The Multi-Aperture Spectroscopic Telescope (MAST)

The Multi Aperture Spectroscopic Telescope (MAST) is a novel spectroscopic array consisting of twenty custom-designed 24-Inch (61 cm) Newtonian telescopes, currently under construction at the newly established Weizmann Astronomical Observatory (WAO) in Ne’ot Smadar, southern Israel. Manufactured by PlaneWave Instruments, each telescope in the array features a prime mirror design operating at F/3, utilizing a parabolic mirror. It has a collective aperture equivalent to a single 2.7 m telescope, providing significant observational power at approximately 10% of the cost of a similar-sized single telescope.

Each telescope feeds light into two optical fibers, one for the science target and the second for the surrounding sky. The fibers termini from all telescopes comprise a ∼5 mm-long quasi-slit unit that can be plugged into one of two instruments on an optical table (situated in a separate clean, temperature-controlled instruments room):

(i) DeepSpec: a low spectral resolution R∼500/600 broadband (350 to 850 nm) high-throughput spectrograph for the classification and follow-up of targets, with emphasis on extra-galactic transients to be discovered by the LAST array on site and ULTRASAT.

(ii) HighSpec: a high-resolution, R~20,000, narrow bandpass spectrograph, with three observing modes centered at the Ca II H&K, Mgb triplet, and Hα lines, for the study of galactic sources, specifically WDs.

Each of the MAST telescopes is equipped with two Few Modes (FM) fused silica, broad-spectrum, 30 μm core optical fibers. The use of FM optical fibers increases the fiber throughput when compared to the use of a single mode fiber for a non-Gaussian and imperfect beam as expected in the case of an astronomical telescope observing under sub-optimal seeing conditions, reaching throughput of over 86% as verified in the lab. The projected fiber core angle on sky is 3.44 arcsec, and the projected separation between the target and sky fibers is about 10 arcmin. As the median seeing at the site measured at Zenith over the course of a year is ∼1.35 arcsec, and the guiding precision of the mount is ≲ 1 arcsec, after an adequate system performance is achieved, the fibers may be upgraded to 25 μm core fibers (2.85 arcsec on the sky), which will result in a 20% increase in the spectral resolution.

The 40 fibers from the MAST telescopes (20 for science, 20 for sky) are combined with five additional fibers from the calibration system (three active and two spares) into a 45-fibers long-slit. The unit is mounted on a linear stage for transitioning between DeepSpec and HighSpec so that the fiber facets can be positioned in each of the two spectrographs collimator focal points.