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  • 1
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    Probing interstellar extinction near the 30 Doradus nebula with red giant stars (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-16
    Description: We have studied the interstellar extinction in a field of ~ 3 arcmin x 3 arcmin located about 6 arcmin southwest of 30 Doradus in the Large Magellanic Cloud (LMC). Hubble Space Telescope observations in the U , B , V , I and Hα bands reveal patchy extinction in this field. The colour–magnitude diagram (CMD) shows an elongated stellar sequence, almost parallel to the main sequence (MS), which is in reality made up of stars of the red giant clump (RC) spread across the CMD by the uneven levels of extinction in this region. Since these objects are all at the same distance from us and share very similar physical properties, we can derive quantitatively both the extinction law in the range 3000–8000 Å and the absolute extinction towards about 100 objects, setting statistically significant constraints on the dust grains properties in this area. We find an extinction curve considerably flatter than the standard Galactic one and than those obtained before for the LMC. The derived value of R V  = 5.6 ± 0.3 implies that in this region larger grains dominate. Upper MS stars span a narrower range of E ( B – V ) values than RC objects, at variance with what has been found elsewhere in the LMC.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Pre-main-sequence stars older than 8 Myr in the Eagle nebula (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-12
    Description: Attention is given to a population of 110 stars in the NGC 6611 cluster of the Eagle nebula that have prominent near-infrared excess and optical colours typical of pre-main-sequence (PMS) stars older than 8 Myr. At least half of those for which spectroscopy exists have a Hα emission line profile revealing active accretion. In principle, the V  – I colours of all these stars would be consistent with those of young PMS objects (〈1 Myr) whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a few per cent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness, their positions in the colour–magnitude diagram and the weak Li absorption lines of the stars studied spectroscopically suggest that most of them are at least eight times older than the ~1 Myr-old PMS stars already known in this cluster and could be as old as ~30 Myr. This is the largest homogeneous sample to date of Galactic PMS stars considerably older than 8 Myr that are still actively accreting from a circumstellar disc and it allows us to set a lower limit of 7 per cent to the disc frequency at ~16 Myr in NGC 6611. These values imply a characteristic exponential lifetime of ~6 Myr for disc dissipation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    The extinction law inside the 30 Doradus nebula (2014)
    Oxford University Press
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    Publication Date: 2014-09-24
    Description: We have studied the interstellar extinction in a field of ~3 arcmin x 3 arcmin at the core of the 30 Doradus nebula, including the central R 136 cluster, in the Large Magellanic Cloud. Observations at optical and near-infrared wavelengths, obtained with the WFC 3 camera on board the Hubble Space Telescope , show that the stars belonging to the red giant clump are spread across the colour–magnitude diagrams because of the considerable and uneven levels of extinction in this region. Since these stars share very similar physical properties and are all at the same distance, they allow us to derive the absolute extinction in a straightforward and reliable way. Thus, we have measured the extinction towards about 180 objects and the extinction law in the range 0.3–1.6 μm. At optical wavelengths, the extinction curve is almost parallel to that of the diffuse Galactic interstellar medium. Taking the latter as a template, the value of R V  = 4.5 ± 0.2 that we measure indicates that in the optical there is an extra grey component due to a larger fraction of large grains. At wavelengths longer than ~1 μm, the contribution of this additional component tapers off as –1.5 , like in the Milky Way, suggesting that the nature of the grains is otherwise similar to those in our Galaxy, but with a ~2.2 times higher fraction of large grains. These results are consistent with the addition of ‘fresh’ large grains by supernova explosions, as recently revealed by Herschel and ALMA (Atacama Large Millimeter Array) observations of SN 1987A.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    X-ray illumination of the ejecta of supernova 1987A (2011)
    Nature Publishing Group (NPG)
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    Publication Date: 2011-06-10
    Description: When a massive star explodes as a supernova, substantial amounts of radioactive elements--primarily (56)Ni, (57)Ni and (44)Ti--are produced. After the initial flash of light from shock heating, the fading light emitted by the supernova is due to the decay of these elements. However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium. The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellanic Cloud. From 1994 to 2001, the ejecta faded owing to radioactive decay of (44)Ti as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejecta, enabling us to analyse the structure and chemistry of the vanished star.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Larsson, J -- Fransson, C -- Ostlin, G -- Groningsson, P -- Jerkstrand, A -- Kozma, C -- Sollerman, J -- Challis, P -- Kirshner, R P -- Chevalier, R A -- Heng, K -- McCray, R -- Suntzeff, N B -- Bouchet, P -- Crotts, A -- Danziger, J -- Dwek, E -- France, K -- Garnavich, P M -- Lawrence, S S -- Leibundgut, B -- Lundqvist, P -- Panagia, N -- Pun, C S J -- Smith, N -- Sonneborn, G -- Wang, L -- Wheeler, J C -- England -- Nature. 2011 Jun 8;474(7352):484-6. doi: 10.1038/nature10090.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Astronomy, The Oskar Klein Centre, Stockholm University, 106 91 Stockholm, Sweden. josefin.larsson@astro.su.se〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21654749" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    The unusual gamma-ray burst GRB 101225A explained as a minor body falling onto a neutron star (2011)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2011-12-02
    Description: The tidal disruption of a solar-mass star around a supermassive black hole has been extensively studied analytically and numerically. In these events, the star develops into an elongated banana-shaped structure. After completing an eccentric orbit, the bound debris falls into the black hole, forming an accretion disk and emitting radiation. The same process may occur on planetary scales if a minor body passes too close to its star. In the Solar System, comets fall directly into our Sun or onto planets. If the star is a compact object, the minor body can become tidally disrupted. Indeed, one of the first mechanisms invoked to produce strong gamma-ray emission involved accretion of comets onto neutron stars in our Galaxy. Here we report that the peculiarities of the 'Christmas' gamma-ray burst (GRB 101225A) can be explained by a tidal disruption event of a minor body around an isolated Galactic neutron star. This would indicate either that minor bodies can be captured by compact stellar remnants more frequently than occurs in the Solar System or that minor-body formation is relatively easy around millisecond radio pulsars. A peculiar supernova associated with a gamma-ray burst provides an alternative explanation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Campana, S -- Lodato, G -- D'Avanzo, P -- Panagia, N -- Rossi, E M -- Della Valle, M -- Tagliaferri, G -- Antonelli, L A -- Covino, S -- Ghirlanda, G -- Ghisellini, G -- Melandri, A -- Pian, E -- Salvaterra, R -- Cusumano, G -- D'Elia, V -- Fugazza, D -- Palazzi, E -- Sbarufatti, B -- Vergani, S D -- England -- Nature. 2011 Nov 30;480(7375):69-71. doi: 10.1038/nature10592.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉INAF - Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate, Italy. sergio.campana@brera.inaf.it〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22129725" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 6
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    Observing supernova 1987A with the refurbished Hubble Space Telescope (2010)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2010-09-04
    Description: Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 with the use of the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Lyalpha and Halpha lines from shock emission continue to brighten, whereas their maximum velocities continue to decrease. We observe broad, blueshifted Lyalpha, which we attribute to resonant scattering of photons emitted from hot spots on the equatorial ring. We also detect N v lambdalambda1239, 1243 angstrom line emission, but only to the red of Lyalpha. The profiles of the N v lines differ markedly from that of Halpha, suggesting that the N4+ ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉France, Kevin -- McCray, Richard -- Heng, Kevin -- Kirshner, Robert P -- Challis, Peter -- Bouchet, Patrice -- Crotts, Arlin -- Dwek, Eli -- Fransson, Claes -- Garnavich, Peter M -- Larsson, Josefin -- Lawrence, Stephen S -- Lundqvist, Peter -- Panagia, Nino -- Pun, Chun S J -- Smith, Nathan -- Sollerman, Jesper -- Sonneborn, George -- Stocke, John T -- Wang, Lifan -- Wheeler, J Craig -- New York, N.Y. -- Science. 2010 Sep 24;329(5999):1624-7. doi: 10.1126/science.1192134. Epub 2010 Sep 2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20813921" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    An early and comprehensive millimetre and centimetre wave and X-ray study of SN 2011dh: a non-equipartition blast wave expanding into a massive stellar wind (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-14
    Description: Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3–12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition ( e / B  ~ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R –2 . Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s –1 , contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (~1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio e / B .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    H{alpha} photometry of low-mass stars in 47 Tucanae: chromospheric activity and exotica (2013)
    Oxford University Press
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    Publication Date: 2013-12-23
    Description: We have used archival Hubble Space Telescope observations obtained with the Advanced Camera for Surveys to study the Hα emission properties of main-sequence stars in the globular cluster 47 Tucanae. Using a combination of multiband observations in the F 606 W , F 814 W and F 658 N bands, we search for stars showing Hα excess emission. An accurate photometric measurement of their Hα equivalent width allows us to identify objects with large Hα emission, which we attribute to mass accretion rather than enhanced chromospheric activity. The spatial position of some of these stars is coincident with that of known X-ray sources, and their location in the colour–magnitude diagram allows us to classify them as active binaries or cataclysmic variables (CVs). We show that this method, commonly adopted to study accreting discs in young stellar objects, can be successfully used to identify and characterize candidate CVs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Five supernova survey galaxies in the southern hemisphere. II. the supernova rates (2011)
    Springer
    Details
    Publication Date: 2011-09-01
    Print ISSN: 0571-7256
    Electronic ISSN: 1573-8191
    Topics: Physics
    Published by Springer
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  • 10
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    PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. II. NGC 346 IN THE SMALL MAGELLANIC CLOUD (2011)
    Institute of Physics
    Details
    Publication Date: 2011-09-19
    Print ISSN: 0004-637X
    Electronic ISSN: 1538-4357
    Topics: Physics
    Published by Institute of Physics
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