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Context. V1309 Sco is an example of a red nova, a product of the merger between non-compact stars. V1309 Sco is particularly important within the class of red novae due to the abundance of photometric data of the progenitor binary before the merger. Aims. We aim to investigate the spatio-kinematic and chemical properties of the circumstellar environment, including deriving the physical conditions and establishing the origins of the different circumstellar components. Methods. We used radiative transfer modelling of molecular emission in sub-millimetre spectra to examine the properties of the molecular gas, and we used forbidden line diagnostics from optical spectra to constrain the electron density and temperature using forbidden line diagnostics. We compared line intensities from shock models to observations to look for and constrain shocks. Results. We derived a new kinematical distance of 5.6 kpc to the source. The detection of ro-vibrational H2 and sub-millimetre HCO+ emission in 2016 and 2019, respectively, indicate active shock interactions within the circumstellar environment. The velocity profiles of both H2 and HCO+, as well as the moment-1 maps of sub-millimetre CO and 29SiO, indicate a bipolar structure that may be asymmetric. The sub-millimetre and optical molecular emission exhibits temperatures of 35–113 and 200 K, respectively, whilst the atomic gas is much hotter, with temperatures of 5–15 kK, which may be due to shock heating. Conclusions. The detection of a bipolar structure in V1309 Sco indicates further similarities with the structure of another Galactic red nova, V4332 Sgr. It provides evidence that bipolar structures may be common in red novae. All collected data are consistent with V1309 Sco being a kinematically and chemically complex system. [ABSTRACT FROM AUTHOR]

Red novae are optical transients erupting at luminosities typically higher than those of classical novae. Their outbursts are believed to be caused by stellar mergers. We present millimeter/submillimeter-wave observations with the Atacama Large (sub)Millimeter Array (ALMA) and the Submillimeter Array (SMA) of the three best-known Galactic red novae, V4332 Sgr, V1309 Sco, and V838 Mon. The observations were taken 22, 8, and 14 yr after their respective eruptions and reveal the presence of molecular gas at excitation temperatures of 35–200 K. The gas displays molecular emission in rotational transitions with very broad lines (full width ~400 km s−1). We found emission of CO, SiO, SO, SO2 (in all three red novae), H2S (covered only in V838 Mon), and AlO (present in V4332 Sgr and V1309 Sco). No anomalies were found in the isotopic composition of the molecular material, and the chemical (molecular) compositions of the three red novae appear similar to those of oxygen-rich envelopes of classical evolved stars (RSGs, AGBs, post-AGBs). The minimum masses of the molecular material that was most likely dispersed in the red-nova eruptions are 0.05, 0.01, and 10−4M⊙ for V838 Mon, V4332 Sgr, and V1309 Sco, respectively. The molecular outflows in V4332 Sgr and V1309 Sco are spatially resolved and appear bipolar. The kinematic distances to V1309 Sco and V4332 Sgr are 2.1 and 4.2 kpc, respectively. The kinetic energy stored in the ejecta of the two older red-nova remnants of V838 Mon and V4332 Sgr is of the order of 1046 erg, similar to values found for some post-AGB (pre-PN) objects whose bipolar ejecta were also formed in a short-duration eruption. Our observations strengthen the link between these post-AGB objects and red novae and support the hypothesis that some of the post-AGB objects were formed in a common-envelope ejection event or its most catastrophic outcome, a merger. [ABSTRACT FROM AUTHOR]

We present optical and infrared spectroscopy of V1309 Sco, an object that erupted in 2008 in a stellar-merger event. During the outburst, V1309 Sco displayed characteristics typical of red transients, a class of objects similar to V838 Mon. Our observations were obtained in 2009 and 2012, i.e. months and years after the eruption of V1309 Sco, and illustrate severe changes in the remnant, mainly in its circumstellar surroundings. In addition to atomic gas observed in earlier epochs, we identified molecular bands of TiO, VO, H2O, ScO, AlO, and CrO. The infrared bands of CrO we analyse are the first astronomical identification of the features. Over the whole period covered by our data, the remnant was associated with a cool (≲1000 K) outflow with a terminal velocity of about 200 km s-1. Signatures of warmer atomic gas, likely to be still dissipating the energy of the 2008 outburst, dramatically decreased their brightness between 2009 and 2012. In addition, the source of optical continuum disappeared sometime before 2012, likely owing to the formation of new dust. The final stage of V1309 Sco's evolution captured by our spectra is an object remarkably similar to an older red transient, V4332 Sgr. In addition to providing a detailed view on the settling of the eruptive object, the observations presented here reinforce the conclusion that all the Galactic red transients are a manifestation of the same phenomenon, i.e. a stellar merger. The late spectra of V1309 Sco also suggest peculiarities in the chemical composition of the remnant, which still need to be explored. [ABSTRACT FROM AUTHOR]

Context. Phosphorus-bearing compounds have only been studied in the circumstellar environments of the asymptotic giant branch star IRC +10 216 and the protoplanetary nebula CRL 2688, both carbon-rich objects, and the oxygen-rich red supergiant VY CMa. The current chemical models cannot reproduce the high abundances of PO and PN derived from observations of VY CMa. No observations have been reported of phosphorus in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars. Aims.We aim to set observational constraints on the phosphorous chemistry in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars, by focussing on the Mira-type variable star IK Tau. Methods. Using the IRAM 30m telescope and the Submillimeter Array, we observed four rotational transitions of PN (J = 2-1; 3-2; 6-5; 7-6) and four of PO (J = 5=2-3=2; 7=2-5=2; 13=2-11=2; 15=2-13=2). The IRAM 30m observations were dedicated line observations, while the Submillimeter Array data come from an unbiased spectral survey in the frequency range 279-355 GHz. Results. We present the first detections of PN and PO in an oxygen-rich asymptotic giant branch star and estimate abundances X(PN=H2) ≈ 3 × 10-7 and X(PO=H2) in the range 0:5-6:0 × 10-7. This is several orders of magnitude higher than what is found for the carbon-rich asymptotic giant branch star IRC +10 216. The diameter (≲0''7) of the PN and PO emission distributions measured in the interferometric data corresponds to a maximum radial extent of about 40 stellar radii. The abundances and the spatial occurrence of the molecules are in very good agreement with the results reported for VY CMa. We did not detect PS or PH3 in the survey. Conclusions. We suggest that PN and PO are the main carriers of phosphorus in the gas phase, with abundances possibly up to several 10-7. The current chemical models cannot account for this, underlining the strong need for updated chemical models that include phosphorous compounds. [ABSTRACT FROM AUTHOR]

We report the first detection of pure rotational transitions of TiO and TiO2 at (sub-)millimeter wavelengths towards the red supergiant VYCMa. A rotational temperature, Trot, of about 250K was derived for TiO2. Although Trot was not well constrained for TiO, it is likely somewhat higher than that of TiO2. The detection of the Ti oxides confirms that they are formed in the circumstellar envelopes of cool oxygen-rich stars and may be the "seeds" of inorganic-dust formation, but alternative explanations for our observation of TiO and TiO2 in the cooler regions of the envelope cannot be ruled out at this time. The observations suggest that a significant fraction of the oxides is not converted to dust, but instead remains in the gas phase throughout the outflow. [ABSTRACT FROM AUTHOR]

We report the first identification of the optical bands of the B2Σ+-X 2S+ system of AlO in the red supergiant VYCMa. In addition to TiO, VO, ScO, and YO, which were recognized in the optical spectrum of the star long time ago, AlO is another refractory molecule which displays strong emission bands in this peculiar star. Simulating the bands of AlO, we derive a rotational temperature of the circumstellar gas of Trot = 700K. By resolving individual rotational components of the bands, we derive the kinematical characteristics of the gas, finding that the emission is centred at the stellar radial velocity and its intrinsic width is 13.5 kms-1 (full width at half maximum). It is the narrowest emission among all (thermal) features observed in VYCMa so far. The temperature and line widths suggest that the emission arises in gas located within ∼20 stellar radii, where the outflow is still being accelerated. This result contradicts equilibrium-chemistry models which predict substantial AlO abundances only to within a few stellar radii. We argue that non-equilibrium models involving propagation of shocks are needed to explain the observations. [ABSTRACT FROM AUTHOR]