H. Kellermann

Relative stability of two laser frequency combs for routine operation on HARPS and FOCES

We report on the installation of a laser frequency comb (LFC) at the HARPS spectrograph, which we characterize relative to a second LFC that we had brought to HARPS for testing. This allowed us for the first time to probe the relative stability of two independent astronomical LFCs over an extended wavelength range. Both LFCs covered the spectral range of HARPS at least from 460 to 690 nm. After optimization of the fiber coupling to HARPS to suppress modal noise, a relative stability of the two LFCs in the low cm/s range was obtained. In combination with the results of our four earlier LFC test campaigns on HARPS, the available data now cover a time span of more than six years.

Stability of the FOCES spectrograph using an astro-frequency comb as calibrator

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.

A new fiber slit assembly for the FOCES spectrograph

After successful operation at the Calar Alto telescope until 2009, and extensive lab tests at the Munich University Observatory the high resolution Échelle spectrograph FOCES (Fiber Optics Cassegrain Échelle Spectrograph) is now about to be reinstalled at the 2 m Wendelstein Observatory in the German Alps. For this new phase of operation FOCES will be equipped with new components that will improve time stability and wavelength calibration. With these modifications FOCES will meet the requirements for performing precision radial velocity measurements on a competitive level. One of the key features of the upgraded spectrograph is the new calibration system, which uses a laser frequency comb as reference light source. Another aspect is the possibility to perform simultaneous wavelength calibration, while recording science data. For this purpose a new 4-fiber slit has been developed, which opens up the possibility to feed light from different sources at the same time through the entrance slit of the spectrograph. We present a detailed characterization of this new device, based on the results of extensive lab tests performed at the Munich University Observatory.

Line profile analysis of the laser frequency comb in FOCES

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.

WES—Weihai Echelle Spectrograph

The Weihai Echelle Spectrograph (WES) is the first fiber-fed echelle spectrograph for astronomical observation in China. It is primarily used for chemical abundance and asteroseismology studies of nearby bright stars, as well as radial velocity (RV) detections for exoplanets. The optical design of WES is based on the widely demonstrated and well-established white-pupil concept. We describe the WES in detail and present some examples of its performance. A single exposure echelle image covers the spectral region 371-1100 nm in 107 spectral orders over the rectangular CCD. The spectral resolution R = lambda/Delta lambda changes from 40,600 to 57,000 through adjusting the entrance slit width from full to 2.2 pixels sampling at the fiber-exit. The limiting magnitude scales to V = 8 with a signal-to-noise ratio of more than 100 in V for an hour exposure, at the spectral resolution R approximate to 40,000 in the median seeing of 1 7 at Weihai Observatory for the 1 m telescope. The RV measurement accuracy of WES is estimated to be <10 m s(-1) in 10 months (302 days) and better than 15 m s(-1) in 4.4 years (1617 days) in the recent data processing.

Multi-fiber coupling through a miniature lens system into the FOCES spectrograph

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.

A new generation of spectral extraction and analysis package for Fiber Optics Cassegrain Echelle Spectrograph (FOCES)

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.