Observations of Five Southern-Hemisphere Cataclysmic Binary Stars

TL;DR

The paper presents a coordinated observational study of five southern cataclysmic variables using new SAAO spectroscopy and time-series photometry, augmented by archival data from TESS, ATLAS, ASAS-SN, Gaia, and others. Through radial-velocity analysis and period searches, the authors derive precise orbital periods and classify each system: a long-period dwarf nova (6dF0752-54), an eclipsing magnetic CV (J0916-26), an SW Sex-type novalike (GSC08944), a short-period eclipsing novalike with persistent negative superhumps (MGAB-V253), and a complex high/low-state dwarf nova with eclipses and an S-wave (DDE 45). The study highlights diverse CV phenomenology, including ellipsoidal variations, SW Sex-type line behavior, positive and negative superhumps, and eclipses, illustrating how multi-epoch spectroscopy combined with long-baseline photometry enhances CV demographics and constrains population models. These results also demonstrate the usefulness of combining meter-class telescope data with space- and ground-based surveys to obtain robust orbital solutions and to contextualize CVs within nearby stellar populations.

Abstract

We present observations and analyses of five little-studied cataclysmic binary stars in the southern celestial hemisphere. Our new observations are from the South African Astronomical Observatory. The objects and salient results are as follows: (i) 6dF0752-54 is a dwarf nova with an orbital period Porb = 5.05 hr that shows a contribution from a mid-M type secondary in its mean spectrum. (ii) J0916-26 had been suspected of being a magnetic CV with an eclipse period of 3.37 hr. Our spectrum corroborates this classification. (iii) GSC 08944 is a novalike variable with Porb = 3.80 hr. Archival photometry also shows a persistent photometric period near 4.03 hr, apparently from a positive super- hump. Its emission line behavior is consistent with an SW Sextantis-type novalike. (iv) MGAB-V253, also Gaia20eys, had been identified as a short-period eclipsing novalike with Porb = 1.44 hr. Our spectrum shows shows broad emission lines consistent with this, and the extensive TESS data show a persistent modulation near 1.35 hr, evidently a negative superhump. It is less luminous than most novalikes, but significantly brighter than quiescent dwarf novae with comparably short periods. (v) Finally, DDE 45 shows a complicated variability history, cycling rapidly between high and low states for a time and more recently showing outbursts resembling a U Gem-type dwarf nova. We find a 2.07 hr radial velocity period, which also appears in archival TESS photometry. The emission lines are double-peaked, with an orbital S-wave similar to low-inclination dwarf novae. To be published in Astronomical Journal.

Figures (16)

• Figure 1: Upper: Mean fluxed spectrum of 6dF 0752-54. Middle: H$\alpha$ radial velocities from 2025 February, folded on the orbital period, together with the best-fitting sinusoid. Lower: TESS photometry of 6dF 0752-54 averaged into bins on the orbital period.
• Figure 2: Mean of six 1000-s spectra of J0916-26 taken 2025 Feb. 15, with some prominent emission features labeled.
• Figure 3: Archival photometry of J0916$-$26 folded on our adopted ephemeris. The Gaia points are single observations, while all the others are averaged into 100 phase bins per cycle.
• Figure 4: Time series photometry of J0916$-$26 from the SAAO SHOC. The different symbols are from different nights, keyed by the last four digits of the Julian date. The lower panel magnifies the phases near eclipse.
• Figure 5: Upper: The mean fluxed spectrum of GSC08944, from 2025 February. Lower: Weighted-average radial velocities of the H$\alpha$ and H$\beta$ emission lines, folded on the adopted orbital period, with the best-fitting sinusoid.