Beschreibung: Eight years of optical photometry from OGLE-III are presented of the optical counterpart to the high-mass X-ray binary system, SMC X-1. The optical data provide the best view to date of the modulation of the light from the system at the binary period of 3.9 d. In addition, it is shown for the first time that the light is also modulated at the superorbital period – a period associated with the precessing of a warped accretion disc around the neutron star partner. The implications for the sources of the various components of the optical light in this system are discussed.

Beschreibung: We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars has been extracted from the latest edition of the Optical Gravitational Lensing Experiment collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The P 1O / P F period ratios of our anomalous RRd stars are within a range of 0.725–0.738, while ‘classical’ double-mode RR Lyrae variables have period ratios in the range of 0.742–0.748. In contrast to the typical RRd stars, in the majority of the anomalous pulsators, the F-mode amplitudes are higher than the 1O-mode amplitudes. The light curves associated with the F-mode in the anomalous RRd stars show different morphology than the light curves of, both, regular RRd stars and single-mode RRab stars. Most of the anomalous double-mode stars show long-term modulations of the amplitudes (Blazhko-like effect). Translating the period ratios into the abundance parameter, Z , we find for our stars Z (0.002, 0.005) – an order of magnitude higher values than typical for RR Lyrae stars. The mass range of the RRd stars inferred from the W I versus P F diagram is (0.55–0.75) M . These parameters cannot be accounted for with single star evolution assuming a Reimers-like mass-loss. Much greater mass-loss caused by interaction with other stars is postulated. We blame the peculiar pulsation properties of our stars to the parametric resonance instability of the 1O-mode to excitation of the F- and 2O-modes as with the inferred parameters of the stars 2 1O F + 2O .

Beschreibung: We have studied the long-term (~ years) temporal variability of the prototype supersoft X-ray source (SSS) CAL 83 in the Large Magellanic Cloud, using data from the massive compact halo object (MACHO) and Optical Gravitational Lensing Experiment (OGLE) projects. The CAL 83 light curve exhibits dramatic brightness changes of ~1 mag on time-scales of ~450 d, and spends typically ~200 d in the optical low state. Combined with archival XMM–Newton X-ray observations these represent the most extensive X-ray/optical study to date of this system, and reveal in much greater detail that the X-ray light curve is anticorrelated with the optical behaviour. This is remarkably similar to the behaviour of the ‘transient’ SSS, RX J0513.9–6951, where the SSS outbursts recur on a time-scale of ~168 d, and also anticorrelate with the optical flux. We performed simple blackbody fits to both high- and low-state X-ray spectra, and find that the blackbody temperature and luminosity decrease when the optical counterpart brightens. We interpret these long-term variations in terms of the limit cycle model of Hachisu and Kato, which provides further support for these systems containing massive (~1.3 M ) white dwarfs. In addition, we have refined their orbital periods in the MACHO and OGLE-III light curves to values of 1.047529(1) d and 0.762956(5) d for CAL 83 and RX J0513.9–6951, respectively.

Beschreibung: We report the discovery of a possible planet in microlensing event MOA-2010-BLG-353. This event was only recognized as having a planetary signal after the microlensing event had finished, and following a systematic analysis of all archival data for binary lens microlensing events collected to date. Data for event MOA-2010-BLG-353 were only recorded by the high-cadence observations of the OGLE and MOA survey groups. If we make the assumptions that the probability of the lens star hosting a planet of the measured mass ratio is independent of the lens star mass or distance, and that the source star is in the Galactic bulge, a probability density analysis indicates the planetary system comprises a $0.9^{+1.6}_{-0.53}$   M Saturn mass planet orbiting a $0.18^{+0.32}_{-0.11}$  M red dwarf star, $6.43^{+1.09}_{-1.15}$  kpc away. The projected separation of the planet from the host star is $1.72^{+0.56}_{-0.48}$  au. Under the additional assumption that the source is on the far side of the Galactic bulge, the probability density analysis favours a lens system comprising a slightly lighter planet.

Beschreibung: RR Lyrae pulsating stars have been extensively used as tracers of old stellar populations for the purpose of determining the ages of galaxies, and as tools to measure distances to nearby galaxies. There was accordingly considerable interest when the RR Lyrae star OGLE-BLG-RRLYR-02792 (referred to here as RRLYR-02792) was found to be a member of an eclipsing binary system, because the mass of the pulsator (hitherto constrained only by models) could be unambiguously determined. Here we report that RRLYR-02792 has a mass of 0.26 solar masses M[symbol see text] and therefore cannot be a classical RR Lyrae star. Using models, we find that its properties are best explained by the evolution of a close binary system that started with M[symbol see text] and 0.8M[symbol see text]stars orbiting each other with an initial period of 2.9 days. Mass exchange over 5.4 billion years produced the observed system, which is now in a very short-lived phase where the physical properties of the pulsator happen to place it in the same instability strip of the Hertzsprung-Russell diagram as that occupied by RR Lyrae stars. We estimate that only 0.2 per cent of RR Lyrae stars may be contaminated by systems similar to this one, which implies that distances measured with RR Lyrae stars should not be significantly affected by these binary interlopers.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pietrzynski, G -- Thompson, I B -- Gieren, W -- Graczyk, D -- Stepien, K -- Bono, G -- Moroni, P G Prada -- Pilecki, B -- Udalski, A -- Soszynski, I -- Preston, G W -- Nardetto, N -- McWilliam, A -- Roederer, I U -- Gorski, M -- Konorski, P -- Storm, J -- England -- Nature. 2012 Apr 4;484(7392):75-7. doi: 10.1038/nature10966.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile. pietrzyn@astrouw.edu.pl〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22481359" target="_blank"〉PubMed〈/a〉

Beschreibung: The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Howes, L M -- Casey, A R -- Asplund, M -- Keller, S C -- Yong, D -- Nataf, D M -- Poleski, R -- Lind, K -- Kobayashi, C -- Owen, C I -- Ness, M -- Bessell, M S -- Da Costa, G S -- Schmidt, B P -- Tisserand, P -- Udalski, A -- Szymanski, M K -- Soszynski, I -- Pietrzynski, G -- Ulaczyk, K -- Wyrzykowski, L -- Pietrukowicz, P -- Skowron, J -- Kozlowski, S -- Mroz, P -- England -- Nature. 2015 Nov 26;527(7579):484-7. doi: 10.1038/nature15747. Epub 2015 Nov 11.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Research School of Astronomy and Astrophysics, Australian National University, Australian Capital Territory 2601, Australia. ; Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK. ; Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland. ; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210, USA. ; Department of Physics and Astronomy, Division of Astronomy and Space Physics, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden. ; School of Physics, Astronomy and Mathematics, Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK. ; Max-Planck-Institut fur Astronomie, Konigstuhl 17, D-69117 Heidelberg, Germany. ; Sorbonne Universites, UPMC Universite Paris 6 et CNRS, UMR 7095, Institut d'Astrophysique de Paris, 98 bis Boulevard Arago, 75014 Paris, France. ; Universidad de Concepcion, Departamento de Astronomia, Casilla 160-C, Concepcion, Chile. ; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26560034" target="_blank"〉PubMed〈/a〉

Beschreibung: Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth's) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet's temperature is much lower, 〈60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gould, A -- Udalski, A -- Shin, I-G -- Porritt, I -- Skowron, J -- Han, C -- Yee, J C -- Kozlowski, S -- Choi, J-Y -- Poleski, R -- Wyrzykowski, L -- Ulaczyk, K -- Pietrukowicz, P -- Mroz, P -- Szymanski, M K -- Kubiak, M -- Soszynski, I -- Pietrzynski, G -- Gaudi, B S -- Christie, G W -- Drummond, J -- McCormick, J -- Natusch, T -- Ngan, H -- Tan, T-G -- Albrow, M -- DePoy, D L -- Hwang, K-H -- Jung, Y K -- Lee, C-U -- Park, H -- Pogge, R W -- Abe, F -- Bennett, D P -- Bond, I A -- Botzler, C S -- Freeman, M -- Fukui, A -- Fukunaga, D -- Itow, Y -- Koshimoto, N -- Larsen, P -- Ling, C H -- Masuda, K -- Matsubara, Y -- Muraki, Y -- Namba, S -- Ohnishi, K -- Philpott, L -- Rattenbury, N J -- Saito, To -- Sullivan, D J -- Sumi, T -- Suzuki, D -- Tristram, P J -- Tsurumi, N -- Wada, K -- Yamai, N -- Yock, P C M -- Yonehara, A -- Shvartzvald, Y -- Maoz, D -- Kaspi, S -- Friedmann, M -- New York, N.Y. -- Science. 2014 Jul 4;345(6192):46-9. doi: 10.1126/science.1251527.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA. ; Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland. ; Turitea Observatory, Palmerston North, New Zealand. ; Department of Physics, Chungbuk National University, Cheongju 371-763, Republic of Korea. cheongho@astroph.chungbuk.ac.kr. ; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. ; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA. Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland. ; Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK. ; Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA. Universidad de Concepcion, Departamento de Astronomia, Casilla 160-C, Concepcion, Chile. ; Auckland Observatory, Auckland, New Zealand. ; Possum Observatory, Patutahi, New Zealand. ; Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland, New Zealand. ; Possum Observatory, Patutahi, New Zealand. Auckland University of Technology, Auckland, New Zealand. ; Perth Exoplanet Survey Telescope, Perth, Australia. ; Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. ; Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA. ; Department of Physics, Chungbuk National University, Cheongju 371-763, Republic of Korea. ; Korea Astronomy and Space Science Institute, Daejeon 305-348, Republic of Korea. ; Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601, Japan. ; University of Notre Dame, Department of Physics, 225 Nieuwland Science Hall, Notre Dame, IN 46556-5670, USA. ; Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland, New Zealand. ; Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand. ; Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, Okayama 719-0232, Japan. ; Department of Earth and Space Science, Osaka University, Osaka 560-0043, Japan. ; Department of Physics, University of Auckland, Private Bag 92-019, Auckland 1001, New Zealand. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK. ; Nagano National College of Technology, Nagano 381-8550, Japan. ; Department of Earth, Ocean and Atmospheric Sciences, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada. ; Tokyo Metropolitan College of Aeronautics, Tokyo 116-8523, Japan. ; School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand. ; Mount John University Observatory, Post Office Box 56, Lake Tekapo 8770, New Zealand. ; Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555, Japan. ; School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978, Israel.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24994642" target="_blank"〉PubMed〈/a〉

Beschreibung: Most known extrasolar planets (exoplanets) have been discovered using the radial velocity or transit methods. Both are biased towards planets that are relatively close to their parent stars, and studies find that around 17-30% (refs 4, 5) of solar-like stars host a planet. Gravitational microlensing, on the other hand, probes planets that are further away from their stars. Recently, a population of planets that are unbound or very far from their stars was discovered by microlensing. These planets are at least as numerous as the stars in the Milky Way. Here we report a statistical analysis of microlensing data (gathered in 2002-07) that reveals the fraction of bound planets 0.5-10 AU (Sun-Earth distance) from their stars. We find that 17(+6)(-9)% of stars host Jupiter-mass planets (0.3-10 M(J), where M(J) = 318 M( plus sign in circle) and M( plus sign in circle) is Earth's mass). Cool Neptunes (10-30 M( plus sign in circle)) and super-Earths (5-10 M( plus sign in circle)) are even more common: their respective abundances per star are 52(+22)(-29)% and 62(+35)(-37)%. We conclude that stars are orbited by planets as a rule, rather than the exception.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cassan, A -- Kubas, D -- Beaulieu, J-P -- Dominik, M -- Horne, K -- Greenhill, J -- Wambsganss, J -- Menzies, J -- Williams, A -- Jorgensen, U G -- Udalski, A -- Bennett, D P -- Albrow, M D -- Batista, V -- Brillant, S -- Caldwell, J A R -- Cole, A -- Coutures, Ch -- Cook, K H -- Dieters, S -- Prester, D Dominis -- Donatowicz, J -- Fouque, P -- Hill, K -- Kains, N -- Kane, S -- Marquette, J-B -- Martin, R -- Pollard, K R -- Sahu, K C -- Vinter, C -- Warren, D -- Watson, B -- Zub, M -- Sumi, T -- Szymanski, M K -- Kubiak, M -- Poleski, R -- Soszynski, I -- Ulaczyk, K -- Pietrzynski, G -- Wyrzykowski, L -- England -- Nature. 2012 Jan 11;481(7380):167-9. doi: 10.1038/nature10684.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Probing Lensing Anomalies Network (PLANET) Collaboration, Institut d'Astrophysique de Paris, Universite Pierre & Marie Curie, UMR7095 UPMC-CNRS, 98 bis boulevard Arago, 75014 Paris, France. cassan@iap.fr〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22237108" target="_blank"〉PubMed〈/a〉

Beschreibung: In the era of precision cosmology, it is essential to determine the Hubble constant to an accuracy of three per cent or better. At present, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC), which, being our second-closest galaxy, serves as the best anchor point for the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to measure stellar parameters and distances precisely and accurately. The eclipsing-binary method was previously applied to the LMC, but the accuracy of the distance results was lessened by the need to model the bright, early-type systems used in those studies. Here we report determinations of the distances to eight long-period, late-type eclipsing systems in the LMC, composed of cool, giant stars. For these systems, we can accurately measure both the linear and the angular sizes of their components and avoid the most important problems related to the hot, early-type systems. The LMC distance that we derive from these systems (49.97 +/- 0.19 (statistical) +/- 1.11 (systematic) kiloparsecs) is accurate to 2.2 per cent and provides a firm base for a 3-per-cent determination of the Hubble constant, with prospects for improvement to 2 per cent in the future.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pietrzynski, G -- Graczyk, D -- Gieren, W -- Thompson, I B -- Pilecki, B -- Udalski, A -- Soszynski, I -- Kozlowski, S -- Konorski, P -- Suchomska, K -- Bono, G -- Moroni, P G Prada -- Villanova, S -- Nardetto, N -- Bresolin, F -- Kudritzki, R P -- Storm, J -- Gallenne, A -- Smolec, R -- Minniti, D -- Kubiak, M -- Szymanski, M K -- Poleski, R -- Wyrzykowski, L -- Ulaczyk, K -- Pietrukowicz, P -- Gorski, M -- Karczmarek, P -- England -- Nature. 2013 Mar 7;495(7439):76-9. doi: 10.1038/nature11878.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Universidad de Concepcion, Departamento de Astronomia, Casilla 160-C, Concepcion, Chile. pietrzyn@astrouw.edu.pl〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23467166" target="_blank"〉PubMed〈/a〉