2MASS Picture of the Week Archive Captions

Atlas Image Mosaic, covering 15.0´ × 15.0´ on the sky, of the infrared source NGC 2264 IRS1, which is part of the larger NGC 2264 star-forming region. The source is a very young intermediate-mass star, still embedded in its natal cloud, just north of the tip of the famous Cone Nebula (for a beautiful optical view of the field by David Malin, visit this page). The bright optical star W 178 can be seen just to south of the source; the nebulous tip of the optical Cone can also be seen in the 2MASS image, just to the southeast. The source was previously imaged in the near-infrared by Schreyer et al. (1997, A&A, 326, 347), and they noted a jet-like feature to the northeast of IRS1, and also the infrared-bright (Ks-only) compact cluster immediately to the southeast. IRS1 is surrounded by a cluster of embedded lower-mass stars. Another cluster of embedded stars can be seen ~6´ to the northwest in the 2MASS image. IRS1 and its neighbors are all part of the larger Monoceros OB1 cloud complex, where stars are actively forming.


Atlas Image, covering 5.0´ × 5.0´ on the sky, of the planetary nebula (PN) NGC 40 (HD 826). This image, as well as previous near-infrared images by Latter et al. (1995, ApJS, 100, 159), show an elliptical-shaped shell highlighted by the bright east and west lobes. NGC 40's morphology is consistent with models of "barrel"-shaped PNe (Mellema 1995, MNRAS, 277, 173). Hora, Latter, & Deutsch (1999, ApJS, 124, 195) point out that material has broken through and expanded beyond the shell, forming faint filaments of gas. They detect weak 2.2 µm molecular hydrogen (H2) emission and tentatively conclude that the emission is shock-excited. PNe are formed as stars like our Sun lose their outer envelopes to the interstellar medium at the end of their lives. Hora et al. conclude that H2 emission is not directly tied to a PN's morphology, but that bipolar morphology is intimately related to the mass of the progenitor star. It remains a mystery why relatively high-mass, high mass-loss-rate asymptotic giant branch progenitors shed material in an axisymmetric fashion. The bright source within the bright nebula is the hot central star of the PN, originally the core of the dying star, which will eventually become a white dwarf and cool off over billions of years. (A portion of the diffraction spike of the brightest member of the nearby multiple star system BD+71 8 [SAO 4061] can faintly be seen to the north of the PN.)


Atlas Images, each covering 4.8´ × 4.8´ on the sky, of the comets C/1998 K1 (Mueller) and C/1998 M2 (LINEAR). Occasionally, 2MASS accidentally encounters solar system bodies during its routine operations (see the Solar System Objects page of the 2MASS Image Gallery and discussion of the known asteroid, comet, planet, and satellite associations in the Second Incremental Data Release). As reported in IAU Circular No. 7500, M. Sykes, R. Cutri, J. Fowler, D. Tholen, & M. Skrutskie found "prediscovery" apparitions of these two comets, before their optical discoveries, in 2MASS Atlas Images acquired at the Northern Facility on Mount Hopkins and Southern Facility on Cerro Tololo, respectively. Comet C/1998 K1 was seen on 1998 April 4.316 UT at Ks=14.7, J-H=0.3, and H-Ks=0.2, and on May 10.223 at Ks=14.9, J-H=0.5, and H-Ks=0.0. Comet C/1998 M2 was seen on May 4.404 at Ks=14.3, J-H=0.5, and H-Ks=0.0. Both comets showed some coma, but with no obvious tail.


Atlas Image mosaic, covering 10.0´ × 10.0´ on the sky, of the galactic open star cluster Messier 11 (M11), also known as the Wild Duck. M11 (NGC 6705) is one of the more populous and compact open clusters in the Milky Way, close to the Galactic plane (l=27.3°, b = -2.8°) toward the constellation Scutum. From an analysis of deep optical CCD photometry of the cluster, Brocato, Castellani, & DiGiogio (1993, AJ, 105, 2192) determined that the stars are at a distance of 1.7 kpc (5542 light years) from us and have an age of ~150 million years, making the cluster intermediate in age. Solomon & McNamara (1980, AJ, 85, 432) estimated the reddening to the cluster to be E(B-V)~0.42 mag. 2MASS has obtained near-infrared photometry for the cluster during routine operations; to see the color-color diagram, click here, and to see the color-magnitude diagram, click here. In the latter diagram, we overlay a theoretical isochrone at solar metallicity (Gonzales & Wallerstein 2000, PASP, 112, 1081) with age 150 Myr (green line), showing that the assumed age, distance, and reddening are consistent with the main sequence and red giant stars in M11. The blue line indicates contamination due primarily to older giants in the foreground and background; the isochrone is solar age at 1 kpc distance with the same reddening. Image mosaic by S. Van Dyk (IPAC).































Return to the 2MASS Home Page