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

Larry Molnar

Calvin College

Grand 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 Date

I (m

ag

)

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

)

3/7/4

3/8/4

3/9/4

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

)

1/18/4

3/13/4

3/15/4

3/20/4

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

)

1/18/4

3/13/4

3/15/4

3/20/4

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