Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.00471

Eppur binaria non è esclusa: Pulsations in CZ Tuc appear to be tidally excited by its veiled companion

Piotr A. Kołaczek-Szymański·Patryk Iwanek·Jim Fuller·Dorota M. Skowron·Grzegorz Pojmański·Igor Soszyński
View original source ↗Read source document ↗Export metadata ↓

Abstract

Long secondary periods (LSPs), observed in about one-third of pulsating red giants, remain unexplained despite decades of study, with binarity and non-radial oscillations as the leading competing hypotheses. If LSP variables are indeed interacting, eccentric binary systems consisting of a red giant and a substellar object, tidally excited oscillations (TEOs) would be expected to appear in a fraction of them. Therefore, detection of TEOs offers an independent test of the binary scenario that has not previously been applied to LSP stars. Using a combined, approximately 80-year light curve assembled from Digital Access to a Sky Century @ Harvard (DASCH), Hipparcos, and All Sky Automatic Survey (ASAS) photometry, we find that CZ Tucanae (CZ Tuc) exhibits a pulsation period of $55.4734\pm0.0074$ days along with its LSP of $443.62\pm0.12$ days, with a ratio of $7.9970\pm0.0024$ - consistent with a TEO. Theoretical models show the observed amplitude of the candidate TEO could be produced after adopting the estimated fundamental parameters of CZ Tuc. Our findings identify CZ Tuc as the first candidate LSP star with a TEO, providing independent evidence for binarity among at least a subset of these enigmatic variables.

Explore related subjects

astro-ph.SR

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Piotr A. Kołaczek-Szymański, Patryk Iwanek, Jim Fuller, Dorota M. Skowron, Grzegorz Pojmański, Igor Soszyński. 2026-09-30. Eppur binaria non è esclusa: Pulsations in CZ Tuc appear to be tidally excited by its veiled companion. https://arxiv.org/abs/2610.00471

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Velocity dispersion of Solar Energetic Particles in turbulent heliosphere

Solar Energetic Particles (SEPs) are a signature of solar eruptions, and to link them to acceleration mechanisms many studies investigate their injection time at the Sun, $t_{sun}$. We assess velocity dispersion analysis (VDA), an often-used method to derive $t_{sun}$. We use full-orbit simulations of 1--100 MeV SEP protons in a novel model of the interplanetary magnetic turbulence superposed on a Parker Spiral magnetic field. The turbulence is described analytically as dominant transverse fluctuations that are 2D with respect to the mean field, supplemented with a minor contribution of asymptotically slab turbulence modes. We determine simulated SEP intensities for three turbulence strengths and use VDA to obtain $t_{sun}$ and the apparent path length $s$ of the SEPs, employing an SEP onset threshold to mimic a realistic energetic proton background before the SEP event. We find that turbulence strongly affects $t_{sun}$ and $s$. For weak and moderate turbulence, VDA estimates of $t_{sun}$ are 2-16 minutes after the actual solar injection time, and the path lengths are 0.2-0.3 au longer than the Parker spiral. For strong turbulence, the path lengths are $>5$ au, considerably longer than those typically obtained from SEP observations. We also investigate the effect of energy-dependence of the pre-event proton background, and find that different background spectra result in 5-20-minute difference in VDA injection times, depending on the heliolongitude. We conclude that in many cases VDA-derived injection times include a significant contribution from turbulence and/or the pre-event background and are not an accurate estimate of the acceleration time.

astro-ph.SR↗
arXiv2026

Will a Supernova explode in CD-30°11223?

Accretion of He-rich matter onto a low-mass CO WD from a He-rich donor may lead to an explosive event of SN Ia proportion, though with low peak luminosity and peculiar nucleosynthesis. Recently such a possibility for some binaries with He-accreting WDs has been questioned, suggesting that, if the effects of rotation are accounted for in the evolution of the accretor, the latter does not explode, but it becomes a WD with a massive He-buffer. We investigate the expected evolution of the currently detached binary CD-3011223 harboring a 0.74Msun CO WD and a 0.47Msun donor with a He-burning core and a very thin H-envelope. We use the stellar evolution code FuNS to compute the evolution of CD-3011223 up to the epoch when the two components come into contact and through the RLOF phase of the donor. With respect to our earlier study of the system PTF J2238+743015.1, we also include the transport of angular momentum due to magnetic instabilities (magnetic model). During the H-accretion phase, the effects of rotation in the accretor are negligible. In the "magnetic model", the angular momentum deposited by the accreted matter is very efficiently redistributed along the whole WD due to magnetic instabilities, so that the angular velocity of the accreted layers remains very low. During the He-accretion phase, the accretor experiences two very strong He-flashes, which result in the ejection from the binary system of a large part of the matter previously accreted. The system ends its life as a CO core capped by a massive He/C/O-envelope (Delta M_env ~ 0.194Msun) and an extremely low-mass companion, remnant of the donor, like in a rotating model not including the effects of magnetic field. The system CD-3011223 cannot be regarded as the potential progenitor of Supernova Ia. Such a conclusion applies also to all detached binary systems having similar masses of components and orbital periods.

astro-ph.SR↗
arXiv2026

Spectroscopic follow-up of compact object binary candidates from Gaia DR3: White dwarfs, neutron stars, black holes, and the parallax zeropoint

Astrometry and radial velocities (RVs) from Gaia DR3 yielded orbits for hundreds of thousands of binary systems, including several samples proposed to contain black holes (BHs), neutron stars (NSs), and white dwarfs (WDs). We present results of a systematic spectroscopic follow-up program targeting these objects. Beginning with a sample of 227 sources, we used a combination of archival data and many-epoch spectroscopic follow-up to characterize more than 200. We obtained 1292 high-quality RVs over a period of four years using the TRES and FEROS spectrographs, achieving a typical precision of 50 m/s and at least 10 RVs for 60 sources. We use these data to test the Gaia orbital solutions and tighten constraints on orbital parameters and component masses. Joint fitting of astrometry and RVs allows us to directly constrain flux ratios, verifying that undetected companions are genuinely dark. We find that ~60% of the astrometric candidates indeed host compact objects, including the two known Gaia BHs, 27 NS candidates, and a dozen massive WDs. We show that tight WD+WD binaries may masquerade as NSs within this sample. The spectroscopic candidates have lower purity: ~50% have spurious solutions, and a majority of the rest are post-mass-transfer binaries or hierarchical triples. Joint astrometry+RV fits of binaries with dark companions yield direct, parallax-independent distance measurements. Using 40 such systems, we measure the Gaia DR3 parallax zeropoint for astrometric orbital solutions. We find $Z=-0.0362\pm0.0053$ mas, consistent with the single-star zeropoint for sources of similar color and magnitude. These results will guide the selection of cleaner candidate samples from Gaia DR4, where a longer observing baseline will enable discovery of many more compact object binaries. RV follow-up will remain important for confirming individual systems, particularly those with extreme parameters.

astro-ph.SR↗