Atlas Image mosaic, covering 7.0´ × 7.0´ on the sky, of Tonantzintla 2 (Pismis 26), which is one of the least-known Galactic globular clusters. At l=350.8° and b=-3.4°, it is quite close to the Galactic Center. From V and I photometry using the ESO 3.6-m NTT, Bica, Ortolani, & Barbuy (1996, A&AS, 120, 153) found that the positions of red giant branch and horizontal branch stars on the optical color-magnitude diagram indicate that the chemical composition of the cluster stars are similar to those in 47 Tucanae. They also found a reddening to the cluster which implies an extinction of AV~4 magnitudes, and a distance from us of 6.4 kpc (20,900 light years). Bica et al. conclude that Ton 2 belongs to the bulge population of the Milky Way, but is only moderately "metal-rich". Image mosaic by S. Van Dyk. Look also at preliminary 2MASS near-infrared color-color and color-magnitude diagrams. (These include all stars in the Atlas Image Mosaic detected by the 2MASS pipeline processing; crowding affects and limits the detections and photometry of stars in the densest regions of the cluster.)
Atlas Image mosaic, covering 1° × 1° on the sky, of Messier 17 (M17), aka the Omega Nebula, the Swan Nebula, the Horseshoe Nebula, and the Lobster Nebula, located in the constellation Sagittarius. It is roughly 5,000 light years from the Sun. The 2MASS image penetrates the obscuring veil of dust and reveal the otherwise invisible contents of a dark molecular cloud. The giant molecular cloud associated with M17 is one of the most luminous and active star-forming complexes in the Milky Way, and contains one of the youngest and richest stellar clusters in our galaxy. Although the gas in the molecular cloud is too cold to emit visible or near-infrared light, traces of the densest portions of the cloud can still be seen as dark, obscuring, cloudy structures in the 2MASS mosaic, by E. Kopan (IPAC). (N.B.: The full JPG image is 12.7 Mb in size! A smaller version [1.4 Mb] can be obtained here.)
Atlas Image mosaic, covering 6.0´ × 6.0´ on the sky, of the planetary nebula NGC 6781. Planetary nebulae (PNe) are formed as low-mass stars, like the Sun, reach the end of their lives and lose their outer envelopes to the interstellar medium. NGC 6781 has a very similar "ring-like" morphology to the famous PN, the Ring Nebula (M57). The red glow of NGC 6781's ring in the near-infrared is due to 2.12 µm emission from molecular hydrogen (H2), which is strong in the 2MASS Ks band. Although the main ring is quite bright, the fainter H2 filaments within and halo emission outside of the bright ring, as studied by Kastner et al. (1994, ApJ, 421, 600), can just barely be seen in the 2MASS image. Kastner et al. postulate that if all PNe showing axial symmetry, and therefore, possessing bipolar structure, are H2-bright, as first found by Zuckerman & Gatley (1988, ApJ, 324, 501), then ring-like PNe, like NGC 6781, with strong shocked H2 emission may be bipolar nebulae viewed with an inclined polar axis with respect to the plane of the sky. The bright ring is the equatorial torus, from a high-density slow wind from the evolving star, whereas the fainter halo structures are the polar lobes and the remnants of a faster, low-density wind. For NGC 6781 the lobe geometry may be a bipolar cylinder with half the radius of and within the bright torus. Near-infrared observations, such as those by 2MASS, provide very important information about PNe and the evolution of stars like our Sun.
