Technical Description

The Wisconsin H-Alpha Mapper is a specialized instrument to study the distribution and kinematics of diffuse, ionized gas in the Milky Way. WHAM consists of a custom built 0.6-meter telescope and a dual-etalon 15-cm Fabry-Perot spectrometer housed in an environmentally protective trailer. In its primary spectral mode, WHAM records a spectrum spanning 200 km/s (about 4 Å near Hα) with 8-12 km/s velocity resolution from a one-degree, spatially integrated beam of the sky. With its large-aperture design and modern CCD technology, WHAM can detect emission as faint as 0.05 Rayleighs in a 30-sec exposure. For gas at 10,000 K, this observed intensity corresponds to an emission measure of about 0.1 cm-6 pc, more than 10 million times fainter than the Orion Nebula.

WHAM's first major product was the Northern Sky Survey. By fully mapping the Hα emission within about ±100 km/s of the Local Standard of Rest (LSR) over the portion of the Galaxy visible from Kitt Peak, we can now explore the spatial and kinematic structure of the warm, ionized component of the ISM in our Galaxy. This new survey of ionized gas is analogous to previous surveys of neutral hydrogen made through the 21-cm radio line. Using both surveys, we can now also explore the relationship between the diffuse ionized and neutral gas. An example of what we hope to learn from such methods can be found in Reynolds, Tufte, Kung, McCullough, & Heiles, 1995, ApJ, 448, 715.

WHAM is a completely remote and robotic observing facility. We have taken special care to allow all aspects of operation to be controlled from any location. Our remote capabilities are based on telescope control software written by Jeff Percival that is also used by the WIYN telescope. Although the instrument is located in Arizona, nearly all WHAM observations have been operated remotely from Wisconsin. For a typical night, an observer plans and schedules targets before the evening begins then configures the instrument and initiaties the observations. WHAM collects the data and closes up for the night autonomously.


WHAM spent a year in Wisconsin (November 1995 - November 1996) at Pine Bluff Observatory for testing and software development. It then moved to Kitt Peak, Arizona on November 19, 1996 and began the Hα survey, which took about two years. With the map of Galactic Hα emission under its belt, WHAM gathered data from Kitt Peak to explore the detailed physics of the ionized ISM. Optical emission lines from He, S+, N+, O, and O++ are routinely observed by WHAM.

In April 2008, WHAM was removed from Kitt Peak. The instrument spent six months in Madison refurbishment and upgrades. It was installed at the Cerro Tololo Interamerican Observatory in Chile in March of 2009. From Chile, the WHAM group is completing the Hα survey as well as continuing to explore other optical emission lines and the extended gaseus structures associated with the Magellanic System.

The WHAM project is funded primarily through grants from the National Science Foundation with additional support provided by the University of Wisconsin Graduate School, the UW Department of Physics, and the UW Department of Astronomy. Much of the hardware was built and assembled by the University of Wisconsin Space Astronomy Laboratory and the Physical Sciences Laboratory.

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