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 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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 82 71 Measured data and derived quantities for
classified sources in NGC 2024
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See also:
J/ApJ/598/375 : Chandra X-ray observations of NGC 2024 (Skinner+, 2003)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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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
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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*
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 09-May-2008