A Collaborative Variable Star Observing Project for Introductory Astronomy

1. A Collaborative Variable Star Observing Project for Introductory Astronomy R. Carey Woodward, Jr. University of Wisconsin—Fond du Lac

2. Motivation • Astronomy students should observe something in the sky… • …preferably something that changes. • Usual choices—Sun, Moon, planets—not suitable for 2nd semester (stars & galaxies). • Sunspot sketches? Not many sunspots this solar cycle. • Most stars constant…but not all.

3. Variable stars • Usually covered mid-semester. • Several types; many periods. • Period and type can be identified by light curve: plot of brightness over time.

4. Eclipsing binary

5. Late-stage unstable stars • Cepheid: high mass; period > 1 day. • RR Lyrae: medium mass; period < 1 day. • Both have same light curve shape.

6. Advantages • Some change in timescale that fits in a semester (hours or days). • Some are naked-eye objects. • Determining type and period challenging but reasonable for intro astronomy.

7. Drawbacks and solutions • Many observations needed. • Pool all class observations. • Adds collaborative element to project. • Students could “google” star. • Never mention star’s name! • Choose star near others to defeat smartphone apps.

8. The project: First year • Observations start after variable stars covered; end week before end of class. • Students given finder chart and instructions to find star. • “Field trips” after 2-3 classes to point out star with laser pointer. • Students estimate magnitude by comparison with nearby stars.

9. Finder/estimator chart

10. The project: First year (cont’d) • Students e-mail me observations in spreadsheet (CSV) I supply. • I consolidate all data in Excel spreadsheet, adding light curve and adjustable phase diagram. • Students determine which data are good, what type of star it is, and its period. • Short written report (results and justification) due at final exam time.

11. First year light curve Nobody got it, except by chance (or cheating)!

12. The project: Second year • Starts earlier (after magnitude system covered in class). • Each observation entered in one-shot “survey” in Desire2Learn: • Date, time, and location of observation • Magnitude (to nearest tenth) • Comments (seeing, etc.) • Must be entered within 24 hours!

13. The project: Second year (cont’d) • Three observation deadlines throughout semester (for five required observations). • Observations graded and feedback posted (in D2L gradebook) after each deadline. • Includes correct magnitude range for that date/time • I monitor data, make observations myself at key times if necessary. • Deadlines flexed if/as weather dictates.

14. The project: Second year (cont’d) • I edit observations, consolidate good ones, post data as before.

15. The project: Second year (cont’d) • Final report in (editable) survey in D2L: • What is the period? • How did you determine the period? • What is the uncertainty in the period? • What is the type of variable star? • How did you determine the type? • Grade is 70% observation, 30% analysis (with more detailed breakdown given)

16. Results • Only 64% did the analysis! • Of those, 68% correctly determined the type… • …and 35% found a correct or plausible period.

17. Conclusions • Variable star observing project works, but requires frequent feedback and editing of class data (and decent weather). • I will probably do this again, but will… • Start earlier and add another 1-2 observations • Give range of possible periods • Count analysis more and/or give 0 if omitted • Probably pre-empt for strong solar max