Transcript The Downside of EF Eridani

The Downside of EF Eridani
Frederick M. Walter
Stony Brook
University
There’ve been strange things done to this former sun by the nearby white dwarf star.
The twisted yield of the magnetic field draws in matter from afar.
The CV crowd would gasp aloud if they could ever see
The very queer magnetosphere of EF Eridani.
The SMARTS EF Eri Team
Tom Harrison (UNM)
Steve Howell (NOAO)
Stella Kafka (CalTech)
Koji Mukai (GSFC)
Axel Schwope (AIP)
Paula Szkody (UW)
The Faces of EF Eridani
2 April 2008
29 August 2008
EF Eridani - a History
•Counterpart of 2A 0311-227
•First detected in 1974 by Ariel V
•Identified as a polar in 1978
•Bright soft X-ray source 1978 - 1997
•First reported low state: 1990
•Extended low state 1997 - 2009
•Brief high states in 2006, 2008 (2),
2009
EF Eridani: Characteristics
•A polar
•Orbital period: 81 minutes
•Non-eclipsing
•Primary: cool WD, T~ 9500K
•Magnetic field ~ 12 MG
•Secondary: unseen, M<0.05M
Image: P. Marenfeld/NOAO
EF Eridani - Low State
“It’s dead, Jim”
Harrison et al. 2004
EF Eridani - Low State
SMARTS 1.5m, 19 October 2004
Howell et al. 2006
EF Eridani - Light Curve
SMARTS 1.3m/ANDICAM (plus some 0.9m)
EF Eridani - Phased Light Curve
21 August 2003 - 11 March 2009
Low State Ephemeris
Based on the low state B light curve
through August 2008
min = JD 2453716.61108 (heliocentric)
P = 0.05626586 days (adopted)
min = phase 0.41 in the Bailey et al.
(1982) ephemeris
Light Curve Stability
Colors represent different observing seasons
Light Curve Instability
B~0.2 dm/dt
~1.e-14 M/yr
Mini-accretion event - December 2006
EF Eridani - Phased Light Curve
10-13 December 2006
EF Eridani - Phased Light Curves
Sinusoidal Fits
I: 0.07 0.01
min: 0.73 0.02
V: 0.072  0.003
min: 0.05  0.01
B: 0.080  0.001
min: 0.994 
0.002
U: 0.086  0.006
min: 0.01 0.01
21 August 2003 - 11 March 2009
EF Eridani - Phased Light Curves
Sinusoidal Fits
K: 0.57 0.02
min: 0.48 0.02
H: 0.70 0.03
min: 0.60  0.01
J: 0.35  0.06
min : 0.55  0.03
21 August 2003 - 11 March 2009
EF Eridani - Phased Light Curves
Cyclotron
Hot Spot
Wavelength Dependence
Low state light curve
UV points from Szkody et al. 2006
H from the Secondary?
It’s not quite dead, the spectra said, though the Hydrogen lines are weak
But they swerve and they bend and the velocity tends to imply a binary
beat.
The near-infrared leads one instead to see that the donor is small
And the hydrogen plumes ought to consume the secondary in no time at all.
5 years of low state H
SMARTS 1.5m RC spectrograph
H on Small Telescopes. II
CTIO 4.0m Feb 10-13 2008
Red: H Blue: H
H on a Big Telescope
Gemini South/ GMOS 16 Feb 2009
Low State
H-
Trailed
Spectrum
GMOS-S
16 February 2009
70 x 60 seconds
Low State H Doppler Tomogram
GMOS-S
16 February 2009
70 x 60 seconds
Caveats:
•Relation of
photometric phase
to binary phase
unknown
•System  velocity
unknown
The Last High State
B mag; duration about 75
days
It continues today to perplex
’bout the way that the wind interacts with such passion.
Still it brightens some nights, at least at first sight, in a transient and tremulous fashion.
When it increases its light and the X-rays get bright you may think that it’s gonna stay high,
So you contact the team and push on with your scheme but in 2 months its gone from the sky.
H in the high state
SMARTS/CTIO
1.5m RC
All Velocities
+: high
o: low (GMOS)
-: low (4m)
High/Low State Comparison
Summary. I.
EF Eri has a stable low state.
•The hot spot dominates at UBV
•There are occasional mini-accretion episodes,
with B up to 0.2 mag
•Cyclotron emission dominates at JHK
No intermediate state has been seen.
The high state and low state H velocities
and tomograms show similarities … and differences.
H is not from the secondary, but is from the far
side of the center of mass.
Summary. II.
The secondary remains unseen.
Even in the low state, accretion (including cyclotron)
dominates.
EF Eri: all accretion, all the time!
There’ve been strange things done to this former sun by the nearby white dwarf star.
The twisted yield of the magnetic field draws in matter from afar.
The CV crowd would gasp aloud if they could ever see
The very queer magnetosphere of EF Eridani.
It’s not quite dead, the spectra said, though the Hydrogen lines are weak
But they swerve and they bend and the velocity tends to imply a binary beat.
The near-infrared leads one instead to see that the donor is small
And the hydrogen plumes ought to consume the secondary in no time at all
It continues today to perplex ‘bout the way that the wind interacts with such passion.
Still it brightens some nights, at least at first sight, in a transient and tremulous fashion.
When it increases its light and the X-rays get bright you may think that it’s gonna stay high,
So you contact the team and push on with your scheme but in 2 months its gone from the sky.
There’ve been strange things done to this former sun by the nearby white dwarf star.
The twisted yield of the magnetic field draws in matter from afar.
The CV crowd would gasp aloud if they could ever see
The very queer magnetosphere of EF Eridani.
High/Low State Comparison