Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...497..721n&link_type=abstract
Astrophysical Journal v.497, p.721
Astronomy and Astrophysics
Astronomy
36
Ism: Structure, Methods: Statistical, Galaxy: Open Clusters And Associations: General, Stars: Formation, Stars: Pre-Main-Sequence
Scientific paper
We study clustering of pre-main-sequence stars in the Orion, Ophiuchus, Chamaeleon, Vela, and Lupus star-forming regions. We calculate the average surface density of companions, Sigma ( theta ), as a function of angular distance, theta , from each star. We employ the method developed by Larson in a 1995 study for the calculation. In most of the regions studied, the function can be fitted by two power laws ( Sigma ~ theta gamma ) with a break as found by Larson for the Taurus star-forming region. The power index, gamma , is smaller at small separations than at large separations. The power index at large separations shows significant variation from region to region (-0.8 < gamma < -0.1), while the power index at small separations does not ( gamma ~ -2). The power index at large separations relates to the distribution of the nearest-neighbor distance. When the latter can be fitted by the Poisson distribution, the power index is close to 0. When the latter is broader than the Poisson distribution, the power index is negatively large. This correlation can be interpreted as the result of the variation in the surface density within the region. At large separations, the power-law fit may indicate star formation history in the region and not the spatial structure like the self-similar hierarchical, or fractal, one. Because of the velocity dispersion, stars move from their birthplaces, and the surface density of coeval stars decreases with their age. When a star-forming region contains several groups of stars with different ages, a power law may fit the average surface density of companions for it. The break of the power law is located around 0.01-0.1 pc. There is a clear correlation between the break position and the mean nearest-neighbor distance. The break position may reflect dispersal of newly formed stars.
Hanawa Tomoyuki
Nakajima Yasushi
Nakano Makoto
Tachihara Kengo
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