J/ApJ/800/51 DUSTiNGS II. Metal-poor dusty AGB stars (Boyer+, 2015)
An infrared census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS).
II. Discovery of metal-poor dusty AGB stars.
Boyer M.L., McQuinn K.B.W., Barmby P., Bonanos A.Z., Gehrz R.D.,
Gordon K.D., Groenewegen M.A.T., Lagadec E., Lennon D., Marengo M.,
McDonald I., Meixner M., Skillman E., Sloan G.C., Sonneborn G.,
van Loon J.TH., Zijlstra A.
<Astrophys. J., 800, 51 (2015)>
=2015ApJ...800...51B 2015ApJ...800...51B
ADC_Keywords: Galaxies, nearby ; Photometry, infrared ; Stars, giant
Keywords: galaxies: dwarf; galaxies: stellar content; infrared: stars;
Local Group; stars: AGB and post-AGB; stars: carbon
Abstract:
The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6
and 4.5µm imaging survey of 50 nearby dwarf galaxies designed to
identify dust-producing asymptotic giant branch (AGB) stars and
massive stars. Using two epochs, spaced approximately six months
apart, we identify a total of 526 dusty variable AGB stars (sometimes
called "extreme" or x-AGB stars; [3.6]-[4.5]>0.1mag). Of these, 111
are in galaxies with [Fe/H]←1.5 and 12 are in galaxies with
[Fe/H]←2.0, making them the most metal-poor dust-producing AGB stars
known. We compare these identifications to those in the literature and
find that most are newly discovered large-amplitude variables, with
the exception of ~30 stars in NGC185 and NGC147, 1 star in
IC1613, and 1 star in Phoenix. The chemical abundances of the x-AGB
variables are unknown, but the low metallicities suggest that they are
more likely to be carbon-rich than oxygen-rich and comparisons with
existing optical and near-IR photometry confirm that 70 of the x-AGB
variables are confirmed or likely carbon stars. We see an increase in
the pulsation amplitude with increased dust production, supporting
previous studies suggesting that dust production and pulsation are
linked. We find no strong evidence linking dust production with
metallicity, indicating that dust can form in very metal-poor
environments.
Description:
The DUSTiNGS (DUST in Nearby Galaxies with Spitzer) observations and
photometry are described in detail in Paper I (Boyer et al. 2015,
J/ApJS/216/10). In brief, each galaxy was imaged simultaneously at 3.6
and 4.5um to at least the half-light radius (rh) in two epochs between
2011 and 2012 June. The average epoch separation is 180days.
Eight of the DUSTiNGS targets were also observed with Spitzer during
the cryogenic mission. The observations for these galaxies are
described in detail in Jackson et al. (2007ApJ...656..818J 2007ApJ...656..818J,
2007ApJ...667..891J 2007ApJ...667..891J) and Boyer et al. (2009, J/ApJ/697/1993). Since
this epoch occurs prior to the DUSTiNGS observations, we refer to it
as "epoch 0".
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 36 46 Variable AGB and x-AGB star candidates summary
table3.dat 123 710 Variable star candidates
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See also:
J/ApJS/216/10 : DUSTiNGS. I. The Good Source Catalog (Boyer+, 2015)
J/AJ/149/78 : SAGE-SMC survey candidate IR variables (Polsdofer+, 2015)
J/MNRAS/446/1584 : IRAC point sources for M32 (Jones+, 2015)
J/A+A/566/A44 : gr photometry of Sextans A and Sextans B (Bellazzini+, 2014)
J/MNRAS/439/2618 : VISTA variables in Sagittarius dSph (McDonald+, 2014)
J/MNRAS/427/2647 : Sgr dSph stars spectral classification (McDonald+, 2012)
J/ApJ/753/71 : Mass-loss return from LMC evolved stars. VI. (Riebel+, 2012)
J/AJ/144/4 : Dwarf galaxy param. in the Local Group (McConnachie+, 2012)
J/AJ/142/103 : Cool evolved stars in SAGE-SMC (Boyer+, 2011)
J/A+A/532/A78 : Long-period variables in NGC 147 and NGC 185 (Lorenz+, 2011)
J/ApJS/193/23 : Fundamental stellar param. in 47 Tucanae (McDonald+, 2011)
J/MNRAS/411/1597 : LMC point source classification in SAGE-Spec (Woods+, 2011)
J/AcA/59/239 : VI LCs of LMC long-period variables (Soszynski+, 2009)
J/A+A/503/913 : Synthetic spectrophotom. for C-rich giants (Aringer+, 2009)
J/ApJ/697/1993 : Spitzer study of AGB stars. III. (Boyer+, 2009)
J/AJ/137/4810 : LMC-SAGE AGB star candidates (Srinivasan+, 2009)
J/MNRAS/394/795 : AGB stars in Fornax dSph galaxy (Whitelock+, 2009)
J/AJ/137/3139 : LMC SAGE. New variable evolved stars and YSOs (Vijh+, 2009)
J/AJ/136/1242 : LMC long-period variables from MACHO (Fraser+, 2008)
J/MNRAS/385/1045 : JHKsIc of AGB in Phoenix dwarf gal. (Menzies+, 2008)
J/AJ/135/1395 : omega Cen Spitzer photometry (Boyer+, 2008)
J/ApJ/664/850 : Spitzer observations of stars in M33 (McQuinn+, 2007)
J/MNRAS/376/313 : Carbon star in Magellanic Cloud (Groenewegen+, 2007)
J/AJ/132/2268 : SAGE calibration stars (Meixner+, 2006)
J/MNRAS/369/751 : Near-infrared photometry of carbon stars (Whitelock+, 2006)
J/A+A/445/69 : JHK' photometry of C stars in NGC 147 (Sohn+, 2006)
J/A+A/424/125 : Carbon stars in IC10 (Demers+, 2004)
J/A+A/418/33 : RI photometry of C stars in NGC 147 (Battinelli+, 2004)
J/A+A/417/479 : RI photometry of NGC 185 carbon stars (Battinelli+, 2004)
J/A+A/416/111 : C stars in Wolf-Lundmark-Melotte galaxy (Battinelli+, 2004)
J/A+A/403/93 : AGB stars photometry in NGC 185 and NGC 147 (Nowotny+, 2003)
J/A+A/367/759 : Variable stars in IC 1613 (Mantegazza+, 2001)
J/A+A/363/29 : Variable stars in IC 1613 (Antonello+, 2000)
J/AJ/120/1801 : C stars in Pegasus, DDO 210 and Tucana (Battinelli+, 2000)
J/AJ/119/2780 : C stars in IC 1613 (Albert+, 2000)
J/A+AS/97/729 : JHKL'M obs. of O-Rich late-type star (Le Bertre 1993)
http://irsa.ipac.caltech.edu/data/SPITZER/DUSTiNGS/ : DUSTiNGS IRSA home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Gal Galaxy identifier
13 A1 --- f_Gal [ad] Galaxy added or lacks completeness (1)
15- 19 F5.2 [Sun] [Fe/H] [-2.3/-1.1]? Metallicity (2)
21- 24 F4.2 [Sun] e_[Fe/H] [0.04/0.3]? [Fe/H] uncertainty
26- 27 I2 --- Nagb2 [0/13]? Number of variable AGB stars detected
at the 2σ level (3)
29 I1 --- Nagb3 [0/9]? Number of variable AGB stars detected
at the 3σ level (3)
31- 32 I2 --- Nx2 [0/18]? Number of variable x-AGB stars
detected at the 2σ level (3)
34- 36 I3 --- Nx3 [0/217]? Number of variable x-AGB stars
detected at the 3σ level (3)
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Note (1): Flag as follows:
a = Galaxy added by CDS in this table to enlighten its presence in table 3.
These galaxies are not in table 1 of the paper because the variables
identified in them don't have colors/magnitudes typical of AGB stars,
so their variables are "unidentified".
d = These galaxies have <75% complete photometry at M3.6=-6mag due either to
their distance or to crowding, though all galaxies reach 75% completeness
by M3.6=-6.8mag (Paper I; Boyer et al. 2015, J/ApJS/216/10). The estimated
size of the AGB population should be considered a lower limit in these
cases. Photometric incompleteness does not affect the estimated size of
the x-AGB population except within the central ∼1' region of IC10 and
0.5' in NGC185.
Note (2): Metallicities from McConnachie (2012, J/AJ/144/4), also see Paper I
(Boyer et al. 2015, J/ApJS/216/10).
Note (3): Number of variable stars within the given color-magnitude space
detected at the 2σ and 3σ level (Section 3.2). This is
the maximum number of variables allowing for the uncertainty in
(m-M)0 (see Table 1 from Paper I; Boyer et al. 2015, J/ApJS/216/10).
The number of sources included here are confined to the spatial area
covered by all epochs and wavelengths (see Table 2 from Paper I).
AGB sources are included here if they are brighter than M3.6=-6mag.
This number does not include x-AGB star candidates.
x-AGB sources are included here if they are redder than
[3.6]-[4.5]=0.1mag and brighter than M3.6=-8mag or
redder than [3.6]-[4.5]=1.0mag (Figure 1(b)).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Gal Galaxy identifier
13- 18 I6 --- Seq [8412/227035] Variable star candidate
GSC identifier (1)
20- 21 I2 h RAh Hour of Right Ascension (J2000)
23- 24 I2 min RAm Minute of Right Ascension (J2000)
26- 30 F5.2 s RAs Second of Right Ascension (J2000)
32- 32 A1 --- DE- Sign of the Declination (J2000)
33- 34 I2 deg DEd Degree of Declination (J2000)
36- 37 I2 arcmin DEm Arcminute of Declination (J2000)
39- 42 F4.1 arcsec DEs Arcsecond of Declination (J2000)
44- 48 F5.2 mag <m3.6> [13.4/19.9] Mean Spitzer/IRAC 3.6 micron
band magnitude
50- 53 F4.2 mag e_<m3.6> [0.02/0.2] The 1σ error in <m3.6>
55- 59 F5.2 mag <m4.5> [13/19.5] Mean Spitzer/IRAC 4.5 micron
band magnitude
61- 64 F4.2 mag e_<m4.5> [0.02/0.3] The 1σ error in <m4.5>
66- 69 F4.2 mag A3.6 [0.1/2] Spitzer 3.6um band amplitude (2)
71- 74 F4.2 mag e_A3.6 [0.04/0.4] The 1σ error in A3.6
76- 79 F4.2 mag A4.5 [0/1.9] Spitzer 4.5um band amplitude (2)
81- 84 F4.2 mag e_A4.5 [0.04/0.7] The 1σ error in A4.5
86 I1 --- sig [2/3] Variability detection σ value
88 A1 --- Type [XAU] Star type (3)
90- 94 F5.2 [Msun/yr] logDdot [-9.5/-6.1]? Log of dust production rate (7)
96 I1 --- Nep [2/3] Number of epochs (4)
98 A1 --- Flag [BEp] Variable flag (5)
100-123 A24 --- Notes Additional notes (6)
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Note (1): The GSC is the "good-source catalog", described in Paper I
(Boyer et al. 2015, J/ApJS/216/10 and available on IRSA:
http://irsa.ipac.caltech.edu/data/SPITZER/DUSTiNGS/;
in Simbad)
Note (2): We define the amplitude as the difference between the maximum and
minimum magnitude.
Note (3): Stars are classified as described in Section 3.1 as follows:
X = x-AGB (extreme Asymptotic Giant Branch; 526 stars),
A = AGB (Asymptotic Giant Branch; 115 stars) or
U = unknown (69 sources).
Note (4): Most variable stars were found by comparing epochs 1 and 2, but some
were only detected as variable by including epoch 0 (Section 2.2 and
see the "Description" section above).
For those detected via epoch 0, the mean magnitude in this table
includes all 3 epochs.
Note (5): the measured fluxes may be affected by the collowing situations:
B = lies near a bright star,
E = near the frame edge or,
p = Column Pulldown.
Note (6): Variables are flagged as:
LPV = long-period variable,
Mira = Mira variable,
C = C-rich star
O = O-rich star
RSG? = possible Red SuperGiant candidate (those brighter than the
dash-dot line in Fig. 1).
References are:
A00 = Albert et al. (2000, J/AJ/119/2780),
BD00 = Battinelli & Demers (2000, J/AJ/120/1801),
BD04a = Battinelli & Demers (2004, J/A+A/418/33),
BD04b = Battinelli & Demers (2004, J/A+A/417/479),
BD04c = Battinelli & Demers (2004, J/A+A/416/111),
DB02 = Demers & Battinelli (2002AJ....123..238D 2002AJ....123..238D),
D04 = Demers et al. (2004, J/A+A/424/125),
G07 = Gullieuszik et al. (2007A&A...475..467G 2007A&A...475..467G),
K01 = Kurtev et al. (2001A&A...378..449K 2001A&A...378..449K),
L11 = Lorenz et al. (2011, J/A+A/532/A78),
M08 = Menzies et al. (2008, J/MNRAS/385/1045),
N03 = Nowotny et al. (2003, J/A+A/403/93), and
S06 = Sohn et al. (2006, J/A+A/445/69).
Note (7): Dust-production rates (Ddot) are derived only for x-AGB candidates,
and the possible D/dt saturation limit is not applied to numbers
in this table (Section 6.2).
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History:
From electronic version of the journal
References:
Boyer et al. Paper I. 2015ApJS..216...10B 2015ApJS..216...10B J/ApJS/216/10
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 29-Jun-2015