1. Astronomy 1020 Stellar Astronomy Spring_2015 Day-32

3. Course Announcements Smartworks Chapter 14: Friday 2 Dark night observing sessions left: Mon. Apr. 13 & Thurs. Apr. 16 Reports are due Wed. Apr. 22

4. Astronomy in the Fall, 2015 ASTR-1010/1011 - Planetary Astronomy + Lab (H,R) ASTR-1020/1021 - Stellar Astronomy + Lab (R) ASTR-2010 - Problems in Planet Astronomy ASTR-2011 - Intro. to Observational Astronomy ASTR-4000/4001 – Astrophotography & Lab ASTR-4170 – Special Topics in Astronomy Photometry and Filter Systems TR; 3:30-5:00pm; B310

5.  H II regions (about 10 4 K):  Hydrogen heated and ionized by ultraviolet light from hot, luminous stars (O and the hottest B).  Ionized: stripped of one or more electrons.

6.  At lower temperatures, hydrogen is in single, neutral atoms.  This gas emits radio waves with = 21 cm.  Light of this wavelength penetrates the dust.  Good for mapping the Milky Way.

7.  Many clouds are cold enough for hydrogen to be in the H 2 molecule.  These are called molecular clouds.  Dense and cold, and appear dark.

8.  Temperatures are around 10 K, with densities as high as 10 10 molecules/cm 3.  Emit radio waves.  Many other molecules are in the mix.

9.  Some clouds can have masses as large as 10 million times that of the Sun: giant molecular clouds.  On average, 120 light-years in size.  Stars form in these molecular clouds.

10.  Molecular clouds are cold and dense.  Some places in the cloud are denser than average.  Self-gravity will make these regions collapse.

11.  Rate of collapse is slowed by magnetic fields, turbulence, and angular momentum (spin).  Collapse and fragmentation lead to dense star-forming molecular-cloud cores.  The Sun began in one of these cores.

12.  Molecular cores collapse under their own gravity.  Center shrinks fastest; outer layers later.  This produces a dense protostar.

13.  Spin of core produces a disk of material around the protostar.  Material falls onto the growing protostar from the disk.  Our Solar System began this way.

14.  The interstellar material that becomes stars and planets must have the key elements for life if those planets are going to have it.  Water and oxygen have been detected in some star-forming regions.

15. Concept Quiz—H II Regions In H II regions, the hydrogen gas is in what form? A.doubly ionized hydrogen B.once-ionized hydrogen C.neutral hydrogen atoms D.hydrogen molecules

16. Protostars  Protostars are large, cool, and luminous.  They will emit infrared light.  Infrared studies of molecular regions reveal protostars and their disks.

17.  The protostar continues to accrete more material.  It continues to shrink and radiate away energy, balancing pressure and gravity.  The interior temperature and pressure rise.

18.  The low temperature of dust means that it glows in the infrared.  100 K dust:  10 K dust: MATH TOOLS 15.1

19.  The protostar’s energy source is gravitational energy.  As it shrinks, temperature rises in the core.  Hydrogen fusion begins in the core: It becomes a main sequence star.

20.  The temperature in the core must be hot enough for fusion, 10 million K.  Very low-mass stars (< 0.08 M  ) never start hydrogen fusion.  These are called brown dwarfs.

21. Concept Quiz—Energy What is the source of energy for a protostar on the Hayashi track? A.hydrogen fusion B.bipolar jets C.gravitational contraction D.angular momentum

22. Evolutionary Tracks  An individual star follows an evolutionary track on the Hertzsprung-Russell diagram.  This is the path of the temperature and luminosity with time.

23. Evolutionary Tracks  Protostars get less luminous (for lower masses), smaller in radius, and hotter.  The star moves on the Hayashi track and arrives on the main sequence.

24. 1,056  A lower-mass star like the Sun is more luminous as a protostar than as a main sequence star, even though it is cooler as a protostar.  This is due to its physical size (radius). MATH TOOLS 15.2

25. Concept Quiz—Evolutionary Tracks Once fusion begins, a star moves to the left on the H-R diagram. Its luminosity does not change, but its temperature rises. The star is A. expanding. B. contracting. C. staying at the same radius. D. can’t tell from the information given