FOCES is a highly stabilized high-resolution optical Échelle spectrograph operated with the 2m telescope at the Wendelstein Observatory. After an extensive temperature- and pressure-stabilization upgrade, reaching the m/s-level, we now focus on the wavelength calibration process. Due to our latest improvements, we are able to perform simultaneous wavelength calibration using our new 4-_ber-slit assembly. This allows us to couple the spectrum of a star and light from a ThAr/UNe hollow cathode lamp or our frequency comb_ at the same time into the spectrograph. We present the design, production process and performance of this new multi-fiber assembly and also evaluate the stability as a test for the upcoming high precision radial velocity measurements in search of exoplanets.
FOCES is a fiber-fed, stabilized high-resolution (R ∼ 70,000) spectrograph attached to the 2m Fraunhofer Telescope in Wendelstein Observatory. An optical, broad-band laser frequency comb with the repetition rate of 25 GHz is used as the wavelength calibration source to obtain the precise radial velocities. We describe our method of modelling the instrumental profiles. A Gaussian plus an empirical spline function are used to fit the line spread function (LSF). We also present the results of obtaining radial velocities from an overlap of stellar spectra and emission lines of the laser frequency comb.
We describe a new generation of spectral extraction and analysis software package (EDRS2) for the Fibre Optics Cassegrain Echelle Spectrograph (FOCES), which will be attached to the 2m Fraunhofer Telescope on the Wendelstein Observatory. The package is developed based on Python language and relies on a variety of third party, open source packages such as Numpy and Scipy. EDRS2 contains generalized image calibration routines including overscan correction, bias subtraction, flat fielding and background correction, and can be supplemented by user customized functions to fit other echelle spectrographs. An optimal extraction method is adopted to obtain the one dimensional spectra, and the output multi order, wavelength calibrated spectra are saved in FITS files with binary table format. We introduce the algorithm and performance of major routines in EDRS2.
We present a new fiber-based light injection system for the high resolution spectrograph FOCES (Fiber Optics Cassegrain Echelle Spectrograph)1 which will soon start operating at the Wendelstein Observatory. The new system consists of several components such as a 4-fiber assembly (for simultaneous calibration), a new miniature lens system to reimage the light leaving the fibers onto the slit, as well as a new slit mask. The whole concept is specifically designed to provide high-accuracy, long-term stability for accurate radial velocity measurements and stellar atmosphere analyses.
We present the results of a series of measurements conducted using the upgraded Fiber Optic Cassegrain Echelle Spectrograph (FOCES)1 intended to be operated at the 2.0 m Fraunhofer Telescope at the Wendelstein Observatory (Germany) in combination with a laser frequency comb as calibrator. Details about the laboratory set-up of the system integrated with FOCES are shown. Different analysis techniques are applied to investigate the calibration precision and the medium-long term stability of the system in term of changes in stellar radial velocity.
High accuracy radial velocity measurement isn’t only one of the most important methods for detecting earth-like
Exoplanets, but also one of the main developing fields of astronomical observation technologies in future. Externally
dispersed interferometry (EDI) generates a kind of particular interference spectrum through combining a fixed-delay
interferometer with a medium-resolution spectrograph. It effectively enhances radial velocity measuring accuracy by
several times. Another further study on multi-delay interferometry was gradually developed after observation success
with only a fixed-delay, and its relative instrumentation makes more impressive performance in near Infrared band.
Multi-delay is capable of giving wider coverage from low to high frequency in Fourier field so that gives a higher
accuracy in radial velocity measurement. To study on this new technology and verify its feasibility at Guo Shoujing
telescope (LAMOST), an experimental instrumentation with single fixed-delay named MESSI has been built and tested
at our lab. Another experimental study on multi-delay spectral interferometry given here is being done as well. Basically,
this multi-delay experimental system is designed in according to the similar instrument named TEDI at Palomar
observatory and the preliminary test result of MESSI. Due to existence of LAMOST spectrograph at lab, a multi-delay
interferometer design actually dominates our work. It’s generally composed of three parts, respectively science optics,
phase-stabilizing optics and delay-calibrating optics. To switch different fixed delays smoothly during observation, the
delay-calibrating optics is possibly useful to get high repeatability during switching motion through polychromatic
interferometry. Although this metrology is based on white light interferometry in theory, it’s different that integrates all
of interference signals independently obtained by different monochromatic light in order to avoid dispersion error caused
by broad band in big optical path difference (OPD).
Exoplanet detection, a highlight in the current astronomy, will be part of puzzle in astronomical and astrophysical future,
which contains dark energy, dark matter, early universe, black hole, galactic evolution and so on. At present, most of the
detected Exoplanets are confirmed through methods of radial velocity and transit. Guo shoujing Telescope well known
as LAMOST is an advanced multi-object spectral survey telescope equipped with 4000 fibers and 16 low resolution fiber
spectrographs. To explore its potential in different astronomical activities, a new radial velocity method named
Externally Dispersed Interferometry (EDI) is applied to serve Exoplanet detection through combining a fixed-delay
interferometer with the existing spectrograph in medium spectral resolution mode (R=5,000-10,000). This new
technology has an impressive feature to enhance radial velocity measuring accuracy of the existing spectrograph through
installing a fixed-delay interferometer in front of spectrograph. This way produces an interference spectrum with higher
sensitivity to Doppler Effect by interference phase and fixed delay. This relative system named Multi-object Exoplanet
Search Spectral Interferometer (MESSI) is composed of a few parts, including a pair of multi-fiber coupling sockets, a
remote control iodine subsystem, a multi-object fixed delay interferometer and the existing spectrograph. It covers from
500 to 550 nm and simultaneously observes up to 21 stars. Even if it’s an experimental instrument at present, it’s still
well demonstrated in paper that how MESSI does explore an effective way to build its own system under the existing
condition of LAMOST and get its expected performance for multi-object Exoplanet detection, especially instrument
stability and its special data reduction. As a result of test at lab, inside temperature of its instrumental chamber is stable
in a range of ±0.5degree Celsius within 12 hours, and the direct instrumental stability without further observation
correction is equivalent to be ±50m/s every 20mins.
Since 2009 the Echelle spectrograph FOCES1 is located at the laboratories of Munich University Observatories under pressure and temperature stabilized conditions. It is intended to be operated at the 2.0m Fraunhofer Telescope at the Wendelstein Observatory and it will remain under lab conditions in Munich until the telescope is fully commissioned. This has given us the unique opportunity to use FOCES as a test bed for a number of different stability issues related to high precision radial velocity spectroscopy, in particular to study spectrograph stability, illumination stability and fiber transport stability. In this paper will be presented the final optical measurement results to test temperature and pressure stabilization in the spectrograph environment with respect to simulations requirements previously published. Using measurements done by a ThAr gas discharge source, we tested the stability of our system by direct 1D spectra analysis and we verified the movement of the spot positions by changing the CCD temperature in the stabilized environment.