* Astronomy

Blobrana · L

2MASS J16223079-1752431

Blobrana · L

RE: U Scorpii

Blobrana · L

Title: Spectroscopy and Multi-colour Photometry of U Scorpii at the Earliest Stage of 2010 Outburst
Authors: Kazuyoshi Imamura, Kenji Tanabe

We have performed our spectroscopic and multi-colour photometric observations of the recurrent nova U Scorpii at the earliest stage of the 2010 outburst. 0.37 days after the discovery of the outburst, we can see broad and prominent emission lines of Balmer series, He I, N II, N III, O I and Mg II on the spectra. The FWHM of H\alpha line yields an expansion velocity of approximately 6200 km/s. This line also accompanies a blue shifted absorption line (so called P Cygni profile). 1.37 days after the discovery, H\alpha line shows a nearly flat-topped profile in contrast to the previous day. From our multi-colour photometry, we can see its rapid decline (one magnitude per day) of the brightness in each colour band.

Read more (136kb, PDF)

Blobrana · L

Title: The Helium Abundance in the Ejecta of U Scorpii
Authors: M. P. Maxwell, M. T. Rushton, M. J. Darnley, H. L. Worters, M. F. Bode, A. Evans, S. P. S. Eyres, M. B. N. Kouwenhoven, F. M. Walter, B. J. M. Hassall

U Scorpii is a recurrent nova which has been observed in outburst on 10 occasions, most recently in 2010. We present near-infrared and optical spectroscopy of the 2010 outburst of U Sco. The reddening of U Sco is found to be E(B-V) = 0.14±0.12, consistent with previous determinations, from simultaneous optical and near-IR observations. The spectra show the evolution of the line widths and profiles to be consistent with previous outbursts. Velocities are found to be up to 14000\,kms^{-1} in broad components and up to 1800\,kms^{-1} in narrow line components, which become visible around day 8 due to changes in the optical depth. From the spectra we derive a helium abundance of N(He)/N(H) = 0.073±0.031 from the most reliable lines available; this is lower than most other estimates and indicates that the secondary is not helium-rich, as previous studies have suggested.

Read more (126kb, PDF)

Blobrana · L

Title: Eclipses During the 2010 Eruption of the Recurrent Nova U Scorpii
Authors: Bradley E. Schaefer, Ashley Pagnotta, Aaron LaCluyze, Daniel E. Reichart, Kevin M. Ivarsen, Joshua B. Haislip, Melissa C. Nysewander, Justin P. Moore, Arto Oksanen, Hannah L. Worters, Ramotholo R. Sefako, Jaco Mentz, Shawn Dvorak, Tomas Gomez, Barbara G. Harris, Arne Henden, Thiam Guan Tan, Matthew Templeton, W. H. Allen, Berto Monard, Robert D. Rea, George Roberts, William Stein, Hiroyuki Maehara, Thomas Richards, Chris Stockdale, Tom Krajci, George Sjoberg, Jennie McCormick, Mikhail Revnivtsev, Sergei Molkov, Valery Suleimanov, Matthew J. Darnley, Michael F. Bode, Gerald Handler, Sebastien Lepine, Michael Shara

The eruption of the recurrent nova U Scorpii on 28 January 2010 is now the all-time best observed nova event. We report 36,776 magnitudes throughout its 67 day eruption, for an average of one measure every 2.6 minutes. This unique and unprecedented coverage is the first time that a nova has any substantial amount of fast photometry. With this, two new phenomena have been discovered: the fast flares in the early light curve seen from days 9-15 (which have no proposed explanation) and the optical dips seen out of eclipse from days 41-61 (likely caused by raised rims of the accretion disk occulting the bright inner regions of the disk as seen over specific orbital phases). The expanding shell and wind cleared enough from days 12-15 so that the inner binary system became visible, resulting in the sudden onset of eclipses and the turn-on of the supersoft X-ray source. On day 15, a strong asymmetry in the out-of-eclipse light points to the existence of the accretion stream. The normal optical flickering restarts on day 24.5. For days 15-26, eclipse mapping shows that the optical source is spherically symmetric with a radius of 4.1 R_sun. For days 26-41, the optical light is coming from a rim-bright disk of radius 3.4 R_sun. For days 41-67, the optical source is a center-bright disk of radius 2.2 R_sun. Throughout the eruption, the colors remain essentially constant. We present 12 eclipse times during eruption plus five just after the eruption.

Read more (1477kb, PDF)

Blobrana · L

Title: U Sco 2010 outburst: observational evidence of an underlying ONeMg white dwarf
Authors: Elena Mason

This paper presents U Sco nebular spectra collected in the period March-May 2010 after the binary outburst on Jan 28, 2010. The spectra display strong [Ne V] and [Ne III] lines that can be used to compute the relative abundance of [Ne/O]. The value obtained ([Ne/O]=1.69) is higher than the typical [Ne/O] abundance found in classical novae from CO progenitors and suggests that U Sco has a ONeMg white-dwarf progenitor. It follows that U Sco will not explode as a SN Ia but rather collapse to become a neutron star or a millisecond pulsar.

Read more (157kb, PDF)

Blobrana · L

Title: The early blast wave of the 2010 explosion of U Scorpii
Authors: J.J. Drake, S. Orlando

Three-dimensional hydrodynamic simulations exploring the first 18 hours of the 2010 January 28 outburst of the recurrent nova U Scorpii have been performed. Special emphasis was placed on capturing the enormous range in spatial scales in the blast. The pre-explosion system conditions included the secondary star and a flared accretion disk. These conditions can have a profound influence on the evolving blast wave. The blast itself is shadowed by the secondary star, which itself gives rise to a low-temperature bow-shock. The accretion disk is completely destroyed in the explosion. A model with a disk gas density of 10^{15} cm^{-3} produced a blast wave that is collimated and with clear bipolar structures, including a bipolar X-ray emitting shell. The degree of collimation depends on the initial mass of ejecta, energy of explosion, and circumstellar gas density distribution. It is most pronounced for a model with the lowest explosion energy (10^{43} erg) and mass of ejecta (10^{-8} solar masses). The X-ray luminosities of three of six models computed are close to, but consistent with, an upper limit to the early blast X-ray emission obtained by the Swift satellite, the X-ray luminosity being larger for higher circumstellar gas density and higher ejecta mass. The latter consideration, together with estimates of the blast energy from previous outbursts, suggests that the mass of ejecta in the 2010 outburst was not larger than 10^{-7} solar masses.

Read more (354kb)

Blobrana · L

Blobrana · L

U Scorpii is in outburst.

The recurrent novae rises from minimum (V~18) to a maximum (V~7.7) in under six hours.
The outburst was discovered by Barbara Harris.

Blobrana · L

U Scorpii - A Ticking Time Bomb

Astronomers from Sheffield and Southampton Universities and Winchester College have identified a star that will light up the night sky with a massive explosion. The star, known as U Scorpii will explode within the next 700,000 years - a blink of an eye in astronomical terms. These Type Ia supernovae, as they are known, may hold the key to the fate of the Universe itself.
Read more (684kb, PDF)

Expand (34kb, 1024 x 768)

Position(200): RA 16 22 30.68 , Dec -17 52 42.1

U Scorpii is a recurrent novae, that usually has a magnitude of 17.6, with an outburst magnitude of 8. The brightening from minimum to maximum takes about 5 hours, and a decline to two magnitudes below maximum in about 38 hours; this makes U Scorpii one of the fastest nova known.
The last three eruptions, in 1979, 1987, and 1999, were all discovered by amateur astronomers. The current pattern of eruptions is once every 10 ± 2 years.