Romuald Tylenda

V4332 Sagittarii: a circumstellar disc obscuring the main object

Context. V4332 Sgr experienced an outburst in 1994 whose observational characteristics in many respects resemble those of the eruption of V838 Mon in 2002. It has been proposed that these objects erupted because of a stellar-merger event. Aims. Our aim is to derive, from observational data, information on the present (10–15 yrs after the outburst) nature and structure of the object. Methods. We present and analyse a high-resolution (R ≈ 21 000) spectrum of V4332 Sgr obtained with the Subaru Telescope in June 2009. Various components (stellar-like continuum, atomic emission lines, molecular bands in emission) in the spectrum are analysed and discussed. We also investigate a global spectral energy distribution (SED) of the object mostly derived from broadband optical and infrared photometry. Results. The observed continuum resembles that of an ∼M 6 giant. The emission features (atomic and molecular) are most probably produced by radiative pumping. The observed strengths of the emission features strongly suggest that we only observe a small part of the radiation of the main object responsible for pumping the emission features. An infrared component seen in the observed SED, which can be roughly approximated by two blackbodies of ∼950 and ∼200 K, is ∼50 times brighter than the M 6 stellar component seen in the optical. This further supports the idea that the main object is mostly obscured for us. Conclusions. The main object in V4332 Sgr, an ∼M 6 (super)giant, is surrounded by a circumstellar disc, which is seen almost edgeon so the central star is obscured. The observed M 6 spectrum probably results from scattering the central star spectrum on dust grains at the outer edge of the disc.

High-resolution optical spectroscopy of V838 Monocerotis in 2009

Context. V838 Mon erupted at the beginning of 2002. In the course of the outburst the object evolved to low effective temperatures and declined as a very late M-type supergiant. Among various scenarios proposed to explain the nature of the outburst, the most promising is a stellar merger event. Aims. We aim at studying the structure and evolution of the object in the decline from the 2002 eruption. Methods. We obtained spectroscopic observations of V838 Mon in January−March 2009 with UVES/VLT. The results are analysed and compared with similar observations obtained in October 2005 with HIRES/Keck. Results. The most striking difference between 2009 and 2005 is a complete absence of the B3 V component and of the [FeII] emission lines in 2009. The present spectrum displays only the spectrum of the 2002 eruption remnant. It resembles that of an ∼M6 giant, although the molecular bands in V838 Mon are deeper than those in standard stellar spectra of a similar spectral class. Several atomic lines, which displayed P-Cyg profiles in 2005, are now dominated by pure absorptions. Some of these lines, however, show a narrow emission component, which, as we argue, measures the radial velocity of V838 Mon. The resulting heliocentric velocity is 71 km s −1 , which very well agrees with the velocity obtained from SiO maser observations. The atomic lines and the molecular bands show very complex kinematics. In some atomic lines and high-excitation molecular bands we observe matter infalling in the object atmosphere. The infall components were already observed in 2005, but were less pronounced and present in fewer lines than in 2009. We argue that the most negative radial velocity components seen in the resonance atomic lines and in the low-excitation molecular bands were formed in the ejecta of the 2002 eruption. The B3 V companion most probably became engulfed in an opaque dusty matter of the 2002 V838 Mon ejecta.

Infrared properties of planetary nebulae with (WR) central stars

We have gathered from the literature near and mid infrared (photometric and spectroscopic) data for Galactic planetary nebulae, with special attention to planetary nebulae surrounding Wolf-Rayet type central stars ((WR) PN). These data have been analyzed to obtain insight into the dust-properties of (WR) PN and their evolutionary status. We have found that a sizeable fraction of (WR) PN seems to contain hot dust (1000{2000 K), probably located in the winds of the central stars. The mean dust temperature is shown to decrease with decreasing (WC) spectral type. This is in line with suggestions that the (WC) sequence is an evolutionary sequence from late to early types. (WR) PN in dierent diagrams, when compared to those of non-(WR) PN, suggest that (WR) PN form a homogeneous class of planetary nebulae. There is an unusually large proportion of (WR) PN showing PAH features in their spectra.

VLT/UVES spectroscopy of V4332 Sagittarii in 2005: The best view on a decade-old stellar-merger remnant

V4332 Sgr is a red transient (red nova) whose eruption was observed in 1994. The remnant of the eruption shows a unique optical spectrum: strong emission lines of atoms and molecules superimposed on an M-type stellar spectrum. The stellar-like remnant is presumably embedded in a disc-like dusty envelope seen almost face-on. The observed optical spectrum is assumed to result from interactions of the central-star radiation with dust and gas in the disc and outflows initiated in 1994. We reduced and measured a high-resolution (R = ~40 000) spectrum of V4332 Sgr obtained with VLT/UVES in April/May 2005. The spectrum comes from the ESO archives and is the best quality spectrum of the object ever obtained. We identified and measured over 200 emission features belonging to 11 elements and 6 molecules. The continuous, stellar-like component can be classified as ~M3. The interstellar reddening was estimated to be 0.35 < E(B-V) < 0.75. From radial velocities of interstellar absorption features in the NaI D lines, we estimated a lower limit of ~5.5 kpc to the distance of V4332 Sgr. The spectrum of V4332 Sgr considerably evolved between 2005 and 2009. The object significantly faded in the optical, which resulted from cooling of the main remnant by 300-350 K, corresponding to its spectral-type change from M3 to M5-6. The object increased in luminosity by ~50%, however, implying a significant expansion of its dimensions. Most of the emission features seen in 2005 significantly faded or even disappeared from the spectrum of V4332 Sgr in 2009. These resulted from fading of the optical central-star radiation and a decrease of the optical thickness of the cirumstellar matter. V4332 Sgr bears several resemblances to V1309 Sco, which erupted in 2008. This can indicate a similar nature of the eruptions of the two objects. The outburst resulted from merger of a contact binary in V1309 Sco.

Light echo of V838 Monocerotis: properties of the echoing medium ⋆

Context. The light echo phenomenon that accompanied the 2002 eruption of V838 Mon allows one to study the properties of the diffuse dusty matter in the vicinity of the object. Aims. We are aiming at obtaining estimates of the optical thickness of the circumstellar matter in front of V838 Mon, as well as optical properties of dust grains in the echoing medium. In particular, we are interested in studying whether the echoing medium can be responsible for the observed faintness of the B-type companion of V838 Mon when compared to three B-type stars that are seen in the vicinty of V838 Mon and are believed to be at the same distance as V838 Mon. Methods. We used the V838 Mon light echo images obtained by the Hubble Space Telescope (HST) in different filters and epochs. From the images we derived the total brightness of the echo and its surface brightness. The results of the measurements were compared to model light echoes. Results. The present study allowed us to estimate the optical thickness of the matter in front of the object and the mean cosine value of the scattering angle of dust grains in three HST filters. Conclusions. The optical thickness of the echoing matter is not sufficient to explain the observed difference in brightness between the B-type companion of V838 Mon and the other three B-type stars observed in the vicinity of V838 Mon. Implications of this result are discussed. Our estimate of the mass of the diffuse matter seen in the light echo shows that the matter cannot have resulted from a past mass loss activity of V838 Mon. We probably observe remnants of an interstellar cloud from which V838 Mon and other members of the observed cluster were formed.

Astronomical detection of radioactive molecule 26 AlF in the remnant of an ancient explosion

Decades ago, γ-ray observatories identified diffuse Galactic emission at 1.809 MeV1–3 originating from β+ decays of an isotope of aluminium, 26Al, that has a mean lifetime of 1.04 million years4. Objects responsible for the production of this radioactive isotope have never been directly identified owing to insufficient angular resolutions and sensitivities of the γ-ray observatories. Here, we report observations of millimetre-wave rotational lines of the isotopologue of aluminium monofluoride that contains the radioactive isotope (26AlF). The emission is observed towards CK Vul, which is thought to be a remnant of a stellar merger5–7. Our constraints on the production of 26Al, combined with the estimates on the merger rate, make it unlikely that objects similar to CK Vul are major producers of Galactic 26Al. However, the observation may be a stepping stone for unambiguous identification of other Galactic sources of 26Al. Moreover, a high content of 26Al in the remnant indicates that, before the merger, the CK Vul system contained at least one solar-mass star that evolved to the red giant branch.Thirty years after an initial, tentative detection, the molecule 26AlF has now been firmly detected in space, by the observation of four different rotational transitions towards stellar merger remnant CK Vul. Curiously, CK Vul and similar objects are unlikely to be major sources of Galactic 26Al.

Theoretical Models for the Evolution of Planetary Nebulae Nuclei Tested by Observations

We compare theoretical evolutionary tracks of planetary nebulae nuclei with observational data on over a hundred planetary nebulae in the (log L, log Teff, log texp) space. The simultaneous use of the three coordinates eliminates some interpretation that might be proposed when looking at the (log L, log Teff) plane and at the (Mv, log texp) only. The inconsistencies which we find between theory and observations could be partly removed by adopting a different distance scale.

Problems of Ionization of Nova Envelopes in the Nebular Stage. The Models for Nova Delphini 1967

The analysis of spectra of novae in the nebular stage shows that the absorption of ultraviolet radiation produced by a central source is the main mechanism of ionization of nova envelopes. The ionization and thermal equilibria are generally satisfied except the late nebular and post-nova stages when the recombination time is longer then one year. In the case when [OI] lines are observed in the spectrum of a nova, the envelope is expected to be optically thick in the Lyman continuum. Due to large overabundances of CNO elements observed in novae, the absorption of ionizing photons by these elements is important and must be taken into account in model calculations.

The Continuous Radiation Emitted by the Accretion Disks in Cataclysmic Binaries. The Dwarf Nova SS Cyg during Outburst and the Old Novae V603 Aql and RR Pic

A steady—state model of the accretion disk around a white dwarf, including the boundary layer and the hot spot, has been constructed. The calculated distribution of radiation has been compared with the observations of the dwarf nova SS Cyg during outburst and the old novae V603 Aql and RR Pic.