Metallicities of the<i>β</i>Cephei stars from low-resolution ultraviolet spectra

Niemczura, E.; Daszyńska‐Daszkiewicz, J.

doi:10.1051/0004-6361:20040396

Cited by 42 publications

(37 citation statements)

References 72 publications

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“…It is of importance to emphasize that the mild N enrichment observed in some stars has little incidence on the metal content, as this element is only a minor contributor to Z (∼5%). As can be seen in Table 8, the metallicity of the studied β Cephei stars is unremarkable and typical of the values observed for early B-type dwarfs in the solar neighbourhood, in accordance with recent works based on UV data (Niemczura & Daszyńska-Daszkiewicz 2005). It can be noticed that the Sun is markedly more metal-rich than young, nearby B stars.…”

Section: Conclusion and Prospectssupporting

confidence: 90%

“…An exhaustive literature search was not attempted. Instead, a comparison was made with atmospheric parameters obtained using three independent methods: (a) T eff primarily derived from Strömgren photometry and log g from profile fitting of Hγ (GL); (b) both parameters estimated from Walraven colour indices, or from Geneva and Strömgren photometry when these data were not available (Heynderickx et al 1994); (c) temperatures based on the continuum fitting of low-resolution IUE data (Niemczura & Daszyńska-Daszkiewicz 2005). As can be seen in Fig.…”

Section: Physical Parametersmentioning

confidence: 99%

“…stellar opacities) of these objects are precisely known. Noteworthy attempts to determine the effective temperature and global metallicity of several β Cephei stars from International Ultraviolet Explorer (IUE) data have recently been presented (Niemczura & Daszyńska-Daszkiewicz 2005), but more robust estimates are likely to be obtained from a detailed analysis of high-quality Non-radial 11 Handler et al (2006) optical data. Furthermore, a knowledge of the abundances of the individual chemical species is preferable in the context of theoretical modelling, as early-type stars may present significant departures from a scaled solar mixture.…”

Section: Introductionmentioning

confidence: 99%

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Abundance analysis of prime B-type targets for asteroseismology

Morel¹,

Butler

Aerts

et al. 2006

A&A

158

222

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Seismic modelling of the β Cephei stars promises major advances in our understanding of the physics of early B-type stars on (or close to) the main sequence. However, a precise knowledge of their physical parameters and metallicity is a prerequisite for correct mode identification and inferences regarding their internal structure. Here we present the results of a detailed NLTE abundance study of nine prime targets for theoretical modelling: γ Peg, δ Cet, ν Eri, β CMa, ξ 1 CMa, V836 Cen, V2052 Oph, β Cep and DD (12) Lac (hereafter 12 Lac). The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our curve-of-growth abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on their equatorial rotational velocity, ΩR, from seismic or line-profile variation studies: β Cep (ΩR ∼ 26 km s −1 ), V2052 Oph (ΩR ∼ 56 km s −1 ), δ Cet (ΩR < 28 km s −1 ) and ξ 1 CMa (ΩR sin i < ∼ 10 km s −1 ). The existence of core-processed material at the surface of such largely unevolved, slowly-rotating objects is not predicted by current evolutionary models including rotation. We draw attention to the fact that three stars in this subsample have a detected magnetic field and briefly discuss recent theoretical work pointing to the occurrence of diffusion effects in β Cephei stars possibly capable of altering the nitrogen surface abundance. On the other hand, the abundances of all the other chemical elements considered are, within the errors, indistinguishable from the values found for OB dwarfs in the solar neighbourhood. Despite the mild nitrogen excess observed in some objects, we thus find no evidence for a significantly higher photospheric metal content in the studied β Cephei stars compared to non-pulsating B-type stars of similar characteristics.

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Section: Conclusion and Prospectssupporting

confidence: 90%

Section: Physical Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Abundance analysis of prime B-type targets for asteroseismology

Morel¹,

Butler

Aerts

et al. 2006

A&A

158

222

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“…In terms of the color excess, E(B − V), it amounts to 0.028 ± 0.009 mag (Niemczura & Daszyńska-Daszkiewicz 2005) as derived from IUE spectroscopy. Using Strömgren photometry (Crawford et al 1970 For the last observations, the larger the symbol, the larger the weight that was adopted.…”

Section: The Orbit Of Aa-ab (Rbt 1aaab)mentioning

confidence: 82%

Massive pulsating stars observed by BRITE-Constellation

Pigulski

Cugier

Popowicz

et al. 2016

A&A

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Context. Asteroseismology of massive pulsating stars of β Cep and SPB types can help us to uncover the internal structure of massive stars and understand certain physical phenomena that are taking place in their interiors. We study β Centauri (Agena), a triple system with two massive fast-rotating early B-type components which show p-and g-mode pulsations; the system's secondary is also known to have a measurable magnetic field. Aims. This paper aims to precisely determine the masses and detect pulsation modes in the two massive components of β Cen with BRITE-Constellation photometry. In addition, seismic models for the components are considered and the effects of fast rotation are discussed. This is done to test the limitations of seismic modeling for this very difficult case. Methods. A simultaneous fit of visual and spectroscopic orbits is used to self-consistently derive the orbital parameters, and subsequently the masses, of the components. Time-series analysis of BRITE-Constellation data is used to detect pulsation modes and derive their frequencies, amplitudes, phases, and rates of frequency change. Theoretically-predicted frequencies are calculated for the appropriate evolutionary models and their stability is checked. The effects of rotational splitting and coupling are also presented. Results. The derived masses of the two massive components are equal to 12.02 ± 0.13 and 10.58 ± 0.18 M . The parameters of the wider, A-B system, presently approaching periastron passage, are constrained. Analysis of the combined blue-and red-filter BRITEConstellation photometric data of the system revealed the presence of 19 periodic terms, of which eight are likely g modes, nine are p modes, and the remaining two are combination terms. It cannot be excluded that one or two low-frequency terms are rotational frequencies. It is possible that both components of β Cen are β Cep/SPB hybrids. An attempt to use the apparent changes of frequency to distinguish which modes originate in which component did not succeed, but there is potential for using this method when more BRITE data become available. Conclusions. Agena seems to be one of very few rapidly rotating massive objects with rich p-and g-mode spectra, and precisely known masses. It can therefore be used to gain a better understanding of the excitation of pulsations in relatively rapidly rotating stars and their seismic modeling. Lacking proper mode identification, the pulsation frequencies found in β Cen cannot yet be used to constrain the internal structure of the components, but it may be possible to achieve this in the future with the use of spectroscopy and spectropolarimetry. In particular, these kinds of data can be used for mode identification since they provide new radial velocities. In consequence, they may help to improve the orbital solution, derive more precise masses, magnetic field strength and geometry, inclination angles, and reveal rotation periods. They may also help to assign pulsation frequencies to components. Finally, the case studied here ...

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“…5, especially in y and v, in agreement with the results of the frequency analysis (see the fourth and the penultimate paragraphs of Section 3). The primary's limb-darkening coefficients were interpolated from table 2 of Walter Van Hamme 1 for T eff = 22 500 K, log g = 3.85 (see Section 5.1) and [M/H] = 0 (Thoul et al 2003;Niemczura & Daszyńska-Daszkiewicz 2005). Unfortunately, since nothing is known about the secondary component except that it is much fainter than the primary, the central surface brightness of the secondary, Js, which EBOP uses as a fundamental parameter, must be derived indirectly.…”

Section: The Ebop Solutionsmentioning

confidence: 99%

The 2003–2004 multisite photometric campaign for the β Cephei and eclipsing star 16 (EN) Lacertae with an appendix on 2 Andromedae, the variable comparison star

Jerzykiewicz

Handler

Daszyńska‐Daszkiewicz

et al. 2015

Mon. Not. R. Astron. Soc.

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A multisite photometric campaign for the β Cephei and eclipsing variable 16 Lacertae is reported. 749 h of high-quality differential photoelectric Strömgren, Johnson and Geneva time-series photometry were obtained with ten telescopes during 185 nights. After removing the pulsation contribution, an attempt was made to solve the resulting eclipse light-curve by means of the computer program EBOP. Although a unique solution was not obtained, the range of solutions could be constrained by comparing computed positions of the secondary component in the Hertzsprung-Russell diagram with evolutionary tracks.For three high-amplitude pulsation modes, the uvy and the Geneva U BG amplitude ratios are derived and compared with the theoretical ones for spherical-harmonic degrees ℓ 4. The highest degree, ℓ = 4, is shown to be incompatible with the observations. One mode is found to be radial, one is ℓ = 1, while in the remaining case ℓ = 2 or 3.The present multisite observations are combined with the archival photometry in order to investigate the long-term variation of the amplitudes and phases of the three high-amplitude pulsation modes. The radial mode shows a non-sinusoidal variation on a time-scale of 73 yr. The ℓ = 1 mode is a triplet with unequal frequency spacing, giving rise to two beat-periods, 720.7 d and 29.1 yr. The amplitude and phase of the ℓ = 2 or 3 mode vary on time-scales of 380.5 d and 43 yr.The light variation of 2 And, one of the comparison stars, is discussed in the Appendix.

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Metallicities of theβCephei stars from low-resolution ultraviolet spectra

Cited by 42 publications

References 72 publications

Abundance analysis of prime B-type targets for asteroseismology

Abundance analysis of prime B-type targets for asteroseismology

Massive pulsating stars observed by BRITE-Constellation

The 2003–2004 multisite photometric campaign for the β Cephei and eclipsing star 16 (EN) Lacertae with an appendix on 2 Andromedae, the variable comparison star

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