Long-term trends in the NICMOS Camera 2 obscuration pattern and aberrations
Phase retrieval measurements of well-exposed NICMOS Camera 2 star images show that long-term changes occurred in coma and the cold mask position over the 1997-1998 lifespan of the instrument. These caused time-dependent variations in the PSF diffraction pattern, notably the shape of the Airy rings and the positions of bands in the diffraction spikes. These effects are evident in both direct and coronagraphic images when two observed PSFs obtained at different times are subtracted from each other. The derived trends have been implemented in Version 5 of Tiny Tim. PSF monitoring programs for NICMOS after the cryocooler is in place should include similar exposures so that any further cold mask shifting can be tracked.
Wide-Field Infrared Survey Telescope–Astrophysics Focused Telescope Assets coronagraphic operations: lessons learned from the Hubble Space Telescope and the James Webb Space Telescope
Abstract. The coronagraphic instrument (CGI) currently proposed for the Wide-Field Infrared Survey Telescope–Astrophysics Focused Telescope Assets (WFIRST-AFTA) mission will be the first example of a space-based coronagraph optimized for extremely high contrasts that are required for the direct imaging of exoplanets reflecting the light of their host star. While the design of this instrument is still in progress, this early stage of development is a particularly beneficial time to consider the operation of such an instrument. We review current or planned operations on the Hubble Space Telescope and the James Webb Space Telescope with a focus on which operational aspects will have relevance to the planned WFIRST-AFTA CGI. We identify five key aspects of operations that will require attention: (1) detector health and evolution, (2) wavefront control, (3) observing strategies/postprocessing, (4) astrometric precision/target acquisition, and (5) polarimetry. We make suggestions on a path forward for each of these items.
Pedagogy of the “Not”: Negation, Exodus, and Postdigital Temporal Regimes
Postdigital capitalist time is an incessant acceleration that acts to homogenize time and wed us to the present, to which we have to constantly catch up. While the impulse of this is no doubt economic (the realization of value), it is crucially undergirded by a pedagogical logic wherein we have to perpetually learn and re-learn the latest apps, social media configurations, operating systems, and so on. Political strategies of resistance thus need to be bolstered by an alternative mode of educational life, and I propose a pedagogy of the “not” as one possibility. Such a pedagogy is an act of suspension that sustains a detachment from the present, clearing out oppositions and thereby exposing us to a radical indeterminacy and potentiality that is always untimely. Suspension is the praxis of negation, which means that negation operates by keeping sense indeterminate to meaning and signification. Rather than suppressing, disavowing, or annihilating the stated content, negation retains even that which is negated. While this would appear as a form of exopedagogy, which withdraws from the dialectic of the private/public, I instead argue that it redefines the terms of any dialectic, redefining the very categories exopedagogy withdraws from. Before concluding, I spend some time with Sandy Grande’s important critiques of Eurocentrism and progress in Western critical education, demonstrating how negation as suspension circumvents these errors through its accommodation of—or, better, insistence on—variegated temporalities and forms of life.