* Astronomy

Members Login
Post Info TOPIC: Gliese 86b


L

Posts: 131433
Date:
RE: Gliese 86b
Permalink  
 


Title: Orbital and Evolutionary Constraints on the Planet Hosting Binary GJ 86 from the Hubble Space Telescope
Authors: J. Farihi, Howard E. Bond, P. Dufour, N. Haghighipour, G. H. Schaefer, J. B. Holberg, M. A. Barstow, M. R. Burleigh

This paper presents new observations of the planet-hosting, visual binary GJ 86 (HR 637) using the Hubble Space Telescope. Ultraviolet and optical imaging with WFC3 confirms the stellar companion is a degenerate star and indicates the binary semimajor axis is larger than previous estimates, with a > 28 AU. Optical STIS spectroscopy of the secondary reveals a helium-rich white dwarf with C2 absorption bands and Teff = 8180 K, thus making the binary system rather similar to Procyon. Based on the 10.8 pc distance, the companion has 0.59 solar masses and descended from a main-sequence A star of 1.9 solar masses with an original orbital separation a > 14 AU. If the giant planet is coplanar with the binary, the mass of GJ 86Ab is between 4.4 and 4.7 Jupiter masses. The similarity of GJ 86 and Procyon prompted a re-analysis of the white dwarf in the latter system, with the tentative conclusion that Procyon hosts a planetesimal population. The periastron distance in Procyon is 20% smaller than in alpha Cen AB, but the metal-enriched atmosphere of Procyon B indicates that the planet formation process minimally attained 25 km bodies, if not small planets as in alpha Cen.

Read more (5153kb, PDF)



__________________


L

Posts: 131433
Date:
Permalink  
 


Expand


__________________


L

Posts: 131433
Date:
RE: Gleise 876
Permalink  
 


The planet recently discovered around Gleise 876 is unlikely to bear life because its orbit is so close to the star, giving the planet an extremely high surface temperature.

M class stars have usually considered unsuitable for SETI observations.

The "Goldilocks" analogy suggested that planets whose temperature was "just right" for liquid water, and life, would orbit so close to their star that they would be tidally locked.
As a result, the world would quickly become "too hot" on one side, and "too cold" on the other: the atmosphere would boil off on the light side, and freeze out on the dark side. These dwarf stars also flare, producing X and UV radiation that would challenge any life on the surface.

"Simple theory said that terrestrial planets in orbit around M stars will be uninhabitable, and uninhabited. But we are not confined to simple theory any more. Recent models predict sustainable atmospheres and substellar liquid water regimes…A growing appreciation for natural sun screens that developed early in the evolution of life on Earth, and a speculation that niche sterilizing events might actually speed evolution towards complex life, make M stars worth considering once again. And reconsider them we will!" - Jill Tarter, Director of the Centre for SETI Research at the SETI Institute.


__________________


L

Posts: 131433
Date:
RE: Gliese 86b
Permalink  
 


Gliese 86 (Gl 86, and also known as HD 13445) is seen in the southern constellation Eridanus (The River).
It is a bright, rather cool K1 dwarf star, somewhat less massive than the Sun (about 0.79 solar mass).
It is also intrinsically fainter than the Sun (about 0.4 solar luminosity). However, since it is quite nearby, about 35 light-years only (10.9 +/-0.08 pc), its apparent magnitude is comparatively bright and it is just at the limit of what can be seen with the unaided eye (mV= 6.12).
Contrary to most stars with known planetary companions, Gliese 86 contains less metals than our Sun, by a factor of two.


40 min of H band imaging with SDI at the ESO VLT (north up east to the left). This image is taken through the SDI narrow band filter with a central wavelength of 1.575 nm. It is one out of four simultaneously taken images. The bright star in the centre is the exoplanet host star Gl 86A. The about 10 magnitude fainter companion Gl 86B is located ∼2 arcsec east of the primary.
Several bright speckles are clearly visible close to the primary star.


Title: Gl86B: a white dwarf orbits an exoplanet host star
Authors:
M. Mugrauer, R. Neuhaeuser

In this letter we present our first high contrast NACO/SDI observations of the exoplanet host star Gl 86 and results from NACO spectroscopy. Els et al. (2001) found a faint co-moving companion located only ~2 arcsec east of the exoplanet host star Gl 86A.
Our high contrast SDI observations rule out additional stellar companions from 1AU up to 23AU, and are sensitive for faint T dwarf companions down to 35MJup. We present evidence for orbital motion of Gl 86B around the exoplanet host star Gl 86A, which finally confirms that this is a bound binary system.

With the given photometry from Els et al. (2001) and the obtained NACO spectroscopy we prove that the companion Gl 86B is a cool white dwarf with an effective temperature of 5000 +/-500K.
This is the first confirmed white dwarf companion to an exoplanet host star and the first observational confirmation that planets survive the post main sequence evolution of a star from which they are separated by only one to two dozen astronomical units (giant phase and planetary nebula) as expected from theory.

Read More (PDF 830kb)


Position(2000): RA 32.600005 , Dec -50.825314

Name: GI86 b
M.sini: 4.01 MJ
Semi-major axis: 0.11 AU
Orbital period: 15.766 +/- 0.04 d.
Eccentricity: 0.046 +/- 0.004
Omega (deg): 266
T_peri (JD-2450000): 1146.54


-- Edited by Blobrana at 08:27, 2005-06-16

__________________


L

Posts: 131433
Date:
RE: New Discovery
Permalink  
 




Observed Properties of Exoplanets: Masses, Orbits, and Metallicities
Authors:
G.Marcy, R.P.Butler, D.A.Fischer, S.S.Vogt, J.T.Wright, C. G. Tinney, H. R.A. Jones.

We review the observed properties of exoplanets found by the Doppler technique which has revealed 152 exoplanets to date. We focus on our ongoing 18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian Telescopes carried out with a uniform Doppler precision of 3 m/s. The 104 planets detected in our survey have masses as low as 15 M_Earth orbiting between 0.03 and 5.5 AU.
The mass distribution rises toward the lowest detectable masses as dN/dM is proportional to M^-1.1. Nearly all giant planets orbiting within 2 AU of all FGK stars within 30 pc have now been discovered.
The distribution of semi-major axes rises from 0.3 - 3.0 AU (dN/dlog a)
, but remains unknown for larger orbits. Extrapolation suggests that 12% of the FGK stars harbour exoplanets within 20 AU. The median orbital eccentricity is 0.25 (excluding those tidally circularized), lower than previously measured.
Planets orbiting beyond 3 AU continue to exhibit non-zero eccentricity, suggesting that the circular orbits of giant planets in our Solar System are unusual.
The occurrence rate of ''hot Jupiters'' of FGK stars is 1.2�0.2%.
The probability of occurrence of planets varies as the square of the stellar metal abundance, P \propto N^2_Fe, ranging from 3% for stars of subsolar metallicity to 25% for stars with Fe/H (less than) +0.3.
Nearly 14% of planet-bearing stars harbour multiple-planet systems, occasionally locked in resonances. Kepler and COROT should measure the occurrence of earth-sized planets. The Space Interferometry Mission (SIM) will detect planets with masses as low as 3 M_ Earth orbiting within 2 AU of nearby stars and will measure masses, orbits and multiplicity.
These candidate rocky planets will motivate spectroscopic follow-up by the ''Terrestrial Planet Finder'' and Darwin.

Read More (PDF)

__________________


L

Posts: 131433
Date:
Gliese 86b
Permalink  
 


Astronomers have now discovered an Earth-like planet orbiting a distant normal star. Previously over 150 gas-giant planets like Jupiter had been so discovered. Slight, fast, but regular wobbles of nearby small M-dwarf star Gliese 876 showed evidence for a planet with a likely mass slightly higher than a minimum six times the mass of Earth. The planet's small mass indicates that it is likely terrestrial in nature, similar in composition to the inner planets of our Solar System. If indeed made predominantly of rock, the planet's surface gravity would not even be able to contain the gasses of a Jupiter-like planet. 

*THIS IMAGE HAS BEEN REMOVED AS A RESULT OF A DMCA TAKEDOWN REQUEST* -- Sparklit

The newly discovered planet would not make a good vacation spot for humans, however, as it orbits so close that the surface temperature probably tops a searing 200 degrees Celsius. The system is illustrated in thedrawing, as seen from a hypothetical moon orbiting one of the two Jupiter-like planets already known. The newly discovered terrestrial-like planet is depicted in the insert. Gliese 876 lies only 15 light-years away and is visible with binoculars toward the constellation of Aquarius.



-- Edited by Blobrana on Wednesday 16th of November 2011 11:48:07 PM

__________________


L

Posts: 131433
Date:
RE: GJ 876 Planetary System
Permalink  
 


The GJ 876 Planetary System -- A Progress Report
Authors: G. Laughlin, R. P. Butler, D. A. Fischer, G. W. Marcy, S. S. Vogt, A. S. Wolf.

We present an updated analysis of the GJ 876 planetary system based on an augmented data set that incorporates 65 new high-precision radial velocities obtained with the Keck telescope from 2001 to 2004.
These new radial velocities permit a more accurate characterization of the planet-planet interactions exhibited by the system.
Self-consistent three-body orbital fits (which incorporate both the estimated instrumental uncertainties and 6 m/s Gaussian stellar jitter) continue to show that GJ 876 b and GJ 876 c are participating in a stable and symmetric 2:1 resonance condition in which the lowest order, eccentricity type mean-motion resonance variables are all librating.
The planets are also locked in a secular resonance which causes them to librate about apsidal alignment. The small libration widths of all three resonances likely point to a dissipative history of differential migration for the two planets in the system.


The red dwarf GJ 876 (RA=22 53, DEC=14 16) is observable from both hemispheres, and is distinguished by being the fortieth-nearest stellar system, with a Hipparcos-determined distance of 4.69 pc.


Read more (PDF)


__________________


L

Posts: 131433
Date:
RE: PSR B1257+12
Permalink  
 


Hum,
Of course the smallest planet orbiting outside our Solar System to date was discovered by two astronomers orbiting around a pulsar called PSR B1257+12.
The new world is about one fifth the size of Pluto, (0.02 Earth masses).
The other planets in the system have masses of 4.3, and 3.9 Earth masses
Compared to our solar system, the three planets would fit within the orbit of Mercury with the respective orbital periods of 25, 66 and 98 days.
There is some evidence that the pulsar may have an asteroid belt that appears to be located well beyond the orbit of Mars, just like it happens in our solar system.

A pulsar is a spinning neutron star producing powerful beams of radiation.
The new planet is orbiting inside a large cloud of hot, charged gas that surrounds the pulsar and is some 1,500 light-years away from Earth in the constellation Virgo.
Details of the work were announced at an astronomy meeting held in Aspen, US in February 2005
Pulsars are formed from the collapsed cores of so-called "supergiant" stars that have exploded.
The discovery was made by Alex Wolszczan of Pennsylvania State University, US, and Maciej Konacki of the California Institute of Technology (Caltech).
The orbit of the new planet is close to the average distance from our Sun to the asteroid belt.
The orbits of three planets discovered orbiting the same pulsar in 1992 were almost in exact proportion to the spacings between Mercury, Venus and Earth in our Solar System.
Wolszczan and Konacki say the new planet could mark the fringes of the pulsar's planetary system, just like Pluto marks the edge of ours.

The new planet was discovered with the Arecibo radio telescope in Puerto Rico.
The 6.2 ms pulsar, PSR B1257+12, has been regularly timed with the Arecibo telescope since late 1990.
Assuming the standard pulsar mass of 1.4 solar masses, the derived masses of planets B and C are 4.3+/-0.2 and 3.9+/-0.2 M⊕, respectively.
The corresponding orbital inclinations of 53° +/-4° and 47° +/-3° (or 127° and 133°) imply that the two orbits are almost coplanar.
This result, together with the known near 3:2 resonance between the orbits of the two planets, strongly supports the hypothesis of a disk origin of the PSR B1257+12 planetary system.


__________________


L

Posts: 131433
Date:
RE: Gliese 876d
Permalink  
 


The team measures a minimum mass for the planet of 5.9 Earth masses, orbiting Gliese 876 with a period of 1.94 days at a distance of 0.021 astronomical units (AU), or 2 million miles. The orbital plane is tilted 40 degrees to our line of sight.


Expand

"In a two-day orbit , it's about 200 degrees Celsius too hot for liquid water. That tends to lead us to the conclusion that the most probable composition of this thing is like the inner planets of this solar system--a nickel-iron rock, a rocky planet, a terrestrial planet." - Marcy, Butler, theoretical astronomer.


Download Movie

This animation shows the newly discovered planet and its two larger siblings as they orbit the M dwarf star Gliese 876. The star and the orbits are to scale; the planet sizes are exaggerated. In addition, the orbits are shown inclined at an angle of 50 degrees, which is how they appear in our sky.

The outermost planet, known as Gliese 876b, was discovered in 1998. It orbits the star once every 61 Earth days, and has about twice the mass of Jupiter, our own solar system's largest planet.
That makes it roughly 600 times the mass of the Earth. The middle planet, Gliese 876c, was discovered in 2001. It orbits the star once every 30 days and has about half the mass of Jupiter, or roughly 150 times the mass of the Earth.

The new planet has about twice the radius of the Earth and about seven-and-a-half times it’s mass, and orbits the star once every two days.


Download Movie

This animation takes us on a flythrough of the Gliese 876 system. The star, the orbits and the sizes of all three known planets are to scale.

We first see the outermost planet, Gliese 876b, which was discovered in 1998. It orbits the star once every 61 Earth days, and has about twice the mass of Jupiter, our own solar system's largest planet.
That makes it roughly 600 times the mass of the Earth. Next we see the middle planet, Gliese 876c, which was discovered in 2001. It orbits the star once every 30 days and has about half the mass of Jupiter, or roughly 150 times the mass of the Earth.

Finally we come to the newly discovered planet. It has about twice the radius of the Earth and about seven-and-a-half times its mass, and it orbits the star once every two days.


Expand

These three graphs show the observational data and the best theoretical fit for each of the three planets known to orbit the star Gliese 876. From top to bottom the panels are for the newly discovered planet, the middle planet and the outermost planet. The vertical axes (which are different for each) refer to the tiny back-and-forth motions the orbiting planets cause in their parent star. The colours refer to the year the observations were made. The wide variations seen in the second panel reflect the strong gravitational perturbations the planets exert on one another.

__________________


L

Posts: 131433
Date:
RE: Gliese 876 planet
Permalink  
 


Researchers speaking today at the National Science Foundation announced the discovery of the smallest extrasolar planet yet found - one that resembles our own planet much more than any other yet discovered.

The planet is between 6 to 9 times the mass of Earth and orbits its host star once every 1.9 days at a distance of 2 million miles. The surface of the planet is hot and has been estimated from observations and calculations to be between 400-700F.
The host star which this planet circles is Gliese 876, (Gl 876), a small red dwarf 5 times less massive than the Sun. It is therefore considerably less luminous: about 600 times less than the Sun. It is also very close to us, at only 15.2 light-years. This makes it the 40th closest star to our Sun .

"155 extrasolar planets have been discovered over the past decade. To date all of these planets are gas giants - similar to Jupiter and Saturn with masses 100 to 1000 times that of Earth. Last year we reported two Neptune-class planets. Today we report a new type of planet - much lower than any reported around a sunlike star. It is more similar to Earth than any previously discovered planet. We have no analogy like this in our solar system. We do not know its composition - whether it is all rock or some chimera of rock, ice, and a thick atmosphere - perhaps a hybrid of Earth and Uranus." Geoff Marcy, astronomer.



The discovery of this planet was serendipitous. There were two previously discovered Jupiter-sized planets orbiting this star further out.
"These two planets pull on each other and change their orbits notably every year. We were using the Keck telescope to study these two planets and discovered this small planet fortuitously using the Doppler effect. we would have announced this 3 years ago except for the signal of a third planet" - Paul Butler.
Numerous improvements have been made in use of the Doppler effect.

"This technology allows us to measure the speed of a star to an accuracy +/- 1 meter per second - that's human walking speed"
"For the first time we are able to find our planetary kin among the stars" - Geoff Marcy.


Previously well known as Ross 780, it is located in the southeastern part of Constellation Aquarius, the Water Bearer.
Like other red dwarf stars, it is not visible to the naked eye.



-- Edited by Blobrana at 19:29, 2005-06-13

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

Please log in to post quick replies.



Create your own FREE Forum
Report Abuse
Powered by ActiveBoard