Study of Dust Structure nearby Asymptotic Giant Branch Star using IRAS Survey

This study performed an investigation of a dust environment, in the far-infrared bands (60 and 100 µm) of Infrared Astronomical Satellite (IRAS) survey, using the Sky View Virtual Observatory (https://skyview.gsfc.nasa.gov/current/). A far-infrared cavity structure (depression in the far-infrared background emission) of major diameter ∼ 61.8 pc and minor diameter ∼ 46.5 pc, in the sky coordinate, R.A. (J2000) = 21h 32m 44.47s and Dec. (J2000) = +55d 15m 16.8s, at a distance ∼ 3.58 kpc was found to lie around a carbon-rich Asymptotic Giant Branch star. We studied the temperature and mass of the dust, radiation intensity distribution, visual extinction, and far-infrared spectral distribution of the cavity structure using the softwares Aladin v2.5, SalsaJ, and ORIGIN 8.5. The range of temperature of dust was observed between 22.24 ± 0.81 K to 23.27 ± 0.21 K, and the entire mass of the cavity was determined to be 2.19 × 1031 kg. In addition, the fluctuating nature of the dust color temperature and Planck function was observed along major and minor diameters of the structure. Moreover, an opposite relationship of dust color temperature and visual extinction was found within the structure. Finally, from the far-infrared spectral distribution, abrupt reduction at 60 µm flux rather than a continual increase was observed, the connection between the AGB wind and the ambient interstellar medium could be the possible reason behind this. Our results obey the similar trends obtained for the other cavity structures in the previous studies; these findings validate the existing results for a new cavity structure around AGB star within the galactic coordinate -6o < b < +6o.

Common-envelope evolution with an asymptotic giant branch star

Common-envelope phases are decisive for the evolution of many binary systems. Cases with asymptotic giant branch (AGB) primary stars are of particular interest because they are thought to be progenitors of various astrophysical transients. In three-dimensional hydrodynamic simulations with the moving-mesh code AREPO, we study the common-envelope evolution of a 1.0 M⊙ early-AGB star with companions of different masses. Although the stellar envelope of an AGB star is less tightly bound than that of a red giant, we find that the release of orbital energy of the core binary is insufficient to eject more than about twenty percent of the envelope mass. Ionization energy that is released in the expanding envelope, however, can lead to complete envelope ejection. Because recombination proceeds largely at high optical depths in our simulations, it is likely that this effect indeed plays a significant role in the considered systems. The efficiency of mass loss and the final orbital separation of the core binary system depend on the mass ratio between the companion and the primary star. Our results suggest a linear relation between the ratio of final to initial orbital separation and this parameter.

Detection of infrared fluorescence of carbon dioxide in R Leonis with SOFIA/EXES

We report on the detection of hot CO2 in the O-rich asymptotic giant branch star R Leo based on high spectral resolution observations in the range 12.8−14.3 μm carried out with the Echelon-cross-Echelle Spectrograph (EXES) mounted on the Stratospheric Observatory for Infrared Astronomy (SOFIA). We found ≃240 CO2 emission lines in several vibrational bands. These detections were possible thanks to a favorable Doppler shift that allowed us to avoid contamination from telluric CO2 features. The highest excitation lines involve levels at an energy of ≃7000 K. The detected lines are narrow (average deconvolved width ≃2.5 km s−1) and weak (usually ≲10% the continuum). A ro-vibrational diagram shows that there are three different populations, warm, hot, and very hot, with rotational temperatures of ≃550, 1150, and 1600 K, respectively. From this diagram, we derived a lower limit for the column density of ≃2.2 × 1016 cm−2. Further calculations based on a model of the R Leo envelope suggest that the total column density can be as large as 7.0 × 1017 cm−2 and the abundance with respect to H2 ≃2.5 × 10−5. The detected lines are probably formed due to the de-excitation of CO2 molecules from high energy vibrational states, which are essentially populated by the strong R Leo continuum at 2.7 and 4.2 μm.

SN 2018zd: an unusual stellar explosion as part of the diverse Type II Supernova landscape

ABSTRACT We present extensive observations of SN 2018zd covering the first ∼450 d after the explosion. This SN shows a possible shock-breakout signal ∼3.6 h after the explosion in the unfiltered light curve, and prominent flash-ionization spectral features within the first week. The unusual photospheric temperature rise (rapidly from ∼12 000 to above 18 000 K) within the earliest few days suggests that the ejecta were continuously heated. Both the significant temperature rise and the flash spectral features can be explained by the interaction of the SN ejecta with the massive stellar wind ($0.18^{+0.05}_{-0.10}\, \rm M_{\odot }$), which accounts for the luminous peak ($L_{\rm max} = [1.36\pm 0.63] \times 10^{43}\, \rm erg\, s^{-1}$) of SN 2018zd. The luminous peak and low expansion velocity (v ≈ 3300 km s−1) make SN 2018zd like a member of the LLEV (luminous SNe II with low expansion velocities) events originating due to circumstellar interaction. The relatively fast post-peak decline allows a classification of SN 2018zd as a transition event morphologically linking SNe IIP and SNe IIL. In the radioactive-decay phase, SN 2018zd experienced a significant flux drop and behaved more like a low-luminosity SN IIP both spectroscopically and photometrically. This contrast indicates that circumstellar interaction plays a vital role in modifying the observed light curves of SNe II. Comparing nebular-phase spectra with model predictions suggests that SN 2018zd arose from a star of $\sim 12\, \rm M_{\odot }$. Given the relatively small amount of 56Ni ($0.013\!-\!0.035 \rm M_{\odot }$), the massive stellar wind, and the faint X-ray radiation, the progenitor of SN 2018zd could be a massive asymptotic giant branch star that collapsed owing to electron capture.

The impact of starbursts on element abundance ratios

ABSTRACT We investigate the impact of bursts in star formation on the predictions of one-zone chemical evolution models, adopting oxygen (O), iron (Fe), and strontium (Sr), as representative α, iron-peak, and s-process elements, respectively. To this end, we develop and make use of the Versatile Integrator for Chemical Evolution (VICE), a python package designed to handle flexible user-specified evolutionary parameters. Starbursts driven by a temporary boost of gas accretion rate create loops in [O/Fe]–[Fe/H] evolutionary tracks and a peak in the stellar [O/Fe] distribution at intermediate values. Bursts driven by a temporary boost of star formation efficiency have similar effects, and they also produce a population of α-deficient stars during the depressed star formation phase following the burst. This α-deficient population is more prominent if the outflow rate is tied to a time-averaged star formation rate (SFR) instead of the instantaneous SFR. Theoretical models of Sr production predict a strong metallicity dependence of supernova and asymptotic giant branch star yields, though comparison to data suggests an additional, nearly metallicity-independent source. Evolution of [Sr/Fe] and [Sr/O] during a starburst is complex because of this metallicity dependence and the multiple time-scales at play. Moderate amplitude (10–20 per cent) sinusoidal oscillations in SFR produce loops in [O/Fe]–[Fe/H] tracks and multiple peaks in [O/Fe] distributions, a potential source of intrinsic scatter in observed sequences. We investigate the impact of a factor ∼2 enhancement of Galactic star formation ∼2 Gyr ago, as suggested by some recent observations. VICE is publicly available at &lt;http://pypi.org/project/vice/&gt;.

Study of a Far Infrared Cavity Around a Post-Asymptotic Giant Branch Star at Galactic Latitude -0.1º

We present dust color temperature, Planck function and visual extinction distributions of a far infrared cavity FIC19+30 found to be located around post-AGB star namely AGB20+29 at the galactic plane. Minimum and maximum dust color temperature of the core region of the cavity was found to be (22.17±0.23) K and (22.41±0.29) K respectively with offset value 0.24 K which suggests that the cavity is isolated and stable. The product of dust color temperature and visual extinction was found to be in the order of 10-4 K mag. The distribution of Planck function along the extension (major diameter) and compression (minor diameter) was found to be non-uniform distribution. Specifically dust particles are oscillating in order to get dynamical equilibrium which may be the cause of grain temperature. It further suggests that the dust particles in the cavities might not be in the thermal equilibrium possibly due to pressure driven events of nearby AGB stars. There is continuous increase in flux density with increase in wavelength as in case of nebula which suggests that number density of dust particles increase according to the increase in wavelength and vice-versa.

An in-depth reanalysis of the alleged type Ia supernova progenitor Henize 2−428

Context. The nucleus of the planetary nebula Hen 2-428 is a short orbital-period (4.2 h), double-lined spectroscopic binary, whose status as a potential supernova type Ia progenitor has raised some controversy in the literature. Aims. With the aim of resolving this debate, we carried out an in-depth reanalysis of the system. Methods. Our approach combines a refined wavelength calibration, thorough line-identifications, improved radial-velocity measurements, non-LTE spectral modeling, as well as multi-band light-curve fitting. Our results are then discussed in view of state-of-the-art stellar evolutionary models. Results. Besides systematic zero-point shifts in the wavelength calibration of the OSIRIS spectra which were also used in the previous analysis of the system, we found that the spectra are contaminated with diffuse interstellar bands. Our Voigt-profile radial velocity fitting method, which considers the additional absorption of these diffuse interstellar bands, reveals significantly lower masses (M1 = 0.66 ± 0.11 M⊙ and M2 = 0.42 ± 0.07 M⊙) than previously reported and a mass ratio that is clearly below unity. Our spectral and light curve analyses lead to consistent results, however, we find higher effective temperatures and smaller radii than previously reported. Moreover, we find that the red-excess that was reported before to prove to be a mere artifact of an outdated reddening law that was applied. Conclusions. Our work shows that blends of He II λ 5412 Å with diffuse interstellar bands have led to an overestimation of the previously reported dynamical masses of Hen 2−428. The merging event of Hen 2−428 will not be recognised as a supernova type Ia, but most likely leads to the formation of a H-deficient star. We suggest that the system was formed via a first stable mass transfer episode, followed by common envelope evolution, and it is now composed of a post-early asymptotic giant branch star and a reheated He-core white dwarf.

Physical properties of the fluorine and neutron-capture element-rich PN Jonckheere 900

ABSTRACT We performed detailed spectroscopic analyses of a young C-rich planetary nebula (PN) Jonckheere 900 (J900) in order to characterize the properties of the central star and nebula. Of the derived 17 elemental abundances, we present the first determination of eight elemental abundances. We present the first detection of the [F iv] 4059.9 Å, [F v] 13.4 μm, and [Rb iv] 5759.6 Å lines in J900. J900 exhibits a large enhancement of F and neutron-capture elements Se, Kr, Rb, and Xe. We investigated the physical conditions of the H2 zone using the newly detected mid-IR H2 lines while also using the previously measured near-IR H2 lines, which indicate warm (∼670 K) and hot (∼3200 K) temperature regions. We built the spectral energy distribution (SED) model to be consistent with all the observed quantities. We found that about 67 per cent of all dust and gas components (4.5 × 10−4 M⊙ and 0.83 M⊙, respectively) exists beyond the ionization front, indicating the critical importance of photodissociation regions in understanding stellar mass loss. The best-fitting SED model indicates that the progenitor evolved from an initially ∼2.0 M⊙ star that had been in the course of the He-burning shell phase. Indeed, the derived elemental abundance pattern is consistent with that predicted by an asymptotic giant branch star nucleosynthesis model for a 2.0 M⊙ star with Z = 0.003 and partial mixing zone mass of 6.0 × 10−3 M⊙. Our study demonstrates how accurately determined abundances of C/F/Ne/neutron-capture elements and gas/dust masses help us understand the origin and internal evolution of the PN progenitors.