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Exploring the Low-Mass Initial Mass Function in Young Clusters and Star-Forming Regions

Abstract : The determination of the lower-end of the initial mass function (IMF) provides strong constraints on star formation theories. We report here on a search for isolated planetary-mass objects in the 3 Myr-old star-forming region IC 348 and on a wider survey of the 30 Myr-old open cluster IC 4665. IC 4665 is a fairly young (~30Myr) star cluster and is 356 pc distant towards the constellation Ophiuchus. Proper motion is low at -4 to -7.5 mas/yr and extinction is also low and present at Av~ 0.59 ± 0.15 mag. WIRCam Y , J, H and Ks observations were made using the CFHT and spanned 10 cluster fields (of total footprint ∼1.1sq.deg) and two control fields of 20′x20′ each. Colour/magnitude diagrams were used to compare the catalogue objects to the 30 and 50 Myr BT-SETTL models for photometric selection. Further colour/colour diagrams were then iteratively used to further filter these objects into a final cluster candidate member list, with 590 unique objects. Contamination by field stars can be assessed using the control fields and M- and L- dwarf space densities. This part requires further analysis. Probing into the lowest-mass end of the IMF in IC 348 required deep, narrowband CH4off and CH4on images. These were were obtained with CFHT/WIRCam over 0.11 sq.deg. over the central part of IC 348, along with z′, J, H and Ks band images. Young T-dwarfs were identified from their 1.69 μm methane absorption bands. Three faint T-dwarf candidates were detected with CH4on−CH4off colours >0.4 mag. Extinction was estimated for each candidate and lies in the range Av ~ 5 − 12 mag. Comparisons with T-dwarf spectral models, and colour/colour and colour/magnitude diagrams, reject two of the three candidates because of their extreme z′ − J blueness. The one remaining object is not thought to be a foreground field dwarf because of a number density argument and also its strong extinction Av~ 12 mag, or thought to be a background field T-dwarf which would be expected to be much fainter. Models and diagrams give this object a preliminary T6 spectral type. With a few Jupiter masses, the young T-dwarf candidate reported here is potentially amongst the youngest, lowest mass objects detected in a star-forming region so far. Its frequency is consistent with the extrapolation of current lognormal IMF estimates down to the planetary mass domain.
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Contributor : Andrew Burgess <>
Submitted on : Monday, March 14, 2011 - 12:45:39 PM
Last modification on : Thursday, November 19, 2020 - 3:54:29 PM
Long-term archiving on: : Wednesday, June 15, 2011 - 2:57:10 AM


  • HAL Id : tel-00576460, version 1



Andrew Burgess. Exploring the Low-Mass Initial Mass Function in Young Clusters and Star-Forming Regions. Astrophysics [astro-ph]. Université de Grenoble, 2010. English. ⟨tel-00576460⟩



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