Intro to Stellar Astrophysics L1 1 PHYS 2013/2913 Introduction to Stellar Astrophysics John O’Byrne School of Physics Room

Intro to Stellar Astrophysics L1 2 Introduction ä ‘Text’ - Introduction to Stellar Astrophysics will be closely followed. ($8.50 from the Copy Centre - or order order R from ($8.50 from the Copy Centre - or order order R from ä Various other texts are an option ä WebCT used - esp. learning goals, links ä One assignment in 2 parts

Intro to Stellar Astrophysics L1 3 Rationale ä Astrophysics has long been one of the driving forces for the advancement of physics in general. It has been closely linked to advances in quantum mechanics and nuclear physics in particular. ä Stellar astrophysics in particular is also firmly rooted in classical physics - the familiar laws of mechanics, hydrostatics and thermodynamics. ä For this reason stellar astrophysics is presented here as a synthesis of some of the physics you know and an introduction to astrophysics in general.

Intro to Stellar Astrophysics L1 4 Broad outline ISA covers the following topics: ä An overview of the universe, introducing distance scales. ä A review of the tools of astrophysics and their limitations. ä Introduction to basic astronomical concepts: magnitudes, colour indices, distance modulus, etc. ä Basic principles of stellar spectroscopy, including line formation. ä Stellar classification and the Hertzsprung-Russell diagram. ä The physics of stars and the fundamental equations for stellar modelling. ä Variable stars and the mechanisms giving rise to the instability strip. See the text Introduction for ‘Assessment and Learning Goals’

Intro to Stellar Astrophysics L1 5 Motivation: Explain this image © Sébastien Lebouc -

Intro to Stellar Astrophysics L1 6 The scale of things “Cosmic Voyage” aka “Powers of 10” Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.” Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.” Douglas Adams, The Hitchhiker’s Guide to the Galaxy Douglas Adams, The Hitchhiker’s Guide to the Galaxy

Intro to Stellar Astrophysics L1 7 Planets Historically: ä ä ≥10 3 km in regular orbit around a star ä ä 9 in our solar system IAU GA 2006: Observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation “planets”…Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

Intro to Stellar Astrophysics L1 8 Planet definition A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

Intro to Stellar Astrophysics L1 9 Planet definition All other objects except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”. Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects - now officially called “plutoids”. Eris

Intro to Stellar Astrophysics L1 10 Stars ä ä self-luminous spheroidal mass of gravitationally bound gas. ä ä luminosity due to nuclear reactions in the core. ä ä occur singly or in clusters ä ä sizes range from ä ä ~km (neutron “stars”) ä ä ~10 4 km (white dwarfs ) ä ä ~10 6 km (sun) ä ä ~10 9 km (supergiants) ä ä mass from   0.08 M  to ~150 M  (?)

Intro to Stellar Astrophysics L1 11 ä Binary/multiple systems ä Stellar associations ä Open (galactic) clusters ä ~ stars, a few pc in size, young, associated with spiral arms of our galaxy ä Globular clusters ä ~ stars, ~30 pc in size, old, form a halo around our galaxy Groups of stars

Intro to Stellar Astrophysics L1 12 ä Part of the general Interstellar Medium (ISM) ä Ranging from small globules to Giant Molecular Clouds ä Masses from 1 to 10 6 M , primarily H ä perhaps 1% of the mass of the stars in the galaxy ä Density up to 10 6 cm -3 ä Temperatures from ~10 K to 200 K (in the clouds) ä Dust ~1% of the mass of the gas - scatters and absorbs light Gas and dust clouds

Intro to Stellar Astrophysics L1 13 Gas and dust clouds

Intro to Stellar Astrophysics L1 14

Intro to Stellar Astrophysics L1 15 Our galaxy is a spiral (disk) galaxy usually known as the Milky Way ä Disk diameter ~ 50 kpc ä Halo diameter ~100 kpc ä Mass ~ M  The Milky Way

Intro to Stellar Astrophysics L1 16 Spirals ä Mass ~10 9 to M  ä Luminosity ~10 8 to L  ä Diameter ~5 to 50 kpc Irregulars ä Mass ~10 8 to M  ä Luminosity ~10 7 to 10 9 L  ä Diameter ~1 to 10 kpc Galaxies Ellipticals ä Mass ~10 5 to M  ä Luminosity ~10 5 to L  ä Diameter ~1 to 200 kpc

Intro to Stellar Astrophysics L1 17 Galaxies

Intro to Stellar Astrophysics L1 18 And more..