We present equivalent widths of the [OII]λ3727 and Hα nebular emission lines for 77 brightest cluster galaxies (BCGs) selected from the 160 Square Degree ROSAT X-ray survey. We find no [OII]λ3727 or Hα emission stronger than −15Å or −5Å, respectively, in any BCG. The corresponding emission line luminosities lie below L ∼ 6×10 40 erg s −1 , which is a factor of 30 below that of NGC1275 in the Perseus cluster. A comparison to the detection frequency of nebular emission in BCGs at z ∼ < 0.35 drawn from the Brightest Cluster Survey (Crawford et al. 1999) indicates that we should have detected roughly one dozen emission-line galaxies, assuming the two surveys are selecting similar clusters in the X-ray luminosity range 10 42 erg s −1 to 10 45 erg s −1 . The absence of luminous nebular emission (ie., Perseus-like systems) in our sample is consistent with an increase in the number density of strong cooling flow (cooling core) clusters between z = 0.5 and today. The decline in their numbers at higher redshift could be due to cluster mergers and AGN heating.

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We report on progress at the Northrop Grumman Aerospace Systems (NGAS) starshade testbed. The starshade testbed is a 42.8 m, vacuum chamber designed to replicate the Fresnel number of an equivalent full-scale starshade mission, namely the flagship New Worlds Observer (NWO) configuration. Subscale starshades manufactured by the NGAS foundry have shown 10 -7 starlight suppression at an equivalent full-mission inner working angle of 85 milliarseconds. In this paper, we present an overview of the experimental set up, scaling relationships to an equivalent full-scale mission, and preliminary results from the testbed. We also discuss potential limitations of the current generation of starshades and improvements for the future.

We present and compare experimental results in high contrast imaging representing the state of the art in coronagraph and starshade technology. These experiments have been undertaken with the goal of demonstrating the capability of detecting Earth-like planets around nearby Sun-like stars. The contrast of an Earth seen in reflected light around a Sun-like star would be about 1.2 × 10 −10. Several of the current candidate technologies now yield raw contrasts of 1.0 × 10 −9 or better, and so should enable the detection of Earths, assuming a gain in sensitivity in post-processing of a factor of 10. We present results of coronagraph and starshade experiments conducted at visible and infrared wavelengths. Cross-sections of dark fields are directly compared as a function of field angle and bandwidth. The strength and differences of the techniques are compared.