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First Photometric Investigations of the Solar-type Binary FV CVn in Multiple Systems
摘要： FV CVn is a solar-type (G7) eclipsing binary whose analysis has so far been ignored. We observed it from 2014 January to 2018 May. The ?rst photometric and orbital period investigation are presented here, combined with spectroscopic observations obtained by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The current preliminary solutions show that FV CVn is a new W-subtype contact binary with a mass ratio of q?=?M2/M1?=?2.44(±0.20) and a temperature difference of ? = - K. The orbital period investigation suggests that a cyclic variation of A?=?0.0184(±0.0034) days and P3?=?17.65(±0.076) years exists in FV CVn. This cyclic variation is analyzed for the light-travel-time effect (LTTE) via the presence of a third body with a minimum mass of M3min?=?0.73(±0.018) Me, and an orbital semimajor axis shorter than 5.27(±1.62) au. This is in agreement with the presence of a large quantity of a third light in the system. Photometric solutions suggest that the third body contributes about 26.4(±6.3)% in Rc, and 29.0(±5.9)% in Ic to the total light of the multiple system. The additional component may play an important role in the origin and evolution of central close binary. New radial velocities are needed in the future to check the accuracy of the absolute parameters.
关键词： stars: individual (FV CVn),stars: binaries (including multiple): close,stars: evolution,stars: binaries: spectroscopic,stars: binaries: eclipsing,stars: solar-type
更新于2025-09-09 09:28:46
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Eclipsing spotted giant star with K2 and historical photometry
摘要： Context. Stars can maintain their observable magnetic activity from the pre-main sequence (PMS) to the tip of the red giant branch. However, the number of known active giants is much lower than active stars on the main sequence (MS) since the stars spend only about 10% of their MS lifetime on the giant branch. Due to their rapid evolution it is di?cult to estimate the stellar parameters of giant stars. A possibility for obtaining more reliable stellar parameters for an active giant arises when it is a member of an eclipsing binary system. Aims. We have discovered EPIC 211759736, an active spotted giant star in an eclipsing binary system during the Kepler K2 Campaign 5. The eclipsing nature allows us to much better constrain the stellar parameters than in most cases of active giant stars. Methods. We have combined the K2 data with archival HATNet, ASAS, and DASCH photometry, new spectroscopic radial velocity measurements, and a set of follow-up ground-based BVRC IC photometric observations, to ?nd the binary system parameters as well as robust spot models for the giant at two di?erent epochs. Results. We determined the physical parameters of both stellar components and provide a description of the rotational and long-term activity of the primary component. The temperatures and luminosities of both components were examined in the context of the Hertzsprung–Russell diagram. We ?nd that both the primary and the secondary components deviate from the evolutionary tracks corresponding to their masses in the sense that the stars appear in the diagram at lower masses than their true masses. Conclusions. We further evaluate the proposition that traditional methods generally result in higher masses for active giants than what is indicated by stellar evolution tracks in the HR diagram. A possible reason for this discrepancy could be a strong magnetic ?eld, since we see greater di?erences in more active stars.
关键词： stars: fundamental parameters,stars: evolution,starspots,stars: late-type,binaries: eclipsing,stars: activity
更新于2025-09-04 15:30:14
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A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars
摘要： Aims. Hot subdwarf stars represent a poorly understood late phase of stellar evolution. While binary evolution plays an important role for the formation of B-type subdwarfs (sdB), the origin of the helium dominated subclass of O-type subdwarfs (He-sdO) is still unknown. We search for chemical signatures of their genesis by means of quantitative spectral analyses of high-quality visual and ultraviolet spectra. Methods. Four prototypical He-sdO stars, one belonging to the nitrogen-rich and three to the C-rich subclass, were selected for which archival far-ultraviolet spectra from the FUSE satellite as well as high-resolution visual and UVA spectra taken with the ESO-UVES/FEROS spectrographs are available. Using Tlusty200/Synspec49 to compute line blanketed- non-local thermodynamic equilibrium (NLTE) model atmospheres and synthetic spectra, atmospheric parameters and the abundances patterns have been derived. The ?nal models included H, He, C, N, O, Ne, Mg, Al, Si, P, S, Fe, and Ni represented by the most detailed model atoms available. Because of the enrichment of either nitrogen or carbon, it turned out, that models including these elements at the appropriate high abundance provide su?ciently accurate approximations to the temperature strati?cation of full models. Results. No indications for binarity were found, neither radial velocity variations nor photometric evidence for the presence of a companion could be detected. All stars have helium-dominated atmospheres almost free of hydrogen and temperatures between 42 000 K and 47 000 K while their surface gravities lie between log g = 5.4 and 5.7. The abundance pattern of CD–31?4800 displays the signatures of CNO burning, while heavier elements are subsolar by about 0.4 dex, except for Ne and Si which are close to solar. The abundance patterns of the C-rich He-sdOs are more complex. A slightly subsolar metallicity is accompanied by N-enrichment and O-de?ciency, less pronounced than in CD–31?4800. Neon is mildly to strongly enriched, up to a factor of ten with respect to the sun in LS IV +10? 9. The nickel-to-iron ratio is signi?cantly super-solar. Using spectral energy distributions and Gaia parallaxes the masses of the stars were determined. They are found to scatter around the canonical mass for the core helium ?ash, although the uncertainties are large. Conclusions. The abundance pattern observed for CD–31?4800 is consistent with predictions of models for slow (cold) mergers of pairs of equal mass helium WDs except for the low oxygen abundance observed. Models for composite mergers were considered for the C-rich stars, but predict abundance pattern dissimilar to those determined. [CW83] 0904?02, though, may be a candidate for a composite He-WD merger, as it rotates and appears to be more massive than the other program stars. New evolutionary models for the hot ?asher scenario predict abundance patterns similar to those determined for the C-rich stars. Hence, C-rich He-sdO may well result from late He ?ashes with deep-mixing episodes.
关键词： stars: evolution,subdwarfs,stars: atmospheres,stars: abundances
更新于2025-09-04 15:30:14