* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars/galaxy News -> EF Eridani
Post Info TOPIC: EF Eridani
Blobrana


L

Posts: 131433
Date:
RE: EF Eridani
Permalink  
 

Title: Analysing the Low State of EF Eridani with Hubble Space Telescope Ultraviolet Spectra
Authors: Paula Szkody, Anjum Mukadam, Boris T. Gaensicke, Ryan K. Campbell, Thomas E. Harrison, Steve B. Howell, Jon Holtzman, Frederick M. Walter, Arne Henden, William Dillon, Owen Boberg, Shannon Dealaman, Christian S. Perone

Time-resolved spectra throughout the orbit of EF Eri during its low accretion state were obtained with the Solar Blind Channel on the Advanced Camera for Surveys onboard the Hubble Space Telescope. The overall spectral distribution exhibits peaks at 1500 and 1700A, while the UV light curves display a quasi-sinusoidal modulation over the binary orbit. Models of white dwarfs with a hot spot and cyclotron emission were attempted to fit the spectral variations throughout the orbit. A non-magnetic white dwarf with a temperature of ~10,000K and a hot spot with central temperature of 15,000K generally matches the broad absorptions at 1400 and 1600A with those expected for the quasimolecular H features H2 and H+2 . However, the flux in the core of the Lyalpha absorption does not go to zero, implying an additional component, and the flux variations throughout the orbit are not well matched at long wavelengths. Alternatively, a 9500K white dwarf with a 100 MG cyclotron component can fit the lowest (phase 0.0) fluxes, but the highest fluxes (phase 0.5) require an additional source of magnetic field or temperature. The 100 MG field required for the UV fit is much higher than that which fits the optical/IR wavelengths, which would support previous suggestions of a complex field structure in polars.

Read more (1238kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: XMM-Newton observations of EF Eridani: the textbook example of low-accretion rate polars
Authors: A.D. Schwope, A. Staude, D. Koester, J. Vogel

Archival X-ray observations of EF Eridani obtained in a low state revealed distinct X-ray detections at a luminosity L_X ~ 2 x  10^29 erg/s, three orders of magnitude below its high state value. The plasma temperature was found to be as low as kT <≈ 2 keV, a factor 10 below the high state. The X-ray/UV/IR spectral energy distribution suggests faint residual accretion rather than coronal emission as being responsible for the low-state X-ray emission. EF Eri thus showed a clear transition from being shock-dominated in the high state to be cyclotron-dominated in the low state. From the optical/UV spectral energy distribution we re-determine the photospheric temperature of the white dwarf to ~10000K. Contrary to earlier claims, WD model atmospheres produce sufficient UV flux to reproduce the published GALEX flux and orbital modulation.
Read more (68kb, PDF)

__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars/galaxy News -> EF Eridani


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard