Friday, May 30, 2008

Kepler Bandpass

Kepler Bandpass
Originally uploaded by Astro Guy
The transmission functions for the Johnson B,V,R,I filters are shown from left to right in blue, green, red and magenta respectively and have been scaled to peak at 100% transmission. The Kepler bandpass is shown in black which peaks at approximately 70% throughput. The CoRoT whitelight bandpass is shown by the dot-dashed line. The MOST bandpass is shown by the dashed line. The spectrum for an A2V star is shown in cyan, which peaks in the UV and the spectrum for a M2V star is shown in orange which peaks in the infrared. The two spectra have been scaled to have equal flux in the Johnson V filter.

If two stars of two different spectral types have equal brightness in the V filter, then one would like to know what is the difference in flux over the Kepler bandpass for the two stars. One starts by defining that a G2V star will have equal brightness in the V filter and Kepler bandpass. This definition provides a natural way to scale the artificial spectra and to compute the flux difference in the V filter and Kepler bandpass as a function of spectral type. The Figure demonstrates how a hot A2V and cool M2V star with equal brightness in the V filter can have quite different brightnesses through the Kepler bandpass with extends to the near infrared part of the spectrum.

No comments: