J/ApJS/281/64 Variability in YSOs from unTimely 10yr obs. (Zhang+, 2025)
Mining young stellar objects in unTimely: probing variability and physical
properties.
Zhang J., Zhang Y., Kang Z., Zou Hu, Li C., Fan D., Zhao Y., Shi J.
<Astrophys. J. Suppl. Ser., 281, 64 (2025)>
=2025ApJS..281...64Z 2025ApJS..281...64Z
ADC_Keywords: YSOs; Photometry, infrared; Stars, variable; Extinction;
Effective temperatures; Stars, masses; Stars, ages
Keywords: Young stellar objects ; Pre-main sequence stars ;
Light curve classification ; Time series analysis ; Light curves ;
Time domain astronomy ; Stellar properties ; Stellar physics
Abstract:
We present a comprehensive analysis of variability in young stellar
objects (YSOs) using a decade-long mid-infrared photometric dataset
from the unTimely catalog. With its enhanced sensitivity and extended
temporal coverage compared to previous surveys like NEOWISE, the
catalog enables the detection of subtle variability patterns and
long-term brightness fluctuations in YSOs. We characterize their
variability using 12 statistical features and identify 17,795 variable
YSOs in the W2 band. Through spectral energy distribution fitting, key
physical properties such as mass, age, and luminosity are derived,
revealing evolutionary trends. The YSOs are classified into six types
of variability: linear (0.4%), curved (16.2%), periodic (2.0%), burst
(3.0%), drop (1.0%), and irregular (42.9%), with 15.7% exhibiting
combined secular and irregular behaviors. The extended observational
baseline significantly improves the detection of stochastic phenomena
(e.g., bursts and drops) and complex light-curve morphologies. Our
analysis confirms that the mass-luminosity relation of our sample is
broadly consistent with Padova and Trieste Stellar Evolution Code
pre-main-sequence isochrones; only a small number of low-mass objects
deviate at >3σ, likely reflecting measurement and modeling
uncertainties. Combined with the observed correlation between
variability types and evolutionary stages, these results advance our
understanding of the mechanisms driving the observed brightness
changes.
Description:
In this study, we perform a comprehensive analysis of variable sources
using photometric data from the unTimely catalog
(Meisner+ 2023AJ....165...36M 2023AJ....165...36M).
The unTimely Catalog is built from time-resolved unWISE coadds, which
stack exposures from each 6 month sky pass of the WISE and NEOWISE
missions from 2010 to 2020. It includes data from both the W1 (3.4um)
and W2 (4.6um) bands. Typically, each sky position has 16 distinct
observational epochs per band, with each epoch representing a median
of 12 exposures coadded over approximately 1 day.
Subsequent analysis requires multiband photometric properties,
obtained via positional crossmatching with the following datasets. For
mid-infrared photometry, we utilize the AllWISE (Cutri+ 2013, II/328)
catalog. Additionally, we incorporate data from the Two Micron All Sky
Survey (2MASS) All-Sky Point Source Catalog (see II/246).
See Section 2.3.
We query the SIMBAD database to identify astronomical objects within a
2" radius of each variable source. See Section 3.1.
We also crossmatch our variable sources with the
Kuhn+ (2021, J/ApJS/254/33) Galactic plane catalog (SPICY) containing
120,000 YSO candidates, identified using Spitzer/IRAC observations.
This catalog integrates IRAC photometry from the GLIMPSE survey with
NIR JHKs data from 2MASS, UKIDSS, and VISTA Variables in the Via Lactea.
See Section 3.3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 106 3852 Properties of young stellar objects
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
II/328 : AllWISE Data Release (Cutri+ 2013)
II/363 : The band-merged unWISE Catalog (Schlafly+, 2019)
J/ApJ/743/156 : NEOWISE obs. of NEOs: preliminary results (Mainzer+, 2011)
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/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/224/5 : Herschel Orion Protostar Survey (HOPS): SEDs (Furlan+, 2016)
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)
J/AJ/163/263 : 323 YSOs properties with ZTF (Hillenbrand+, 2022)
J/A+A/686/A269 : Young Stellar Objects from LAMOST & ZTF surveys (Zhang+, 2024)
J/A+A/696/A196 : SED modeling of YSOs in the OSFC (Gezer+, 2025)
J/ApJS/278/10 : WISE color and variability study of SPICY YSOs (Neha+, 2025)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- WISEA ALLWISE identifier (JHHMMSS.ss+DDMMSS.s)
21- 30 F10.6 deg RAdeg Right Ascension from WISE (J2000)
32- 41 F10.6 deg DEdeg [-88/88] Declination from WISE (J2000)
43- 47 F5.2 mag AV [0/48.6] The V band extinction
49- 53 F5.2 mag e_AV [0/20.3] Uncertainty in AV
55- 59 I5 K Teff [2578/13720] YSO effective temperature
61- 63 I3 K e_Teff [59/632] Uncertainty in Teff
65- 69 F5.2 [Lsun] logL [-2.6/3.51] log YSO luminosity
71- 74 F4.2 [Lsun] e_logL [0/3.3] Uncertainty in logL
76- 79 F4.2 Msun Mass [0.02/5.6] YSO mass
81- 86 F6.2 Myr Age [0.5/889.2] YSO age
88- 96 A9 --- VType Light curve classification (1)
98-106 A9 --- CType Combined variability behavior (burst, drop or
irregular)
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Note (1): Light curve classification (scheme introduced by
Park+ 2021, J/ApJ/920/132) as follows:
linear = false-alarm probability of the Lomb-Scargle periodogram (LSP;
FAPLSP) <0.01 and a period >20yr (2x10yr) (28 occurrences)
curved = periods range from 1825 days (5yr) to 7300 days (20yr) with a
false-alarm probability FAPLSP<0.01 (808 occurrences)
periodic = FAPLSP<0.01, with Lomb-Scargle periods between 200 and 1825days
(80 occurrences)
burst = intermittent brightness peaks superimposed on otherwise stable
flux levels: magnitude difference criterion of
|median(m)-min(m)|>0.8xΔW2, where m denotes magnitude
(175 occurrences)
drop = intermittent faintness peaks superimposed on a backdrop of stable
flux: magnitude difference criterion of
|median(m)-max(m)|>0.8xΔW2, where m denotes magnitude
(43 occurrences)
irregular = random light-curve behavior: general variability condition
SD/σ>20, where SD is the standard deviation
(2718 occurrences)
See Section 5.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 30-Jun-2026