2MASS Picture of the Week Archive Captions

Atlas Image mosaic, covering 11.7´ × 25.0´ on the sky, of the Herbig Be star MWC 297 (IRAS 18250-0351), also known as the variable star NZ Serpentis. In the near-infrared 2MASS image one can see an extended reflection nebula and dust clouds around the star. Based on optical-to-near-infrared photometry, the star is behind ~8 magnitudes of visual extinction, at a distance of ~450 pc (1470 ly). Bergner et al. (1988, Astrofizica, 28, 529) found from UBVRIJHK photometry that the star is variable at all wavelengths, likely due to changes in dust obscuration in the nebula in which the star is still embedded. Optical spectra by Andrillat & Jaschek (1998, A&AS, 131, 479) show no absorption lines, only emission lines from the young star's extended atmosphere, which indicate an underlying spectrum of a massive late O- or early B-type star. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 15.0´ × 29.9´ on the sky, of Abell 426, better known as the Perseus Cluster, a nearby rich galaxy cluster. The cluster is notable with its prominent grouping of bright galaxies near the core and an exceptionally strong deficiency of spiral galaxies. The cluster is dominated by NGC 1275, the strong radio source Perseus A, ther bright galaxy seen near the center of the 2MASS image mosaic; the bizarre galaxy has an active nucleus, with bright, extended radio lobes, and evidence that the galaxy is the remnant of a recent merger. The x-ray emission from the cluster, and the fact that the cluster hosts several galaxies with active nuclei, pronounced radio structures, enhanced far-infrared emission, and signs of strong gravitational interactions, have been interpreted as signs of a merger of galaxy clusters. Studies of the Perseus cluster are hampered by its low galactic latitude (l=150.6°, b=-13.3°), resulting in a high density of Galactic foreground stars and appreciable extinction in the optical. In the 2MASS near-infrared image the extinction has been substantially reduced, and the galaxy light appears much smoother than it does in the optical.


Atlas Image mosaic, covering 34.6´ × 33.1´ on the sky, of the southern star-forming region RCW 38. (N.B.: The mosaic is 3.7 Mb!) Zoom in on the central cluster (IRS2; Frogel & Persson 1974, ApJ, 192, 351) in the inner 6´ × 6´ of the nebula; a number of massive O stars are embedded within a dense, heavily obscuring cloud. Ligori et al. (1994, MemSAI, 65, 815) find an age of ~2 Myr for the stars in IRS2, showing that the star formation is very recent and still ongoing. RCW 38 is at a distance of ~1.7 kpc (~5500 light years) from us, near the famous Vela supernova remnant and the Gum nebula. As seen in the 2MASS near-infrared Image mosaic, the nebulosity associated with RCW 38 is extensive across a large area, with dust lanes and patches running throughout. Other, smaller obscured star-forming regions are nearby, with less-obscured young, massive stars and associated reflection nebulae also in the field. A high-resolution view in the near-infrared of IRS2 was recently obtained by ESO's Very Large Telescope. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 21.0´ × 21.0´ (in full mosaic) on the sky, of the nearby spiral NGC 253, which is a prototypical starburst galaxy. Starburst galaxies are those that are experiencing intense recent star formation, often concentrated at a galaxy's nucleus or along the galaxy's spiral arms. The nucleus of NGC 253 as seen in the 2MASS Image mosaic is a very bright source of near-infrared emission. Compare the 2MASS image mosaic to an equivalent large-scale optical image of the galaxy. In the near-IR the very prominent and patchy dust lanes seen in the optical image are far less obvious; the overall light distribution in the near-IR is smoother, even though the galaxy disk is significantly inclined. What is obvious in the near-IR is the barred nature of this galaxy (Forbes & DePoy 1992, A&A, 259, 97; Scoville et al. 1985, ApJ, 289, 129), which is not as evident in the optical. A number of bright knots of red supergiant stars and some dusty patchiness are also seen along the arms and bar. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 12.0´ × 12.0´ (in full mosaic) on the sky, of GGD 27. This object is the center of an active young star formation region obscured optically by dense molecular gas and dust along our line of sight. In the 2MASS near-infrared image a number of point sources in this region can be seen, along with the extended and wispy bipolar reflection nebulosity, which corresponds to a bipolar molecular outflow, with a dynamical age of about 105 years (Yamashita et al. 1989, ApJ, 347, 894). Particularly noticeable is the reddish core region of the source, where the most embedded star formation is taking place. Imaging of this core region at slightly longer wavelengths than the 2MASS bandpasses (3.8 and 4.7 µm) by Aspin et al. (1994, A&A, 292, L9) reveal several sources so obscured they are not seen at 2 µm. Image mosaic by S. Van Dyk (IPAC).
































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