J/ApJ/763/101 Massive field OB stars in the SMC (Lamb+, 2013)
The initial mass function of field OB stars in the Small Magellanic Cloud.
Lamb J.B., Oey M.S., Graus A.S., Adams F.C., Segura-Cox D.M.
<Astrophys. J., 763, 101 (2013)>
=2013ApJ...763..101L 2013ApJ...763..101L
ADC_Keywords: Photometry, UBV ; Magellanic Clouds ; Stars, OB ; Stars, masses ;
Spectral types
Keywords: galaxies: stellar content; Magellanic Clouds; stars: early-type;
stars: formation; stars: fundamental parameters;
stars: luminosity function, mass function
Abstract:
Some theories of star formation suggest massive stars may only form in
clustered environments, which would create a deficit of massive stars
in low-density environments. Observationally, Massey (2002, Cat. II/236)
finds such a deficit in samples of the field population in the Small
and Large Magellanic Clouds, with an initial mass function (IMF) slope
of ΓIMF∼4. These IMF measurements represent some of the
largest known deviations from the standard Salpeter IMF slope of
ΓIMF=1.35. Here, we carry out a comprehensive investigation of
the mass function above 20M☉ for the entire field population of
the Small Magellanic Cloud (SMC), based on data from the Runaways and
Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). This is
a spatially complete census of the entire field OB star population of
the SMC obtained with the IMACS multi-object spectrograph and MIKE
echelle spectrograph on the Magellan telescopes. Based on Monte Carlo
simulations of the evolved present-day mass function, we find the
slope of the field IMF above 20M☉ is ΓIMF=2.3±0.4. We
extend our IMF measurement to lower masses using BV photometry from
the OGLE II survey. We use a statistical approach to generate a
probability distribution for the mass of each star from the OGLE
photometry, and we again find ΓIMF=2.3±0.6 for stellar
masses from 7M☉ to 20M☉. The discovery and removal of ten
runaways in our RIOTS4 sample steepens the field IMF slope to
ΓIMF=2.8±0.5. We discuss the possible effects of binarity
and star formation history on our results, and conclude that the steep
field massive star IMF is most likely a real effect.
Description:
Runaways and isolated O-type star spectroscopic survey of the SMC
(RIOTS4) targets the complete sample of 374 SMC field OB stars, as
identified in Oey et al. (2004, J/AJ/127/1632).
We made observations with IMACS on the Magellan Baade telescope at the
Las Campanas Observatory between 2006 September and 2010 December.
We also observed 48 stars with MIKE on the Magellan Clay telescope
between 2010 November and 2011 October.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 73 128 RIOTS4 spectral catalog (Runaways and Isolated
O-Type Star Spectroscopic Survey of the SMC)
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See also:
II/236 : UBVR CCD survey of the Magellanic clouds (Massey+, 2002)
III/195 : Atlas of Optical Spectral Classification OB Stars (Walborn+ 1990)
J/A+A/562/A125 : OGLE-III SMC massive stars VI phot. (Kourniotis+, 2014)
J/AJ/140/416 : IR photometry of massive stars in the SMC (Bonanos+, 2010)
J/MNRAS/386/826 : Radial velocities of SMC massive stars (Evans+, 2008)
J/A+A/466/277 : VLT-FLAMES survey of massive stars (Hunter+, 2007)
J/A+A/452/179 : Ages of SMC young clusters and field stars (Chiosi+, 2006)
J/AJ/127/1632 : UBVR(UIT) photometry of O and OB stars in SMC (Oey+, 2004)
J/AJ/127/1531 : Star formation history of SMC (Harris+, 2004)
J/MNRAS/353/601 : 2dF survey of the Small Magellanic Cloud (Evans+, 2004)
J/AJ/123/855 : Magellanic Clouds Phot. Survey: the SMC (Zaritsky+, 2002)
J/AJ/116/180 : Magellanic clouds ultraviolet observations (Parker+ 1998)
J/AcA/48/147 : OGLE SMC BVI photometry (Udalski+ 1998)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- [M2002] [1600/83678] Identifier from Massey (II/236,
<[M2002] SMC NNNNNN> in Simbad)
7- 11 F5.2 mag Bmag [12.4/15.1] The B band magnitude (1)
13- 17 F5.2 mag Vmag [12.5/15.3] The V band magnitude (1)
19- 24 F6.2 mag Mbol [-14.4/-9.6] Bolometric absolute magnitude
26- 30 F5.2 mag Q [-1.2/-0.8] The reddening free parameter (2)
32- 35 F4.2 mag Av [0.05/2.1] The V band extinction
37- 41 I5 K Teff [19000/47750] Effective temperature
43- 46 F4.1 Msun Mass [20/75] Star mass
48- 51 F4.1 Msun E_Mass Upper limit uncertainty in Mass
53- 56 F4.1 Msun e_Mass Lower limit uncertainty in Mass
58- 73 A16 --- SpT MK spectral type
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Note (1): Photometric errors are typically ∼0.03mag in B and ∼0.02mag
in V (Massey 2002, Cat. II/236).
Note (2): QUBR is the reddening free parameter given by Equation (1):
QUBR=(mU-mR)-1.396(mB-mR). See section 2.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Oct-2014