1. Age-Activity-Rotation Relationship in Solar-Type Stars
Giancarlo Pace PHD student
European Southern Observatory
Universita’ di Trieste
In collaboration with Luca Pasquini (supervisor at ESO)

2. Chr. Act. age & Star Formation Rate During late-type stars MS lifetime
chromospheric activity
and
rotation
decay
Chr. Act.
Chromospheric age
observed
for Field Stars
age
Ages + metallicities
Chemical evolution
&
Star Formation Rate

3. Our Goal: Decaying Law New-Generation Telescopes
Skumanich, 1972
Improved by Barry et al., 1987
Low resolution
spectra
New-Generation Telescopes
Good data also for old and
intermediate age Open Clusters

4. Indicator of Chromospheric Activity
Emission core of the Ca II K line
1 A index
Flux
High resolution (R=60000),
high S/N spectra
UVES at Kueyen VLT
HIRES at Keck
v rot
from Cross Correlation Profiles

5. Targets: 3 coeval pairs HYADES & PRAESEPE, 0.6 Gyr
15 and 7 stars respectively
IC 4651 & NGC 3680, ~1.5 Gyr
5 and 2 stars
M67 and the Sun, ~4.5 Gyr
7 stars in M67
Sun data from White and Livingston, 1981

6. Data Analysis Spectra normalization and rectification
Subtraction of the IS absorption
Index measurement
Subtraction of the photospheric contribution
Calibration in fluxes

7. age 0.6 Gyr 1.7 Gyr 4.5 Gyr Average spectra for each
Cluster and for the Sun over the
Solar-photosphere model
1.7 Gyr
age
4.5 Gyr

8. IC 4651 + NGC 3680 = M67 + Sun Abrupt decay within ~1.5 Gyr
Vertical bars = peak to peak spread
IC NGC 3680 =
M67 + Sun
Coeval pairs ~ same levels
Abrupt decay within
~1.5 Gyr
then no evolution
NO POWER LAW

9. Abrupt decay after 0.6 Gyr
Easy
explanation of the
Vaughan Preston gap

10. CONCLUSIONS
High resolution, high S/N spectra of 36 stars in 5 open clusters were taken to study rotation and chromospheric activity.
Abrupt decay before ~1.5 Gyr
Natural explanation of the Vaughan Preston gap
Later on the activity remains constant
The rotational velocity has a similar trend
Chromospheric ages can be reliable up to ~1.5 Gyr

11. Chromospheric Activity of 46 field stars
34 inactive, 4 intermediate, 8 active stars
Active <t1 , t2<intermediate<t2,inactive>t2