In this section
@article{Christian:2025:1538-3873/ae265b,
author = {Christian, DJ and Keenan, FP and Rose, SJ and Poppenhaeger, K},
doi = {1538-3873/ae265b},
journal = {Publications of the Astronomical Society of the Pacific},
pages = {124201--124201},
title = {The X-Ray Flare Spectrum of HR 1099: The Search for Photopumped Ne <scp>ix</scp> Line Emission},
url = {http://dx.doi.org/10.1088/1538-3873/ae265b},
volume = {137},
year = {2025}
}
TY - JOUR
AB - <jats:title>Abstract</jats:title> <jats:p> We present high resolution X-ray spectroscopy of the active late-type star HR 1099 obtained with the Chandra Low Energy Transmission Grating Spectrometer. A spectrum extracted from the early stages of a flare was created to search for enhanced emission due to line coincidence photopumping at X-ray wavelengths, rather than the usual optical and ultraviolet cases. Specifically, we have identified a scheme where a He-like Ne <jats:sc>ix</jats:sc> line at 11 Å is photopumped by He-like Na <jats:sc>x</jats:sc> , which predicts intensity enhancement in the Ne <jats:sc>ix</jats:sc> 82.76 Å transition under the high electron density and large coronal pathlength conditions found in stellar and solar flares. We previously tentatively identified a Ne <jats:sc>ix</jats:sc> enhancement in a solar flare spectrum, but the result was extremely uncertain. However, Ne <jats:sc>ix</jats:sc> 82.76 Å was detected at the 3-sigma level in the Chandra spectrum, leading to a measured Ne <jats:sc>ix</jats:sc> 82.76/13.45 intensity ratio of 0.21 ± 0.08. By contrast, the theoretical ratio from the CHIANTI database is at most 0.031, indicating an enhancement factor of at least 7 ± 3 for the 82.76 Å line, in agreement with the expected value of ∼7–15 from a photopumping plasma model. This confirms detection, for the first time to our knowledge, of X-ray photopumping in an astrophysical object. We note that the identification of such X-ray photopumping in other spatially unresolved sources provides in principle a new diagnostic for independently determining th
AU - Christian,DJ
AU - Keenan,FP
AU - Rose,SJ
AU - Poppenhaeger,K
DO - 1538-3873/ae265b
EP - 124201
PY - 2025///
SN - 0004-6280
SP - 124201
TI - The X-Ray Flare Spectrum of HR 1099: The Search for Photopumped Ne <scp>ix</scp> Line Emission
T2 - Publications of the Astronomical Society of the Pacific
UR - http://dx.doi.org/10.1088/1538-3873/ae265b
UR - https://doi.org/10.1088/1538-3873/ae265b
VL - 137
ER -
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