Other HST images used during THE LIFE AND DEATH OF BOB (a.k.a. NGC 6397) IN AN INTRODUCTORY COLLEGE-LEVEL ASTRONOMY COURSE Dr. C. Renee James NASA Top Stars 2010

In a course as rich as a college-level stars and galaxies course, it would be unthinkable to feature only one image. Bob is simply the anchor – a reference point for the students. But other HST images are used to illustrate concepts along the way. The following are slides from my Fall 2009 class that show the use of HST imagery throughout our exploration of Bob. Dr. C. Renee James NASA Top Stars 2010

LIGHT The initial topic that students choose to explore. Electromagnetic spectrum is introduced. Emission and absorption of light, atomic energy levels are next. In class, students get to witness neon, helium, hydrogen discharge tubes, learning that “energized, low-density gases produce emission spectra.” Dr. C. Renee James NASA Top Stars 2010

Emission Spectra In Space… Need VERY low density gas so atoms don’t bump into each other much. Need energy source Planetary Nebulae are good examples VERY hot, dense star in center energizes low- density gas Eskimo Nebula shown here. Dr. C. Renee James NASA Top Stars 2010

Orion Nebula Jillions of new, hot stars being born, flooding the gas with UV (high-energy) light that kicks those little electrons up the steps. Dr. C. Renee James NASA Top Stars 2010

Butterfly Nebula ( Dr. C. Renee James NASA Top Stars 2010

Spectrum Representations Students freehand an intensity – color graph for the spectra they witness in class. A spectroscope that displays the graph on the screen verifies their observations. Then I show them the following nebular spectrum. Dr. C. Renee James NASA Top Stars 2010

What a nebular spectrum looks like: Dr. C. Renee James NASA Top Stars 2010

CONNECTIONS Thus the connection between the emission spectra they OBSERVE IN CLASS and actual objects in the universe is made Class is built on connections, which is why Bob keeps coming back to haunt them. Moving on to additional images used to illustrate the concepts in class… Dr. C. Renee James NASA Top Stars 2010

Star formation Around week 8 of 15, after digesting light, magnitudes, parallax, determining stellar masses (from binary observations), and cluster HR diagrams, students find that Bob’s main sequence doesn’t span the entire range of masses, and they ask WHY NOT?! (see main Bob presentation for more on this) At this point, we look at how stars form so that we can determine how they shine and why Bob’s main sequence is so limited. But since there aren’t examples of star formation in Bob, I look elsewhere… Dr. C. Renee James NASA Top Stars 2010

Eagle Nebula (also known as the Pillars of Creation) About 6500ly from earth; About 10,000 solar systems would fit into the length of the tallest column. Huge cloud currently experiencing multiple collapses into stars & solar systems. (interesting side note: P. Scowen was the labbie for my first undergrad astronomy class) Dr. C. Renee James NASA Top Stars 2010

COLLAPSING FURTHER If we had the time to wait around, regions of the Eagle Nebula might look like this piece of the Orion Nebula, whose stars are farther along in the formation process. Many “proplyds” visible – protoplanetary disks, which are the ‘pancakes’ from which planetary systems are formed. Dr. C. Renee James NASA Top Stars 2010

Dr. C. Renee James NASA Top Stars 2010

STILL FURTHER Eventually the stars will “turn on” and blow the leftover gas and dust away. The Pleiades are a prime example of a young cluster. Note how blue the stars appear! And how tenuous the leftover gas and dust appears. [Note: the youthfulness of the Pleiades comes back when we explore HR diagrams. Its main sequence spans a much greater range of temperatures, unlike Bob’s, which ends a bit hotter than the Sun] Dr. C. Renee James NASA Top Stars 2010

Dr. C. Renee James NASA Top Stars 2010

So where are star-forming regions? Inside the disks of galaxies, mostly, where there’s enough gas and dust. Bob is currently not forming new stars, but here’s a place that IS: Dr. C. Renee James NASA Top Stars 2010

Brand spankin’ new photo (11/5/2009) of star- forming region in nearby galaxy M83: Dr. C. Renee James NASA Top Stars 2010

Then we explore a couple of chapters on stellar lives and deaths to find out what’s happening with Bob’s stars. This exploration includes such HST favorites as… Dr. C. Renee James NASA Top Stars 2010

The “cat’s eye” nebula. A sun-like star that has shed its outer layers. WHAT KIND OF SPECTRUM PRODUCED? WHY? WD in center Dr. C. Renee James NASA Top Stars 2010

Supernova 1994D in Distant Galaxy Dr. C. Renee James NASA Top Stars 2010

Hubble Space Telescope view of a piece of the Crab Nebula Dr. C. Renee James NASA Top Stars 2010

At this point, we kill off Bob… With the deaths of stars, we have to say goodbye to NGC 6397, complete with funeral (see main presentation) For the remainder of the semester, we focus on galaxies and cosmology, for which there are numerous HST images to exemplify the concepts. My particular favorites are the Hubble Deep Field and Ultra Deep Field. But since we’ve dispensed with Bob, I leave incorporating these into your class as an exercise for the reader. Dr. C. Renee James NASA Top Stars 2010