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The Sun in Context…
Edward F. Guinan (葛輔華) Laurence DeWarf Villanova University
Talking Points • The Sun as the Gold Standard
• The Sun:up close and personal --
high resolution images at all wavelengths
• The Sun in context of solar-type stars
• (Helio / Astereoseismolgy)
• Magnetic Activity –Sunspots / Irradiance
• Zero-point of the rotation- Age-Activity
• relations
• Is the Sun a good example of a
• solar-type star?
• Conclusions
Up Close and Personal
with the Sun:
Because the Sun is close, we can
Resolve features smaller than 20 km
And, for example, make in situ
measures of the solar wind
Size of Texas
Sunspot Region And Solar
Granulation From Convective Motion
SORCE
Some Solar Space Missions
The solar corona, as observed by SDO’s AIA, for temperatures from 1 million degrees (blue), through 1.5 million (green), and 2 million (red), on 2010/08/01. This image serves as a background for magnetic field lines emerged onto the Sun. The locations of the major changes coincide with major solar activity on August 1, 2010. Credit: NASA, Lockheed Martin’s Solar and Astrophysics Laboratory.
The Sun as the Gold Standard A Benchmark to study other stars
At d = 4.85 x 10-6 pc, the Sun as the nearest
Star has by far the best determined
properties of any other star
Mass: 1.9891 (+/-0.0001) x 1033 g (Masses of most stars not directly
known- inferred. Eclipsing binaries – best masses ~1-5%
precision)
Diameter: 1,392,539 (+/- 0.1) km (~109.1 D-earth). Stars- best radii
from eclipsing binaries (1-2% ) / interferometry + distance
Distance: 149,597,870.7 (+/-0.1) km ; best stellar parallax distance
(alpha Cen AB/ Proxima 1.34pc
Mean Photospheric Temp: 5778 +/-3 K (from Irradiance
/distance). Spectral Analysis
Luminosity: 3.846 (+/-0.001) x 1033 erg/s (nearest stars typically 5-
20% uncertainties) / over 11 yr activity cycle ~0.2% variations.
Age: 4.567 +/-0.003 billion yrs. Radiometric age from meteorite
samples / helioseismic age are now in good agreement). Even
the best determined stellar ages typically have >10-30%
uncertainties. Asteroseimology is helping to improve stellar ages.
Rotation Period: f(latitude) = 25.6 d (at equator) / 1.99 km/sl Use in
Rotation-Age-Activity relations to estimate ages of other stars.*
Chemical Composition: spectra R > 200,000 , S/N >10,000 – most
elements and isotopes measured; Helium measured in Coronal;
surface abundances (some problems with Oxygen). Example-
Lithium under abundant relative to meteorites / other solar-like
stars. (See plot)
Irradiances (continuous bolometric flux measures back to 1978) *
Typical TSI: 1365 – 1367 watts/m2 (over ~11-yr activity cycle) but
large sunspots produce up to 0.4% light variations . Kepler is as
precies of solar irradiance measures but not internally Calibrated
and short time only ~90d.
Sun in Time Age-Activity Plot
Age (Gyr)0 2 4 6 8 10
log
LX
26
27
28
29
30
31
Fitting Equation:
y = y0 + ax
b
y0 = 31.84 +/- 1.512
a = -3.338 +/- 1.575
b = 0.2176 +/- 0.09613
EK Dra
1 UMa1 Ori
BE Cet1 Cet
Com
15 Sge
18 Sco
Sun
Cen A
Hyi
51 Peg
16 Cyg A
The Sun (age= 4.567 Gyr and <Lx> = 2 x 10+27 erg/s)
provides a zero-point for the Log Lx - Age relation for
Solar-type stars. But the Sun may be ~2 x higher coronal
X-ray emission than solar-age stars (discussed later)
Sun in Time Age-Rotation Relationship
Age (Gyr)
0 2 4 6 8 10
Pro
t (d
ays
)
0
10
20
30
40
50
EK Dra
1 UMa
1 Ori
Com
15 Sge
BE Cet
1 Cet
18 Sco
Sun
Cen A
Hyi
16 Cyg A
Fitting Equation:
y = y0 + ax
b
y0 = -0.3235 ± 2.3834
a = 10.6477 ± 2.6212
b = 0.5386 ± 0.0939
NGC 6819
The Sun (age = 4.57 Gyr and P(rot) = 25.6 d) provide the
benchmark for the P(rot) – Age relation for Solar-type stars
G0-5 V Stars
Age: 4.567 +/-0.003 billion yrs. Radiometric age from meteorite
samples / helioseismic age are now in good agreement). Even
the best determined stellar ages typically have >10-30%
uncertainties. Asteroseimology is helping to improve stellar ages.
Rotation Period: f(latitude) = 25.6 d (at equator) / 1.99 km/sl Use in
Rotation-Age-Activity relations to estimate ages of other stars.*
Chemical Composition: spectra R > 200,000 , S/N >10,000 – most
elements and isotopes measured; Helium measured in Coronal;
surface abundances (some problems with Oxygen). Example-
Lithium under abundant relative to meteorites / other solar-like
stars. (See plot)
---Irradiances (continuous bolometric flux measures back to 1978)
* Typical TSI: 1365 – 1367 watts/m2 (over ~11-yr activity cycle) but
large sunspots produce up to 0.4% light variations . Kepler is as
precies of solar irradiance measures but not internally Calibrated
and short time only ~90d.
The low Lithium abundance of the Sun may not be so
peculiar. A recent study by Israelian et al. (Nature 2012)
shows that solar-type stars hosting planets (shown by filled
red circles) also tend to have lower Lithium abundances
HIGH PRECISION PHOTOMETRY
USE Activity Proxies (C-14/ Be-10) to extend the time base of solar activity and irradiance back 10,000 yrs in the past. (cannot do this for another star)
From Sami Solanki et al. (Nature 2004). The Sun is more active at present (prior to 2000) than it has been for over 8000 years according to a new method or determining the level of sunspot activity in the past.
Solar Interior: Core temperature/ nuclear fusion
rates known from Neutrino Solar Telescopes that
probe into the core/ Standard Model now ~OK
Solar Structure: Helioseismology- GONG/
SOHO, MDI & others – permit the interior of the Sun
to be probed in exquisite detail and provides detailed
checks on the Standard Solar Model/ Map
circulations, depth of Convective Zone, Tachocline,
effects of magnetic field on subsurface flows and
much more. Variations of flows over magnetic activity
cycle/ Some anamolies between Helioseismic results
and interior models remain. (TBD Juergen Ch-D)
When John Bahcall's theory about solar neutrinos was finally vindicated after nearly 40 years, he said, "I feel like dancing I'm so happy.“ Photo with Ray Davis <- Homestake Experiment
Because of it’s proximity, the Sun is the only star (other than nearby SN) whose nuclear fusion core can
be studied with Neutrino Telescopes
Borexino Neutrino detector
Sudbury Neutrino Obs. - Neutrinos react
with the heavy water (D2O)
Solar Neutrino Astronomy –Now excellent Agreement with Solar Interior Models – Other than the Sun only SN Explosions can be deteted
Helioseismology / Asteroseismology
3D Sunspot: The subsurface structure (sound speed) below a sunspot as derived
from Doppler measurements by MDI. Using the technique of time-distance helioseismology, 3 planes are shown. The surface intensity shows the sunspot with the dark central umbra surrounded by the somewhat brighter, filamentary penumbra. The 2nd plane cuts from the surface to 24,000 km deep showing areas of faster sound speed as reddish colors and slower sound speed as bluish colors. The third plane (bottom) is a horizontal cut at a depth of 22,000 km showing the horizontal variation of sound speed. Credit: NASA/GSFC/SOHO
The solar rotation rate changes with change in the level of solar activity. The change can be seen clearly by
subtracting out the time averaged rotation rate from the rotation rate at each epoch. The change in the rotation rate as a function of radius and latitude is shown. The results shown are in m/s and the error in the results is of 1 m/s. These results were obtained with data obtained by GONG over solar cycle 23. Note the shifting pattern of the changes.
MIN
MAX
The Sun in Context:
How well does the Sun fit in with
similar age, solar-type stars
(solar twins)
Some examples:
Asteroseismology
Light variations (starspots)
Coronal X-rays
Oscillations on Alpha Cen A (Butler et al., ApJ 2004, VLT+AAT)
KIC 9844088: a Solar Analog in the Kepler Field
The G dwarf KIC 9844088, with Teff = 5500 K, has spot activity indicating a 18.3-day rotation period => ~ 3.5 Gyr age
For comparison, a light curve of the Sun from Unruh et al 2008
Comparison of SOHO and Kepler Solar-type Stars (Basri et al. 2010 )
The Sun’s Coronal X-ray Luminosity Compared with two “Solar Twins” of comparable age. Note the Sun’s X-ray Luminosity is currently 2x larger. (from DeWarf, Datin, Guinan ApJ 2010)
From Sami Solanki et al. (Nature 2004). The Sun is more active at present (prior to 2000) than it has been for over 8000 years according to a new method or determining the level of sunspot activity in the past.
Estimation of Sun’s Time Averaged Coronal X-ray Luminosity (Sunspot/ Be-10 proxies). Agrees with 18 Sco and alpha Cen
The Solar Twin (18 Sco) vs. Sun Property Sun 18 Sco Spectral Type G2 V G2 Va V(mag) -26.75 +5.504C B-V +0.648 +0.65C Mv(mag) +4.83 +4.77 Mass(Mo) 1.0 0.98B-1.0D Radius(Ro) 1.0 0.97 +/- 0.12E Temperature(K) 5777 5789+/-30D [M/H] 0.00 0.03+/-0.03B Rot. Period(days) 25 .6 22.7 +/- .5B Var./Activity Cycle ~11yrs. 9-14 yrs Age(Gyr) 4.567 4.2-5.0 Log Lx(ergs/s) ~6 - 30 x1026 1- 8 x 1026 Mt. Wilson <s> index 0.171 0.16-.184H Log(g) (cm s-2) 4.44 4.41 +/- 0.06B
Estimation of the mean Lx of the Sun from last 400 yrs Some Conclusions
The Sun in almost everyway can be used as
a standard / calibrator Star for the study of
other Solar-type stars. But keep in mind that
The Sun’s has been an atypical high activity
state (Grand Max) over the last 100 yrs.
The Solar Twin 18 Sco (almost an exact
match to the Sun could serve as a “Night
time Sun”. (HIP 56948 is also good.)
It will be important to carry out
Astereoseismogy of selected “solar twins” to
Compare to the Sun.
Thank You
).
