scholarly journals NGC 6611 601: A hot pre-main sequence spectroscopic binary containing a centrifugal magnetosphere host star

2021 ◽  
Author(s):  
M E Shultz ◽  
E Alecian ◽  
V Petit ◽  
S Bagnulo ◽  
T Böhm ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Magnetic Star ◽  
Be Stars ◽  
Strong Emission ◽  
Surface Magnetic Field ◽  
Spectroscopic Binary ◽  
Be Star ◽  
Hα Emission ◽  
Strong Surface

Abstract W 601 (NGC 6611 601) is one of the handful of known magnetic Herbig Ae/Be stars. We report the analysis of a large dataset of high-resolution spectropolarimetry. The star is a previously unreported spectroscopic binary, consisting of 2 B2 stars with a mass ratio of 1.8, masses of 12 M⊙ and 6.2 M⊙, in an eccentric 110-day orbit. The magnetic field belongs to the secondary, W 601 B. The Hα emission is consistent with an origin in W 601 B’s centrifugal magnetosphere; the star is therefore not a classical Herbig Be star in the sense that its emission is not formed in an accretion disk. However, the low value of log g = 3.8 determined via spectroscopic analysis, and the star’s membership in the young NGC 6611 cluster, are most consistent with it being on the pre-main sequence. The rotational period inferred from the variability of the Hα line and the longitudinal magnetic field 〈Bz〉 is 1.13 d. Modelling of Stokes V and 〈Bz〉 indicates a surface dipolar magnetic field Bd between 6 and 11 kG. With its strong emission, rapid rotation, and strong surface magnetic field, W 601 B is likely a precursor to Hα-bright magnetic B-type stars such as σ Ori E. By contrast, the primary is an apparently non-magnetic (Bd < 300 G) pre-main sequence early B-type star. In accordance with expectations from magnetic braking, the non-magnetic primary is apparently more rapidly rotating than the magnetic star.

scholarly journals Chandra X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion

2020 ◽  
Vol 641 ◽  
pp. L8 ◽  
Author(s):  
Lidia M. Oskinova ◽  
Richard Ignace ◽  
Paolo Leto ◽  
Konstantin A. Postnov
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Main Sequence ◽  
Light Curves ◽  
Intermediate Mass ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Hot Gas ◽  
Nonthermal Emission ◽  
Strong Surface

Context. KQ Vel is a peculiar A0p star with a strong surface magnetic field of about 7.5 kG. It has a slow rotational period of nearly 8 years. Bailey et al. (A&A, 575, A115) detected a binary companion of uncertain nature and suggested that it might be a neutron star or a black hole. Aims. We analyze X-ray data obtained by the Chandra telescope to ascertain information about the stellar magnetic field and/or interaction between the star and its companion. Methods. We confirm previous X-ray detections of KQ Vel with a relatively high X-ray luminosity of 2 × 1030 erg s−1. The X-ray spectra suggest the presence of hot gas at > 20 MK and, possibly, of a nonthermal component. The X-ray light curves are variable, but data with better quality are needed to determine a periodicity, if any. Results. We interpret the X-ray spectra as a combination of two components: the nonthermal emission arising from the aurora on the A0p star, and the hot thermal plasma filling the extended shell that surrounds the “propelling” neutron star. Conclusions. We explore various alternatives, but a hybrid model involving the stellar magnetosphere along with a hot shell around the propelling neutron star seems most plausible. We speculate that KQ Vel was originally a triple system and that the Ap star is a merger product. We conclude that KQ Vel is an intermediate-mass binary consisting of a strongly magnetic main-sequence star and a neutron star.

scholarly journals Spectroscopic Observations of Be Stars in the Photographic and Visual Regions

1982 ◽  
Vol 98 ◽  
pp. 109-124 ◽  
Author(s):  
Arne Slettebak
Keyword(s):  
Main Sequence ◽  
Review Paper ◽  
Planetary Nebulae ◽  
Be Stars ◽  
Early Type ◽  
Spectroscopic Observations ◽  
Be Star ◽  
Hα Emission

The term “Be star” has been used at times to describe classes of objects which are physically rather different from one another. While it could include early-type supergiant stars with Hα emission, early-type pre-main sequence nebular variables, or quasi-planetary nebulae like MWC 349, I will limit this review paper to a discussion of the “classical” Be stars. These are defined as stars of luminosity classes III to V, usually rapid rotators, which show normal B-type spectra with superposed Balmer (and sometimes Fe II) emission. Included also, however, will be the Oe stars and the A-type shell stars, which seem to represent extensions of the classical Be phenomenon to higher and lower temperatures, respectively.

scholarly journals The Magnetic Be Star Sigma Orionis E

1987 ◽  
Vol 92 ◽  
pp. 82-83 ◽  
Author(s):  
C. T. Bolton ◽  
A. W. Fullerton ◽  
D. Bohlender ◽  
J. D. Landstreet ◽  
D. R. Gies
Keyword(s):  
Magnetic Field ◽  
Field Structure ◽  
High Signal ◽  
Rotational Period ◽  
Magnetic Field Structure ◽  
The Past ◽  
Distribution Of Elements ◽  
Be Star ◽  
Hα Emission ◽  
The Magnetic Field

Over the past two years, we have obtained high resolution high signal/noise (S/N) spectra of the magnetic Be star σ Ori E at the Canada-France-Hawaii Telescope and McDonald Observatory. These spectra, which cover the spectral regions 399-417.5 and 440-458.5 nm and the Hα line and have typical S/N>200 and spectral resolution ≃0.02 nm, were obtained at a variety of rotational phases in order to study the magnetic field structure, the distribution of elements in the photosphere, and the effects of the magnetic field on the emission envelope. Our analysis of these spectra confirms, refines and extends the results obtained by Landstreet & Borra (1978), Groote & Hunger (1982 and references therein), and Nakajima (1985).The Hα emission is usually double-peaked, but it undergoes remarkable variations with the 1.19081 d rotational period of the star, which show that the emitting gas is localized into two regions which co-rotate with the star.

scholarly journals The Possible Role of Radiative Acceleration in Supporting Extended Atmospheres in Be Stars

1976 ◽  
Vol 70 ◽  
pp. 377-382 ◽  
Author(s):  
R. L. Kurucz ◽  
R. E. Schild
Keyword(s):  
Effective Temperature ◽  
Detailed Calculation ◽  
Be Stars ◽  
Be Star ◽  
Hα Emission ◽  
Two Peaks ◽  
Radiative Acceleration ◽  
Emission Strength ◽  
Peaked Function

A detailed calculation of the radiative acceleration in B-type stars shows it to be a double-peaked function of effective temperature at small optical depths. The two peaks are shown to coincide approximately with peaks in the distribution of mean Hα emission strength as a function of B - V color in Be stars. These facts suggest that radiation may play an important role in the support of the Be star extended atmosphere.

scholarly journals Search for Magnetic Stars at Early Stages of Evolution

1993 ◽  
Vol 137 ◽  
pp. 669-671
Author(s):  
Yu. V. Glagolevskij
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Rotation Velocity ◽  
Electric Vector ◽  
Magnetic Star ◽  
Stellar Rotation ◽  
Magnetic Stars ◽  
Hydrogen Lines ◽  
Direction Of Polarization ◽  
Gaseous Envelope

Young stars, as a rule, are too faint for measurements of magnetic field either by photographic method with the use of Zeeman analizer, or photoelectrically from hydrogen lines. That is why it is necessary to look for indirect ways of magnetic field detection, for example, by measurement of polarization. Ae/Be Herbig stars without a magnetic field are surrounded by a gaseous envelope in the form of a globe or a spheroid, flattened along the rotational axes (as dependent on stellar rotation velocity), and also by a gaseous-dust accretion disc in the plane of equator. There are powerful flows in gaseous envelopes of stars, connected with mass loss and accretion. If a star is a magnetic oblique rotator (as a magnetic star of the Main Sequence), then the gaseous envelope may acquire the shape of alon-gated ellipsoid with the major axes coincident with that of dipole (Dolginov et al., 1979). From the poles there arises a jet flow controlled by a magnetic field, as in He-r and He-w stars, having already reached the Main Sequence (Barker et al., 1982). Calculations show (Dolginov et al., 1979), that maximum polarization in the extended envelope p ≈ 4% arises when the ratio of ellipsoid axes is ≈ 2.5b. The electric vector of the dominating oscillation of the light wave is perpendicular to the plane through the axis of symmetry of the ellipsoid and the line of sight. Naturally, the magnetosphere rotates together with the star, involving the gaseous envelope, resulting in the variation of the degree and direction of polarization. Additional polarization is created by the polar jets, where the direction of the dominating oscillations of the electric vector is perpendicular to the axis of the polar stream, and value of maximal polarization may reach 5% along the beam.

scholarly journals Be Star Surveys in Open Clusters with Balmer-line Photometry

2000 ◽  
Vol 175 ◽  
pp. 63-66
Author(s):  
Gemma Capilla ◽  
Juan Fabregat ◽  
Deborah Baines
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Open Clusters ◽  
Balmer Line ◽  
Be Stars ◽  
Late Type ◽  
Efficient Tool ◽  
Be Star ◽  
Almost All ◽  
Evolutionary Interpretation

AbstractWe present CCD Hα and Hβ photometry of young open clusters. We show that the comparison of the α and β photometric indices provides an efficient tool for identifying emission line stars. We report on the discovery of several new Be stars.The preliminary results of our survey are the following: i. the younger clusters (age < 10 Myr) are almost lacking of Be stars, ii. clusters in the age interval 10–30 Myr are rich in Be stars. Almost all of them are of spectral types earlier than B5, while late-type Be stars are scarce. These results point towards an evolutionary interpretation of the Be phenomenon, in the sense that Be stars are close to the end of their main sequence lifetime.

Spectroscopic Investigations of Herbig-Ae-Be-Stars

1982 ◽  
Vol 98 ◽  
pp. 501-507
Author(s):  
Ulrich Finkenzeller
Keyword(s):  
Mass Loss ◽  
Radiation Pressure ◽  
Stellar Wind ◽  
Main Sequence ◽  
Physical Structure ◽  
Pressure Effects ◽  
Theoretical Knowledge ◽  
Be Stars ◽  
Be Star ◽  
Moderate Mass

“Herbig-Ae-Be-Stars” are assumed to be pre-main sequence objects of moderate mass with line emitting envelopes of an unknown nature. From our present theoretical knowledge it is not clear whether the physical structure of these envelopes is dominated by mass accretion or mass loss induced by a stellar wind or radiation pressure effects. Radial velocities and remarks on peculiarities are given for the star HD 200 775, which seems to represent a typical Herbig-Ae-Be-star fairly well. A catalogue of about 60 supposed Herbig-Ae-Be-stars is presented and comments, in particular on the brighter members, are invited.

scholarly journals Magnetars and white dwarf pulsars

2016 ◽  
Vol 25 (09) ◽  
pp. 1641025 ◽  
Author(s):  
Ronaldo V. Lobato ◽  
Manuel Malheiro ◽  
Jaziel G. Coelho
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
White Dwarf ◽  
Alternative Model ◽  
Gamma Ray ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Rotation Periods ◽  
Strong Surface

The anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely [Formula: see text][Formula: see text]G, and for that reason are known as magnetars. However, in the last years, some SGRs/AXPs with low surface magnetic fields [Formula: see text]–[Formula: see text][Formula: see text]G have been detected, challenging the magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-ray energy emission as an ordinary pulsar. Following this fact, an alternative model based on WDs pulsars has been proposed to explain this special class of pulsars. In this model, AXPs and SGRs as dense and magnetized WDs can have surface magnetic field [Formula: see text]–[Formula: see text] G and rotate very fast with frequencies [Formula: see text][Formula: see text]rad/s, consistent with the observed rotation periods [Formula: see text]–12)[Formula: see text]s.

scholarly journals Periodic Variations and Mass Loss in Be Stars

1994 ◽  
Vol 162 ◽  
pp. 287-298 ◽  
Author(s):  
Hideyuki Saio
Keyword(s):  
Angular Momentum ◽  
Mass Loss ◽  
Mass Loss Rate ◽  
Rotation Period ◽  
Be Stars ◽  
Surface Magnetic Field ◽  
Upper Limit ◽  
Short Period ◽  
Angular Momentum Loss ◽  
Be Star

We discuss the connection between the periodic light variations and the equatorial mass loss of Be stars. The observed properties of the short period (~ day) variations seem to indicate that they arise in the photosphere. An upper limit for the surface magnetic field of Be stars is derived from the rate of angular momentum loss expected from the typical mass loss-rate in Be stars. The upper limit suggests that surface magnetic fields of Be stars are too weak to make a spot. We argue that the periodic variations of Be stars are explained by nonradial pulsations whose periods on the stellar surface are much longer than the rotation period. They transport angular momentum from the core to the envelope to accelerate the surface regions. If this mechanism works sufficiently well, the rotation speed near the surface will reach to the critical velocity and an excretion disk will be formed around the star. A simple model for a steady-state excretion disk around a Be star is found to be consistent with the density structure inferred from the IR fluxes.

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