The Emission Line Universe: Galactic Sources of Emission Lines

1. The Emission Line Universe: Galactic Sources of Emission Lines Stephen S. Eikenberry University of Florida 22 November 2006

2. OUTLINE • Introduction • Infrared Emission Lines • Nebular Galactic Emission Line Sources • Stellar Galactic Emission Line Sources • Summary & Future Prospects

3. What are “Galactic” Sources? • Essentially all emission lines arise from discrete objects within a galaxy  almost all objects discussed in WS XVIII are fundamentally “Galactic” • But … others here will cover HII regions, AGN, integrated galaxy spectra, etc. • I’ll focus on “other” Galactic sources of emission

4. What are “Galactic” Sources?

5. II. Why Infrared Emission Lines? • Infrared – why bother? • Hydrogen has transitions in the infrared (IR), but UV (Lyman) and optical (Balmer) are stronger • Then again … optical – why bother? Lyman >> Balmer … • But, the Universe is more transparent to Balmer lines than Lyman lines • Even though Lyman is intrinsically brighter, Balmer is often more useful

6. II. Why Infrared Emission Lines? • The Galaxy is more transparent to IR than optical emission • Why? Because most dust grains are smaller than ~1 m • Thus, they do not absorb/scatter well at wavelengths  > 1 m • For instance, in the K-band (~2.2 m) AK ~ 0.1 AV (magnitudes!) • For many Galactic sources, IR is the ONLY waveband

7. Example: The Galactic Center POSS-B POSS-R POSS “IR”

8. Example: The Galactic Center 2MASS-J 2MASS-H 2MASS-K

9. Example: The Galactic Center • AK ~ 3 mag (~6% transmission) • AV ~30 mag (~10-12 transmission!!) POSS-R 2MASS-K

10. IR/Optical Difference:Detectors • CCDs do not function well @  >1.0 m • The “bandgap” energy of silicon (~1.0 eV) corresponds to this wavelength (the “bandgap cutoff” of silicon) • Instead of silicon, We use other (poorer) semiconductor materials • HgCdTe (0.9-2.5 m) • InSb (1-5.5 m) • Si:As BIB (~5-28 m)

11. Current IR Detectors • HgCdTe: Current state-of-the art arrays • QE ~70% (1-2.5 m) • Read noise ~10 e- • 2048x2048-pixel format • InSb: Current state-of-the-art arrays • QE >90% (1-5.5m) • Read noise ~25 e- • 2048x2048-pixel format

12. IR/Optical Difference: Cryogenics • For sensitive observations, we need kT  hc/ (why??) • (If not, thermal self-emission of the detector dominates over celestial sources) • 1-2.5 m  T < 70-80K (i.e. HgCdTe) • 1-5 m  T < 30-40K (i.e. InSb) • 5-30 m  T < 4-8K (i.e. Si:As BIB)

13. Implications of cryogenics • Vacuum systems (for thermal isolation) • Large cryostats • Cryogenic liquids: • LN2 77K • LHe  4K • Mechanical cryocoolers: • Ultra-pure He • Compressors • “Cold heads”

14. IR Obs: Atmospheric IR Transmission

15. IR Obs: Atmospheric IR Transmission

16. IR Obs: Atmospheric IR Transmission

17. IR Obs: Atmospheric IR Emission

18. Atmospheric IR Emission • Dominant source of in-band background

19. Important IR Lines: Hydrogen Paschen Series Brackett Series

20. Important IR Lines: Hydrogen Pfund Series

21. IR Hydrogen Lines: Trouble Paschen Series Brackett Series

22. IR Hydrogen Lines: Trouble Pfund Series

23. IR Hydrogen Lines: Implications • None of the “IR” hydrogen series have (ground) observable “” transitions (!) • From the ground, we cannot observe the equivalent of the Balmer decrement • We can combine Pa/Br (two strongest easily-observable transitions of each series) • “IR decrement” of sorts • But … these two have no common energy levels • Greater physical uncertainty in parameters

24. Important IR Lines: Molecules • Not many molecular transitions are easily observed in the optical • “Hard” optical/UV radiation dissocates them (!) • Many molecular transitions observable in the IR from “cool” objects • Particularly strong are H2 ro-vibrational transitions (many from 1-3 m; strongest at 2.12 m) • Also, CO bandheads at 2.3-2.5 m • Mostly seen in absorption in cool giant stars • Also seen in emission occasionally (more later)

25. III. Nebular Sources in the Galaxy • Galactic HII Regions • Planetary Nebulae • Supernova Remnants

26. Galactic HII Regions • These are generally covered elsewhere in the Winter School lectures • Important point: hydrogen is dominant (why?) • One Milky Way –centric point: while most past work has been done in the optical/UV (even in our Galaxy), IR is still important for current/future work

27. Galactic HII Regions: Why IR? Example: Cepheus A POSS “IR” POSS-B 2MASS-J

28. Planetary Nebulae: Why? • PNe are the (near-)final evolutionary phase for most stars in the Universe • The PNe phase is responsible for the return of chemically-enriched material to the ISM • They exhibit very interesting outflow physics • They are PRETTY!

29. Planetary Nebulae: Why?

30. Planetary Nebulae • What can PNe emission lines tell us? • Electron density • Electron temperature • Ionic abundance • H2 shows shock vs radiative excitation • [FeII] shows shocks • Kinematics of Outflows & Morphology

31. PNe: Electron Density • Key transitions: 4S3/2-2D5/2 and 4S3/2-2D3/2 for [OII] and [SII] • Also [ClII] & [ArIV] • Why? From Stanghellini & Kaler

32. PNe: Other basics • Similar diagnostics for electron temperatures • Combine temperatures & densities with models  ionic abundances • Major sources of uncertainty for Planetary Nebulae diagnostics: • distance • internal extinction (throws off line ratios; less so in the IR)

33. PNe: IR Spectra

34. PNe: H2 Diagnostics • H2 lines can be excited by both fluorescence and by thermal (collisional/shock) mechanisms • At low densities, with UV excitation of cool (T ~100K) material have 2.12/2.25-micron ratio of ~1.7 • These are 1-0 S(1) and 2-1 S(1) transitions • At higher densities (>104 cm-3), this ratio increases and becomes a good probe of temperature (up to ~1000K)

35. PNe: [FeII] Diagnostics • Fe usually “depletes” onto dust grains in ISM • shocks break up dust  greatly increase Fe abundance in ISM (temporarily) • Thus, [FeII] provides excellent shock diagnostic (kinematics, density) for PNe • Typically only seen in the fastest-moving PNe shocks

36. PNe: Outflows & Morphology • Contrary to simple expectations, most PNe seem to be VERY non-spherical (!) • Most show very eye-catching aspheric symmetry • Strong indications of collimated outflows in some

37. Collimation : “mild” “high”

38. Point-symmetry is pervasive…

39. Planetary Nebulae Point-symmetry is usually associated with: • Bipolarity - A progressive variation in the direction of the outflows • episodic events of (collimated) mass-loss. Thus, point-symmetry indicates the presence of a Bipolar, Rotating, Episodic Jet or Collimated Outflow ( BRET). A few representative examples next …

40. Point-symmetry  morphology--BRET  kinematicsIn a true BRET morphology is reflected in its kinematics

41. Possible Models for Morphologies

42. There is a wide range of speeds in the COFsfrom a few tens to several hundred km/s…. MyCn18, first PN to break the ~500 km/s barrier…now other examples such as He 3-1475 and Mz 3… However, their masses (~1028-29 g), kinetic energy (~1043-44 ergs) and mechanical power (~1033-34 ergs/s) still are poorly determined in most cases …

43. MHD models with magnetic axis tilted with respect to bipolar wind axis…

44. Mastrodemos & Morris 1999 Binary cores: COFs and axis-symmetry may be produced either by : -Wind accretion from AGB onto WD or MS companion Wind accretion may produce bipolar COFs that explain plane – symmetry, such as in the case of M2-9 (Soker & Livio 2001) Soker & Rappaport 2000

45. …or via RLOF after a CE phase where low mass secondary is destroyed during an unstable mass transfer process, forming an accretion disk… Some expected implications of binary core on COFs Accretion through RLOF is short-lived at end of AGB .

46. Morpho/Kinematics: Conclusions • COFs as BRETs (Poly-polar or P-S) are ubiquitous in PNe. • COFs develop since the very early stages of formation of the proto-PN. • Although their velocities are now well characterized, their masses, kinetic energy and luminosities need better determination to confront ionized, atomic and molecular parameters with stellar power input (radiative, gravitational, etc.)