Suchergebnisse

Yakut, Kadri/0000-0003-2380-9008; Vernieri, Daniele/0000-0003-4379-2549; Carloni, Sante/0000-0003-2373-2653; Liberati, Stefano/0000-0002-7632-7443; Berry, Christopher P L/0000-0003-3870-7215; Kocsis, Bence/0000-0002-4865-7517; Maggio, Elisa/0000-0002-1960-8185; de la Cruz Dombriz, Alvaro/0000-0002-7072-9396; Pasic, Vedad/0000-0003-2115-0422; arca-sedda, manuel/0000-0002-3987-0519; Kocsis, Bence/0000-0002-4865-7517; Blazquez-Salcedo, Jose Luis/0000-0002-8156-8372; Stergioulas, Nikolaos/0000-0002-5490-5302; Husa, Sascha/0000-0002-0445-1971; Vitagliano, Vincenzo/0000-0001-7724-8133; Oliveri, Roberto/0000-0002-7497-871X; Zilhao, Miguel/0000-0002-7089-5570; Wojnar, Aneta/0000-0002-1545-1483; Hejda, Filip/0000-0002-4157-6730; Ramazanoglu, Fethi Mubin/0000-0003-3075-1457; Askar, Abbas/0000-0001-9688-3458; Said, Jackson Levi/0000-0002-7835-4365; Weltman, Amanda/0000-0002-5974-4114; Sopuerta, Carlos F./0000-0002-1779-4447; Luna, Raimon/0000-0001-6898-6708; Bon, Edi/0000-0002-0465-8112; Cardoso, Vitor/0000-0003-0553-0433; Pappas, George/0000-0003-3344-3759; Pratten, Geraint/0000-0003-4984-0775; Gualtieri, Leonardo/0000-0002-1097-3266; Bullock, James S/0000-0003-4298-5082; Hertog, Thomas/0000-0002-9021-5966; Wardell, Barry/0000-0001-6176-9006; Sakellariadou, Mairi/0000-0002-2715-1517; Brito, Richard/0000-0002-7807-3053; Valiante, Rosa/0000-0003-3050-1765; Kokkotas, Kostas/0000-0001-6048-2919; Sotiriou, Thomas/0000-0002-9089-4866; Maselli, Andrea/0000-0001-8515-8525; Kavanagh, Bradley/0000-0002-3634-4679; Messenger, Chris/0000-0001-7488-5022; van de Meent, Maarten/0000-0002-0242-2464; Ramos Buades, Antoni/0000-0002-6874-7421; Gerosa, Davide/0000-0002-0933-3579; Raposo, Guilherme/0000-0001-5912-5586; Hinderer, Tanja/0000-0002-3394-6105; Stamerra, Antonio/0000-0002-9430-5264; Kimura, Masashi/0000-0001-5427-5593; Krolik, Julian/0000-0002-2995-7717; Cerda-Duran, Pablo/0000-0003-4293-340X; Chaty, Sylvain/0000-0002-5769-8601; Kramer, Michael/0000-0002-4175-2271; Stalevski, Marko/0000-0001-5146-8330; Sintes, Alicia M/0000-0001-9050-7515; Blanco-Pillado, Jose J./0000-0003-2260-9047; Chrusciel, Piotr Tadeusz/0000-0001-8362-7340; Garcia-Bellido, Juan/0000-0002-9370-8360; Pani, Paolo/0000-0003-4443-1761; Nichols, David/0000-0002-4758-9460; Montero, Miguel/0000-0001-6270-6402; Berti, Emanuele/0000-0003-0751-5130; Schmidt, Patricia/0000-0003-1542-1791; Tamanini, Nicola/0000-0001-8760-5421; Minamitsuji, Masato/0000-0002-0643-2758; Tauris, Thomas/0000-0002-3865-7265; Herdeiro, Carlos/0000-0002-9619-2013; Velhinho, Jose/0000-0002-3219-903X; Emparan, Roberto/0000-0003-2457-0203; Nardini, Germano/0000-0002-3523-0477; Tamfal, Tomas/0000-0003-1773-9349; Stein, Leo/0000-0001-7559-9597; Obers, Niels/0000-0003-4947-8526; Annulli, Lorenzo/0000-0001-9921-1331; Horesh, Assaf/0000-0002-5936-1156; Burrage, Clare/0000-0002-7337-0470; Bulik, Tomasz/0000-0003-2045-4803; Bosnjak, Zeljka Marija/0000-0001-6536-0320; Ma, Yin-Zhe/0000-0001-8108-0986; Le Tiec, Alexandre/0000-0003-3288-2012; Capelo, Pedro Rosado/0000-0002-1786-963X; Blas, Diego/0000-0003-2646-0112; Colleoni, Marta/0000-0002-7214-9088; Byrnes, Christian/0000-0003-2583-6536; Whiting, Bernard F/0000-0002-8501-8669; Peiris, Hiranya/0000-0002-2519-584X; Vicente, Rodrigo/0000-0002-3150-9315; Rakic, Nemanja/0000-0002-2514-0793; Drew, Amelia/0000-0001-8252-602X; Aloy, Miguel-Angel/0000-0002-5552-7681; Barausse, Enrico/0000-0001-6499-6263; RUIZ MORALES, ESTER/0000-0002-0995-595X ; WOS: 000476748700001 ; The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. and of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. the hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. the synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. the purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'. ; COST (European Cooperation in Science and Technology)European Cooperation in Science and Technology (COST) [CA16104]; Polish National Science Center (NCN) [UMO-2016/23/B/ST9/02732, DEC-2012/07/E/ST9/01360]; Carl Tryggers Foundation [CTS 17:113]; STFCScience & Technology Facilities Council (STFC) [ST/R00045X/1]; European Union's H2020 ERC Consolidator Grant 'Matter and strong-field gravity: New frontiers in Einstein's theory' [MaGRaTh-646597]; Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC) [ST/P000703/1]; Ministry of Education and Science of the Republic of Serbia [176003, 176001]; FNPFoundation for Polish Science [TEAM/2016-3/19]; Austrian Research Fund (FWF)Austrian Science Fund (FWF) [P 29517-N16]; Polish National Center of Science (NCN) [2016/21/B/ST1/00940]; European Research Council (ERC) under the European UnionEuropean Research Council (ERC) [638435]; Hungarian National Research, Development, and Innovation Office [NKFIH KH-125675]; Swiss National Science Foundation (SNF)Swiss National Science Foundation (SNSF) [200020-168988]; European Union's H2020 ERC [DarkGRA-757480]; H2020-MSCA-RISE-2015 Grant [690904]; NSFNational Science Foundation (NSF) [PHY-090003, PHY-1607130, AST-1716715]; PRACE [PPFPWG]; Simons Foundation; Ministry of Economy, Industry and Competitiveness of Spain; Slovenian Research AgencySlovenian Research Agency - Slovenia; EU H2020 under ERC [BinGraSp-714626]; Spanish MINECO [AYA2015-66899-C2-1-P, RYC-2015-19074]; Generalitat ValencianaGeneralitat Valenciana [PROMETEOII-2014-069]; NASA by the Chandra X-ray Center [PF6-170152]; NASANational Aeronautics & Space Administration (NASA) [NAS8-03060]; Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [117F296]; H2020-MSCA-RISE-2017 Grant [FunFiCO-777740]; Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [117F295]; National Science Centre of Poland - European Union [665778]; DAAD Germany-GreeceDeutscher Akademischer Austausch Dienst (DAAD) [57340132]; GWAVES of ARIS-GRNET(Athens) [pr002022]; Royal Society UKRoyal Society of London [UF160547-BHbeyGR]; [RGF - R1 - 180073]; [TUBITAK-117F188]; Science and Technology Facilities CouncilScience & Technology Facilities Council (STFC) [ST/R00045X/1] Funding Source: researchfish ; This article is based upon work from COST Action CA16104 'GWverse', supported by COST (European Cooperation in Science and Technology). We would like to thank Walter del Pozzo for useful comments. AA acknowledges partial support from the Polish National Science Center (NCN) through the grant UMO-2016/23/B/ST9/02732 and is currently supported by the Carl Tryggers Foundation through the grant CTS 17:113. LB acknowledges support from STFC through Grant No. ST/R00045X/1. VC acknowledges financial support provided under the European Union's H2020 ERC Consolidator Grant 'Matter and strong-field gravity: New frontiers in Einstein's theory' grant agreement no. MaGRaTh-646597. TPS acknowledges partial support from Science and Technology Facilities Council Consolidated Grant ST/P000703/1. KB acknowledges support from the Polish National Science Center (NCN) grant: Sonata Bis 2 (DEC-2012/07/E/ST9/01360). EB acknowledges financial support from projects 176003 and 176001 by the Ministry of Education and Science of the Republic of Serbia. TB was supported by the TEAM/2016-3/19 grant from FNP. PC acknowledges support from the Austrian Research Fund (FWF), Project P 29517-N16, and by the Polish National Center of Science (NCN) under grant 2016/21/B/ST1/00940. BK acknowledges support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme ERC-2014-STG under grant agreement No 638435 (GalNUC) and from the Hungarian National Research, Development, and Innovation Office grant NKFIH KH-125675. GN is supported by the Swiss National Science Foundation (SNF) under grant 200020-168988. PP acknowledges financial support provided under the European Union's H2020 ERC, Starting Grant agreement no. DarkGRA-757480. US acknowledges H2020-MSCA-RISE-2015 Grant No. 690904, NSF Grant No. PHY-090003 and PRACE Tier-0 Grant No. PPFPWG. the Flatiron Institute is supported by the Simons Foundation. PAS acknowledges support from the Ramon y Cajal Programme of the Ministry of Economy, Industry and Competitiveness of Spain. EB supported by NSF Grants No. PHY-1607130 and AST-1716715. KB, AC, AG, NI, TP and GZ acknowledge financial support from the Slovenian Research Agency. SB acknowledges support by the EU H2020 under ERC Starting Grant, no. BinGraSp-714626. PC-D is supported by the Spanish MINECO (grants AYA2015-66899-C2-1-P and RYC-2015-19074) and the Generalitat Valenciana (PROMETEOII-2014-069). DG is supported by NASA through Einstein Postdoctoral Fellowship Grant No. PF6-170152 by the Chandra X-ray Center, operated by the Smithsonian Astrophysical Observatory for NASA under Contract NAS8-03060. RE acknowledges financial support provided by the Scientific and Technical Research Council of Turkey (TUBITAK) under the grant no. 117F296. JAF is supported by the Spanish MINECO (AYA2015-66899-C2-1-P), by the Generalitat Valenciana (PROMETEOII-2014-069), and by the H2020-MSCA-RISE-2017 Grant No. FunFiCO-777740. FMR is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) project 117F295. IR was supported by the POLONEZ programme of the National Science Centre of Poland which has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 665778.; r AS thanks the Spanish Ministry of Economy, Industry and Competitiveness, the Spanish Agencia Estatal de Investigacion, the Vicepresidencia i Conselleria d'Innovacio, Recerca i Turisme del Govern de les Illes Balears, the European Commission, the European Regional Development Funds (ERDF). NS acknowledges support from DAAD Germany-Greece Grant (ID 57340132) and GWAVES (pr002022) of ARIS-GRNET(Athens). HW acknowledges financial support by the Royal Society UK under the University Research Fellowship UF160547-BHbeyGR and the Research Grant RGF - R1 - 180073. KY is supported by TUBITAK-117F188.

LIGO and Virgo's third observing run revealed the first neutron star–black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements creating optical/near-infrared 'kilonova' emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter, and independently measure the local expansion rate of the Universe. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility. The Zwicky Transient Facility observed ~48% of S200105ae and ~22% of S200115j's localization probabilities, with observations sensitive to kilonovae brighter than −17.5 mag fading at 0.5 mag d in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude ~22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii. © 2020, The Author(s), under exclusive licence to Springer Nature Limited. ; This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant no. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK) and University of Sydney (Australia). This work was based on observations obtained with the 48-inch Samuel Oschin Telescope and the 60-inch Telescope at the Palomar Observatory as part of the ZTF project. ZTF is supported by the National Science Foundation under grant no. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington (UW), Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee and Lawrence Berkeley National Laboratories. Operations are conducted by Caltech Optical Observatories, IPAC, and UW. The work is partly based on the observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. The KPED team (M.W.C., R.G.D., D.A.D., M.F., S.R.K., E.S. and R.R.) thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1-m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). SED Machine is based upon work supported by the National Science Foundation under grant no. 1106171 The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). M.W.C. acknowledges support from the National Science Foundation with grant no. PHY-2010970. S.A. gratefully acknowledges support from a GROWTH PIRE grant (1545949). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. E.C.K. acknowledges support from the G.R.E.A.T. research environment and the Wenner-Gren Foundations. F.F. gratefully acknowledges support from NASA through grant 80NSSC18K0565, from the NSF through grant PHY-1806278, and from the DOE through CAREER grant DE-SC0020435. With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star-black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M < 0.04 M at polar viewing angles, or M < 0.03 M if the opacity is κ < 2 cmg. Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be χ < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs. ; This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. GROWTH is a collaborative project among California Institute of Technology (USA), University of Maryland College Park (USA), University of Wisconsin Milwaukee (USA), Texas Tech University (USA), San Diego State University (USA), University of Washington (USA), Los Alamos National Laboratory (USA), Tokyo Institute of Technology (Japan), National Central University (Taiwan), Indian Institute of Astrophysics (India), Indian Institute of Technology Bombay (India), Weizmann Institute of Science (Israel), The Oskar Klein Centre at Stockholm University (Sweden), Humboldt University (Germany), Liverpool John Moores University (UK), and University of Sydney (Australia). D.A.G. acknowledges support from Hubble Fellowship grant HST-HF2-51408.001-A. Support for program No. HST-HF251408.001-A is provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We gratefully acknowledge Amazon Web Services, Inc., for a generous grant (PS_IK_ FY2019_Q3_ Caltech_Gravitational_Wave) that funded our use of the Amazon Web Services cloud computing infrastructure to process the DECam data. P.E.N. acknowledges support from the DOE through DE-FOA-0001088, Analytical Modeling for Extreme-Scale Computing Environments. D.A.P. and D.A.G. performed the work associated with this project at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. This work was partially supported by a grant from the Simons Foundation. A.J.C.-T. thanks I. Agudo, J. Cepa, V. Dhillon, J. A. Font, A. MartinCarrillo, S. R. Oates, S. B. Pandey, E. Pian, R. Sanchez-Ramirez, A. M. Sintes, V. Sokolov, and B.-B. Zhang for fruitful conversations. F.F. gratefully acknowledges support from NASA through grant 80NSSC18K0565 and from the NSF through grant PHY1806278. M.B., A.G., E.K., S.D., and J.S. acknowledge support from the G.R.E.A.T research environment funded by the Swedish National Science Foundation. J.S. acknowledges support from the Knut and Alice Wallenberg Foundation. J.S.B. and K.Z. are partially supported by a Gordon and Betty Moore Foundation Data-Driven Discovery grant. D.A.H.B. acknowledges research support from the National Research Foundation of South Africa. M.W.C. is supported by the David and Ellen Lee Postdoctoral Fellowship at the California Institute of Technology. S.N. and G.R. are grateful for support from VIDI, Projectruimte, and TOP Grants of the Innovational Research Incentives Scheme (Vernieuwingsimpuls) financed by the Netherlands Organization for Scientific Research (NWO). H.K. and K.Z. thank the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant No. 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. D.D. is supported by an Australian Government Research Training Program Scholarship. P.G. is supported by NASA Earth and Space Science Fellowship (ASTRO18F-0085). D.L.K. was supported by NSF grant AST-1816492. Y.D.H. thanks the support by the program of China Scholarships Council (CSC) under grant No. 201406660015. A.K.H.K. acknowledges support from the Ministry of Science and Technology of the Republic of China (Taiwan) through grants 107-2628-M-007-003 and 1082628-M-007-005-RSP. V.Z.G. acknowledges support from the University of Washington College of Arts and Sciences, Department of Astronomy, and the DIRAC Institute. University of Washington's DIRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences and the Washington Research Foundation. M.J. and A.C. acknowledge the support of the Washington Research Foundation Data Science Term Chair fund and the UW Provost's Initiative in Data-Intensive Discovery. S.M. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant-1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. M.G. is supported by the Polish NCN MAESTRO grant 2014/14/A/ST9/00121. This research has made use of the VizieR catalog access tool, CDS, Strasbourg, France (doi:10.26093/cds/vizier). The original description of the VizieR service was published in A&AS 143, 23. This project used data obtained with the Dark Energy Camera (DECam), which was constructed by the Dark Energy Survey (DES) collaborating institutions: Argonne National Lab, University of California Santa Cruz, University of Cambridge, Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas-Madrid, University of Chicago, University College London, DES-Brazil consortium, University of Edinburgh, ETH-Zurich, University of Illinois at Urbana-Champaign, Institut de Ciencies de l'Espai, Institut de Fisica d'Altes Energies, Lawrence Berkeley National Lab, Ludwig-Maximilians Universitat, University of Michigan, National Optical Astronomy Observatory, University of Nottingham, Ohio State University, University of Pennsylvania, University of Portsmouth, SLAC National Lab, Stanford University, University of Sussex, and Texas A&M University. Funding for DES, including DECam, has been provided by the U.S. Department of Energy, National Science Foundation, Ministry of Education and Science (Spain), Science and Technology Facilities Council (UK), Higher Education Funding Council (England), National Center for Supercomputing Applications, Kavli Institute for Cosmological Physics, Financiadora de Estudos e Projetos, Fundacao Carlos Chagas Filho de Amparo a Pesquisa, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico and the Ministerio da Ciencia e Tecnologia (Brazil), the German Research Foundation-sponsored cluster of excellence "Origin and Structure of the Universe," and the DES collaborating institutions. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. This work is partly based on data obtained with the instrument OSIRIS, built by a Consortium led by the Instituto de Astrofisica de Canarias in collaboration with the Instituto de Astronomia of the Universidad Autonoma de Mexico. OSIRIS was funded by GRANTECAN and the National Plan of Astronomy and Astrophysics of the Spanish Government. Some of the observations reported in this paper were obtained with the Southern African Large Telescope (SALT). Polish participation in SALT is funded by grant No. MNiSW DIR/WK/2016/07.