J/ApJ/752/59 Low-mass population in L1641 (Hsu+, 2012)
The low-mass stellar population in L1641: evidence for environmental
dependence of the stellar initial mass function.
Hsu W.-H., Hartmann L., Allen L., Hernandez J., Megeath S.T., Mosby G.,
Tobin J.J., Espaillat C.
<Astrophys. J., 752, 59 (2012)>
=2012ApJ...752...59H 2012ApJ...752...59H
ADC_Keywords: Equivalent widths ; Spectral types ; Photometry, VRI ; YSOs ;
Photometry, infrared
Keywords: stars: formation; stars: low-mass;
stars: luminosity function, mass function; stars: pre-main sequence;
surveys
Abstract:
We present results from an optical photometric and spectroscopic
survey of the young stellar population in L1641, the low-density
star-forming region of the Orion A cloud south of the Orion Nebula
Cluster (ONC). Our goal is to determine whether L1641 has a large
enough low-mass population to make the known lack of high-mass stars a
statistically significant demonstration of environmental dependence of
the upper mass stellar initial mass function (IMF). Our spectroscopic
sample consists of IR-excess objects selected from the Spitzer/IRAC
survey and non-excess objects selected from optical photometry. We
have spectral confirmation of 864 members, with another 98 probable
members; of the confirmed members, 406 have infrared excesses and 458
do not. Assuming the same ratio of stars with and without IR excesses
in the highly extincted regions, L1641 may contain as many as ∼1600
stars down to ∼0.1M☉, comparable within a factor of two to the
ONC. Compared to the standard models of the IMF, L1641 is deficient in
O and early B stars to a 3σ-4σ significance level,
assuming that we know of all the massive stars in L1641.
Description:
We obtained V- and I-band optical photometry with the Ohio State
Multi-Object Spectrograph (OSMOS) on the MDM 2.4m Hiltner telescope,
on the nights of 2010 December 7-8 and December 8-9. Most fields were
observed with the exposure sequence once on each night, but a few
fields were only observed on one night. The astrometric solutions are
in general good within one pixel, or 0.55".
Approximately 75% of our optical spectra were obtained with Hectospec,
the fiber-fed multiobject spectrograph on the 6.5m MMT on Mt. Hopkins.
With 17 observations from 2006 to 2011, a total of 2369 stars were
observed in the spectral coverage of 3650-9200å, providing a
∼6.2Å resolution.
Another 25% of our spectra were obtained with IMACS, the
Inamori-Magellan Areal Camera & Spectrograph on the Magellan Baade
telescope, with a resolution of 4Å and spectral coverage of
approximately 4000-9000Å. From 17 observations in 2010 and 2011, a
total of 715 stars were observed.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 104 865 Confirmed members in L1641
table3.dat 104 102 Probable members in L1641
table4.dat 108 161 YSOs with strong emission lines
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
J/ApJS/207/5 : YSOs in LDN 1641 with Hectochelle spectra (Fang+, 2013)
J/ApJ/722/1092 : Optical photometry of the ONC. II. (Da Rio+, 2010)
J/AJ/139/950 : JHKs photometry in ONC (Robberto+, 2010)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/A+A/504/461 : YSOs in L1630N and L1641 (Fang+, 2009)
J/A+A/489/1409 : IR photometry and spectroscopy in L1641N (Galfalk+, 2008)
J/A+A/337/403 : Low-mass stars evolutionary models (Baraffe+ 1998)
J/AJ/113/1733 : Orion Nebula Cluster population (Hillenbrand 1997)
Byte-by-byte Description of file: table[23].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Running sequence number
5- 12 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000)
14- 21 F8.5 deg DEdeg Declination in decimal degrees (J2000)
23- 30 F8.3 mag Vmag [12/23]?=-100 V band magnitude
32- 39 F8.3 mag Imag [11/20]?=-100 I band magnitude
41- 48 F8.3 mag Jmag [9/18]?=-100 2MASS J band magnitude
50- 57 F8.3 mag Hmag [8/17]?=-100 2MASS H band magnitude
59- 66 F8.3 mag Kmag [7/17]?=-100 2MASS Ks band magnitude
68- 71 A4 --- SpT MK spectral type
73- 75 F3.1 --- e_SpT ? Uncertainty in SpT
77 A1 --- r_SpT Origin of SpT (1)
79 A1 --- IR [Y/N] IR excess? (2)
81- 88 F8.3 0.1nm EWHa Hα equivalent width
90- 92 F3.1 0.1nm EWLi ? Lithium equivalent width
94-104 A11 "Y/M/D" Date ? Date of the observation (3)
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Note (1): Flag as follows:
c = Data from Hectospec spectra.
d = Data from IMACS spectra.
e = Data from Fang et al. (2009, Cat. J/A+A/504/461). No spectral-typing
error estimate.
Note (2): Criteria for IR excess are defined in Gutermuth et al. (2009,
Cat. J/ApJS/184/18) and Megeath et al. (2012AJ....144..192M 2012AJ....144..192M).
Note (3): Local date at the beginning of the night.
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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- 3 I3 --- Seq [6/861] Running sequence number
5- 12 F8.5 deg RAdeg Right Ascension in decimal degrees (J2000)
14- 21 F8.5 deg DEdeg Declination in decimal degrees (J2000)
23- 28 F6.2 0.1nm W5577 ? Equivalent width of [OI] 5577Å
30- 35 F6.2 0.1nm W6300 ? Equivalent width of [OI] 6300Å
37- 42 F6.2 0.1nm W6363 ? Equivalent width of [OI] 6363Å
44- 47 F4.1 0.1nm W6538 ? Equivalent width of [NII] 6548Å
49- 54 F6.2 0.1nm W6583 ? Equivalent width of [NII] 6583Å
56- 60 F5.2 0.1nm W6678 ? Equivalent width of HeI 6678Å
62- 67 F6.2 0.1nm W6716 ? Equivalent width of [SII] 6716Å
69- 74 F6.2 0.1nm W6731 ? Equivalent width of [SII] 6731Å
76- 80 F5.2 0.1nm W7773 ? Equivalent width of [OI] 7773Å
82- 87 F6.2 0.1nm W8446 ? Equivalent width of [OI] 8446Å
89- 94 F6.2 0.1nm W8498 ? Equivalent width of [CaII] 8498Å
96-101 F6.2 0.1nm W8542 ? Equivalent width of [CaII] 8542Å
103-108 F6.2 0.1nm W8662 ? Equivalent width of [CaII] 8662Å
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History:
From electronic version of the journal
References:
Hsu et al. 2013ApJ...764..114H 2013ApJ...764..114H Cat. J/ApJ/764/114
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 31-Jan-2014