Rapid variability of accretion in AM Herculis

Free access article

Issue		A&A Volume 396, Number 1, December II 2002


Page(s)		213 - 217
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20021405

A&A 396, 213-217 (2002)
DOI: 10.1051/0004-6361:20021405

Rapid variability of accretion in AM Herculis

D. de Martino¹, G. Matt², B. T. Gänsicke³, R. Silvotti¹, J. M. Bonnet-Bidaud⁴ and M. Mouchet^{5, 6}

¹ Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
    e-mail: demartino@na.astro.it; silvotti@na.astro.it
² Dipartimento di Fisica, Universita' degli Studi Roma Tre, via della Vasca Navale, Roma, Italy
    e-mail: matt@fis.uniroma3.it
³ Astronomy Group, University of Southampton, Hampshire, UK
    e-mail: btg@astro.soton.ac.uk
⁴ Service d'Astrophysique Saclay, Gif-Sur-Yvette, France
    e-mail: bobi@discovery.saclay.cea.fr
⁵ LUTH FRE2462 du CNRS, Observatoire de Paris, Section de Meudon, 92195 Meudon Cedex, France
⁶ Université Denis Diderot, Place Jussieu, 75005 Paris, France
    e-mail: martine.mouchet@obspm.fr

(Received 25 July 2002 / Accepted 5 September 2002 )

Abstract
We present the last pointed observation of AM Her carried out during the life of the BeppoSAX satellite. It was bright at the beginning of the observation, but dropped to the lowest X-ray level ever observed so far. The X-ray emission during the bright period is consistent with accretion occurring onto the main pole of the magnetized white dwarf. The rapid change from the active state to the low deep state indicates a drop by a factor of 17 in the accretion rate and hence that accretion switched-off. The short timescale (less than one hour) of this variation still remains a puzzle. Optical photometry acquired simultaneousy during the low state shows that the white dwarf remains heated, although a weak emission from the accretion stream could be still present. Cyclotron radiation, usually dominating the V and R bands, is negligible thus corroborating the possibility that AM Her was in an off-accretion state. The X-ray emission during the inactive state is consistent with coronal emission from the secondary late type star.

Key words: accretion, accretion disks -- stars: binaries: close -- stars: novae, cataclysmic variables -- stars: individual: AM Her -- X-rays: stars

Offprint request: D. de Martino, demartino@na.astro.it

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.