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

Abstract

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 Pobs = 65.18 min, which represents either the synodic (beat) period or the spin period of the white dwarf (WD). The period ratio is either Pspin/Porb = 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 ∼K6. Dynamic models, fitting the photometry, limit the distance to between 1270 and 2500 pc for masses of the secondary star, M2, between 0.16 and 1.0 M⊙, well within the Gaia EDR3 confidence limits. Employing a luminosity selection inspired by binary population studies yields a mean M2 = 0.32 M⊙ with a 2σ upper limit of 0.60 M⊙ and a mean distance d = 1596 pc with a 2σ upper limit of 1980 pc. The secondary star is located in its Hertzsprung-Russell diagram at a mean Teff, 2 = 4120 K and log(L2/L⊙) = − 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 τ ∼ 3 × 105 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.

Hitting a New Low: The Unique 28 hr Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)

“…More recently, low-accretion states have been detected in several confirmed or suspected IPs, including V1323 Her (Andronov et al 2014), FO Aqr (Littlefield et al 2016;Kennedy et al 2017), DW Cnc (Segura Montero et al 2020), Swift J0746.3-1608(Bernardini et al 2019Beuermann et al 2022), and YY Dra itself (Breus et al 2017), though as we noted in Section 3.3, the previously observed YY Dra low states do not show evidence of a cessation of accretion. Additionally, Covington et al (2022) have identified low states in V1223 Sgr, V1025 Cen, V515 And, and RX J2133.7 + 5107, and they conclude that low states in IPs are more common than previously realized.…”

“…Of the other IPs that have been observed in low states, only in J1832 has the accretion rate been observed to decline to negligible levels. Similar to YY Dra, J1832 shows no variability related to the WD's rotation during its deep low states (Beuermann et al 2022), but J1832 has the added advantage of being a deeply eclipsing system. Beuermann et al (2022) showed that when J1832 enters a deep low state, its optical eclipse depth becomes imperceptibly shallow, suggesting that there is no remaining accretion luminosity and hence no accretion.…”

“…Similar to YY Dra, J1832 shows no variability related to the WD's rotation during its deep low states (Beuermann et al 2022), but J1832 has the added advantage of being a deeply eclipsing system. Beuermann et al (2022) showed that when J1832 enters a deep low state, its optical eclipse depth becomes imperceptibly shallow, suggesting that there is no remaining accretion luminosity and hence no accretion. Due to gaps in ground-based observational coverage of J1832, it is unclear how long J1832ʼs deep low states last or how long it takes for the system to fall into one.…”

Hitting a New Low: The Unique 28 h Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)

“…More recently, low-accretion states have been detected in several confirmed or suspected IPs, including V1323 Her (Andronov et al 2014), FO Aqr (Littlefield et al 2016;Kennedy et al 2017), DW Cnc (Segura Montero et al 2020), Swift J0746.3-1608(Bernardini et al 2019Beuermann et al 2022), and YY Dra itself (Breus et al 2017), though as we noted in Sec. 3.3, the previously observed YY Dra low states do not show evidence of a cessation of accretion.…”

“…Similar to YY Dra, J1832 shows no variability related to the WD's rotation during its deep low states (Beuermann et al 2022), but J1832 has the added advantage of being a deeply eclipsing system. Beuermann et al (2022) showed that when J1832 enters a deep low state, its optical eclipse depth becomes imperceptibly shallow, suggesting that there is no remaining accretion luminosity and hence no accretion. Due to gaps in ground-based observational coverage of J1832, it is unclear how long J1832's deep low states last or how long it takes for the system to fall into one.…”