Multiplicity among chemically peculiar stars

Carrier, F.; North, P.; Babel, J.

doi:10.1051/0004-6361:20021122

Cited by 100 publications

(144 citation statements)

References 66 publications

Supporting

Mentioning

115

Contrasting

Order By: Relevance

“…1 the isochrone log t = 8.3 defines in the H-R diagram the early evolution envelope of the magnetic Ap star region [1,2]. These results are in agreement with the results of the studies of spectroscopic binary systems (e.g., [10]) and of the study of Ap stars in the cluster NGC 2516 with an age of log t = 8.2 ± 0.1 [11]. Regarding the evolution of magnetic field strength with time, it seems that the strongest magnetic fields appear in the middle of the main-sequence band.…”

Section: Discussionsupporting

confidence: 89%

Evolution of magnetic fields in stars across the upper main sequence

Hubrig¹,

Schöller²,

North³

2005

AIP Conference Proceedings

View full text Add to dashboard Cite

Abstract.To properly understand the physics of upper main sequence stars it is particularly important to identify the origin of their magnetic fields. Recently, we confirmed that magnetic fields appear in Ap stars of mass below 3 M ⊙ only if they have already completed at least approximately 30% of their main-sequence lifetime [1,2]. The absence of stars with strong magnetic fields close to the ZAMS might be seen as an argument against the fossil field theories. Here we present the results of our recent magnetic survey with FORS 1 at the VLT in polarimetric mode of a sample of A, B and Herbig Ae stars with previously undetected magnetic fields and briefly discuss their significance for our understanding of the origin of the magnetic fields in intermediate mass stars. BASIC DATAA large variety of physical processes occur in the atmospheres of upper main sequence stars that have not yet been fully incorporated into stellar models, or even securely identified and understood. These processes include convection, turbulence, meridional circulation currents, diffusion of trace elements within the dominant hydrogen plasma, and mass loss through stellar winds. The chemically peculiar stars (Ap and Bp stars) play a key role in our efforts to understand the relevant physics, since it is in these stars that the effects of the various processes acting below, in and above the stellar atmospheres are most clearly visible. Ap and Bp stars are main-sequence A and B stars in the spectra of which the lines of some elements are abnormally strong (e.g., Si, Sr, rare earths) or weak (in particular, He). They undergo periodic variations of magnitude (in various photometric bands) and spectral line equivalent widths and the known periods of variability range from half a day to several decades. Among Ap stars, the magnetic chemically peculiar stars are particularly important. For a long time, Ap stars were the only non-degenerate stars besides the sun in which direct detections of magnetic fields had been achieved. Today, they still represent a major fraction of the known magnetic stars. These stars generally have large-scale organized magnetic fields that can be diagnosed through observations of circular polarization in spectral lines. The unique large-scale organization of the magnetic fields in these stars, which in many cases appears to occur essentially under the form of a single large dipole located close to the centre of the star, contrasts with the magnetic field of late-type stars, which is most probably subdivided in a large number of small dipolar elements scattered across the stellar surface. The fact that magnetic fields of Ap stars are more readily observable

show abstract

Section: Discussionsupporting

confidence: 89%

Evolution of magnetic fields in stars across the upper main sequence

Hubrig¹,

Schöller²,

North³

2005

AIP Conference Proceedings

View full text Add to dashboard Cite

show abstract

“…Only a few double-lined spectroscopic binary systems (which can be considered as very small clusters) containing a magnetic Ap star are currently known, and in all studied systems the Ap components with M < 3 M have already completed a significant fraction of their main-sequence life (e.g., Wade et al 1996;North et al 1998;Carrier et al 2002).…”

Section: Cluster Members With Accurate Hipparcos Parallaxesmentioning

confidence: 99%

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

Hubrig¹,

North

Schöller

2007

Astron Nachr

Self Cite

View full text Add to dashboard Cite

We re-discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M are concentrated towards the centre of the main-sequence band. In contrast, stars with masses M > 3 M seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main-sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0 • in slower rotating stars of mass M > 3 M too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M . The obliquity angle distribution as inferred from the distribution of r-values appears random at the time magnetic stars become observable on the H-R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90 • or 0 • for M < 3 M . The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M , no similar trend is found for stars with M < 3 M . However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories.

show abstract

“…In contrast, many non-oscillating Ap (noAp) stars are detected in Based on observations collected at the European Southern Observatory (La Silla, Chile) under programs 074.C-0102, 075.C-0234, 076.C-0073, 079.C-0170, 080.C-0032, and 082.C-0308. SB systems (Carrier et al 2002). Moreover, other types of pulsating variables (e.g., β Cep stars, δ Sct stars, or classical Cepheids) are often found in SB systems as well.…”

Section: Introductionmentioning

confidence: 99%

A radial-velocity survey of Ap stars with HARPS

Hartmann

Hatzes

2015

A&A

View full text Add to dashboard Cite

Context. Chemically peculiar Ap stars are main-sequence stars of spectral type B8-F3 which show large overabundances of some chemical elements (e.g., Si, Sr, Cr), especially of rare-earth elements, compared to normal A-type stars. Furthermore, they have strong, global magnetic fields and low rotational velocities. Some Ap stars exhibit high-overtone, low-degree, non-radial p-mode pulsations with periods of 6-24 min and are called rapidly oscillating Ap (roAp) stars. Interestingly, no roAp star is known to be a spectroscopic binary (SB), while many non-oscillating Ap (noAp) stars are found in SB systems. Aims. The goal of this survey was to carry out a systematic search for sub-stellar and stellar companions around Ap stars. Methods. Between 2004 and 2009, we observed 65 chemically peculiar stars with the HARPS spectrograph at the 3.6-m telescope at the European Southern Observatory (La Silla, Chile). The radial-velocity (RV) measurements were obtained using a new software called HARPS-TERRA which is based on a least-squares matching of each individual spectrum to a high signal-to-noise ratio template for each star. Results. We find significant variability with a period of 93.2 days and a semi-amplitude of 11.85 km s −1 in the RVs of HD 42659, a star of our sample that belongs to the group of roAp stars. This variability is caused by a stellar companion with a minimum mass of 0.47 M in a slightly eccentric (e = 0.146) orbit at a separation of 0.55 AU.Conclusions. This detection makes HD 42659 the first confirmed SB around a roAp star in a relatively close orbit. It shows that tidal interactions in binaries do not necessarily inhibit pulsations in Ap stars.

show abstract

Multiplicity among chemically peculiar stars

Cited by 100 publications

References 66 publications

Evolution of magnetic fields in stars across the upper main sequence

Evolution of magnetic fields in stars across the upper main sequence

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

A radial-velocity survey of Ap stars with HARPS

Contact Info

Product

Resources

About