Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHigh-resolution spectroscopy of QY Sge -- An obscured RV Tauri variable?
47
0
0.0
(
0
)
Authors
N. Kameswara Rao
Ask ChatGPT about the research
No Arabic abstract
The first high-resolution optical spectra of QY Sge are presented and discussed. Menzies & Whitelock (1988) on the basis of photometry and low-resolution spectra suggested that this G0I supergiant was obscured by dust and seen only by scattered light from a circumstellar reflection nebula. The new spectra confirm and extend this picture. Photospheric lines are unusually broad indicating scattering of photons from dust in the stellar wind. Presence of very broad Na D emission lines is confirmed. Sharp emission lines from low levels of abundant neutral metal atoms are reported for the first time. An abundance analysis of photospheric lines shows that the stellar atmosphere is of approximately solar composition but with highly condensible (e.g., Sc and Ti) elements depleted by factors of 5 to 10.
rate research
Read More
Analysis of the surface composition of the suspected cool RV Tauri star CE Vir shows no systematic trend in depletions of elements with respect to condensation temperature. However, there is a significant depletion of the elements with respect to the first ionization potential of the element. The derived Li abundance of log $epsilon$ (Li) = 1.5$pm$0.2 indicates production of Li in the star. Near infrared colours indicate sporadic dust formation close to the photosphere.
An abundance analysis is presented and discussed for a sample of 14 RV Tauri stars. The present abundance data and those from our previous papers and by other workers are combined in an attempt to further understanding of the dust-gas separation process which afflicts many RV Tauri variables. We propose that a stars intrinsic (i.e., initial) metallicity is given by the photospheric zinc abundance. Variables warmer that about 5000 K and with an initial metallicity [Fe/H] $geq$ $-$1 are affected by dust-gas separation. Variables of all metallicities and cooler than about $T_{rm eff} simeq 5000$ K are unaffected by dust-gas separation. The RV Tauri variables show a spread in their C abundances with the lower boundary of the points in the C versus Zn plane falling close to the predicted trend for giants after the first dredge-up. The upper boundary is inhabited by a few stars that are carbon-rich. The O abundances in the mean follow the predicted trend from unevolved stars in line with the expectation that photospheric O abundance is unaffected by the first dredge-up. An evolutionary scenario involving mass loss by a first ascent or early-AGB red giant, the primary star of a binary, is sketched.
We present an analysis of the Chandra High Energy Transmission Grating Spectrometer observation of the rapidly rotating P_(rot)=0.94 d post T Tauri (~20 Myr old) star PZ Telescopii, in the Tucana association. Using two different methods we have derived the coronal emission measure distribution, em(T), and chemical abundances. The em(T) peaks at log T = 6.9 and exhibits a significant emission measure at temperatures log T > 7. The coronal abundances are generally ~0.5 times the solar photospheric values that are presumed fairly representative of the composition of the underlying star. A minimum in abundance is seen at a first ionization potential (FIP) of 7-8 eV, with evidence for higher abundances at both lower and higher FIP, similar to patterns seen in other active stars. From an analysis of the He-like triplet of Mg XI we have estimated electron densities of ~10^(12)-10^(13) cm^(-3). All the coronal properties found for PZ Tel are much more similar to those of AB Dor, which is slightly older than PZ Tel, than to those of the younger T Tauri star TW Hya. These results support earlier conclusions that the soft X-ray emission of TW Hya is likely dominated by accretion activity rather than by a magnetically-heated corona. Our results also suggest that the coronae of pre-main sequence stars rapidly become similar to those of older active main-sequence stars soon after the accretion stage has ended.
Aim: The focus of this paper is on two famous but still poorly understood RV Tauri stars: RV Tau and DF Cyg. We aim at confirming their suspected binary nature and deriving their orbital elements to investigate the impact of their orbits on the evolution of these systems. This research is embedded into a wider endeavour to study binary evolution of low- and intermediate-mass stars. Method: The high amplitude pulsations were cleaned from the radial-velocity data to better constrain the orbital motion. We used Gaia DR2 parallaxes in combination with the SEDs to compute their luminosities which were complemented with the ones computed using a period-luminosity-colour relation. The ratio of the circumstellar infrared flux to the photospheric flux obtained from the SEDs was used to estimate the orbital inclination of each system. Results: DF Cyg and RV Tau are binaries with spectroscopic orbital periods of 784$pm$16 days and 1198$pm$17 days, respectively. These orbital periods are found to be similar to the long-term periodic variability in the photometric time series, indicating that binarity indeed explains the long-term photometric variability. Both systems are surrounded by a circumbinary disc which is grazed by our line-of-sight. As a result, the stellar photometric flux is extinct periodically with the orbital period. Our derived orbital inclinations enabled us to obtain accurate companion masses for DF Cyg and RV Tau. Analysis of the Kepler photometry of DF Cyg revealed a power spectrum with side lobes around the fundamental pulsation frequency. This modulation corresponds to the spectroscopic orbital period and hence to the long-term photometric period. Finally we report on the evidence of high velocity absorption features related to the H$_{alpha}$ profile in both objects, indicating outflows launched from around the companion.
We present the photometric results of the eclipsing cataclysmic variable (CV) WZ Sge near the period minimum ($P_{min}$). Eight new mid-eclipse times were determined and the orbital ephemeris was updated. Our result shows that the orbital period of WZ Sge is decreasing at a rate of $dot{P}=-2.72(pm0.23)times{10^{-13}},s s^{-1}$. This secular decrease, coupled with previous detection of its donor, suggest that WZ Sge is a pre-bounce system. Further analysis indicates that the observed period decrease rate is about $1.53$ times higher than pure gravitational radiation (GR) driving. We constructed the evolutionary track of WZ Sge, which predicts that $P_{min}$ of WZ Sge is $sim77.98 (pm0.90)$ min. If the orbital period decreases at the current rate, WZ Sge will evolve past its $P_{min}$ after $sim25.3$ Myr. Based on the period evolution equation we find $dot{M}_{2}simeq4.04(pm0.10)times10^{-11}M_{odot}yr^{-1}$, which is compatible with the current concept of CV evolution at ultrashort orbital periods.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
