UVSTAR observations of Adara (<i>ϵ</i> CMa): 575–1250 Å

Gregorio, A.; Stalio, R.; Broadfoot, L.; Castelli, F.; Hack, Margherita; Holberg, J. B.

doi:10.1051/0004-6361:20020049

Cited by 6 publications

(3 citation statements)

References 39 publications

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“…For example, such a radiation was observed for the star ǫ CMa (B2 II); it was found that the observed EUV flux at λ < 504 Å (He I continuum) is significantly greater than the computed one (Cassinelli et al 1995). Later Gregorio at al. (2002), using both the ATLAS9 model atmospheres of Kurucz (1993) and the spherical model atmospheres of Aufdenberg et al (1999), showed that a more satisfactory agreement with the observed EUV flux for the star ǫ CMa can be achieved; however, the observed flux has a different shape than the predicted one.…”

Section: Discussionmentioning

confidence: 91%

Carbon, nitrogen and oxygen abundances in atmospheres of the 5–11 M⊙ B-type main-sequence stars

Lyubimkov¹,

Lambert²,

Poklad³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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Fundamental parameters and the carbon, nitrogen and oxygen abundances are determined for 22 B-type stars with distances d 600 pc and slow rotation (v sin i 66 km s −1 ). The stars are selected according to their effective temperatures T eff and surface gravities log g, namely: T eff is between 15300 and 24100 K and log g is mostly greater than 3.75; therefore, stars with medium masses of 5-11 M ⊙ are selected. Theory predicts for the stars with such parameters that the C, N and O abundances in their atmospheres should correspond to their initial values. Non-LTE analysis of C II, N II and O II lines is implemented. The following mean C, N and O abundances are obtained: log ǫ(C) = 8.31±0.13, log ǫ(N) = 7.80±0.12 and log ǫ(O) = 8.73±0.13. These values are in very good agreement with recent data on the C, N and O abundances for nearby B stars from other authors; it is important that different techniques are applied by us and other authors. When excluding for the stars HR 1810 and HR 2938, which can be mixed, we obtain the following mean abundances for the remaining 20 stars: log ǫ(C) = 8.33±0.11, log ǫ(N) = 7.78±0.09 and log ǫ(O) = 8.72±0.12; these values are in excellent agreement with a present-day Cosmic Abundance Standard (CAS) of Nieva & Przybilla.The derived mean N and O abundances in unevolved B stars are very close to the solar photospheric abundances, as well as to the protosolar ones. However, the mean C abundance is somewhat lower than the solar one; this small but stable carbon deficiency is confirmed by other authors. One may suggest two possibilities to explain the observed C deficiency. First, current non-LTE computations of C II lines are still partially inadequate. In this case the C deficiency is invalid, so one may conclude that the Sun and the local unevolved B stars have the same metallicity. This would mean that during the Sun's life (i.e., for the past 4.5 · 10 9 yr) the metallicity of the solar neighbourhood has not markedly changed; so, an intensive enrichment of the solar neighbourhood by metals occurred before the Sun's birth. Second, the C deficiency in the local B stars is valid; it is supposed that the Sun can migrate during its life from inner parts of the Galactic disk where it has born, so its observed chemical composition can differ from the composition of young stars in its present neighbourhood.

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Section: Discussionmentioning

confidence: 91%

Carbon, nitrogen and oxygen abundances in atmospheres of the 5–11 M⊙ B-type main-sequence stars

Lyubimkov¹,

Lambert²,

Poklad³

et al. 2012

Monthly Notices of the Royal Astronomical Society

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“…Here the deviations from LTE play a secondary role, with the major contribution from the transition to a spherical, extended atmosphere from a plane geometry. Later, more satisfactory agreement was obtained [22] with the observations on ε CMa; however, although the level of the calculated UV flux agreed better on the average with the observations, the wavelength distributions of the flux in the calculations and the observations were substantially different. In addition, the observed intensities of the spectrum lines in the UV region under consideration were too strong compared to the calculations [22].…”

Section: The Adequacy Of the Models For Stellar Atmospheresmentioning

confidence: 60%

Possible Overionization of C II, N II, and O II Ions in the Atmospheres of Early B- and Late O-Type Stars

Lyubimkov

2013

Astrophysics

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The reliability of C, N, and O abundances determined from lines of C II, N II, and O II in the mainsequence (MS) early B-and late O-type stars is examined. This analysis is based on a fact of K for N II and O II) yield the undistorted C, N and O abundances, and their average values agree very well with modern estimates for the sun. This confirms that the metallicity of B-and O-type MS stars in the Sun's vicinity is the same as that of the sun. An explanation is given for the slight deficit of carbon found for the early B-type MS stars in previous work. It is noted that when an alternative method based on examining the ionization balance (e.g., He I-II, C II-III, Ne I-II, Si III-IV) is used to determine the parameters T eff and log g, the overionization problem essentially vanishes; however, this method leads to a systematic enhancement in the values of T eff and log g. The overionization problem can be solved by shifting to an Astrophysics, Vol. 56, No. 4, December, 2013

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“…The lack of DIBs in HD 52089 is likely due to its short distance and the very low interstellar extinction in its direction. In addition, HD 52089 is not only the hottest star in our sample, but also the strongest ultraviolet source in the night sky [74], which may be able to photodissociate DIB carriers.…”

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confidence: 97%

Unveiling the Evolutionary State of Three B Supergiant Stars: PU Gem, ϵ CMa, and η CMa

Sánchez Arias,

Németh,

de Almeida

et al. 2023

Galaxies

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We aim to combine asteroseismology, spectroscopy, and evolutionary models to establish a comprehensive picture of the evolution of Galactic blue supergiant stars (BSG). To start such an investigation, we selected three BSG candidates for our analysis: HD 42087 (PU Gem), HD 52089 (ϵ CMa), and HD 58350 (η CMa). These stars show pulsations and were suspected to be in an evolutionary stage either preceding or succeding the red supergiant (RSG) stage. For our analysis, we utilized the 2-min cadence TESS data to study the photometric variability, and we obtained new spectroscopic observations at the CASLEO observatory. We used non-LTE radiative transfer models calculated with CMFGEN to derive their stellar and wind parameters. For the fitting procedure, we included CMFGEN models in the iterative spectral analysis pipeline XTgrid to determine their CNO abundances. The spectral modeling was limited to changing only the effective temperature, surface gravity, CNO abundances, and mass-loss rates. Finally, we compared the derived metal abundances with prediction from Geneva stellar evolution models. The frequency spectra of all three stars show stochastic oscillations and indications of one nonradial strange mode, fr= 0.09321 d−1 in HD 42087 and a rotational splitting centred in f2= 0.36366 d−1 in HD 52089. We conclude that the rather short sectoral observing windows of TESS prevent establishing a reliable mode identification of low frequencies connected to mass-loss variabilities. The spectral analysis confirmed gradual changes in the mass-loss rates, and the derived CNO abundances comply with the values reported in the literature. We were able to achieve a quantitative match with stellar evolution models for the stellar masses and luminosities. However, the spectroscopic surface abundances turned out to be inconsistent with the theoretical predictions. The stars show N enrichment, typical for CNO cycle processed material, but the abundance ratios did not reflect the associated levels of C and O depletion. We found HD 42087 to be the most consistent with a pre-RSG evolutionary stage, HD 58350 is most likely in a post-RSG evolution and HD 52089 shows stellar parameters compatible with a star at the TAMS.

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UVSTAR observations of Adara (ϵ CMa): 575–1250 Å

Cited by 6 publications

References 39 publications

Carbon, nitrogen and oxygen abundances in atmospheres of the 5–11 M⊙ B-type main-sequence stars

Carbon, nitrogen and oxygen abundances in atmospheres of the 5–11 M⊙ B-type main-sequence stars

Possible Overionization of C II, N II, and O II Ions in the Atmospheres of Early B- and Late O-Type Stars

Unveiling the Evolutionary State of Three B Supergiant Stars: PU Gem, ϵ CMa, and η CMa

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