DOCSLIB.ORG

Research Found a Dramatic Decline in Arctic Sea Ice Due to Global Warming, Leading to Localized Increase in Evaporation, Air Humidity, Cloud Cover, and Rainfall

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Research Found a Dramatic Decline in Arctic Sea Ice Due to Global Warming, Leading to Localized Increase in Evaporation, Air Humidity, Cloud Cover, and Rainfall Current Affairs - June 2020 Month June 2020 Type Science and Technology 40 Current Affairs were found in Month - June 2020 for Type - Science and Technology Science 1. A National Centre of Polar and Ocean Research (NCPOR) Research found a dramatic decline in Arctic sea ice due to global warming, leading to localized increase in evaporation, air humidity, cloud cover, and rainfall. NCPOR noted that largest decline in Arctic sea ice in the past 41 years happened in July 2019. In last 40 years (1979-2018), sea ice has been declining at a rate of ‘-4.7%’ per decade, while its rate was found to be ‘-13%’ in July 2019. If this continues, there would be no ice left in the Arctic sea by 2050, which would be dangerous for humanity. Worrying element is that volume of ice formation during winters is unable to keep pace with volume of ice loss during summers. 2. A study of a microscopic ancient marine algae (Coccolithophores) led by National Centre for Polar and Ocean Research (NCPOR) has found that there is a decrease in concentration of oceanic calcium carbonate (CaCO3) in Southern Indian ocean. It is attributed to increase in concentration of another single-celled algae known as diatoms. This will affect growth and skeleton structure of coccolithophores, with potential significance for world ocean ecosystem. Coccolithophores are single-celled algae living in the upper layers of the world's oceans, playing key role in marine ecosystems and global carbon cycle. Coccolithophores calcify marine phytoplankton that produces up to 40% of open ocean calcium carbonate and responsible for 20% of global net marine primary productivity. Coccolithophores also help remove CO2 from atmosphere and ocean by consuming it during photosynthesis. Research revealed that reduction of coccolithophore diversity in early summer and late summer periods is due to an increase in presence of diatom algae, which occurs after sea ice breakdown with climate change and ocean acidification, and increases silicate concentration in Southern Ocean. Results point to climate change as a major reason for the altered coccolithophore calcification rate. 3. A study of space weather storms over India by Indian Institute of Geomagnetism (IIG) found that the occurrence of equatorial spread F (ESF) irregularities and GPS scintillations are significantly affected by geomagnetic storms depending upon time of onset of geomagnetic storm. Earth's magnetic field lines are nearly horizontal over magnetic equator due to which equatorial ionosphere is a bed for a variety of plasma instabilities to cause plasma disturbances and plasma irregularities. These irregularities pose severe problems to communication and navigation systems. Understanding thermosphere‐ionosphere-magnetosphere interactions that control electrodynamics behind dynamical evolution of ionospheric irregularities under disturbed periods like geomagnetic storms is important in developing communication / navigation systems. 4. Amid tremendous increase in demand of transparent conducting glasses (TCG) with high light transparency, Centre for Nano and Soft Matter Sciences Bengaluru (CeNS) has developed a novel recipe for fabrication of TCG which brings down its production cost by 80% compared to tin-doped indium oxide (ITO) based technology which is currently in use. Newly fabricated TCG consists of metal mesh on a glass substrate with thin overlayers of metal oxides. The design is attractive as hybrid electrode possesses excellent conductive property of metal mesh while offering an oxide surface finish for conductive glass. 5. Astronaumers discovered a rare space object that looks like both asteroid and comet, called Active Asteroid and named 2019 LD2. It has an orbit like an asteroid and a tail like a comet. It shares orbit of Jupiter and is a part of asteroid swarm called Jupiter Trojans. This object is first that emits gas just like a comet. The asteroid was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS). This discovery also provides that Jupiter Trojans have large amounts of ice beneath their surfaces. Active Asteroids are celestial bodies that look like comet and have asteroid like orbit. The first active asteroid discovered was Elst Pizarro. 6. Astronomers at Nainital Based Aryabhatta Research Institute of Observational Sciences (ARIES) found that stars of varied ages can co-exist in open clusters. This challenges earlier understanding that stars in an open cluster have the same age. Scientists measured light from three poorly studied open clusters NGC 381, NGC 2360, and Berkeley 68 observed using the 1.3-m telescope at Devasthal. They found two different stellar evolutionary sequences in cluster NGC 2360, which has been observed in very few open clusters in Milky Way Galaxy until now. Clusters are found to be relatively older, having ages between 446 Million years to 1778 million years. Researchers also stated that mass distributions of stars belonging to clusters have shown preferential distribution of massive stars in inner part of clusters, while low mass stars are found towards outer region of clusters. It is believed that some of the very low mass stars have in fact, left their parent clusters and may be roaming as a free star like our own Sun. Their study lent important insight about the stellar and dynamical evolution of these clusters. 7. Fossilized millipede-like Silurian Period creature called Kampecaris obanensis(approximately 450 million years old) is discovered on island of Kerrera in Scottish Inner Hebrides(Scotland), which is likely to be world’s oldest-known land animal. Fossils of oldest-known plant with a stem, called Cooksonia, were also found in the same ancient lake region as Kampecaris. 8. IIT-Bombay Researchers created Indian beneficiary chip “Dhruva”, which can be utilized in cell phones and route gadgets to discover locations and route inside India. Dhruva will get signals from India’s NAVIC group of navigation satellites. 9. Indian Space Research Organisation (ISRO) received a patent for its Liquid Cooling and Heating Garment (LCHG), a protective garment for human spaceflight. It is a close fitting long garment that covers entire body as a single piece lightweight comfort inner wear. 10. Institute of Microbial Technology Chandigarh (IMTECH) validated clinical utility of Foldscope in diagnosis of diseases using various patient samples. Study evaluated use of Foldscope in clinical diagnosis of oral and urinary tract infections and evaluated its efficacy as a motivational tool for improving oral health among school children in India. Study identifies that Foldscope is particularly convenient to diagnose urinary tract infection (UTI) and monitor kidney stone. Using this tool, one can easily monitor own-kidney stone status at home with a simple glass-slide, a Foldscope and a phone in hand. Such monitoring could perhaps avoid kidney stone reaching a painful state or surgery in recurring cases. 11. International Researchers (Including researchers from Aryabhatta Research Institute of Observational Sciences Nainital (ARIES)), are observing changes in a very high energy gamma-ray emitting blazar ‘1ES 0806+524’ using seven optical telescopes. A blazar is a feeding super-massive black-hole (SMBH) in heart of a distant galaxy that produces a high-energy jet viewed face-on from Earth. Study explained large flares as result of propagation of a shock in relativistic jet that accelerates electrons to high energies followed by subsequent cooling. 12. Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) and Breathe Applied Sciences, a company incubated at JNCASR for transfer of technology based on lab-scale research on reducing CO2 to methanol and other useful chemicals and fuels. In pilot mode, the current capacity of CO2 conversion is 300 kg per day, which can be scaled upto 500 tons in an industrial scale, within a year. 13. NASA Stated that 5 Asteroids passed by Earth Safely on June 3, Including 170 feet wide 2020 KE4 as nearest flyer. It passed by Earth within a distance of 0.01966 astronomical units (1.8 Miles approx). 14. NASA and Italian Space Agency Research state that Saturn’s moon Titan has been moving away from its host planet hundred times faster than previously understood, at rate of about 4 inches (11 centimeters) every year. Moon starts drifting away from its host planet because as a moon orbits, its gravity pulls on a planet which causes a temporary bulge in planet as it passes. With time, energy created by subsiding and bulging, transfers from planet to moon and nudging it farther out. Our own moon drifts 1.5 inches (3.8 centimeters) from the Earth each year. While scientists have known that Saturn was formed 4.6 billion years ago, there has been more of an uncertainty about planet’s rings and when its system of more than 80 moons was formed. Titan is currently 1.2 million kilometers from Saturn. Revised drift Data has suggested that moon started out much closer to Saturn, meaning that whole system expanded more quickly than previously believed. 15. NASA discovered youngest known magnetar (a type of neutron star) named “Swift J1818.0-1607” about 16,000 light years away from Earth - It belongs to a special class of objects called “magnetars”, estimated to be 240 years old. It has a magnetic field up to 1,000 times stronger than a typical neutron star and about 100 million times stronger than the most powerful magnets made by humans. It was first discovered in March 2020 by NASA’s Neil Gehrels Swift Observatory when when a large amount of X-rays were emitted by it. European Space Agency and NASA then studied this magnetar and found that it was the youngest one. 16. NASA unveiled first results of Bose-Einstein condensate experiments under which particles can be manipulated free from Earthly constraints. Bose-Einstein Condensates were predicted by Indian Mathematician Satyendra Nath Bose and Albert Einstein almost a century ago. 5th State (BEC) is a state of matter that is typically formed when a gas of bosons is cooled to temperatures close to absolute zero.
Load more

Recommended publications
  • Subaru and Salt Spectroscopy of Chemically Peculiar Hot Subdwarfs
    BearWorks College of Natural and Applied Sciences 12-20-2017 Subaru and salt spectroscopy of chemically peculiar hot subdwarfs C. Simon Jeffery Naslim Neelamkodan Vincent M. Woolf Steven M. Crawford Roy H. Østensen Missouri State University Follow this and additional works at: https://bearworks.missouristate.edu/articles-cnas Recommended Citation Jeffery, C. Simon, Naslim Neelamkodan, Vincent M. Woolf, Steven M. Crawford, and Roy H. Østensen. "Subaru and SALT spectroscopy of chemically peculiar hot subdwarfs." Open Astronomy 26, no. 1 (2017): 202-207. This article or document was made available through BearWorks, the institutional repository of Missouri State University. The work contained in it may be protected by copyright and require permission of the copyright holder for reuse or redistribution. For more information, please contact [email protected]. Open Astron. 2017; 26: 202–207 Research Article C. Simon Jeffery*, Naslim Neelamkodan, Vincent M. Woolf, Steven M. Crawford, andRoyH. Østensen Subaru and SALT spectroscopy of chemically peculiar hot subdwarfs https://doi.org/10.1515/astro-2017-0439 Received Oct 16, 2017; accepted Nov 06, 2017 Abstract: The majority of hot subdwarfs lie on or close to the helium main-sequence. Many have hydrogen-rich surfaces, but a substantial fraction of the hotter subdwarfs have hydrogen-depleted or hydrogen-deficient surfaces. Amongst the former, three were known to show extraordinary overabundances of heavy elements including zirconium and lead. Using Subaru/HDS, we commenced a high-resolution survey of hydrogen-depleted subdwarfs to discover new members of the class. UVO 0825+15, was found to exhibit strong lead lines, to be an intrinsic variable in K2 field 5, and to have a relatively high space motion.
    [Show full text]
  • The Elm Survey. Iv. 24 White Dwarf Merger Systems∗
    The Astrophysical Journal, 751:141 (13pp), 2012 June 1 doi:10.1088/0004-637X/751/2/141 C 2012. The American Astronomical Society. All rights reserved. Printed in the U.S.A. THE ELM SURVEY. IV. 24 WHITE DWARF MERGER SYSTEMS∗ Mukremin Kilic1, Warren R. Brown2, Carlos Allende Prieto3,4, S. J. Kenyon2, Craig O. Heinke5, M. A. Agueros¨ 6, and S. J. Kleinman7 1 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA; [email protected] 2 Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA 3 Instituto de Astrof´ısica de Canarias, E-38205 La Laguna, Tenerife, Spain 4 Departamento de Astrof´ısica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain 5 Department of Physics, CCIS 4-183, University of Alberta, Edmonton, AB, T6G 2E1, Canada 6 Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USA 7 Gemini Observatory, 670 North A’ohoku Place, Hilo, HI 96720, USA Received 2012 January 5; accepted 2012 March 30; published 2012 May 16 ABSTRACT We present new radial velocity and X-ray observations of extremely low mass (ELM, ∼0.2 M) white dwarf (WD) candidates in the Sloan Digital Sky Survey Data Release 7 area. We identify seven new binary systems with 1–18 hr orbital periods. Five of the systems will merge due to gravitational wave radiation within 10 Gyr, bringing the total number of merger systems found in the ELM Survey to 24. The ELM Survey has now quintupled the known merger WD population.
    [Show full text]
  • SALT ANNUAL REPORT 2017 BEGINNING of a NEW ERA Multi-Messenger Events: Combining Gravitational Wave and Electromagnetic Astronomy
    SALT ANNUAL REPORT 2017 BEGINNING OF A NEW ERA Multi-messenger events: combining gravitational wave and electromagnetic astronomy A NEW KIND OF SUPERSTAR: KILONOVAE − VIOLENT MERGERS OF NEUTRON STAR BINARIES On 17 August 2017 the LIGO and Virgo gravitational wave observatories discovered their first candidate for the merger of a neutron star binary. The ensuing explosion, a kilonova, which was observed in the lenticular galaxy NGC 4993, is the first detected electromagnetic counterpart of a gravitational wave event. One of the earliest optical spectra of the kilonova, AT However, a simple blackbody is not sufficient to explain the 2017gfo, was taken using RSS on SALT. This spectrum was data: another source of luminosity or opacity is necessary. featured in the multi-messenger summary paper by the Predictions from simulations of kilonovae qualitatively full team of 3677 collaborators. Combining this spectrum match the observed spectroscopic evolution after two with another SALT spectrum, as well as spectra from the days past the merger, but underpredict the blue flux in Las Cumbres Observatory network and Gemini–South, the earliest spectrum from SALT. From the best-fit models, Curtis McCully from the Las Cumbres Observatory and the team infers that AT 2017gfo had an ejecta mass of his colleagues were able to follow the full evolution of 0.03 solar masses, high ejecta velocities of 0.3c, and a the kilonova. The spectra evolved very rapidly, from low mass fraction ~0.0001 of high-opacity lanthanides blue (~6400K) to red (~3500K) over the three days they and actinides. One possible explanation for the early observed.
    [Show full text]
  • Stellar Winds from Hot Low-Mass Stars
    Astrophysics and Space Science DOI 10.1007/s•••••-•••-••••-• Stellar winds from hot low-mass stars W.-R. Hamann1 c Springer-Verlag •••• Abstract Stellar winds appear as a persistent fea- on the track from the Asymptotic Giant Branch (AGB) ture of hot stars, irrespective of their wide range to the white dwarf cooling sequence. Extreme helium of different luminosities, masses, and chemical com- (EHe) stars and subdwarf-O (sdO) stars are further position. Among the massive stars, the Wolf-Rayet types of low-mass stars which are found to display signs types show considerably stronger mass loss than the of mass-loss. Their evolutionary origin is attributed to O stars. Among hot low-mass stars, stellar winds are binarity (Saio and Jeffery 2002; Heber 2009). seen at central stars of planetary nebulae, where again Prototype for an O-type star with mass loss is the O5 the hydrogen-deficient stars show much stronger winds supergiant ζ Puppis. Striking evidence for the stellar than those central stars with “normal” composition. wind comes from the P-Cygni profiles of resonance lines We also studied mass-loss from a few extreme helium in the UV (cf. Fig. 2, left panel). However, these pro- stars and sdOs. Their mass-loss rate roughly follows the files are often saturated and therefore not sensitive for same proportionality with luminosity to the power 1.5 a precise determination of the mass-loss rates. The op- as the massive O stars. This relation roughly marks tical spectrum shows mostly “normal” absorption lines, a lower limit for the mass loss from hot stars of all while Hα is in emission (cf.
    [Show full text]
  • Stellar Winds and Mass Loss from Extreme Helium Stars 3
    Mon. Not. R. Astron. Soc. 000, 1–13 (2008) Printed 7 November 2018 (MN LATEX style file v2.2) Stellar Winds and Mass Loss from Extreme Helium Stars C.S. Jeffery⋆ & W.-R. Hamann† Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland Institut f¨ur Physik und Astronomie, Universit¨at Potsdam, University Campus Golm, Haus 28, Karl-Liebknecht-Str. 24/25, 14476 Potsdam Accepted ..... Received ..... ; in original form ..... ABSTRACT Extreme helium stars are very rare low-mass supergiants in a late stage of evolution. They are probably contracting to become white dwarfs following a violent phase of evolution which caused them to become hydrogen-deficient giants, possibly R CrB stars. Using the latest generation of models for spherically expanding stellar atmospheres, we set out to measure mass-loss rates for a representative fraction of these stars. We have used high-resolution ultraviolet and optical spectra, and ultraviolet, optical and near-infrared photometry from a variety of archives. Overall atmospheric parameters have mostly been taken from previ- ous analyses and checked for consistency. Mass-loss rates were measured by fitting the P- Cygni and asymmetric profiles of C, N and Si ultraviolet resonance lines and lie in the range −10 −7 −1 1.5 10 − 10 M⊙yr . These rates follow a Castor-type (M˙ ∝ L ) relation marking a lower limit for the mass loss from hot stars of all kinds. The mass-loss rates of the studied stars also show a strong correlation with their proximity to the Eddington limit. There is no firm evidence for variability in the stellar wind, although photospheric pulsations have been reported in many cases.
    [Show full text]
  • The Central Star of the Planetary Nebula N 66 in the Large Magellanic Cloud: a Detailed Analysis of Its Dramatic Evolution 1983–2000?,??
    A&A 409, 969–982 (2003) Astronomy DOI: 10.1051/0004-6361:20031109 & c ESO 2003 Astrophysics The central star of the planetary nebula N 66 in the Large Magellanic Cloud: A detailed analysis of its dramatic evolution 1983–2000?;?? W.-R. Hamann1,M.Pe˜na2,G.Gr¨afener1,andM.T.Ruiz3;??? 1 Professur Astrophysik, Universit¨at Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany 2 Instituto de Astronom´ıa, Universidad Nacional Aut´onoma de M´exico, Apdo. Postal 70-264, 04510 M´exico, DF, M´exico 3 Depto. de Astronom´ıa, Universidad de Chile, Casilla 36-D, Santiago, Chile Received 31 March 2003 / Accepted 11 July 2003 Abstract. The central star of the planetary nebula N 66 (alias WS 35, SMP 83 and HV 5967) in the Large Magellanic Cloud enhanced its brightness dramatically in 1993 and 1994. Within the subsequent four years it returned to the previous level. Its spectrum resembles that of a Wolf-Rayet star of the nitrogen sequence (WN4.5). We monitored the object intensively from ground and with the Hubble Space Telescope. Now we present the complete set of spectroscopic observations from the different epochs before, during and after the brightness outburst of N 66. The stellar spectra from the different epochs are analyzed in detail by means of most advanced non-LTE models for expanding stellar atmospheres. The main results are: the luminosity, log L=L = 4:6, before and after the outburst is exceptionally high for a central star of a planetary nebula. During the outburst in 1994, it even climbed up to log L=L = 5:4 for about one year.
    [Show full text]
  • API Publications 2016-2019
    2016 King, A. and Muldrew, S. I., Black hole winds II: Hyper-Eddington winds and feedback, 2016, MNRAS, 455, 1211 Carbone, D., Exploring the transient sky: from surveys to simulations, 2016, AAS, 227, 421.03 van den Heuvel, E., The Amazing Unity of the Universe, 2016 (book), Springer Ellerbroek, L. E. ., Planet Hunters: the Search for Extraterrestrial Life, 2016 (book), Reak- tion Books Lef`evre, C., Pagani, L., Min, M., Poteet, C., and Whittet, D., On the importance of scattering at 8 µm: Brighter than you think, 2016, A&A, 585, L4 Min, M., Rab, C., Woitke, P., Dominik, C., and M´enard, F., Multiwavelength optical prop- erties of compact dust aggregates in protoplanetary disks, 2016, A&A, 585, A13 Babak, S., Petiteau, A., Sesana, A., Brem, P., Rosado, P. A., Taylor, S. R., Lassus, A., Hes- sels, J. W. T., Bassa, C. G., Burgay, M., and 26 colleagues, European Pulsar Timing Array limits on continuous gravitational waves from individual supermassive black hole binaries, 2016, MNRAS, 455, 1665 Sclocco, A., van Leeuwen, J., Bal, H. E., and van Nieuwpoort, R. V., Real-time dedispersion for fast radio transient surveys, using auto tuning on many-core accelerators, 2016, A&C, 14, 1 Tramper, F., Sana, H., Fitzsimons, N. E., de Koter, A., Kaper, L., Mahy, L., and Moffat, A., The mass of the very massive binary WR21a, 2016, MNRAS, 455, 1275 Pinilla, P., Klarmann, L., Birnstiel, T., Benisty, M., Dominik, C., and Dullemond, C. P., A tunnel and a traffic jam: How transition disks maintain a detectable warm dust component despite the presence of a large planet-carved gap, 2016, A&A, 585, A35 van den Heuvel, E., Neutron Stars, 2016, ASCO Conference, 20 Van Den Eijnden, J., Ingram, A., and Uttley, P., The energy dependence of quasi periodic oscillations in GRS 1915+105, 2016, AAS, 227, 411.07 Calzetti, D., Johnson, K.
    [Show full text]
  • Blue Large-Amplitude Pulsators As a New Class of Variable Stars
    Blue large-amplitude pulsators as a new class of variable stars Paweł Pietrukowicz1∗, Wojciech A. Dziembowski1;2, Marilyn Latour3, Rodolfo Angeloni4;5;6, Ra- dosław Poleski1;7, Francesco di Mille8, Igor Soszynski´ 1, Andrzej Udalski1, Michał K. Szymanski´ 1, Łukasz Wyrzykowski1, Szymon Kozłowski1, Jan Skowron1, Dorota Skowron1, Przemek Mróz1, Michał Pawlak1 & Krzysztof Ulaczyk1;9 1Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland 2Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland 3Dr. Karl Remeis-Observatory & ECAP, Astronomical Institute, Friedrich-Alexander University Erlangen- Nuremberg, Sternwartstr. 7, 96049, Bamberg, Germany 4Departamento de Física y Astronomía, Universidad de La Serena, Av. Cisternas 1200 Norte, La Serena, Chile 5Instituto de Investigación Multidisciplinar en Ciencia y Tecnología, Universidad de La Serena, Av. Raúl Bitrán 1305, La Serena, Chile 6Gemini Observatory, Casilla 603, La Serena, Chile 7Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA 8Las Campanas Observatory, Casilla 601, La Serena, Chile 9Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK ∗e-mail: [email protected] Regular intrinsic brightness variations observed in many stars are caused by pulsations. These pulsa- tions provide information on the global and structural parameters of the star. The pulsation periods range from seconds to years, depending on the compactness of the star and properties of the matter that forms its outer layers. Here, we report the discovery of more than a dozen of previously un- known short-period variable stars: blue large-amplitude pulsators. These objects show very regular arXiv:1706.07802v1 [astro-ph.SR] 23 Jun 2017 brightness variations with periods in the range of 20–40 min and amplitudes of 0.2–0.4 mag in the optical passbands.
    [Show full text]
  • SALT Revisits DY Cen: a Rapidly-Evolving Strontium-Rich
    MNRAS 000, 1–11 (2014) Preprint 11 February 2020 Compiled using MNRAS LATEX style file v3.0 SALT revisits DY Cen: a rapidly-evolving strontium-rich single helium star C. Simon Jeffery1,2⋆, N. Kameswara Rao3, and David L. Lambert4 1Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK 2School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland 3Indian Institute of Astrophysics, Bangalore 560034, India 4The W. J. McDonald Observatory and Department of Astronomy, University of Texas at Austin, Austin, TX 78712-1083, USA Accepted . Received . ; in original form . ABSTRACT The hydrogen-deficient star DYCen has been reported as an RCrB-type variable, an extreme helium star (with some hydrogen), and as a single-lined spectroscopic binary. It has been associated with a dramatic change in visual brightness and colour corresponding to a change in effective temperature ( Teff ) of some 20000K in the last century. To characterize the binary orbit and Teff changes more precisely, new high- resolution spectroscopy has been obtained with SALT. The previous orbital period is not confirmed; previous measurements may have been confused by the presence of pulsations. Including data from earlier epochs (1987, 2002, and 2010), self-consistent spectral analyses from all four epochs demonstrate an increase in Teff from 18800 to 24400K between 1987 and 2015. Line profiles demonstrate that the surface rotation has increased by a factor two over the same interval. This is commensurate with the change in Teff and an overall contraction. Rotation will exceed critical if contraction continues. The 1987 spectrum shows evidence of a very high abundance of the s-process element strontium.
    [Show full text]
  • White-Dwarf-Merger Outcomes Simon Jeffery Armagh Observatory
    White-Dwarf-Merger Outcomes Simon Jeffery Armagh Observatory Friday, 20 April 12 Double-White-Dwarf Mergers and Connections Between Extreme Helium Stars, R CrB stars, Hot Subdwarfs, and, Possibly, Type Ia Supernovae mostly with Karakas, Zhang, Yu and Saio Friday, 20 April 12 Outline • Double-White-Dwarf Binaries • Double-White-Dwarf Mergers • Hydrogen-Deficient Stars • CO+He mergers • He+He Mergers [Xianfei Zhang] • Some Statistics • Other DD Merger outcomes Friday, 20 April 12 Double White Dwarf Binaries • Binary star evolution produces DWDs • Gravitational-wave radiation implies orbit shrinks • What happens next? –i) violent interaction –ii) stable interaction • Keys: –stability, efficiency, progenitors • Can we identify the products? Friday, 20 April 12 Low-mass DWDs Many new DWD binaries found (Kilic et al. 2011, Marsh et al. , Brown et al., ...). Discrepancies about stability. Predicted mass-period distribution sensitive to physics (eg WD cooling). All agree many short-period systems will merge. What happens next? 5 Friday, 20 April 12 Gravitational wave evolution Post CE-system LISA visible LISA invisible Gravitational wave Gravitational strength Orbital Period (log s) Friday, 20 April 12 Reflections on stability - Mdot q=1 q=2/3 M>˙ M˙ Edd Han & Webbink 1999 Friday, 20 April 12 Reflections on stability: progenitor stats q=1 q=2/3 CO+HE Violent accretion HE+HE Direct impact accretion AM CVn Nelemans 2001 Friday, 20 April 12 Reflections on stability: pyrotechnics What happens when accretion rates < “violent” ? Piersanti et al. 2011, IAU Symp 281 9 Friday, 20 April 12 Reflections on stability: synchronization q=1 q=2/3 Marsh et al. 2004 (but see talk by Sepinsky) Friday, 20 April 12 Reflections on efficiency Han & Webbink 1999 Assume spherical symmetry and q=2/3 require M<˙ M˙ Edd Marcello’s talk: β=0.7➝ q=0.4 Hydro simulation non-spherical β≈1 for q=0.4 Friday, 20 April 12 Double White Dwarf Mergers Friday, 20 April 12 evolution of a 0.9+0.6 M CO WD Yoon et al.
    [Show full text]
  • The Lack of X-Ray Pulsations in the Extreme Helium Star BD+37 442 and Its Possible Stellar Wind X-Ray Emission
    MNRAS 466, 2918–2921 (2017) doi:10.1093/mnras/stw3335 Advance Access publication 2016 December 23 The lack of X-ray pulsations in the extreme helium star BD+37◦442 and its possible stellar wind X-ray emission Sandro Mereghetti,1‹ Nicola La Palombara,1 Andrea Tiengo2,1,3 and Paolo Esposito4 1INAF – IASF Milano, Via E. Bassini 15, I-20133 Milano, Italy 2Scuola Universitaria Superiore IUSS Pavia, Piazza della Vittoria 15, I-27100 Pavia, Italy 3Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Via A. Bassi 6, I-27100 Pavia, Italy 4Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090-GE Amsterdam, the Netherlands Downloaded from https://academic.oup.com/mnras/article/466/3/2918/2736293 by guest on 30 September 2021 Accepted 2016 December 19. Received 2016 December 19; in original form 2016 November 2 ABSTRACT We report the results of a new XMM–Newton observation of the helium-rich hot subdwarf BD+37◦442 carried out in 2016 February. The possible periodicity at 19 s seen in a 2011 shorter observation is not confirmed, thus dismissing the evidence for a binary nature. This implies that the observed soft X-ray emission, with a luminosity of a few 1031 erg s−1, originates in BD+37◦442 itself, rather than in an accreting neutron star companion. The X-ray spectrum is well fit by thermal plasma emission with a temperature of 0.22 keV and non-solar element abundances. Besides the overabundance of He, C and N already known from optical/UV studies, the X-ray spectra indicate also a significant excess of Ne.
    [Show full text]
  • A Summary of the Different Classes of Stellar Pulsators
    A Summary of the Different Classes of Stellar Pulsators A summary of all the classes of pulsating stars and their main properties as described in Chapter 2 is given in the tables below. This list originated from a combination of observational discoveries, measured stellar properties, and theoretical developments. Observers who found a new type of pulsator either named it after the prototype or gave the class a name according to the ob- served characteristics of the oscillations. Several pulsators, or even groups of pulsators, were afterwards found to originate from the same physical mech- anism and were thus merged into one and the same class. We sort this out here in Tables A.1 and A.2 in order to avoid further confusion on pulsating star nomenclature. The effective temperature and luminosity indicated in Tables A.1 and A.2 should be taken as rough indications only of the borders of instability strips. Often the theory is not sufficiently refined to consider these boundaries as final. Moreover, there is overlap between various classes where so-called hy- brid pulsators, whose oscillations are excited in two different layers and/or by two different mechanisms, occur. Finally, new discoveries are being made frequently, which then drive new theoretical developments possibly leading to new instability regions. The results from the future observing facilities as described in Chapter 8 will surely lead to new classes and/or subclasses with lower amplitudes compared to what is presently achievable. In the tables below, F stands for fundamental radial mode, FO for first radial overtone and S for strange mode oscillations.
    [Show full text]