Properties and nature of Be stars

Harmanec, P.; Božić, H.; Percy, John R.; Yang, S.; Ruždjak, Domagoj; Sudar, D.; Wolf, M.; Iliev, L.; Huang, Lin; Buil, C.

doi:10.1051/0004-6361:20020453

Cited by 33 publications

(48 citation statements)

References 39 publications

(38 reference statements)

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“…This additional scatter is probably caused by the rapid line-profile variations. Harmanec et al (2002b) argued that the RV curves of Be star binaries, based on He i line profiles, might be affected by the phase-locked V/R changes, and that this may lead to the overestimation of the orbital semi-amplitudes. That this is indeed the case for several studied Be binaries (γ Cas, ϕ Per, κ Dra, V839 Her and V832 Cyg) was shown in Harmanec (2003).…”

Section: Rv Changes Orbital Solutions and A New Ephemerismentioning

confidence: 99%

Properties and nature of Be stars

Ruždjak

Božić

Harmanec

et al. 2009

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Context. One way to understand the still mysterious Be phenomenon is to study the time variations of particular Be stars with a long observational history. ζ Tau is one obvious candidate. Aims. Using our rich series of spectral and photometric observations and a critical compilation of available radial velocities, spectrophotometry of Hα, and UBV photometry, we characterize the pattern of time variations of ζ Tau over about a century. Our goal is to find the true timescales of its variability and confront them with the existing models related to various aspects of the Be phenomenon. Methods. Spectral reductions were carried out using the IRAF and SPEFO programs. The HEC22 program was used for both photometric reductions and transformations to UBV. Orbital solutions were derived with the latest publicly available version of the program FOTEL, period analyses employed both the PDM and Fourier techniques -programs HEC27 and PERIOD04.

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Section: Rv Changes Orbital Solutions and A New Ephemerismentioning

confidence: 99%

Properties and nature of Be stars

Ruždjak

Božić

Harmanec

et al. 2009

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“…Following Okazaki, we adopt α = 3.5 which according to him corresponds to the theoretical value for a subsonic region of an isothermal disk. The stellar rotational parameter f was chosen close to break-up at the equator, in the accordance with the recent studies of particular well observed Be stars by Harmanec et al (2002);Harmanec (2002Harmanec ( , 2003 as well as theoretical arguments by Townsend et al (2004);Frémat et al (2005). The outer radius of the disk, ξR, was chosen large enough not to interfere with the confined mode.…”

Section: The Reference Modelmentioning

confidence: 99%

“…For that reason we have chosen two well-known Be stars that are members of binary systems, γ Cas = HD 5394 and 59 Cyg = V832 Cyg. Their most probable basic physical properties were recently derived by Harmanec (2002) and Harmanec et al (2002), respectively. An apparent advantage of choosing Be stars in binary systems is that one can take the value of parameter ξ in such a way that the upper limit to ξR is given by the dimensions of the corresponding Roche lobe around the Be star in question 1 .…”

Section: A Trial Application To Two Well-known Be Binariesmentioning

confidence: 99%

Is the model of one-armed oscillations able to explain the long-termV/Rchanges of Be stars?

Fiřt

Harmanec

2006

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Context. Many scientists studying Be stars currently adopt the model of one-armed oscillations as the correct explanation of the cyclic longterm V/R variations observed for a number of Be stars. We test the ability of this model to be used for the predictions of V/R variations in real observed Be stars. Aims. The behavior of the one-armed oscillations can be described as a solution of linearized hydrodynamical equations with the presence of "distorted" gravitational potential and a radiation force. Methods. We developed a new computer program to model one-armed oscillations in Be star disks, which includes both the pressure force and the quadrupole term in the gravitational potential, related to the obliquity of a rapidly rotating star inside the disk. Moreover, we slightly improved the model in an effort to decrease the number of input parameters with the help of NLTE stellar atmosphere models. Results. We carried out detailed tests of the dependence of V/R "periods" predicted by the model on all individual input parameters. We arrived at the following results: (1) the model has great potential to explain not only the cause of the cyclic long-term V/R changes but also some of the observed statistical properties of the phenomenon. (2) The model in its present linear form cannot be considered as proven. Its ability to predict the duration of V/R cycles for individual well observed Be stars is insufficient. Changing some of the input parameters of the model, which are still loosely constrained by observations and/on current understanding of the disks, like the radial density distribution in the disk, one can easily arrive at any desired cycle length from, say, 1 to 20 years. Conclusions. Clearly, a much more sophisticated non-linear and self-consistent model of disk structure and its oscillations will be needed before a truly quantitative test of a one-armed model vs. observations will be possible.

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“…Božić et al 1995;Koubský et al 2010;Nemravová et al 2012;Peters et al 2013). The basic reasons for the RV curve of the strong Hα emission wings giving the most reliable estimate of the true orbital motion of the Be primary can be found in Ruždjak et al (2009) or Harmanec et al (2002). The errors of the method depend on the signal-to-noise ratio (S/N) of the particular spectrum and on the shape of the profile.…”

Section: Spectroscopic Observations and Their Reductionsmentioning

confidence: 99%

HD 161306: a radiatively interacting Be binary?

Koubský

Kotková

Kraus

et al. 2014

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The spectrum of the Be star HD 161306 is shown to vary periodically with a period of ∼100 days. The radial velocity of the He i 6678 Å emission peak varying in antiphase to the radial velocity of the Hα emission wings component suggests that the star is a binary similar to φ Per, 59 Cyg, or FY CMa, i.e. a radiatively interacting Be binary -a rare case among Be stars. This type of object is also called a φ Per-type binary or Be + sdO binaries. The range of radial-velocity variations of the strong emission peak in the helium line observed in HD 161306 is about 180 km s −1 , similar to what is observed for these systems. We therefore conclude that HD 161306 may represent another case of a Be star with a hot subdwarf companion.

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Properties and nature of Be stars

Cited by 33 publications

References 39 publications

Properties and nature of Be stars

Properties and nature of Be stars

Is the model of one-armed oscillations able to explain the long-termV/Rchanges of Be stars?

HD 161306: a radiatively interacting Be binary?

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