HARPS spectropolarimetry of Herbig Ae/Be stars

Hubrig, S.; Ilyin, I.; Schöller, M.; Curto, G. Lo

doi:10.1002/asna.201311948

Cited by 59 publications

(59 citation statements)

References 42 publications

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“…The normalisation of the spectra to the continuum level consisted of several steps described in detail by Hubrig et al (2013). The Stokes I and V parameters were derived following Ilyin (2012), and null polarisation spectra were calculated by combining the subexposures in such a way that polarisation canceled out.…”

Section: Potsdam Reduction and Analysismentioning

confidence: 99%

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

Przybilla

Fossati

Hubrig

et al. 2016

A&A

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Aims. We report the detection of a magnetic field in the helium-strong star CPD −57 • 3509 (B2 IV), a member of the Galactic open cluster NGC 3293, and characterise the star's atmospheric and fundamental parameters. Methods. Spectropolarimetric observations with FORS2 and HARPSpol are analysed using two independent approaches to quantify the magnetic field strength. A high-S/N FLAMES/GIRAFFE spectrum is analysed using a hybrid non-LTE model atmosphere technique. Comparison with stellar evolution models constrains the fundamental parameters of the star. Results. We obtain a firm detection of a surface averaged longitudinal magnetic field with a maximum amplitude of about 1 kG. Assuming a dipolar configuration of the magnetic field, this implies a dipolar field strength larger than 3.3 kG. Moreover, the large amplitude and fast variation (within about 1 day) of the longitudinal magnetic field implies that CPD −57 • 3509 is spinning very fast despite its apparently slow projected rotational velocity. The star should be able to support a centrifugal magnetosphere, yet the spectrum shows no sign of magnetically confined material; in particular, emission in Hα is not observed. Apparently, the wind is either not strong enough for enough material to accumulate in the magnetosphere to become observable or, alternatively, some leakage process leads to loss of material from the magnetosphere. The quantitative spectroscopic analysis of the star yields an effective temperature and a logarithmic surface gravity of 23 750 ± 250 K and 4.05 ± 0.10, respectively, and a surface helium fraction of 0.28 ± 0.02 by number. The surface abundances of C, N, O, Ne, S, and Ar are compatible with the cosmic abundance standard, whereas Mg, Al, Si, and Fe are depleted by about a factor of 2. This abundance pattern can be understood as the consequence of a fractionated stellar wind. CPD −57 • 3509 is one of the most evolved He-strong stars known with an independent age constraint due to its cluster membership.

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Section: Potsdam Reduction and Analysismentioning

confidence: 99%

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

Przybilla

Fossati

Hubrig

et al. 2016

A&A

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“…The normalization of the spectra to the continuum level consisted of several steps described in detail by Hubrig et al (2013). The Stokes I and V parameters were derived following the ratio method described by Donati et al (1997), and null polarization spectra were calculated by combining the subexposures in such a way that the intrinsic source polarization cancels out, yielding a diagnostic null N spectrum.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

et al. 2016

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Due to the knowledge of the rotation period and the presence of a rather strong surface magnetic field, the sharp-lined young Herbig Ae star HD 101412 with a rotation period of 42 d has become one of the most well-studied targets among the Herbig Ae stars. High-resolution HARPS polarimetric spectra of HD 101412 were recently obtained on seven different epochs. Our study of the spectral variability over the part of the rotation cycle covered by HARPS observations reveals that the line profiles of the elements Mg, Si, Ca, Ti, Cr, Mn, Fe, and Sr are clearly variable while He exhibits variability that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous spectral lines, Ti, Cr, and Fe. Over the time interval covered by the available spectra, the longitudinal magnetic field changes sign from negative to positive polarity. The distribution of field values obtained using Ti, Cr, and Fe lines is, however, completely different compared to the magnetic field values determined in previous low-resolution FORS 2 measurements, where hydrogen Balmer lines are the main contributors to the magnetic field measurements, indicating the presence of concentration of the studied iron-peak elements in the region of the magnetic equator. Further, we discuss the potential role of contamination by the surrounding warm circumstellar matter in the appearance of Zeeman features obtained using Ti lines.

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Section: Observations and Data Reductionmentioning

confidence: 99%

HARPS spectropolarimetry of three sharp-lined Herbig Ae stars: New insights

Järvinen

Carroll

Hubrig

et al. 2015

A&A

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Aims. Recently, several arguments have been presented that favour a scenario in which the low detection rate of magnetic fields in Herbig Ae stars can be explained by the weakness of these fields and rather large measurement uncertainties. Spectropolarimetric studies involving sharp-lined Herbig Ae stars appear to be a promising approach for the detection of such weak magnetic fields. These studies offer a clear spectrum interpretation with respect to the effects of blending, local velocity fields, and chemical abundances, and allow us to identify a proper sample of spectral lines appropriate for magnetic field determination. Methods. High-resolution spectropolarimetric observations of the three sharp-lined (v sin i < 15 km s −1 ) Herbig Ae stars HD 101412, HD 104237, and HD 190073 have been obtained in recent years with the HARPS spectrograph in polarimetric mode. We used these archival observations to investigate the behaviour of their longitudinal magnetic fields. To carry out the magnetic field measurements, we used the multi-line singular value decomposition (SVD) method for Stokes profile reconstruction. Results. We carried out a high-resolution spectropolarimetric analysis of the Herbig Ae star HD 101412 for the first time. We discovered that different line lists yield differences in both the shape of the Stokes V signatures and their field strengths. They could be interpreted in the context of the impact of the circumstellar matter and elemental abundance inhomogeneities on the measurements of the magnetic field. On the other hand, due to the small size of the Zeeman features on the first three epochs and the lack of near-IR observations, circumstellar and photospheric contributions cannot be estimated unambiguously. In the SVD Stokes V spectrum of the SB2 system HD 104237, we detect that the secondary component, which is a T Tauri star, possesses a rather strong magnetic field B z = 129 ± 12 G, while no significant field is present in the primary component. Our measurements of HD 190073 confirm the presence of a variable magnetic field and indicate that the circumstellar environment may have a significant impact on the observed polarization features.

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HARPS spectropolarimetry of Herbig Ae/Be stars

Cited by 59 publications

References 42 publications

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

B fields in OB stars (BOB): Detection of a magnetic field in the He-strong star CPD −57° 3509

Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

HARPS spectropolarimetry of three sharp-lined Herbig Ae stars: New insights

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