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Abstract Solar filaments exist as stable structures for extended periods of time before many of them form the core of a coronal mass ejection (CME). We examine the properties of an erupting filament on 2017 May 29–30 with high-resolution Hei10830 Å and Hαspectra from the Dunn Solar Telescope, full-disk Dopplergrams of Hei10830 Å from the Chromospheric Telescope, and EUV and coronograph data from SDO and STEREO. Pre-eruption line-of-sight velocities from an inversion of Heiwith the HAZEL code exhibit coherent patches of 5 Mm extent that indicate counter-streaming and/or buoyant behavior. During the eruption, individual, aligned threads appear in the Heivelocity maps. The distribution of velocities evolves from Gaussian to strongly asymmetric. The maximal optical depth of Hei10830 Å decreased fromτ= 1.75 to 0.25, the temperature increased by 13 kK, and the average speed and width of the filament increased from 0 to 25 km s−1and 10 to 20 Mm, respectively. All data sources agree that the filament rose with an exponential acceleration reaching 7.4 m s−2that increased to a final velocity of 430 km s−1at 22:24 UT; a CME was associated with this filament eruption. The properties during the eruption favor a kink/torus instability, which requires the existence of a flux rope. We conclude that full-disk chromospheric Dopplergrams can be used to trace the initial phase of on-disk filament eruptions in real time, which might potentially be useful for modeling the source of any subsequent CMEs.
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This content will become publicly available on August 5, 2026
A Multispecies Atmospheric Escape Model with Excited Hydrogen and Helium: Application to HD209458b
Abstract Atmospheric escape shapes exoplanet evolution and star–planet interactions, with HeI10830 Å absorption serving as a key tracer of mass loss in hot gas giants. However, transit depths vary significantly across observed systems for reasons that remain poorly understood. HD209458b, the archetypal hot-Jupiter, exhibits relatively weak HeI10830 Å and Hαabsorption, which has been interpreted as evidence for a high H/He ratio (98/2), possibly due to diffusive separation. To investigate this possibility and other processes that control these transit depths, we reassess excitation and de-excitation rates for metastable helium and explore the impact of diffusion processes, stellar activity, and tidal forces on the upper atmosphere and transit depths using a model framework spanning the whole atmosphere. Our model reproduces the observed HeItransit depth and Hαupper limit, showing strong diffusive separation. We match the observations assuming a photoelectron efficiency of 20%–40%, depending on the composition of the atmosphere, corresponding to mass-loss rates of 1.9–3 × 1010g s−1. We find that the HeI10830 Å transit depth is sensitive to both stellar activity and diffusion processes, while Hαis largely unaffected due to its strong dependence on Lyαexcitation. These differences may help explain the system-to-system scatter seen in population-level studies of the HeIline. While HeIdata alone may not tightly constrain mass-loss rates or temperatures, they do confirm atmospheric escape and help narrow the viable parameter space when interpreted with physically motivated models. Simultaneous observations of HeI, Hα, and stellar activity indicators provide powerful constraints on upper atmosphere dynamics and composition, even in the absence of full transmission spectra.
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- Award ID(s):
- 1912507
- PAR ID:
- 10653522
- Publisher / Repository:
- IoP Science
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 989
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 68
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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