J/ApJ/945/108 Red supergiants from HST, Spitzer and Gaia (Johnson+, 2023)
A multiwavelength classification and study of red supergiant candidates in
NGC 6946.
Johnson J.R., Koplitz B., Williams B.F., Dalcanton J.J., Dolphin A.,
Girardi L.
<Astrophys. J., 945, 108 (2023)>
=2023ApJ...945..108J 2023ApJ...945..108J
ADC_Keywords: Stars, giant; Photometry, HST; Optical; Photometry, infrared;
Stars, ages; Extinction
Keywords: Massive stars ; Stellar evolution ; Stellar populations
Abstract:
We have combined resolved stellar photometry from Hubble Space
Telescope (HST), Spitzer, and Gaia to identify red supergiant (RSG)
candidates in NGC 6946, based on their colors, proper motions, visual
morphologies, and spectral energy distributions. We start with a large
sample of 17865 RSG candidates based solely on HST near-infrared
photometry. We then chose a small sample of 385 of these candidates
with Spitzer matches for a more detailed study. Using evolutionary
models and isochrones, we isolate a space where RSGs would be found in
our photometry catalogs. We then visually inspect each candidate and
compare them to Gaia catalogs to identify and remove foreground stars.
As a result, we classify 95 potential RSGs, with 40 of these being in
our highest- quality sample. We fit the photometry of the populations
of stars in the regions surrounding the RSGs to infer their ages.
Placing our best candidate RSG stars into three age bins between 1 and
30Myr, we find 27.5% of the candidates falling between 1-10Myr, 37.5%
between 10-20 Myr, and 35% between 20-30Myr. A comparison of our
results to the models of massive star evolution shows some agreement
between model luminosities and the luminosities of our candidates for
each age. Three of our candidates appear significantly more consistent
with binary models than single-star evolution models.
Description:
We employed archival HST (Version 3) imaging taken with the Advanced
Camera for Survey (ACS) instrument with the Wide-Field Channel (WFC)
F435W, F606W, and F814W filters along with the Wide-Field Channel 3
(WFC3) instrument with the Infrared Channel (IR) F110W and F160W
filters. All the HST data used in this paper can be found in MAST:
doi:10.17909/T97P46. The HST observations (spanning 2010 August to
2019 January) are listed in Table 1. See Section 2.1. for further
explanations.
We supplemented our HST photometry with Spitzer bands using the
catalog from Khan (2017, J/ApJS/228/5). The photometry was taken with
the 3.6, 4.5, 5.8, 8um filters on the Infrared Array Camera (IRAC) on
board the Spitzer Space Telescope. See Section 2.2.
We further culled our sample of red supergiant (RSG) candidates by
visual inspection and comparison with Gaia. See Section 2.4.
Objects:
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RA (ICRS) DE Designation(s)
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20 34 52.33 +60 09 13.2 NGC 6946 = MCG+10-29-006
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 70 141 NGC 6946 HST observations
table2.dat 57 17865 The position and photometry of our "HST Only"
sample of 17865 stars
table3.dat 103 137 Photometry for each candidate
table4.dat 29 137 *Full list of results from MATCH
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Note on table4.dat: To determine an age distribution for each of the RSG
candidates we used MATCH (Dolphin 2002MNRAS.332...91D 2002MNRAS.332...91D &
2013ApJ...775...76D 2013ApJ...775...76D). This program models the CMDs to infer star
formation history (SFH) for that stellar population. The resulting SFH
from MATCH includes a distribution of ages, metallicities, and
uncertainties on these values. We use the distribution of ages as a
proxy for the probability that the RSG candidate is of a certain age.
See Section 3.1.
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/138/1003 : IR photometry of massive LMC stars (Bonanos+, 2009)
J/ApJ/715/1094 : Census of self-obscured massive stars (Khan+, 2010)
J/A+A/545/A43 : HII regions in NGC 628 and NGC 6946 (Cedres+, 2012)
J/A+A/537/A146 : Stellar models with rot. 0.8<M<120, Z=0.014 (Ekstrom+, 2012)
J/A+A/562/A75 : Spectra of 8 supergiants in nearby gal. (Britavskiy+, 2014)
J/ApJ/791/105 : SNe progenitor masses prob. distribution (Williams+, 2014)
J/ApJS/215/9 : PHAT X. UV-IR photometry of M31 stars (Williams+, 2014)
J/ApJS/228/5 : Spitzer phot. of ∼1million stars in M31 & 15 gal. (Khan, 2017)
J/ApJ/846/145 : PHAT. XIX. Formation history of M31 disk (Williams+, 2017)
J/ApJ/860/39 : HST observations of nearby core-collapse SNe (Williams+, 2018)
J/A+A/622/A50 : Calibrated grid of rot. single star models (Higgins+, 2019)
J/ApJ/881/54 : Masses of SNR progenitors in M83 (Williams+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- ID Image identifier
11- 15 I5 --- PID [12331/15216] Proposal identifier
17- 20 I4 yr Obs.Y [2010/2019] Year of the observation
22- 23 I2 "month" Obs.M [1/12] Month of the observation
25- 26 I2 d Obs.D [2/30] Day of the observation
28- 36 F9.5 deg RAdeg [308.5/308.9] Right Ascension (J2000)
38- 45 F8.5 deg DEdeg [60/60.21] Declination (J2000)
47- 55 F9.5 deg V3-Axis [166.5/347] The V3 axis
57- 59 I3 s Exp [99/987] Exposure time
61- 70 A10 --- Filter Filter name
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 F11.7 deg RAdeg [308.58/308.9] Right Ascension (J2000) (1)
13- 22 F10.7 deg DEdeg [60/60.23] Declination (J2000) (1)
24- 29 F6.3 mag F435Wmag [21.66/39.2]?=99.999 HST ACS/WFC F435W band
magnitude (2)
31- 36 F6.3 mag F606Wmag [19.98/38.01]?=99.999 HST ACS/WFC F606W band
magnitude (2)
38- 43 F6.3 mag F814Wmag [19.46/31.7]?=99.999 HST ACS/WFC F814W band
magnitude (2)
45- 50 F6.3 mag F110Wmag [18.48/22.43] HST WFC3 F110W band magnitude
52- 57 F6.3 mag F160Wmag [17.4/21.3] HST WFC3 F160W band magnitude
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Note (1): From the HST catalogs.
Note (2): A 99.999 indicates start was not recovered in this filter.
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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- 3 A3 --- --- [RSG]
5- 8 I4 --- ID [51/6822] RSG candidate identifier (G1)
10- 20 F11.7 deg RAdeg [308.6/308.85] HST Right Ascension (J2000)
22- 31 F10.7 deg DEdeg [60/60.2] HST Declination (J2000)
33- 41 F9.5 deg RASdeg [308.6/308.85] Spitzer Right Ascension (J2000)
43- 50 F8.5 deg DESdeg [60/60.2] Spitzer Declination (J2000)
52- 57 F6.3 mag F435Wmag [23.1/32]?=99.999 HST ACS/WFC F435W band
magnitude (1)
59- 64 F6.3 mag F606Wmag [21.1/29.8]?=99.999 HST ACS/WFC F606W band
magnitude (1)
66- 71 F6.3 mag F814Wmag [19.99/26]?=99.999 HST ACS/WFC F814W band
magnitude (1)
73- 78 F6.3 mag F110Wmag [18.93/22.37] HST WFC3 F110W band magnitude
80- 85 F6.3 mag F160Wmag [17.87/21.3] HST WFC3 F160W band magnitude
87- 91 F5.2 mag 3.6mmag [12.66/18.7] Spitzer/IRAC 3.6um band magnitude
93- 97 F5.2 mag 4.5mmag [12.89/19] Spitzer/IRAC 4.5um band magnitude
99- 103 F5.2 mag 5.8mmag [10.2/16.83] Spitzer/IRAC 5.8um band magnitude
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Note (1): A 99.999 indicates start was not recovered in this filter.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- --- [RSG]
5- 8 I4 --- ID [51/6822] RSG candidate identifier (G1)
10- 12 F3.1 mag dAv [0/2.6]? Differential extinction within the
region being measured
14- 17 F4.2 mag Av [0.8/2.6]? Foreground extinction in the region
19- 20 I2 Myr Age [0/29]? Age result
22- 29 A8 --- Flags Candidate status flag(s) (1)
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Note (1): Status flag as follows:
A = good candidate.
B = potential binary system candidate.
C = star is a potential low-mass contaminant (AGB star).
F = a potential foreground star.
M = the HST and Spitzer sources may have been mismatched.
1 = candidate belongs to the primary sample comprised of
only single matches between HST and Spitzer sources.
2 = the candidate belongs to the secondary sample of candidates
that had multiple matches between HST and Spitzer sources.
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Global notes:
Note (G1): The number corresponds to the index in the Spitzer catalog.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Feb-2025