arXiv subjects

Belinda Kalomeni

Publications and source records attributed to Belinda Kalomeni.

4 recordsLinked to original sources

arXiv2026

Photometric Modulations on Intermediate Timescales in the Symbiotic Binaries

We present a multi-band study of three symbiotic binaries using combined ground- and space-based monitoring that spans up to 14 years. These datasets enable a systematic investigation of variability on intermediate timescales (tens of days) and the detection of shorter-period signals. All systems display coherent photometric modulations that are distinct from the orbital cycles. In AX Per, a dominant 75-day signal and its 37-day harmonic are identified, which we interpret as pulsations of the cool giant. CI Cyg exhibits a stable modulation between 70 and 74 days, which likely arises from a combination of pulsation and circumstellar or disk-related variability. For Z And, we confirm a persistent modulation between 55 and 60 days, consistent with semiregular pulsations of the cool component. Additionally, space-based data reveal further short-period variability, including coherent signals at 26.7 and 66.6 minutes in Z And and CI Cyg, respectively, and a quasi-periodic modulation near 0.95 days in AX Per. These detections suggest the presence of rapid activity driven by accretion or rotation, superposed on the intermediate timescale behavior. Our results show that the observed variability in these symbiotic binaries reflects the combined effects of cool giant pulsation, circumstellar or disk activity, and possible rotation of the hot component. The multi-timescale behavior revealed here offers new constraints on mass transfer and activity cycles in interacting binaries.

astro-ph.SR↗

arXiv2026

A Binary-Based Reassessment of the Age and Stellar Properties of NGC 7789 Using Twelve Binary Components

We present a binary-based reassessment of the age of the intermediate-age open cluster NGC 7789, together with well-constrained stellar parameters for twelve components in six SB2 systems, including two eclipsing binaries. Our analysis employs a unified modelling framework that combines radial-velocity orbits, TESS light curves, and blue-to-IR spectral energy distributions (SEDs), providing a robust alternative to traditional isochrone-based age determinations. By adopting common cluster-wide parameters (age, distance, and line-of-sight extinction) when solving for the stellar parameters of the binary components, we obtain a coherent set of masses, radii, effective temperatures, and luminosities for all twelve stars. The combined SED, eclipsing-binary, and radial-velocity analysis yields a well-constrained cluster age of $1.26 \pm 0.09$ Gyr and an extinction of $A_V = 0.90 \pm 0.05$ mag, while remaining consistent with the Gaia DR3 distance of $d \simeq 2.06$ kpc used as an external prior. An independent Gaia DR3 astrometric analysis gives a distance of $2082 \pm 142$ pc and confirms the membership of all six systems. The twelve binary components occupy the turnoff and subgiant regions of the cluster, enabling stringent evolutionary tests: in the radius--mass, radius--temperature, and temperature--mass diagrams, they show excellent agreement with modern stellar evolution models for the derived cluster parameters. NGC 7789 thus serves as a valuable benchmark for multi-observable, binary-based age determinations in open cluster studies.

astro-ph.SR↗

arXiv2021

Light curve properties of SN 2017fgc and HV SNe Ia

Photometric and spectroscopic observations of type Ia supernova (SN) 2017fgc which cover the period from $-$12 to +137 days since the $B$-band maximum are presented. SN 2017fgc is a photometrically normal SN Ia with the luminosity decline rate, $ Δm_{15} (B)_{true} $= 1.10 $ \pm $ 0.10 mag. Spectroscopically, it belongs to the High Velocity (HV) SNe Ia group, with the Si II $λ$6355 velocity near the $B$-band maximum estimated to be 15,200 $ \pm $ 480 km $s^{-1}$. At the epochs around the near-infrared secondary peak, the $R$ and $I$ bands show an excess of $\sim$0.2 mag level compared to the light curves of the normal velocity (NV) SNe Ia. Further inspection of the samples of HV and NV SNe Ia indicates that the excess is a generic feature among HV SNe Ia, different from NV SNe Ia. There is also a hint that the excess is seen in the V band, both in SN 2017fgc and other HV SNe Ia, which behaves like a less prominent shoulder in the light curve. The excess is not obvious in the B band (and unknown in the U band), and the color is consistent with the fiducial SN color. This might indicate the excess is attributed to the bolometric luminosity, not in the color. This excess is less likely caused by external effects, like an echo or change in reddening but could be due to an ionization effect, which reflects an intrinsic, either distinct or continuous, difference in the ejecta properties between HV and NV SNe Ia.

astro-ph.HE↗

arXiv2008

Variation of the Light and Period of the Magnetic Cataclysmic Variable Am Her

Ground-based long-term optic variability of AM Her, covering the period between 2003-2008, has been conducted to study the features seen in both low and high states of the system. Low-state analysis shows the presence of short-term, low-amplitude light variations of about 0.02-0.03 mag with a mean power time between 16 s and 226 s. Brightness variations on the order of 0.7--2 mag, which could be due to the stellar activity of the component in the system, are also detected. A total of 30 years times of minimum light given in the literature are combined with nine times of minima obtained in this study. We represented the (observed--calculated) diagram by a parabolic curve and also by two broken lines. Under the assumption of a parabolic variation, we estimate an increase in period, dP/dt=7.5(1.2)x10^{-9} days yr^{-1}, with a mass transfer rate of dM/dt = 8(2)x10^{-9} M_{\odot} yr^{-1}, in agreement with the previous findings by a different method.

astro-ph↗