J/AJ/170/19 Classification of Upper Sco stars from spectroscopy (Luhman, 2025)
The initial mass function of stars and brown dwarfs in the Upper Sco Association
Luhman K.L.
<Astron. J., 170, 19 (2025)>
=2025AJ....170...19L 2025AJ....170...19L
ADC_Keywords: Star Forming Region; Stars, dwarfs; Spectroscopy; Infrared;
Optical; Photometry; MK spectral classification; Stars, late-type
Keywords: Brown dwarfs ; L dwarfs ; Star formation ; Initial mass function ;
Circumstellar disks ; Star forming regions
Abstract:
I present infrared spectroscopy of 37 brown dwarf candidates in the
Upper Scorpius (Upper Sco) association, 35 of which are classified as
young and cool, making them likely members. This sample includes many
of the faintest spectroscopically confirmed members (K=16-17mag),
which should have masses down to ∼0.007-0.01M☉ for the range of
ages in Upper Sco (7-14Myr). Using my updated membership catalog for
Upper Sco, I have estimated the initial mass function (IMF) for a
field in the center of the association that encompasses ∼80% of the
known members. I have derived IMFs in the same manner for previous
membership samples in three other star-forming populations, consisting
of IC 348, Taurus, and Chameleon I. When using logarithmic mass bins,
the substellar IMFs for Upper Sco and the other young regions are
roughly flat down to the completeness limits of ∼0.01M☉. These
IMFs are broadly similar to mass functions recently measured for the
solar neighborhood. Finally, I have used W1-W2 colors to search for
excess emission from circumstellar disks among the late-type objects
in my new census of Upper Sco. I measure an excess fraction of 52/200
for members with spectral types of M6.25-M9.5, which is similar to
results from previous membership catalogs. For the L-type members, it
is difficult to detect the small W2 excess emission produced by
typical disks around brown dwarfs because of the large uncertainties
in spectral types, which preclude accurate estimates of the
photospheric colors. Thus, W2 photometry provides poor constraints on
the presence of disks for the L-type members of Upper Sco.
Description:
I performed near-IR spectroscopy on 37 brown dwarf candidates in Upper
Sco and one disk-bearing star in Ophiucus. I have also analyzed new
and archival near-IR and optical spectra of 37 candidates for low-mass
stars in Upper Sco and other populations in Sco-Cen, which have been
identified with astrometry and photometry from Gaia DR3 (I/355). The
observational data was taken between 2017 and 2024 with the following
telescopes/instruments:
- The SpeX medium-resolution spectrograph and imager at the NASA
Infrared Telescope Facility (IRTF) in Hawaii, USA (0.8-2.5um, R=150).
- The Cerro Tololo Ohio State Multi-Object Spectrograph (COSMOS) on
the 4m Blanco telescope at Cerro Tololo Inter-American Observatory
(CTIO) in Chile (0.55-0.95um, R=4Å).
- The Gemini Near-Infrared Spectrograph (GNIRS) at the Gemini North
telescope in Hawaii, USA (0.9-2.5um, R=600).
- The FLoridA Multi-object Imaging Near-infrared Grism Observational
Spectrometer 2 (FLAMINGOS-2) stationed at Gemini South on Cerro
Pachon in Chile (0.9-1.8um, R=400).
- The European Southern Observatory (ESO) Faint Object Spectrograph
and Camera (EFOSC) on the ESO New Technology Telescope (NTT) in La
Silla, Chile (0.6-1um, R=13Å).
Moreover, I have generated an updated compilation for Upper Sco that
contains 1753 sources, 274 of which are later than M6 and thus are
likely to be substellar. This is the largest sample of probable brown
dwarfs with spectral classifications in any young stellar population.
Mid-IR images from WISE and the Spitzer Space Telescope provide the
best constraints on IR excess emission for members of Upper Sco, which
can be evidence of circumstellar disks. For each >M6 member of Upper
Sco, I have adopted W1 and W2 from either the AllWISE Source Catalog
(II/328) or the CatWISE2020 Catalog (II/365), giving preference to the
measurements with smaller errors.
Objects:
--------------------------------------------------------------------------
RA (2000) DE Designation(s)
--------------------------------------------------------------------------
16 12 00.00 -23 23 59.9 NAME Upper Sco Association = [KC2019] Theia 45
16 15 00.00 -24 11 59.9 Sco-Cen = NAME Upper Sco-Cen
--------------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 161 75 Spectroscopic data for candidate members of Sco-Cen
table3.dat 187 1753 Adopted members of Upper Sco with spectral
classifications at l=343-360 and b=10-30
table5.dat 137 260 W2 excess flags for >M6 members of Upper Sco
fig2/* . 61 Spectra of candidate members of Sco-Cen (Data
behind Figures 2 & 3)
--------------------------------------------------------------------------------
See also:
III/117 : MK Classifications of Close Visual Binaries (Corbally, 1984)
III/135A : Henry Draper Catalogue and Extension (Cannon+ 1918-1924; ADC 1989)
II/240 : The DENIS database first release (Epchtein+, 1999)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
II/328 : AllWISE Data Release (Cutri+ 2013)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
II/367 : The VISTA Hemisphere Survey (VHS) catalog DR5 (McMahon+, 2020)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
II/365 : The CatWISE2020 catalog (updated version 28-Jan-2021) (Marocco+, 2021)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)
J/A+A/333/619 : Upper Scorpius OB association Lithium survey (Preibisch+ 1998)
J/AJ/117/354 : OB associations from Hipparcos (de Zeeuw+, 1999)
J/ApJ/525/466 : Young low-mass stars and brown dwarfs in IC 348 (Luhman+, 1999)
J/AJ/120/479 : Low-mass stars in the Upper Sco association (Ardila+, 2000)
J/A+A/372/173 : ISOCAM observations of the rho Ophiuchi cloud (Bontemps+, 2001)
J/A+A/378/116 : Classification & vsini of Vega-type and PMS stars (Mora+, 2001)
J/AJ/121/1040 : PMS members of upper Scorpius OB association (Preibisch+, 2001)
J/AJ/124/404 : Upper Scorpius OB assoc. Lithium surv. II. (Preibisch, 2002)
J/AJ/126/2421 : 2MASS-Selected sample of ultracool dwarfs (Cruz+, 2003)
J/AJ/126/2971 : UBVRI photometry of 131 Herbig Ae/Be (Vieira+, 2003)
J/ApJ/651/L49 : Upper Sco OB association IRAC observations (Carpenter+, 2006)
J/MNRAS/373/95 : ZYJHK survey of Upper Sco association (Lodieu+, 2006)
J/AJ/132/866 : New M dwarfs in solar neighborhood (Riaz+, 2006)
J/AJ/131/3016 : Low-mass objects in Upper Scorpius (Slesnick+, 2006)
J/A+A/460/695 : Search for Associations Containing Young stars (Torres+, 2006)
J/MNRAS/374/372 : ZYJHK photometry in Upper Sco (Lodieu+, 2007)
J/AJ/136/1290 : Ultracool dwarfs from the 2MASS (Reid+, 2008)
J/ApJ/688/377 : Low-mass objects in Upper Scorpius. II. (Slesnick+, 2008)
J/ApJ/699/1196 : JHKs light curves of 2MASS J05352184-0546085 (Gomez+, 2009)
J/ApJ/703/1511 : Wide binaries in Taurus and Upper Sco (Kraus+, 2009)
J/ApJ/712/925 : Transition circumstellar disks in Ophiuchus (Cieza+, 2010)
J/ApJS/190/100 : NIR proper motion survey using 2MASS (Kirkpatrick+, 2010)
J/MNRAS/418/1231 : New brown dwarfs in upper Sco (Dawson+, 2011)
J/A+A/527/A24 : Spectra of low-mass stars in Upper Sco (Lodieu+, 2011)
J/ApJ/746/154 : Improved kinematic plx for Sco-Cen members (Pecaut+, 2012)
J/ApJ/754/30 : VISTA IR phot. of σ Ori cluster (Pena Ramirez+, 2012)
J/MNRAS/435/2474 : USco ZYJHK1K2 photometry and proper motions (Lodieu+, 2013)
J/A+A/562/A127 : NIR integral field spec. of 15 M-L dwarfs (Bonnefoy+, 2014)
J/ApJ/786/97 : Photospheric properties of T Tauri stars (Herczeg+, 2014)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/MNRAS/448/2737 : New PMS K/M Stars in Upper Scorpius (Rizzuto+, 2015)
J/ApJS/225/10 : Kinematic analysis of M7-L8 dwarfs (Faherty+, 2016)
J/MNRAS/461/794 : Scorpius-Centaurus K-Type Stars (Pecaut+, 2016)
J/AJ/154/46 : Proper motions & phot. for members of Cha I (Esplin+, 2017)
J/AJ/153/46 : Spectroscopy of candidate members in Taurus (Luhman+, 2017)
J/AJ/156/75 : Circumstellar disks in the Upper Sco association (Esplin+, 2018)
J/AJ/156/76 : New young stars and brown dwarfs in Upper Sco (Luhman+, 2018)
J/AJ/158/54 : New Taurus memb. from stellar to planetary masses (Esplin+, 2019)
J/AJ/159/282 : Membership in Ophiuchus & Upper Scorpius complex (Esplin+, 2020)
J/AJ/160/44 : Upper Scorpius spectroscopy and photometry (Luhman+, 2020)
J/MNRAS/503/2265 : VISTA and Subaru/HSC obs. of Upper Scorpius (Lodieu+, 2021)
J/A+A/664/A111 : Free-floating planet candidates in Upp Sco & Oph (Bouy+, 2022)
J/AJ/163/24 : Stellar populations in the Sco-Cen complex (Luhman, 2022)
J/AJ/163/25 : Circumst. disk populations in the Sco-Cen complex (Luhman, 2022)
J/AJ/163/26 : Sp. of Sco-Cen memb & sp. classif in other clouds (Luhman+, 2022)
J/other/NatAs/6.89 : Upper Scorpius members (Miret-Roig+, 2022)
J/A+A/667/A163 : Upper Scorpius and Ophiuchus members (Miret-Roig+, 2022)
J/ApJ/951/139 : W filter YSOs detect. VI. sigma Orionis members (Damian+, 2023)
J/AJ/165/269 : TW Hya association candidate members (Luhman, 2023)
J/A+A/685/A118 : Young (sub)stellar obj. X-Shooter spec (Almendros-Abad+, 2024)
J/ApJS/271/55 : A full-sky 20pc census of stars & BDs (Kirkpatrick+, 2024)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 ? Gaia DR3 (I/355) source name
21- 44 A24 --- Name Source name from UKIDSS (II/319) or VISTA
VHS (II/367)
46- 55 F10.6 deg RAdeg ? Gaia DR3 (I/355) right ascension
(ICRS at Epoch 2016.0)
57- 66 F10.6 deg DEdeg ? Gaia DR3 (I/355) declination
(ICRS at Epoch 2016.0)
68- 77 F10.6 deg RAUdeg ? Right ascension from UKIDSS (II/319) or
VISTA VHS (II/367) (J2000)
79- 88 F10.6 deg DEUdeg ? Declination from UKIDSS (II/319) or
VISTA VHS (II/367) (J2000)
90- 96 A7 --- SpType Spectral type (1)
98- 99 A2 --- Young Young? (2)
101- 111 A11 --- Instrument Instrument for spectroscopy (3)
113- 123 A11 "Y:M:D" Date Date of spectroscopy
125- 161 A37 --- Files Link to the spectrum files in CSV format
(added by CDS)
--------------------------------------------------------------------------------
Note (1): Uncertainties are 0.25 and 0.5 subclass for optical and IR
spectral types, respectively, unless indicated otherwise.
Note (2): Flag occurrences as follows:
Y = Yes (64 occurrences)
N = No (2 occurrences)
Y? = Yes? (4 occurrences)
? = ? (5 occurrences)
Note (3): Instruments as follows:
COSMOS = Cerro Tololo Ohio State Multi-Object Spectrograph (COSMOS) on the
4m Blanco telescope at Cerro Tololo Inter-American Observatory
(CTIO) in Chile; 13 occurrences
EFOSC = European Southern Observatory (ESO) Faint Object Spectrograph and
Camera (EFOSC) on the ESO New Technology Telescope (NTT) in La
Silla, Chile; 15 occurrences
FLAMINGOS-2 = The FLoridA Multi-object Imaging Near-infrared Grism
Observational Spectrometer 2 (FLAMINGOS-2) stationed at Gemini
South on Cerro Pachon in Chile; 5 occurrences
GNIRS = the Gemini Near-Infrared Spectrograph (GNIRS) at the Gemini
North telescope in Hawaii, USA; 21 occurrences
SpeX = The SpeX medium-resolution spectrograph and imager at the NASA
Infrared Telescope Facility (IRTF) in Hawaii, USA; 21 occurrences
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaEDR3 ? Gaia EDR3 (I/350) source name
21- 39 A19 --- UGCS UKIDSS Galactic Clusters Survey (II/319)
source name
41- 58 A18 --- 2MASS 2MASS Point Source Catalog (II/246) source
name
60- 112 A53 --- Name Other source name
114- 123 F10.6 deg RAdeg Right ascension (ICRS)
125- 134 F10.6 deg DEdeg Declination (ICRS)
136- 141 A6 --- Ref Reference for right ascension and declination
(1)
143- 165 A23 --- SpType Spectral type
167- 179 A13 --- r_SpType Spectral type reference (2)
181- 187 A7 --- Adopt Adopted spectral type
--------------------------------------------------------------------------------
Note (1): Coordinates reference as follows:
Gaia = Gaia EDR3 (I/350); 1629 occurrences
2MASS = 2MASS Point Source Catalog (II/246); 3 occurrences
UKIDSS = UKIDSS Galactic Clusters Survey DR10 (II/319, DR9); 116 occurrences
VHS = VISTA Hemispher Survey DR6 (II/367, DR5); 1 occurrence
bry = Bryan+ (2016ApJ...827..100B 2016ApJ...827..100B); 1 occurrence
ire = Ireland+ (2011ApJ...726..113I 2011ApJ...726..113I); 1 occurrence
lac = Lachapelle+ (2015ApJ...802...61L 2015ApJ...802...61L); 1 occurrence
Note (2): Spectral type reference as follows:
1 = Houk & Smith-Moore (1988mcts.book.....H 1988mcts.book.....H)
2 = Cannon & Pickering, 1993 (III/135A)
3 = Luhman+2018 (J/AJ/156/76)
4 = Dawson+ (2014MNRAS.442.1586D 2014MNRAS.442.1586D)
5 = Esplin+2018 (J/AJ/156/75)
6 = Luhman & Esplin, 2020 (J/AJ/160/44)
7 = Rizzuto+2015 (J/MNRAS/448/2737)
8 = Preibisch+1998 (J/A+A/333/619)
9 = Bouy+2022 (J/A+A/664/A111)
10 = Measured in this work with the spectrum from Bouy+2022 (J/A+A/664/A111)
11 = Lodieu+ (2008MNRAS.383.1385L 2008MNRAS.383.1385L)
12 = Bonnefoy+2014 (J/A+A/562/A127)
13 = Luhman & Esplin, 2022 (J/AJ/163/26)
14 = Lodieu+2006 (J/MNRAS/373/95)
15 = Kunkel (1999) PhD Thesis
16 = Hiltner+ (1969ApJ...157..313H 1969ApJ...157..313H)
17 = Manara+ (2020A&A...639A..58M 2020A&A...639A..58M)
18 = Pecaut & Mamajek, 2016 (J/MNRAS/461/794)
19 = Pena Ramirez+ (2016A&A...586A.157P 2016A&A...586A.157P)
20 = This work
21 = Houk (1982mcts.book.....H 1982mcts.book.....H)
22 = Corbally (1984ApJ...285..195C 1984ApJ...285..195C)
23 = Aller+ (2013ApJ...773...63A 2013ApJ...773...63A)
24 = Martin+ (2004AJ....127..449M 2004AJ....127..449M)
25 = Martin+ (2010A&A...517A..53M 2010A&A...517A..53M)
26 = Slesnick+2008 (J/ApJ/688/377)
27 = Chinchilla+ (2020A&A...633A.152C 2020A&A...633A.152C)
28 = Preibisch+2002 (J/AJ/124/404)
29 = Mora+2001 (J/A+A/378/116)
30 = Vieira+2003 (J/AJ/126/2971)
31 = Reid+2008 (J/AJ/136/1290)
32 = Ardila+2000 (J/AJ/120/479)
33 = Walter+ (1994AJ....107..692W 1994AJ....107..692W)
34 = Kirkpatrick+2010 (J/ApJS/190/100)
35 = Allers & Liu (2013ApJ...772...79A 2013ApJ...772...79A)
36 = Faherty+2016 (J/ApJS/225/10)
37 = Torres+2006 (J/A+A/460/695)
38 = Gizis (2002ApJ...575..484G 2002ApJ...575..484G)
39 = Herczeg & Hillenbrand, 2014 (J/ApJ/786/97)
40 = Slesnick+2006 (J/AJ/131/3016)
41 = Riaz+2006 (J/AJ/132/866)
42 = Best+ (2017ApJ...837...95B 2017ApJ...837...95B)
43 = Lodieu+ (2018MNRAS.473.2020L 2018MNRAS.473.2020L)
44 = Kraus+ (2015ApJ...807....3K 2015ApJ...807....3K)
45 = Cody+ (2017ApJ...836...41C 2017ApJ...836...41C)
46 = Lafreniere+ (2011ApJ...730...42L 2011ApJ...730...42L)
47 = Lachapelle+ (2015ApJ...802...61L 2015ApJ...802...61L)
48 = David+ (2019ApJ...872..161D 2019ApJ...872..161D)
49 = Ansdell+ (2016ApJ...816...69A 2016ApJ...816...69A)
50 = Prato+ (2002ApJ...569..863P 2002ApJ...569..863P)
51 = Preibisch+2001 (J/AJ/121/1040)
52 = Almendros-Abad+2024 (J/A+A/685/A118)
53 = Cruz+2003 (J/AJ/126/2421)
54 = Bejar+ (2008ApJ...673L.185B 2008ApJ...673L.185B)
55 = Herczeg+ (2009ApJ...696.1589H 2009ApJ...696.1589H)
56 = Lodieu+2021 (J/MNRAS/503/2265)
57 = Kraus & Hillenbrand (2007ApJ...664.1167K 2007ApJ...664.1167K)
58 = Lodieu+2011a (J/A+A/527/A24)
59 = Muller+ (2011A&A...535L...3M 2011A&A...535L...3M)
60 = Kraus & Hillenbrand, 2009 (J/ApJ/703/1511)
61 = Pecaut+2012 (J/ApJ/746/154)
62 = Biller+ (2011ApJ...730...39B 2011ApJ...730...39B)
63 = Lafreniere+ (2008ApJ...689L.153L 2008ApJ...689L.153L)
64 = Luhman+2017 (J/AJ/153/46)
65 = Mann+ (2016AJ....152...61M 2016AJ....152...61M)
66 = David+ (2016Natur.534..658D 2016Natur.534..658D)
67 = Stauffer+ (2017AJ....153..152S 2017AJ....153..152S)
68 = Stauffer+ (2018AJ....155...63S 2018AJ....155...63S)
69 = Cohen & Kuhi (1979ApJS...41..743C 1979ApJS...41..743C)
70 = Prato+ (2003ApJ...584..853P 2003ApJ...584..853P)
71 = Eisner+ (2005ApJ...623..952E 2005ApJ...623..952E)
72 = Murphy (1969AJ.....74.1082M 1969AJ.....74.1082M)
73 = Martin+ (1998MNRAS.300..733M 1998MNRAS.300..733M)
74 = Prato (2007ApJ...657..338P 2007ApJ...657..338P)
75 = McClure+ (2010ApJS..188...75M 2010ApJS..188...75M)
76 = Lodieu+ (2015A&A...584A.128L 2015A&A...584A.128L)
77 = David+ (2016ApJ...816...21D 2016ApJ...816...21D)
78 = Carpenter+2006 (J/ApJ/651/L49)
79 = Luhman (2005ApJ...633L..41L 2005ApJ...633L..41L)
80 = Martin (1998AJ....115..351M 1998AJ....115..351M)
81 = Esplin & Luhman, 2020 (J/AJ/159/282)
82 = Allers & Liu, 2020 (J/PASP/132/J4401)
83 = Cieza+2010 (J/ApJ/712/925)
84 = Bowler+ (2011ApJ...743..148B 2011ApJ...743..148B)
85 = Bowler+ (2014ApJ...784...65B 2014ApJ...784...65B)
86 = Brandner+ (1997A&A...321..220B 1997A&A...321..220B)
87 = Bouvier & Appenzeller (1992A&AS...92..481B 1992A&AS...92..481B)
88 = Bowler+ (2017AJ....154..165B 2017AJ....154..165B)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaEDR3 ? Gaia EDR3 (I/350) source name
21- 39 A19 --- UGCS UKIDSS Galactic Clusters Survey (II/319)
source name
41- 57 A17 --- 2MASS 2MASS Point Source Catalog (II/246) source
name
59- 80 A22 --- Name Other source name
82- 91 F10.6 deg RAdeg Right ascension (ICRS)
93- 102 F10.6 deg DEdeg Declination (ICRS)
104- 109 A6 --- Ref Reference for right ascension and declination
(1)
111- 116 F6.3 mag W1mag [10.9/16.6] WISE W1 magnitude
118- 122 F5.3 mag e_W1mag [0.01/0.06] Error in W1mag
124- 129 F6.3 mag W2mag [10.7/16] WISE W2 magnitude
131- 135 F5.3 mag e_W2mag [9e-3/0.12] Error in W2mag
137 A1 --- Exc Excess present in W2? (2)
--------------------------------------------------------------------------------
Note (1): Coordinates reference as follows:
Gaia = Gaia EDR3 (I/350); 149 occurrences
UKIDSS = UKIDSS Galactic Clusters Survey DR10 (II/319, DR9); 110 occurrences
VHS = VISTA Hemispher Survey DR6 (II/367, DR5); 1 occurrence
Note (2): Flag as follows:
Y = Yes (52 occurrences)
N = No (161 occurrences)
? = ? (47 occurrences)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 25-Mar-2026