J/ApJ/951/139 W filter YSOs detection. VI. sigma Orionis members (Damian+, 2023)
A novel survey for young substellar objects with the W-band filter.
VI. Spectroscopic census of substellar members and the IMF of the
σ Orionis cluster.
Damian B., Jose J., Biller B., Herczeg G.J., Albert L., Allers K.,
Zhang Z., Liu M.C., Dubber S., Paul KT, Chen W.-P., Lalchand B.,
Sharma T., Oasa Y.
<Astrophys. J., 951, 139 (2023)>
=2023ApJ...951..139D 2023ApJ...951..139D
ADC_Keywords: Clusters, open ; Photometry, infrared ; Spectra, infrared; YSOs;
Spectral types; Stars, ages; Stars, masses; Effective temperatures
Keywords: Brown dwarfs ; Initial mass function ; Star forming regions ;
Low mass stars
Abstract:
Low-mass stars and substellar objects are essential in tracing the
initial mass function (IMF). We study the nearby young σ Orionis
cluster (d∼408pc, age∼1.8Myr) using deep near-infrared (NIR)
photometric data in the J, W, and H bands from WIRCam on the
Canada-France-Hawaii Telescope. We use the water absorption feature to
select brown dwarfs photometrically and confirm their nature
spectroscopically with IRTF-SpeX. Additionally we select candidate
low-mass stars for spectroscopy and analyze their membership and those
of literature sources using astrometry from Gaia DR3. We obtain NIR
spectra for 28 very-low-mass stars and brown dwarfs and estimate their
spectral type between M3 and M8.5 (masses ranging between 0.3 and
0.01M☉). Apart from these, we also identify five new
planetary-mass candidates which require further spectroscopic
confirmation of youth. We compile a comprehensive catalog of 170
spectroscopically confirmed members in the central region of the
cluster, for a wide mass range of ∼19-0.004M☉. We estimate the
star-to-brown-dwarf ratio to be ∼4, within the range reported for
other nearby star-forming regions. With the updated catalog of members
we trace the IMF down to 4MJup and we find that a two-segment power
law fits the substellar IMF better than a log-normal distribution.
Description:
Photometric data for σ Orionis cluster was obtained using the
Wide-field InfraRed Camera (WIRCam) on the Canada-France-Hawaii
Telescope (CFHT). The field of view of WIRCam is ∼21'x21', with a
sampling of 0.3"/pix. The observations were carried out on 2016-09-11
(J, H, and W bands) and 2016-11-08 (W band) as part of programs 16BF22
(PI: Bonnefoy) and 16BC17 (PI: Artigau) using a single pointing
centered at RA=84.700,DE=-2.568°. Along with the broadband J and H
filters we have also used our custom filter centered on the water
absorption feature at 1.45um (W band filter) with total integration
times of 630s, 630s, and 4095s respectively.
Within the CFHT survey field, we have identified a total of
170 low-mass members, covering a spectral range from the bright O9.5V
star σ Ori at the center of the cluster to the faintest L-type
brown dwarfs in the region. This membership catalog comprises of 132
known members with spectral classification, nine that lack spectral
classification from previous works, 28 low-mass members observed in
this study (see Sections 4 and 5.1) and one additional L3.5 source
(S Ori 65) that is located at the edge of our survey field and due to
low signal-to-noise ratio is undetected by WIRCam.
We performed spectroscopic follow-up observations of the 28 low-mass
candidate members in the σ Orionis cluster (17 identified in
Section 3.2 and 11 identified in Section 3.3). These targets were
observed with the SpeX instrument on the 3.2m NASA Infrared Telescope
Facility (IRTF) in the low-resolution prism mode (R∼150) spanning the
period January 2021-January 2022. The spectral coverage of SpeX in
low-resolution mode is 0.7-2.5um.
Objects:
---------------------------------------------------------------------------
RA (ICRS) DE Designation(s)
---------------------------------------------------------------------------
05 38 42.00 -02 36 00.0 σ Orionis Cluster = NAME sig Ori Cluster
---------------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 164 175 Complete membership catalog of sources in the
σ Orionis cluster
table2.dat 70 170 Physical parameters of the member sources of
σ Orionis cluster
sp/* . 28 *IRTF/SpeX individual spectra in FITS format
(Data behind Figure 6)
--------------------------------------------------------------------------------
Note on sp/*: The spectra are flux calibrated and corrected for
telluric absorption. The spectral type of these sources range between
M3-M8.5.
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/A+A/337/403 : Low-mass stars evolutionary models (Baraffe+ 1998)
J/AN/325/705 : RIJHKs of low-mass stars in sigma Ori (Bejar+, 2004)
J/MNRAS/356/89 : sigma Ori low-mass stars (Kenyon+, 2005)
J/ApJS/173/104 : Stellar population in Chamaeleon I (Luhman, 2007)
J/AJ/134/411 : Properties of IC 348 members (Muench+, 2007)
J/A+A/488/167 : Low-mass stars in σ Ori & λ Ori (Sacco+, 2008)
J/ApJS/190/100 : NIR proper motion survey using 2MASS (Kirkpatrick+, 2010)
J/ApJ/743/64 : Deep IR photometry of σ Ori cluster (Bejar+, 2011)
J/ApJ/748/14 : ONC population data from WFI observations (Da Rio+, 2012)
J/ApJ/754/30 : VISTA IR phot. of σ Ori cluster (Pena Ramirez+, 2012)
J/A+A/548/A56 : X-shooter sp. of 12 young stellar objects (Rigliaco+, 2012)
J/ApJS/208/9 : Intrinsic colors & temperatures of PMS stars (Pecaut+, 2013)
J/ApJ/778/96 : Spitzer and NEWFIRM observations of NGC 6334 (Willis+, 2013)
J/ApJ/786/97 : Photospheric properties of T Tauri stars (Herczeg+, 2014)
J/ApJ/794/36 : σ Orionis cluster stellar pop. (Hernandez+, 2014)
J/ApJ/810/158 : M,L,T dwarfs fundamental param. & SEDs (Filippazzo+, 2015)
J/AJ/154/256 : VLM stars and BDs in Upper Sco using Gaia DR1 (Cook+, 2017)
J/ApJ/836/98 : YSOs search in Stock 8 with opt. to IR photom. (Jose+, 2017)
J/AJ/153/46 : Spectroscopy of candidate members in Taurus (Luhman+, 2017)
J/ApJ/858/41 : PS1 proper-motion survey for BDs. I. Taurus (Zhang+, 2018)
J/A+A/629/A114 : sigma Ori GTC+INT spectroscopy (Caballero+, 2019)
J/ApJ/870/32 : Kinematics in young star clusters & assoc. (Kuhn+, 2019)
J/MNRAS/486/1718 : System IMF of 25 Ori (Suarez+, 2019)
J/A+A/621/A14 : Blind photometric study of NGC 2264 region (Venuti+, 2019)
J/AJ/163/64 : Adopted members of Corona Australis (Esplin+, 2022)
J/A+A/670/A37 : Spatial & dynamical structure of NGC2264 (Flaccomio+, 2023)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 I1 --- Set [1/4] Subset of objects (1)
3- 24 A22 --- ID Object ID, this work
26- 27 A2 --- f_ID Flag on object (2)
29- 35 F7.4 deg RAdeg [84.5/84.9] Right Ascension (J2000)
37- 43 F7.4 deg DEdeg [-2.8/-2.38] Declination (J2000)
45- 49 F5.2 mag Jmag [4.75/20.3] CFHT/WIRCAM J band magnitude
51- 54 F4.2 mag e_Jmag [0.0/0.26] Uncertainty in Jmag
56- 60 F5.2 mag Wmag [12.28/20.24]? CFHT/WIRCAM W-band (1.45um)
magnitude
62- 65 F4.2 mag e_Wmag [0.0/0.13]? Uncertainty in Wmag
67- 71 F5.2 mag Hmag [4.64/19.3] CFHT/WIRCAM H band magnitude
73- 76 F4.2 mag e_Hmag [0.0/0.25] Uncertainty in Hmag
78- 82 F5.2 --- Q [-1.97/0.3]? reddening insensitive Q-index,
Equation 1
84- 87 F4.2 --- e_Q [0/0.4]? Uncertainty in Q
89-120 A32 --- SIMBAD Name taken from SIMBAD
122-143 A22 --- SpT Spectral Type(s) (3)
145-153 A9 --- Ref Reference(s) (4)
155-164 A10 "Y/M/D" Date IRTF/SpeX observation date for 28 sources;
column added by CDS
--------------------------------------------------------------------------------
Note (1): Subset(s) of sources as follows:
1 = Sources with spectroscopic membership from previous works
(142 occurrences).
Spectral type for these sources are taken from Simbad and
their corresponding references are given in the last column
2 = Photometric and astrometric candidates- spectroscopically
followed-up in this work (12 occurrences).
Spectral type for these sources were estimated in this work
(refer section 5.1).
The spectral types presented within the parentheses were
estimated based on the spectral index following
Zhang+ (2018, J/ApJ/858/41) (refer section 5.2).
All these sources were classified as gravity class VL-G.
3 = Sources identified as members in literature that lack
spectral type - spectroscopically followed-up in this work
(16 occurrences).
Spectral type for these sources were estimated in this work
(refer section 5.1).
The spectral types presented within the parentheses were
estimated based on the spectral index following
Zhang+ (2018, J/ApJ/858/41) (refer section 5.2).
All these sources were classified as gravity class VL-G. With
the exception of WBIS 053841.6-023028.9, as
the spectral and gravity classification scheme of Zhang+ (2018)
are applicable only for M5 and later spectral type objects.
4 = Newly proposed planetary-mass candidates (5 occurrences).
Note (2): Flags on sources as follows:
* = Sources above the CFHT WIRCam saturation limit whose J and
H-band magnitudes are replaced with 2MASS (Cutri+ 2003, II/246) data;
** = This object lies at the edge of the CFHT WIRCam survey area
and is undetected in our observation. The J and H VISTA
photometric data from Pena Ramirez+ (2012, J/ApJ/754/30)
is provided in the table.
d = This source has been previously identified as a member in
Caballero (2008MNRAS.383..375C 2008MNRAS.383..375C).
Note (3): Spectral types are either taken from Simbad or derived in
this work; See Note (1).
Note (4): References as follows:
1 = Bejar et al. 1999ApJ...521..671B 1999ApJ...521..671B
2 = Barrado y Navascues et al. 2001A&A...377L...9B 2001A&A...377L...9B
3 = Bejar et al. 2001ApJ...556..830B 2001ApJ...556..830B
4 = Zapatero Osorio et al. 2002A&A...384..937Z 2002A&A...384..937Z
5 = Barrado y Navascues et al. 2003A&A...404..171B 2003A&A...404..171B
6 = Caballero et al. 2006A&A...445..143C 2006A&A...445..143C
7 = Caballero 2007AN....328..917C 2007AN....328..917C
8 = Pena Ramirez et al. (2012, J/ApJ/754/30)
9 = Rigliaco et al. (2012, J/A+A/548/A56)
10 = Canty et al. 2013MNRAS.435.2650C 2013MNRAS.435.2650C
11 = Hernandez et al. (2014, J/ApJ/794/36)
12 = Bozhinova et al. (2016, J/ApJ/794/36)
13 = Zapatero Osorio et al. 2017ApJ...842...65Z 2017ApJ...842...65Z
14 = Caballero et al. (2019, J/A+A/629/A114)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 22 A22 --- ID Object ID, this work
24- 30 F7.4 deg RAdeg [84.5/84.9] Right Ascension (J2000)
32- 38 F7.4 deg DEdeg [-2.8/-2.38] Declination (J2000)
40- 43 A4 --- SpT Spectral Type (1)
45- 49 I5 K Teff [1581/31900]? Surface effective temperature (2)
51- 55 F5.2 [Lsun] logLs [-3.47/4.72]? Log, bolometric luminosity (2)
57 A1 -- l_Age Limit flag on Age
58- 63 F6.2 Myr Age [0.5/100]? Age (2)
65- 70 F6.3 Msun Mass [0.004/18.7]? Mass (2)
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Note (1): For the sources spectroscopically observed with IRTF in this work,
the best-fitting spectral type estimated in section 5.1 is given.
Note (2): The Teff, Lbol and mass values for O, B and A spectral
type sources are taken from table 5 of
Pecaut & Mamajek (2013, J/ApJS/208/9).
For the F to L spectral type sources the Teff, Lbol, age and mass were
estimated as detailed in section 5.3.
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History:
From electronic version of the journal
References:
Allers et al. Paper I. 2020PASP..132j4401A 2020PASP..132j4401A Cat. J/PASP/132/J4401
Jose et al. Paper II. 2020ApJ...892..122J 2020ApJ...892..122J
Dubber et al. Paper III. 2021MNRAS.505.4215D 2021MNRAS.505.4215D
Dubber et al. Paper IV. 2023MNRAS.520.3383D 2023MNRAS.520.3383D
Lalchand et al. Paper V. 2022AJ....164..125L 2022AJ....164..125L
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 22-Aug-2025