| dc.contributor.advisor | Reiners, Ansgar Prof. Dr. | |
| dc.contributor.author | Johnson, Erik N. | |
| dc.date.accessioned | 2024-07-17T08:46:00Z | |
| dc.date.available | 2024-07-24T00:50:07Z | |
| dc.date.issued | 2024-07-17 | |
| dc.identifier.uri | http://resolver.sub.uni-goettingen.de/purl?ediss-11858/15376 | |
| dc.identifier.uri | http://dx.doi.org/10.53846/goediss-10619 | |
| dc.format.extent | 161 | de |
| dc.language.iso | eng | de |
| dc.rights.uri | http://creativecommons.org/licenses/by/4.0/ | |
| dc.subject.ddc | 530 | de |
| dc.title | Stellar Activity and Radial Velocities in M Dwarfs | de |
| dc.type | doctoralThesis | de |
| dc.contributor.referee | Dreizler, Stefan Prof. Dr. | |
| dc.date.examination | 2024-06-28 | de |
| dc.subject.gok | Physik (PPN621336750) | de |
| dc.description.abstracteng | Stellar activity is one of the principal obstacles to achieving sub 1 m/s radial velocity
precision in exoplanet detection surveys. Understanding how stellar activity affects the
stellar environment is crucial to mitigating or eliminating unexpected radial velocity excursions
that mask planetary signals. We look at the two extreme ends of stellar activity
in M dwarfs.
First, we characterize over 14,000 spectra from 345 M dwarfs of the CARMENES1
Guaranteed Time Observations (GTO) sample and quantify a quiet sample within that
set of stars. We were able to reduce the interfering effects of molecular line continuum
contamination on measurement methods by normalizing the effect out. In so doing we
developed a new measurement method, the Molecular Normalized Index (MNI). This allowed
us to detail the behavior of Ca II IRT (InfraRed Triplet), Hα, Na I D1&2, and He I D3
from the quietest stars to the point where emission in these profiles becomes dominant.
We found that Hα profiles can be well explained by the combination of an emission and
absorption profile. From this we also noticed a significant gap separating out the low
activity stars, with Hα profiles in absorption or with low wing emission, from emission
profile stars. This gap may be related to the rapid spin down hypothesis. We observed
that, for the quietest stars, the Hα absorption strongly correlates with stellar effective
temperature. Given the prevailing thought that Hα in M dwarfs should respond to stellar
activity induced chromospheric heating by first becoming more absorptive before filling
in and going into emission, this strong correlation with effective temperature for the maximally
absorptive stars should not occur. We also find no evidence for this initial increase
in Hα absorption. We therefore present a modified model in which the Hα absorption
that correlates with the effective temperature is due to a basal amount of chromospheric
heating that is unlikely to be related to the heating by stellar activity that causes Hα emission.
The result of this is that as a quiet star gains active chromospheric regions the wider
Hα emission profile of these regions will combine with the Hα absorption from what
remains of the quiet chromosphere.
Second, we examine the extreme other end of stellar activity in M dwarfs by examining
the extremely active, young, rapidly rotating star, GJ 3270. We simultaneously observed
this star for a total of 7.7 h with photometric and spectroscopic instruments. We combined
our data with TESS observations conducted roughly one month prior to our observation
period. We found two large flares during our observation period, one of which released
3.6 × 10^32 erg of energy and had a post-flare co-rotating feature. We tracked this feature
for 90 minutes through the asymmetries it caused in the chromospheric activity indicators.
We concluded that this feature was likely similar to post-flare arcadal loops on the Sun.
To sum up our results we found that the chromosphere of M dwarfs is likely heated by
a mechanism that is not related to stellar activity and on active M dwarfs that individual
active regions can be tracked as they rotate across the stellar disk. | de |
| dc.contributor.coReferee | Peter, Hardi Prof. Dr. | |
| dc.contributor.thirdReferee | Hatzes, Artie Prof. Dr. | |
| dc.subject.eng | stars: activity | de |
| dc.subject.eng | stars: flare | de |
| dc.subject.eng | stars: chromospheres | de |
| dc.subject.eng | stars: late-type | de |
| dc.subject.eng | stars: rotation | de |
| dc.subject.eng | star: GJ3270 | de |
| dc.subject.eng | stars: solar neighborhood | de |
| dc.subject.eng | stars: low mass | de |
| dc.subject.eng | techniques: radial velocities | de |
| dc.subject.eng | techniques: spectroscopic | de |
| dc.subject.eng | techniques: photometric | de |
| dc.identifier.urn | urn:nbn:de:gbv:7-ediss-15376-0 | |
| dc.affiliation.institute | Fakultät für Physik | de |
| dc.description.embargoed | 2024-07-24 | de |
| dc.identifier.ppn | 1895791367 | |
| dc.notes.confirmationsent | Confirmation sent 2024-07-17T09:15:01 | de |