TESS light curves of cataclysmic variables – I – Unknown periods in long-known stars

Abstract

Cataclysmic variables (CVs) exhibit a plethora of variable phenomena many of which require long, uninterrupted light curves to reveal themselves in detail. The month long datasets provided by TESS are well suited for this purpose. TESS has the additional advantage to have observed a huge number of stars, among them many CVs. Here, a search for periodic variations in a sample of CVs of the novalike and old novae subtypes is presented. In 10 of the 15 targets either previously unseen positive or negative superhumps or unusual features in known superhumps are identified. The TESS light curves demonstrate that the occurrence of superhumps in these types of CVs is not an exception but quite common. For 8 systems new or improved values for the orbital period are measured. In TV Col the long-sought optical manifestation of the white dwarf spin period is first seen in form of its orbital sideband. The mystery of multiple photometric periods observed in CP Pup in the past is explained by irregularly occurring anomalous states which are reflected in the light curve.

Nine New Cataclysmic Variable Stars with Negative Superhumps

“…Only two (TZ Per and V392 Hya) of the nine stars in this work have had their orbital periods measured by previous authors, leaving seven for which we will be determining the orbital period and the hump period for the first time. PSHs are commonly found during the superoutbursts that characterize SU UMa-type DNe (Kato et al 2009), but recent studies have shown that they are also present in NLs (Bruch 2022(Bruch , 2023a(Bruch , 2023b. In addition, an accretion disk precession signal has also been found in PSH systems, and we are therefore unable to determine whether the hump belongs to NSHs or PSHs based on the type of star and the presence or absence of the precession signal alone.…”

“…NSHs are another hump modulation a few percent shorter than the orbital period, and are found in CVs and low-mass X-ray binaries (LMXBs, Retter et al 2002). Since the discovery of the first NSH system (TV Col; Motch 1981), an increasing number of NSH systems have been discovered (e.g., Olech et al 2009;Armstrong et al 2013;Sun et al 2022Sun et al , 2023cBruch 2022Bruch , 2023aBruch , 2023b. A large number of studies have suggested that the NSHs originate from the interaction between the reverse precession of the nodal line from the tilted disk and the orbital motion of the binary (e.g., Bonnet-Bidaud et al 1985;Patterson 1999;Harvey et al 1995), but there is still no consensus on the exact physical process.…”

Flare Hunting in Hot Subdwarf and White Dwarf Stars from Cycles 1–5 of TESS Photometry

“…CVs have also been proposed in the TASC WG8 target list as they consist of a WD primary and a mass transferring secondary. However, it is difficult to identify flare events in the light curves of CVs since they exhibit rich variable properties across different timescales from seconds to millennia (Bruch 2022). The majority of outbursts are not triggered by flare events (e.g., superhumps), leading to severe contamination in our identification.…”

Tilted discs in six poorly studied cataclysmic variables

“…PDCSAP tries to reduce effects of instrumental nature, but can sometimes introduce systematics in periodograms, and analysis should proceed with care. Bruch (2022) found in particular that the additional conditioning in PDCSAP may distort DNe light curves, and chose to use the simpler SAP technique in order to search for periodic variations in CVs. We use SAP light curves too in all analysis to follow.…”