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Magnetic and Chemical Structures in Stellar Atmospheres
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We present an investigation of the magnetic field geometries and inhomogeneous distribution of chemical elements in the atmospheres of peculiar A and B stars. Our study combines high-quality spectroscopic and spectropolarimetric stellar observations with the development and application of novel techniques for theoretical interpretation of the shapes and variability of stellar line profiles. In particular, we extend the method of Doppler imaging to the analysis of spectra in the four Stokes parameters, making it possible to derive detailed and reliable stellar magnetic maps simultaneously with the imaging chemical inhomogeneities.

The magnetic Doppler imaging is applied to study of magnetic topologies and distributions of chemical elements in the peculiar stars α2 CVn and 53 Cam. We found that the magnetic field geometry of 53 Cam is considerably more complex than a low-order multipolar topology, commonly assumed for magnetic A and B stars. Our Doppler imaging analysis also led to a discovery and study of spots of enhanced mercury abundance in the atmosphere of α And, a star where the presence of a global magnetic field is unlikely.

The ESO 3.6-m telescope is used to collect unique, very high spectral- and time-resolution observations of rapidly oscillating peculiar A (roAp) stars and to reveal line profile variations due to stellar pulsations. We present a detailed characterization of the spectroscopic pulsational behaviour and demonstrate a remarkable diversity of pulsations in different spectral lines. The outstanding variability of the lines of rare-earth elements is used to study propagation of pulsation waves through the stellar atmospheres and identify pulsation modes. This analysis led to a discovery of a non-axisymmetric character of pulsations in roAp stars.

Our study of chemical stratification in the atmosphere of the roAp star γ Equ provides a compelling evidence for significant variation of the chemical composition with depth. We find a combined effect of extreme chemical anomalies and a growth of pulsation amplitude in the outermost atmospheric layers to be the most likely origin of the high-amplitude pulsational variations of the lines of rare-earth elements.

Observations of cool magnetic CP stars are obtained with the ESO Very Large Telescope and are used for empirical investigation of the anomalies in the atmospheric temperature structure. We show that the core-wing anomaly of the hydrogen Balmer lines observed in some cool CP stars can be attributed to a hot layer at an intermediate atmospheric depth.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2003. , p. 38
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 832
Keyword [en]
Astronomy, chemically peculiar stars, high-resolution spectroscopy, magnetic fields, Doppler imaging, rapidly oscillating Ap stars
Keyword [sv]
Astronomi
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:uu:diva-3383ISBN: 91-554-5611-1 (print)OAI: oai:DiVA.org:uu-3383DiVA, id: diva2:162583
Public defence
2003-05-22, Häggsalen, Ångströmlaboratoriet, Uppsala, 09:30
Opponent
Supervisors
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
List of papers
1. Doppler imaging of stellar magnetic fields: I. Techniques
Open this publication in new window or tab >>Doppler imaging of stellar magnetic fields: I. Techniques
2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 381, no 2, p. 736-756Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90271 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
2. LTE spectrum synthesis in magnetic stellar atmospheres.: The interagreement of three independent polarised radiative transfer codes
Open this publication in new window or tab >>LTE spectrum synthesis in magnetic stellar atmospheres.: The interagreement of three independent polarised radiative transfer codes
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2001 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 374, no 1, p. 265-279Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90272 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
3. Doppler imaging of stellar magnetic fields: II. Numerical experiments
Open this publication in new window or tab >>Doppler imaging of stellar magnetic fields: II. Numerical experiments
2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 388, no 3, p. 868-888Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90273 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
4. Doppler imaging of stellar magnetic fields
Open this publication in new window or tab >>Doppler imaging of stellar magnetic fields
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2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 389, no 2, p. 420-438Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90274 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
5. Magnetic Doppler imaging of 53 Cameliopardalis in all four Stokes parameters
Open this publication in new window or tab >>Magnetic Doppler imaging of 53 Cameliopardalis in all four Stokes parameters
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2004 In: Astronomy & Astrophysics, Vol. 414, no 4, p. 613-632Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90275 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
6. The variability of the HgII λ3984 line of the mercury-manganese star α Andromedae
Open this publication in new window or tab >>The variability of the HgII λ3984 line of the mercury-manganese star α Andromedae
2002 In: The Astrophysical Journal, ISSN 0004-637X, Vol. 575, no 1, p. 449-460Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90276 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
7. Time-resolved spectroscopy of the roAp star γ Equ
Open this publication in new window or tab >>Time-resolved spectroscopy of the roAp star γ Equ
2001 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 374, no 2, p. 615-628Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90277 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
8. Pulsational and rotational line profile variations of the roAp stars α Cir and HR 3831
Open this publication in new window or tab >>Pulsational and rotational line profile variations of the roAp stars α Cir and HR 3831
2001 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 377, no 2, p. L22-L25Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90278 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
9. Abundance stratification and pulsations in the atmosphere of the roAp star γ Equulei
Open this publication in new window or tab >>Abundance stratification and pulsations in the atmosphere of the roAp star γ Equulei
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2002 In: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 384, no 2, p. 545-553Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90279 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved
10. Interpretation of the core-wing anomaly of Balmer line profiles of cool Ap stars
Open this publication in new window or tab >>Interpretation of the core-wing anomaly of Balmer line profiles of cool Ap stars
2002 In: The Astrophysical Journal, ISSN 0004-637X, Vol. 578, no 1, p. L75-L78Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90280 (URN)
Available from: 2003-04-23 Created: 2003-04-23Bibliographically approved

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