2MASS Picture of the Week Archive Captions

Atlas Image mosaic, covering 50´ × 100´ on the sky, of the Great Nebula in Orion. This image mosaic, of course, has already appeared in our Image Gallery, but this particular version is special. First, it commemorates the very last 2MASS Picture of the Week, as we move into our Extended Mission. Second, the mosaic was constructed by stacking together 17 out of 20 special repeat survey scans of Orion obtained at different epochs. (The results from these scans appeared in Carpenter, Hillenbrand, & Skrutskie [2001, AJ, 121, 3160], where these authors confirmed the near-infrared variability of 1235 stars, many of which are likely pre-main-sequence objects.) In other words, the effective total exposure time for this image mosaic is 17 × 7.8 sec, which is nearly 133 sec. These special scans will not be part of the upcoming All-Sky Data Release, but will be among the publicly-released data products during our Extended Mission, which will continue through 2004. (N.B.: The full mosaic is 9.2 Mb in size!!) Image mosaic by E. Kopan and R. Hurt (IPAC).


Atlas Image mosaic, covering 40´ × 40´ on the sky, of the rho Ophiuchi Dark Cloud. (The image has been binned to 2´´ × 2´´ pixels.) At only about 150 pc (489 light years) distance from us, this cloud is one of the closest regions of low-mass stars in formation. As such, its stellar, dusty, and gaseous contents have been intensively studied at a number of wavelengths, from radio to X-rays. Shown in this 2MASS image is only a few components of the larger Cloud, primarily the dark nebula LDN 1688, toward the center of the image. A number of embedded protostellar and young stellar objects, as well as patchy, filamentary, and streamer-like dust clouds, are also seen. The 2MASS color-color diagram shows that the extinction within the cloud exceeds 30 visual magnitudes. This image mosaic was derived with version 1.0 of Montage, an astronomical image mosaic service supported by NASA's Computational Technologies project. (N.B.: The full mosaic is 1.4 Mb in size!.) Image mosaic by R. Hurt (IPAC).


Atlas Image mosaic, covering 50´ × 50´ on the sky, of the famous Rosette Nebula, also more prosaicly known as Sharpless 275. Surprised by its appearance? In the 2MASS image the beautiful nebulosity, which so characterizes the Rosette, as seen in, for example, David Malin's optical image, all but vanishes. The optical nebulosity is emission from the HII, or ionized hydrogen, region surrounding the central young star cluster, NGC 2244. Only the stars of this cluster, as well as many more Milky Way stars in the nebula's field, are seen in the 2MASS image. Also not strongly detected is emission in the near-infrared from molecular hydrogen gas. Park & Sung (2002, AJ, 123, 892) recently measured from optical imaging the extinction and distance to NGC 2244 of about 1.5 visual magnitudes and 1.66 kpc (about 5400 light years), respectively. They also derive an age for the main sequence stars in the cluster of about 2 Myr, with a spread of 6 Myr in the age of several pre-main-sequence stars. The 2MASS color-color and color-magnitude diagrams show that this extinction, distance, and cluster age are reasonably consistent with the near-infrared photometry. The many stars in the field which are not members of the cluster can also be seen in these diagrams. (N.B.: The full mosaic is 5.3 Mb in size!.)


Atlas Image mosaic of the central 11´ × 11´ of the nearby spiral galaxy IC 342. This Scd-type galaxy is seen nearly face-on toward the constellation Camelopardalis and is thought to be very similar to our own Milky Way Galaxy. Along with Maffei 1 and 2 and Dwingeloo 1 and 2, IC 342 comprises a small group of galaxies that is very nearby (at only about 2 Mpc, or 6.5 million light years) to our own Local Group, which contains the Galaxy. The IC 342 group is within about 10° of the Galactic plane, thus, very near the "Zone of Avoidance." IC 342 covers nearly half a degree on the sky in the optical (about 1.5° in atomic hydrogen gas!). Its spiral arms are seen as quite diffuse, especially by 2MASS. (For a larger 2MASS view of IC 342, visit the Large Galaxy Atlas.) Its central region is more luminous, even in the near-infrared, and is gas-rich (Crosthwaite et al. 2001, AJ, 122, 797; see a map of atomic and molecular gas, corresponding approximately to the region shown in the 2MASS image). Image mosaic by S. Van Dyk (IPAC).
































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