UVX

1. UVX Nick Cowan UW Astronomy May 2005

2. What’s a UVX? Wien Tail for ordinary stars O’Connell 1999 UVX Blue-end of an elliptical galaxy’s spectrum

3. Crazy Gamma-Ray Stuff? No, just Crazy Hot Stars.

4. Outline • UVX in elliptical galaxies • Candidates for the UVX

5. What took so long? • Few long-lived space-based UV telescopes. • Galaxies have low surface brightnesses in the UV. • UV detectors have poor quantum efficiencies. • Have to filter out L emission and “red leak”.

6. Elliptical Galaxies in a slide • Ellipsoidal conglomeration of stars. • 107-1013 solar masses. • 10-1-102 kpc in size. • Not much ISM. • Full of old stars. • Lot o’ globular clusters. • Sometimes have AGN.

7. E/S0 galaxies and bulges have UVX

8. UVX has constant surface brightness Bad data reduction

9. The UVX is metal-rich! Metal Rich Metal Poor As in 2500 A As in 1500 A

10. UVX doesn’t depend on color (not much)

11. GALEX/SDSS Results ~Metallicity ~Age ~Dynamics

12. GCs can’t account for the UVX Absorption from MgI and MgH

13. These stars are really blue.

14. Mass loss allows older stars to masquerade as hot young stars…

15. Late Stages of Stellar Evolution(what your mommy told you)

16. Late Stages of Stellar Evolution(X-rated version)

17. Zero Age Horizontal Branch • 4,000-40,000 K surface T • ~0.5 Msolar He core • ~0-0.3 Msolar H envelope • Scatter in mass-loss leads to scatter in envelope mass and initial temperatures. • Typically come in via the RGB and exit via the AGB.

18. Standard Horizontal Branch and Metallicity • High metallicity stars populate the “Red Clump” and the cool end of the HB. • Low metallicity stars populate the aptly-named HB. • Really low metallicity stars populate the oxymoronicly vertical “Extreme HB”. Or do they?

19. Horizontal Branch Morphology

20. Parameters for UVX stars • Age • Y • Z • Y/Z • Mass Loss

21. Position on the ZAHB is super sensitive to mass-loss

22. Comparing to Simulations

23. Why a Blue HB is confusing(the same reason why Pam still shows up in Playboy) (Bad news for K-correction)

24. Do we actually see these things? NGC 2808 Sweigart 2002

25. Other sources of UV fluxin ellipticals • Young stellar populations. • Low-luminosity AGNs. • Hot gas. • Blue stragglers.

26. Binaries and Dynamic Effects • GCs are a good testing ground for stellar interactions. • Mergers and collisions form blue stragglers. • Roche-lobe mass-loss leads to exposed He cores. • Higher metallicity stars have more extended envelopes so might suffer greater mass-loss. • No sign of AGB-Manqué

27. Conclusions • UVX tells us about the strange late stages of stellar evolution. • Observations show that there is a large variability of UVX. • However, this variability does not correlate with any obervables. • Simulations predict that the behavior of these stars should be highly sensitive to mass-loss (which in turn has strange dependences on observables). • We don’t know how to nail down mass loss observationaly so UVX is not a useful metric yet.

28. Summary • Elliptical galaxies aren’t as boring as you thought. • Old, metal-rich stars can be blue, too. • Someone really ought to figure out this mass-loss stuff.

29. Good Canadian kid References • Rich et al. 2005 ApJL 619 107-110 • Thomas et al. 2005 ApJ 621 673-694 • Brown 2003 astro-ph/0308509 • Gil De Paz 2003 AAS Meeting 203 • O’Connell 1999 Annu. Rev. A & A • Dorman 1996 astro-ph/9612008 The puck American goalie