* Astronomy

Members Login
Post Info
TOPIC: White dwarf planets


L

Posts: 131433
Date:
White Dwarf Planetary Systems
Permalink  
 


Title: The Fate of Exomoons in White Dwarf Planetary Systems
Author: Matthew J. Payne, Dimitri Veras, Boris T. Gaensicke, Matthew J. Holman

Roughly 1000 white dwarfs are known to be polluted with planetary material, and the progenitors of this material are typically assumed to be asteroids. The dynamical architectures which perturb asteroids into white dwarfs are still unknown, but may be crucially dependent on moons liberated from parent planets during post-main-sequence gravitational scattering. Here, we trace the fate of these exomoons, and show that they more easily achieve deep radial incursions towards the white dwarf than do scattered planets. Consequently, moons are likely to play a significant role in white dwarf pollution, and in some cases may be the progenitors of the pollution itself.

Read more (344kb, PDF)



__________________


L

Posts: 131433
Date:
White dwarf Debris Disks
Permalink  
 


Title: The Frequency of Debris Disks at White Dwarfs
Authors: Sara D. Barber, Adam J. Patterson, Mukremin Kilic, S. K. Leggett, P. Dufour, J. S. Bloom, D. L. Starr

We present near- and mid-infrared photometry and spectroscopy from PAIRITEL, IRTF, and Spitzer of a metallicity-unbiased sample of 117 cool, hydrogen-atmosphere white dwarfs from the Palomar-Green survey and find five with excess radiation in the infrared, translating to a 4.3+2.7-1.2% frequency of debris disks. This is slightly higher than, but consistent with the results of previous surveys. Using an initial-final mass relation, we apply this result to the progenitor stars of our sample and conclude that 1-7Msol stars have at least a 4.3% chance of hosting planets; an indirect probe of the intermediate-mass regime eluding conventional exoplanetary detection methods. Alternatively, we interpret this result as a limit on accretion timescales as a fraction of white dwarf cooling ages; white dwarfs accrete debris from several generations of disks for ~10Myr. The average total mass accreted by these stars ranges from that of 200km asteroids to Ceres-sized objects, indicating that white dwarfs accrete moons and dwarf planets as well as Solar System asteroid analogues.

Read more (7278kb, PDF)



__________________


L

Posts: 131433
Date:
RE: White dwarf planets
Permalink  
 


Title: The habitability and detection of Earth-like planets orbiting cool white dwarfs
Authors: L. Fossati, S. Bagnulo, C. A. Haswell, M. R. Patel, R. Busuttil, P. M. Kowalski, D. V. Shulyak, M. F. Sterzik

Since there are several ways planets can survive the giant phase of the host star, we examine the habitability and detection of planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU would remain in the Continuous Habitable Zone (CHZ) for ~8 Gyr. We show that photosynthetic processes can be sustained on such planets. The DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, hence non-magnetic white dwarfs are compatible with the persistence of complex life. Polarisation due to a terrestrial planet in the CHZ of a cool white dwarf is 10^2 (10^4) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a viable way to detect close-in rocky planets around white dwarfs. Multi-band polarimetry would also allow reveal the presence of a planet atmosphere, providing a first characterisation. Planets in the CHZ of a 0.6 M_sun white dwarf will be distorted by Roche geometry, and a Kepler-11d analogue would overfill its Roche lobe. With current facilities a Super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known cool white dwarf. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue.

Read more (94kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Transit surveys for Earths in the habitable zones of white dwarfs
Authors: Eric Agol (University of Washington)

To date the search for habitable Earth-like planets has primarily focused on nuclear burning stars. I propose that this search should be expanded to cool white dwarf stars that have expended their nuclear fuel. I define the continuously habitable zone of white dwarfs, and show that it extends from ~0.005 to 0.02 AU for white dwarfs with masses from 0.4-0.9 solar masses, temperatures less than 10,000 K, and habitable durations of at least 3 Gyr. As they are similar in size to Earth, white dwarfs may be completely eclipsed by terrestrial planets that orbit edge-on, which can easily be detected with ground-based telescopes. If planets can migrate inward or reform near white dwarfs, I show that a global robotic telescope network could carry out a transit survey of nearby white dwarfs placing interesting constraints on the presence of habitable Earths. If planets were detected, I show that the survey would favour detection of planets similar to Earth: similar size, temperature, rotation period, and host star temperatures similar to the Sun. The Large Synoptic Survey Telescope (LSST) could place even tighter constraints on the frequency of habitable Earths around white dwarfs. The confirmation and characterization of these planets might be carried out with large ground and space telescopes.

Read more  (49kb, PDF )

__________________


L

Posts: 131433
Date:
Permalink  
 

Title: Ancient planetary systems are orbiting a large fraction of white dwarf stars
Authors: B. Zuckerman, C. Melis, B. Klein, D. Koester, M. Jura

Infrared studies have revealed debris likely related to planet formation in orbit around ~30% of youthful, intermediate mass, main sequence stars. We present evidence, based on atmospheric pollution by various elements heavier than helium, that a comparable fraction of the white dwarf descendants of such main sequence stars are orbited by planetary systems. These systems have survived, at least in part, through all stages of stellar evolution that precede the white dwarf. During the time interval (~200 million years) that a typical polluted white dwarf in our sample has been cooling it has accreted from its planetary system the mass of one of the largest asteroids in our solar system (e.g., Vesta or Ceres). Usually, this accreted mass will be only a fraction of the total mass of rocky material that orbits these white dwarfs; for plausible planetary system configurations we estimate that this total mass is likely to be at least equal to that of the Sun's asteroid belt, and perhaps much larger. We report abundances of a suite of 8 elements detected in the little studied star G241-6 that we find to be among the most heavily polluted of all moderately bright white dwarfs.

Read more (307kb, PDF)

__________________


L

Posts: 131433
Date:
Permalink  
 

Astronomers keep turning up new exoplanets, and as the count rises, they keep edging closer to finding worlds like our own pale blue dot. Astronomer Jay Farihi thinks Earth-like worlds might be even more common in the universe than previously expected, based on evidence from rocky planets few astronomers are studying: The ones that don't exist anymore.
Farihi research subjects are white dwarfs. In our galaxy, about 90 percent of stars will end their lives in this incredibly dense state once the star sheds its outer material and only the core remains. This is the fate of our sun. White dwarfs usually have atmospheres composed of the light elements helium and hydrogen, as the heavy elements have settled to the core. But about 20 percent of white dwarfs are different, showing heavy elements-what astronomers call "metals"-in their atmospheres.

Read more

__________________


L

Posts: 131433
Date:
Permalink  
 

Looking for Planets Around White Dwarfs
Our Solar System is such a nice, ordered place. Eight planets have been happily circling our sun for 4.6 billion years, and the whole system is stable enough to life to have formed on at least one planet. And the solar system looks like it will continue to be a nice, stable place to live, at least for another six billion years. At that time, the sun will run out of hydrogen fuel, swell up into a red giant star (swallowing Mercury, Venus, and maybe Earth in the process), expel about half of its mass as a planetary nebula, and then shrink into a white dwarf. When the sun loses mass, its gravitational pull will weaken a little. This will cause the remaining planets to move outwards in their orbits a little bit, but they should remain bound to the white dwarf sun, forever circling the ashes of our star.

Source

__________________


L

Posts: 131433
Date:
B1257+12
Permalink  
 


Title: The Pulsar Planets: A Test Case of Terrestrial Planet Assembly
Authors: Brad Hansen, Hsin-Yi Shih, Thayne Currie

We model the assembly of planets from planetary embryos under the conditions suggested by various scenarios for the formation of the planetary system around the millisecond pulsar B1257+12. We find that the most likely models fall at the low angular momentum end of the proposed range. Models that invoke supernova fallback produce such disks, although we find that a solar composition disk produces a more likely evolution than one composed primarily of heavy elements. Furthermore, we find that dust sedimentation must occur rapidly as the disk cools, in order that the solid material be confined to a sufficiently narrow range of radii. A quantitative comparison between the observations and the best-fit models shows that the simulations can reproduce the observed eccentricities and masses, but have difficulty reproducing the compactness of the pulsar planet system. Finally, we examine the results of similar studies of solar system terrestrial planet accumulation and discuss what can be learned from the comparison.

Read more (177kb, PDF)

__________________


L

Posts: 131433
Date:
RE: White dwarf planets
Permalink  
 


Among the most poignant sights in the heavens are white dwarfs. Although they have a mass comparable to our suns, they are among the dimmest of all stars and becoming ever dimmer; they do not follow the usual pattern relating stellar mass to brightness. Astronomers think white dwarfs must not be stars so much as the corpses of stars. Each white dwarf was once much like our sun and shone with the same brilliance. But then it began to run out of fuel and entered its stormy death throes, swelling to 100 times its previous size and brightening 10,000-fold, before shedding its outer layers and shrivelling to a glowing cinder the size of Earth. For the rest of eternity, it will sit inertly, slowly fading to blackness.

Read more

__________________


L

Posts: 131433
Date:
Permalink  
 

Astronomers have turned to an unexpected place to study the evolution of planets - dead stars.
Observations made with NASAs Spitzer Space Telescope reveal six dead "white dwarf" stars littered with the remains of shredded asteroids.
This might sound pretty bleak, but it turns out the chewed-up asteroids are teaching astronomers about the building materials of planets around other stars.

Source

__________________
1 2 3  >  Last»  | Page of 3  sorted by
Quick Reply

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard