Light Curves of the Dwarf Nova U Gem: A Diagnostic of Accretion Disk Evolution

Larry MolnarCalvin CollegeGrand Rapids,Michigan

Outline

• Calvin-Rehoboth Twin Telescopes Project• Dwarf Novae• U Gem• Preliminary Light Curves

Calvin-Rehoboth Twin Telescope Project

• NSF-CCLI funding• Two 16” OGS telescopes

– One in Grand Rapids, MI• Hands-on experience for students• Development platform for remote site

– One in Rehoboth, NM (35.5N,108.6W)• Unattended robotic operation• High throughput

Dwarf Novae

• White dwarf + red dwarf• Red dwarf fills Roche Lobe• Angular momentum loss leads to mass

transfer via an accretion stream, and formation of an accretion disk

• Disk conditions do not permit steady-state

U Gem

• Brightness: 10-14 magnitude• Mass ratio: 0.25• Orbital period: 4.24 hours• Outburst time scale: 3-4 months• Inclination: hot spot is eclipsed by red

dwarf

10

10.5

11

11.5

12

12.5

13

13.5

14

2453020 2453030 2453040 2453050 2453060 2453070 2453080 2453090

Julian DateI (

mag

)

U Gem

12.6

12.7

12.8

12.9

13.0

13.1

13.2

13.3

13.4

13.5

2453078.55 2453078.60 2453078.65 2453078.70 2453078.75 2453078.80 2453078.85

Julian Date [3/13/4]

I (m

ag)

U Gem

Check 6

10.1

10.3

10.5

10.7

10.9

11.1

11.3

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Orbital Phase

I (m

ag)

3/7/43/8/43/9/4

U Gem

12.8

13

13.2

13.4

13.6

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Orbital Phase

I (m

ag)

1/18/43/13/43/15/43/20/4

U Gem

12.9

13

13.1

13.2

13.3

13.4

-0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20

Orbital Phase

I (m

ag)

1/18/43/13/43/15/43/20/4

U Gem

Conclusions

• U Gem data demonstrate capabilities of new system

• Comparison of eclipses before and after outburst are consistent with accretion disk radius increasing gradually through the quiescent phase