Shulyak, Denis V.

[["dc.bibliographiccitation.firstpage","4094"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Monthly Notices of the Royal Astronomical Society"],["dc.bibliographiccitation.lastpage","4104"],["dc.bibliographiccitation.volume","445"],["dc.contributor.author","Fossati, Luca"],["dc.contributor.author","Kolenberg, Katrien"],["dc.contributor.author","Shulyak, Denis V."],["dc.contributor.author","Elmasli, A."],["dc.contributor.author","Tsymbal, V."],["dc.contributor.author","Barnes, T. G."],["dc.contributor.author","Guggenberger, Elisabeth"],["dc.contributor.author","Kochukhov, Oleg"],["dc.date.accessioned","2018-11-07T09:31:09Z"],["dc.date.available","2018-11-07T09:31:09Z"],["dc.date.issued","2014"],["dc.description.abstract","The stellar parameters of RR Lyrae stars vary considerably over a pulsation cycle, and their determination is crucial for stellar modelling. We present a detailed spectroscopic analysis of the pulsating star RR Lyr, the prototype of its class, over a complete pulsation cycle, based on high-resolution spectra collected at the 2.7-m telescope of McDonald Observatory. We used simultaneous photometry to determine the accurate pulsation phase of each spectrum and determined the effective temperature, the shape of the depth-dependent microturbulent velocity, and the abundance of several elements, for each phase. The surface gravity was fixed to 2.4. Element abundances resulting from our analysis are stable over the pulsation cycle. However, a variation in ionization equilibrium is observed around minimum radius. We attribute this mostly to a dynamical acceleration contributing to the surface gravity. Variable turbulent convection on time-scales longer than the pulsation cycle has been proposed as a cause for the Blazhko effect. We test this hypothesis to some extent by using the derived variable depth-dependent microturbulent velocity profiles to estimate their effect on the stellar magnitude. These effects turn out to be wavelength dependent and much smaller than the observed light variations over the Blazhko cycle: if variations in the turbulent motions are entirely responsible for the Blazhko effect, they must surpass the scales covered by the microturbulent velocity. This work demonstrates the possibility of a self-consistent spectroscopic analysis over an entire pulsation cycle using static atmosphere models, provided one takes into account certain features of a rapidly pulsating atmosphere."],["dc.identifier.doi","10.1093/mnras/stu2044"],["dc.identifier.isi","000346963300058"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31475"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Oxford Univ Press"],["dc.relation.issn","1365-2966"],["dc.relation.issn","0035-8711"],["dc.title","An in-depth spectroscopic analysis of RR Lyr Variations over the pulsation cycle"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","2548"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Monthly Notices of the Royal Astronomical Society"],["dc.bibliographiccitation.lastpage","2557"],["dc.bibliographiccitation.volume","418"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Seifahrt, Andreas"],["dc.contributor.author","Reiners, Ansgar"],["dc.contributor.author","Kochukhov, Oleg"],["dc.contributor.author","Piskunov, Nikolai E."],["dc.date.accessioned","2018-11-07T08:49:03Z"],["dc.date.available","2018-11-07T08:49:03Z"],["dc.date.issued","2011"],["dc.description.abstract","Close M dwarf binaries and higher multiples allow the investigation of rotational evolution and mean magnetic flux unbiased from scatter in inclination angle and age since the orientation of the spin axis of the components is most likely parallel and the individual systems are coeval. Systems composed of an early-type (M0.0-M4.0) and a late-type (M4.0-M8.0) component offer the possibility to study differences in rotation and magnetism between partially and fully convective stars. We have selected 10 of the closest dM systems to determine the rotation velocities and the mean magnetic field strengths based on spectroscopic analysis of FeH lines of Wing-Ford transitions at 1 mu m observed with Very Large Telescope/CRIRES. We also studied the quality of our spectroscopic model regarding atmospheric parameters including metallicity. A modified version of the Molecular Zeeman Library (MZL) was used to compute Landeg-factors for FeH lines. Magnetic spectral synthesis was performed with the synmast code. We confirmed previously reported findings that less massive M dwarfs are braked less effectively than objects of earlier types. Strong surface magnetic fields were detected in primaries of four systems (GJ 852, GJ 234, LP 717-36 and GJ 3322), and in the secondary of the triple system GJ 852. We also confirm strong 2-kG magnetic field in the primary of the triple system GJ 2005. No fields could be accurately determined in rapidly rotating stars with nu sin i > 10 km s(-1). For slowly and moderately rotating stars, we find the surface magnetic field strength to increase with the rotational velocity nu sin i which is consistent with other results from studying field stars."],["dc.identifier.doi","10.1111/j.1365-2966.2011.19644.x"],["dc.identifier.isi","000298088100036"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/21363"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-blackwell"],["dc.relation.issn","0035-8711"],["dc.title","Rotation, magnetism and metallicity of M dwarf systems"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A88"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","520"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Ryabchikova, Tanya"],["dc.contributor.author","Kildiyarova, R."],["dc.contributor.author","Kochukhov, Oleg"],["dc.date.accessioned","2018-11-07T08:39:29Z"],["dc.date.available","2018-11-07T08:39:29Z"],["dc.date.issued","2010"],["dc.description.abstract","Aims. Among the known Ap stars, HD 101065 is probably one of the most interesting objects, demonstrating very rich spectra of rare-earth elements (REE). Strongly peculiar photometric parameters of this star can not be fully reproduced by any modern theoretical calculations, even those accounting for realistic chemistry of its atmosphere. In this study we investigate a role of missing REE line opacity and construct a self-consistent atmospheric model based on accurate abundance and chemical stratification analysis. Methods. We employed the LLMODELS stellar model atmosphere code together with DDAFIT and SYNTHMAG software packages to derive homogeneous and stratified abundances for 52 chemical elements and to construct a self-consistent model of HD 101065 atmosphere. The opacity in REE lines is accounted for in details, by using up-to-date extensive theoretical calculations. Results. We show that REE elements play a key role in the radiative energy balance in the atmosphere of HD 101065, leading to the strong suppression of the Balmer jump and energy redistribution very different from that of normal stars. Introducing new line lists of REEs allowed us to reproduce, for the first time, spectral energy distribution of HD 101065 and achieve a better agreement between the unusually small observed Stromgren c(1) index and the model predictions. Using combined photometric and spectroscopic approaches and based on the iterative procedure of abundance and stratification analysis we find effective temperature of HD 101065 to be T(eff) = 6400 K."],["dc.identifier.doi","10.1051/0004-6361/200913750"],["dc.identifier.fs","581149"],["dc.identifier.isi","000283064200095"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9685"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/19008"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Realistic model atmosphere and revised abundances of the coolest Ap star HD 101065"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","428"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","441"],["dc.bibliographiccitation.volume","338"],["dc.contributor.author","Kochukhov, Oleg"],["dc.contributor.author","Petit, P."],["dc.contributor.author","Strassmeier, K. G."],["dc.contributor.author","Carroll, T. A."],["dc.contributor.author","Fares, R."],["dc.contributor.author","Folsom, C. P."],["dc.contributor.author","Jeffers, Sandra V."],["dc.contributor.author","Korhonen, H."],["dc.contributor.author","Monnier, J. D."],["dc.contributor.author","Morin, Julien"],["dc.contributor.author","Rosen, L."],["dc.contributor.author","Roettenbacher, R. M."],["dc.contributor.author","Shulyak, D."],["dc.date.accessioned","2018-11-07T10:24:19Z"],["dc.date.available","2018-11-07T10:24:19Z"],["dc.date.issued","2017"],["dc.description.abstract","Magnetic fields are essential ingredients of many physical processes in the interiors and envelopes of cool stars. Yet their direct detection and characterization is notoriously difficult, requiring high-quality observations and advanced analysis techniques. Significant progress has been recently achieved by several types of direct magnetic field studies on the surfaces of cool, active stars. In particular, complementary techniques of field topology mapping with polarization data and total magnetic flux measurements from intensity spectra have been systematically applied to different classes of active stars, leading to interesting and occasionally controversial results. In this paper, we summarize the current status of direct magnetic field studies of cool stars and investigations of surface inhomogeneities caused by the field, based on the material presented at the Cool Stars 19 splinter session."],["dc.identifier.doi","10.1002/asna.201713310"],["dc.identifier.isi","000400944700007"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/42634"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","PUB_WoS_Import"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","1521-3994"],["dc.relation.issn","0004-6337"],["dc.title","Surface magnetism of cool stars"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A151"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","537"],["dc.contributor.author","Nesvacil, N."],["dc.contributor.author","Lueftinger, T."],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Obbrugger, M."],["dc.contributor.author","Weiss, W."],["dc.contributor.author","Drake, N. A."],["dc.contributor.author","Hubrig, S."],["dc.contributor.author","Ryabchikova, Tanya"],["dc.contributor.author","Kochukhov, Oleg"],["dc.contributor.author","Piskunov, Nikolai E."],["dc.contributor.author","Polosukhina, N."],["dc.date.accessioned","2018-11-07T09:15:34Z"],["dc.date.available","2018-11-07T09:15:34Z"],["dc.date.issued","2012"],["dc.description.abstract","Context. In atmospheres of magnetic main-sequence stars, the diffusion of chemical elements leads to a number of observed anomalies, such as abundance spots across the stellar surface. Aims. The aim of this study was to derive a detailed picture of the surface abundance distribution of the magnetic chemically peculiar star HD 3980. Methods. Based on high-resolution, phase-resolved spectroscopic observations of the magnetic A-type star HD 3980, the inhomogeneous surface distribution of 13 chemical elements (Li, O, Si, Ca, Cr, Mn, Fe, La, Ce, Pr, Nd, Eu, and Gd) has been reconstructed. The INVERS12 code was used to invert the rotational variability in line profiles to elemental surface distributions. Results. Assuming a centered, dominantly dipolar magnetic field configuration, we find that Li, O, Mg, Pr, and Nd are mainly concentrated in the area of the magnetic poles and depleted in the regions around the magnetic equator. The high abundance spots of Si, La, Ce, Eu, and Gd are located between the magnetic poles and the magnetic equator. Except for La, which is clearly depleted in the area of the magnetic poles, no obvious correlation with the magnetic field has been found for these elements otherwise. Ca, Cr, and Fe appear enhanced along the rotational equator and the area around the magnetic poles. The intersection between the magnetic and the rotational equator constitutes an exception, especially for Ca and Cr, which are depleted in that region. Conclusions. No obvious correlation between the theoretically predicted abundance patterns and those determined in this study could be found. This can be attributed to a lack of up-to-date theoretical models, especially for rare earth elements."],["dc.identifier.doi","10.1051/0004-6361/201117097"],["dc.identifier.fs","596778"],["dc.identifier.isi","000300416800151"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9586"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/27720"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Multi-element Doppler imaging of the CP2 star HD 3980"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","48"],["dc.bibliographiccitation.issue","1-2"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","52"],["dc.bibliographiccitation.volume","334"],["dc.contributor.author","Morin, Julien"],["dc.contributor.author","Jardine, M."],["dc.contributor.author","Reiners, Ansgar"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Beeck, Benjamin"],["dc.contributor.author","Hallinan, G."],["dc.contributor.author","Hebb, L."],["dc.contributor.author","Hussain, G. A. J."],["dc.contributor.author","Jeffers, Sandra V."],["dc.contributor.author","Kochukhov, Oleg"],["dc.contributor.author","Vidotto, A."],["dc.contributor.author","Walkowicz, Lucianne M."],["dc.date.accessioned","2018-11-07T09:28:17Z"],["dc.date.available","2018-11-07T09:28:17Z"],["dc.date.issued","2013"],["dc.description.abstract","Magnetic fields are regarded as a crucial element for our understanding of stellar physics. They can be studied with a variety of methods which provide complementary - and sometimes contradictory - information about the structure, strength and dynamics of the magnetic field and its role in the evolution of stars. Stellar magnetic fields can be investigated either with direct methods based on the Zeeman effect or through the observation of activity phenomena resulting from the interaction of the field with the stellar atmosphere. In this Cool Stars 17 Splinter Session we discussed the results obtained by the many ongoing studies of stellar activity and direct studies of surface magnetic fields, as well as the state-of-the-art techniques on which they are based. We show the strengths and limitations of the various approaches currently used and point out their evolution as well as the interest of coupling various magnetism and activity proxies. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim"],["dc.description.sponsorship","Alexander von Humboldt foundation"],["dc.identifier.doi","10.1002/asna.201211771"],["dc.identifier.isi","000325859900012"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30735"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","1521-3994"],["dc.relation.issn","0004-6337"],["dc.title","Multiple views of magnetism in cool stars"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A14"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","551"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Ryabchikova, Tanya"],["dc.contributor.author","Kochukhov, Oleg"],["dc.date.accessioned","2018-11-07T09:27:21Z"],["dc.date.available","2018-11-07T09:27:21Z"],["dc.date.issued","2013"],["dc.description.abstract","Aims. As a well-established procedure for the vast majority of normal main-sequence stars, determination of atmospheric and stellar parameters turns to be a challenging process in case of magnetic chemically peculiar stars. Inhomogeneous distribution of chemical elements and strong magnetic fields make most of the standard photometric and spectroscopic calibrations inapplicable for this class of stars. In this work we make use of available observed energy distributions calibrated to absolute units, stellar parallaxes, high-resolution spectroscopic observations, and advanced stellar atmosphere models to derive parameters of three bright Ap stars: 33 Lib, gamma Equ, and beta CrB. Methods. Model atmospheres and fluxes were computed with the LLmodels code. SYNTH3 and SYNTHMAG codes were used to compute profiles of individual spectral lines involved in abundance analysis. Results. For each of the stars, we construct a self-consistent atmospheric models assuming normal and depleted helium compositions and derive empirically stratification profiles of certain elements. The effective temperatures and surface gravities are found from the simultaneous fit to spectroscopic, photometric, and spectrophotometric observations calibrated to absolute units. We show that using advanced model atmospheres and accurate stellar parallaxes allows one to derive stellar radii with high accuracy, and these are consistent with those obtained from independent but more complicated interferometric observations."],["dc.identifier.doi","10.1051/0004-6361/201220425"],["dc.identifier.isi","000316460600014"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10021"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30512"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Fundamental parameters of bright Ap stars from wide-range energy distributions and advanced atmospheric models"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A35"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","563"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Reiners, Ansgar"],["dc.contributor.author","Seemann, U."],["dc.contributor.author","Kochukhov, Oleg"],["dc.contributor.author","Piskunov, Nikolai E."],["dc.date.accessioned","2018-11-07T09:43:00Z"],["dc.date.available","2018-11-07T09:43:00Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. Magnetic fields play a pivotal role in the formation and evolution of low-mass stars, but the dynamo mechanisms generating these fields are poorly understood. Measuring cool star magnetism is a complicated task because of the complexity of cool star spectra and the subtle signatures of magnetic fields. Aims. Based on detailed spectral synthesis, we carry out quantitative measurements of the strength and complexity of surface magnetic fields in the four well-known M dwarfs GJ 388, GJ 729, GJ 285, and GJ 406 that populate the mass regime around the boundary between partially and fully convective stars. Very high-resolution (R = 100 000), high signal-to-noise (up to 400), near-infrared Stokes I spectra were obtained with CRIRES at ESO's Very Large Telescope covering regions of the FeH Wing-Ford transitions at 1 mu m and Na I lines at 2.2 mu m. Methods. A modified version of the Molecular Zeeman Library (MZL) was used to compute Lande g-factors for FeH lines. We determined the distribution of magnetic fields by magnetic spectral synthesis performed with the SYNMAST code. We tested two different magnetic geometries to probe the influence of field orientation effects. Results. Our analysis confirms that FeH lines are excellent indicators of surface magnetic fields in low-mass stars of type M, particularly in comparison to profiles of Na I lines that are heavily affected by water lines and that suffer problems with continuum normalization. The field distributions in all four stars are characterized by three distinct groups of field components, and the data are consistent neither with a smooth distribution of different field strengths nor with one average field strength covering the full star. We find evidence of a subtle difference in the field distribution of GJ 285 compared to the other three targets. GJ 285 also has the highest average field of 3.5 kG and the strongest maximum field component of 7-7.5 kG. The maximum local field strengths in our sample seem to be correlated with rotation rate. While the average field strength is saturated, the maximum local field strengths in our sample show no evidence of saturation. Conclusions. We find no difference between the field distributions of partially and fully convective stars. The one star with evidence of field distribution different from the other three is the most active star (i.e. with X-ray luminosity and mean surface magnetic field) rotating relatively fast. A possible explanation is that rotation determines the distribution of surface magnetic fields, and that local field strengths grow with rotation even in stars in which the average field is already saturated."],["dc.identifier.doi","10.1051/0004-6361/201322136"],["dc.identifier.fs","609676"],["dc.identifier.isi","000333798000035"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10910"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/34081"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Exploring the magnetic field complexity in M dwarfs at the boundary to full convection"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1629"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Monthly Notices of the Royal Astronomical Society"],["dc.bibliographiccitation.lastpage","1642"],["dc.bibliographiccitation.volume","443"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Paladini, C."],["dc.contributor.author","Li Causi, G."],["dc.contributor.author","Perraut, K."],["dc.contributor.author","Kochukhov, Oleg"],["dc.date.accessioned","2018-11-07T09:35:19Z"],["dc.date.available","2018-11-07T09:35:19Z"],["dc.date.issued","2014"],["dc.description.abstract","By means of numerical experiments we explore the application of interferometry to the detection and characterization of abundance spots in chemically peculiar (CP) stars using the brightest star epsilon UMa as a case study. We find that the best spectral regions to search for spots and stellar rotation signatures are in the visual domain. The spots can clearly be detected already at a first visibility lobe and their signatures can be uniquely disentangled from that of rotation. The spots and rotation signatures can also be detected in near-infrared at low spectral resolution but baselines longer than 180 m are needed for all potential CP candidates. According to our simulations, an instrument like VEGA (or its successor e. g. Fibered and spectrally Resolved Interferometric Equipment New Design) should be able to detect, in the visual, the effect of spots and spots+rotation, provided that the instrument is able to measure V-2 approximate to 10(-3), and/or closure phase. In infrared, an instrument like AMBER but with longer baselines than the ones available so far would be able to measure rotation and spots. Our study provides necessary details about strategies of spot detections and the requirements for modern and planned interferometric facilities essential for CP star research."],["dc.identifier.doi","10.1093/mnras/stu1259"],["dc.identifier.isi","000340436800054"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/32358"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Oxford Univ Press"],["dc.relation.issn","1365-2966"],["dc.relation.issn","0035-8711"],["dc.title","Interferometry of chemically peculiar stars: theoretical predictions versus modern observing facilities"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A103"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","552"],["dc.contributor.author","Reiners, Ansgar"],["dc.contributor.author","Shulyak, D."],["dc.contributor.author","Anglada-Escude, Guillem"],["dc.contributor.author","Jeffers, Sandra V."],["dc.contributor.author","Morin, Julien"],["dc.contributor.author","Zechmeister, Mathias"],["dc.contributor.author","Kochukhov, Oleg"],["dc.contributor.author","Piskunov, Nikolai E."],["dc.date.accessioned","2018-11-07T09:26:23Z"],["dc.date.available","2018-11-07T09:26:23Z"],["dc.date.issued","2013"],["dc.description.abstract","Stellar activity signatures such as spots and plages can significantly limit the search for extrasolar planets. Current models of activity-induced radial velocity (RV) signals focus on the impact of temperature contrast in spots according to which they predict the signal to diminish toward longer wavelengths. The Zeeman effect on RV measurements counteracts this: the relative importance of the Zeeman effect on RV measurements should grow with wavelength because the Zeeman displacement itself grows with lambda, and because a magnetic and cool spot contributes more to the total flux at longer wavelengths. In this paper, we model the impact of active regions on stellar RV measurements including both temperature contrast in spots and line broadening by the Zeeman effect. We calculate stellar line profiles using polarized radiative transfer models including atomic and molecular Zeeman splitting over large wavelength regions from 0.5 to 2.3 mu m. Our results show that the amplitude of the RV signal caused by the Zeeman effect alone can be comparable to that caused by temperature contrast; a spot magnetic field of similar to 1000 G can produce a similar RV amplitude as a spot temperature contrast of similar to 1000 K. Furthermore, the RV signal caused by cool and magnetic spots increases with wavelength, in contrast to the expectation from temperature contrast alone. We also calculate the RV signal caused by variations in average magnetic field strength from one observation to the next, for example due to a magnetic cycle, but find it unlikely that this can significantly influence the search for extrasolar planets. As an example, we derive the RV amplitude of the active M dwarf AD Leo as a function of wavelength using data from the HARPS spectrograph. Across this limited wavelength range, the RV signal does not diminish at longer wavelengths but shows evidence for the opposite behavior, consistent with a strong influence of the Zeeman effect. We conclude that the RV signal of active stars does not vanish at longer wavelength but sensitively depends on the combination of spot temperature and magnetic field; in active low-mass stars, it is even likely to grow with wavelength."],["dc.identifier.doi","10.1051/0004-6361/201220437"],["dc.identifier.fs","602592"],["dc.identifier.isi","000317912000102"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10133"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30285"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/279347/EU//WAVELENGTH STANDARDS"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Radial velocity signatures of Zeeman broadening"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]