High Altitude Observatory (HAO) – National Center for Atmospheric Research (NCAR)
The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation. An Equal Opportunity/Affirmative Action Employer.
A Person [- al, -nel] History of HAO
Andrew Skumanich
Formerly with
High Altitude Observatory
National Center for Atmospheric Research
HAO 75th Anniversary
1 September 2015
SUBJECTS
1) Solar-Stellar Chromospheres & the Square Root of Age law
2) Radiative Transfer & Non-Local Thermodynamic Equilibrium
for the Two-level Atom
3) Stokes Polarimetry & Solar Magnetic Fields
4) The Phantom of the Observatory
& The Internal Structure of Differentially Rotating Stars
2
Solar Disk Ca II K Absorption Line
Wavelength
Posi
tion
on
Sola
r D
isk
Chromospheres
• Chromospheres Identified by Ca II H & K
emission in Main Sequence Stars
• Seen at solar eclipse as thin emission shell
between disk (photosphere) & corona
• Seen on disk as emission reversal in center
of strong absorption lines of Ca II H & K
• Main Sequence G stars (solar type)
• T(photosphere) = 5800 K
• T(minimum) = 4400 K
• T(chromosphere) = 6000-10,000 K
• T( corona ) = 1,000,000 K
• Main Seq M stars (red dwarf, ½ solar mass)
•T(photosphere) = 3400 K
3
Spectra of dwarf-e Stars: O C Wilson 1956
K H
wavelength
dG1e
dM2e
4
Ca II Emission, Stellar Kinematics,
Clusters, Rotation and Age 1953 Delhaye - dMe stars: small residual motion compared to dM: dMe young
1953 Vyssotsky & Skumanich - dG stars spectrally differentiated, ‘A’ & ‘B’ groups
dG ‘A have small residual dispersions (17 km/s) : YOUNG, HK emission?
dG ‘B contains the Sun, have larger dispersions (24 km/s): OLD, like SUN
1957 Vyssotsky & Dyer – Confirms Delhaye : dMe (11 km/s) & dM (30 km/s) dMe young
1963 Skumanich – ‘A = dGe & ‘B = dG: dGe young
1963 Wilson – Younger Open Clusters have stronger HK emission : Age vs. Cluster difference?
1964 Wilson & Skumanich – KHe field stars on Zero Age Main Sequence: d*e stars young
1965 Wilson – Deceleration of Rotation & Decreasing Chromospheric Emission
1967 Weber & Davis – Magnetized Solar Wind Deceleration of Rotation
1967 Kraft - Clusters & Field dGe stars show that Rotation declines with Age
5
Wilson & Skumanich 1964 L
um
inosi
ty i
nd
ex
Color Index
|
dG2
Solar
6
TEMP
|
dG2
Solar
|
|
|
|
|
|
|
|
|
MEAN INSTRUMENTAL HK FLUX vs COLOR
color
Wilson 1967
---e
e = Chromospheric HK emission amplitude,
Numbers give eye estimated strength
7
TIME SCALES FOR Ca II EMISSION DECAY, ROTATIONAL
BRAKING AND LITHIUM DEPLETION
1971
8
Radiative Transfer & Non-Local Thermodynamic Equilibrium
for the Two-Energy-Level Atom
“I stand in the peculiar and unenviable position of claiming that all existing
theories of line formation, including all solutions for the two-level atom, are
devoid of physical meaning. I now have one convert to my cause, viz. Pecker.
If you are willing, …, meet me in Munich. We (you and I) have some exciting
work to do”.
Grant Athay, letter to AS dated 19 Aug 1965
Consequence of the Munich Trip
An Integral Equation for the Line Source Function and Its Numerical Solution,
R Grant Athay and A Skumanich, Annales d’Astrophysique 1967
AUTHORSHIP: “In this and in subsequent papers we adopt the convention of
listing the authors names alphabetically without implications as to senior
authorship.”
In a series of papers (1968, ’69,’71), the A&S algorithm (Buck Frye) was used to
explore the nature of the Ca II K & H emission core as related to observed phenomena.
Additional studies were undertaken on the general nature of line formation in Stellar
Atmospheres.
9
NOTE: Q2 + U2 + V2 = I2 but <Q>2 + <U>2 +<V>2 < <I>2
Earliest Magnetic Field Programs at HAO Chromospheric Emission Line Observations
at the 40-cm coronagraph at Climax, CO
CIRCULAR ANALYSIS
• Magnetograph I : Hal Zirin, Bob Lee, Dave Rust, Joe Rush, 1963
• Magneto I Prominence Balmer α Analysis by David Rust, 1965 PhD thesis
• Magnetograph II : E. Tandberg-Hansen, Bob Lee, Jack Harvey, 1968
• Magneto II Prominence He I D3 Analysis by Jack Harvey, 1969 PhD thesis
• Zeeman Interpretation Difficult due to Resonance Scattering Polarization
Polarization Analysis–Quantitative, Precision Measurements
of Spectrally-Resolved Stokes Profiles
Stokes I Instrument
• Stokes I –Polarizer Analysis Concept: J. Beckers (1968),
Project Scientist: E. Tandberg Hansen (1969), House (1972)
Instrument Team: Baur, Curtis, Hull, Rush, Project Scientist
Project Support: Lacey, I. Lee, Rogers, Harper, Smartt, Elmore, T Wilson, Tisone
Features
• One measures linear as well as circular polarization (polarization ellipse)
• One measures polarization at each of 100 or so wavelengths
• One can use any line in the visible spectrum
• Instrumental polarization is very low
• Scattered light is very low, permitting off-limb (Prominence) observation
• Analytic Zeeman Inversion algorithm by Auer, Heasley & House (1977) – AHH
• Hanle Inversion algorithm by House (1977)
11
Evans Facility:
“Big Dome”
Richard B. Dunn
Solar Telescope
Observing
Facilities at
Sacramento
Peak
Observatory
Sunspot,
New Mexico
HAO Stokes Polarimeter
(“Stokes I”)
• Implemented at Sac Peak Big Dome
• Wavelength-stepped full Stokes
polarization measurements
• Flexible wavelength 390 – 700 nm
• Single-point detectors
• Very high sensitivity to polarization
• Modest spatial resolution
• Crude spatial sampling
• Operated 1974 – 1978
HAO Stokes I Observations of a Sunspot
Spot Data & Analysis by J. B. Gurman,
1979 Ph D thesis
14
• Stokes II –Project Scientist : House (1972), Querfeld (1978)
• Instrument Team: Baur, Elmore, R. H. Lee, Querfeld, Rogers, Project Scientist
• Project Support: Smartt (SPO), Mohr, Staufer, Wendler, Schick, Tisone
• AHH inversion scheme
• Hanle Depolarization algorithm by Landi delg’Ignocenti (1982)
Stokes II – Enhanced Version of Stokes I Instrument
• Linear array detectors – no need to step across the spectrum (improved speed)
• Increased wavelength range: 390 – 1095 nm (Disk, Prominences & Corona)
• Orderly spatial raster maps of the solar disk
15
Stokes II
• Stokes II observations: began June 1979 &
terminated at the end of October 1980
• “The failure of the diagnostic [inversion]
program for disk data … presents a
clear and important challenge to solar
physicists” HAO Ann Report 1980
• 1982: Skumanich (at urging of Athay) studies
AHH Inversion algorithm. System of Equations
OVERCONSTRAINED
• Skumanich & Lites: New Inversion Method
(1987)
• Stokes II Spot Analysis Successful–
Lites & Skumanich (1989)
• The Advanced Stokes Polarimeter (1989)
16
The Phantom of the Observatory
The Internal Structure of a Differentially Rotating Sun
Jackson, MacGregor & Skumanich
On the Use of the Self-Consistent-Field Method in the Construction
of Models for Rapidly Rotating Main-Sequence Stars
Astrophysical Journal 2004
Development of Hanle Effect Code for Determining
Prominence Magnetic Fields
“Much of the code development was carried out in an extremely
competent manner by S. Jackson” - Landi Degl’Innocenti1984
17
ACKNOWLEDGEMENT
I thank the following for their help
Joan Burkpile
Bruce Lites
Andy Stanger
&
Mary B. Skumanich
18
HAO Stokes I Observations of Prominences
2 hr before eruption
12 min after eruption
• Observations in He I D3 line
• Hanle effect analysis (not Zeeman): scattering polarization in weak magnetic field
• Theoretical and observational work by House, Smartt, Landi degl’Innocenti, Athay,
Bommier, Querfeld
• High polarimetric sensitivity of Stokes I instrument permitted meaningful analysis of
weak polarization
• Analysis of many prominences
indicated largely horizontal
fields
• Some hint of inverse polarity
• Ultimate goal toward which we
still strive: magnetic conditions
leading to prominence
eruption
• Although the Stokes I and II instruments produced limited scientific results, the
data from these instruments spurred advances in instrumentation, data analysis,
interpretation, and theory associated with the polarization in the solar spectrum
-- e.g. the first systematic center-limb observations in 1978 of non-magnetic
resonance line polarization (the “Second Solar Spectrum”) by J. O. Stenflo: