A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate

Details A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate

2003-09-19

arxiv.org/abs/astro-ph/0309530v1

Astron.Astrophys.412:821-828,2003

Astronomy and Astrophysics

Astrophysics

7 pages A&A-Latex, 1 Figure, accepted for publication in A&A

Scientific paper

10.1051/0004-6361:20031498

Using the HST Fine Guidance Sensor, we have measured a high precision astrometric parallax of the cataclysmic variable EX Hydrae, pi=15.50+-0.29mas. From the wavelength-integrated accretion-induced energy flux, we derive a quiescent accretion luminosity for EX Hya of Lacc = (2.6+-0.6)x10e32 erg. The quiescent accretion rate then is Mdot=(6.2\+-1.5)x10e-11 (M1/0.5Msun)^(-1.61})Msun/yr. The time-averaged accretion rate, which includes a small correction for the rare outbursts, is 6% higher. We discuss the system parameters of EX Hya and deduce M1=0.4-0.7Msun, M2=0.07-0.10Msun, and i=76.0deg-77.6deg, using recent radial velocity measurements of both components and restrictions imposed by other observational and theoretical constraints. We conclude that the secondary is undermassive, overluminous, and expanded over a ZAMS star of the same mass. Near the upper limit to M1, the accretion rate of the white dwarf coincides with that due to near-equilibrium angular momentum loss by gravitational radiation and angular momentum transfer from the orbit into the spin-up of the white dwarf. Near the lower mass limit, the correspondingly higher accretion rate requires that either an additional angular momentum loss process is acting besides gravitational radiation or that accretion occurs on a near-adiabatic time scale. The latter possibility would imply that EX Hya is in a transient phase of high mass transfer and the associated spin-up of the white dwarf.

Affiliated with

Also associated with

No associations

Rating

A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-69944