Astrophys. J., 810, 159 (2015/September-2)
Substellar objects in nearby young clusters (SONYC) IX: the planetary-mass domain of Chamaeleon-I and updated mass function in Lupus-3.
MUZIC K., SCHOLZ A., GEERS V.C. and JAYAWARDHANA R.
Abstract (from CDS):
Substellar Objects in Nearby Young Clusters–SONYC–is a survey program to investigate the frequency and properties of substellar objects in nearby star-forming regions. We present new spectroscopic follow-up of candidate members in Chamaeleon-I (∼2 Myr, 160 pc) and Lupus 3 (∼1 Myr, 200 pc), identified in our earlier works. We obtained 34 new spectra (1.5-2.4 µm, R ∼ 600) and identified two probable members in each of the two regions. These include a new probable brown dwarf in Lupus 3 (NIR spectral type M7.5 and Teff = 2800 K), and an L3 (Teff = 2200 K) brown dwarf in Cha-I, with masses below the deuterium-burning limit. Spectroscopic follow-up of our photometric and proper motion candidates in Lupus 3 is almost complete (90%), and we conclude that there are very few new substellar objects left to be found in this region, down to 0.01-0.02 M☉ and Av ≤ 5. The low-mass portion of the mass function in the two clusters can be expressed in the power-law form dN/dM ∝ M–α, with α∼0.7, in agreement with surveys in other regions. In Lupus 3 we observe a possible flattening of the power-law IMF in the substellar regime: this region seems to produce fewer brown dwarfs relative to other clusters. The IMF in Cha-I shows a monotonic behavior across the deuterium-burning limit, consistent with the same power law extending down to 4-9 Jupiter masses. We estimate that objects below the deuterium-burning limit contribute of the order of 5%-15% to the total number of Cha-I members.
brown dwarfs - open clusters and associations: individual: (Chamaeleon I, Lupus 3) - stars: formation - stars: luminosity function, mass function
Table 2: [MSG2015] NN (Nos 1-15) for Chamaeleon-I, [MSG2015] NN (Nos16-34) for Lupus 3. Table 3: SONYC Lup3-NN (Nos 28-29) added.
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