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ASTR 551, Majewski [SPRING 2012]. Lecture Notes

ASTR 551 (Majewski) Lecture Notes


SURVEY OF THIN DISK PROPERTIES: AGE & STAR FORMATION HISTORY

We want to understand better the sequence of events in the formation of the Galactic stellar populations.

We have seen that accretion and an extended formation for the outer Galaxy is implied by a number of avenues.

What was the relative timing of halo formation to the inner Galaxy?

The goal of this section of the course is to understand what we know of the age/chemical properties of the inner Galaxy.

I discuss the thin disk and thick disk separately under assumption that IPII thick disk are separate populations, but, a priori, there is no reason to believe that they may be so distinct from one another.


NUCLEOCOSMOCHRONOLOGY

Use of long-lived radioactive isotopes to derive ages of the nucleosynthetic events that created them.


WHITE DWARF LUMINOSITY FUNCTION


OPEN CLUSTERS


RED CLUMP

The red edge of the HB red clump is well defined for MSTO stars from 0.8 to 1.3 solar masses (ages 2-16 Gyr).

Jimenez et al. (1998) used red clump from HIPPARCOS to determine the maximum metallicity of red clump stars as [Fe/H] = +0.3.

With this assessment of maximum disk metallicity, now plot isochrones for that metallicity.

Conclude --> minimum age of disk >~ 8 Gyr, likely more.


STROMGREN PHOTOMETRY


ASTEROSEISMOLOGICAL AGES

Of course, as we saw earlier, a very promising age dating method will be that given by asteroseismology, particularly from the large sample that is going to be provided by Kepler in combination with APOGEE chemistry. This project is just starting, so stay tuned!

The hope is that asteroseismology (which can reveal the mass of, say, a giant, which, with a known metallicity, tells you its age) with precise chemistry will be the most reliable means to age date the disk.


STELLAR CHROMOSPHERE ACTIVITY AND A DISK STAR FORMATION ACTIVITY


SUMMARY

Many method indicate disk age around tdisk ~ 12 Gyr (modulo usual age scale concerns).

Definition of "disk" a concern:


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All material copyright © 2003,2006,2012 Steven R. Majewski. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 551 at the University of Virginia.