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Blobrana


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V391 Pegasi
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Title: V391 Peg: identification of the two main pulsation modes from ULTRACAM u'g'r' amplitudes
Authors: Roberto Silvotti, Suzanna Randall, Vik S. Dhillon, Tom R. Marsh, Chris D. Savoury, Sonja Schuh, Gilles Fontaine, Pierre Brassard

V391 Peg (HS2201+2610) is an extreme horizontal branch subdwarf B (sdB) star, it is an hybrid pulsator showing p- and g-mode oscillations, and hosts a 3.2/sini M_Jup planet at an orbital distance of about 1.7 AU. In order to improve the characterisation of the star, we measured the pulsation amplitudes in the u'g'r' SLOAN photometric bands using ULTRACAM at the William Herschel 4.2 m telescope and we compared them with theoretical values. The preliminary results presented in this article conclusively show that the two main pulsation periods at 349.5 and 354.1 s are a radial and a dipole mode respectively. This is the first time that the degree index of multiple modes has been uniquely identified for an sdB star as faint as V391 Peg (B=14.4), proving that multicolour photometry is definitely an efficient technique to constrain mode identification, provided that the data have a high enough quality.

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Blobrana


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Title: The planet-hosting subdwarf B star V391 Pegasi is a hybrid pulsator
Authors: R. Lutz, S. Schuh, R. Silvotti, S. Bernabei, S. Dreizler, T. Stahn, S. D. Huegelmeyer

A noticeable fraction of subdwarf B stars shows either short-period (p-mode) or long-period (g-mode) luminosity variations, with two objects so far known to exhibit hybrid behaviour, i.e. showing both types of modes at the same time. The pulsating subdwarf B star V391 Pegasi (or HS2201+2610), which is close to the two known hybrid pulsators in the log g - Teff plane, has recently been discovered to host a planetary companion. In order to learn more about the planetary companion and its possible influence on the evolution of its host star (subdwarf B star formation is still not well understood), an accurate characterisation of the host star is required. As part of an ongoing effort to significantly improve the asteroseismic characterisation of the host star, we investigate the low-frequency behaviour of HS2201+2610. We obtained rapid high signal-to-noise photometric CCD (B-filter) and PMT (clear-filter) data at 2m-class telescopes and carried out a careful frequency analysis of the light curves. In addition to the previously known short-period luminosity variations in the range 342s-367s, we find a long-period variation with a period of 54min and an amplitude of 0.15 per cent. This can most plausibly be identified with a g-mode pulsation, so that HS2201+2610 is a new addition to the short list of hybrid sdB pulsators. Along with the previously known pulsating subdwarf B stars HS0702+6043 and Balloon090100001 showing hybrid behaviour, the new hybrid HS2201+2610 is the third member of this class. This important property of HS2201+2610 can lead to a better characterisation of this planet-hosting star, helping the characterisation of its planetary companion as well. Current pulsation models cannot yet reproduce hybrid sdBV stars particularly well and improved pulsation models for this object have to include the hybrid behaviour.

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Blobrana


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Posts: 131433
Date:
Peg V392b
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An international team of astronomers is one step closer to answering the question, "Will the world end with a bang or a whimper?"
Using an array of telescopes around the globe, a team of 23 researchers led by Italian astronomer Dr. Roberto Silvotti of the Observatorio Astronomico di Capodimonte in Naples has spent seven years investigating the pulses of the star V391 Pegasi. This international collaboration has resulted in the discovery of a new planet Peg V392b the oldest planet known so far in the universe.

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Blobrana


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RE: Red giant survivor planet
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Planets circling close to their star such as Earth around the Sun aren't necessarily doomed to being swallowed up by that star, according to a new observation.
Stars such as our own expand into 'red giants' in their old age, engulfing nearby planets. Now a planet has been sighted circling close to V 391 Pegasi, a star that has gone through the red-giant phase to become what is known as a hot B-type subdwarf. The planet, it seems, survived this process.

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Blobrana


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Astronomers have found a planet that appears to have survived the death throes of its parent star.
V 391 Pegasi b has somehow ridden out the "red giant" phase in which old stars that have exhausted their hydrogen fuel expand their outer layers.
Inner planets - like V 391 Pegasi b, and perhaps Earth one day - would expect to be consumed in the process.
The newly discovered planet's large size may have been a factor, the team reports in the journal Nature.

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Blobrana


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Posts: 131433
Date:
V391 Pegasi
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Astronomers have detected the first planet orbiting a star that has passed through the red giant phase, the massive bloating that befalls sun-like stars when their nuclear fuel begins to run out.
The so-called exoplanet likely survived a close brush with its star, V391 Pegasi, despite once orbiting at roughly the same distance that lies between the sun and Earth, according to a study published in Nature.

V 391 Pegasi.kmz
Google Sky file

-- Edited by Blobrana at 16:57, 2008-01-12

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Blobrana


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Posts: 131433
Date:
Red giant survivor planet
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Astronomers detect red giant survivor planet
10 billion years old
Italian astronomers have detected a planet that survived the red giant expansion of its home star. The researchers say that the discovery could be a sneak peek at the fate that awaits the Earth, some four or five billion years from now.

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(Jan 23, 2003):
A planet was discovered by a team at the European Southern Observatory (ESO), that orbits around the giant star HD 47536 in the southern constellation, Canis Major (The Great Dog). The Jupiter-like planet orbits a Red Giant star--more than 400 light-years away and the second most distant planetary system yet.

-- Edited by Blobrana at 16:22, 2007-09-12

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