J/MNRAS/504/565 Infrared variable stars in M32 (Jones+, 2021)
Infrared variable stars in the compact elliptical galaxy M32.
Jones O.C., Nally C., Sharp M.J., McDonald I., Boyer M.L., Meixner M.,
Kemper F., Ferguson A.M.N., Goldman S.R., Rich R.M.
<Mon. Not. R. Astron. Soc., 504, 565-575 (2021)>
=2021MNRAS.504..565J 2021MNRAS.504..565J (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, variable ; Photometry, infrared
Keywords: stars: late-type - galaxies: individual: M32 -
galaxies: stellar content - infrared: galaxies - infrared: stars -
stars: AGB and post-AGB
Abstract:
Variable stars in the compact elliptical galaxy M32 are identified,
using three epochs of photometry from the Spitzer Space Telescope at
3.6 and 4.5µm, separated by 32 to 381d. We present a high-fidelity
catalogue of sources detected in multiple epochs at both 3.6 and
4.5µm, which we analysed for stellar variability using a joint
probability error-weighted flux difference. Of these, 83 stars are
identified as candidate large-amplitude, long-period variables, with
28 considered high-confidence variables. The majority of the variable
stars are classified as asymptotic giant branch star candidates using
colour-magnitude diagrams. We find no evidence supporting a younger,
infrared-bright stellar population in our M32 field.
Description:
Observations of M32 (program ID 11103) were made with the Infrared
Array Camera (IRAC) on the Spitzer Space Telescope using the 3.6 and
4.5um filters. The three epochs were taken over a 13 month period
(Table 1) during the post-cryogenic mission. Each pointing consists of
23 dithered exposures of 30s in each IRAC filter. The region where
both 3.6 and 4.5um data are available covers an area of
approximately 5x5-arcmin2 around the centre of M32, with a pixel
size of 0.6-arcsec2. This corresponds to a 1.3kpc2 field-of-view.
The individual point-source lists (three epochs at 3.6 and 4.5um) for
the regions where both 3.6 and 4.5um data are available are
cross-matched using a 1-arcsec radius via the Bayesian-based code NWAY
(Salvato et al., 2018MNRAS.473.4937S 2018MNRAS.473.4937S), producing a high-fidelity
catalogue of over 1000 M32 sources detected in multiple epochs at both
3.6 and 4.5um.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 194 1091 Catalogue of point sources for M32
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See also:
J/A+A/539/A138 : RR Lyr variable stars in M32 (Fiorentino+, 2012)
J/MNRAS/446/1584 : IRAC point sources for M32 (Jones+, 2015)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- ID [1/1387] Point-source ID
6- 13 F8.5 deg RAdeg Right Ascension (J2000)
15- 22 F8.5 deg DEdeg Declination (J2000)
24- 30 F7.3 mag [3.6]-1 [0/18.6]?=-99.0 Epoch 1 magnitude in [3.6]
32- 38 F7.3 mag e_[3.6]-1 [0/0.2]?=-99.0 Error epoch 1 magnitude
in [3.6]
40- 46 F7.3 mag [3.6]-2 [0/18.3]?=-99.0 Epoch 2 magnitude in [3.6]
48- 54 F7.3 mag e_[3.6]-2 [0/0.2]?=-99.0 Error epoch 2 magnitude
in [3.6]
56- 62 F7.3 mag [3.6]-3 [0/18.5]?=-99.0 Epoch 3 magnitude in [3.6]
64- 70 F7.3 mag e_[3.6]-3 [0/0.2]?=-99.0 Error epoch 3 magnitude
in [3.6]
72- 78 F7.3 mag [4.5]-1 [0/18.8]?=-99.0 Epoch 1 magnitude in [4.5]
80- 86 F7.3 mag e_[4.5]-1 [0/0.3]?=-99.0 Error epoch 1 magnitude
in [4.5]
88- 94 F7.3 mag [4.5]-2 [0/18.9]?=-99.0 Epoch 2 magnitude in [4.5]
96-102 F7.3 mag e_[4.5]-2 [0/0.3]?=-99.0 Error epoch 2 magnitude
in [4.5]
104-110 F7.3 mag [4.5]-3 [0/19.1]?=-99.0 Epoch 3 magnitude in [4.5]
112-118 F7.3 mag e_[4.5]-3 [0/0.3]?=-99.0 Error epoch 3 magnitude
in [4.5]
120-126 F7.3 --- V[3.6]-12 [0/16.1]?=-99.0 Variability index at [3.6]
for interval 12
128-134 F7.3 --- V[3.6]-13 [0/17.3]?=-99.0 Variability index at [3.6]
for interval 13
136-142 F7.3 --- V[3.6]-23 [0/13.2]?=-99.0 Variability index at [3.6]
for interval 23
144-150 F7.3 --- V[4.5]-12 [0/7.7]?=-99.0 Variability index at [4.5]
for interval 12
152-158 F7.3 --- V[4.5]-13 [0/9.6]?=-99.0 Variability index at [4.5]
for interval 13
160-166 F7.3 --- V[4.5]-23 [0/10.2]?=-99.0 Variability index at [4.5]
for interval 23
168-173 F6.3 mag [3.6]mean [14.8/18.3] Mean [3.6] magnitude
175-180 F6.3 mag [4.5]mean [14.3/18.9] Mean [4.5] magnitude
182-186 F5.3 mag Amp[3.6] [0.0/1.8] Observed [3.6] Amplitude
188-192 F5.3 mag Amp[4.5] [0.0/1.5] Observed [4.5] Amplitude
194 I1 --- Var [0.0/2.0] Variable star classification
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Acknowledgements:
Olivia Jones, olivia.jones(at)stfc.ac.uk
(End) Patricia Vannier [CDS] 15-Mar-2022