Jakub Ostrowski J. Daszyńska-Daszkiewicz H. Cugier

Transcription

1 Resolving the evolutionary stage of HD on the basis of its oscillation spectrum Jakub Ostrowski J. Daszyńska-Daszkiewicz H. Cugier August 12, 2015, Honolulu

2 Introduction HD (B2 Ib/II - very poorly determined parameters!) SPBsg (Saio et al., 2006, ApJ 650, 1111) Ostrowski & Daszyńska-Daszkiewicz 2015, MNRAS 447, 2378 Our previous result: a supergiant, M ~ 16 M, H-shell burning phase

3 HD

4 HD New determination of parameters for HD Based on the archive "HARPS spectra of CoRoT targets", prepared in the framework of the FP7 project n SpaceInn - Exploitation of Space Data for Innovative Helio- and Asteroseismology T eff = ± 1000 K log L/M = 3.85 ± 0.05 log g = 3.00 ± 0.15 V rot sini = 65 ± 5 km/s HD is a more massive and hotter star than it was believed before

5 Analysed models MESA (Paxton et al. 2011, 2013, 2015) Non-adiabatic pulsation code of Dziembowski (1977) X = 0.70, Z = OPAL & AGSS09 Ω = 0.2 Ω crit Ledoux criterion for convection Mass-loss by Vink et al. 2001

6 L/M Can HD be a main sequence star?

7 Instability parameter, η main sequence

8 Instability parameter, η supergiant

9 Theoretical amplitudes Rotational frequency splitting: Vrotsini = 65 km/s, varied (Vrot, i) Photometric amplitudes, AV, calculated with the formula of Daszyńska-Daszkiewicz et al εmax estimated using the observed frequency spectrum and mentioned formula for AV ε [0, 0.002], randomly drawn for each mode AV > 0.3 mmag

10 Theoretical amplitudes main sequence

11 Theoretical amplitudes main sequence

12 Theoretical amplitudes blue supergiant

13 Conclusions HD is rather in the MS evolutionary stage Problems with explanation of high-frequency peaks of HD and the slope of the observed spectrum Modes with higher spherical degree l have to be considered to explain the observed spectrum Calculations of stellar pulsations of massive stars (M > 20 M ) are difficult due to a very complicated internal structure

14 Thank you! A complex approach to the blue-loop problem J. Ostrowski* & J. Daszyńska-Daszkiewicz^ Astronomical Institute of the University of Wrocław Introduction The problem of the blue loops during the core helium burning, outstanding for almost fifty years (e.g., Lauterborn et al. 1971), is one of the most difficult and poorly understood problems in stellar physics. The emergence of the blue loops depends on many details of evolution calculations, in particular on chemical composition, opacity, mixing processes etc. There are non-linear interactions between these factors which further complicate interpretation of the results. To tackle the problem we used a modern stellar evolution code MESA to calculate a large grid of evolutionary tracks with masses in the range of solar masses from the zero age main sequence to the depletion of helium in the core. We are mainly focused on more massive models, which are often believed not to be able to produce a blue loop (e.g., Walmswell et al. 2015). Here, we compare the properties of models with initial mass of 16.0 M in order to understand the mechanisms that lead to emerging of the blue loops. Take a look at my poster as well! Parameters of evolutionary models The HR diagram with evolutionary tracks for models with the initial mass of M = 16 M. Ω indicates the ratio of the rotational velocity to its critical value and f is the adjustable parameter of convective overshooting for the hydrogen core (1st value), helium core (2nd value) and non-burning convective zone (3rd value). The models selected for a detailed comparison are marked with dots. Blue supergiant (BSG) MESA (Paxton et al. 2011, 2013, 2015) Initial mass: M = 16.0 M Initial hydrogen abundance, X = 0.70, initial metal abundance, Z = OPAL opacity tables (Iglesias & Rogers 1996) computed for the AGSS09 mixture (Asplund et al. 2009) Differential rotation in shelluar approximation Ledoux criterion for convective instability Mixing length parameter αmlt = 1.8 Exponential prescription for convective overshooting (Herwig 2000) Mass-loss by Vink et al (log Teff > 4.0) & de Jager et al (log Teff < 4.0) Bottom of the red giant branch (RGB bottom) Top of the red giant branch (RGB top) Abundances of hydrogen and helium as a function of the fractional mass for three selected stages of evolution of a star with the initial mass M = 16 M, assuming varied Ω and overshooting from the non-burning convective zone (fnb). FM7 p.55 The same as above but the profile of the mean Rosseland opacity is presented. The same as above but the gradient of the mean molecular weight (μ) is presented. Results Blue loops are also possible in models with masses M > 13.0 M The profile of the μ-gradient developed during evolution on the main sequence is crucial for the formation of the blue loops. Models which produce a blue loop have the μ-gradient profile erased by the outer convective zone during the RGB evolution. In non-rotating models inward overshooting from the non-burning convective zone is a indispensable condition for emergence of the blue loops (this is in agreement with our previous results, Ostrowski & Daszyńska-Daszkiewicz 2015) With rotation enabled, inward overshooting from the non-burning convective zone is no longer necessary to produce a blue loop. Rotational mixing modifies the internal structure of a star, especially chemical abundances and μ-gradient, and the effect may be sufficient without the additional overshooting. Models with emerged blue loops have more hydrogen and less helium in the layers above the μ-gradient zone than models that do not loop and hence the hydrogen shell has more fuel available. Higher hydrogen abundance means also higher opacity above the helium core. Both of these effects suppress emergence of the blue loops (Walmswell et al. 2015) but the related effect of erased μgradient is much stronger. Contact details: *ostrowski@astro.uni.wroc.pl, ^daszynska@astro.uni.wroc.pl Bibliography Asplund, M., Grevesse, N., Sauval, A. J., Scott, P.: 2009, ARA&A 47, 481 Herwig, F.: 2000, A&A, 360, 952 Iglesias, C. A., Rogers, F. J.: 1996, ApJ 464, 943 de Jager, C., Nieuwenhuijzen, H., van der Hucht, K. A.: 1988, A&AS 72, 259 Lauterborn, D., Refsdal, S., Weigert, A.: 1971, A&A 10, 97 Ostrowski, J, Daszyńska-Daszkiewicz, J.: 2015, MNRAS 447, 2378 Paxton, B., Bildsten, L., Dotter, A., et al.: 2011, ApJS 192, 3 Paxton, B., Cantiello, M., Arras, P., et al.: 2013, ApJS 208, 4 Paxton, B., Marchant, P., Schwab, J., et al.: 2015, arxiv: v1 Vink, J. S., de Koter, A., Lamers, H. J. G. L. M.: 2001, A&A 369, 574 Walmswell, J. J., Tout, C. A., Eldridge, J. J.: 2015, MNRAS 447, 2951 Acknowledgements The work was financially supported by the Polish NCN grants 2013/09/N/ST9/00611, 2011/01/M/ST9/05914, 2011/01/ B/ST9/05448.