V1460 Her: a fast spinning white dwarf accreting from an evolved donor star

Abstract

We present time-resolved optical and ultraviolet spectroscopy and photometry of V1460 Her, an eclipsing cataclysmic variable with a 4.99 h orbital period and an overluminous K5-type donor star. The optical spectra show emission lines from an accretion disc along with absorption lines from the donor. We use these to measure radial velocities, which, together with constraints upon the orbital inclination from photometry, imply masses of M1 = 0.869 ± 0.006 M⊙ and M2 = 0.295 ± 0.004 M⊙ for the white dwarf and the donor. The radius of the donor, R2 = 0.43 ± 0.002 R⊙, is ≈50 per cent larger than expected given its mass, while its spectral type is much earlier than the M3.5 type that would be expected from a main sequence star with a similar mass. HST spectra show strong N v 1240 Å emission but no C iv 1550 Å emission, evidence for CNO-processed material. The donor is therefore a bloated, over-luminous remnant of a thermal-timescale stage of high mass transfer and has yet to re-establish thermal equilibrium. Remarkably, the HST ultraviolet data also show a strong 30 per cent peak-to-peak, 38.9 s pulsation that we explain as being due to the spin of the white dwarf, potentially putting V1460 Her in a similar category to the propeller system AE Aqr in terms of its spin frequency and evolutionary path. AE Aqr also features a post-thermal timescale mass donor, and V1460 Her may therefore be its weak magnetic field analogue since the accretion disc is still present, with the white dwarf spin-up a result of a recent high accretion rate.

Confirmation of a Second Propeller: A High-inclination Twin of AE Aquarii

“…Meintjes et al (2015) review the major observational and theoretical studies of AE Aqr. Several additional IPs with WD rotation periods near 30 s have recently been identified (e.g., Ashley et al 2020;Lopes de Oliveira et al 2020), but their magnetic fields are apparently insufficient to power an AE Aqr-like propeller. AE Aqr and these other IPs may require a recent episode of thermal timescale mass transfer to spin up their WDs to these extreme rates (Schenker et al 2002).…”

Optical detection of the rapidly spinning white dwarf in V1460 Her

“…One such short period white dwarf has been recently-discovered in V1460 Her (Ashley et al 2020). V1460 Her is an eclipsing cataclysmic variable with a 4.99 h orbital period and an over-luminous K5-type donor star.…”

“…V1460 Her is an eclipsing cataclysmic variable with a 4.99 h orbital period and an over-luminous K5-type donor star. It is the third fastest spinning white dwarf known amongst the cataclysmic variables, with a spin period of 38.875(5) sec (Ashley et al 2020). Amongst cataclysmic variable stars, only the white dwarfs in AE Aqr (33 sec) and CTCV J2056-3014 (29.6 sec, Lopes de Oliveira et al 2020) spin faster, although the X-ray binary HD 49798 contains a 𝑃 spin = 13 sec compact component that might be a white dwarf (Israel et al 1997;Mereghetti et al 2011).…”

“…Since discovering the rapid pulsations betraying the presence of the white dwarf spin in V1460 Her's HST UV data (Ashley et al 2020), we have obtained multiple epochs of high-speed optical photometry in an effort to detect and monitor the spin. In this paper we present the results of this campaign aimed at establishing the spin history of the magnetic white dwarf V1460 Her since its recent discovery.…”

Radio and optical observations of the possible AE Aqr twin, LAMOST J024048.51+195226.9

“…These systems however both have at least partial discs and are accretion powered; i.e. apart from harbouring rapidly spinning WDs, they are similar to normal IPs, rather than to AE Aqr(Lopes de Oliveira et al 2020;Ashley et al 2020). 2 Available from https://github.com/IanHeywood/oxkat/…”