Carbon-rich Wolf-Rayet Stars Research Articles

The Long-period Spectroscopic Orbit and Dust Creation in the Wolf–Rayet Binary System WR 125

Several long-period binaries with a carbon-rich Wolf–Rayet star and an OB star produce dust in their wind collisions. In eccentric binaries, this is seen most strongly near periastron passage. The exact conditions leading to dust creation require the orbital properties to be determined, which is difficult owing to their long periods. Recently, the binary system WR 125 (WC7 + O9III) began a dust-creation episode seen through an infrared outburst first detected by NEOWISE-R, which was the first outburst detected since 1991. We present new near- and mid-infrared photometry, which we use to show consistency between the two outbursts and derive an orbital period of 28.12−0.05+0.10 yr. We use a long time series of optical spectra to place the first constraints on its orbital elements, on the assumption that this system will produce dust near periastron. The orbit has a mild eccentricity of 0.29 ± 0.12 and is only derived for the Wolf–Rayet component, as the O star’s radial velocities have noise that is likely larger than the expected semiamplitude of the orbit. We also present SOFIA/FORCAST grism spectroscopy to examine the infrared spectral energy distribution of the dust during this outburst, comparing its properties to other WCd binaries, and deriving a dust temperature of 580 K in 2021. This collection of observations will allow us to plan future observations of this system and place the system in the context of dust-creating Wolf–Rayet binaries.

Light Curves of the Explosion of ONe White Dwarf + CO White Dwarf Merger Remnant and Type Icn Supernovae

Type Icn supernovae (SNe Icn) are a newly detected, rare subtype of interacting stripped-envelope supernovae that show narrow P Cygni lines of highly ionized carbon, oxygen, and neon in their early spectra due to the interactions of the SNe ejecta with dense hydrogen- and helium-deficient circumstellar material (CSM). It has been suggested that SNe Icn may have multiple progenitor channels, such as the explosion of carbon-rich Wolf–Rayet stars or the explosion of stripped-envelope SNe, which undergo binary interactions. Among the SNe Icn, SN 2019jc shows unique properties, and previous work inferred that it may stem from the ultrastripped supernova, but other possibilities still exist. In this work, we aim to simulate the light curves from the explosions of oxygen-neon and carbon-oxygen double white dwarf (WD) merger remnants and to further investigate whether the corresponding explosions can appear as some particular SNe Icn. We generate the light curves from the explosive remnants and analyze the influence of different parameters on the light curves, such as the ejecta mass, explosion energy, mass of 56Ni, and CSM properties. Comparing our results with some SNe Icn, we found that the light curves from the explosions of double WD merger remnants can explain the observable properties of SN 2019jc, from which we infer that this special SN Icn may have a different progenitor. Our results indicate that double WD merger may be an alternative model in producing at least one of the SNe Icn.

Predicting observable infrared signatures of nanosilicates in the diffuse interstellar medium.

The destruction time scale of dust in the diffuse interstellar medium is estimated to be an order of magnitude shorter than its residence time. Nevertheless, dust is observed in the interstellar medium, leading to the conclusion that reformation and grain growth must take place. Direct observations of nanometre-sized silicate grains, the main constituent of interstellar dust, would provide a smoking gun for the occurrence of grain condensation in the diffuse interstellar medium. Here we employ quantum chemical calculations to obtain the mid-infrared (IR) optical properties of a library of Mg-end member silicate nanoparticles with olivine (Mg2SiO4) and pyroxene (MgSiO3) stoichiometries. We use this library as an input for a foreground-screen model to predict the spectral appearance of the absorption profile due to mixtures of bulk and nanoparticle silicates towards bright background sources. The mid-IR spectrum observed towards an O8V star or a carbon-rich Wolf-Rayet star starts to change when ∼3% of the silicate mass is in the form of nanosilicates. We predict that a 3-10% nanosilicate fraction can be detected with the James Webb Space Telescope (JWST) using the mid-IR instrument (MIRI). With our upcoming JWST observations using MIRI, we will be able to detect or place limits on the nanosilicate content in the diffuse interstellar medium, and thus potentially directly confirm interstellar dust formation.

A spectroscopic multiplicity survey of Galactic Wolf-Rayet stars

Context. It is now well established that the majority of massive stars reside in multiple systems. However, the effect of multiplicity is not sufficiently understood, resulting in a plethora of uncertainties about the end stages of massive-star evolution. In order to investigate these uncertainties, it is useful to study massive stars just before their demise. Classical Wolf-Rayet stars represent the final end stages of stars at the upper-mass end. The multiplicity fraction of these stars was reported to be ∼0.4 in the Galaxy but no correction for observational biases has been attempted. Aims. The aim of this study is to conduct a homogeneous radial-velocity survey of a magnitude-limited (V ≤ 12) sample of Galactic Wolf-Rayet stars to derive their bias-corrected multiplicity properties. The present paper focuses on 12 northern Galactic carbon-rich (WC) Wolf-Rayet stars observable with the 1.2 m Mercator telescope on the island of La Palma. Methods. We homogeneously measured relative radial velocities (RVs) for carbon-rich Wolf-Rayet stars using cross-correlation. Variations in the derived RVs were used to flag binary candidates. We investigated probable orbital configurations and provide a first correction of observational biases through Monte-Carlo simulations. Results. Of the 12 northern Galactic WC stars in our sample, seven show peak-to-peak RV variations larger than 10 km s−1, which we adopt as our detection threshold. This results in an observed spectroscopic multiplicity fraction of 0.58 with a binomial error of 0.14. In our campaign, we find a clear lack of short-period (P < ∼100 d), indicating that a large number of Galactic WC binaries likely reside in long-period systems. Finally, our simulations show that at the 10% significance level, the intrinsic multiplicity fraction of the Galactic WC population is at least 0.72.

The First Candidate Colliding-wind Binary in M33

Abstract We present the detection of the first candidate colliding-wind binary (CWB) in M33, located in the giant H ii region NGC 604. The source was first identified in archival Chandra imaging as a relatively soft X-ray point source, with the likely primary star determined from precise astrometric alignment between archival Hubble Space Telescope and Chandra imaging. The candidate primary star in the CWB is classified for the first time in this work as a carbon-rich Wolf–Rayet star with a likely O-star companion based on spectroscopy obtained from Gemini-North. We model the X-ray spectrum using Chandra and XMM-Newton observations, and find the CWB to be well fit as a ∼1 keV thermal plasma with a median unabsorbed luminosity in the 0.5–2.0 keV band of L X ∼ 3 × 1035 erg s−1, making this source among the brightest of CWBs observed to date. We present a long-term light curve for the candidate CWB from archival Chandra and XMM-Newton observations, and discuss the constraints placed on the binary by this light curve, as well as the X-ray luminosity at maximum. Finally, we compare this candidate CWB in M33 to other well-studied, bright CWBs in the Galaxy and Magellanic Clouds, such as η Car.

Simulations of light curves and spectra for superluminous Type Ic supernovae powered by magnetars

Numerous superluminous supernovae (SLSNe) of Type Ic have been discovered and monitored in the last decade. The favored mechanism at their origin is a sustained power injection from a magnetar. This study presents non-local thermodynamic equilibrium (NLTE) time-dependent radiative transfer simulations of various single carbon-rich Wolf–Rayet star explosions influenced by magnetars of diverse properties and covering from a few days to one or two years after explosion. Nonthermal processes are treated; the magnetar-power deposition profile is prescribed; dynamical effects are ignored. In this context, the main influence of the magnetar power is to boost the internal energy of the ejecta on week-long time scales, enhancing the ejecta temperature and ionization, shifting the spectral energy distribution to the near-UV (even for the adopted solar metallicity), creating blue optical colors. Varying the ejecta and magnetar properties introduces various stretches and shifts to the light curve (rise time, peak or nebular luminosity, light curve width). At maximum, all models show the presence of O II and C II lines in the optical, and more rarely O III and C III lines. Non-thermal effects are found to be negligible during the high-brightness phase. After maximum, higher energy explosions are hotter and more ionized, and produce spectra that are optically bluer. Clumping is a source of spectral diversity after maximum. Clumping is essential to trigger ejecta recombination and yield the presence of O I, Ca II, and Fe II lines from a few weeks after maximum until nebular times. The UV and optical spectrum of Gaia16apd at maximum or the nebular spectrum of LSQ14an at +410 d are compatible with some models that assume no clumping. However, most observed SLSNe Ic seem to require clumping from early post-maximum to nebular times (e.g., SN 2007bi at +46 and +367 d; Gaia16apd at +43 d).

INFRARED OBSERVATIONS OF THE QUINTUPLET PROPER MEMBERS USING SOFIA/FORCAST AND GEMINI/TReCS

ABSTRACT Since their discovery, the Quintuplet proper members (QPMs) have been somewhat mysterious in nature. Originally dubbed the “cocoon stars” due to their cool featureless spectra, high-resolution near-infrared imaging observations have shown that at least two of the objects exhibit “pinwheel” nebulae consistent with binary systems with a carbon-rich Wolf–Rayet star and O/B companion. In this paper, we present 19.7, 25.2, 31.5, and 37.1 μm observations of the QPMs (with an angular resolution of 3.2″–3.8″) taken with the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST) in conjunction with high-resolution (∼0.1″–0.2″) images at 8.8 and 11.7 μm from the Thermal-Region Camera Spectrograph (TReCS). DUSTY models of the thermal dust emission of two of the four detected QPMs, Q2 and Q3, are fitted by radial density profiles that are consistent with constant mass-loss rates ( ). For the two remaining sources, Q1 and Q9, extended structures (∼1″) are detected around these objects in high-resolution imaging data. Based on the fitted dust masses, Q9 has an unusually large dust reservoir ( ) compared to typical dusty Wolf–Rayet stars, which suggests that it may have recently undergone an episode of enhanced mass loss.

A survey for hot central stars of planetary nebulae – I. Methods and first results

We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for $K_s \ge 14$ Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebulae, and are likely to come from massive progenitor populations, and themselves be more massive than any sample of planetary nebulae known. Our survey has identified thousands of such candidates.

Dust Formation around Wolf-Rayet Stars

We discuss the observational evidence in favour of dust formation around massive, evolved carbon-rich Wolf-Rayet stars. Large dust shells containing (amorphous carbon) grains are observed in persistent dust makers, such as the pinwheel system WR104 (WC9+OB) and periodic/episodic dust makers, such asWR140 (WC7+O) close to periastron. Problems with the nucleation and growth of dust in such harsh environments are discussed. It is probable that mixing of carbon-rich material from the WC star plus hydrogen from an OB companion, together with efficient shielding via the shocked region of their colliding winds, provides the necessary ingredients. Many problems with the nucleation and growth remain to be addressed.

On the stellar origin of the Ne-22 excess in cosmic rays

view Abstract Citations (95) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the stellar origin of the Ne-22 excess in cosmic rays Casse, M. ; Paul, J. A. Abstract The Ne-22 excess at a cosmic ray source is considered in terms of an Ne-22-rich component injected and accelerated by carbon-rich Wolf-Rayet stars. The overabundance of Ne-22 relative to Ne-20 predicted at the surface of these stars is estimated to a factor of approximately 120 with regard to solar system abundances. The carbon-rich W-R contribution to the primary cosmic ray flux would have to be at maximum 1/60 in order to produce an Ne-22 excess of about 3 at the cosmic ray source. This component would be energized by strong stellar winds, producing quasi-standing shocks around the W-R stars. Publication: The Astrophysical Journal Pub Date: July 1982 DOI: 10.1086/160132 Bibcode: 1982ApJ...258..860C Keywords: Carbon Stars; Isotopic Enrichment; Neon Isotopes; Primary Cosmic Rays; Stellar Winds; Wolf-Rayet Stars; Abundance; Nuclear Fusion; Particle Flux Density; Stellar Atmospheres; Space Radiation full text sources ADS |