spectrograph (R=100,000, 0.38-0.9 microns) has been fully characterized at the 2 meter Automatic Spectroscopy Telescope (AST) at Fairborn Observatory in Arizona during its pilot survey of 12 bright FGK dwarfs in 2015. This instrument has delivered sub m/s Doppler precision for bright reference stars (e.g., 0.7 m/s for Tau Ceti over 60 days) with 5-30 min exposures and 0.7 m/s long-term instrument stability, which is the best performance among all of the known Doppler spectrographs to our knowledge. This performance was achieved by maintaining the instrument in a very high vacuum of 1 micron torr and about 0.5 mK (RMS) long-term temperature stability through an innovative close-loop instrument bench temperature control. It has discovered a 21 Earth-mass planet (P=43days) around a bright K dwarf and confirmed three super-Earth planetary systems, HD 1461, 190360 and HD 219314. This instrument will be used to conduct the Dharma Planet Survey (DPS) in 2016-2019 to monitor ~100 nearby very bright FGK dwarfs (most of them brighter than V=8) at the dedicated 50-inch Robotic Telescope on Mt. Lemmon. With very high RV precision and high cadence (~100 observations per target randomly spread over 450 days), a large number of rocky planets, including possible habitable ones, are expected to be detected. The survey also provides the largest single homogenous high precision RV sample of nearby stars for studying low mass planet populations and constraining various planet formation models. Instrument on-sky performance is summarized.
High-resolution broadband spectroscopy at near-infrared wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar. Observations of stars were performed with the “TEDI” interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec near-infrared echelle spectrograph. These are the first multidelay EDI demonstrations on starlight, as earlier measurements used a single delay or laboratory sources. We demonstrate very high (10×) resolution boost, from original 2700 to 27,000 with current set of delays (up to 3 cm), well beyond the classical limits enforced by the slit width and detector pixel Nyquist limit. Significantly, the EDI used with multiple delays rather than a single delay as used previously yields an order of magnitude or more improvement in the stability against native spectrograph point spread function (PSF) drifts along the dispersion direction. We observe a dramatic (20×) reduction in sensitivity to PSF shift using our standard processing. A recently realized method of further reducing the PSF shift sensitivity to zero is described theoretically and demonstrated in a simple simulation which produces a 350× times reduction. We demonstrate superb rejection of fixed pattern noise due to bad detector pixels—EDI only responds to changes in pixel intensity synchronous to applied dithering. This part 1 describes data analysis, results, and instrument noise. A section on theoretical photon limited sensitivity is in a companion paper, part 2.
Jian Ge, Scott Powell, Bo Zhao, Frank Varosi, Bo Ma, Sirinrat Sithajan, Jian Liu, Rui Li, Nolan Grieves, Sidney Schofield, Louis Avner, Hali Jakeman, William Yoder, Jakob Gittelmacher, Michael Singer, Matthew Muterspaugh, Michael Williamson, J. Maxwell
One of the most astonishing results from the HARPS and Kepler planet surveys is the recent
discovery of close-in super-Earths orbiting more than half of FGKM dwarfs. This new
population of exoplanets represents the most dominant class of planetary systems known to date,
is totally unpredicted by the classical core-accretion disk planet formation model. High cadence
and high precision Doppler spectroscopy is the key to characterize properties of this new
population and constrain planet formation models.
A new robotic, compact high resolution optical spectrograph, called TOU (formerly called
EXPERT-III), was commissioned at the Automatic Spectroscopic Telescope (AST) at Fairborn
Observatory in Arizona in July 2013 and has produced a spectral resolution of about 100,000 and
simultaneous wavelength coverage of 0.38-0.9 μm with a 4kx4k back-illuminated Fairchild CCD
detector. The instrument holds a very high vacuum of 1 micro torr and about 2 mK temperature
stability over a month. The early on-sky RV measurements show that this instrument is
approaching a Doppler precision of 1 m/s (rms) for bright reference stars (such as Tau Ceti) with
5 min exposures and better than 3 m/s (P-V, RMS~1 m/s) daily RV stability before calibration
exposures are applied. A pilot survey of 20 V<9 FGK dwarfs, including known super-Earth
systems and known RV stable stars, is being launched and every star will be observed ~100
times over ~300 days time window between this summer and next spring, following up with a
full survey of ~150 V< 10 FGKM dwarfs in 2015-2017.
The Navy Precision Optical Interferometer (NPOI) was designed from the beginning to support baseline boot- strapping with equally-spaced array elements. The motivation was the desire to image the surfaces of resolved stars with the maximum resolution possible with a six-element array. Bootstrapping two baselines together to track fringes on a third baseline has been used at the NPOI for many years, but the capabilities of the fringe tracking software did not permit us to bootstrap three or more baselines together. Recently, both a new backend (VISION; Tennessee State Univ.) and new hardware and firmware (AZ Embedded Systems and New Mexico Tech, respectively) for the current hybrid backend have made multi-baseline bootstrapping possible.
Jian Ge, Scott Powell, Bo Zhao, Sidney Schofield, Frank Varosi, Craig Warner, Jian Liu, Sirinrat Sithajan, Louis Avner, Hali Jakeman, Jakob Gittelmacher, William Yoder, Matthew Muterspaugh, Michael Williamson, J. Maxwell
High resolution infrared spectroscopy has been a major challenging task to accomplish in astronomy due to the enormous size and cost of IR spectrographs built with traditional gratings. A silicon immersion grating, due to its over three times high dispersion over a traditional reflective grating, offers a compact and low cost design of new generation IR high resolution spectrographs. Here we report the on-sky performance of the first silicon immersion grating spectrometer, called Florida IR Silicon immersion grating spectromeTer (FIRST), commissioned at the 2-meter Automatic Spectroscopic Telescope (AST) of Fairborn Observatory in Arizona in October 2013. The measured spectral resolution is R=50,000 with a 50 mm diameter spectrograph pupil and a blaze angle of 54.7 degree. The 1.4-1.8 m wavelength region (the Red channel) is completely covered in a single exposure with a 2kx2k H2RG IR array while the 0.8-1.35 μm region is nearly completely covered by the cross-dispersed echelle mode (the Blue channel) at R=50,000 in a single exposure. The instrument is operated in a high vacuum (about 1 micro torr) and cryogenic temperatures (the bench at 189K and the detector at 87K) and with a precise temperature control. It is primarily used for high precision Doppler measurements (~3 m/s) of low mass M dwarf stars for the identification and characterization of extrasolar planets. A plan for a high cadence and high precision survey of habitable super-Earths around ~150 nearby M dwarfs and a major upgrade with integral field unit low resolution spectroscopy are also introduced.
We report the system design and predicted performance of the Florida IR Silicon immersion grating
spectromeTer (FIRST). This new generation cryogenic IR spectrograph offers broad-band high resolution
IR spectroscopy with R=72,000 at 1.4-1.8 μm and R=60,000 at 0.8-1.35 μm in a single exposure with a
2kx2k H2RG IR array. It is enabled by a compact design using an extremely high dispersion silicon
immersion grating (SIG) and an R4 echelle with a 50 mm diameter pupil in combination with an Image
Slicer. This instrument is operated in vacuum with temperature precisely controlled to reach long term
stability for high precision radial velocity (RV) measurements of nearby stars, especially M dwarfs and
young stars. The primary technical goal is to reach better than 4 m/s long term RV precision with J<9 M
dwarfs within 30 min exposures. This instrument is scheduled to be commissioned at the Tennessee State
University (TSU) 2-m Automatic Spectroscopic Telescope (AST) at Fairborn Observatory in spring 2013.
FIRST can also be used for observing transiting planets, young stellar objects (YSOs), magnetic fields,
binaries, brown dwarfs (BDs), ISM and stars.
We plan to launch the FIRST NIR M dwarf planet survey in 2014 after FIRST is commissioned at the
AST. This NIR M dwarf survey is the first large-scale NIR high precision Doppler survey dedicated to
detecting and characterizing planets around 215 nearby M dwarfs with J< 10. Our primary science goal is
to look for habitable Super-Earths around the late M dwarfs and also to identify transiting systems for
follow-up observations with JWST to measure the planetary atmospheric compositions and study their
habitability. Our secondary science goal is to detect and characterize a large number of planets around M
dwarfs to understand the statistics of planet populations around these low mass stars and constrain planet
formation and evolution models. Our survey baseline is expected to detect ~30 exoplanets, including 10
Super Earths, within 100 day periods. About half of the Super-Earths are in their habitable zones and one
of them may be a transiting planet. The AST, with its robotic control and ease of switching between
instruments (in seconds), enables great flexibility and efficiency, and enables an optimal strategy, in terms
of schedule and cadence, for this NIR M dwarf planet survey.
An innovative compact - yet high resolution - cross-dispersed echelle spectrograph has been designed, built, and
deployed at TSU's 2-meter robotic telescope for initial tests and commissioning. This design is based on a single
mode fiber (SMF) and it eliminates mode noise in fiber-fed spectrographs which is important for m/s precision
exoplanet Doppler searches. The use of SMFs removes modal variation, makes the design compact and the
camera focus slow and stable at the price of lower throughput. This can be improved by using adaptive optics
or by placing it in space; the compact design is well suited for such deployment.
VISION is the next generation science camera for the Navy Optical Interferometer (NOI). In comparison to
the current beam combiner of NOI, VISION will deliver higher precision data products and better
exibility by
incorporating single mode bers for spatial ltering and by using low-noise detectors. VISION can coherently
combine up to six telescope beams using an image-plane combination scheme. This results in simultaneous
measurement of 15 visibility amplitudes and 10 independent closure phases that can be used to reconstruct
multipixel images of stars.
An optical technique called "interferometric spectral reconstruction" (ISR) is capable of increasing a spectrograph's
resolution and stability by large factors, well beyond its classical limits. We have demonstrated a 6-
to 11-fold increase in the Triplespec effective spectral resolution (R=2,700) to achieve R=16,000 at 4100 cm-1to 30,000 at 9600 cm-1 by applying special Fourier processing to a series of exposures with different delays
(optical path differences) taken with the TEDI interferometer and the near-infrared Triplespec spectrograph at
the Mt. Palomar Observatory 200 inch telescope. The TEDI is an externally dispersed interferometer (EDI) used
for Doppler radial velocity measurements on M-stars, and now also used for ISR. The resolution improvement
is observed in both stellar and telluric features simultaneously over the entire spectrograph bandwidth (0.9-2.45
μm). By expanding the delay series, we anticipate achieving resolutions of R=45,000 or more. Since the delay is
not continuously scanned, the technique is advantageous for measuring time-variable phenomena or in varying
conditions (e.g. planetary fly-bys). The photon limited signal to noise ratio can be 100 times better than a
classic Fourier Transform Spectrometer (FTS) due to the benefit of dispersion.
The TripleSpec Exoplanet Discovery Instrument (TEDI) is optimized to detect extrasolar planets orbiting midto-
late M dwarfs using the Doppler technique at infrared wavelengths. TEDI is the combination of a Michelson
interferometer and a moderate-resolution near-infrared spectrograph, TripleSpec, mounted on the Cassegrain
focus of the Palomar 200-inch Hale Telescope. Here we present results from observations of a radial velocity
standard star and a laboratory source over the past year. Our results indicate that focus effects within the
interferometer, combined with non-common-path errors between the ThAr calibration source and starlight, limit
our performance to several 100 m/s. An upgraded version of TEDI, TEDI 2.0, will eliminate this behavior by
mixing ThAr with starlight in a scrambled fiber before a redesigned interferometer with minimal focal effects.
The TripleSpec - Exoplanet Discovery Instrument (TEDI) is a device to use interferometric spectroscopy for the radialvelocity
detection of extrasolar planets at infrared wavelengths (0.9 - 2.4 μm). The instrument is a hybrid of an
interferometer and a moderate resolution echelle spectrograph (TripleSpec, R=2,700,) at the Cassegrain focus of the
Palomar 200" telescope. We describe our experimental diagnostic program using laboratory sources and standard stars in
different optical configurations, along with performance analysis and results. We explain our instrumental upgrade
development to achieve a long-term performance that can utilize our demonstrated, < 10 m/s, short-term velocity
precision.
The TEDI (TripleSpec - Exoplanet Discovery Instrument) is the first instrument dedicated to the near infrared radial
velocity search for planetary companions to low-mass stars. The TEDI uses Externally Dispersed Interferometry (EDI), a
combination of interferometry and multichannel dispersive spectroscopy. We have joined a white-light interferometer
with the Cornell TripleSpec (0.9 - 2.4 μm) spectrograph at the Palomar Observatory 200" telescope and begun an
experimental program to establish both the experimental and analytical techniques required for precision IR velocimetry
and the Doppler-search for planets orbiting low mass stars and brown dwarfs.
The TEDI (TripleSpec Exoplanet Discovery Instrument) will be the first instrument fielded specifically for finding low-mass
stellar companions. The instrument is a near infra-red interferometric spectrometer used as a radial velocimeter.
TEDI joins Externally Dispersed Interferometery (EDI) with an efficient, medium-resolution, near IR (0.9 - 2.4 micron)
echelle spectrometer, TripleSpec, at the Palomar 200 telescope. We describe the instrument and its radial velocimetry
demonstration program to observe cool stars.
During the last two years we have used the Palomar Testbed Interferometer to observe several explosive variable stars, including V838 Monocerotis, V1663 Aquilae and recently RS Ophiuchi. We observed V838 Monocerotis approximately 34 months after its eruption, and were able to resolve the ejecta. Observations of V1663 Aql were obtained starting 9 days after peak brightness and continued for 10 days. We were able to resolve the milliarcsecond-scale emission and follow the expansion of the nova photosphere. When combined with radial-velocity information, these observations can be used to infer the distance to the nova. Finally we have resolved the recurrent nova RS Oph and can draw some preliminary conclusions regarding the emission morphology.
A new observing mode for the Palomar Testbed Interferometer was developed in 2002-2003 which enables differential astrometry at the level of 20 micro-arcseconds (μas) for binary systems with separations of several hundred milli-arcseconds (mas). This phase-referenced mode is the basis of the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES), a search for giant planets orbiting either the primary or secondary star in fifty binary systems. We present the first science results from the PHASES search. The properties of the stars comprising binary systems are determined to high precision. The mutual inclinations of several hierarchical triple star systems have been determined. We will present upper limits constraining the the existence of giant planets
in a few of the target systems.
The Palomar Testbed Interferometer has observed several binary star
systems whose separations fall between the interferometric coherence
length (a few hundredths of an arcsecond) and the typical atmospheric
seeing limit of one arcsecond. Using phase-referencing techniques we
measure the relative separations of the systems to precisions of a few
tens of micro-arcseconds. We present the first scientific results of
these observations, including the astrometric detection of the faint third stellar component of the kappa Pegasi system.
Atmospheric turbulence is a serious problem for ground-based
interferometers. It places tight limits on both sensitivity and
measurement precision. Phase referencing is a method to overcome these
limitations via the use of a bright reference star. The Palomar
Testbed Interferometer was designed to use phase referencing and so
can provide a pair of phase-stabilized starlight beams to a second
(science) beam combiner. We have used this capability for several
interesting studies, including very narrow angle astrometry. For close
(1-arcsecond) pairs of stars we are able to achieve a differential
astrometric precision in the range 20--30 micro-arcseconds.
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