Stellar active regions, including spots and faculae, can create radial velocity (RV) signals that interfere with the detection and mass measurements of low-mass exoplanets. In doing so, these active regions affect each spectral line differently, but the origin of these differences is not fully understood. Here we explore how spectral line variability correlated with S-index (Ca H and K emission) is related to the atomic properties of each spectral line. Next, we develop a simple analytic stellar atmosphere model that can account for the largest sources of line variability with S-index. Then, we apply this model to HARPS spectra of
Aside from the well-studied sodium doublet, the potassium D lines are the only optical emissions in Mercury's exosphere that are amply bright to contrast with the dayside disk. Measurements of the K exosphere are limited compared to Na, but the K regolith abundance is better constrained, so new insights may help to understand surface–exosphere coupling. We use imaging spectroscopy to map the K brightness over Mercury's evening hemisphere, which shows an enhancement at low to midlatitudes, well equatorward of the Na peak. Both Na and K are brighter in the south, but the ratio between northern and southern hemisphere K emission appears less symmetric than that of Na. The disk-averaged Na/K column density ratio is between 70 and 130. During the same night, the dayside emission was mapped, we used a high-resolution spectrograph to attempt to resolve the Na and K line widths on the nightside. Forward-modeling the alkaline line profiles with hyperfine structure gives Na D1 and D2 line widths of 1114 ± 50 K and 1211 ± 45 K, respectively. D2 may appear hotter solely because its higher opacity adds preferentially to the profile wings. The K line width is surprisingly cold and cannot be easily distinguished from the instrumental line width, even at
- NSF-PAR ID:
- 10366395
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Planetary Science Journal
- Volume:
- 3
- Issue:
- 4
- ISSN:
- 2632-3338
- Format(s):
- Medium: X Size: Article No. 87
- Size(s):
- Article No. 87
- Sponsoring Org:
- National Science Foundation
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