J/ApJS/278/10 WISE color and variability study of SPICY YSOs (Neha+, 2025)
Illuminating youth: decades of mid-infrared variability and color evolution of
young stellar objects.
Neha S., Sharma S.
<Astrophys. J. Suppl. Ser., 278, 10 (2025)>
=2025ApJS..278...10N 2025ApJS..278...10N
ADC_Keywords: YSOs; Photometry, infrared; Colors; Stars, variable
Keywords: Young stellar objects ; Star formation
Abstract:
The variability of young stellar objects (YSOs) is a crucial tool for
understanding the mechanisms driving flux changes. In this study, we
present an infrared variability analysis of a large sample of over
20,000 candidate YSOs, using data from the ALLWISE and NEOWISE
surveys, which span around a decade with a 6 month cadence. We applied
Lomb-Scargle periodogram analysis and linear fitting to the light
curves, classifying them into distinct categories: secular (linear,
curved, and periodic) and stochastic (burst, drop, and irregular). Our
findings show that 5467 (26.2%±0.3%) of the sources exhibit
variability, with most (19.7%±0.3%) showing irregular variations,
followed by curved and periodic variations. In addition, 235 burst
sources and 122 drop sources were identified. Variability is more
pronounced in Class I sources with a higher fraction of variables
(36.3%±0.6%) compared to Class II (22.1%±0.4%) and Class III
(22.5%±1.0%) sources. The color (W1-W2) versus magnitude analysis
(W2) using linear fitting shows that the "redder-when-brighter" trend
is more prevalent (85.4%±0.5%) among YSOs. In contrast, the
"bluer-when-brighter" (BWB) trend is more common in younger sources
compared to more evolved ones, having a BWB fraction of 29.0%±1.1%
for Class I to 4.0%±0.9% for Class III.
Description:
We used the Spitzer/Infrared Array Camera (IRAC) Candidate YSOs
(SPICY) catalog of Kuhn+ (2021, J/ApJS/254/33), which includes
117,446 YSO candidates selected from the Spitzer/IRAC survey. The
sources are between l∼255° and 110° in the Galactic midplane.
Since we aim to study the infrared variability, we crossmatched all
these sources in the Wide-field Infrared Survey Explorer (WISE)
catalog with a search radius of 2". The coordinate search of the
sources with the WISE database resulted in 42,501 sources for further
analysis.
We performed an infrared color and variability study of a final sample
of 20,893 candidate YSOs using the SPICY catalog and archival data
from the WISE survey consisting of data from both the ALLWISE and
NESOWISE spanning about a decade with a typical 6 month cadence.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 213 20893 Variability statistics of individual objects
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See also:
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
II/328 : AllWISE Data Release (Cutri+ 2013)
II/363 : The band-merged unWISE Catalog (Schlafly+, 2019)
II/365 : The CatWISE2020 catalog (updated version 28-Jan-2021) (Marocco+, 2021)
J/AJ/121/3160 : JHK photometry near the Trapezium region (Carpenter+, 2001)
J/ApJ/733/50 : Mid-IR phot. monitoring of the ONC (Morales-Calderon+, 2011)
J/A+A/557/A77 : VR light curves of AA Tau in 2007-2013 (Bouvier+, 2013)
J/AJ/145/59 : Opt. and mid-IR photometry of PTF 10nvg (Hillenbrand+, 2013)
J/AJ/147/82 : Monitoring of disk-bearing stars in NGC 2264 (Cody+, 2014)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/ApJS/211/3 : NIR photometry variability in ρ Oph (Parks+, 2014)
J/AJ/150/132 : JHK photometry of 1203 variables in ONC (Rice+, 2015)
J/MNRAS/465/3011 : VVV high amplitude NIR var. stars (Contreras Pena+, 2017)
J/ApJ/854/170 : Methanol (CH3OH) & OH masers in NGC 6334I (Hunter+, 2018)
J/AJ/155/99 : IR var. among YSOs in Serpens South cluster (Wolk+, 2018)
J/ApJ/883/6 : WISE LCs of Red MSX massive YSOs (Uchiyama+, 2019)
J/MNRAS/495/3614 : IR and sub-mm variability in protostars (Contreras+, 2020)
J/ApJS/254/33 : Gal. midplane Spitzer/IRAC cand. YSOs (SPICY) (Kuhn+, 2021)
J/ApJ/920/132 : NEOWISE 6.5yr variability in YSOs (Park+, 2021)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- WISEA YSO name (JHHMMSS.ss+DDMMSS.s) (1)
21- 30 F10.6 deg RAdeg [125.6/346.5] Right Ascension (J2000) (1)
32- 41 F10.6 deg DEdeg [-64/62.3] Declination (J2000) (1)
43- 47 F5.2 --- SED [-2.6/4.8]? Spectral index for YSO class (1)
49- 57 A9 --- Class YSO class (1)
59- 60 I2 --- Np [16/21] Number of data points in WISE W2
band light curve
62- 66 F5.2 mag W2magAvg [6/13.7] Mean magnitude in WISE W2 band
light curve
68- 72 F5.2 mag W2magMed [5.8/13.7] Median magnitude in WISE W2 band
light curve
74- 81 E8.2 --- sigW2Flux [0.016/601] Standard deviation (flux) in
WISE W2 band light curve
83- 90 E8.2 --- errW2Flux [0.096/81.1] Uncertainty (flux) in WISE W2
band light curve
92- 95 F4.2 mag delW2mag [0.02/3.8] Magnitude difference between
brightest and faintest mag
97- 105 F9.4 d Period [199/8334] Lomb-Scargle periodogram
(LSP) period (see Section 3.1)
107- 115 E9.3 --- FLP [0/1] Flase alarm probability in LSP
bootstrapping
117- 126 E10.3 --- slope [-0.22/0.18] Slope in linear fit to the
light curve
128- 136 E9.3 --- e_slope [1.8e-05/0.2] Uncertainty in slope
138- 143 F6.3 --- r-value [-0.99/0.98] Spearman rank correction
coefficient of slope
145- 149 F5.3 --- e_r-value [0.006/0.5] Uncertainty in r-value
151- 159 E9.3 --- p-value [1.1e-11/0.7] p-value of Slope
161- 169 E9.3 --- e_p-value [1e-10/0.4] Uncertainty in p-value
171- 177 F7.2 --- W1-W2slope [-350.5/41.5] Slope in color (W1-W2) vs
magnitude W2 diagram
179- 186 F8.2 --- e_W1-W2slope [0.01/12620] Uncertainty in W1-W2slope
188- 193 F6.3 --- Rank [-1/0.99] Pearson rank correlation
coefficient of slope-color
195- 203 E9.3 --- p-valueCol [4.5e-18/1] P-value of slope-color
205- 213 A9 --- LCType Type of Light curve (2)
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Note (1): Taken from Kuhn+ 2021, J/ApJS/254/33 ( in Simbad)
Note (2): Type of light curve as follows:
Linear = (216 occurrences)
Curved = (589 occurrences)
Periodic = (190 occurrences)
Burst = (235 occurrences)
Drop = (122 occurrences)
Irregular = (4115 occurrences)
NV = Non-variable (15426 occurrences)
See Table 1.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Feb-2026