Detached Shell Carbon Stars: Tracing Thermal Pulses on the Asymptotic Giant Branch

We consider whether the subset of carbon-rich asymptotic giant branch (AGB) stars that exhibit detached, expanding circumstellar shells may reveal the past histories of these stars as having undergone helium shell flashes (thermal pulses) on the AGB. We exploit newly available Gaia parallaxes and photometry, along with archival infrared photometry, to obtain refined estimates of the luminosities of all (12) known detached shell carbon stars. We examine the relationship between these luminosities and the estimated dynamical ages (ejection times) of the detached shells associated with the 12 stars, which range from ∼1000 to ∼30,000 yr. When arranged according to detached shell dynamical age, the (implied) luminosity evolution of the known detached shell carbon stars closely follows the predicted “light curves” of individual thermal pulses obtained from models of AGB stars. The comparison between data and models suggests that detached shell carbon stars are descended from ∼2.5 to 4.0 M ⊙ progenitors. We conclude that detached shell carbon stars may serve as effective tracers of the luminosity evolution of AGB thermal pulses.

Rate of losing energy in Quantum Redshift

The paper simulates the losing energy of the electromagnetic waves in a non-expansion space and no gravitational Redshift. We use the distance and Redshift of 93,060 nearby space objects, including stars, quasars, white dwarfs, and carbon stars, for obtaining the rate of losing the energy of their waves during traveling in space. Quantum Redshift disagrees expansion of space and describes Redshift by losing the energy of electromagnetic waves over time. In the Quantum Redshift, regardless of the material and type of the space objects (stars, quasars, white dwarfs, and carbon stars), the Redshift depends on the distance and temperature of the space objects, and the temperature of space. We have used SIMBAD Astronomical Database. We have retrieved this information from almost 2,200,000 records. The objects' temperature is between 671 and 99,575 K. The distance of the objects is between 413.13 and 0.5 (mas). The paper obtains the average rate of losing the waves' energy for different objects in different distances. The results show that by increasing the distance of space objects, the rate of losing the energy of their electromagnetic waves will be decreased. The paper inspires investigating the expansion space theory by the Quantum Redshift.

A high positive correlation between the distance and temperature of the hottest nearby space objects

The paper uses the distance and temperature of 47,111 hottest nearby space objects including stars, quasars, white dwarf, and carbon stars. We have used SIMBAD Astronomical Database and obtained this information from 930,000 records. The range of temperature of the hottest objects is between 6158 and 99,575 K. Also, the distance of the objects is between 231.7375 and 1 (mas). We report the correlation between the distance and temperature of these hot objects at the temperature upper than 6632 K is equal to 0.135063 and will be increased to 0.32001 at temperatures upper than 9860 K. Also, the correlation between the temperature and distance of objects hotter than 12,000 K is equal to 0.270218.

Extended view on the dust shells around two carbon stars

Context. Stars on the asymptotic giant branch lose considerable amounts of matter through their dust-driven stellar winds. A number of such sources have been imaged by Herschel/PACS, revealing a diverse sample of different morphological types. Among them are a few examples which show geometrically thin, spherically symmetric shells which can be used to probe the mass loss history of their host stars. Aims. We aim to determine the physical properties of the dust envelope around the two carbon stars U Hya and W Ori. With the much-improved spatial constraints from the new far-infrared maps, our primary goal is to measure the dust masses contained in the shells and see how they fit the proposed scenarios of shell formation. Methods. We calculated the radiative transfer of the circumstellar dust envelope using the 1D code More of DUSTY (MoD). Adopting a parametrised density profile, we obtained a best-fit model in terms of the photometric and spectroscopic data, as well as a radial intensity profile based on Herschel/PACS data. For the case of U Hya, we also computed a grid of circumstellar envelopes by means of a stationary wind code and compare the results of the two modelling approaches. Results. The Herschel/PACS maps show U Hya surrounded by a detached shell of 114′′ (0.12 pc) in radius, confirming the observations from previous space missions. The dust masses calculated for the shell by the two approaches are consistent with respect to the adopted dust grain properties. In addition, around W Ori, we detect for the first time a weak spherically symmetric structure with a radius of 92′′ (0.17 pc) and a dust mass of (3.5 ± 0.3) × 10−6 M⊙.

High-resolution laser spectroscopy of the linear SiC2Si molecule and its astrophysical implications

Small silicon-carbon clusters are important gas-phase constituents of stellar atmospheres, and are thought to play a role as potential seeds of the interstellar dusts formed in the envelopes of evolved carbon stars. Here we present the high-resolution optical spectra of the linear SiC2Si molecule (l-Si2C2) studied via laboratory experiments. The l-Si2C2 molecules are generated in a supersonically expanding planar plasma by discharging a silane-acetylene-argon gas mixture. The optical absorption spectra in the 5000−5300 Å region are recorded using sensitive pulsed cavity ring-down spectroscopy. In total, five optical absorption bands belonging to the $ \tilde{C} ^{3}\Sigma_{u} ^{-} $ – $ \tilde{X} ^{3}\Sigma_{g} ^{-} $ electronic transition system of l-Si2C2 are measured with fully resolved spin splitting fine structures in individual rotational transitions. Accurate spectroscopic constants for both $ \tilde{X} ^{3}\Sigma_{g} ^{-} $ and $ \tilde{C} ^{3}\Sigma_{u} ^{-} $ states of l-Si2C2, including the spin-spin interaction constants and spin-rotation interaction constants, are determined from the experimental spectra, which can be used to simulate these optical bands with different temperatures. Using the determined spectroscopic constants, optical spectra of l-Si2C2 simulated with different rotational excitation temperatures are compared to the stellar spectra of evolved carbon stars V Hya and IRAS 12311−23509, where the triatomic SiC2 are known to be abundant. Tentative assignments of the l-Si2C2 spectral features in the stellar spectra are discussed.