Panchromatic Studies of Galactic Stellar Populations

June 16th, 2011 Very Wide Field Surveys - STScI

Panchromatic Studies of Galactic Stellar Populations

Jason Kalirai (STScI)

Outline- The role that Galactic stellar populations play in astrophysics.- The current “State of the Art” – The ACS Survey of Galactic Globular Clusters.- Why go panchromatic? Hints from an HST survey of 47 Tuc.- The potential of synergistic UV, optical, and IR imaging and spectroscopy.

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Apr 04th, 2011 University of British Columbia



J. Dalcanton (2010, priv comm)


J. Dalcanton (2010, priv comm.)

Summary1.) Imaging observations of nearby (resolved) stellar populations have provided some of our most important constraints on global astrophysical relations. Calibration of models, IMF, stellar evolution rates, age-metallicity relation, SF law, feedback relations,…2.) These studies directly inform both galactic and extragalactic astronomy.




Example: When did baryonic structure formation begin? Star clusters are excellent tracers of parent population star formation histories



Sandage (1953) Buonanno et al. (1994)

The Color-Magnitude DiagramMessier 3 (Photographic plates from 200”)



The Milky Way’s Globular Clusters

M80NGC 2808

M55

NGC 6397

M92 Omega Cen




The Current State of the ArtThe HST/ACS Survey of Galactic Globular Clusters (Sarajedini et al. 2007)- Homogenous photometry and reduction.- Modeled consistently with updated physics.- Large sample of 60+ clusters.



The Current State of the ArtThe HST/ACS Survey of Galactic Globular Clusters (Sarajedini et al. 2007)- Homogenous photometry and reduction.- Modeled consistently with updated physics.- Large sample of 60+ clusters.

NGC 6362 - Dotter et al. (2010) Dotter et al. (2010)




The Current State of the ArtThe HST/ACS Survey of Galactic Globular Clusters (Sarajedini et al. 2007)- Homogenous photometry and reduction.- Modeled consistently with updated physics.- Large sample of 60+ clusters.- Only V and I optical filters.- Small fields of view.



The Current State of the ArtWhat about the Infrared?- We have never had a high-resolution wide-field IR imager in space!



Wide Field Deep IR Photometry Measure the stellar inventory of the Milky Way. Calibration of stellar evolution models at red wavelengths. Measure the initial mass function and its dependency on environment. Characterize the hydrogen burning limit. Push into sub-stellar evolutionary studies (L and T dwarfs).

Resolved Stellar Populations in the Near IR


Carina Nebula - NASA, ESA, N. Smith (UC Berkeley), and the Hubble Heritage Team (STScI/AURA)

Hubble Space Telescope ACS/WFC - STScI-PRC07-16A

Why Go Panchromatic with a Large Field of View? Calibrate UV – IR color-magnitude relations. Increase the sensitivity of main-sequence turnoff fitting methods .

Probe complete stellar populations, from the cores to periphery.




Example: Towards more accurate ages

Main-Sequence Turnoff Fitting- Well separated filters in .- Superb sensitivity.- Large field of view.



Based on HST/ACS and HST/WFC3 Data Collected as a Part of GO-11677 (PI H. Richer)UBC: Harvey RicherAMNH: Mike Shara, David Zurek HIA/NRC: Greg Fahlman, Peter StetsonSwinburne: Jarrod HurleySTScI: Jay Anderson, Aaron Dotter UBC: Jeremy Heyl, Ryan Goldsbury, Kristen WoodleyUCLA: Brad Hansen, Mike Rich, David ReitzelUW: Ivan King







ACS/WFC visible color-magnitude diagram



WFC3/IR color-magnitude diagram



WFC3/UVIS and IR color-magnitude diagrams (1 HST orbit per filter)



A panchromatic data set: The color-magnitude relation



- NIRSpec can be extremely effective at obtaining large (~10,000 stars) statistical samples of stellar spectra in dense fields. Depending on density, 10-40% of all stars can be recovered.

- This technique is very efficient because it can be done by reconfiguring the MSA only, without dithering. Sky background exposures are obtained “for free”.

- This technique could be employed in globular clusters, star forming regions, the Galactic disk, and the bulge - provided the user requires a statistical sampling of stars.

+ Targets in operable shutter x Targets outside shutters

NIRSpec MSA in Dense Stellar FieldsJason Tumlinson & Jay Anderson



Looking Forward to Stellar Population Studies

1.) The Ages of Field Stars and SFHs Stellar ages possible through gyrochronology, age-activity relations, eclipsing binaries.

2.) Improving the Variable Star Distance Ladder Probe intrinsic variations in cepheid P-L relation in all southern spirals to 8 Mpc. Calibrate absolute lum. of type Ia SNe through LPV characterization in distant galaxies.

3.) Measuring the Properties of the First Populations Cool subdwarfs are the low mass (metal-poor) end of population II stars Direct photometric selection of most metal-poor halo stars.

4.) Towards a Complete Stellar Inventory: The Mass Function of Stars and the Galactic Mass Budget L0 dwarfs out to 2.1 kpc, T0 dwarfs to 100 pc. 50 million white dwarfs!

5.) Calibration of Stellar Evolution Models

6.) Most of the above in star clusters and nearby galaxies (e.g., LMC/SMC).


Imaging billions of southern hemisphere stars with wide-field, deep, multi-color, time-series photometry will revolutionize our understanding of stellar populations

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Panchromatic Studies of Galactic Stellar Populations