ASTR 511 [R. W. O'Connell]


INTRODUCTION TO ULTRAVIOLET ASTRONOMY

Astro on orbit

Astro-2 UV observatory in Shuttle payload bay.


A. THE UV BANDS


B. MOTIVATION FOR UV OBSERVATIONS

Highest density (bits per unit wavelength) of astrophysical information on stars and gas
  1. Continuum sources

    • Stellar flux maximum (F_lam units) occurs at ~ 2900 Å/T4.

        Energy distributions of hot stars (over 10,000 K) peak in UV.

        Most important: massive main sequence stars over 3 Msun, responsible for most element synthesis, ionization, dissociation, and kinetic energy input to galaxies.

        For cooler stars (< 8000 K), the UV is in the Wien limit, implying high sensitivity to temperature (e.g. to measure main sequence turnoff in integrated light of stellar populations)

    • Hard nonthermal sources

    • "Big blue bump" in AGN = inner accretion disk?

  2. Atomic & molecular spectral features

    • Many strong (often resonance) transitions of important species occur in UV:

        H, D, H2, He, C, N, O, Mg, Si, S, Fe

    • Uniquely valuable:

      • Lyman series and metallic features in stars, ISM, IGM;
      • Atomic deuterium (offset from HI features);
      • O VI, C IV, N V (gas at 105-6K);
      • Carbon abundances from C III, C IV;
      • Lyman discontinuity (rest wavelength 912 Å) in high redshift galaxies;
      • Near-UV: [O II] and [Ne V] plasma diagnostics, Balmer jump stellar T,g diagnostic.

  3. Low sky background

  4. Sensitivity to dust

  5. Isolation of hot components in dominant cool sources: e.g. stellar chromospheres, hot stars/AGN in E galaxies

  6. Restframe UV shifted to readily-observed optical window in high redshift (z > 1) galaxies and AGN. E.g. "Lyman-break galaxies"

Key research areas:

C. MISSIONS

Historical Gaps:


D. UV INSTRUMENTATION


E. UV DETECTORS


F. SPACE ASTRONOMY: SPECIAL TECHNICAL REQUIREMENTS

Columbia



General references: Web links:



Last modified November 2009 by rwo


Text copyright © 2000-2009 Robert W. O'Connell. Images in public domain. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 511 at the University of Virginia.