J/ApJS/265/18 Opt. spectra of blue MIR objects in LMC (Ishioka+, 2023)
The nature of blue stars with mid-infrared excesses in the Large Magellanic
Cloud.
Ishioka R., Chu Y.-H., Edmister A., Gruendl R.A., Zhang L., Zhu J.
<Astrophys. J. Suppl. Ser., 265, 18 (2023)>
=2023ApJS..265...18I 2023ApJS..265...18I
ADC_Keywords: Magellanic Clouds; YSOs; Photometry, infrared; Spectra, optical;
Colors; Magnitudes, absolute; Reddening; Spectral types;
Effective temperatures
Keywords: Large Magellanic Cloud ; Young stellar objects ;
Stellar classification
Abstract:
We present low-resolution optical spectra and classifications of
92 blue objects with mid-infrared excesses in the Large Magellanic
Cloud. The majority of these objects were selected with the criteria
of U-B<0 and V<17 from the potential young stellar object (YSO)
candidates in Gruendl & Chu (GC09; 2009, J/ApJS/184/172), which were
identified based on Spitzer Infrared Array Camera and Multiband
Imaging Photometer for Spitzer observations in conjunction with
optical photometry from the Magellanic Clouds Photometric Survey. Many
of the sample objects have ambiguous classifications. We examined the
properties of these 92 objects using low-resolution optical spectra
obtained with the SOAR 4.1m Telescope at Cerro Pachon and the Blanco
4m Telescope at Cerro Tololo Inter-American Observatory, supplemented
by available photometric and imaging observations. We estimated the
spectral types, temperatures, and luminosities of these objects from
the optical to near-IR spectral energy distributions based on the
photometric data, and further examined stellar absorption line
features in the optical spectra to verify the spectral types. The
interstellar/circumstellar environments, assessed from nebular line
imaging observations and nebular lines detected in the stellar
spectra, further helped constrain the nature of stars. Among these
92 objects, we confirm 42 stars as YSOs, and the remaining 50 objects
as protoplanetary nebulae, post-AGB/RGB stars, blue evolved massive
stars, stars with dust in vicinity, or uncertain classifications. Our
results show that the photometric criteria in GC09 are generally
effective in the initial selection of YSO candidates, and the low-
resolution spectroscopy combined with environment assessment can be
useful to better constrain the classifications and ameliorate most
ambiguities.
Description:
The pilot observations for six objects were done during the
commissioning period of the Goodman Spectrograph on the Southern
Astrophysical Research (SOAR) 4.1m Telescope at Cerro Pachon on
2009 January 9-10 and 2009 March 16. We subsequently acquired
observing time on the Blanco 4m Telescope at Cerro Tololo
Inter-American Observatory (CTIO) and the SOAR Telescope to take
spectra of our Spitzer sample of blue stars with mid-IR excesses.
Follow-up observations of five objects were made with the Cerro Tololo
Ohio State Multi-Object Spectrograph (COSMOS) on the Blanco Telescope
on 2020 December 10-11. Table 2 presents the journal of spectroscopic
observations. See Section 3.1.
We also used higher-quality Hα, I-band, and near-IR images of
star-forming complexes in the LMC obtained using the Blanco 4m
Telescope at CTIO in several observing runs since 2005.
See Section 3.2.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 173 93 Blue stars with IR excesses
table2.dat 40 106 Journal of spectroscopic observations
table3.dat 112 93 Estimates from photometric data
table4.dat 158 93 Environments, line properties, estimated T, logL,
and classification
table5.dat 270 93 Classifications in literature
tablea1.dat 60 13 List of 13 additional targets without U-B<0
tablea2.dat 57 19 List of 19 targets which were not observed
refs.dat 44 59 References
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See also:
B/mk : Catalogue of Stellar Spectral Classifications (Skiff, 2009- )
III/147 : Studies of LMC stellar content (Rousseau+ 1978)
III/92 : A Library of Stellar Spectra (Jacoby+ 1984)
III/136 : Optical spectrophotometry of WR C and O Stars (Torres+ 1987)
III/195 : Atlas of Optical Spectral Classification OB Stars (Walborn+ 1990)
II/228 : DENIS Catalogue toward Magellanic Clouds (DCMC) (Cioni+ 2000)
II/236 : UBVR CCD survey of the Magellanic clouds (Massey+, 2002)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/288 : IRSF Magellanic Clouds Point Source Catalog (Kato+ 2007)
II/351 : VISTA Magellanic Survey (VMC) catalog (Cioni+, 2011)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
VII/23 : Nebulae in the Magellanic Clouds (Davies+ 1976)
J/AJ/103/1205 : Stellar Content of LH 9 and 10 in the LMC (Parker+ 1992)
J/ApJS/91/659 : Ultracompact HII regions radio images (Kurtz+ 1994)
J/A+A/299/755 : Stellar evolution. II. Post-AGB (Bloecker+, 1995)
J/ApJ/452/210 : UBV photometry in LH 47/48 (Oey+ 1995)
J/A+AS/125/419 : Obscured AGB in Magellanic Clouds. I. (Loup+ 1997)
J/AJ/117/238 : LMC extended catalog (Bica+, 1999)
J/AJ/124/2039 : LMC Blue variable stars from MACHO (Keller+, 2002)
J/AJ/128/1606 : Magellanic Clouds Phot. Survey (MCPS) (Zaritsky+, 2004)
J/A+A/456/623 : VLT-FLAMES survey of massive stars (Evans+, 2006)
J/AJ/132/2268 : SAGE calibration stars (Meixner+, 2006)
J/ApJ/652/458 : BVRHα phot. of candid. Be stars (Wisniewski+, 2006)
J/AJ/134/1963 : MACHO r,b light curves of MC EBs (Faccioli+, 2007)
J/ApJS/178/56 : CO obs. of LMC Giant Molecular clouds (Fukui+, 2008)
J/AJ/136/18 : LMC SAGE. New candidate YSOs (Whitney+, 2008)
J/AJ/138/1003 : IR photometry of massive LMC stars (Bonanos+, 2009)
J/ApJ/695/511 : Young massive stars in LHA 120-N 44 (Chen+, 2009)
J/ApJS/184/172 : High- & intermediate-mass YSOs in the LMC (Gruendl+, 2009)
J/ApJ/699/150 : Spectral classif. of Massive YSOs in LMC (Seale+, 2009)
J/ApJ/707/1417 : HST view of YSOs in the LMC (Vaidya+, 2009)
J/MNRAS/405/1349 : LMC PNe [OIII] 5007Å and Hβ flux (Reid+, 2010)
J/ApJ/721/357 : YSOs in the LMC star-forming region N206 (Romita+, 2010)
J/AJ/142/103 : Cool evolved stars in SAGE-SMC and SAGE-LMC (Boyer+, 2011)
J/A+A/530/A108 : VLT-FLAMES Tarantula Survey (Evans+, 2011)
J/AcA/61/103 : VI light curves of LMC eclipsing binaries (Graczyk+, 2011)
J/A+A/531/A157 : LMC planetary nebulae (VMC Survey II) (Miszalski+, 2011)
J/A+A/530/A90 : Opt. bright post-AGB population of LMC (van Aarle+, 2011)
J/MNRAS/411/1597 : LMC point source classif. in SAGE-Spec (Woods+, 2011)
J/A+A/542/A66 : YSOs in 9 LMC star forming regions (Carlson+, 2012)
J/MNRAS/425/355 : Hot stars in LMC UKST Hα survey (Reid+, 2012)
J/ApJ/789/139 : Three O-type binaries photometry in LMC (Morrell+, 2014)
J/AJ/148/124 : Herschel key program Heritage (Seale+, 2014)
J/A+A/564/A40 : VFTS. O-type stellar content of 30 Dor (Walborn+, 2014)
J/A+A/574/A13 : VFTS. B-type stars classification and RV (Evans+, 2015)
J/A+A/584/A5 : Massive LMC stars AAOmega spectroscopy (Evans+, 2015)
J/MNRAS/454/1468 : LMC post-AGB, post-RGB star and YSOs (Kamath+, 2015)
J/AcA/66/421 : EBs in the Magellanic System (Pawlak+, 2016)
J/A+A/598/A84 : OB-type spectroscopic binaries (Almeida+, 2017)
J/MNRAS/470/3250 : SAGE LMC point-sources classification (Jones+, 2017)
J/AJ/154/199 : Survey of the MAgellanic Stellar History (Nidever+, 2017)
J/other/NewA/56.28 : Be stars in MC star clusters NIR properties (Paul+, 2017)
J/A+A/614/A147 : NGC 2070 point sources radial velocities (Castro+, 2018)
J/A+A/636/A48 : VMC Survey. XXXVII. MC AGB stars (Groenewegen+, 2020)
J/ApJ/898/85 : CII em-line stars in LMC with MagE spectra (Margon+, 2020)
J/A+A/641/A142 : Post-AGB cand. in LMC & SMC SALT spectra (Szczerba+, 2020)
J/MNRAS/494/458 : VMC XXXVI. Young stellar var. in LMC (Zivkov+, 2020)
J/A+A/658/A36 : Transition disks around evolved stars (Kluska+, 2022)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Sequential identifier used in this work
4 A1 --- m_Seq Component ID on Seq
6- 23 A18 --- [GC2009] Position-based identifier,
Gruendl & Chu (2009, J/ApJS/184/172)
25- 25 A1 --- f_Umag Flag on Umag (1)
27- 31 F5.2 mag Umag [9.9/17.7]? U-band magnitude
from MCPS unless flagged
33- 36 F4.2 mag e_Umag [0.01/0.24]? Uncertainty in Umag
38- 38 A1 --- f_Bmag Flag on Bmag (1)
40- 44 F5.2 mag Bmag [10.6/18] B-band magnitude
from MCPS unless flagged
46- 49 F4.2 mag e_Bmag [0.01/0.3]? Uncertainty in Bmag
51- 51 A1 --- f_Vmag Flag on Vmag (1)
53- 57 F5.2 mag Vmag [10.5/18] V-band magnitude
from MCPS unless flagged
59- 62 F4.2 mag e_Vmag [0.01/0.21]? Uncertainty in Vmag
64- 64 A1 --- f_Imag Flag on Imag (1)
66- 70 F5.2 mag Imag [10.38/17.2]? I-band magnitude
from MCPS unless flagged
72- 75 F4.2 mag e_Imag [0.01/0.3]? Uncertainty in Imag
77- 81 F5.2 mag Jmag [10.67/16.6]? J-band magnitude (2)
83- 86 F4.2 mag e_Jmag [0.02/0.2]? Uncertainty in Jmag (2)
88- 92 F5.2 mag Hmag [10.64/16.41]? H-band magnitude (2)
94- 97 F4.2 mag e_Hmag [0.02/0.3]? Uncertainty in Hmag (2)
99-103 F5.2 mag Ksmag [10/16]? Ks-band magnitude (2)
105-108 F4.2 mag e_Ksmag [0.02/0.3]? Uncertainty in Ksmag (2)
110-114 F5.2 mag 3.6mag [7.7/14.6]? Spitzer/IRAC 3.6um-band
magnitude (3)
116-119 F4.2 mag e_3.6mag [0.05/0.12]? Uncertainty in 3.6mag (3)
121-125 F5.2 mag 4.5mag [7.7/14]? Spitzer/IRAC 4.5um-band magnitude (3)
127-130 F4.2 mag e_4.5mag [0.03/0.11]? Uncertainty in 4.5mag (3)
132-136 F5.2 mag 5.8mag [6.9/13.4]? Spitzer/IRAC 5.8um-band
magnitude (3)
138-141 F4.2 mag e_5.8mag [0.03/0.3]? Uncertainty in 5.8mag (3)
143-147 F5.2 mag 8.0mag [5.6/12]? Spitzer/IRAC 8.0um-band magnitude (3)
149-152 F4.2 mag e_8.0mag [0.05/0.3]? Uncertainty in 8.0mag (3)
154-157 F4.2 mag 24mag [0.06/9.1]? Spitzer/MIPS 24um-band
magnitude (3)
159-162 F4.2 mag e_24mag [0.01/0.3]? Uncertainty in 24mag (3)
164-168 F5.2 mag 70mag [-3.2/2]? Spitzer/MIPS 70um-band magnitude (3)
170-173 F4.2 mag e_70mag [0.2/0.3]? Uncertainty in 70mag (3)
--------------------------------------------------------------------------------
Note (1): Reference as follows:
d = Ducati (2002, II/237)
c = Chen et al. (2009, J/ApJ/695/511)
i = Denis (2005, II/263)
m = Massey (2002, II/236)
n = Cioni et al. (2000, II/228)
p = Parker et al. (1992, J/AJ/103/1205)
a = Castro et al. (2018, J/A+A/614/A147)
Note (2): JHK are from 2MASS (II/246) or IRSF (Kato+ 2007, II/288).
Note (3): Spitzer IRAC and MIPS measurements are from
Gruendl & Chu (2009, J/ApJS/184/172).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/111] Sequential identifier used in this work
5- 6 A2 --- Tel Telescope (1)
8- 11 I4 yr Obs.Y [2009/2020] Observation date, year
13- 14 I2 "month" Obs.M Observation date, month
16- 17 I2 d Obs.D Observation date, day in month
19- 20 I2 h Obs.h Observation date, hour (UT)
22- 23 I2 min Obs.m Observation date, minute
25- 28 F4.1 s Obs.s Observation date, seconds
30- 33 I4 s Exp [3/1200] Exposure time
35- 35 I1 --- N [1/3] Number of observations
37- 40 F4.2 --- Airmass [1.2/2.1] Airmass
--------------------------------------------------------------------------------
Note (1): Telescopes as follows:
B = Blanco+RC-Spectrograph (84 occurrences)
S = SOAR+Goodman (17 occurrences)
B' = Blanco+COSMOS (5 occurrences)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Sequential identifier used in this work
4 A1 --- m_Seq Component ID on Seq
6- 23 A18 --- [GC2009] Position-based identifier,
Gruendl & Chu (2009, J/ApJS/184/172)
25- 30 F6.3 mag B-V [-0.22/0.91]? B-V color
32- 37 F6.3 mag U-B [-2.04/0.36]? U-B color
39- 43 F5.2 mag B-V0 [-0.33/0.1]? Dereddened B-V color
45- 48 F4.2 mag e_B-V0 [0/0.04]? Uncertainty in B-V0 (4)
50- 54 F5.2 mag U-B0 [-2.7/0.26]? Dereddened U-B color
56- 59 F4.2 mag e_U-B0 [0/0.03]? Uncertainty in U-B0 (4)
61- 64 F4.2 mag AV [0.02/3.73] V-band reddening
66- 69 F4.2 mag e_AV [0/0.2]? Uncertainty in AV (4)
71- 75 F5.2 mag VMag [-8.71/-2.3] Absolute dereddened V-band
magnitude
77- 80 F4.2 mag e_VMag [0/0.2]? Uncertainty in VMag (4)
82 A1 --- f_Tph Flag on Tph (5)
84- 88 I5 K Tph [8500/50000] Photometrically-derived
effective temperature (5)
90- 93 I4 K e_Tph [0/4500]? Uncertainty in Tph (5)
95- 97 F3.1 [Lsun] logLph [3.2/6.4] Log of photometrically-derived
luminosity
99-102 F4.2 [Lsun] e_logLph [0/0.2]? Uncertainty in logLph (4)
104-107 A4 --- SpT Spectral type (6)
109-112 A4 --- Lum Luminosity class (6)
--------------------------------------------------------------------------------
Note (4): Values with null uncertainties mean the value was estimated just
from B-V value.
Note (5): Values with f_Tph=* have significantly different Tph from the
temperature estimated from spectral features.
Note (6): Spectral type and luminosity class are assigned for the estimated
temperature and VMag.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Subset Subset (7)
14- 16 I3 --- Seq Sequential identifier used in this work
17 A1 --- m_Seq Component ID on Seq
19- 36 A18 --- [GC2009] Position-based identifier,
Gruendl & Chu (2009, J/ApJS/184/172)
38- 51 A14 --- HST Multiplicity detected in HST archival
images (8)
53 A1 --- HII [NY] Large scale environment, HII region
55 A1 --- GMC [NY] Large scale environment, GMC
57 A1 --- Dust [NY] Large scale environment, Dusty region
60 A1 --- l_ScHII Limit flag on ScHII
62 A1 --- u_ScHII Uncertainty flag on ScHII
64- 67 F4.2 pc ScHII [0.2/5]? Size of compact HII region or
nebulae
69 A1 --- f_ScHII Flag on ScHII, d=measured from HST archival
images
71- 73 A3 --- Ha Hα line features (9)
75- 76 A2 --- Hb Hβ line features (9)
80- 83 F4.2 --- NII/Ha [0.02/0.75]? Line ratio, [NII]/Hα
85- 88 F4.2 --- OIII/Hb [0.05/7]? Line ratio, [OIII]/Hβ
90- 93 F4.2 --- SII [0.4/2.32]? Line ratio, [SII], 6716/6731
95- 96 A2 --- fBGN Dd=nebular emission from nebulosity of
background environment
98-102 I5 K Teff [7250/50000] Surface effective temperature (10)
104 A1 --- f_Teff Flag on Teff, P=measured from spectra
106-111 F6.4 [Lsun] logL [3.2/6.4] Log of luminosity (10)
113-117 F5.3 mag AV2 [0.02/3.4] V-band reddening (10)
119-126 A8 --- SpT2 Spectral Type (10)
128 A1 --- f_SpT2 Flag on SpT, P=measured from spectra
130-158 A29 --- Notes Remarks (11)
--------------------------------------------------------------------------------
Note (7): Subset of sources as follows:
YSO = Young Stellar Objects;
Star+dust = stars with dust in vicinity;
Blue Evolved = Blue Evolved Massive Stars (LBV, OB[e]SGs or OB giants in CSN);
PPN = proto-planetary nebulae;
post AGB = post-AGB/RGB stars;
Other = other, uncertain classifications.
Note (8): Multiplicity detected in HST archival images; code as follows:
M = multiple stars with peak counts higher than one tenth of the main star;
S = no stars with peak counts higher than one tenth of the main star;
* = Multiplicity detected in SOAR images or CTIO archival image.
Blank if no HST archival images.
Note (9): Features of Hα and Hβ lines in stellar spectra.
E/A/pC = emission/absorption/P Cygni-like;
capital/lower-case = stronger/weaker;
left/right order = broader/narrower;
$ = [OIII] lines are in absorption, which means background emission
is oversubtracted.
Note (10): Temperature, luminosity, AV, and spectral types estimated from
photometry and spectroscopy except where flagged and only spectra were
used.
Note (11): Remarks include:
var = Variables, except for eclipsing binaries;
bin = Eclipsing or spectroscopic binaries.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq Sequential identifier used in this work
4 A1 --- m_Seq Component ID on Seq
6- 23 A18 --- [GC2009] Position-based identifier,
GC09 (Gruendl & Chu 2009, J/ApJS/184/172)
25- 42 A18 --- Class Classification, this work
44- 46 A3 --- Class-GC09 Classification, GC09 (G1)
48- 82 A35 --- Class-Lit Classification(s) from literature
84- 99 A16 --- r_Class-Lit Reference(s) for Class-Lit
(see refs.dat file)
101-110 A10 --- SpT-TW Spectral Type, this work
112-161 A50 --- SpT-Lit Spectral Type(s) from literature
163-176 A14 --- r_SpT-Lit Reference(s) for SpT-Lit
(see refs.dat file)
178-215 A38 --- Var Variability (Period in parenthesis)
from literature
217-229 A13 --- r_Var Reference(s) for Var (see refs.dat file)
231-257 A27 --- ONames Other name(s)
259-267 A9 --- Note Note
269-270 I2 --- r_Note ? Reference for Note (see refs.dat file)
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Byte-by-byte Description of file: tablea*.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [3/88] Sequential identifier used in this
work
4 A1 --- f_Seq d=Not observed
6- 23 A18 --- [GC2009] Position-based identifier, GC09
(Gruendl & Chu 2009, J/ApJS/184/172G)
25- 29 F5.2 mag Vmag [9.8/18.3] MCPS V-band magnitude
31- 35 F5.2 mag U-B [-1.2/2]? MCPS U-B color
37- 41 F5.2 --- U-B2 [-0.93/-0.52]? U-B from other literature
sources
43- 45 A3 --- Class-GC09 Classification, GC09 (G1)
47- 60 A14 --- Comm-GC09 Comment from GC09
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Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ref Reference code
4- 22 A19 --- BibCode Bibcode of the reference
24- 44 A21 --- Comm Corresponding VizieR catalog
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Global notes:
Note (G1): Classification from GC09:
Up to 3 classes can be found in this column. When a single class is
listed, the classification has a high confidence; when several classes
are listed in the column, the first classification should be
considered as "probable", the following classifications giving
possible alternatives.
D = Diffuse source: moderate contamination among our initial sample
by "sources" that are local enhancements within filamentary dust
emission most notably either at intersections between filaments or
at sharp bends in filaments.
G = Background galaxy
S = "normal" stars (objects exhibiting normal stellar photospheric
emission and excess mid-IR emission due to circumstellar dust). May be
followed by a second class, e.g. "SD"' for stars with photometric
contamination from diffuse emission, or "SC" for stars with an IR
excess that could possibly be YSOs.
C = Young Stellar Objects (YSO). A "C" alone means that the object can
be considered as a "definite YSOs". When "C" is followed by another
classification, the object can be considered as a "probable YSOs".
When "C" appears as 2nd or 3rd choice, the object is likely not an YSO,
but this classification cannot be ruled out: such objects are
"possible YSOs".
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-Apr-2023