Seismology%20of%20Be%20stars%20with%20CoRoT

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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
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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

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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

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Variability in Be stars

• Short-term variability present in the
  quasi-totality of 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

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Example of multiperiodicity in light curves

• 19 Mon

• Upper panelfolded in phase
• with P10.191d ?
• Lower panel folded in phase
• with P20.204d 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.
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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)

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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
• P10.5029d l2, m2 Df0.21, 0.39, 0.60 mHz
• P50.2814d l3, m3 Df0.33 mHz

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m Cen pulsation beating effect
Rivinius et al., 1998
The overall reconstructed amplitude (solid
lines) circles Df1-2 squares Df1-3 dots
Df2-3
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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! Prot12d Ppuls0.19d
• w Ori (Neiner et al. 2003) a  classical  Be
  star
• Prot1.29d Ppuls0.97d
• magnetic fields several hundreds of Gauss

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Observed frequencies in b Cep (Telting et al.
1997)
f356.979 mHz f458.819 mHz f160.764
mHz f562.697 mHz f664.618 mHz f262.269 mHz

- Quintuplet fine structure of f1, f3 , f4 , f5
, f6 - f1 and f2 independent
magnetic splitting identification of modes ?
information on the evolutionary stage
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Radial mode ? f1 (l2, m0) 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 l2 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)
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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 lt 1mmag for lgt4 in early Be stars
• (Balona Kambe 1999)
• search of low-amplitude g modes in late Be stars

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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!

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Be stars as potential targets for
asteroseismology with COROT

• About 70 Be stars with 6ltVlt9.5 in the cones of
  COROT (seismology fields) including 15 new Be
  stars with Vlt8.0 (GAUDI)
• 18 Be stars as secondary targets candidates for
  the core programme of asteroseismology
• Faint Be stars with 12ltVlt16.5 in the exoplanet
  fields as part of the Additional Programme

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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)

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Photometric variability Hipparcos (Hubert
Floquet )

• Some of the targets observed by Hipparcos
  periodicity found!

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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!

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Spectroscopy GAUDI

• for 6 lt V lt 8 ? spectra in GAUDI
• 17 new Be stars discovered in GAUDI (Neiner,
  Hubert Catala, 2004)
• But
• No spectrum if V gt 8
• Additional data for studying variability are
  needed

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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 gt 8
• Detection of variability

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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
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• Gravitational darkening effects

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(Frémat Zorec)
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(No Transcript)
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Results for primary fields
Centre
Main target Be target Type V vsini Teff log g Variability
HD 171234170580 HD 171219 B8e 7.65 300 13590 3.07
HD 171834 HD 171219 B8e 7.65 300 13590 3.07
HD 175726 HD 175869 B9IIIe 5.56 164 11810 3.25
HD 177552 -
HD 181555180642 HD 181231 B9Ve 8.58 250 13658 3.73
HD 181367 B8e 9.36 279 13500 3.65
? Only late Be stars in these primary targets
fields.
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Anticentre
Main target Be target Type V vsini Teff log g Variability
HD 43318 -
HD 43587 HD 43285 B6Ve 6.07 240 14000 3.78 0.45 d
HD 43913 A0e 7.88
HD 45067 -
HD 46558 HD 45901 B2Ve 8.8 164 26518 3.73 phot
HD 46484 B1Ve 7.74 120 27000 3.60 3.29 d
HD 47359 B0.5Ve 8.87
HD 4993349434 HD 49330 B0e 8.92 300 27000 3.82 0.28 d
HD 49585 B0.5Ve 9.13 253 26042 3.75 0.61 d
HD 50209 B9Ve 8.33 180 11809 3.62 0.66 0.59 d
HD 50696 B1Ve 8.83 350 21300 3.45 0.31 d
HD 52265 HD 50891 B0pe 8.88 0.54 d
HD 51193 B1Vnne 8.06 215 22994 3.62 0.61 5.5 d
HD 51404 B3e 9.3 342 22500 4.2 0.37 d
HD 51452 B0IIIne 8.08 298 29887 3.88 spec
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• 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)

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Field HD 171234 HD 170580
171219
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Field HD 175726
175869
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Field 181555 HD 180642
181367
181231
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Field HD 43587
43285
HD 43913
43913
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47359
Field HD 46558
46484
46484
HD 47359
45901
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Field HD 49933 HD 49434
49330
50696
49585
50209
Diapositive 29
? 3 early Be stars outside the CCDs with this
position of the CCDs
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Field HD 52265
50891
51193
51452
HD 50891
51404
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HR diagram of Be secondary targets
4 Be stars
Apparent Location
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HR diagram of Be secondary targets
4 Be stars
Rotation effect
W/Wc 0.95
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HR diagram of Be secondary targets
in the CCDs
2 Be stars in the CCDs 2 Be stars
Real Location
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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

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Preparatory programmes in exoplanet fields

• Be stars as targets for seismology in exoplanet
  fields (12ltVlt16)
• 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

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Detection of Be stars in the exoplanet fields

• uvby photometry Ha,Hb narrow filters by 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

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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
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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 Vlt14!
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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, Befor Additional Programmes of
  COROT

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Giraffe a multi-object spectrograph
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VLT-GIRAFFE spectrograph
In Medusa mode 132 spectra R6000-30000 Requir
ed astrometric precision 0.2 Field
?26 Fibers Minimal separation 12
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Search for Be stars with VLT-GIRAFFE

• Domains
• LR06 (644nm - 710nm R8600) Ha
• - emission line starsBe, Ae/Be
• LR02 (397nm - 456nm R6400) H?, H?, blue He I,
  Mg II
• - stellar types and fundamental parameters
• For B9 stars, 1h exposure time, V 15, S/N ?
  100

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Giraffe field f25 ? 0.1364 deg2
a200018h50 d2000000
Statistics towards the galactic centre according
to the Besançon model of stellar population
synthesis of the Galaxy (Robin et al. 2003)
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Expected detection of Be stars in the exoplanet
fields

• Centre direction
• 200 Be stars (12ltVlt16)
• in 1 deg2
• Exoplanet CCDs 1.3x2.5 deg2

• Anti-centre direction
• 30 Be stars (12ltVlt16)
• in 1 deg2
• Exoplanet CCDs 1.3x2.5 deg2

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)
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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 CCDs