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: