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Progress report on the determination of absolute
magnitudes using Strömgren photometry.
C. Jordi, E. Solano
Universitat de Barcelona
LAEFF, Madrid
COROT week 9: Dec-2005
Dec 5-9, 2005
Progress report on absolute magnitudes: COROT week 9
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Contents of COROTSKY: seismology programme
• Stars brighter than V=9, centre & anticentre directions.
• 12000 stars. 6820 stars later than A5.
• Hierarchical criteria for assigning Mv to a target.
 The criteria was reviewed in COROT week 7 (see Jordi,
Solano & Ribas).
 Already adopted in COROTSKY (see Charpinet’s
presentation in CW8.
Dec 5-9, 2005
Progress report on absolute magnitudes: COROT week 9
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(5) Absolute magnitude from Strömgren / Physpar
• “Stars with Strömgren photometry in the Physpar windows
not having / < 0.1”.
• 12 stars of “region1” (O-B)
•3
stars of “region 2” (A0-A2)
• 249 stars of “region 3” (late A) post-Hipp. calib (CW7)
Mv = 1.88 + 5.2 (b-y) o – 9.1 co + + 4.9 mo + 2.7 10-6 vsini2
• 278 stars of “region 4” (F0-G2) post-Hipp. calib (CW7)
Mv = Mv(ZAMS,) - 0.13 + 1.57  - (8.9+29.6 ) co + 0.22 [Fe/H]
• Stars of “region 5” (from G2) PENDING
• 50 stars of “regions 6-8” (B0-G5 supergiants)
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Progress report on absolute magnitudes: COROT week 9
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G2-K type stars: Mv calibration
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Definition of a well-controlled stellar sample

Complete uvby- photometry in Hauch & Mermilliod (1998)

Classified as “region 5” with PHYSPAR

V in Hipparcos and Hauck & Mermilliod (1998) in agreement

At least 2 measurements in Hauck & Mermilliod (1998)

Spectral type in Hipparcos in agreement with photometry

Not anomalous location in colour-colour diagrams

Not supergiants according to photometry

Not luminosity classes I & II according to spectral type in Hipparcos

Not peculiar, variable or belonging in multiple systems (HIP flags)

Not variable or joint photometry in Hauck & Mermilliod (1998)

Not variable or belonging in multiple systems according to SIMBAD
303 stars: 272 with /<0.15
104 with /<0.1
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Progress report on absolute magnitudes: COROT week 9
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How do the pre-Hipparcos
calibrations behave?
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Olsen(1984)
A trend with metallicity
A slight trend with evolution
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COROTSKY
What’s happening
here?
Dec 5-9, 2005
Progress report on absolute magnitudes: COROT week 9
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Let’s see an example
• HD46241. Δ(Mv)=-6.809. Classified by Physpar as K0V.
• π : 6.3
• σ(π)/ π: 0.149  d= 159 pc.  Av = 0
• V= 5.83  Mv(π) = -0.18
 It cannot be a MS star
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COROTSKY
What’s happening
here?
T
• GKM giants have Mv in the range [0.0, -0.5]
T
T• GKM MS have Mv > 5
T
• Stars having ΔMv < -5 are giants wrongly
T
t
classified.
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COROTSKY
Why so many
giants?
T
• GKM Main Sequence stars with V < 9.5 are nearby
T
stars  they have good parallaxes  classified in
T
group (2): σ(π)/π<0.1
T
• Stars with V < 9.5 not having good parallaxes must
T
be far  they must be giants.
t
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Building the new calibration ...
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largest dependency
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Same approach as for F0-G2 calibration
1) stars with / < 5 % (104 stars, small bias, unreddened)
least-squares fit with 3-sigma clipping
Mv()-Mv(ZAMS, (b-y) o)= 0.238 – [ 5.49 + 18.89(b-y)o ] co
2) stars with / < 15 % (272 stars, unreddened)
least-squares fit with 3-sigma clipping
Mv()- Mv = +0.08 – 6.78 mo
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The new calibration ...
Mv = Mv(ZAMS,) + 0.238 – [ 5.49 + 18.89(b-y)o ] co – 6.78 mo
± 0.018
0.58
7.36
0.40
Valid for -0.10 < co < 0.25
-0.05 < mo < 0.11
0.36 < (b-y)o< 0.60
Dec 5-9, 2005
 = 0.11 mag
Progress report on absolute magnitudes: COROT week 9
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COROTSKY
24 stars; /<6%
=0.40
Trends have been removed
=0.28
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Conclusions
• A new Strömgren calibration has been derived for the G Main
Sequence stars.
• Both systematic and random errors have been reduced.
• 249 late-A + 278 F0-G2 + 30 G2-K0 MS stars with Mv derived from
Strömgren photometry using post-Hipparcos calibrations ready to be
delivered to COROTSKY.
•… BUT still too many stars without information on Mv…
• New method: Spectral type & luminosity: σ(Mv) = 1 subtype
- SIMBAD has been explored but VizieR has not.
- To explore all the catalogues contained in VizieR using VO-like
tools (e.g. vizquery).
Dec 5-9, 2005
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