Planned intervention: On Wednesday April 3rd 05:30 UTC Zenodo will be unavailable for up to 2-10 minutes to perform a storage cluster upgrade.
Published August 9, 2017 | Version v1
Presentation Open

Exploring the Time Evolution of Cool Metallic Absorption Features in UV Burst Spectra

  • 1. Pacific Lutheran University

Contributors

  • 1. Harvard-Smithsonian Center for Astrophysics

Description

UV bursts are compact brightenings in active regions that appear in UV images. They are identified through three spectroscopic features: (1) broadening and intensification of NUV/FUV emission lines, (2) the presence of optically thin Si IV emission, and (3) the presence of absorption features from cool metallic ions. Properties (2) and (3) imply that bursts exist at transition region temperatures (≥ 80,000 K) but are located in the cooler lower chromosphere (~ 5,000 K). Their energetic and dynamical properties remain poorly constrained. Improving our understanding of this phenomena could help us further constrain the energetic and dynamical properties of the chromosphere, as well as give us insight into whether or not UV bursts contribute to chromospheric and/or coronal heating. We analyzed the time evolution of UV bursts using spectral data from the Interface Region Imaging Spectrograph (IRIS). We inspected Si IV 1393.8 Å line profiles for Ni II 1393.3 Å absorption features to look for signs of heating. Weakening of absorption features over time could indicate heating of the cool ions above the burst, implying that thermal energy from the burst could rapidly conduct upward through the chromosphere. To detect the spectral profiles corresponding to bursts, we applied a four-parameter Gaussian fit to every profile in each observation and took cuts in parameter space to isolate the bursts. We then manually reviewed the remaining profiles by looking for a statistically significant appearance of Ni II 1393.3 Å absorption. We quantified these absorption features by normalizing the Si IV 1393.8 Å emission profiles and measuring the maximum fractional extinction in each. Our preliminary results indicate that Ni II 1393.3 Å absorption may undergo a cycle of strengthening and weakening throughout a burst’s lifetime. However, further investigation is needed for confirmation.

Notes

This work is supported by the NSF-REU solar physics program at SAO, grant number AGS-1560313.

Files

Belmes_presentation.pdf

Files (108.3 MB)

Name Size Download all
md5:0e9b78f152468ee1336bdab49b197e7e
4.9 MB Preview Download
md5:2f47fd8395494d00fa1c31fedf441b06
32.7 MB Download
md5:e1e0cbb15cb2c81c0560c414dc45e228
70.8 MB Download