Globulettes as Seeds of Brown Dwarfs and Free-Floating Planetary-Mass Objects
| Autor: | Tiia Grenman, Gösta F. Gahm, S. Fredriksson, H. Kristen |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | The Astronomical Journal. 133:1795-1809 |
| ISSN: | 1538-3881 0004-6256 |
| Popis: | Some H II regions surrounding young stellar clusters contain tiny dusty clouds, which on photos look like dark spots or teardrops against a background of nebular emission. From our collection of H? images of 10 H II regions gathered at the Nordic Optical Telescope, we found 173 such clouds, which we call globulettes, since they are much smaller than normal globules and form a distinct class of objects. Many globulettes are quite isolated and located far from the molecular shells and elephant trunks associated with the regions. Others are attached to the trunks (or shells), suggesting that globulettes may form as a consequence of erosion of these larger structures. None of our objects appear to contain stellar objects. The globulettes were measured for position, dimension, and orientation, and we find that most objects are smaller than 10 kAU. The Rosette Nebula and IC 1805 are particularly rich in globulettes, for which the size distributions peak at mean radii of ~2.5 kAU, similar to what was found by Reipurth and coworkers and De Marco and coworkers for similar objects in other regions. We estimate total mass and density distributions for each object from extinction measures and conclude that a majority contain |
| Databáze: | OpenAIRE |
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