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Abundances of phosphorus (P) in 45 main sequence F-G type stars (including the Sun by using reflected light from the minor planet Vesta) in the metallicity range [Fe/H] from −0.4 to +0.3 have been determined. The effective temperatures of target stars range from 5500 to 6600 K. Two lines of P i at 9750.75 Å and at 9796.83 Å (multiplet No. 2) are analysed by using a profile fitting method. Significant star-to-star scatters up to 0.4 dex have been found at all metallicities. We find three stars (HD 9826, HD 20010, and HD 82328) in which values of [P/Fe] are lower than −0.20, showing that P is deficient with respect to Fe in these stars. Such objects have never been reported in the past and may have an impact on the theoretical studies of origin and evolution of P. The sample contains 18 stars with confirmed planets (not including the Sun) and no significant difference in abundance of P has been found between stars with planets and those with no confirmed planet.

Morphology of nova ejecta is essential for fully understanding the physical processes involved in nova eruptions. We studied the 3D morphology of the expanding ejecta of the extremely slow nova V1280 Sco with a unique light curve. Synthetic line profile spectra were compared to the observed [O III] 4959, 5007 and [N II] 5755 emission line profiles in order to find the best-fit morphology, inclination angle, and maximum expansion velocity of the ejected shell. We derive the best fitting expansion velocity, inclination, and squeeze as $V_{\rm exp} = 2100^{+100}_{-100}$ \,km\,s$^{-1}$, $i = 80^{+1}_{-3}$ deg, and $squ = 1.0^{+0.0}_{-0.1}$ using [O III] line profiles, and $V_{\rm exp} = 1600^{+100}_{-100}$ \,km\,s$^{-1}$, $i = 81^{+2}_{-4}$ deg, and $squ = 1.0^{+0.0}_{-0.1}$ using [N II] 5755 line profile. A high inclination angle is consistent with the observational results showing multiple absorption lines originating from clumpy gases which are produced in dense and slow equatorially focused outflows. Based on additional observational features such as optical flares near the maximum light and dust formation on V1280 Sco, a model of internal shock interaction between slow ejecta and fast wind proposed for the $\gamma$-ray emission detected in other novae seems to be applicable to this extremely slow and peculiar nova. Increasing the sample size of novae whose morphology is studied will be helpful in addressing long-standing mysteries in novae such as the dominant energy source to power the optical light at the maximum, optical flares near the maximum, clumpiness of the ejecta, and dust formation., Comment: 21 pages, 8 figures, accepted for publication in ApJ

We constructed a comprehensive model atom for NeI -- NeII using the most up-to-date atomic data available and evaluated the non-local thermodynamic equilibrium (NLTE) line formation for NeI and NeII in classical 1D models representing the atmospheres of B-type stars. We find that the large NLTE strengthening of the NeI lines corresponding to the 2p$^5$3p $-$ 2p$^5$3s transitions array occurs due to extremely small photoionization cross-sections of 2p$^5$3s levels that leads to strong overpopulation of these levels relative to their LTE populations. The deviations from LTE for the most NeII lines are small and do not exceed 0.11~dex in the absolute value. We analysed 20 lines of NeI and 13 lines of NeII for twenty-four B-type stars in the temperature range of 10\,400 $\le$ \Teff\ $\le$ 33\,400~K. For five stars, the NLTE leads to consistent abundances of NeI and NeII, while the difference in LTE abundance can reach up to 0.50~dex. The using of the experimental oscillator strengths recently measured by Piracha et al. (2015) leads to smaller line-by-line scatter for the most investigated stars. The averaged neon abundance in twenty-four B-type stars in solar neighborhood is 8.02$\pm$0.05. This value may provide indirect constraints on solar photospheric neon abundance., Comment: 20 pages, 9 figures, accepted to Astrophysical Journal

Blazar OJ287 exhibits large thermal flares at least twice every 12 years. The times of these flares have been predicted successfully using the model of a quasi-Keplerian eccentric black hole binary where the secondary impacts the accretion disk of the primary, creating the thermal flares. New measurements of the historical light curve have been combined with the observations of the 2015 November/December flare to identify the impact record since year 1886, and to constrain the orbit of the binary. The orbit solution shows that the binary period, now 12.062 year, is decreasing at the rate of 36 days per century. This corresponds to an energy loss to gravitational waves that is 6.5 +- 4 % less than the rate predicted by the standard quadrupolar gravitational wave (GW) emission. We show that the difference is due to higher order gravitational radiation reaction terms that include the dominant order tail contributions., to appear in the Proceedings of Gravitational Wave Astrophysics: Early Results from Gravitational Wave Searches and Electromagnetic Counterparts. eds. Gabriela Gonzales and Robert Hynes

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (γ -rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented γ -ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 ± 63) × 10−8 ph cm−2 s−1, corresponding to a luminosity of (2.2 ± 0.1) × 1050 erg s−1, was reached on 2016 December 28. These four γ -ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and γ -ray activity is found. The γ -ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This γ -ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission. © 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society, The data collected by the WEBT collaboration are stored in the WEBT archive at the Osservatorio Astrofisico di Torino INAF (http://www.oato.inaf.it/blazars/webt/); for questions regarding their availability, contact the WEBT President Massimo Villata(massimo.villata@inaf.it).We acknowledge financial contribution from the agreementASI-INAFn. 2017-14-H.0 and from the contract PRIN-SKA-CTA-INAF 2016. This research was partially supported by the Bulgarian National Science Fund of the Ministry of Education and Science under grants DN 08-1/2016, DN 18-13/2017, and KP-06-H28/3 (2018). The Skinakas Observatory is a collaborative project of the University of Crete, the Foundation for Research and Technology -Hellas, and the Max-Planck-Institut fur Extraterrestrische Physik. The Abastumani team acknowledges financial support by the Shota Rustaveli National Science Foundation under contract FR/217554/16. The St. Petersburg University team acknowledges support from Russian Science Foundation grant 17-12-01029. GD and OV gratefully acknowledge the observing grant support from the Institute of Astronomy and Rozhen National Astronomical Observatory, Bulgarian Academy of Sciences, via bilateral joint research project 'Study of ICRF radio-sources and fast variable astronomical objects' (head -G.Damljanovic). This work is a part of the Projects No. 176011 ('Dynamics and Kinematics of Celestial Bodies and Systems'), No. 176004 ('Stellar Physics'), and No. 176021 ('Visible and Invisible Matter in Nearby Galaxies: Theory and Observations') supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia. JE is indebted to DGAPA (Universidad Nacional Autonoma de M ' exico) for financial support, PAPIIT project IN114917. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. Data from the Steward Observatory blazar monitoring project were used. This program is supported by NASA/Fermi Guest Investigator grants NNX12AO93G and NNX15AU81G. We acknowledge support by Bulgarian National Science Programme 'Young Scientists and Postdoctoral Students 2019', Bulgarian National Science Fund under grant DN18-10/2017 and National RI Roadmap Projects DO1-157/28.08.2018 and DO1-153/28.08.2018 of the Ministry of Education and Science of the Republic of Bulgaria. This publication makes use of data obtained at Mets ahovi Radio Observatory, operated by Aalto University in Finland. The Astronomical Observatory of the Autonomous Region of theAostaValley (OAVdA) is managed by the Fondazione Clment Fillietroz-ONLUS, which is supported by the Regional Government of the Aosta Valley, the TownMunicipality of Nus and the 'Unit des Communes valdtaines Mont-milius'. The research at the OAVdA was partially funded by two 'Research and Education' grants from Fondazione CRT. RR acknowledges support from CONICYT project Basal AFB-170002. MM and TM acknowledge support through the Russian Government Program of Competitive Growth of Kazan Federal University. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat a l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d'Etudes Spatiales in France. This work performed in part under DOE Contract DE-AC02-76SF00515. The OVRO 40-m monitoring program is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G, and NSF grants AST-0808050 and AST-1109911. We thank the Swift team for making these observations possible, the duty scientists, and science planners. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. FD thanks S. Covino for his help with the REM data reduction. This research has made use of data obtained from the high-energy Astrophysics Science Archive Research Center (HEASARC) provided by NASA's Goddard Space Flight Center.

Abundances of 21 elements in two 3He stars HD 185330 and 3 Cen A have been analysed relative to the well studied sharp-lined B3 V star iota Her. Six elements (P, Ti, Mn, Fe, Ni, and Br) are over-abundant in these two peculiar stars, while six elements (C, O, Mg, Al, S, and Cl) are under-abundant. Absorption lines of the two rarely observed heavy elements Br II and Kr II are detected in both stars and these elements are both over-abundant. The centroid wavelengths of the Ca II infrared triplet lines in these stars are red-shifted relative to those lines in iota Her and the presence of heavy isotopes of Ca (mass number 44 - 46) in these two stars are confirmed. In spite of these similarities, there are several remarkable differences in the abundance pattern between these two stars. N is under-abundant in HD 185330, as in many Hg-Mn stars, while it is significantly over-abundant in 3 Cen A. P and Ga are both over-abundant in 3 Cen A, while only P is over-abundant and no trace of absorption line of Ga II can be found in HD 185330. Large over-abundances of Kr and Xe are found in both stars, while the abundance ratios Kr / Xe are significantly different between them (-1.4 dex in HD 185330 and +1.2 dex in 3 Cen A). Some physical explanations are needed to account for these qualitative differences., Comment: 12 pages,13 figures, accepted for publication in PASJ

Blazar emission is dominated by non-thermal radiation from a relativistic jet pointing toward us, therefore undergoing Doppler beaming. This is responsible for flux enhancement and contraction of the variability time scales, so that most blazars appear as luminous sources characterized by noticeable and fast flux changes at all frequencies. The mechanisms producing their unpredictable variability are debated and include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the emitting knots or jet regions have also been suggested to explain flaring events or specific properties such as intraday variability, quasi-periodicities, or the delay of radio flux variations relative to optical changes. However, such a geometric interpretation has not been universally accepted because alternative explanations based on changes of physical conditions can also work in many cases. Here we report the results of optical-to-radio monitoring of the blazar CTA 102 by the Whole Earth Blazar Telescope Collaboration and show that the observed long-term flux and spectral variability is best explained by an inhomogeneous, curved jet that undergoes orientation changes. We propose that magnetohydrodynamic instabilities or rotation of a twisted jet cause different jet regions to change their orientation and hence their relative Doppler factors. In particular, the recent extreme optical outburst (six magnitudes) occurred when the corresponding jet emitting region acquired a minimum viewing angle., Comment: 31 pages, 11 figures. This is the accepted version (before Nature editing) of the paper published by Nature, online version at http://dx.doi.org/10.1038/nature24623, Nature 2017/12/04/online

We present a model atom for C I - C II - C III - C IV using the most up-to-date atomic data and evaluated the non-local thermodynamic equilibrium (NLTE) line formation in classical 1D atmospheric models of O-B-type stars. Our models predict the emission lines of C II 9903~\AA\ and 18535~\AA\ to appear at effective temperature \Teff~$\geq$~17\,500~K, those of C II 6151~\AA\ and 6461~\AA\ to appear at \Teff~$>$~25\,000~K, and those of C III 5695, 6728--44, 9701--17~\AA\ to appear at \Teff~$\geq$~35\,000~K (log~$g$=4.0). Emission occurs in the lines of minority species, where the photoionization-recombination mechanism provides a depopulation of the lower levels to a greater extent than the upper levels. For C II 9903 and 18535~\AA, the upper levels are mainly populated from C III reservoir through the Rydberg states. For C III 5695 and 6728--44~\AA, the lower levels are depopulated due to photon losses in UV transitions at 885, 1308, and 1426--28~\AA\ which become optically thin in the photosphere. We analysed the lines of C I, C II, C III, and C IV for twenty-two O-B-type stars with temperature range between 15\,800 $\leq$~\Teff~$\leq$ 38\,000~K. Abundances from emission lines of C I, C II and C III are in agreement with those from absorption ones for most of the stars. We obtained log~$\epsilon_{\rm C}$=8.36$\pm$0.08 from twenty B-type stars, that is in line with the present-day Cosmic Abundance Standard. The obtained carbon abundances in 15~Mon and HD~42088 from emission and absorption lines are 8.27$\pm$0.11 and 8.31$\pm$0.11, respectively., Comment: 22 pages, 11 figures

We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504, and BL Lacertae) on December 18--21, 2015 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe, and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra- and inter-day time scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio- and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio- and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations., 6 pages, 6 figures, accepted by MNRAS

Previously unrecognized weak emission lines originating from high excitation states of Si II (12.84 eV) and Al II (13.08 eV) are detected in the red region spectra of slowly rotating early B-type stars. We surveyed high resolution spectra of 35 B-type stars covering spectral sub-types between B1 and B7 near the main sequence and found the emission line of SiII at 6239.6 A in all 13 stars having spectral sub-types B2 and B2.5. There are 17 stars belonging to sub-type B3 and seven stars among them are found to show the emission line of Si II. The emission line of Al II at 6243.4 A is detected in a narrower temperature range (Teff between 19000K and 23000 K) in nine stars. Both of these emission lines are not detected in cooler (Teff < 16000 K) stars in our sample. The emission line of Si II at 6239.6 A shows a single-peaked and symmetric profile and the line center has no shift in wavelength with respect to those of low excitation absorption lines of Si II. Measured half width of the emission line is the same as those of rotationally broadened low excitation absorption lines of Si II. These observations imply that the emitting gas is not circumstellar origin, but is located at the outermost layer of the atmosphere, covering the whole stellar surface and co-rotates with the star., 6 pages, 4 figures, 2 tables, accepted for publication in Publ. Astron. Soc. Japan

We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb–Scargle periodogram revealed several peaks above the 99% significance level. The longest one—about 95 days—corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.

We analyse the light curve in the R-band gathered during the 2015/16 observing season of OJ287. We did a search for QPOs using several methods in wide time domain. No statistically significant periods were found in the high frequency domain both in the ground data and also in K2 observations. In the longer periods domain the Lomb-Scargle periodogram revealed several peaks above the 99\% significance level. The longest one, about 95-day, corresponds to the ISCO period of the more massive SMBH. The 43-day period could be an alias or can be attributed to accretion in the form of two armed spiral wave.

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We report spectroscopic observations of the resonance lines of singly ionized $^{7}$Be in the blue-shifted absorption line systems found in the post-outburst spectra of two classical novae -- V5668 Sgr (Nova Sagittarii 2015 No.2) and V2944 Oph (Nova Ophiuchi 2015). The unstable isotope, $^{7}$Be, should has been created during the thermonuclear runaway (TNR) of these novae and decays to form $^{7}$Li within a short period (a half-life of 53.22 days). Confirmations of $^{7}$Be are the second and the third ones following the first case found in V339 Del by Tajitsu et al. (2015). The blue-shifted absorption line systems in both novae are clearly divided into two velocity components, both of which contain $^{7}$Be. This means that the absorbing gases in both velocity components consist of products of TNR. We estimate amounts of $^{7}$Be produced during outbursts of both novae and conclude that significant $^{7}$Li should have been created. These findings strongly suggest that the explosive production of $^{7}$Li via the reaction $^{3}$He($\alpha$,$\gamma$)$^{7}$Be and subsequent decay to $^{7}$Li occurs frequently among classical novae and contributes to the process of the Galactic Li enrichment., Comment: 8 pages, 6 figures, accepted for publication in ApJ

The origin of lithium (Li) and its production process have long been an unsettled question in cosmology and astrophysics. Candidates environments of Li production events or sites suggested by previous studies include big bang nucleosynthesis, interactions of energetic cosmic rays with interstellar matter, evolved low mass stars, novae, and supernova explosions. Chemical evolution models and observed stellar Li abundances suggest that at least half of the present Li abundance may have been produced in red giants, asymptotic giant branch (AGB) stars, and novae. However, no direct evidence for the supply of Li from stellar objects to the Galactic medium has yet been found. Here we report on the detection of highly blue-shifted resonance lines of the singly ionized radioactive isotope of beryllium, $^{7}$Be, in the near ultraviolet (UV) spectra of the classical nova V339 Del (Nova Delphini 2013). Spectra were obtained 38 to 48 days after the explosion. $^{7}$Be decays to form $^{7}$Li within a short time (half-life 53.22 days). The spectroscopic detection of this fragile isotope implies that it has been created during the nova explosion via the reaction $^{3}\mbox{He}(\alpha,\gamma)^{7}\mbox{Be}$, and supports the theoretical prediction that a significant amount of $^{7}$Li could be produced in classical nova explosions. This finding opens a new way to explore $^{7}$Li production in classical novae and provides a clue to the mystery of the Galactic evolution of lithium., Comment: 28 pages, 6 figures, published in Nature