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J/ApJ/646/1215      Low-mass stars and brown dwarfs in NGC 2024 (Levine+, 2006)

Low-mass stars and brown dwarfs in NGC 2024: constraints on the substellar mass function. Levine J.L., Steinhauer A., Elston R.J., Lada E.A. <Astrophys. J., 646, 1215-1229 (2006)> =2006ApJ...646.1215L
ADC_Keywords: Clusters, open ; Stars, pre-main sequence ; Photometry, infrared Keywords: infrared: stars - stars: low-mass, brown dwarfs - open clusters and associations: individual (NGC 2024) - stars: luminosity function, mass function - stars: pre-main sequence Abstract: We present results from a near-infrared spectroscopic study of candidate brown dwarfs and low-mass stars in the young cluster NGC 2024. Using FLAMINGOS on the KPNO 2.1m and 4m telescopes, we have obtained spectra of ∼70 new members of the cluster and classified them via the prominent J- and H-band water absorption features. Derived spectral types range from ∼M1 to later than M8 with typical classification errors of 0.5-1 subclasses. By combining these spectral types with JHK photometry, we place these objects on the H-R diagram and use pre-main-sequence evolutionary models to infer masses and ages. The mean age for this low-mass population of NGC 2024 is 0.5Myr, and derived masses range from ∼0.7 to 0.02M with 23 objects falling below the hydrogen-burning limit. The logarithmic mass function rises to a peak at ∼0.2M before turning over and declining into the substellar regime. There is a possible secondary peak at ∼0.035M ; however, the errors are also consistent with a flat IMF in this region. The ratio of brown dwarfs to stars is similar to that found in the Trapezium but roughly twice the ratio found in IC 348, leading us to conclude that the substellar IMF in young clusters may be dependent on the local star-forming environment. Description: All imaging and spectroscopic data included in this work were taken using the Florida Multi-Object Imaging Near-Infrared Grism Observational Spectrometer (FLAMINGOS) mounted on the Kitt Peak National Observatory (KPNO) 2.1m and 4m telescopes as part of the FLAMINGOS giant molecular cloud survey. J-, H-, and K-band images of NGC 2024 were obtained on 2001 November 19 using FLAMINGOS on the KPNO 4m telescope. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 82 71 Measured data and derived quantities for classified sources in NGC 2024
See also: J/ApJ/598/375 : Chandra X-ray observations of NGC 2024 (Skinner+, 2003) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Sequential number, Cl* NGC 2024 LSE NN in Simbad 3 A1 --- n_Seq [d] d for possible background giant 5- 9 A5 --- --- [FLMN_] 10- 25 A16 --- FLMN FLAMINGOS designation (JHHMMSSs-DDMMSSs) 27- 31 F5.2 mag Jmag ? J magnitude 32 A1 --- n_Jmag [b] Jmag derived from FLAMINGOS (1) 34- 38 F5.2 mag Hmag H magnitude 40- 44 F5.2 mag Kmag K magnitude 46 A1 --- l_SpType Limit flag on SpType 47- 51 A5 --- SpType MK spectral type M with subclass 52 A1 --- n_SpType [c] SpType derived from spectroscopy (2) 54- 58 F5.2 mag AV ? Absorption in V band 60- 64 F5.2 --- rK ? K-band veiling index (3) 66- 70 F5.3 [K] logTeff ? Effective temperature 72- 77 F6.3 [solLum] log(L) ? Luminosity 79- 82 F4.2 solMass Mass ? Mass
Note (1): 17, 47, and 68 have J magnitudes derived from FLAMINGOS imaging on the 2.1m telescope. Note (2): Sources 68-71 have spectral types derived from 2.1m spectroscopy. Note (3): the veiling index is the ratio of excess flux over the stellar flux, r = Fex/F*
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 09-May-2008
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