Investigating the absence of stellar CMEs through solar observations

Coronal Mass Ejections (CMEs) remain a focal point of solar and stellar research due to their significant impact on space weather dynamics and exoplanet habitability. Unfortunately, it has so far proven difficult to measure these events on other stars, with only a handful of confirmed detections.  On the Sun, strong flares (X1-class and above) are almost always accompanied by a CME. This connection has not been found for other stars, where strong flares are regularly detected without a CME counterpart. To investigate this discrepancy we compare resolved solar observations taken from the Swedish 1-m Solar Telescope with disk-integrated Sun-as-a-star observations taken from the HARPS-N solar telescope. We studied two strong X-class flares, one of which was accompanied by a large (halo)CME, and one that was not. While we have successfully detected flare-related signatures in the activity indices and the radial velocity profile in the Sun-as-a-star data, we detect no significant differences between the two flares and no indications of the presence of the CME, despite other works having previously detected CMEs in Sun-as-a-star data. We propose that the absence of CME signatures in our data is due to a geometric effect. CMEs far enough away from the disk center are likely to be oriented in such a way that they have limited line-of-sight velocity, and thus cannot produce a strong enough Doppler signature. Therefore, we believe that the lack of observed stellar CMEs is at least partly an observational limitation and does not necessarily represent the underlying physical reality.