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Seismology of Be stars with CoRoT

Seismology of Be stars with CoRoT. Paris-Meudon Observatory: A.M. Hubert, M. Floquet, C. Neiner* Univ. of Valencia : J. Fabregat, J. Gutierrez-Soto, J. Suso Univ. of Sao Paulo : E. Janot-Pacheco, L. Andrade, S. Daflon Royal Observatory of Belgium : Y. Fr é mat *ESA, Estec , RSSD.

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Seismology of Be stars with CoRoT

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  1. Seismology of Be stars with CoRoT Paris-Meudon Observatory: A.M. Hubert, M. Floquet, C. Neiner* Univ. of Valencia: J. Fabregat, J. Gutierrez-Soto, J. Suso Univ. of Sao Paulo: E. Janot-Pacheco, L. Andrade, S. Daflon Royal Observatory of Belgium: Y. Frémat *ESA, Estec, RSSD 1st Brazil-CoRoT meeting

  2. Seismology of Be stars with CoRoT • Overview of Be stars • Be stars as non radial pulsators • What do we expect from COROT? • Preparatory programmes • in “seismo“ fields • in “exoplanet“ fields • Conclusion 1st Brazil-CoRoT meeting

  3. Be stars: main characteristics • Population: about 20% of all B-type stars • Main sequence or slightly evolved • Usually rapidly rotating stars (W/Wc ≥ 0.80) • Equatorially concentrated envelope • Discrete mass loss events: unknown origin • Variability: NRP+ stellar and circumstellar activity • Be phase: non permanent character 1st Brazil-CoRoT meeting

  4. Variability in Be stars… • Short-term variability present in the quasi-totalityof early Be stars, in ~ 50% of mid-types (B4-B5e) and in only 18% of late Be stars (Hipparcos data, Hubert & Floquet 1998) • Short periods commonly detected in photometry and spectroscopy • Multiperiodicity in light curves and line profiles e.g.  Oph (O9.5Ve), Jankov, Janot-Pacheco, Leister 2000 and MOST data; 19 Mon (B1Ve), Neiner, Hubert, Floquet 2003; Balona et al. 2002 1st Brazil-CoRoT meeting

  5. Example of multiperiodicity in light curves • 19 Mon • Upper panel:folded in phase with P1=0.191d  • Lower panel: folded in phase with P2=0.204d after removing P1  • NB: P1and P2 also found from ground-based data by Balona et al. 2002 Variation of the magnitude of 19 Mon from Hipparcos data. 1st Brazil-CoRoT meeting

  6. Be stars as non-radial pulsators… b Cephei, SPB (Slow Pulsating B stars), Be stars Same instability domain (k mechanism) Line profiles modelling support NRP (e.g.Rivinius et al. 2002, Neiner et al. 2004) 1st Brazil-CoRoT meeting

  7. Be stars as non-radial pulsators… • NRP beating and discrete mass loss events? • only one case:  Cen, 15 years of spectroscopic observations modes beating and prediction of epochs of mass loss(Rivinius et al. 1998) 6 periods sorted in 2 groups main mode of each period group: P1=0.5029d l=2, |m|=2 Df=0.21, 0.39, 0.60 mHz P5=0.2814d l=3, |m|=3 Df=0.33 mHz 1st Brazil-CoRoT meeting

  8. m Cen : pulsation beating effect Rivinius et al., 1998 The overall reconstructed amplitude (solid lines); circles: Df1-2; squares: Df1-3; dots: Df2-3 1st Brazil-CoRoT meeting

  9. Be stars as magnetic pulsators • Magnetically pulsating stars? • 2 detections among pulsating early B stars: • Cep(Henrichs et al. 2000): also a slowly rotating Be star! Prot=12d; Ppuls=0.19d w Ori(Neiner et al. 2003): a « classical » Be star Prot=1.29d; Ppuls=0.97d magnetic fields: several hundreds of Gauss 1st Brazil-CoRoT meeting

  10. Observed frequencies in b Cep(Telting et al. 1997) f3=56.979 mHz f4=58.819 mHz f1=60.764 mHz f5=62.697 mHz f6=64.618 mHz f2=62.269 mHz } - Quintuplet fine structure of f1, f3 , f4 , f5 , f6 - f1 and f2: independent magnetic splitting + identification of modes  information on the evolutionary stage 1st Brazil-CoRoT meeting

  11. Radial mode  f1 (l=2, m=0) mode  f2 H-R diagramme: The stars whose radial mode frequency coincides with the observed frequency f1 are connected with the solid lignes, and those whose l=2 mode frequency matches with f2 are shown by the dashed lines. The crossing Points of the solid and dashed lines are the candidate locations for b Cep on the H-R diagramme (from Shibahashi & Aerts, 2000) 1st Brazil-CoRoT meeting

  12. Seismology with COROT • Homogenous data • Long-term continuous coverage: • high accuracy on frequency spectrum - multimode detection - beating • it will allow us to disentangle pulsations from stellar activity (corotating clouds) • Very high photometric accuracy : • detection of high degree modes of low amplitude Amp < 1mmag for l>4 in early Be stars (Balona & Kambe 1999) • search of low-amplitude g modes in late Be stars 1st Brazil-CoRoT meeting

  13. Early and late Be stars: 2 science goals • Early Be stars (B0-B3): pulsations and multiperiodicity already detected from the ground • Is the beating effect of close pulsation periods the cause of the Be phenomenon i.e. the presence of a disk around Be stars? • Effects of fast rotation and magnetic field on the pulsations • Late Be stars (B4-B9): pulsations predicted by theory but the amplitude is too small to be detected from the ground  detection of pulsations with Corot! 1st Brazil-CoRoT meeting

  14. Be stars as potential targets for asteroseismology with COROT • About 70 Be stars with 6<V<9.5 in the cones of COROT (seismology fields) including 15 new Be stars with V<8.0 (GAUDI) • 18 Be stars as secondary targets candidates for the core programme of asteroseismology • Faint Be stars with 12<V<16.5 in the exoplanet fields as part of the Additional Programme 1st Brazil-CoRoT meeting

  15. Preparatory programmes in “seismo“ fields • Be stars as secondary targets candidates in primary fields (long runs) • Photometric variability: periodicity, multiperiodicity • Spectroscopic variability: pulsation modes • Determination of fundamental parameters taking into account fast rotation - Abundances • Search of magnetic fields (EsPaDoNS, CFHT) • Be stars for exploratory fields (short runs) 1st Brazil-CoRoT meeting

  16. Photometric variability: Hipparcos (Hubert & Floquet ) • Some of the targets observed by Hipparcos: periodicity found! 1st Brazil-CoRoT meeting

  17. Ground-based photometry + variability (Fabregat, Gutierrez-Soto, Suso) • Strömgren photometry at the 0.9m in Granada for variability: detection of variability, periodicity and even multiperiodicity for HD 168797 and HD 179405 • NB: HD 168797 has been in a B phase for several years! 1st Brazil-CoRoT meeting

  18. Spectroscopy: GAUDI • for 6 < V < 8 spectra in GAUDI • 17 new Be stars discovered in GAUDI (Neiner, Hubert & Catala, 2004) But: • No spectrum if V > 8 • Additional data for studying variability are needed 1st Brazil-CoRoT meeting

  19. Additional spectroscopy + variability (Hubert, Janot-Pacheco, Andrade) • Spectroscopic observations at the 1.5m at OHP • Spectroscopic observations at the 1.6m at LNA, FEROS, soon EsPaDoNS • Spectrum for Be stars with V > 8 • Detection of variability 1st Brazil-CoRoT meeting

  20. Determination of stellar parameters ( Frémat, Neiner, Daflon, Andrade) • Data : GAUDI + OHP + LNA • 2 independent determinations: Frémat & Neiner + Daflon & Andrade • ~70 Be stars in the eyes of Corot 26000 3.75 253 1st Brazil-CoRoT meeting

  21. Gravitational darkening effects 1st Brazil-CoRoT meeting

  22. (Frémat & Zorec) 1st Brazil-CoRoT meeting

  23. 1st Brazil-CoRoT meeting

  24. Results for primary fields Centre  Only late Be stars in these primary targets fields. 1st Brazil-CoRoT meeting

  25. Anticentre 1st Brazil-CoRoT meeting

  26. Centre: • 5 possible late Be stars including 3 well positioned next to the primary targets • no early Be stars Anticentre: • 3 possible late Be stars well positioned next to the primary targets • 10 possible early Be stars including 3 well positioned next to HD 52265 TOTAL: 18 possible Be stars (8 late, 10 early) including 9 well positioned (6 late and 3 early) 1st Brazil-CoRoT meeting

  27. Field HD 171234 + HD 170580 171219 1st Brazil-CoRoT meeting

  28. Field HD 175726 175869 1st Brazil-CoRoT meeting

  29. Field 181555 + HD 180642 181367 181231 1st Brazil-CoRoT meeting

  30. Field HD 43587 43285 + HD 43913 43913 1st Brazil-CoRoT meeting

  31. 47359 Field HD 46558 46484 46484 + HD 47359 45901 1st Brazil-CoRoT meeting

  32. Field HD 49933 + HD 49434 49330 50696 49585 50209 Diapositive 29  3 early Be stars outside the CCDs with this position of the CCDs 1st Brazil-CoRoT meeting

  33. Field HD 52265 50891 51193 51452 + HD 50891 51404 1st Brazil-CoRoT meeting

  34. HR diagram of Be secondary targets + 4 Be stars Apparent Location 1st Brazil-CoRoT meeting

  35. HR diagram of Be secondary targets + 4 Be stars Rotation effect W/Wc = 0.95 1st Brazil-CoRoT meeting

  36. HR diagram of Be secondary targets = in the CCDs + 2 Be stars in the CCDs + 2 Be stars Real Location 1st Brazil-CoRoT meeting

  37. Results for exploratory fields • ~ 60 possible Be targets for exploratory fields (short runs) • It is better to concentrate on early Be stars, since we have very few early Be stars as secondary targets • 2 already detected with multiperiodicity(Fabregat et al.) : HD 168797 (B3e) and HD 179405 (B5e) • Targets in non-selected primary fields have been well studied  easier candidates 1st Brazil-CoRoT meeting

  38. Preparatory programmes in exoplanet fields • Be stars as targets for seismology in exoplanet fields (12<V<16) • Detection of Be stars in selected fields (in progress) • Determination of fundamental parameters • Selection of the “best “ candidates (early Be stars) • Search of photometric variability 1st Brazil-CoRoT meeting

  39. Detection of Be stars in the exoplanet fields • uvby photometry + Ha,Hb narrow filtersby J. Fabregat and collaborators: • Starting point: emission line stars catalogue of Robertson & Jordan (1989) • No information on spectral types is available • Observations at Calar Alto (Almeria, Spain) • Provide spectral classification for RJHA stars • Find new Be stars in exoplanet fields 1st Brazil-CoRoT meeting

  40. Photometry of emission line stars in potential exoplanet fields to identify B stars Diagramme without reddening [m1]-[c1] 5 emission line stars of RJ are B stars 1st Brazil-CoRoT meeting

  41. Diagramme a-b At least 4 of 5 B emission line stars are confirmed and are probably Be stars + 1 more discovered N.B.: Robertson-Jordan stars limited to V<14! 1st Brazil-CoRoT meeting

  42. Detection of Be stars in the exoplanet fields • Spectroscopy with VLT/GIRAFFE Part of a programme on the Guaranteed Time Observations of the Observatoire de Paris devoted to spectral classification and precise type identification in exoplanet fields of COROT (G. Alecian P.I., Hubert, Deleuil, Neiner, Floquet, Martayan).  In particular to identify specific groups of stars, Hg-Mn, Be…for Additional Programmes of COROT 1st Brazil-CoRoT meeting

  43. Giraffe: a multi-object spectrograph 1st Brazil-CoRoT meeting

  44. VLT-GIRAFFE spectrograph In Medusa mode: 132 spectra R=6000-30000 Required astrometric precision : 0.2” Field =26’ Fibers: Minimal separation ~ 12” 1st Brazil-CoRoT meeting

  45. Search for Be stars with VLT-GIRAFFE Domains: • LR06 (644nm - 710nm; R=8600): Ha - emission line stars:Be, Ae/Be… • LR02 (397nm - 456nm; R=6400): H, H, blue He I, Mg II - stellar types and fundamental parameters For B9 stars, 1h exposure time, V= 15, S/N 100 1st Brazil-CoRoT meeting

  46. Giraffe field: f=25’  0.1364 deg2 a2000=18h50’; d2000=0°00 Statistics towards the galactic centre according to the ‘Besançon’ model of stellar population synthesis of the Galaxy (Robin et al. 2003) 1st Brazil-CoRoT meeting

  47. Centre direction ~ 200 Be stars (12<V<16) in 1 deg2 Exoplanet CCDs ~1.3x2.5 deg2 Anti-centre direction ~ 30 Be stars (12<V<16) in 1 deg2 Exoplanet CCDs ~1.3x2.5 deg2 Expected detection of Be stars in the exoplanet fields Estimation from statistics towards the galactic centre and anti-centre according to the ‘Besançon’ model of stellar population synthesis of the Galaxy (Robin et al. 2003) 1st Brazil-CoRoT meeting

  48. Conclusions • We need early and late Be stars as secondary targets: 2 different science goals • We have 9 out of 18 Be stars (possible secondary targets) which are well positioned in the CCDs, but 6 late and only 3 early • We need to concentrate on early Be stars for the exploratory fields • We already have 2 very interesting exploratory candidates • The final list of faint Be stars for seismology is in preparation; it will be chosen according to the position of the exoplanet CCD’s 1st Brazil-CoRoT meeting

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