Jian Ge, Bo Zhao, Scott Powell, Ji Wang, Adam Fletcher, Liang Chang, John Groot, Xiaoke Wan, Hali Jakeman, Derek Myers, Elliot Grafer, Jian Liu, Frank Varosi, Sidney Schofield, Alexandria Moore, Maria-Ines van Olphen, Jordan Katz, Rory Barnes
This paper is to report the design and performance of a very high Doppler precision cross-dispersed
echelle spectrograph, EXtremely high Precision ExtrasolaR planet Tracker III (EXPERT-III), as part of a
global Exoplanet Tracker (ET) network. The ET network is designed to hunt low mass planets, especially
habitable rocky planets, around GKM dwarfs. It has an extremely high spectral resolution (EHR) mode of
R=110,000 and a high resolution (HR) mode of R=56,000 and can simultaneously cover 0.38-0.9 μm
with a 4kx4k back-illuminated Fairchild CCD detector with a single exposure. EXPERT-III is optimized
for high throughput by using two-prisms cross-disperser and a large core diameter fiber (2 arcsec on sky,
or 80 μm at f/4) to collect photons from the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
average overall detection efficiency is ~6% from above the atmosphere to the detector for the EHR Mode
and about 11% for the HR mode. The extremely high spectral resolution in a compact design (the
spectrograph dimension, 1.34x0.8x0.48 m) is realized by coupling the single input 80 μm telescope fiber
into four 40 μm fibers and re-arranging the four small core diameter fibers into a linear fiber slit array (a
one-to-four fiber image slicer). EXPERT-III is operated in a vacuum chamber with temperature controlled
to ~2 milli-Kelvin rms for an extended period of time. The radial velocity (RV) drift is controlled to
within 10 meters/second (m/s) over a month. EXPERT-III can reach a photon noise limited RV
measurement precision of ~0.3 m/s for a V=8 mag GKM type dwarf with small rotation (vsini =2 km/s) in
a 15 min exposure. EXPERT-III’s RV measurement uncertainties for bright stars are primarily limited by
the Thorium-Argon (ThAr) calibration source (~0.5 m/s). EXPERT-III will serve as an excellent public
accessible high resolution optical spectroscope facility at the KPNO 2.1m telescope.
Doppler searches are extending to the near infrared to detect and characterize habitable planets around low mass stars.
We present an optical design and performance of a near-IR Doppler instrument. This instrument has two operating
modes covering 0.8-1.8 microns. One mode is called IRET, which consists of a fix-delay interferometer and a crossdispersed
echelle spectrograph to simultaneously cover 0.8-1.35 microns with a spectral resolution of R=22000 on a 2k x
2k H2RG IR array. The other mode is called FIRST, which uses a silicon immersion grating as the main disperser to
simultaneously cover 1.4-1.8 microns with a spectral resolution of R=55000 on the same detector as IRET. The triplepass
parabola white pupil design is used to restrain background scatter radiation with stable configuration for precision
radial velocity measurements. We used high index standard glasses for camera optics and VPH gratings as crossdispersers
in both modes. The FIRST mode can be switched in and out conveniently while the IRET mode is kept
without moving parts to increase its stability. This instrument is designed to deliver up to 1 m/s Doppler precision RV
measurements of nearby bright M dwarfs at the Apache Point Observatory 3.5 meter telescope. The instrument is
expected to be operational in the spring 2011.
Jian Ge, Bo Zhao, John Groot, Liang Chang, Frank Varosi, Xiaoke Wan, Scott Powell, Peng Jiang, Kevin Hanna, Ji Wang, Rohan Pais, Jian Liu, Liming Dou, Sidney Schofield, Shaun McDowell, Erin Costello, Adriana Delgado-Navarro, Scott Fleming, Brian Lee, Sandeep Bollampally, Troy Bosman, Hali Jakeman, Adam Fletcher, Gabriel Marquez
We report design, performance and early results from two of the Extremely High Precision Extrasolar
Planet Tracker Instruments (EXPERT) as part of a global network for hunting for low mass planets in the
next decade. EXPERT is a combination of a thermally compensated monolithic Michelson interferometer
and a cross-dispersed echelle spectrograph for extremely high precision Doppler measurements for nearby
bright stars (e.g., 1m/s for a V=8 solar type star in 15 min exposure). It has R=18,000 with a 72 micron
slit and a simultaneous coverage of 390-694 nm. The commissioning results show that the instrument has
already produced a Doppler precision of about 1 m/s for a solar type star with S/N~100 per pixel. The
instrument has reached ~4 mK (P-V) temperature stability, ~1 mpsi pressure stability over a week and a
total instrument throughput of ~30% at 550 nm from the fiber input to the detector. EXPERT also has a
direct cross-dispersed echelle spectroscopy mode fed with 50 micron fibers. It has spectral resolution of
R=27,000 and a simultaneous wavelength coverage of 390-1000 nm.
This paper describes an optical spectrograph design for the Multi-object APO Radial-Velocity Exoplanet Large-area
Survey (MARVELS) instrument. This MARVELS instrument is currently installed at the Sloan 2.5m telescope, and is
capable of simultaneously monitoring 60 stars at high radial velocity precision for a planet survey. The MARVELS
spectrograph consists of an entrance slit (multi-slits), collimator optics, a Volume Phase Holographic (VPH) grating,
camera optics and a 4kx4k CCD camera, which with a 160mm diameter collimated beam provides a spectral resolution
of R =10000. This spectrograph is transmissive and optimized for delivering high throughput and high image quality
over the entire operation bandwidth 500-570nm and the whole 160mmx30mm square shape FOV. The collimator and
camera optics (280 mm largest diameter) are all made of standard optical grade glasses. The f/4 input beams from the
MARVELS monolithic interferometer are converted to f/1.5 beams on the detector by this spectrograph, and form 120
stellar fringe spectra.
We describe the optical design and performance of a cross-dispersed echelle spectrograph designed to deliver high
precision radial velocities. The spectrograph design enables two working modes, a Radial Velocity Mode (RVM) and a
Direct Echelle Mode (DEM). The spectra resolving power of the RVM is R=18000 over 390nm-690nm when used with
1 arcsec slit, and delivering a R=27000 over 390nm-1000nm while using 0.6 arcsec slit for DEM. The focal ratio of this
spectrograph is f/4 and the collimated beam diameter is 85mm. An R2 Echelle with 87 l/mm groove density and a 63
degree normal blaze angle will be used as the main disperse grating. A 45 degree PBM2Y prism operated in a double
pass serves as a cross-disperser to separate the dispersion orders. Two objects spectra will be recorded on the top and
bottom half of the one 4k by 4k CCD (15-micron pixel size) respectively in RVM, while one object spectra will be
recorded on the same entire CCD. The total throughput of this spectrograph, in which consists of all spherical surface
lenses is around 60%.
We report performance of a new generation multi-object Doppler instrument for the on-going
Multi-object APO Radial-velocity Exoplanet Large-area Survey (MARVELS) of the Sloan
Digital Sky Survey III (SDSS-III) program. This instrument is based on dispersed fixed-delay
interferomtry design. It consists of a multi-object fiber-feed, a thermally compensated monolithic
fixed-delay interferometer, a high throughput spectrograph and a 4kx4k CCD camera. The
spectrograph resolving power is R=11,000 and the wavelength coverage is 500-570 nm. The
instrument is capable of measuring 60 stars in a single exposure for high to moderate precision
radial velocity (3-20 m/s) measurements depending on the star magnitudes (V=7.6-12). The
instrument was commissioned at the SDSS telescope in September 2008 and used to collect
science data starting in October 2008. Observations of reference stars show that the measured
photon noise limiting errors are consistent with the prediction for most of the measurements.
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