Post on 04-Feb-2022
Over the past 50 years, an increasing fraction of astronomical observations are made at non-visible wavelengths. We thus learn the basics of multiwavelength astronomy.
Over the past 20 years, an increasing fraction of astronomical observations are based on carefully designed wide-field surveys. The resulting megadatasets require statistical interpretation more than small-sample studies. We thus learn some of the major astronomical surveys
Motivation
The electromagnetic spectrum (= light)
but most wavelengths of light don’t penetrate air(only optical & radio telescopes are ground-based)
Radio telescopes see ionized gas around hot stars in theMilky Way (thermal bremsstrahlung) and relativistic electrons spiralling around magnetic fields (nonthermalsynchrotron). These are produced only in very energeticenvironments (supernova shocks, black hole jets, …)
Top: Cyg ABot: M87Left: 3C288
2-6 cm
Radio galaxies imagedwith the VLA
Interferometric data are the Fouriertransform of the image. Statistical image restoration techniques includeleast squares (CLEAN) & maximum entropy.
Infrared Astronomical Satellite (IRAS)
Early 1980s350,000 mid-IR sources inall-sky survey (12-100 µm)0.2 Jy sensitivity
Spitzer Space Telescope
2003-20070.001 Jy sensitivity (3-50 µm)3” resolution, spectroscopy
Cryogenically cooled bolometersSees mostly interstellar dust (soot, rock, ices)
Gemini North & South 8-m telescopesMauna Kea Hawaii & Chilean Andes
2000s0.3-0.9 µm (visible)1-10 µm (near-IR)
Visible light is mainly produced by thermal gases at 3-50,000 K(stellar photospheres).
Astronomical databases & resourcesPerhaps more than any other scientific field, astronomicalresults are available online:
• Astrophysics Data System: nearly-complete, searchablefull-text (w/ subscription) research literatureadsabs.harvard.edu/abstract_service.html
• SIMBAD and NED: Databases of >10 million Galactic and extragalactic objects with images & referencessimbad.u-strasbg.fr ned.ipac.caltech.edu
• Vizier: Searchable library of >5000 published astronomical catalogs, N~tens to billions vizier.u-strasbg.fr
• NASA archive & mission science centersarchive.stsci.edu/sites.html
• Virtual Observatory: Developing resource for searching widely distributed mega-datasets www.us-vo.org