* Astronomy

Blobrana · L

RE: V445 Puppis

Blobrana · L

The European Southern Observatory's Very Large Telescope has made the first time-lapse movie of an unusual shell of matter ejected by a "vampire star."
The 'vampire star,' known as V445 in the constellation of Puppis ('the Stern'), has been gulping down gas from its close companion star eventually causing it to undergo a nova explosion, becoming 250 times brighter than before and ejecting a large quantity of matter into space.
This enabled a team of astronomers, including UK researchers from the Universities of Warwick and Manchester, to study V445 Puppis in great detail and determine the distance and intrinsic brightness of the outbursting object. The Science and Technology Facilities Council funds UK membership of ESO, allowing our astronomers access to its telescopes to carry out their research.

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Blobrana · L

Stellar Time Bomb Identified
Using ESO's Very Large Telescope and its ability to obtain images as sharp as if taken from space, astronomers have made the first time-lapse movie of a rather unusual shell ejected by a "vampire star", which in November 2000 underwent an outburst after gulping down part of its companion's matter.
The astronomers studied the object known as V445 in the constellation of Puppis ("the Stern") in great detail. V445 Puppis is the first, and so far only, nova showing no evidence at all for hydrogen. It provides the first evidence for an outburst on the surface of a white dwarf dominated by helium.

"This is critical, as we know that Type Ia supernovae lack hydrogen, and the companion star in V445 Pup fits this nicely by also lacking hydrogen, instead dumping mainly helium gas onto the white dwarf" - co-author Danny Steeghs, from the University of Warwick, UK.

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Artist's impression of vampire star

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Title: Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised
Authors: Mariko Kato (Keio Univ.), Izumi Hachisu (Univ. of Tokyo), Seiichiro Kiyota (VSOLJ), Hideyuki Saio (Tohoku Univ.)

V445 Pup (2000) is a unique object identified as a helium nova. Colour indexes during the outburst are consistent with those of free-free emission. We present a free-free emission dominated light curve model of V445 Pup on the basis of the optically thick wind theory. Our light curve fitting shows that (1) the white dwarf (WD) mass is very massive (M_WD >~ 1.35 solar masses), and (2) a half of the accreted matter remains on the WD, both of which suggest that the increasing WD mass. Therefore, V445 Pup is a strong candidate of Type Ia supernova progenitor. The estimated distance to V445 Pup is now consistent with the recent observational suggestions, 3.5 < d < 6.5 kpc. A helium star companion is consistent with the brightness of m_v=14.5 mag just before the outburst, if it is a little bit evolved hot (\log T (K) >~ 4.5) star with the mass of M_He >~ 0.8 M_\sun. We then emphasise importance of observations in the near future quiescent phase after the thick circumstellar dust dissipates away, especially its colour and magnitude to specify the nature of the companion star. We have also calculated helium ignition masses for helium shell flashes against various helium accretion rates and discussed the recurrence period of helium novae.

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