Stereoscopic View of Sagittarius

In Siegel et al. 2011 we presented a stereoscopic view of the central ~ 15 degrees of the Sagittarius dwarf and its closest 4 globular clusters (their Figure 15). There are two techniques with which to view such stereoscopic images that do not require any equipment, either cross-eyed or parallel-eyed viewing. Both methods have their advantages and disadvantages: cross-eyed viewing has the benefit of working for arbitrary image sizes and separations but can produce headaches, while parallel-eyed viewing is more 'natural' and less prone to producing headaches but much more restrictive with regard to image size and separation (the two image centers must be about 7cm apart). Viewing method of choice tends to be a personal preference, on this webpage we present Figure 15 of Siegel et al. (2011) in both cross-eyed and parallel-eyed variants.

For those unfamiliar with how to view stereoscopic images, there are many good tutorials available on the web. One of the most concise and helpful that I've found is located here. Note that distance scales are provided in the plots below for reference, the '25' kpc marker should appear to float above the '31' kpc marker; if the apparent depths are reversed, you're using the wrong technique (i.e., using parallel-eyed vision to view the cross-eyed plot or vice-versa). Practice improves the ease of viewing, and these particular images are somewhat difficult to visualize thanks in part to the large number of M-giant data points. One trick that can be helpful is to focus first on the distance scale, and (when the stereoscopic illusion is clear) gradually shift attention to the rest of the image.

Figure 15: The Sgr dwarf core and globular cluster system as seen in a stereoscopic representation for a viewer at the location of the Sun with ‘eyes’ 2.5 kpc apart along the Galactic Y-axis (i.e., the direction of motion of the LSR). The view approximately corresponds to Galactic longitude along the horizontal axis (increasing from right to left) and Galactic latitude along the vertical axis (increasing from bottom to top), with a total ﬁeld of view ~ 30x30 degrees. The black points represent 2MASS M-giants scaled to a central Sgr core dis- tance of the LM10a N-body model at dSgr = 28 kpc (lower panel) and dSgr = 30 kpc (upper panel). The M giant distribution at the top of the image has been cut oﬀ because of severe contamination by disk M giant stars. Magenta crosses represent the Sgr distances as measured by the Sgr main sequence features seen in the bulge cluster CMDs, and the red circles are the classical Sgr core globular clusters The green line represents the orbit of the Sgr core, with direction of motion indicated by the green arrow. A depth gauge is given on the right hand side of the panels to indicate the appearance of objects at distances of 25, 27, 29, and 31 kpc. The viewer can check that distances appear correctly by verifying that the 25 kpc distance scale marker appears closer than the 31 kpc marker. Note how Ter7 appears to float significantly above the M-giant data (i.e., lie significantly closer to the Sun).

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