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

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

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

Eclipsing binary

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

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

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

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

Finder/estimator chart

The project: First year (cont’d) Students me observations in spreadsheet (CSV) I supply. Students me observations in spreadsheet (CSV) I supply. I consolidate all data in Excel spreadsheet, adding light curve and adjustable phase diagram. 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. 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. Short written report (results and justification) due at final exam time.

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

The project: Second year Starts earlier (after magnitude system covered in class). Starts earlier (after magnitude system covered in class). Each observation entered in one-shot “survey” in Desire2Learn: Each observation entered in one-shot “survey” in Desire2Learn: 1.Date, time, and location of observation 2.Magnitude (to nearest tenth) 3.Comments (seeing, etc.) Must be entered within 24 hours! Must be entered within 24 hours!

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

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

The project: Second year (cont’d) Final report in (editable) survey in D2L: Final report in (editable) survey in D2L: 1.What is the period? 2.How did you determine the period? 3.What is the uncertainty in the period? 4.What is the type of variable star? 5.How did you determine the type? Grade is 70% observation, 30% analysis (with more detailed breakdown given) Grade is 70% observation, 30% analysis (with more detailed breakdown given)

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

Conclusions Variable star observing project works, but requires frequent feedback and editing of class data (and decent weather). 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… 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