Lijiang Exoplanet Tracker (LijET) was designed to detect exoplanets with extremely high precision radial velocity (RV) measurements, and it was mounted on 2.4m telescope at Lijiang Observatory in 2011. The Dispersed Fixed- Delay Interferometry (DFDI) mode of LiJET is a combination of a thermally compensated monolithic michelson interferometer and a cross-dispersed echelle spectrograph. When the slit width is 1.6”, the spectral resolution is 18000. With a 4k x 4k CCD, the spectrograph has wavelength coverage of 390nm-690nm. The temperature stability of the instrument is 25±0.001°C, and the pressure stability of the instrument is 10.9±0.001psi. LiJET realize high precision RV measurements by measuring the phase shifts of fringes in the slit direction. Differential RV is a function of light speed, phase shift, wavelength and optical delay. Thus, optical delay is necessary to be determined accurately to take differential RV measurements to derive precise RV. We used thorium argon (ThAr) and tungsten lamp to calibration the DFDI spectrum of LiJET, and then to calculate the optical delay at different channels on the CCD detector.
KEYWORDS: Telescopes, Imaging systems, Control systems, Control systems design, Astronomy, Web services, Optical filters, Interfaces, Optical instrument design, Charge-coupled devices
The 1.2m Quantum Teleportation Telescope imaging system is a multi-band imaging system with dual channels called ‘red end’ and ‘blue end’. Each channel includes a CCD camera and a filter wheel system, and the blue end contains a focusing system. In order to improve the tracking accuracy, the guiding CCD is designed and deployed. The imaging system studies the mass of the black hole and the structure of AGN by observing the variation of AGN spectral line. In order to improve the observation efficiency, we design and implement a multi-level remote unattended observation and control system. The system adopts the framework of combining RTS2 and EPICS. EPICS is used to realize the individual control of each device. We defined status code and split device properties for debugging purpose or high-level invocating purpose. The EPICS Channel Access is integrated into the RTS2 software and a set of configurations in XML format is designed so that the RTS2 module can find the EPICS application. In the RTS2 layer, we developed a module for the coordinated control of the equipment. The module is responsible for sending instructions to the telescope and the guiding module according to the pre-defined list of observation plans, switching to the corresponding filter, and performing exposure operations. Finally, we developed web service and used web pages as user interface, which makes it convenient for users to control the telescope remotely and complete the observation task.
The Astronomical Imaging System of a 1.2-meter-aperture Telescope is a multi-band imaging system with red and blue channels. The mass and structure of AGN central black hole are studied by observing the change of AGN spectral line. We designed an optical system with dual channels, changing the focal length ratio of telescope from f/8.429 to f/5 through the lens, and divide the optical path into red and blue channels through the beam splitter. The red waveband is 650nm1000nm and the blue waveband is 400nm-650nm. Each channel has a CCD camera. We set up focusing lens before the camera of blue channel to compensate the difference focusing length between red and blue channel after the red channel being focused by adjusting the telescope. For the realization of three groups of broadband photometry and twenty-four groups of narrowband photometry, an automatic filter wheel system is designed to switch the filter. At the same time, in order to reduce the influence of temperature drift of the filter, a constant temperature adjusting system for filter wheel box is carried out. In order to overcome the issue that the telescope itself does not have enough tracking accuracy, a guiding system for the imaging system is designed and implemented. Finally, we designed and implemented a multi-level software control system so that the users can remotely control the telescope.
A guiding system is designed, implemented and tested for our 1.2-meter Quantum-Teleportation Telescope Imaging System, due to the lack of accuracy of its own star tracking function. This paper at first introduces some key technologies of the system including star extraction, offset computation, star tracking, offset conversion and exception handling. The guiding system is implemented as a RTS2 device, and interacts with a guiding CCD and telescope. The workflow control of the guiding process is pushed forward by a finite-state machine. The system is tested in Delingha, Qinghai province. In cloudless condition, the guiding system can work for 15 min continuously, and long-exposure images produced by main CCDs can meet scientific requirements.
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.
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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