J/ApJ/664/850 Spitzer observations of stars in M33 (McQuinn+, 2007)
The M 33 variable star population revealed by Spitzer.
McQuinn K.B.W., Woodward C.E., Willner S.P., Polomski E.F., Gehrz R.D.,
Humphreys R.M., van Loon J.T., Ashby M.L.N., Eicher K., Fazio G.G.
<Astrophys. J., 664, 850-861 (2007)>
=2007ApJ...664..850M 2007ApJ...664..850M
ADC_Keywords: Galaxies, nearby ; Surveys ; Photometry, infrared
Keywords: galaxies: individual (M33) - galaxies: stellar content -
infrared: stars - stars: AGB and post-AGB - stars: variables: other
Abstract:
We analyze five epochs of Spitzer Space Telescope Infrared Array
Camera (IRAC) observations of the nearby spiral galaxy M33. Each
epoch covered nearly a square degree at 3.6, 4.5, and 8.0um. The
point-source catalog from the full data set contains 37650 stars.
The stars have luminosities characteristic of the asymptotic giant
branch and can be separated into oxygen-rich and carbon-rich
populations by their [3.6]-[4.5] colors. The [3.6]-[8.0] colors
indicate that over 80% of the stars detected at 8.0um have dust
shells. Photometric comparison of epochs using conservative criteria
yields a catalog of 2923 variable stars. These variables are most
likely long-period variables amid an evolved stellar population. At
least one-third of the identified carbon stars are variable.
Description:
M33 was mapped at six epochs with IRAC on Spitzer as part of our
Guaranteed Time Observer (GTO) program (program ID 5; PI: R.D. Gehrz).
The map at each epoch consisted of two consecutive astronomical
observing requests (AORs) at all four IRAC wavelengths (3.6, 4.5, 5.8,
and 8.0um). This specific study analyzes only the first five epochs,
which cover a span of 19 months, at 3.6, 4.5, and 8.0um.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 278 37648 Catalog of non-variable point sources for M33
table3.dat 296 2923 Catalog of variable point sources for M33
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See also:
J/AJ/121/870 : BVI photometry of Variables in M33 (Macri+, 2001)
J/AJ/132/1361 : RR Lyrae variables in M33 (Sarajedini+, 2006)
J/MNRAS/371/1405 : Variables in M33 (Hartman+, 2006)
J/A+A/476/1161 : Spitzer photometry of M33 (Verley+, 2007)
Table1 : Journal of Observations
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Observation Date UT Time Number UT Time Number
Outer AOR Inner AOR
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2004 Jan 09 16:01 3636224 17:17 3636480
2004 Jul 22 21:43 3638016 22:56 3637760
2004 Aug 16 03:02 3639040 04:15 3638784
2005 Jan 21 15:14 3640576 16:24 3640320
2005 Aug 25 03:00 13474048 04:13 13474304
2006 Jan 09 23:09 3649792 01:12 3650048
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Note: Inner and outer AORs refer to the two regions M33 was divided into
for observation. The final observations were not used in this study.
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Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- --- [SSTM3307]
10- 28 A19 --- SSTM3307 Source identification, JHHMMSS.ss+DDMMSS.s
30- 38 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000)
40- 48 F9.6 deg DEdeg Declination in decimal degrees (J2000)
50- 55 F6.3 mag 3.6mag1 ? Epoch 1 IRAC 3.6um band magnitude
57- 61 F5.3 mag e_3.6mag1 ? The 1σ error in 3.6mag1
63- 68 F6.3 mag 3.6mag2 ? Epoch 2 IRAC 3.6um band magnitude
70- 74 F5.3 mag e_3.6mag2 ? The 1σ error in 3.6mag2
76- 81 F6.3 mag 3.6mag3 ? Epoch 3 IRAC 3.6um band magnitude
83- 87 F5.3 mag e_3.6mag3 ? The 1σ error in 3.6mag3
89- 94 F6.3 mag 3.6mag4 ? Epoch 4 IRAC 3.6um band magnitude
96-100 F5.3 mag e_3.6mag4 ? The 1σ error in 3.6mag4
102-107 F6.3 mag 3.6mag5 ? Epoch 5 IRAC 3.6um band magnitude
109-113 F5.3 mag e_3.6mag5 ? The 1σ error in 3.6mag5
115-120 F6.3 mag 4.5mag1 ? Epoch 1 IRAC 4.5um band magnitude
122-126 F5.3 mag e_4.5mag1 ? The 1σ error in 4.5mag1
128-133 F6.3 mag 4.5mag2 ? Epoch 2 IRAC 4.5um band magnitude
135-139 F5.3 mag e_4.5mag2 ? The 1σ error in 4.5mag2
141-146 F6.3 mag 4.5mag3 ? Epoch 3 IRAC 4.5um band magnitude
148-152 F5.3 mag e_4.5mag3 ? The 1σ error in 4.5mag3
154-159 F6.3 mag 4.5mag4 ? Epoch 4 IRAC 4.5um band magnitude
161-165 F5.3 mag e_4.5mag4 ? The 1σ error in 4.5mag4
167-172 F6.3 mag 4.5mag5 ? Epoch 5 IRAC 4.5um band magnitude
174-178 F5.3 mag e_4.5mag5 ? The 1σ error in 4.5mag5
180-185 F6.3 mag 8.0mag1 ? Epoch 1 IRAC 8.0um band magnitude
187-191 F5.3 mag e_8.0mag1 ? The 1σ error in 8.0mag1
193-198 F6.3 mag 8.0mag2 ? Epoch 2 IRAC 8.0um band magnitude
200-204 F5.3 mag e_8.0mag2 ? The 1σ error in 8.0mag2
206-211 F6.3 mag 8.0mag3 ? Epoch 3 IRAC 8.0um band magnitude
213-217 F5.3 mag e_8.0mag3 ? The 1σ error in 8.0mag3
219-224 F6.3 mag 8.0mag4 ? Epoch 4 IRAC 8.0um band magnitude
226-230 F5.3 mag e_8.0mag4 ? The 1σ error in 8.0mag4
232-237 F6.3 mag 8.0mag5 ? Epoch 5 IRAC 8.0um band magnitude
239-243 F5.3 mag e_8.0mag5 ? The 1σ error in 8.0mag5
245-250 F6.3 mag <3.6> ? Mean IRAC 3.6um band magnitude
252-257 F6.3 mag <4.5> ? Mean IRAC 4.5um band magnitude
259-264 F6.3 mag <8.0> ? Mean IRAC 8.0um band magnitude
266-271 F6.3 mag 3.6-4.5 ? The IRAC (3.6-4.5) color index
273-278 F6.3 mag 3.6-8.0 ? The IRAC (3.6-8.0) color index
280-284 F5.3 mag 3.6Amp ? Amplitude in IRAC 3.6um band (1)
286-290 F5.3 mag 4.5Amp ? Amplitude in IRAC 4.5um band (1)
292-296 F5.3 mag 8.0Amp ? Amplitude in IRAC 8.0um band (1)
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Note (1): Amplitudes only for variables (table3)
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 06-Jun-2008