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Michalska G.,Wroclaw University | Michalska G.,University of Concepcion | Niemczura E.,Wroclaw University | Pigulski A.,Wroclaw University | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Using photometric and spectroscopic observations of the double-lined early-type eclipsing binary system ALS 1135, a member of the distant OB association Bochum 7, we derived the new physical and orbital parameters of its components. The masses of both components were derived with an accuracy better than 1 per cent, and their radii, with an accuracy better than 3 per cent. Since the primary's mass is equal to about 25M⊙, its radius was subsequently used to derive the age of the system which is equal to 4.3 ± 0.5Myr. The result shows that this method represents a viable alternative to isochrone fitting. A photometric search of the field of ALS 1135 resulted in the discovery of 17 variable stars, including 7 pulsating ones. One of them is a slowly-pulsating B (SPB) star belonging to Vel OB1, the other six are δ Scuti stars. Of the six δ Scuti stars three might belong to Vel OB1, the other two are likely members of Bochum 7. Given the age of Bochum 7, these two stars are probably pre-main-sequence pulsators. In addition, we provide UBVIC photometry for about 600 stars in the observed field. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Koen C.,University of the Western Cape | Kilkenny D.,University of the Western Cape | Pretorius M.L.,South African Astronomical Observatory | Pretorius M.L.,European Southern Observatory | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present photometry which shows that two known hot subdwarf stars, HE 0218-3437 and LB 1516, are variable. LB 1516 exhibits several frequencies in the range 12-25 cycles d-1 (periods of about 1-2 h) with amplitudes less than about 0.003 mag and appears to be a typical slowly pulsating sdB star. Results from a multisite campaign on HE 0218-3437 show the presence of two frequencies only, the lower amplitude variation an apparent subharmonic of the higher amplitude periodicity. It is likely that the star is in a binary system, and that the variability is due to ellipsoidal deformation of the primary star. © 2009 RAS.

Michalska G.,Instytut Astronomiczny | Niemczura E.,Instytut Astronomiczny | Steslicki M.,Instytut Astronomiczny | Williams A.,Perth Observatory
Proceedings of the International Astronomical Union | Year: 2010

We present new physical and orbital parameters of an early-type double-lined eclipsing binary system ALS 1135. The UBV IC light curves and radial velocity curves were modeled simultaneously by means of the Wilson-Devinney code. As a result, we obtained inclination and size of the orbit, as well as masses, radii and effective temperatures of the components. © International Astronomical Union 2011.

Roy R.,Aryabhatta Research Institute of Observational science ARIES | Kumar B.,Aryabhatta Research Institute of Observational science ARIES | Moskvitin A.S.,Special Astrophysical Observatory | Benetti S.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 11 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present BVRI photometric and low-resolution spectroscopic investigation of the Type II core-collapse supernova (SN) 2008gz, which occurred in a star-forming arm and within a half-light radius (solar metallicity region) of the nearby spiral galaxy NGC 3672. The SN event was detected late, and a detailed investigation of its light curves and spectra spanning 200d suggest that it is an event of Type IIP similar to the archetypal SNe 2004et and 1999em. However, in contrast to other events of its class, SN 2008gz exhibits a rarely observed Vmagnitude drop of 1.5 over the period of a month during the plateau to nebular phase. Using an AV of 0.21mag as a lower limit and a distance of 25.5Mpc, we estimate a synthesized 56Ni mass of 0.05 ± 0.01M⊙, a mid-plateau MV of -16.6 ± 0.2mag and a total radiant energy of ~1049erg. The photospheric velocity is observed to be higher than observed for SN 2004et at similar epochs, indicating that the explosion energy was comparable to or higher than that of SN 2004et. A similar trend was also seen for the expansion velocity of H envelopes. By comparing the properties of SN 2008gz with other well-studied events, as well as by using a recent simulation of pre-SN models by Dessart, Livne & Waldman, we infer an explosion energy range of 2-3 × 1051erg, and this coupled with the observed width of the forbidden [Oi] 6300-6364Å line at 275d after the explosion gives an upper limit for the main-sequence (non-rotating, solar metallicity) progenitor mass of 17M⊙. Our narrow-band Hα observation, taken nearly 560d after the explosion, and the presence of an emission kink at zero velocity in the Doppler-corrected spectra of SN indicate that the event took place in a low-luminosity star-forming Hii region. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Sicardy B.,University of Paris Descartes | Sicardy B.,University Pierre and Marie Curie | Sicardy B.,Institut Universitaire de France | Bolt G.,Craigie | And 32 more authors.
Astronomical Journal | Year: 2011

Pluto and its main satellite, Charon, occulted the same star on 2008 June 22. This event was observed from Australia and La Réunion Island, providing the east and north Charon Plutocentric offset in the sky plane (J2000): X = + 12,070.5 ± 4 km (+ 546.2 ± 0.2 mas), Y = + 4,576.3 ± 24 km (+ 207.1 ± 1.1 mas) at 19:20:33.82 UT on Earth, corresponding to JD 2454640.129964 at Pluto. This yields Charon's true longitude L = 153.483 ± 0. ° 071 in the satellite orbital plane (counted from the ascending node on J2000 mean equator) and orbital radius r = 19,564 ± 14 km at that time. We compare this position to that predicted by (1) the orbital solution of Tholen & Buie (the "TB97" solution), (2) the PLU017 Charon ephemeris, and (3) the solution of Tholen et al. (the "T08" solution). We conclude that (1) our result rules out solution TB97, (2) our position agrees with PLU017, with differences of δL = + 0.073 ± 0. ? 071 in longitude, and δr = + 0.6 ± 14 km in radius, and (3) while the difference with the T08 ephemeris amounts to only δL = 0.033 ± 0. ? 071 in longitude, it exhibits a significant radial discrepancy of δr = 61.3 ± 14 km. We discuss this difference in terms of a possible image scale relative error of 3.35 × 10-3in the 2002-2003 Hubble Space Telescope images upon which the T08 solution is mostly based. Rescaling the T08 Charon semi-major axis, a = 19, 570.45 km, to the TB97 value, a=19636 km, all other orbital elements remaining the same ("T08/TB97" solution), we reconcile our position with the re-scaled solution by better than 12 km (or 0.55 mas) for Charon's position in its orbital plane, thus making T08/TB97 our preferred solution. © 2011. The American Astronomical Society. All rights reserved.

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