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High Resolution Imaging of Io's Volcanoes with LBTI Albert Conrad 1 , Jarron Leisenring 2 , Katherine de Kleer 3 , Andy Skemer 2 , Philip Hinz 2 , Michael Skrutskie 4 , Christian Viellet 1 , Imke de Pater 3 , Mario Bertero 5 , Patrizia Boccacci 5 , Denis Defrère, Karl-Heinz Hofmann 6 , Andrea la Camera 5 , Dieter Schertl 6 , John Spencer 7 , Gerd Weigelt 6 , Charles E. Woodward 8 . 1 Large Binocular Telescope Observatory, 933 N. Cherry Ave, Tucson, Arizona 85721; 2 University of Arizona, 1428 E. University Blvd, Tucson, AZ 85721; 3 University of California at Berkeley, Berkeley, CA 94720; 4 University of Virginia, 530 McCormick Road, Charlottesville, VA 22904; 5 University of Genoa, Via Dodecaneso 35, Genova, Italy; 6 Max Planck Institute for Radio Astronomy, Auf dem Huegel 69, Bonn, Germany 53121; 7 Southwest Research Institute, 1050 Walnut Ste. Suite 300, Boulder, CO 80302 ; 8 University of Minnesota, 116 Church St., Minneapolis, MN 55455 Abstract We report new findings in the on-going study of volcanic processes at Loki Patera on Io. From images acquired with the Large Binocular Telescope Interferometer (LBTI) on December 24th, 2013, we detected a strong M-band emission feature at Loki Patera. Using the high resolution Fizeau mode of LBTI, we measured its size, its irregular shape, and its position with respect to Loki's horse-shoe lava lake. We detected and measured locations for 16 additional hot spots, including two enigmatic sources in Colchis Regio. But what is the highest resolution possible from ground-based observatories? We show here Large Binocular Telescope (LBT) images of Io. LBT provides a factor of two improvement in resolution over what has previously been possible. Figure 1 - M-band images of Io. The first 7 images shown in the top row were taken over an approximately 1.5 hour time span on December 24, 2013, using the Large Binocular Telescope Interferometer (LBTI) 1 . The right- most image on the top row is a point source, a star of similar brightness taken on the same night to record the point spread function (PSF). Both images in the bottom row were reconstructed, using independent techniques, from the data shown on the top row [Lessering et al, SPIE, 2014]. The circled features are: (1) Vivasvant, (2) Dazhbog, (3) Surt, (4) Amaterasu, (5) I32A, (6) Mulungu, (7) Fuchi, (8) Loki, (9) Tol-Ava, (10) Pele, (11) Rarog, (12) Lerna, (13) Heno. The M-band images of Io shown in figure 1 provide resolution down to approx. 100 km on Io's surface. In the image of Io shown in figure 1 we see that the large emission region at Loki Patera is resolved. [1] - Hinz, Phil; Arbo, P.; Bailey, V.; Connors, T.; Durney, O.; Esposito, Simone; Hoffmann, W.; Jones, T.; Leisenring, J.; Montoya, M.; Nash, M.; Nelson, M.; McMahon, T.; Pinna, E.; Puglisi, A.; Skemer, A.; Skrutskie, M.; Vaitheeswaran, V., First AO-corrected interferometry with LBTI: steps towards routine coherent imaging observations, SPIE 8445 (2012); [2] – Bertero, M.; Boccacci, P., Image restoration methods for the Large Binocular Telescope (LBT), AAS 323 (2000) Volcanoes on Io are best studied in the 3-5 micron wavelength regime. Thermal emission (150-1500K) peaks in this range of the infrared; this window thus maximizes the fraction of flux coming from thermal emission, while still being sensitive to the hottest (1500+K) eruptions. We therefore observe Io within the atmospheric windows at either 3.8 or 4.7um (L’- or M-band), using the highest resolution available from the ground. Even “by eye” we can see that, along the high resolution baseline (the blue horizontal cuts), the Loki feature is resolved and we have approximately 3 resolution elements across its diameter (as compared to the PSF given by the green horizontal cuts of Pele, which is unresolved). To what level is Loki resolved? Both single Richardson-Lucy and multiple Richardson-Lucy [2] were used to deconvolve the data with respect to the PSF (as measured from a nearby star). Although our analysis of this data continues, we can show here our current knowledge of the location and emission pattern. Based on good agreement of our locations (of known volcanoes) with what appears in the literature, we overlaid our detected Loki feature with this spacecraft image of the lava lake. One portion appears to emanate from the island, while the other lies on the lake itself. MRL SRL x 7 The possibility that we were seeing two distinct emission regions, with a “hollow middle,” was first noticed in the MRL result. This was confirmed via 1-D model fits. What can we learn from this data about the horseshoe lava lake? The 7 SRL results were de-projected and corrected for effects of rotation so that they could be combined to (a) precisely locate the hot spots listed in figure 1 and (b) construct a combined image of the resolved feature at Loki. All known volcanoes agreed well with locations given in the literature. Two unknown sources were in the region of a recent outburst (see de Kleer et al at this meeting).
