Kavli Affiliate: Gregory Herczeg
| First 5 Authors: , , , ,
| Summary:
Time-domain studies of mid-infrared and submillimeter variability have shown
that at least half of protostars are variable. We present a statistical
analysis of mid-infrared variability among young stellar objects (YSOs) in the
distant, massive star-forming region W51 using NEOWISE data. From a catalog of
81 protostars, 527 disk objects, and 37,687 other sources including diskless
pre-main sequence and evolved contaminants, we identified significant
variability in the 3.4 um (W1) and 4.6 um (W2) bands. Because of W51’s distance
(~5.4 kpc) and extinction, the sample mainly includes intermediate- to
high-mass YSOs (>2 Msun), unlike nearby regions dominated by low-mass stars.
This mass bias may affect the observed variability. In W2, 11.1% of protostars,
7.6% of disk objects, and 0.6% of PMS+E sources showed secular variability,
while 8.6%, 2.3%, and 0.5% showed stochastic variability; similar fractions
were found in W1. The variability fraction and amplitude increase toward
earlier stages. Protostars exhibit high-amplitude stochastic changes likely
driven by dynamic accretion and extinction, whereas disk objects show more
secular patterns-linear, curved, or periodic-possibly due to moderate accretion
variations or disk geometry. Color-magnitude analysis shows that protostars
generally redden as they brighten, consistent with enhanced dust emission or
variable extinction, while disk objects show mixed trends: roughly balanced in
W1 but more often bluer in W2, suggesting reduced extinction or hotspot
modulation. These results highlight distinct mechanisms of variability across
evolutionary stages and demonstrate that mid-infrared monitoring offers key
insight into accretion and disk evolution in young stars.
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