Light Curves of the Dwarf Nova
U Gem: A Diagnostic of
Accretion Disk Evolution
Larry Molnar
Calvin College
Grand Rapids,
Michigan
Outline
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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
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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
Julian Date
2453020
10
2453030
2453040
2453050
2453060
2453070
2453080
2453090
U Gem
10.5
11
I (mag)
11.5
12
12.5
13
13.5
14
Julian Date [3/13/4]
2453078.55
2453078.60
12.6
12.7
12.8
U Gem
I (mag)
12.9
13.0
13.1
13.2
13.3
13.4
13.5
Check 6
2453078.65
2453078.70
2453078.75
2453078.80
2453078.85
Orbital Phase
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
10.1
U Gem
10.3
I (mag)
10.5
10.7
10.9
3/7/4
11.1
3/8/4
3/9/4
11.3
Orbital Phase
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
12.8
U Gem
I (mag)
13
13.2
13.4
1/18/4
3/13/4
3/15/4
3/20/4
13.6
1.2
Orbital Phase
-0.20
12.9
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
U Gem
13
I (mag)
13.1
13.2
1/18/4
13.3
3/13/4
3/15/4
3/20/4
13.4
0.20
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