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Diamonds in the Rough: The Oldest Stars in the Galaxy. June 11 th , 2009 - 1. Space Telescope Science Institute: Hubble Science Briefings. Jason Kalirai (STScI). Outline An Introduction: The First Hints on How Stars Evolve. Our Current Picture of Stellar Evolution

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slide1

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 1

Space Telescope Science Institute: Hubble Science Briefings

Jason Kalirai

(STScI)

Outline

An Introduction: The First Hints on How Stars Evolve.

Our Current Picture of Stellar Evolution

A Surprise in our Backyard: The First “Discovered” White Dwarf

Why Search for Dead Stars?

What 120 orbits of Hubble Space Telescope Time Gets You.

Summary and Future Outlook

slide2

June 11th, 2009 - 2

Space Telescope Science Institute: Hubble Science Briefings

An Interesting Correlation: The Hertzsprung-Russell Diagram

Ejnar Hertzsprung (1905)

Parallax:Parallax angle = 1 / (distance to star)

Observation: 1.) Stars with the same parallax have different luminosities.

Giants vs Dwarfs! First luminosity classes created.

2.) Luminosities of some stars are correlated with their colors…

slide3

Luminosity

Temperature

June 11th, 2009 - 3

Space Telescope Science Institute: Hubble Science Briefings

An Interesting Correlation: The Hertzsprung-Russell Diagram

Ejnar Hertzsprung

Henry Norris Russell

Publ. Astrophys. Observ. Potsdam 22, 1, 1911

The Observatory,

Vol. 36, 324, 1913

slide4

“Zur Strahlung der Sterne” (On the Luminosity of the Stars)

- Hertzsprung, E., Zeitschrift fur Wissenschaftliche Photographie (Journal for Scientific

Photography), Vol. 3, 442, 1905

- Hertzsprung, E., Publ. Astrophys. Observ. Potsdam, Vol. 22, 1, 1911

“Giant and Dwarf Stars”

- Russell, H. N., The Observatory, Vol. 36, 324, 1913

“On the Probable Order of Stellar Evolution”

- Russell, H. N., The Observatory, Vol. 37, 165, 1914

“…one corner of the diagram is vacant…There do not seem to be any faint white stars. All of the very faint stars are very red.”

“…the converse propositions are not true; there is no doubt at all that there exist many very bright red stars (such as Arcturus, Aldebaran, Antares, etc.).”

“There appears, from the rather scanty evidence at present available, to be some correlation between mass and luminosity.”

Luminosity

Temperature

June 11th, 2009 - 3a

Space Telescope Science Institute: Hubble Science Briefings

An Interesting Correlation: The Hertzsprung-Russell Diagram

Ejnar Hertzsprung

Henry Norris Russell

Publ. Astrophys. Observ. Potsdam 22, 1, 1911

The Observatory,

Vol. 36, 324, 1913

slide5

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 4

Space Telescope Science Institute: Hubble Science Briefings

Two Key Properties

1.) Star formation produces predominantly low mass stars.

2.) Stellar evolution depends primarily on mass.

slide6

June 11th, 2009 - 5

Space Telescope Science Institute: Hubble Science Briefings

slide7

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 6

Space Telescope Science Institute: Hubble Science Briefings

- Sirius: brightest star in the night sky (V = -1.5).

- 1840’s - exhibits irregular motions on the sky (Bessel 1844).

- Optical detection of companion by Alvan Clark in 1862.

slide8

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 7

Space Telescope Science Institute: Hubble Science Briefings

- 50 year binary orbit 1 Msun companion, but MV = 11.3 (0.003 Lsun)!

- Sirius A and B have similar colors Radius of Sirius B = 1/100 Sirius A.

- Adams (1914; 1925): spectrum is white, gravitational redshift measured.

- White dwarf: very dense remnant of a hydrogen burning star (no fuel).

slide9

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 8

Space Telescope Science Institute: Hubble Science Briefings

White Dwarf Fact Sheet

Composition: Carbon core under extreme pressure….a diamond!

Golden Jubilee Diamond VS Average White Dwarf

Discovery: 1985 1862

Size: 5 cm 1,000,000,000 cm

Mass: 0.1 kg 1 X 1030 kg

Density: 5 g/cm3 1,000,000 g/cm3

Value: >10 million USD -----------------

slide10

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 8a

Space Telescope Science Institute: Hubble Science Briefings

White Dwarf Fact Sheet

Composition: Carbon core under extreme pressure….a diamond!

Golden Jubilee Diamond VS Average White Dwarf

Discovery: 1985 1862

Size: 5 cm 1,000,000,000 cm

Mass: 0.1 kg 1 X 1030 kg

Density: 5 g/cm3 1,000,000 g/cm3

Value: >10 million USD -----------------

Finders Fee:$$$$$ <<10 million USD

slide11

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 9

Space Telescope Science Institute: Hubble Science Briefings

A Few Reasons to Study White Dwarfs

1.) Over 97% of all stars will eventually form white dwarfs.

Unique link to the distribution of first generation stars in old

stellar populations.

2.) White dwarfs cool predictably with time use as chronometers.

3.) Upper mass limit to white dwarf production = lower limit to type II SNe.

4.) Constraining fundamental stellar evolution and stellar mass loss.

5.) Theoretical calibration of evolutionary models of AGB and PN phases.

slide12

Diamonds in the Rough: The Oldest Stars in the Galaxy

Open Star Clusters

(Intermediate age)

1000’s of stars

Globular Star Clusters

(old and rich)

100,000’s of stars

Stellar Associations

(young and sparse)

10’s of stars

June 11th, 2009 - 10

Space Telescope Science Institute: Hubble Science Briefings

How Do We Find These Gems?

Should be faint and blue.

Search rich stellar populations.

slide13

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 11

Space Telescope Science Institute: Hubble Science Briefings

White Dwarfs in Globular Clusters?

Buonanno et al. (1994, A&A, 290, 69)

slide14

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 12

Space Telescope Science Institute: Hubble Science Briefings

Ultra-deep HST Imaging of the Nearest Clusters

Measure the ages of nearby globular clusters using white dwarf cooling theory.

1st study - Messier 4 - 123 orbits of HST/WFPC2 awarded in Cycle 9.

2nd study - NGC 6397 - 126 orbits of HST/ACS awarded in Cycle 13.

3rd study - 47 Tuc - 121 orbits of HST/ACS and WFC3 to be executed in Cycle 17.

Hansen et al. (2007, ApJ, 671, 380)

slide19

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 16

Space Telescope Science Institute: Hubble Science Briefings

The Age of the MW Halo

NGC 6397

126 HST/ACS orbits

Richer et al. (2006, Science, 313, 936)

Hansen et al. (2007, ApJ, 671, 380)

slide20

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 -16a

Space Telescope Science Institute: Hubble Science Briefings

The Age of the MW Halo

NGC 6397

126 HST/ACS orbits

Kalirai et al. (2007, ApJL, 657, 93)

Richer et al. (2006, Science, 313, 936)

Hansen et al. (2007, ApJ, 671, 380)

slide21

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 -16b

Space Telescope Science Institute: Hubble Science Briefings

The Age of the MW Halo

NGC 6397

126 HST/ACS orbits

Kalirai et al. (2007, ApJL, 657, 93)

Richer et al. (2006, Science, 313, 936)

Hansen et al. (2007, ApJ, 671, 380)

slide22

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 -16c

Space Telescope Science Institute: Hubble Science Briefings

The Age of the MW Halo

NGC 6397

126 HST/ACS orbits

Kalirai et al. (2007, ApJL, 657, 93)

Richer et al. (2006, Science, 313, 936)

Hansen et al. (2007, ApJ, 671, 380)

slide23

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 17

Space Telescope Science Institute: Hubble Science Briefings

Signature of a White Dwarf

slide24

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 -17a

Space Telescope Science Institute: Hubble Science Briefings

Signature of a White Dwarf

slide25

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 -17b

Space Telescope Science Institute: Hubble Science Briefings

Signature of a White Dwarf

slide26

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 18

Space Telescope Science Institute: Hubble Science Briefings

Signature of a White Dwarf

NGC 6397

Richer et al. (2006, Science, 313, 936)

Kalirai et al. (2007, ApJL, 657, 93)

Kalirai et al. (2009, ApJ, submitted)

slide27

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 19

Space Telescope Science Institute: Hubble Science Briefings

Dating the Oldest Stars

NGC 6397

126 HST/ACS orbits

Hansen et al. (2007, ApJ, 671, 380)

Conclusions: The Luminosity and Age of the Faintest White Dwarfs

1.) These white dwarfs are more than 1 billion times fainter than the faintest stars

seen with the naked eye!

2.) The first stars formed in our Galaxy 12 Gyr ago, 1.7 Gyr after the Big Bang.

3.) The disk of our Galaxy formed much later, 8 Gyr ago.

slide28

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 20

Space Telescope Science Institute: Hubble Science Briefings

WDs in Globular Clusters: >400 HST orbits!

NGC 6397

126 HST/ACS orbits

Kalirai et al. (2009, ApJ, submitted)

slide29

June 11th, 2009 - 21

Space Telescope Science Institute: Hubble Science Briefings

The End!

slide30

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 22

Space Telescope Science Institute: Hubble Science Briefings

The Age of the MW Disk

White dwarf mass function: Liebert, Bergeron & Holberg (2005)

slide31

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 23

Space Telescope Science Institute: Hubble Science Briefings

Summary of Globular Cluster Work:

White dwarf cooling age of NGC 6397 = 11.5-12.0 Gyr (t = 10.1-12.5 for M4).

NGC 6397: = +3.56 +/- 0.04 mas/yr, = -17.34 +/- 0.04 mas/yr.

Cluster orbit suggests frequent interactions with bulge/disk.

Proper motion cleaned study of low mass cluster mass function.

z = 0.1 extragalactic globular cluster system found.

…and Open Cluster Work:

age/distance/reddening/binary fraction/etc… measured for a large sample.

Mfinal = (0.109 +/- 0.007)Minitial + (0.394 +/- 0.025) Msun.

Age of Galactic disk = 8 Gyr, Age of Galactic halo = 12 Gyr.

Mass loss is more efficient in higher metallicity environments.

NGC 6791 stars evolved along three channels…no age issue, 2nd peak.

slide32

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 24

Space Telescope Science Institute: Hubble Science Briefings

Some CFHT CMDs

slide33

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 - 25

Space Telescope Science Institute: Hubble Science Briefings

Kalirai et al. (2008, ApJ, 676, 594)

Weidemann + Reimers & Koester (1980’s)

Claver et al. (2001)

Dobbie et al. (2004, 2006)

Williams et al. (2004, 2007)

Kalirai et al. (2005)

Liebert et al. (2005)

Kalirai et al. (2008, ApJ, 676, 594)

slide34

Diamonds in the Rough: The Oldest Stars in the Galaxy

June 11th, 2009 -25a

Space Telescope Science Institute: Hubble Science Briefings

Kalirai et al. (2008, ApJ, 676, 594)

Weidemann + Reimers & Koester (1980’s)

Claver et al. (2001)

Dobbie et al. (2004, 2006)

Williams et al. (2004, 2007)

Kalirai et al. (2005)

Liebert et al. (2005)

Kalirai et al. (2008, ApJ, 676, 594)