2MASS Picture of the Week Archive Captions

Atlas Image, covering 6.7´ × 6.7´ on the sky, of the southern open star cluster Collinder 205 (aka Markarian 18). Vogt & Moffat (1973, A&AS, 9, 97) found from optical photometry that the reddening to this cluster varied from about 1.8 to 2.8 visual magnitudes, that the cluster's distance is about 1.6 kpc (5216 light years), and that the earliest spectral type in the cluster is B1. Reed (2000, AJ, 119, 1855) recently included this cluster with the much larger association Vela OB1.


Atlas Image mosaic, covering 8.0´ × 8.0´ on the sky, of the star LkH 221, a probable pre-main-sequence emission-line (T Tauri) star (Weintraub 1990, ApJS, 74, 575). Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 11.0´ × 11.0´ on the sky, of the spiral galaxy NGC 4565. This galaxy, much like other nearby, large edge-on spirals, such as NGC 5907 and NGC 891, resemble our Milky Way as it would be seen edge-on from a distance. Motivated by a flat rotation curve, implying a total mass of dark matter of 3.5×1011 M, Beichman et al. (1999, ApJ, 523, 559), based on deep Infrared Space Observatory ISOCAM observations at 4.5 µm, find that the faint galactic halo likely does not consist of late-M dwarfs distributed spherically, but could not exclude the presence of lower-luminosity brown dwarf stars. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 8.0´ × 8.0´ on the sky, of the infrared source IRAS 22051+5848, seen south of center in the 2MASS image. This source, at a distance of about 750 pc (2445 light years), is a pre-main sequence star reaching the end of an active FU Orionis phase and is embedded in the dark cloud LDN 1165. The fan-like nebula immediately to the southwest is GY 22, and is likely a reflection nebula, scattering light from IRAS 22051+5848. The IRAS source is also the origin of Herbig-Haro (HH) object 354 (not seen in the 2MASS image), an outflow which is unusually separated by a large distance (2.4 pc, or 7.8 light years) from its source (Reipurth, Bally, & Devine 1997, AJ, 114, 2708). The brighter reddish star at the center of the 2MASS image is IRAS 22051+5849, which is also embedded in the same cloud, but is unlikely the source of HH 354. Image mosaic by S. Van Dyk (IPAC).


Atlas Image mosaic, covering 6.0´ × 6.0´ on the sky, of the southern HII, or ionized hydrogen, region RCW 46. This region lies at the eastern edge of a recently-discovered large neutral hydrogen supershell, or giant void, with radius 300 pc (980 light years; McClure-Griffiths et al. 2000, AJ, 119, 2828). The supershell is in an interarm region near the Carina spiral arm in the Milky Way, and the presence of molecular gas and HII regions along the supershell indicate that star formation may have been initiated by the supershell's expansion. Image mosaic by S. Van Dyk (IPAC).































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