Shell Of Gas Research Articles

Line identification and photometric history of the hot post-AGB star Hen 3−1013 (IRAS 14331−6435)

We present a study of the high-resolution optical spectrum for the hot post-asymptotic giant branch (post-AGB) star, Hen 3-1013, identified as the optical counterpart of the infrared sourceIRAS 14331-6435. For the first time the detailed identifications of the observed absorption and emission features in the wavelength range 3700-9000 \AA\ is carried out. Absorption lines of HI, HeI, CI, NI, OI, NeI, CII, NII, OII, SiII, SII, ArII, FeII, MnII, CrII, TiII, CoII, NiII, SIII, FeIII and SIV were detected. From the absorption lines, we derived heliocentric radial velocities of $V_r=-29.6\pm0.4$ km/s. We have identified emission permitted lines of OI, NI, FeII, MgII, SiII and AlII. The forbidden lines of [NI], [FeII], [CrII] and [NiII] have been identified also. Analysis of [NiII] lines in the gaseous shell gives an estimate for the electron density $N_e\sim10^7$ cm$^{-3}$ and the expansion velocity of the nebula $V_{exp}=12$ km/s. The mean radial velocity as measured from emission features of the envelope is $V_r=-36.0\pm0.4$ km/s. The Balmer lines H$\alpha$, H$\beta$ and H$\gamma$ show P Cyg behaviour which indicate ongoing post-AGB mass-loss. Based on ASAS and ASAS-SN data, we have detected rapid photometric variability in Hen 3-1013 with an amplitude up to 0.2 mag in the V band. The star's low-resolution spectrum underwent no significant changes from 1994 to 2012. Based on archival data, we have traced the photometric history of the star over more than 100 years. No significant changes in the star brightness have been found.

Velocity-resolved [O i] 63 μm Emission in the HD 50138 Circumstellar Disk*

Abstract HD 50138 is one of the brightest B[e] stars and is located at a distance of ∼380 pc with strong infrared excess. The star was observed in [O i] 63 μm and [C ii] 158 μm with high velocity resolution with upGREAT on SOFIA. The velocity-resolved [O i] emission provides evidence for a large gas disk, ∼760 au in size, around HD 50138. Whereas previous interferometric observations gave strong evidence for a hot gas and dust disk in Keplerian rotation, our observations are the first to provide unambiguous evidence for a large warm disk around the star. Herschel/PACS observations showed that the [C ii] emission is extended, therefore the [C ii] emission most likely originates from an ionized gas shell created by a past outflow event. We confirm the isolated nature of HD 50138. It is far from any star-forming region and has low proper motion. Neither is there any sign of a remnant cloud from which it could have formed. The extended disk around the star appears to be carbon-poor. It shows OH and [O i] emission, but no CO. The CO abundance appears to be at least an order of magnitude lower than that of OH. Furthermore, 13CO is enriched by more than a factor of five, confirming that the star is not a Herbig Be star. Finally, we note that our high-spectral-resolution [O i] and [C ii] observations provide a very accurate heliocentric velocity of the star, 40.8 ± 0.2 km s−1.

Detection of large-scale Ly α absorbers at large angles to the radio axis of high-redshift radio galaxies using SOAR

We present an investigation of the properties of the extended Ly$\alpha$ halo and the large-scale \ion{H}{I} absorbing structures associated with 5 high-redshift radio galaxies at z $>$ 2, using the Goodman long-slit spectrograph on the SOAR telescope, with the slit placed at large angles ($>$45$^{\circ}$) to the radio axis, to study regions that are unlikely to be illuminated by the active nucleus. Spatially extended Ly$\alpha$ emission is detected with large line widths (FWHM = 1000 -- 2500 km s$^{-1}$), which although impacted by resonant scattering, is suggestive of turbulent motion. We find a correlation between higher blueshifts and higher FWHM, which is an indication that radial motion dominates the bulk gas dynamics perpendicular to the radio axis, although we are unable to distinguish between outflow and infall scenarios due to the resonant nature of the Ly$\alpha$ line. Extended, blueshifted Ly$\alpha$ absorption is detected in the direction perpendicular to the radio axis in three radio galaxies with minimum spatial extents ranging from $\gtrsim$27 kpc to $\gtrsim$35 kpc, supporting the idea that the absorbing structure covers the entire Ly$\alpha$ halo, consistent with being part of a giant, expanding shell of gas enveloping the galaxy and its (detected) gaseous halo.

On the evolutionary state of massive stars in transition phases in M33

The advanced stages of several high-mass stars are characterized by episodic mass loss shed during phases of instability. Key for assigning these stars a proper evolutionary state is to assess the composition and geometry of their ejecta alongside the stellar properties. We selected five hot LBV candidates in M33 to refine their classification, investigate their circumstellar environments and explore their evolutionary properties. Being accessible targets in the near-infrared, we conducted medium-resolution spectroscopy with GNIRS/GEMINI in the $K-$band to investigate their molecular circumstellar environments. Two stars were found to display CO emission, which was modeled to emerge from a circumstellar or circumbinary Keplerian disk/ring. The identification of the carbon isotope $^{13}$C and, for one of the two stars, a significantly low $^{12}$CO/$^{13}$CO ratio, implies an evolved stellar state. As both CO emission stars are highly luminous and hence do not undergo a red supergiant phase, we suggest that stripping processes and equatorial high-density ejecta due to fast rotation are responsible for the enrichment of the stellar surface with processed material from the core. A candidate B[e]SG displays an absorption CO profile, which may be attributed to a jet or stellar pulsations. The featureless infrared spectra of two stars suggest a low-density gas shell or dissipation of the molecule due to the ionizing temperature of the star. We propose spectroscopic monitoring of our targets to evaluate the stability of the CO molecule and assess the time-dependent dynamics of the circumstellar gas structures.

Dust cleansing of star-forming gas

Aims. We explore the possibility that solar chemical composition, as well as the similar composition of the rich open cluster M 67, have been affected by dust cleansing of the presolar or precluster cloud due to the radiative forces from bright early-type stars in its neighbourhood. Methods. We estimate possible cleansing effects using semi-analytical methods, which are essentially based on momentum conservation. Results. Our calculations indicate that the amounts of cleansed neutral gas are limited to a relatively thin shell surrounding the H II region around the early-type stars. Conclusions. It seems possible that the proposed mechanism acting in individual giant molecular clouds may produce significant abundance effects for masses corresponding to single stars or small groups of stars. The effects of cleansing are, however, severely constrained by the thinness of the cleansed shell of gas and by turbulence in the cloud. This is why the mechanism can hardly be important in cleansing masses corresponding to rich clusters, such as the mass of the original M 67.

X-ray binary Beta Lyrae and its donor component structure

AbstractWe show that the structure of magnetized accretion gas flows between the components of the Beta Lyrae system can cause a scattering gas shell that masks completely these components in soft X-ray region. Also we have calculated the inner structure of the donor that is filling a Roche lobe and is preceding a forming of the degenerate dwarf. We show that mass of the degenerate core of the donor is in region 0.3−0.5M⊙.

Numerical simulations of radiative heat effects in a plasma wind-tunnel flow under Mars entry conditions

The Mars atmosphere, consisting mainly of CO2, with a few percent of N2 and other trace gases, is of interest to future space projects. Entry into its gaseous shell is of current significant research interest. For this application, an arc jet driven plasma wind tunnel is available to simulate relevant entry conditions for the planet. Recent improvements and qualification of the test facility, enables the testing on earth of high enthalpy flows with CO2 rich compositions. In order to complement the experimental analysis, numerical simulations of the test facility running at relevant ambient pressures of 600–1000 Pa, corresponding to low altitudes, have been completed. The simulations used a density-based Navier Stokes solver and non-equilibrium chemical and thermal effects which are characteristic of these types of high enthalpy flows. Special interest is given to the radiative heat transfer mechanism. Under these high temperature conditions, radiative effects become more relevant and advanced radiation models must be used. The coupling between the Navier Stokes and radiative transfer equations favours the understanding of plasma wind tunnel flows. The radiative heat is estimated using the k-distribution spectral model, which is appropriate for non-homogeneous radiating media. The numerical results and measurements are compared in order to improve the analysis methods for Mars entry flows.

Modelling the carbon AGB star R Sculptoris

Context. On the asymptotic giant branch (AGB), Sun-like stars lose a large portion of their mass in an intensive wind and enrich the surrounding interstellar medium with nuclear processed stellar material in the form of molecular gas and dust. For a number of carbon-rich AGB stars, thin detached shells of gas and dust have been observed. These shells are formed during brief periods of increased mass loss and expansion velocity during a thermal pulse, and open up the possibility to study the mass-loss history of thermally pulsing AGB stars. Aims. We study the properties of dust grains in the detached shell around the carbon AGB star R Scl and aim to quantify the influence of the dust grain properties on the shape of the spectral energy distribution (SED) and the derived dust shell mass. Methods. We modelled the SED of the circumstellar dust emission and compared the models to observations, including new observations of Herschel/PACS and SPIRE (infrared) and APEX/LABOCA (sub-millimeter). We derived present-day mass-loss rates and detached shell masses for a variation of dust grain properties (opacities, chemical composition, grain size, and grain geometry) to quantify the influence of changing dust properties to the derived shell mass. Results. The best-fitting mass-loss parameters are a present-day dust mass-loss rate of 2 × 10−10 M⊙ yr−1 and a detached shell dust mass of (2.9 ± 0.3) × 10−5 M⊙. Compared to similar studies, the uncertainty on the dust mass is reduced by a factor of 4. We find that the size of the grains dominates the shape of the SED, while the estimated dust shell mass is most strongly affected by the geometry of the dust grains. Additionally, we find a significant sub-millimeter excess that cannot be reproduced by any of the models, but is most likely not of thermal origin.

Sgr A* envelope explosion and the young stars in the centre of the Milky Way

ABSTRACT Sgr A* is the supermassive black hole residing in the centre of the Milky Way. There is plenty of observational evidence that a massive gas cloud fell into the central parsec of the Milky Way ∼6 Myr ago, triggering formation of a disc of young stars and activating Sgr A*. In addition to the disc, there is an unexplained population of young stars on randomly oriented orbits. Here we hypothesize that these young stars were formed by fragmentation of a massive quasi-spherical gas shell driven out from Sgr A* potential well by an energetic outflow. To account for the properties of the observed stars, the shell must be more massive than 105 solar masses, be launched from inside ∼0.01 pc, and the feedback outflow has to be highly super-Eddington albeit for a brief period of time, producing kinetic energy of at least 1055 erg. The young stars in the central parsec of the Galaxy may be a unique example of stars formed from atomic rather than molecular hydrogen, and forged by extreme pressure of black hole outflows.

Feeding supermassive black holes by collisional cascades

The processes driving gas accretion on to supermassive black holes (SMBHs) are still poorly understood. Angular momentum conservation prevents gas within $\sim10\,$pc of the black hole from reaching radii $\sim10^{-3}\,$pc where viscous accretion becomes efficient. Here we present simulations of the collapse of a clumpy shell of swept-up isothermal gas, which is assumed to have formed as a result of feedback from a previous episode of AGN activity. The gas falls towards the SMBH forming clumps and streams, which intersect, collide, and often form a disc. These collisions promote partial cancellations of angular momenta, resulting in further infall and more collisions. This continued collisional cascade generates a tail of gas with sufficiently small angular momenta and provides a viable route for gas inflow to sub-parsec scales. The efficiency of this process hardly depends on details, such as gas temperature, initial virial ratio and power spectrum of the gas distribution, as long as it is not strongly rotating. Adding star formation to this picture might explain the near-simultaneous formation of the S-stars (from tidally disrupted binaries formed in plunging gas streams) and the sub-parsec young stellar disc around Sgr A$^{\!\star}$.

Anodic Plasma Electrolytic Nitrocarburizing of VT22 Titanium Alloy in Carbamide Electrolyte

The influence of the carbamide concentration on the nitrocarburizing temperature and changes in the mass of titanium samples, which are related to the anodic dissolution and high-temperature oxidation of titanium in a vapor‒gas shell, is investigated. The modified layer structure is revealed to contain an external oxide layer (rutile) and an intermediate diffusion layer whose microhardness reaches 770 HV. It is demonstrated that an increase in the nitrocarburizing temperature stimulates growth in the oxide-layer thickness, and the diffusion-layer thickness depends on the carbamide concentration in the solution. It is found that, at 850°С, the surface roughness decreases from 1.0 to 0.3–0.5 μm and the wear rate reduces from 6.7 × 10–7 to (1.2–1.7) × 10–7 due to nitrocarburizing in an electrolyte incorporating 10–15 wt % ammonium chloride and 10–12.5 wt % carbamide.

Sound wave generation by a spherically symmetric outburst and AGN feedback in galaxy clusters II: impact of thermal conduction

We analyze the impact of thermal conduction on the appearance of a shock-heated gas shell which is produced when a spherically symmetric outburst of a supermassive black hole inflates bubbles of relativistic plasma at the center of a galaxy cluster. The presence of the hot and low-density shell can be used as an ancillary indicator for a high rate of energy release during the outburst, which is required to drive strong shocks into the gas. Here we show that conduction can effectively erase such shell, unless the diffusion of electrons is heavily suppressed. We conclude that a more robust proxy to the energy release rate is the ratio between the shock radius and bubble radius. We also revisited the issue of sound waves dissipation induced by thermal conduction in a scenario, where characteristic wavelength of the sound wave is set by the total energy of the outburst. For a fiducial short outburst model, the dissipation length does not exceed the cooling radius in a typical cluster, provided that the conduction is suppressed by a factor not larger than $\sim$100. For quasi-continuous energy injection neither the shock-heated shell nor the outgoing sound wave are important and the role of conduction is subdominant.

Comments: No Consensus

Editor's column Although the oil and gas industry can be full of surprises, its executives tend to rally around a consensus point of view on where the market and industry are headed. For the past 2–3 years, the hundreds of executives from around the globe who attend the annual CERAWeek conference in Houston have painted a grim picture of the present and perhaps the future, and were right in early 2015 when they agreed that the current downturn was looking a lot like the severe one that occurred in the 1980s. But at this year’s gathering, held during the first week of March, there was a lack of consensus about the industry’s short- and medium-term future, and some opinions were at odds with the views that are being played out in the media and other public forums. Although executives at Shell and BP pointed to climate change, or reaction to climate change, as being a real threat on the horizon, others disagreed. Although acceptance of electric vehicles is rising and strides have been made in battery technology. Saudi Aramco’s chief executive officer said alternative vehicles offer little threat to the industry. “I am not losing any sleep over the idea of peak oil demand or stranded resources,” Amin Nasser told the gathering. The success of electric vehicles is not guaranteed, he said, adding that “the future role of oil is widely misunderstood.” But elsewhere at the conference, the chairman of General Motors told the gathering that the company’s “commitment to an all-electric, zero-emissions future is unwavering, regardless of any modifications to future fuel economy standards,” and an electric car was on display. BP called on the industry to reduce greenhouse gas emissions and Shell CEO Ben van Beurden said that the necessity for a lower-carbon future was already here. “There is no other issue with the potential to seriously disrupt our industry on such deep and fundamental levels as climate change,” he said. OPEC and the International Energy Agency (IEA) called on the industry to invest more in oil and gas exploration and production, warning that current investment levels are not high enough to meet future hydrocarbons demand. Others saw oil production from the US, and particularly the Permian Basin, swamping consumption needs for several years. The IEA forecasts that US oil production will represent 60% of new global output to 2023, and that other non-OPEC output will take up the rest. Permian production will soon hit 3 million B/D, and the US may soon overtake Saudi Arabia as the world’s second-largest producer behind only Russia. Some independent producers, however, noted that several companies had missed their unconventional production targets in the fourth quarter of 2017 and will likely do so again in the first quarter of this year. Labor shortages, infrastructure bottlenecks, and lingering problems over “frac hits” may be issues, as well as the reality that many unconventional “child” wells are not nearly as productive as the parent wells. If there was consensus, it was that the industry is in a better place than it was a couple of years ago. Sessions were certainly more optimistic, although cautiously, and there was little talk of oil prices getting out of the $50–65/bbl range. And there was a sense that the uneasy alliance between OPEC and shale producers, which one executive described as “walking a tightrope,” would continue.

An independent distance estimate to the AGB star R Sculptoris

Context. Distance measurements to astronomical objects are essential for understanding their intrinsic properties. For asymptotic giant branch (AGB) stars it is particularly difficult to derive accurate distance estimates. Period-luminosity relationships rely on the correlation of different physical properties of the stars, while the angular sizes and variability of AGB stars make parallax measurements inherently inaccurate. For the carbon AGB star R Sculptoris, the uncertain distance significantly affects the interpretation of observations regarding the evolution of the stellar mass loss during and after the most recent thermal pulse. Aim. We aim to provide a new, independent measurement of the distance to R Sculptoris, reducing the absolute uncertainty of the distance estimate to this source. Methods. R Scl is a semi-regular pulsating star, surrounded by a thin shell of dust and gas created during a thermal pulse ≈2000 years ago. The stellar light is scattered by the dust particles in the shell at a radius of ≈19″. The variation in the stellar light affects the amount of dust-scattered light with the same period and amplitude ratio, but with a phase lag that depends on the absolute size of the shell. We measured this phase lag by observing the star R Scl and the dust-scattered stellar light from the shell at five epochs between June–December 2016. By observing in polarised light, we imaged the shell in the plane of the sky, removing any uncertainty due to geometrical effects. The phase lag gives the absolute size of the shell, and together with the angular size of the shell directly gives the absolute distance to R Sculptoris. Results. We measured a phase lag between the stellar variations and the variation in the shell of 40.0 ± 4.0 days. The angular size of the shell is measured to be 19.″1 ± 0.″7. Combined, this gives an absolute distance to R Sculptoris of 361 ± 44 pc. Conclusions. We independently determined the absolute distance to R Scl with an uncertainty of 12%. The estimated distance is consistent with previous estimates, but is one of the most accurate distances to the source to date. In the future, using the variations in polarised, dust-scattered stellar light, may offer an independent possibility to measure reliable distances to AGB stars.

The Local Bubble: a magnetic veil to our Galaxy

The magnetic field in the local interstellar medium does not follow the large-scale Galactic magnetic field. The local magnetic field has probably been distorted by the Local Bubble, a cavity of hot ionized gas extending all around the Sun and surrounded by a shell of cold neutral gas and dust. However, so far no conclusive association between the local magnetic field and the Local Bubble has been established. Here we develop an analytical model for the magnetic field in the shell of the Local Bubble, which we represent as an inclined spheroid, off-centred from the Sun. We fit the model to Planck dust polarized emission observations within 30° of the Galactic poles. We find a solution that is consistent with a highly deformed magnetic field, with significantly different directions towards the north and south Galactic poles. This work sets a methodological framework for modelling the three-dimensional (3D) structure of the magnetic field in the local interstellar medium, which is a most awaited input for large-scale Galactic magnetic field models.

Polarimetry and spectroscopy of the “oxygen flaring” DQ Herculis-like nova: V5668 Sagittarii (2015)

Context. Classical novae are eruptions on the surface of a white dwarf in a binary system. The material ejected from the white dwarf surface generally forms an axisymmetric shell of gas and dust around the system. The three-dimensional structure of these shells is difficult to untangle when viewed on the plane of the sky. In this work a geometrical model is developed to explain new observations of the 2015 nova V5668 Sagittarii. Aim. We aim to better understand the early evolution of classical nova shells in the context of the relationship between polarisation, photometry, and spectroscopy in the optical regime. To understand the ionisation structure in terms of the nova shell morphology and estimate the emission distribution directly following the light curve’s dust-dip. Methods. High-cadence optical polarimetry and spectroscopy observations of a nova are presented. The ejecta is modelled in terms of morpho-kinematics and photoionisation structure. Results. Initially observational results are presented, including broadband polarimetry and spectroscopy of V5668 Sgr nova during eruption. Variability over these observations provides clues towards the evolving structure of the nova shell. The position angle of the shell is derived from polarimetry, which is attributed to scattering from small dust grains. Shocks in the nova outflow are suggested in the photometry and the effect of these on the nova shell are illustrated with various physical diagnostics. Changes in density and temperature as the super soft source phase of the nova began are discussed. Gas densities are found to be of the order of 109 cm−3 for the nova in its auroral phase. The blackbody temperature of the central stellar system is estimated to be around 2.2 × 105 K at times coincident with the super soft source turn-on. It was found that the blend around 4640 Å commonly called “nitrogen flaring” is more naturally explained as flaring of the O II multiplet (V1) from 4638–4696 Å, i.e. “oxygen flaring”. Conclusions. V5668 Sgr (2015) was a remarkable nova of the DQ Her class. Changes in absolute polarimetric and spectroscopic multi-epoch observations lead to interpretations of physical characteristics of the nova’s evolving outflow. The high densities that were found early-on combined with knowledge of the system’s behaviour at other wavelengths and polarimetric measurements strongly suggest that the visual “cusps” are due to radiative shocks between fast and slow ejecta that destroy and create dust seed nuclei cyclically.

IRC +10 216 in 3-D: morphology of a TP-AGB star envelope.

During their late pulsating phase, AGB stars expel most of their mass in the form of massive dusty envelopes, an event that largely controls the composition of interstellar matter. The envelopes, however, are distant and opaque to visible and NIR radiation: their structure remains poorly known and the mass-loss process poorly understood. Millimeter-wave interferometry, which combines the advantages of longer wavelength, high angular resolution and very high spectral resolution is the optimal investigative tool for this purpose. Mm waves pass through dust with almost no attenuation. Their spectrum is rich in molecular lines and hosts the fundamental lines of the ubiquitous CO molecule, allowing a tomographic reconstruction of the envelope structure. The circumstellar envelope IRC +10 216 and its central star, the C-rich TP-AGB star closest to the Sun, are the best objects for such an investigation. Two years ago, we reported the first detailed study of the CO(2-1) line emission in that envelope, made with the IRAM 30-m telescope. It revealed a series of dense gas shells, expanding at a uniform radial velocity. The limited resolution of the telescope (HPBW 11″) did not allow us to resolve the shell structure. We now report much higher angular resolution observations of CO(2-1), CO(1-0), CN(2-1) and C4H(24-23) made with the SMA, PdB and ALMA interferometers (with synthesized half-power beamwidths of 3″, 1″ and 0.3″, respectively). Although the envelope appears much more intricate at high resolution than with an 11″ beam, its prevailing structure remains a pattern of thin, nearly concentric shells. The average separation between the brightest CO shells is 16″ in the outer envelope, where it appears remarkably constant. Closer to the star (< 40″), the shell pattern is denser and less regular, showing intermediary arcs. Outside the small (r < 0.3″) dust formation zone, the gas appears to expand radially at a constant velocity, 14.5 km s-1, with small turbulent motions. Based on that property, we have reconstructed the 3-D structure of the outer envelope and have derived the gas temperature and density radial profiles in the inner (r < 25″) envelope. The shell-intershell density contrast is found to be typically 3. The over-dense shells have spherical or slightly oblate shapes and typically extend over a few steradians, implying isotropic mass loss. The regular spacing of shells in the outer envelope supports the model of a binary star system with a period of 700 years and a near face-on elliptical orbit. The companion fly-by triggers enhanced episodes of mass loss near periastron. The densification of the shell pattern observed in the central part of the envelope suggests a more complex scenario for the last few thousand years.

The primordial helium abundance determination using multicomponent photoionization modelling of low-metallicity H II regions

The method for the multicomponent photoionization modelling (MPhM) of low-metallicity H II regions surrounding the starburst region was developed. The internal structure of the H II region has been determined using the evolutionary modelling of the superwind bubble surrounding the star-forming region. Models of Chevalier and Clegg (1985) and Weaver et al. (1977) have been used to determine the radial distribution of the gas density, the velocity of gas layers, and the temperature within internal components (the region of the superwind free expansion and the cavity, respectively). The chemical abundances in region of the superwind free expansion were obtained from the evolutionary population synthesis with including of rotating stars. The chemical abundances within cavity were defined by averaging over mass the chemical compositions of mixture of the abundances of gas from superwind and ones within outer component, because of gas evaporation from external component into the cavity. External components of our models describe a high-density, thin shell of gas formed by superwind shock and a typical undisturbed hydrodynamically H II region, respectively. Evolutionary grids of multicomponent low-metallicity models are calculated. A comparative analysis of the results of their calculation with the observed data has been carried out. The ionic abundances averaged over modelling volume as well as chemical composition assumed in models were used to derive the new expressions for ionization-correction factors that were used to redetermine the chemical compositions of 88 H II regions in blue compact dwarf galaxies. It must be noticed that we used for this propose the ionic abundances obtained by Izotov et al. (2007). In result the primordial helium abundance and its enrichment during stellar chemical evolution of matter were determined.

Modeling Type II-P/II-L Supernovae Interacting with Recent Episodic Mass Ejections from Their Presupernova Stars with MESA and SNEC

Abstract We show how dense, compact, discrete shells of circumstellar gas immediately outside of red supergiants affect the optical light curves of Type II-P/II-L supernovae (SNe), using the example of SN 2013ej. Earlier efforts in the literature had used an artificial circumstellar medium (CSM) stitched to the surface of an evolved star that had not gone through a phase of late-stage heavy mass loss, which, in essence, is the original source of the CSM. In contrast, we allow enhanced mass-loss rate from the modeled star during the 16O and 28Si burning stages and construct the CSM from the resulting mass-loss history in a self-consistent way. Once such evolved pre-SN stars are exploded, we find that the models with early interaction between the shock and the dense CSM reproduce light curves far better than those without that mass loss and, hence, having no nearby dense CSM. The required explosion energy for the progenitors with a dense CSM is reduced by almost a factor of two compared to those without the CSM. Our model, with a more realistic CSM profile and presupernova and explosion parameters, fits observed data much better throughout the rise, plateau, and radioactive tail phases as compared to previous studies. This points to an intermediate class of supernovae between Type II-P/II-L and Type II-n SNe with the characteristics of simultaneous UV and optical peak, slow decline after peak, and a longer plateau.

No Evidence of Circumstellar Gas Surrounding Type Ia Supernova SN 2017cbv

Abstract Nearby type Ia supernovae (SNe Ia), such as SN 2017cbv, are useful events to address the question of what the elusive progenitor systems of the explosions are. Hosseinzadeh et al. suggested that the early blue excess of the light curve of SN 2017cbv could be due to the supernova ejecta interacting with a non-degenerate companion star. Some SN Ia progenitor models suggest the existence of circumstellar (CS) environments in which strong outflows create low-density cavities of different radii. Matter deposited at the edges of the cavities should be at distances at which photoionization due to early ultraviolet (UV) radiation of SNe Ia causes detectable changes to the observable Na i D and Ca ii H&amp;K absorption lines. To study possible narrow absorption lines from such material, we obtained a time series of high-resolution spectra of SN 2017cbv at phases between −14.8 and +83 days with respect to B-band maximum, covering the time at which photoionization is predicted to occur. Both narrow Na i D and Ca ii H&amp;K are detected in all spectra, with no measurable changes between the epochs. We use photoionization models to rule out the presence of Na i and Ca ii gas clouds along the line of sight of SN 2017cbv between ∼8 × 1016–2 × 1019 cm and ∼1015–1017 cm, respectively. Assuming typical abundances, the mass of a homogeneous spherical CS gas shell with radius R must be limited to . The bounds point to progenitor models that deposit little gas in their CS environment.