Spectropolarimetry of magnetic stars

Mathys, G.; Hubrig, S.

doi:10.1051/aas:1997366

Cited by 175 publications

(138 citation statements)

References 29 publications

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“…2.1). Figure 7 shows that our measurement of HD 188041 (obtained on 2016-10-08) is in line with previous FORS2 values, but higher than those obtained in the 50s and in the 90s by Babcock (1954Babcock ( , 1958; Mathys (1994); Mathys & Hubrig (1997) and phased with the rotation period given by Landstreet & Mathys (2000). A misalignment of the retarder waveplate would cause a decrease of the absolute value of the magnetic field, and could Longitudinal field measurements of the magnetic star HD 188041.…”

Section: Quality Check Of Field Measurements: Galactic Calibrators Ansupporting

confidence: 89%

First constraints on the magnetic field strength in extra-Galactic stars: FORS2 observations of Of?p stars in the Magellanic Clouds

Bagnulo

Nazé

Howarth

et al. 2017

A&A

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Massive O-type stars play a dominant role in our Universe, but many of their properties remain poorly constrained. In the last decade magnetic fields have been detected in all Galactic members of the distinctive Of?p class, opening the door to a better knowledge of all O-type stars. With the aim of extending the study of magnetic massive stars to nearby galaxies, to better understand the role of metallicity in the formation of their magnetic fields and magnetospheres, and to broaden our knowledge of the role of magnetic fields in massive star evolution, we have carried out spectropolarimetry of five extra-Galactic Of?p stars, as well as a couple of dozen neighbouring stars. We have been able to measure magnetic fields with typical error bars from 0.2 to 1.0 kG, depending on the apparent magnitude and on weather conditions. No magnetic field has been firmly detected in any of our measurements, but we have been able to estimate upper limits to the field values of our target stars. One of our targets, 2dFS 936, exhibited an unexpected strengthening of emission lines. We confirm the unusual behaviour of BI 57, which exhibits a 787 d period with two photometric peaks and one spectroscopic maximum. The observed strengthening of the emission lines of 2dFS 936, and the lack of detection of a strong magnetic field in a star with such strong emission lines is at odd with expectations. Together with the unusual periodic behaviour of BI 57, it represents a challenge for the current models of Of?p stars. The limited precision that we obtained in our field measurements (in most cases as a consequence of poor weather) has led to field-strength upper limits that are substantially larger than those typically measured in Galactic magnetic O stars. Further higher precision observations and monitoring are clearly required.

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Section: Quality Check Of Field Measurements: Galactic Calibrators Ansupporting

confidence: 89%

First constraints on the magnetic field strength in extra-Galactic stars: FORS2 observations of Of?p stars in the Magellanic Clouds

Bagnulo

Nazé

Howarth

et al. 2017

A&A

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“…Spectropolarimetric observations were made during the four nights of 1999 February 1-4 with the Cassegrain echelle spectrograph (CASPEC; Mathys & Hubrig 1997) attached to the ESO 3.6 m telescope. A journal of the observations is reported in Table 1.…”

Section: Observationsmentioning

confidence: 99%

Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Chesneau¹,

Moffat²

2002

PUBL ASTRON SOC PAC

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ABSTRACT. In this paper, we report on an attempt to optically detect localized and/or variable magnetic fields in the single O4 I(n)f star z Puppis and in the WC 8 star in the binary star g 2 Velorum with the spectropolarimeter Cassegrain echelle spectrograph mounted on the ESO 3.6 m telescope. The spectra cover 5700-6800 Å with resolution element 0.2 Å . These stars are sufficiently bright in principle to obtain Stokes V spectra with excellent signal-to-noise ratio and temporal resolution at this telescope. We discuss several procedures adapted to the extraction of the polarized signal from broad lines to put constraints on the global and local magnetic fields. Despite some instrumental difficulties, we report a null longitudinal component of the global magnetic field measurement in z Pup with G. We also find no significant activity in Stokes V above in10 minutes in z Puppis's observable photospheric lines, in a spectral bandpass of 0.2-3 Å . We also report a null detection above for the emission lines of g Vel. Spectral variability in natural light for these stars is 3j ∼ 0.3% V also discussed. Finally, we discuss the potential of such spectropolarimetric techniques in the context of newgeneration spectropolarimeters.

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“…The variability period found by Preston (1972) was confirmed by photometric observations by Wolff & Morrison (1973). Many studies of the magnetic field of HD 24712 have been carried out (Preston 1972;Brown & Landstreet 1981;Mathys 1991Mathys , 1994Mathys & Hubrig 1997;Ryabchikova et al 1997;Leone et al 2000;Wade et al 2000a;Leone & Catanzaro 2004;Ryabchikova et al 2005Ryabchikova et al , 2007. Below we will use some of these measurements for improving the rotational period of the star.…”

Section: Hd 24712mentioning

confidence: 63%

“…For the period search we compiled a list of all published longitudinal magnetic field measurements derived from the spectral lines of Fe-peak elements, which should be among the least variable lines in the spectrum of HD 24712. This list includes the TiCrFe B z data published by Preston (1972), measurements from the Fe i lines by Mathys (1991) and Mathys & Hubrig (1997), longitudinal field derived from the LSD Stokes V profiles of Fe-peak elements by Wade et al (2000a) and Ryabchikova et al (2005), measurements by Leone & Catanzaro (2004) and, finally, measurements from the recent spectroscopic study of pulsations in the atmosphere of HD 24712 performed by Ryabchikova et al (2007). Photopolarimetric longitudinal magnetic field measurements from the Hβ line by Ryabchikova et al (1997) were also included.…”

Section: Rotational Periodmentioning

confidence: 99%

Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712

Rusomarov

Kochukhov

Piskunov

et al. 2013

A&A

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Context. High-resolution spectropolarimetric observations provide simultaneous information about stellar magnetic field topologies and three-dimensional distributions of chemical elements. High-quality spectra in the Stokes IQUV parameters are currently available for very few early-type magnetic chemically peculiar stars. Here we present analysis of a unique full Stokes vector spectropolarimetric data set, acquired for the cool magnetic Ap star HD 24712 with a recently commissioned spectropolarimeter. Aims. The goal of our work is to examine the circular and linear polarization signatures inside spectral lines and to study variation of the stellar spectrum and magnetic observables as a function of rotational phase. Methods. HD 24712 was observed with the HARPSpol instrument at the 3.6-m ESO telescope over a period of 2010-2011. We achieved full rotational phase coverage with 43 individual Stokes parameter observations. The resulting spectra have a signal-to-noise ratio of 300-600 and resolving power exceeding 10 5 . The multiline technique of least-squares deconvolution (LSD) was applied to combine information from the spectral lines of Fe-peak and rare earth elements. Results. We used the HARPSPol spectra of HD 24712 to study the morphology of the Stokes profile shapes in individual spectral lines and in LSD Stokes profiles corresponding to different line masks. From the LSD Stokes V profiles we measured the longitudinal component of the magnetic field, B z , with an accuracy of 5-10 G. We also determined the net linear polarization from the LSD Stokes Q and U profiles. Combining previous B z measurements with our data allowed us to determine an improved rotational period of the star, P rot = 12.45812 ± 0.00019 d. We also measured the longitudinal magnetic field from the cores of Hα and Hβ lines. The analysis of B z measurements showed no evidence for a significant radial magnetic field gradient in the atmosphere of HD 24712. We used our B z and net linear polarization measurements to determine parameters of the dipolar magnetic field topology. We found that magnetic observables can be reasonably well reproduced by the dipolar model, although significant discrepancies remain at certain rotational phases. We discovered rotational modulation of the Hα core and related it to a non-uniform surface distribution of rare earth elements.

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Spectropolarimetry of magnetic stars

Cited by 175 publications

References 29 publications

First constraints on the magnetic field strength in extra-Galactic stars: FORS2 observations of Of?p stars in the Magellanic Clouds

First constraints on the magnetic field strength in extra-Galactic stars: FORS2 observations of Of?p stars in the Magellanic Clouds

Detecting Magnetic Fields in Rotationally Perturbed, Hot Stellar Winds

Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712

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