Spectropolarimetric approach for measuring magnetic fields on brown dwarfs

Hochschulschrift

Zusammenfassung: This thesis presents a novel approach, based on spectropolarimetry of the CrH molecule, for measuring magnetic fields on low-mass stars and brown dwarfs. Its efficacy is demonstrated using the example of the M8.5 dwarf LSR J1835+3259. It is a representative of a small group of brown dwarfs with radio emission, presumably due to their surprisingly high magnetic activity. Both weak and strong magnetic fields can give rise to radio emission in brown dwarfs through the gyrosynchrotron and the electron-cyclotron maser mechanisms respectively, which however are difficult to separate. The present thesis aspires to resolve this puzzle.The vibrational band (0,0) of the CrH (A-X) electronic system is studied in the presence of a magnetic field. It is shown that, as the magnetic field increases and the electronic states pass from the Zeeman to the Paschen-Back regime, the strengths of the magnetic transitions of different polarization states alter differently. This gives rise to net polarization, which can be used as a sensitive diagnostic of magnetic fields.Polarization spectra of the entire (0,0) band of the CrH molecule is calculated for a range of stellar parameters and magnetic field strengths. It is shown for the first time that in cool stellar atmospheres with a moderate to strong magnetic field (< 0.5 kG) the CrH lines produce a broadband polarimetric signal of a few percent. Furthermore, the shape of this signal strongly depends on the magnetic field strength. Based on this fact, the author of this thesis proposes to use the CrH molecule for measuring magnetic fields on low-mass stars and brown dwarfs.

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Albert-Ludwigs-Universität Freiburg, Dissertation, 2015

Klassifikation und Themen

• Klassifikation: Astronomie, Kartographie
• Schlagwort: Polarimetrie ; Brauner Zwerg ; Molekülphysik ; Magnetfeld

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2015
• Urheber: Kuzmychov, Oleksii
• Beteiligte Personen und Organisationen: Berdyugina, Svetlana

Weitere Informationen

• DOI: 10.6094/UNIFR/10657
• URN: urn:nbn:de:bsz:25-freidok-106570
• Rechteinformation: Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:44 MEZ