JWST Observations Reveal Differential Heating in Protostar EC 53 During Burst Cycles
Astronomers used JWST and IGRINS to observe the young protostar EC 53 during both its quiescent and burst phases, finding that CO fundamental and water bending-mode absorption features weaken by roughly a factor of two during bursts. The weakening is attributed primarily to continuum dilution from increased hot emission rather than changes in the absorbing gas itself. The findings shed light on how different radial zones of a protostellar inner disk respond differently during episodic accretion events.
A team of researchers has published two-epoch JWST NIRSpec and MIRI spectroscopic observations of EC 53 (V371 Ser), a well-characterized periodically variable protostar, accepted in The Astrophysical Journal. The spectra captured absorption features in CO overtone (~2.3 µm) and fundamental (~4.6 µm) bands, as well as water stretching (~2.7 µm) and bending (~6.0 µm) modes across quiescent and burst phases. LTE slab modeling indicates gas temperatures of approximately 1800 K for the CO overtone and ~1200 K for the CO fundamental, suggesting the overtone traces hotter gas at smaller disk radii. While the CO fundamental and water bending-mode features weaken by a factor of ~2 during the burst, the water stretching mode shows no compelling variability, and the CO overtone data do not robustly constrain overtone variability. The team introduced a 'relative veiling' formalism—using the quiescent spectrum as an internal reference—to quantify continuum dilution, yielding burst-to-quiescent hot-continuum ratios of 2.9±0.2 (CO overtone) and 1.71±0.11 (CO fundamental). These ratios imply accretion-rate increases of roughly 3.6× and 2.0× respectively, with the discrepancy between the two tracers indicating that inner-disk regions at different temperatures and radii respond differently across the burst cycle. The authors interpret this as evidence for episodic mass buildup in the inner disk during quiescence, followed by more efficient inward transport onto the protostar during the burst.
What's missing
The study relies on only two observational epochs (one quiescent, one burst), which may not capture the full range of variability across multiple burst cycles. The physical mechanism driving the periodicity of EC 53's bursts (e.g., gravitational instability, binary interaction) is not directly constrained by these observations.
What different sources said
- arXiv astro-phCenter
EPISODE II: Variability in the CO and H$_2$O rovibrational absorption lines in a periodically variable protostar EC 53
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