The Downside of EF Eridani

Frederick M. WalterStony 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

Harrison et al. 2004

“It’s dead, Jim”

EF Eridani - Low State

Howell et al. 2006

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 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

Mini-accretion event - December 2006

B~0.2 dm/dt~1.e-14 M/yr

EF Eridani - Phased Light Curve

10-13 December 2006

21 August 2003 - 11 March 2009

Sinusoidal Fits

I: 0.07 0.01min: 0.73 0.02

V: 0.072 0.003min: 0.05 0.01

B: 0.080 0.001min: 0.994 0.002

U: 0.086 0.006min: 0.01 0.01

EF Eridani - Phased Light Curves

EF Eridani - Phased Light Curves

21 August 2003 - 11 March 2009

Sinusoidal Fits

K: 0.57 0.02min: 0.48 0.02

H: 0.70 0.03min: 0.60 0.01

J: 0.35 0.06min : 0.55 0.03

EF Eridani - Phased Light Curves

Hot Spot

Cyclotron

Wavelength Dependence

Low state light curveUV 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 2008Red: H Blue: H

H on a Big Telescope

Gemini South/ GMOS 16 Feb 2009

Low State H- Trailed Spectrum

GMOS-S16 February 200970 x 60 seconds

Low State H Doppler TomogramGMOS-S16 February 200970 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

+: higho: 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 velocitiesand 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