A new ROSAT discovered polar near the lower period limit: RX J1015.5+0904 in Leonis

Details A new ROSAT discovered polar near the lower period limit: RX J1015.5+0904 in Leonis A new ROSAT discovered polar near the lower period limit: RX J1015.5+0904 in Leonis

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26a...331..262b&link_type=abstract

Astronomy and Astrophysics, v.331, p.262-270 (1998)

Astronomy and Astrophysics

Astrophysics

15

Accretion, Accretion Disks, Stars: Individual (Rxj1015.6+0904), Stars: Novae, Cataclysmic Variables, X-Rays: Stars, Polarization

Scientific paper

We have identified the bright, soft, X-ray source RXJ1015.6+0904 detected during the ROSAT All-Sky Survey with a new AM Herculis binary (polar). Its soft X-ray light curve is typical for a system with a one-pole accretion geometry and shows a bright phase lasting about 0.75 of the binary orbit with ROSAT PSPC countrates of up to 10cts/s. The bright phase is interrupted by a 3min long dip with zero countrate where the X-ray emission from the accretion region must be absorbed by the accretion stream crossing our line-of-sight. From the X-ray dip times we derive an orbital period Porb = 79.87946(7)min making this system another member of the new group of polars discovered near the theoretical lower period limit for magnetic CVs. In the optical, the light curve is double-humped and the system varies between V = 16-17mag in the high state. The optical light is highly polarized with the degree of circular polarization varying between -5% and +30% in R and -5% and 22% in I which is a strong indication for the magnetic nature of the system. The shape of the optical light curve and the broad optical continuum component seen as additional light during the bright-phase can be explained by cyclotron emission in a magnetic field of ~ 23MG in the accretion region. At this field strength only the higher cyclotron harmonics are present in the optical and are smeared to an almost featureless continuum at a viewing angle theta ~ 55degr . The orbital inclination of the new AM Her binary can be constrained to 50degr la i la 75degr and the mass ratio must be 6.3 < Q = M1/M2 < 12.5 where the mass of the secondary star is estimated to M2 = 0.09Msun. No features of the late M-type secondary are present in our low-state optical spectra, providing a lower limit for the distance to RXJ1015.6+0904 of d > 100pc Based on observations collected at the European Southern Observatory, La Silla, Chile with the 2.2-m telescope of the Max-Planck-Society in MPI time and with various telescopes in ESO time (ESO No.

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