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Post Info TOPIC: HD 172555
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Hubble Detects 'Exocomets' Taking the Plunge Into a Young Star

Interstellar forecast for a nearby star: Raining comets! NASA's Hubble Space Telescope has discovered comets plunging onto the star HD 172555, which is a youthful 23 million years old and resides 95 light-years from Earth.
The exocomets - comets outside our solar system - were not directly seen around the star, but their presence was inferred by detecting gas that is likely the vaporized remnants of their icy nuclei.
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Blobrana


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Title: A Self-Consistent Model of the Circumstellar Debris Created by a Giant Hypervelocity Impact in the HD172555 System
Authors: B.C. Johnson, C.M. Lisse, C.H. Chen, H. J. Melosh, M.C. Wyatt, P. Thebault, W.G. Henning, E. Gaidos, L.T. Elkins-Tanton, J.C. Bridges, A. Morlok

Spectral modelling of the large infrared excess in the Spitzer IRS spectra of HD 172555 suggests that there is more than 10^19 kg of sub-micron dust in the system. Using physical arguments and constraints from observations, we rule out the possibility of the infrared excess being created by a magma ocean planet or a circumplanetary disk or torus. We show that the infrared excess is consistent with a circumstellar debris disk or torus, located at approximately 6 AU, that was created by a planetary scale hypervelocity impact. We find that radiation pressure should remove submicron dust from the debris disk in less than one year. However, the system's mid-infrared photometric flux, dominated by submicron grains, has been stable within 4 percent over the last 27 years, from IRAS (1983) to WISE (2010). Our new spectral modelling work and calculations of the radiation pressure on fine dust in HD 172555 provide a self-consistent explanation for this apparent contradiction. We also explore the unconfirmed claim that 10^47 molecules of SiO vapour are needed to explain an emission feature at 8 um in the Spitzer IRS spectrum of HD 172555. We find that unless there are 10^48 atoms or 0.05 Earth masses of atomic Si and O vapour in the system, SiO vapour should be destroyed by photo-dissociation in less than 0.2 years. We argue that a second plausible explanation for the 8 um feature can be emission from solid SiO, which naturally occurs in submicron silicate "smokes" created by quickly condensing vaporized silicate.

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Blobrana


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Title: HD 172555: detection of 63 microns [OI] emission in a debris disc
Authors: P. Riviere-Marichalar, D. Barrado, J.-C. Augereau, W. F. Thi, A. Roberge, C. Eiroa, B. Montesinos, G. Meeus, C. Howard, G. Sandell, G. Duchêne, W. R. F. Dent, J. Lebreton, I. Mendigutía, N. Huélamo, F. Mènard, C. Pinte

Context. HD 172555 is a young A7 star belonging to the Beta Pictoris Moving Group that harbours a debris disc. The Spitzer IRS spectrum of the source showed mid-IR features such as silicates and glassy silica species, indicating the presence of a warm dust component with small grains, which places HD 172555 among the small group of debris discs with such properties. The IRS spectrum also shows a possible emission of SiO gas.
Aims. We aim to study the dust distribution in the circumstellar disc of HD 172555 and to asses the presence of gas in the debris disc.
Methods. As part of the GASPS Open Time Key Programme, we obtained Herschel-PACS photometric and spectroscopic observations of the source. We analysed PACS observations of HD 172555 and modelled the Spectral Energy Distribution (SED) with a modified blackbody and the gas emission with a two-level population model with no collisional de-excitation.
Results. We report for the first time the detection of OI atomic gas emission at 63.18 microns in the HD 172555 circumstellar disc. We detect excesses due to circumstellar dust toward HD 172555 in the three photometric bands of PACS (70, 100, and 160 microns). We derive a large dust particle mass of 4.8e-4 Earth masses and an atomic oxygen mass of 2.5e-2*R² Earth masses, where R in AU is the separation between the star and the inner disc. Thus, most of the detected mass of the disc is in the gaseous phase.

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Blobrana


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An astronomer at a Laurel lab helped find proof for the first time of a high-speed impact between two planets in a solar system similar to ours, supporting the theory that an object the size of Mars collided with Earth and formed the moon.
Carey Lisse was the lead author of the paper describing the collision published this month in the Astrophysical Journal. He works at the Johns Hopkins University Applied Physics Lab in Laurel and said he is excited to share the results from his two years of research.

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Planetary Smash-Up Leaves Ring Around Star
Vaporised remains of rock and lava circle a very young star, creating a ring of debris scientists believe formed after a violent crash of two planetary bodies.
The host star is HD 172555, located about 100 light-years away in the southern constellation Pavo.

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A Nasa space telescope has found evidence of a high-speed collision between two burgeoning planets orbiting a young star.
Astronomers say the cosmic smash-up is similar to the one that formed our Moon some four billion years ago, when a Mars-sized object crashed into Earth.
In this case, two rocky bodies are thought to have slammed into one another in the last few thousand years.
Details are to be published in the Astrophysical Journal.

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Two distant planets orbiting a young star apparently smashed into each other at high speeds thousands of years ago in cosmic pileup of cataclysmic proportions, astronomers announced Monday.
Telltale plumes of vaporised rock and lava leftover from the collision revealed its existence to NASA's Spitzer Space Telescope, which picked up signatures from the impact in recent observations.

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Planet Smash-Up Animation NASA JPL Spitzer Space Telescope HD



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Blobrana


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Scientists have spotted the wreckage from a spectacular collision between two planets deep in space. Two rocky worlds the size of the Moon and Mercury slammed into each other recently in cosmic terms - within a few thousand years.

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Planet Smash-Up Sends Vaporised Rock, Hot Lava Flying
NASA's Spitzer Space Telescope has found evidence of a high-speed collision between two burgeoning planets around a young star.
Astronomers say that two rocky bodies, one as least as big as our moon and the other at least as big as Mercury, slammed into each other within the last few thousand years or so - not long ago by cosmic standards. The impact destroyed the smaller body, vaporising huge amounts of rock and flinging massive plumes of hot lava into space.
Spitzer's infrared detectors were able to pick up the signatures of the vaporised rock, along with pieces of refrozen lava, called tektites.
Carey M. Lisse of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., lead author of a new paper, and his team observed a star called HD 172555, which is about 12 million years old and located about 100 light-years away in the far southern constellation Pavo, or the Pea**** (for comparison, our solar system is 4.5 billion years old). The astronomers used an instrument on Spitzer, called a spectrograph, to break apart the star's light and look for fingerprints of chemicals, in what is called a spectrum.

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