2MASS Picture of the Week Archive Captions

Atlas Image mosaic, covering 7.5´ × 7.5´ on the sky, of the globular cluster Palomar 6, which is in the direction of the Galactic bulge. The loose cluster is optically obscured, but more prominent among the surrounding bulge stars in the near-infrared. Ortolani et al. (1995, A&A, 296, 680) determined that the cluster is seen through about four visual magnitudes of extinction, at a distance from us of about 8.9 kiloparsecs (29000 light years), placing it nearby the Galactic center. They determined that the cluster is relatively metal-rich, higher in metals than 47 Tucanae. Although the spatial resolution of 2MASS is insufficient to overcome the extreme stellar crowding within the cluster, 2MASS is well suited for revealing obscured clusters in the Galaxy and for studying the cluster environment. Image mosaic by S. Van Dyk (IPAC). These data are included in the Second Incremental Release!


Atlas Image mosaic, covering 0.5° × 0.5° on the sky, of the galaxy cluster Abell 3558, also known as Shapley 8. This is a rich cluster, which has been the subject of study at a number of wavelengths. The cluster is dominated by a central giant cD galaxy (the brightest galaxy near the center of the 2MASS image), which, interestingly enough, also lies near the center of the larger Shapley concentration, or supercluster, of 25 clusters of galaxies, including Abell 3558. Dantas et al. (1997, ApJ, 485, 447) recently found that the cluster is actually composed of a collection of several groups of galaxies, suggesting that it is a dynamically complex, young cluster of galaxies. One of the data products released by 2MASS is an Extended Source Catalog, much of which consists of galaxies. The 2MASS Processing Pipeline measures magnitudes, sizes, and positions for extended sources through a large number of possible apertures. To see a representative color-color diagram for a 1°-radius area centered on Abell 3558, click here; shown on the diagram are the Bessell & Brett (1988, PASP, 100, 1134) and Koorneef (1983, A&A, 128, 84) tracks for dwarf and giant stars, as well as K-correction tracks for elliptical and spiral galaxies (in steps of redshift z=0.1) and the reddening vector from Rieke & Lebofsky (1985, ApJ, 288, 618). Abell 3558 is at z=0.048. A radius vs. magnitude diagram for the cluster can also be found here. Finally, a source count diagram can be found here (the magenta crosses, shown for reference, are deep, narrow-field generalized galaxy counts from Gardner et al. (1997, ApJ, 480, L99). For a larger 0.58° × 1.33° view of Abell 3558, click here; this image is 9.7 Mb in size! (A meteor streak can be seen through both the large and smaller view.) Image mosaic by E. Kopan (IPAC). These data are included in the Second Incremental Release!


Atlas Image mosaic, covering 0.64° × 1.15° on the sky, of a portion of Baade's Window centered at about l=1.0°, b=-3.9°. (The downloadable image mosaic has been shrunk by 50%, but is still 2.2 Mb in size.) This "window" through our Milky Way Galaxy, discovered by the German-American astronomer Walter Baade early in the last century, is an important region of the sky, because the interstellar extinction, due to intervening dust in the Galactic plane, is substantially lower than other regions of the Galaxy nearby to it. Stanek (1996, ApJ, 460, L37) estimates from optical data that the extinction ranges from 1.26 to 2.79 visual magnitudes. As a result, this window allows astronomers to more easily view and study stars in the Galactic bulge. The chemical composition, ages, masses, and kinematics of these stars can be determined, the distance to the Galactic center can be measured, microlensing events can be discovered and analyzed, and the presence of a stellar bar in the bulge can be inferred, all important aspects to understanding the nature of the Milky Way. The 2MASS near-infrared color-color diagram and color-magnitude diagram for the stars within 1° of (l,b)=(1.0,-3.9) also demonstrate the relatively low extinction for the stellar populations in a region at this general position in the Galaxy. (Shown on the color-color diagram are the Bessell & Brett 1988, PASP, 100, 1134, and Koorneef 1983, A&A, 128, 84, tracks for dwarf and giant stars, as well as the reddening vector from Rieke & Lebofsky 1985, ApJ, 288, 618). Image mosaic by S. Van Dyk (IPAC). These data are included in the Second Incremental Release!


Atlas Image mosaic, covering 33.3´ × 46.1´ on the sky, of the reflection nebulae NGC 2068 and 2071, comprising Messier 78 (M78). This complex is located in the LDN 1630 (Orion B) cloud, at a distance of about 400 pc (1300 light years). Reflection nebulae, particularly in the optical, are dusty regions that scatter and reflect the light from typically bright, hot, blue stars within the regions. They are commonly associated with molecular clouds and the dusty sites of active star formation. The illuminating stars for NGC 2068 (to the south) are HDE 38563A and 38563B, while the illuminating star for NGC 2071 (to the north) is HDE 290861. The two nebulae appear to contain small clusters of stars. A number of embedded, young stellar objects are located throughout this region, highlighted by the large number of dramatic Herbig-Haro outflow sources; Zhao et al. (1999, AJ, 118, 1347) brought the complement of HH objects in M78 to 17. Lada et al. (1991, ApJ, 371, 171) conducted a 2.2 µm survey of L1630, complete to K<13 (the 2MASS data go deeper than this), and concluded that much of the young, embedded star formation is occurring in clusters. Image mosaic by S. Van Dyk (IPAC). These data are included in the Second Incremental Release!


Atlas Image, covering 5.0´ × 5.0´ on the sky, of the supernova remnant (SNR) N49 in the Large Magellanic Cloud (LMC). This appears to be the first near-infrared image of this SNR. The optical, X-ray, near-infrared and radio morphology for N49 all are in general agreement, with an incomplete shell covering nearly 1´ in diameter. Emission due to the hydrogen Paschen beta line and lines of forbidden singly-ionized iron ([Fe II]) in the J and H bands likely dominate what we see. Strong Ks-band emission, as in the case of the SNR IC 443 in our Galaxy, due to molecular hydrogen (H2) line emission excited by shock-molecular cloud interaction, is surprising lacking, given the apparent interaction with an extended dense cloud to the southeast, as deduced by the optical (Vancura et al. 1992, ApJ, 394, 158) and X-ray (Hughes et al. 1998, ApJ, 505, 732) observations. N49 is also intriguing, with its possible association with the soft gamma-ray repeater SGR 0525-66 near the SNR's northern edge, however, this association has not yet been firmly established. SGRs are linked to isolated neutron stars, so if the association holds, this is further possible evidence of a massive stellar progenitor for this SNR. (See also Dickel et al. 1995, ApJ, 448, 623.) These data are included in the Second Incremental Release!
































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