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NOT Summer School 2006
La Palma
Group A
Magnetic star EY Dra
Karsten Brogaard, Karianne Holhjem, Sofia Ramstedt,
Jari Rantala, Christina Thöne
Heidi Korhonen
0
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Outline
• Introduction: magnetic activity in stars
• Photometry



Alfosc-observations
Reductions
Results
• High resolution optical spectroscopy




Alfosc spectroscopy with Grism 17
Reductions
H line analysis
Interpretations
• NIR spectroscopy


Paschen  line
Stellar atmosphere model restrictions
• Summary and future plans
1
Magnetic activity in stars
2
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Magnetic fields on the Sun
• Magnetic fields are
produced by flows of hot
ionized gas in the solar
interior.
• The fields are sustained by
the combination of a
turbulent outer convective
zone and differential
rotation.
3
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Magnetic activity in stars
What do we need?
• Early-type stars
have rapid rotation,
but a radiative
outer layer.
• Late-type stars
have a convective
outer layer, but
slow rotation.
ZAMS Late-type star
EY Dra!
4
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
The solar atmosphere
• PhotosphereG-band continuum
(430.5 nm)
• ChromosphereH, Pa
CaII H & K
• Corona
UV and X-rays
Yohkoh satellite
5
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Magnetic features
SOHO-prominences
in the chromosphere
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
SST-sunspots on the
photosphere and
spicules in the
chromosphere.
SOHO-flare in the lower corona
6
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Stellar light curves
Photometric observations at different rotational
phase can be used to produce a light curve of the
object.
From the lightcurve the spotfilling factor can be
calculated.
7
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Spectral lines
• By doing high resolution
spectroscopy of
chomospheric lines at
different phases,
magnetic features can be
traced as they rotate the
star.
• This requires a rapid
rotating star with broad
lines.
• EY Dra vsin(i)=69 km/s
8
Photometry
9
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Photometry
• Starspots in the photosphere causing light
curve variations
• Rotation period of EY Dra is 0.459 days
• We needed a good phase coverage
• Sets of 3 exposures in V and R band with
ALFOSC
• Differential photometry
10
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Observations
• EYDra, a comparison star and a check star
• Windowing decreased read out time to ~35s
– Rotation of the field was also needed
EYDra
Comparison star
Check star
11
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reductions
• Basic IRAF tasks:
– Zerocombine, flatcombine and ccdproc for
different windows
• Other tasks from apphot package
– Daofind to find the coordinates
– Phot for calculating the magnitudes
12
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Results
• 4 sets during 1st night, 5 during 2nd night
(dots), and their average (stars)
– A few points with large variation, reason unknown
13
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Results
• W shape already seen in 1995: Might be real!
14
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Results
• Inversion using Heidi´s invert-program
– Two active regions can be seen
15
Optical spectroscopy
16
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Spectroscopy
• Data: EYDra
– grism #17 (R=10 000, =6200-6750)
– 1. night: 6 epochs, 2. night: 9 epochs
 remove fringing
– distribution over one rotation
• Calibration
– spectroscopic flats: Halogen lamp (in baffle)
– wavelength calibration: Neon lamp
 beginning/end of each epoch
– atmospheric standard: B(E)-star
– radial velocity standard star
17
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Bias subtraction
• Flat fielding
18
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Spectrum extraction
19
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Spectrum extraction
20
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Spectrum extraction
21
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Identifying lamp spectra
22
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Identifying lamp spectra
23
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Identifying lamp spectra
24
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Assigning the solution to the source spectra
25
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Normalising the continuum
26
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Normalising the continuum
27
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Reduction of spectra
• Resulting spectra
28
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Mistakes...
• Star to slit...star not to slit...wrong star to slit...
• Neon lamp spectrum in absorption!
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
29
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
EY Dra spectrum
H
Fe
TiO
Ca
H
30
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Atmospheric standard star
H
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
H
...turned out to be a BE-star
31
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Radial velocity determination
32
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Radial velocity determination
... fits perfectly, but gives wrong value :-(
33
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
H line analysis
• H line fitting
(splot)
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
34
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
H line analysis
• Equivalent width variations
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
35
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
H line analysis
• Line profile/strength changes
FWHM 95 - 125 km/s (v*sin(i) = 62 km/s)
36
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Comparison to lightcurve
Starspots correspond to increase in H emission
 similar to the Sun
Zur Anzeige wird der QuickTime™
Dekompressor „TIFF (LZW)“
benötigt.
37
IR spectroscopy
38
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Near IR Spectrosopy
•
•
Why NIR?
Why study the Paschen β line?
1) correlation with the Hα
2) restricting the model of the
stellar atmosphere
C.I. Short and J.G. Doyle
Astron. Astrophys. 326, 287-299 (1997)
Astron. Astrophys. 331, L5–L8 (1998)
39
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
The Paschen β line
• λ=12818 A=1,2μm
40
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Observations
• NOTCam, high-res camera, J-band, grism #1,
44 μm slit
• Frame 50 9
• Dithering ABBA for skysubtraction (or ABBC,
or BAAB)
• (Target – standard star – target) for removal
of lines from the earth´s atmosphere
• Spectra of lamps for flatfielding and
wavelength callibration
41
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Data reduction procedure
•
•
•
•
•
•
Bad pixel mask
Flat field
Skysubtraction
Shift and combine ABBA sequence
Extract spectra like for the optical case
Divide target by standard star
42
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Prelimary results
• The Paschen β is not seen in emission or
absorption
43
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Comparison to theory
• The pa-β line profile
depends on the pressure in
the chromosphere
• Pressure is messured as
log mTR where mTR is the
coloumn mass above the
bottom of the transition
region (g cm-2)
44
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Comparison to theory
• We can restrict the model to
log mTR < -4
-4
-4,2
-4
-4,2
45
Summary and outlook
46
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Scientific conclusions
• Two active regions on EY Dra:
separation 180˚
 common in active stars
• Correlation with H line strength
• Restriction of stellar atmosphere models:
Pressure: log mTR < -4
47
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Future work
• reduce NIR spectra
• redo wavelength calibration:
radial velocity standard
• write the report
• write an article
... And drink more wine :-)
48
NOT Summer School 2006
8.7.2006
Karsten Brogaard, Karianne Holhjem, Jari Rantala, Sofia Ramstedt, Christina Thöne, Heidi Korhonen
Thanks for your attention!
From the 5 most stupid observers of the
summer school ;-)
49
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