J/ApJ/541/977 HST observations of low-mass stars in IC 348 (Najita+, 2000)
From stars to superplanets:
the low-mass initial mass function in the young cluster IC 348.
Najita J.R., Tiede G.P., Carr J.S.
<Astrophys. J. 541, 977 (2000)>
=2000ApJ...541..977N 2000ApJ...541..977N
ADC_Keywords: Clusters, open ; Stars, late-type ; MK spectral classification ;
Photometry, infrared
Mission_Name: HST
Keywords: stars: late-type - stars: low-mass, brown dwarfs -
stars: luminosity function, mass function - stars: pre-main-sequence
Abstract:
We investigate the low-mass population of the young cluster IC 348
down to the deuterium-burning limit, a fiducial boundary between brown
dwarf and planetary mass objects, using a new and innovative method
for the spectral classification of late-type objects. Using
photometric indices, constructed from HST/NICMOS narrowband imaging,
that measure the strength of the 1.9µm water band, we determine the
spectral type and reddening for every M-type star in the field,
thereby separating cluster members from the interloper population. Due
to the efficiency of our spectral classification technique, our study
is complete from ∼0.7 to 0.015M☉. The mass function derived for
the cluster in this interval, dN/dlogM∝M0.5, is similar to
that obtained for the Pleiades, but appears significantly more
abundant in brown dwarfs than the mass function for companions to
nearby Sunlike stars. This provides compelling observational evidence
for different formation and evolutionary histories for substellar
objects formed in isolation versus as companions. Because our
determination of the IMF is complete to very low masses, we can place
interesting constraints on the role of physical processes such as
fragmentation in the star and planet formation process and the
fraction of dark matter in the Galactic halo that resides in
substellar objects.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 78 23 Standard Stars
table4.dat 133 193 Data for objects in the IC 348a fields
table6.dat 54 17 Objects with separations of less than 8"
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Object name (J1-4423 = [HJS91] 4423)
10- 15 A6 --- SpType MK spectral type (1)
18- 22 F5.2 mag Kmag ? K magnitude (2)
24- 27 F4.2 mag AV ? Absorption in V band
29- 35 E7.2 Jy F166 F166N flux, centered on 1.66µm
37- 43 E7.2 Jy e_F166 rms uncertainty on F166
45- 51 E7.2 Jy F190 F190N flux, centered on 1.90µm
53- 59 E7.2 Jy e_F190 rms uncertainty on F190
61- 67 E7.2 Jy F215 F215N flux, centered on 2.15µm
69- 75 E7.2 Jy e_F215 rms uncertainty on F215
77- 78 A2 --- Notes [c-k ] Individual notes (3)
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Note (1): Unless otherwise noted, spectral types are from Kirkpatrick et al.,
1991ApJS...77..417K 1991ApJS...77..417K
Note (2): Unless otherwise noted, K photometry are from
Leggett, 1992ApJS...82..351L 1992ApJS...82..351L
Note (3): Notes:
c: Spectral type from Keenan & McNeil, 1989ApJS...71..245K 1989ApJS...71..245K, Cat. III/150
d: Spectral type from Henry et al., 1994AJ....108.1437H 1994AJ....108.1437H
e: Spectral type from Walter et al., 1988AJ.....96..297W 1988AJ.....96..297W
f: Weak-lined T Tauri stars (WTTS); K photometry and extinction from
Kenyon & Hartmann, 1995, Cat. J/ApJS/101/117
g: Spectral type from Gliese, 1969, Cat. V/35
h: Counts were above the saturation limit in the last read.
Photometric values are based on counts corrected for saturation
by the calnica pipeline.
i: Spectral type from Hartmann et al., 1991AJ....101.1050H 1991AJ....101.1050H
j: Spectral type from Kirkpatrick et al., 1995AJ....109..797K 1995AJ....109..797K
k: K photometry from Forrest et al., 1988ApJ...330L.119F 1988ApJ...330L.119F, and
Henry & Kirkpatrick, 1994AJ....108.1437H 1994AJ....108.1437H
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- NTC Sequential number, FFF-NN
(Cl* IC 348 NTC FFFNN in Simbad)
7 A1 --- Note [e] Note on observations (1)
9- 10 I2 h RAh Right ascension (J2000)
12- 13 I2 min RAm Right ascension (J2000)
15- 19 F5.2 s RAs Right ascension (J2000)
21 A1 --- DE- Declination sign (J2000)
22- 23 I2 deg DEd Declination (J2000)
25- 26 I2 arcmin DEm Declination (J2000)
28- 31 F4.1 arcsec DEs Declination (J2000)
33- 35 I3 --- LRL ? Luhman et al., 1998ApJ...508..347L 1998ApJ...508..347L, number
Cl* IC 348 LRL NNN in Simbad
37- 39 I3 --- L99 ? Luhman et al., 1999, Cat. J/ApJ/525/466,
number Cl* IC 348 LRL NNN in Simbad
41- 43 I3 --- H98 ? Herbig et al., 1998, Cat. J/ApJ/497/736
number, Cl* IC 348 H NNN in Simbad
45- 51 F7.3 mJy F166 F166N flux, centered on 1.66µm
53- 57 F5.3 mJy e_F166 rms uncertainty n F166
59- 65 F7.3 mJy F190 F190N flux, centered on 1.90µm
67- 71 F5.3 mJy e_F190 rms uncertainty n F190
73- 79 F7.3 mJy F215 F215N flux, centered on 2.15µm
81- 85 F5.3 mJy e_F215 rms uncertainty n F215
87- 91 F5.2 --- QH2O Reddening-independent water index (2)
93- 96 F4.2 --- e_QH2O rms uncertainty on QH2O
98-102 F5.2 mag AK Absorption in K band
104-107 F4.2 mag e_AK rms uncertainty on AK
109-113 F5.2 mag Kmag K magnitude (3)
115-118 F4.2 mag e_Kmag rms uncertainty on Kmag
120-121 A2 --- l_SpType [≤ >] Limit flag on SpType
122-126 A5 --- SpType Spectral type
128-131 F4.1 --- e_SpType ? rms uncertainty on spectral subtype (4)
133 A1 --- n_SpType [fg] Spectral type determination (5)
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Note (1):
e: Star appears on the edge of a field and was observed twice.
All values are based on the average combined flux of both observations.
Note (2): Reddening-independent water index:
QH2O = -2.5log(F166/F190) + 1.37x2.5log(F190/F215)
where F166, F190, and F215 are the fluxes in the F166N, F190N, and
F215N filters, respectively. This index measures the strength of the
1.9µm H2O absorption band.
Note (3): If K<11.0, then K is quoted from Luhman et al.
(1998ApJ...508..347L 1998ApJ...508..347L) if available
Note (4): Error is in subtypes. Stars with spectral types later than M9
have QH2O strengths that indicate they are cooler than spectral
class M9. Such types are indicative of these cooler temperatures and
are not meant as an extension of the formally defined M spectral class.
Note (5): Spectral type determination:
f: Spectral type calculated with the QH2O index.
g: Spectral type from Luhman et al., 1998ApJ...508..347L 1998ApJ...508..347L, "Optical" type.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Prim Primary name
9- 14 A6 --- Second Secondary name
17- 20 F4.2 arcsec Sep Separation
22- 26 F5.2 mag K01 Dereddened K magnitude of the primary
28- 32 F5.2 mag K02 Dereddened K magnitude of the secondary
34- 37 A4 --- SpType1 Spectral type of the primary
39- 42 A4 --- SpType2 Spectral type of the secondary
44- 47 F4.2 mag AK1 Absorption in K band of the primary
49- 52 F4.2 mag AK2 Absorption in K band of the secondary
54 A1 --- ID Identification letter in fig. 14
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History:
From ApJ electronic version
(End) James Marcout, Patricia Bauer [CDS] 05-Dec-2000