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 August 2008

EF Eridani - a History Counterpart of 2A First detected in 1974 by Ariel V Identified as a polar in 1978 Bright soft X-ray source First reported low state: 1990 Extended low state 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 Harrison et al “It’s dead, Jim”

EF Eridani - Low State Howell et al SMARTS 1.5m, 19 October 2004

EF Eridani - Light Curve SMARTS 1.3m/ANDICAM (plus some 0.9m)

EF Eridani - Phased Light Curve 21 August March 2009

Low State Ephemeris Based on the low state B light curve through August 2008  min = JD (heliocentric) P = days (adopted)  min = phase 0.41 in the Bailey et al. (1982) ephemeris

Light Curve Stability Colors represent different observing seasons

Light Curve Instability Mini-accretion event - December 2006  B~0.2  dm/dt ~1.e-14 M  /yr

EF Eridani - Phased Light Curve December 2006

21 August March 2009 Sinusoidal Fits I: 0.07  0.01  min : 0.73  0.02 V:   min : 0.05  0.01 B:   min :  U:   min : 0.01  0.01 EF Eridani - Phased Light Curves

21 August March 2009 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

EF Eridani - Phased Light Curves Hot Spot Cyclotron

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 Red: H  Blue: H 

H  on a Big Telescope Gemini South/ GMOS 16 Feb 2009

Low State H-  Trailed Spectrum GMOS-S 16 February x 60 seconds

Low State H  Doppler Tomogram GMOS-S 16 February 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