JWST Observations Reveal Differential Heating in Protostar EC 53 During Burst Cycles
Researchers used NASA's James Webb Space Telescope to observe the young protostar EC 53 across two epochs, detecting absorption features in carbon monoxide and water vapor that vary between quiescent and burst phases. The study found that the CO fundamental and H₂O bending-mode features weaken by a factor of ~2 during bursts, primarily due to changes in continuum emission rather than gas composition changes. These findings suggest that different regions of the inner disk respond differently during episodic accretion cycles, with mass accumulating during quiescence and then efficiently transferring onto the protostar during bursts.
Astronomers analyzed two-epoch JWST observations of EC 53 (V371 Ser), a periodically variable protostar known for distinct quiescent and burst phases. The spectroscopic data revealed absorption in multiple molecular features: CO overtone and fundamental bands, and H₂O stretching and bending modes. Using local thermodynamic equilibrium modeling, the team determined gas temperatures of ~1800 K for the CO overtone and ~1200 K for the CO fundamental, with the hotter gas tracing smaller radii closer to the protostar. While the H₂O stretching-mode absorption showed no clear variability, the CO fundamental and H₂O bending modes weakened significantly during the burst phase. The researchers introduced a "relative veiling" formalism to quantify continuum changes, finding burst-to-quiescent hot-continuum ratios of 2.9±0.2 for the CO overtone and 1.71±0.11 for the CO fundamental. These ratios imply accretion-rate variations of ~3.6 and ~2.0 respectively, suggesting that inner-disk regions at different temperatures and radii respond differently across the burst cycle.
What's missing
The study does not discuss potential limitations in the LTE slab modeling assumptions or how non-LTE effects might affect the derived temperatures and column densities. Additionally, the paper does not address how results from this single source might generalize to other episodically accreting protostars or whether similar observations of other variable protostars exist for comparison.
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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