A census of very-low-mass stars and brown dwarfs in the σ Orionis cluster

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Volume 505 / No 3 (October III 2009)

A&A, 505 3 (2009) 1115-1127

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Table 2:

Comparison of the numbers of low-mass stars and brown dwarfs as a function of the distance from the cluster centre (D), from 5 to 30 arcmin in radius.
D	Stars^a,b	BD^c	R1^d	Stars^a	BD^c	R1^e
			%			%
5	24 (25)	5	20.8 (10.2)	27 (25)	3	11.1 (5.8)
10	64 (43)	24	37.5 (22.4)	77 (43)	13	16.9 (10.8)
15	93 (62)	37	39.8 (23.9)	109 (62)	24	22.0 (14.0)
20	128 (81)	51	39.8 (24.4)	147 (81)	37	25.2 (16.2)
25	163 (108)	59	36.2 (21.8)	186 (108)	42	22.6 (14.3)
30	198 (120)	73	36.9 (23.0)	223 (120)	56	25.2 (16.4)

^a In this table, low-mass stars are defined as objects with masses between 0.5 and 0.08 $M_{\odot }$ (for the purpose of the indices). ^b The numbers in brackets take into account the most massive members ( $J \leq 12$ mag; $M \geq 0.5$ $M_{\odot }$ ) of $\sigma$ Orionis taken Mayrit catalogue (Caballero 2008c), yielding the $R_{\rm SS}$ or R1 ratios defined by Briceño et al. (2002) and Luhman et al. (2003), respectively. ^c In this table, brown dwarfs are defined as objects with masses between 0.08 and 0.02 $M_{\odot }$ (for the purpose of the indices). ^d The results on the left-hand side assume a distance of 352 pc from Hipparcos. ^e The results on the right-hand side assume a distance of 440 pc (Sherry et al. 2004; Brown et al. 1994).

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