Observations of SunLike Stars

1
Observations of Sun-Like Stars and their
Implications for Long Term Solar Activity
Jeffrey C. Hall Lowell Observatory Flagstaff, AZ
2
Background
The Discovery of Stellar Activity Cycles,
1966-1978
Does the chromospheric activity of main-sequence
stars vary with time, and if so, how?
3
Background
The Solar-Stellar Connection, 1978-1989
Nimbus-7 and successors Absolute measurements of
TSI discovery of its variation
IUE and successors Absolute flux measurements
from space ? Development of analytical models
of outer stellar atmospheres ? Contemporaneous
with VAL models
Hardorp, The Sun Among the Stars
I Identification of solar analogs in parameter
space
4
Background
The Solar-Stellar Connection, 1978-1989
Examination of solar analogs in the time
domain ...the phase of Ca II maximum flux
corresponds to light minimum.
5
Background
The Solar-Stellar Connection, 1978-1989
Motivation to express stellar observations in
terms of physical quantities
HD 82885
1.09 Å FWHM
1 Å rectangle
6
Background
Solar Analogs, 1989-2009
Two provocative solar-stellar hypotheses Is
there a simple solar cycle-climate
correlation? Are stars significantly dimmer in
Maunder minima?
We have found very few good solar analogs, and
almost no twins Present time domain surveys are
magnitude limited The best-observed solar twin
is 18 Scorpii ? Sun-like variations, but has
abundance issues, probably younger
Present observational focus Narrower target set
than the Mt. Wilson survey Maunder minimum
candidates
7
Variations of Sun-Like Stars
Long Term Variations Broad Patterns
8
Variations of Sun-Like Stars
Long Term Variations Activity and Brightness
Mount Wilson Lowell Fairborn contemporaneous
HK photometry
9
Variations of Sun-Like Stars
Long Term Variations Solar Analogs
10
Variations of Sun-Like Stars
Short Term Variations Multiple Periods Field
Properties
A quick aside the SSS stellar cycles program
11
Grand Minima
Evidence for Transitions
There is some evidence for Maunder Minimum
transitions in the Mount Wilson Observatory data
set
12
Grand Minima
Maunder Minimum Candidate Stars
HD 10700 (? Cet) is a promising candidate
Physical units clearly preferred over either S or
R'
13
Grand Minima
Effects of Grand Minima on Stellar Brightness
Possible evidence of an activity-brightness
pattern transition?
14
The Stellar Perspective
Implications for the Solar Activity Cycle
Transitions between direct and inverse
activity-brightness variations may occur at
activity levels only slightly above the modern
solar maximum
Long term observations of good solar analogs
indicate the 0.1 TSI variation of the solar
cycle is not unusual
The chromospheric variations of 18 Sco are
comparable in amplitude and absolute level to the
modern solar cycle....but...!
Activity-brightness correlation has disappeared
in the last 2 seasons
15
The Stellar Perspective
Implications for the Maunder Minimum
The frequency of apparent grand minima in our
data set is consistent with the solar record of
the past millennium
The magnetic state of flat activity stars does
not appear to be markedly different than that of
the modern solar minimum
16
Prospects for the Future
The Next Generation of Solar-Stellar Studies
Expanded proxies and wavelength coverage
Contemporaneous photometry is essential, and
requires higher precision than even the excellent
Fairborn data
A significant sample of solar twins probably
requires synoptic observing programs to V 11
17
Online Resources
http//www.lowell.edu/users/jch/sss Catalog,
data reduction techniques and docs Time series
and results Layperson-level information and
blog
Solar Analogs II September 20-23,
2009 http//www.lowell.edu/workshops/SolarAnalogs
II