Magellan Echellette

Magellan Echellette. It is a high-resolution optical spectrograph permanently mounted on the Baade Telescope, one of the twin 6.5-meter Magellan Telescopes located at the Las Campanas Observatory in Chile. The instrument, known by its acronym MagE, was developed by a team led by the Carnegie Observatories to provide efficient, moderate-resolution spectroscopy across a wide wavelength range. Its primary scientific role is to enable detailed chemical abundance studies of stars within the Milky Way and its satellite galaxies, as well as to investigate the interstellar medium and distant quasars.

Overview

The spectrograph was constructed as a facility instrument for the Magellan Telescopes, a collaborative project involving the Carnegie Institution for Science, Harvard University, the University of Arizona, the University of Michigan, and the Massachusetts Institute of Technology. It saw first light in the late 2000s and has been a workhorse instrument for the Baade Telescope ever since. The design philosophy prioritized observational efficiency and reliability for a broad range of astrophysics programs, from surveying metal-poor stars in the Galactic halo to following up transients discovered by projects like the All-Sky Automated Survey for Supernovae.

Design and Instrumentation

The instrument employs a classic Schmidt camera design coupled with a Volume Phase Holographic grating, which provides its echellette dispersion format. It is fed by a fiber optic cable from the telescope's Cassegrain focus, allowing for stable calibration and the use of various entrance apertures, including a long slit for extended objects. Key components include a deep-depletion CCD detector from Semiconductor Technology Associates that is sensitive out to near-infrared wavelengths and a suite of comparison lamps, such as thorium-argon and iron-argon, for precise wavelength calibration. The entire spectrograph is housed in a thermally controlled enclosure to ensure stability during long exposures.

Scientific Capabilities and Performance

MagE delivers a continuous spectral coverage from approximately 3000 Ångströms in the ultraviolet to beyond 1 micron in the near-infrared in a single exposure, a capability rare for optical spectrographs. It operates at a resolving power (R ~ 4,100) that is optimally suited for measuring absorption lines from elements like iron, magnesium, and calcium in stellar atmospheres, as well as for detecting diffuse interstellar bands. Its high throughput and sensitivity have made it particularly effective for observing faint, distant stars in systems like the Sagittarius Dwarf Spheroidal Galaxy and for obtaining redshifts of high-redshift quasars and gamma-ray burst afterglows.

Key Discoveries and Observations

The instrument has been pivotal in advancing the field of Galactic archaeology. It has provided detailed chemical compositions for hundreds of ancient stars in the Milky Way, helping to map the accretion history of the Galactic halo and constrain the nature of the first stars after the Big Bang. Notable programs include the Magellan Planet Search Program follow-up spectroscopy and studies of extremely metal-poor stars identified by the SkyMapper survey. It has also been used to observe the interstellar medium of the Magellanic Clouds and to characterize the host galaxies of supernovae discovered by the Dark Energy Survey.

Operational History

Following its commissioning, the spectrograph quickly became a heavily subscribed instrument for the Magellan Telescopes user community. Its operation is supported by the staff of the Las Campanas Observatory and the instrument team at the Carnegie Observatories in Pasadena, California. Over the years, it has undergone several upgrades to its detector system and calibration software to maintain its performance. Data from the instrument are processed using a dedicated pipeline, and its observations have contributed to numerous publications in journals like The Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society.

Category:Astronomical instruments Category:Spectrographs Category:Magellan Telescopes