KEYWORDS: Point spread functions, Stars, Coronagraphy, Speckle, Sensors, Telescopes, Signal to noise ratio, Space operations, Hubble Space Telescope, Charge-coupled devices
The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) contains the only currently operating coronagraph in space that is not trained on the Sun. In an era of extreme-adaptive-optics-fed coronagraphs, and with the possibility of future space-based coronagraphs, we re-evaluate the contrast performance of the STIS CCD camera. The 50CORON aperture consists of a series of occulting wedges and bars, including the recently commissioned BAR5 occulter. We discuss the latest procedures in obtaining high-contrast imaging of circumstellar disks and faint point sources with STIS. For the first time, we develop a noise model for the coronagraph, including systematic noise due to speckles, which can be used to predict the performance of future coronagraphic observations. Further, we present results from a recent calibration program that demonstrates better than 10 − 6 point-source contrast at 0.6″, ranging to 3 × 10 − 5 point-source contrast at 0.25″. These results are obtained by a combination of subpixel grid dithers, multiple spacecraft orientations, and postprocessing techniques. Some of these same techniques will be employed by future space-based coronagraphic missions. We discuss the unique aspects of STIS coronagraphy relative to ground-based adaptive-optics-fed coronagraphs.
In the past 20 years, the Hubble Space Telescope (HST) STIS coronagraphic instrument has observed more than 100 stars, obtaining more than 4,000 readouts since its installment on HST in 1997 and the numbers are still increasing. We reduce the whole STIS coronagraphic archive at the most commonly observed positions (Wedge A0.6 and A1.0) with new post-processing methods, and present our results here. We are able to recover all of the 32 previously reported circumstellar disks, and obtain better contrast close to the star. For some of the disks, our results are limited by the over subtraction of the methods, and therefore the major regions of the disks can be recovered except the faintest regions. We also explain our efforts in the calibration of its new BAR5 occulting position, enabling STIS to explore inner regions as close as 0.2 00 .
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