All Sky Maps of Stellar Emission at Optical and Submillimeter Wavelengths

Richard Simon, NRAO

This page was most recently updated on 1997/03/26

Observing Stars with the MMA

An important component of the total sky emission at millimeter wavelengths will be thermal emission from ordinary stars. In the accompanying figure, two views of the entire sky are presented at visible wavelengths (about 550 nm) and at millimeter wavelengths (350 microns, or 850 GHz). The projections are centered on 12 hours Right Ascension (with RA increasing to the right in the usual convention) and 0 degrees Declination.

Starting with over 118,000 stars in the Hipparcos Input Catalog and the Catalog of Nearby Stars (complete to 7.3 to 7.7 magnitude as well has having many selected stars to much fainter magnitudes), the magnitude, color, and spectral type for each star was used to calculate the expected thermal emission at 850 GHz, the maximum frequency contemplated for observations with the Millimeter Array. All stars which could be detected with the MMA in less than 10 minutes (with an SNR >= 5) were selected, yielding 6,206 stars. This includes most visible stars brighter than about magnitude 6, along with many fainter stars. The MMA was assumed to be observing at 850 GHz, using dual polarization and 8 GHz bandwidth, with good sky conditions and receivers operating at twice the quantum noise limit.

For the all sky map at visible wavelengths all stars from the input catalog were selected down to a limiting magnitude of 6.20, yielding 6,250 stars.

For both maps the size of each star symbol indicates its relative brightness, in steps of about a factor of 2.5 (roughly 1 magnitude steps). For the visible map, stars plotted with all but the smallest symbols are brighter than magnitude 5.0. For the 850 GHz map, stars plotted with all but the smallest symbols are brighter than 3.5 mJy, and could be reliably detected in 1 minute or less.

The most obvious difference between the two maps is the relative prominence of the galactic plane at visible wavelengths, highlighted by hot blue stars at ~ kiloparsec distances. In contrast, the millimeter sky is dominated by closer, cooler stars whose nearby spatial distribution does not strongly mirror the overall disk structure of our galaxy.

A Postscript version of the figure below (1.2 Mbytes) is available. (Postscript figure) *