In this installment, we travel to Kitt Peak in the Arizona-Sonoran Desert to “speckle” binary stars and finally learn what the impressive-sounding Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne group does! (If you missed our prior Tele Vue Scientific installments, you can click to read Part 1 and Part 2).
4x Powermate and Speckle Imaging at Kitt Peak
Introduction Often practiced by amateur astronomers doing planetary work, “lucky” imaging was invented by professional astronomers to try to “freeze” distortion of starlight passing through our planet’s turbulent atmosphere. This is done by taking many short exposures of a target, instead of one long one. Amateurs usually align and stack the best quality photos to create an image. Professionals use their data to perform speckle interferometry involving complex math. Speckle interferometry is useful in refining the orbits of close binary stars. The introduction to a 2014 paper, “Kitt Peak Speckle Interferometry of Close Visual Binary Stars,” explains how this works.
The resolutions of conventional visual binary observations were seeing limited until Labeyrie (1970) devised speckle interferometry as a way to circumvent seeing limitations and realize the full diffraction-limited resolution of a telescope. The light from a close binary passing through small cells in the atmosphere produces multiple binary star images which, if observed at high enough magnification with short exposures (typically 10 to 30 milliseconds), will “freeze” out the atmospheric turbulence and thus overcome seeing-limitations. Although the multiple double star images are randomly scattered throughout the image (often superimposed), their separation and position angle remains constant, allowing these two parameters to be extracted via Fourier analysis (autocorrelation).
The paper says that this technique, made practical with the introduction of the CCD camera, resulted in an order of magnitude improvement in binary star data measurement over visual observations. Speckle interferometry then became the preferred technique for characterizing close binary stars.
Back in December 2018, we featured some spectacular wide-field, deep-sky images by Diego Cartes Saavedra in Chile. All the images were taken with his Tele Vue-76 APO refractor and Tele Vue TRF-2008 0.8x Reducer/Flattener. This combination achieves a 380mm focal length at f/5, ideal for imaging large swaths of deep sky. You can still read the original blog at Tele Vue-76: Imaging the Southern Hemisphere. At the end of that post, we wished Diego continued success in his astrophotographic journey. Ever since, we’ve followed his progress through his postings on the AstroBin imaging hosting platform for astrophotographers. We felt it was time to “catch up” with him and post some of his latest captures in this gallery blog.
NGC 6188 ─ The Fighting Dragons of Ara (Hubble Palette)
Prior generations of supernovae explosions spread dust and gas in this complicated region of space. Continued explosions compressed this material and sparked the formation of new massive stars. Stellar winds from these stars intricately sculpted the region into areas of glowing gas, reflection nebulae, and dark clouds of dense matter. The resulting dark, dusty lanes conjure up images of two dragons. Light from open cluster NGC 6193 illuminates the large blue reflection nebula where the dragons face off. The dense, blue object at the lower-right is pk336-00.1 (also NGC 6164 & NGC 6165) ─ an emission nebula formed from the expanding outer layers of a giant, hot, O-type star at the center. Around this compact object is the faded outer ring of reflected blue dust from earlier shedding events. This image was awarded an AstroBin “Top Pick” nomination.
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