arXiv subjects

N. Ikonnikova

Publications and source records attributed to N. Ikonnikova.

3 recordsLinked to original sources

arXiv2024

Discovery of a hot post-AGB star in Galactic globular cluster E3

We report a new hot post-asymptotic giant branch (PAGB) star in the Galactic globular cluster (GC) E3, which is one of the first of the identified PAGB stars in a GC to show a binary signature. The star stands out as the brightest source in E3 in the \mbox{\em Astrosat}/UVIT images. We confirmed its membership with the cluster E3 using Gaia DR3 kinematics and parallax measurements. We supplemented the photometric observations with radial velocities (RVs) from high-resolution spectroscopic observations at two epochs and with ground- and space-based photometric observations from 0.13 $μ$m to 22 $μ$m. We find that the RVs vary over $\sim$6 \kms\ between the two epochs. This is an indication of the star being in a binary orbit. A simulation of possible binary systems with the observed RVs suggests a binary period of either 39.12 days or 17.83 days with mass ratio q$\geq$1.0. The [Fe/H] derived using the high-resolution spectra is $\sim -$0.7 dex, which closely matches the cluster metallicity. The spectroscopic and photometric measurements suggest \Teff\ and $\log g$ of the star as 17\,500$\pm$1\,000~K and 2.37$\pm$0.20~dex, respectively. Various PAGB evolutionary tracks on the Hertzsprung--Russell (H-R) diagram suggest a current mass of the star in the range 0.51$-$0.55 \Msun. The star is enriched with C and O abundances, showing similar CNO abundances compared to the other PAGB stars in GCs with the evidence of the third dredge-up on the AGB phase.

astro-ph.SR↗

arXiv2022

Orbital parameters and activity of ZZ Tau -- a low mass young binary with circumbinary disc

We present the results of our new observations of the young binary ZZ Tau with a circumbinary disc. The system was found to consist of two coeval (age $<2$ Myr) classical T Tauri stars with the total mass $0.86 \pm 0.09$ M$_\odot$, orbital period $46.8 \pm 0.8$ yr, semimajor axis $88.2 \pm 2.1$ mas, eccentricity $0.58 \pm 0.02$ and the orbital inclination $123.^{\rm o} 8 \pm 1.^{\rm o} 0.$ The accretion rate of ZZ Tau A and ZZ Tau B are approximately $7\times 10^{-10}$ and $2\times 10^{-10}$ M$_\odot$ yr$^{-1},$ respectively. No correlation was found between the long-term photometric variability of ZZ Tau and orbital position of its components. The periodic light variations with $P=4.171 \pm 0.002$ days was observed in the $BVRI$ bands presumably connected with an accretion (hot) spot on the surface of the primary (ZZ Tau A). At the same time no periodicity was observed in the $U$ band nor in the emission line profile variations probably due to the significant contribution of ZZ Tau B's emission, which dominates shortward of $λ\approx 0.4\,μ$m. We argue that the extinction in the direction to the primary is noticeably larger than that to the secondary. It appeared that the rotation axis of the primary is inclined to the line of sight by $\approx 31^{\rm o} \pm 4^{\rm o}.$ We concluded also that ZZ Tau is the source of an CO molecular outflow, however, ZZ Tau IRS rather than ZZ Tau is the source of the Herbig-Haro object HH393.

astro-ph.SR↗

arXiv2014

Monitoring evolved stars for binarity with the HERMES spectrograph

Binarity is often invoked to explain peculiarities that can not be explained by the standard theory of stellar evolution. Detecting orbital motion via the Doppler effect is the best method to test binarity when direct imaging is not possible. However, when the orbital period exceeds the duration of a typical observing run, monitoring often becomes problematic. Placing a high-throughput spectrograph on a small semi- robotic telescope allowed us to carry out a radial-velocity survey of various types of peculiar evolved stars. In this review we highlight some findings after the first four years of observations. Thus, we detect eccentric binaries among hot subdwarfs, barium, S stars, and post- AGB stars with disks, which are not predicted by the standard binary interaction theory. In disk objects, in addition, we find signs of the on- going mass transfer to the companion, and an intriguing line splitting, which we attribute to the scattered light of the primary.

astro-ph.SR↗