J1832.4-1627, the first eclipsing stream-fed intermediate polar

We present a photometric study of the newly discovered eclipsing intermediate polar J183221.56-162724.25 (in short J1832) with an orbital period of 8.87 h. The system features a box-like deep eclipse with a full width at 50% depth of 1970 +/- 2 s and a large-amplitude coherent pulsation with P-obs = 65.18 min, which represents either the synodic (beat) period or the spin period of the white dwarf (WD). The period ratio is either P-spin/P-orb = 0.1091 or 0.1225, respectively. The eclipsed light originates almost entirely from the two accretion spots and columns on the WD, with characteristics indicative of pole flipping. There is no evidence for an accretion disk, and we identify J1832 as the first deeply eclipsing stream-fed intermediate polar. Our grizy photometry in eclipse yielded an i-band AB magnitude of the Roche-lobe-filling secondary star of 18.98(3), an extinction EB-V = 0.54 +/- 0.17, and a spectral type similar to K6. Dynamic models, fitting the photometry, limit the distance to between 1270 and 2500 pc for masses of the secondary star, M-2, between 0.16 and 1.0 M-circle dot, well within the Gaia EDR3 confidence limits. Employing a luminosity selection inspired by binary population studies yields a mean M-2 = 0.32 M-circle dot with a 2 sigma upper limit of 0.60 M-circle dot and a mean distance d = 1596 pc with a 2 sigma upper limit of 1980 pc. The secondary star is located in its Hertzsprung-Russell diagram at a mean T-eff,T-2 = 4120 K and log(L-2/L-circle dot) = - 0.92, from where the binary can evolve into either a polar or an ultracompact binary with a highly magnetic primary. The system displays a variable accretion rate, lapses repeatedly into short-lived low states of negligible accretion, and currently displays an orbital period that decreases on a timescale of tau similar to 3 x 10(5) yr. X-ray observations, optical spectroscopy, and spectropolarimetry have a high potential for studies of the properties of J1832 as an individual object and of stream-fed accretion in general.

Automated summary

We present a photometric study of the newly discovered eclipsing intermediate polar J183221.56-162724.25, revealing its characteristics and parameters through photometric measurements and dynamic modeling.