Dby. Navascues et al., From the top to the bottom of the main sequence: A complete mass function of the young open cluster M35, ASTROPHYS J, 546(2), 2001, pp. 1006-1018
We present very deep and accurate photometry of the open cluster M35. We ha
ve observed this association in the Cousins R, I filters, together with the
Johnson V filter. We have covered a region of 27.5 x 27.5 square arcmin, e
quivalent to a fifth of the total area of the cluster. The data range from
I-c = 12.5 to 23.5 mag, and the color intervals are 0.4 less than or equal
to (V - I)c less than or equal to 3.0, 0.5 less than or equal to (R - I)(c)
less than or equal to 2.5. Roughly, these values span from 1.6 M. down to
the substellar limit, in the case of cluster members. By using the location
of the stars on color-magnitude and color-color diagrams, we have selected
candidate members of this cluster. We have merged our sample with previous
ly published data and obtained a color-magnitude diagram for the complete s
tellar population of the cluster, covering the spectral range early B-mid M
. Based on the distribution of field and cluster stars in color-magnitude a
nd color-color diagrams, we estimate that two-thirds of these candidates ar
e likely to be true members of M35. These stars approximately double the nu
mber of stars identified as candidate members of this cluster (similar to 2
700). We provide the photometry and accurate positions of these stars. The
deep photometry has allowed us to study the mass segregation within the clu
ster, the luminosity function, and mass function. We show that in the magni
tude range 13 less than or equal to I-c less than or equal to 22 there is a
reduced mass segregation, in opposition to what happens to higher mass sta
rs, where the mass segregation is stronger. The luminosity function behaves
essentially as the one characteristic of the Pleiades, presenting a peak a
t I-c similar to 19 mag (M-I similar to 9). Combining our photometry with p
revious data corresponding to more massive stars, we find that the mass fun
ction increases monotonically, when plotted in a log-log form, until it rea
ches similar to0.8 M. (alpha = 2.59). It remains shallower for less massive
stars (alpha = 0.81 for 0.8-0.2 M.), whereas a decrease is observed for st
ars close to the substellar regime. These different behaviors suggest that
at least three mechanisms play a role in the formation of stellar and subst
ellar objects. The total mass of the cluster is similar to 1600 M. in the a
rea covered by this study.