Author Topic: Astronomy & Planetary Science Thread  (Read 442036 times)

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #120 on: 07/27/2017 05:42 pm »
OK, they found that 3 out of 104 were really false positives, where only one was expected (statistically), then figured out why so it can be avoided in the future.
It's not clear to me Cabrera et al looked at all 104 of those planets, they were looking at specific planets for followup.
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Clearly valuable, but it does not change the overall exo-planet statistics much.  If you are trying to do any sort of planetary census, there are much bigger sources of error.  If you are zooming in on one particular star, though, it's worth double checking.
It's also important to note that these are K2 planets. K2 data is open to all: Discoveries are made by whoever publishes first and aren't validated by the Kepler team, so this doesn't necessarily have any implication for the main Kepler catalog. My impression is the normal Kepler validation process includes tests that would have flagged these.

Thanks for clarifying this was for K2, as that makes my posts up thread irrelevant here.

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #121 on: 07/27/2017 06:50 pm »
A Tale of Three Stellar Cities

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Using new observations from ESO’s VLT Survey Telescope, astronomers have discovered three different populations of young stars within the Orion Nebula Cluster. This unexpected discovery adds very valuable new insights for the understanding of how such clusters form. It suggests that star formation might proceed in bursts, where each burst occurs on a much faster time-scale than previously thought.

OmegaCAM — the wide-field optical camera on ESO’s VLT Survey Telescope (VST) — has captured the spectacular Orion Nebula and its associated cluster of young stars in great detail, producing a beautiful new image. This object is one of the closest stellar nurseries for both low and high-mass stars, at a distance of about 1350 light-years [1].

But this is more than just a pretty picture. A team led by ESO astronomer Giacomo Beccari has used these data of unparallelled quality to precisely measure the brightness and colours of all the stars in the Orion Nebula Cluster. These measurements allowed the astronomers to determine the mass and ages of the stars. To their surprise, the data revealed three different sequences of potentially different ages.

“Looking at the data for the first time was one of those ‘Wow!’ moments that happen only once or twice in an astronomer's lifetime,” says Beccari, lead ­author of the paper presenting the results. “The incredible quality of the OmegaCAM images revealed without any doubt that we were seeing three distinct populations of stars in the central parts of Orion.”

Monika Petr-Gotzens, co-author and also based at ESO Garching, continues, “This is an important result. What we are witnessing is that the stars of a cluster at the beginning of their lives didn’t form altogether simultaneously. This may mean that our understanding of how stars form in clusters needs to be modified.”

The astronomers looked carefully at the possibility that instead of indicating different ages, the different brightnesses and colours of some of the stars were due to hidden companion stars, which would make the stars appear brighter and redder than they really were. But this idea would imply quite unusual properties of the pairs, which have never before been observed. Other measurements of the stars, such as their rotation speeds and spectra, also indicated that they must have different ages [2].

“Although we cannot yet formally disprove the possibility that these stars are binaries, it seems much more natural to accept that what we see are three generations of stars that formed in succession, within less than three million years,” concludes Beccari.

The new results strongly suggest that star formation in the Orion Nebula Cluster is proceeding in bursts, and more quickly than had been previously thought.

http://www.eso.org/public/news/eso1723/

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #122 on: 07/27/2017 08:16 pm »
BBC article with additional reporting on the story.

Signal may be from first 'exomoon'

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But Dr Kipping said this is not the best way to gauge the potential detection.
He told BBC News: "We're excited about it... statistically, formally, it's a very high probability. But do we really trust the statistics? That's something unquantifiable. Until we get the measurements from Hubble, it may as well be 50-50 in my mind."
The candidate moon is known as Kepler-1625b I and is observed around a star that lies some 4,000 light-years from Earth. On account of its large size, team members have dubbed it a "Nep-moon".
A current theory of planetary formation suggests such an object is unlikely to have formed in place with its Jupiter-mass planet, but would instead be an object captured by the gravity of the planet later on in the evolution of this planetary system.
The researchers could find no predictions of a Neptune-sized moon in the literature, but Dr Kipping notes that nothing in physics prevents one.
A handful of possible candidates have come to light in the past, but none as yet has been confirmed.
"I'd say it's the best [candidate] we've had," Dr Kipping told me.
"Almost every time we hit a candidate, and it passes our tests, we invent more tests until it finally dies - until it fails one of the tests... in this case we've applied everything we've ever done and it's passed all of those tests. On the other hand, we only have three events."

http://www.bbc.co.uk/news/science-environment-40741545

Offline hop

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Re: Exoplanets And Stars Thread
« Reply #123 on: 07/28/2017 07:31 am »
Here's Alex Teachey and David Kipping (authors of the exomoon paper) talking about the result, and why they ended up going public now


Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #124 on: 07/28/2017 09:53 am »
Good news for James Cameron as if you can get moons the size of Neptune there's nothing to say you couldn't get moons the size of Earth around a super sized gas giant. So you would end up with a system as seen in the film like Avatar if you had more than one of them.

Offline rubtest

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Re: Exoplanets And Stars Thread
« Reply #125 on: 07/28/2017 10:06 am »
Was there any search for tiny moons around the biggest MOONS in the solar systems like Titan , Ganymede ?
I am almost sure it is gravitational an impossibility because of the Jupiter / Saturn strong gravitational fields.

Offline Star One

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Exoplanets And Stars Thread
« Reply #126 on: 07/28/2017 06:52 pm »
New Nature article about the possible exomoon discovery with some useful quotes.

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Jean Schneider, an exomoon hunter at the Paris Observatory, says that the authors were right to make this candidate public. Now, he says, “other people can re-analyse the Kepler data for Kepler-1625 b and make their own opinion”.

Astronomer David Bennett at the University of Notre Dame in Indiana agrees. “I don’t consider it to be terribly controversial to put a paper on the arXiv before it is peer reviewed,” he says. “It is often the case that the journal doesn’t really find the best person to review the paper,” he adds. “If it is posted on arXiv.org, then you might get much more useful comments from a real expert who wasn’t picked by the journal to review the paper.”

http://www.nature.com/news/why-astronomers-reluctantly-announced-a-possible-exomoon-discovery-1.22377
« Last Edit: 07/28/2017 06:52 pm by Star One »

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #127 on: 08/01/2017 02:36 am »
Four new short-period giant planets discovered

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Astronomers have detected four new giant exoplanets as part of the Hungarian-made Automated Telescope Network-South (HATSouth) exoplanet survey. The newly found alien worlds are about the size of Jupiter, but less massive. They transit moderately bright stars and have short orbital periods.

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According to the paper, HATS-45b is the largest and most massive exoworld of all the newly discovered exoplanets. It has a radius of about 1.29 Jupiter radii and is 30 percent less massive than our solar system's biggest planet. It orbits its parent star every 4.19 days.

HATS-46b has the longest orbital period and is the least massive of the newly found quartet. It has only 17 percent of the mass of Jupiter, however a radius of approximately 0.9 Jupiter radii. It takes this planet 4.74 days to fully circle its host.

HATS-43b and HATS-44b are similar in radius—1.18 and 1.07 Jupiter radii respectively. HATS-43b has a mass of 0.26 Jupiter masses, while HATS-44b is about two times more massive—0.56 Jupiter masses. The shortest orbital period among the four newly identified planets belongs to HATS-44b, which orbits its star in just 2.74 days. When it comes to HATS-43b, it takes it approximately 4.39 days to circle its parent star.

Offline Phil Stooke

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Re: Exoplanets And Stars Thread
« Reply #128 on: 08/01/2017 02:57 am »
"Was there any search for tiny moons around the biggest MOONS in the solar systems like Titan , Ganymede ?"

I can't give a source at the moment, but I believe there have been searches for rings and moons around the larger moons of Saturn, at least.

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #129 on: 08/01/2017 04:40 pm »

Exomoons: Rare in Inner Stellar Systems?

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With all this in mind, every paper that comes out of HEK gets my attention. Kipping (Columbia University), working with graduate student Alex Teachey and citizen scientist Allan Schmitt, has now produced a paper that takes a significant step as the investigation proceeds. We have no detection yet — more about that in a moment — but we do have a broader result showing that exomoons are unusual in the inner regions of the systems surveyed.

Kipping and Teachey looked at 284 viable moon-hosting Kepler planetary candidates to search for moons around planets from Earth to Jupiter in size and distances from their stars of 0.1 to 1 AU. This finding seems to be getting less attention in the press than it deserves, so let’s dig into the paper on it:

Our results place new upper limits on the exomoon population for planets orbiting within about 1 AU of their host star, upper limits that are remarkably low. We have also analyzed subsets of the ensemble to test the effect of various data cuts, and we have identified the regime in which the OSE model presented in Heller (2014) breaks down, which we call the “Callisto Effect” — beyond 20 planetary radii, discrepancies appear in the results.

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Back to the paper:

Our analysis suggests that exomoons may be quite rare around planets at small semi-major axes, a finding that supports theoretical work suggesting moons may be lost as planets migrate inward. On the other hand, if the dearth of exomoons can be read as a reliable indicator of migration, our results suggest a large fraction of the planets in the ensemble have migrated to their present location.

And that is a pointer to which we need to pay attention. Is a lack of exomoons a marker for planetary migration? If further analysis determines that it is, then we’ve found an extremely handy tool for studying the formation history of other stellar systems

https://www.centauri-dreams.org/?p=38214

Offline Star One

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Exoplanets And Stars Thread
« Reply #130 on: 08/03/2017 08:32 am »
Hubble detects exoplanet with glowing water atmosphere

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Scientists have discovered the strongest evidence to date for a stratosphere on a planet outside our solar system, or exoplanet. A stratosphere is a layer of atmosphere in which temperature increases with higher altitudes.

“This result is exciting because it shows that a common trait of most of the atmospheres in our solar system — a warm stratosphere — also can be found in exoplanet atmospheres,” said Mark Marley, study co-author based at NASA’s Ames Research Center in California’s Silicon Valley. “We can now compare processes in exoplanet atmospheres with the same processes that happen under different sets of conditions in our own solar system.”

Reporting in the journal Nature, scientists used data from NASA’s Hubble Space Telescope to study WASP-121b, a type of exoplanet called a “hot Jupiter.” Its mass is 1.2 times that of Jupiter, and its radius is about 1.9 times Jupiter’s — making it puffier. But while Jupiter revolves around our sun once every 12 years, WASP-121b has an orbital period of just 1.3 days. This exoplanet is so close to its star that if it got any closer, the star’s gravity would start ripping it apart. It also means that the top of the planet’s atmosphere is heated to a blazing 4,600 degrees Fahrenheit (2,500 degrees Celsius), hot enough to boil some metals. The WASP-121 system is estimated to be about 900 light-years from Earth — a long way, but close by galactic standards.

https://astronomynow.com/2017/08/02/hubble-detects-exoplanet-with-glowing-water-atmosphere/

Astronomers discover ‘heavy metal’ supernova rocking out

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Following the recent discovery of one of these “superluminous supernovas”, a team of astronomers led by Matt Nicholl from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., has uncovered vital clues about where some of these extraordinary objects come from.

Cambridge University’s Gaia Science Alerts team discovered this supernova, dubbed SN 2017egm, on May 23, 2017 with the European Space Agency’s Gaia satellite. A team led by Subo Dong of the Kavli Institute for Astronomy and Astrophysics at Peking University used the Nordic Optical Telescope to identify it as a superluminous supernova.

SN 2017egm is located in a spiral galaxy about 420 million light years from Earth, making it about three times closer than any other superluminous supernova previously seen. Dong realized that the galaxy was very surprising, as virtually all known superluminous supernovas have been found in dwarf galaxies that are much smaller than spiral galaxies like the Milky Way.

Building on this discovery, the CfA team found that SN 2017egm’s host galaxy has a high concentration of elements heavier than hydrogen and helium, which astronomers call “metals”. This is the first clear evidence for a metal-rich birthplace for a superluminous supernova. The dwarf galaxies that usually host superluminous supernovas are known to have a low metal content, which was thought to be an essential ingredient for making these explosions.

“Superluminous supernovas were already the rock stars of the supernova world,” said Nicholl. “We now know that some of them like heavy metal, so to speak, and explode in galaxies like our own Milky Way.”

https://astronomynow.com/2017/08/02/astronomers-discover-heavy-metal-supernova-rocking-out/
« Last Edit: 08/03/2017 09:06 am by Star One »

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #131 on: 08/03/2017 07:33 pm »
Disintegrating Rocky Exoplanets

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We discuss a new class of exoplanets that appear to be emitting a tail of dusty effluents. These disintegrating planets are found close to their host stars and have very hot, and likely molten, surfaces. The properties of the dust should provide a direct probe of the constituent material of these rocky bodies.

https://arxiv.org/abs/1708.00633

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #132 on: 08/03/2017 07:53 pm »
Gravity Waves Detected In Sun's Interior Reveal Rapidly Rotating Core

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Scientists using the ESA/NASA SOHO solar observatory have found long-sought gravity modes of seismic vibration that imply the Sun’s core is rotating four times faster than its surface.

http://m.esa.int/Our_Activities/Space_Science/Space_Science/Gravity_waves_detected_in_Sun_s_interior_reveal_rapidly_rotating_core

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #133 on: 08/04/2017 08:10 pm »
Bad News For Proxima b: An Earth-Like Atmosphere Might Not Survive There

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So it’s not all bad news, but it doesn’t inspire a lot of confidence either. Unless Proxima b is a volcanically-active planet and subject to a lot of cometary impacts, it is not likely be temperate, water-bearing world. Most likely, its climate will be analogous to Mars – cold, dry, and with water existing mostly in the form of ice. And as for indigenous life emerging there, that’s not too likely either.

These and other recent studies have painted a rather bleak picture about the habitability of red dwarf star systems. Given that these are the most common types of stars in the known Universe, the statistical likelihood of finding a habitable planet beyond our Solar System appears to be dropping. Not exactly good news at all for those hoping that life will be found out there within their lifetimes!

But it is important to remember that what we can say definitely at this point about extra-solar planets is limited. In the coming years and decades, next-generation missions – like the James Webb Space Telescope (JWST) and the Transiting Exoplanet Survey Satellite (TESS) –  are sure to paint a more detailed picture. In the meantime, there’s still plenty of stars in the Universe, even if most of them are extremely far away!

https://www.universetoday.com/136641/bad-news-proxima-b-earth-like-atmosphere-might-not-survive/amp/

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #134 on: 08/09/2017 02:56 pm »
Four Earth-sized planets detected orbiting the nearest sun-like star





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A new study by an international team of astronomers reveals that four Earth-sized planets orbit the nearest sun-like star, tau Ceti, which is about 12 light years away and visible to the naked eye. These planets have masses as low as 1.7 Earth mass, making them among the smallest planets ever detected around nearby sun-like stars. Two of them are super-Earths located in the habitable zone of the star, meaning they could support liquid surface water.

The planets were detected by observing the wobbles in the movement of tau Ceti. This required techniques sensitive enough to detect variations in the movement of the star as small as 30 centimeters per second.

"We are now finally crossing a threshold where, through very sophisticated modeling of large combined data sets from multiple independent observers, we can disentangle the noise due to stellar surface activity from the very tiny signals generated by the gravitational tugs from Earth-sized orbiting planets," said coauthor Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz.

According to lead author Fabo Feng of the University of Hertfordshire, UK, the researchers are getting tantalizingly close to the 10-centimeter-per-second limit required for detecting Earth analogs. "Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth's habitability through comparison with these analogs," Feng said. "We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals."

The outer two planets around tau Ceti are likely to be candidate habitable worlds, although a massive debris disc around the star probably reduces their habitability due to intensive bombardment by asteroids and comets.

The same team also investigated tau Ceti four years ago in 2013, when coauthor Mikko Tuomi of the University of Hertfordshire led an effort in developing data analysis techniques and using the star as a benchmark case. "We came up with an ingenious way of telling the difference between signals caused by planets and those caused by star's activity. We realized that we could see how star's activity differed at different wavelengths and use that information to separate this activity from signals of planets," Tuomi said.

The researchers painstakingly improved the sensitivity of their techniques and were able to rule out two of the signals the team had identified in 2013 as planets. "But no matter how we look at the star, there seem to be at least four rocky planets orbiting it," Tuomi said. "We are slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system."

Color difference makes a difference: four planet candidates around tau Ceti

If confirmed, there would seem to be decent room for an Earth mass planet in the middle of the habitable zone which wouldn't currently be detectable.

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #135 on: 08/09/2017 06:49 pm »
Is Tau Ceti more sunlike than either of the Alpha Centauri stars then?

Offline Bob Shaw

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Re: Exoplanets And Stars Thread
« Reply #136 on: 08/09/2017 07:12 pm »
Have any planets been *really* detected around Bernard's Star? It would be rather nice!

Online zubenelgenubi

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Re: Exoplanets And Stars Thread
« Reply #137 on: 08/09/2017 07:37 pm »
Re: nearest sun-like star

Star                      Mass, in solar masses   Spectral Type (Sun = G2V)

Alpha Centauri A    1.10                           G2V

Alpha Centauri B    0.91                            K1V

Sirius A                 2.02                            A1V

Epsilon Eridani       0.82                            K2V

Procyon A             1.50                            F5V-IV

Epsilon Indi A        0.76                             K5V

Tau Ceti                0.78                            G8V


They may be applying data in a partly-subjective manner to claim "nearest sun-like star:"
distance, Main Sequence star near 1 solar mass, not part of a binary or multiple star system, etc.
« Last Edit: 08/09/2017 07:46 pm by zubenelgenubi »
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Offline Bynaus

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Re: Exoplanets And Stars Thread
« Reply #138 on: 08/09/2017 07:38 pm »
It is noteworthy that if the planetary system is aligned with the debris disk (which seems very likely), the true masses of the four planets are about double their minimum masses. So the inner two planets would be large super-Earths, whereas the outer two would be mini-Neptunes.

@StarOne: I think of these three stars, Alpha Cen A is most sun-like. It is also a G2V type, is only 10% more massive and has a similar rotation period. Then Tau Ceti, then Alpha Cen B.

@Bob Shaw: the planets that van de Kamp thought were there (in the 1960ies) do not exist, this we know for sure. Otherwise, we only have upper limits on mass/distance (<7.5 Earth masses in the habitable zone, e.g.). The Red Dots project is bound to find out!
More of my thoughts: www.final-frontier.ch (in German)

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #139 on: 08/09/2017 08:23 pm »
It is noteworthy that if the planetary system is aligned with the debris disk (which seems very likely), the true masses of the four planets are about double their minimum masses. So the inner two planets would be large super-Earths, whereas the outer two would be mini-Neptunes.

@StarOne: I think of these three stars, Alpha Cen A is most sun-like. It is also a G2V type, is only 10% more massive and has a similar rotation period. Then Tau Ceti, then Alpha Cen B.

@Bob Shaw: the planets that van de Kamp thought were there (in the 1960ies) do not exist, this we know for sure. Otherwise, we only have upper limits on mass/distance (<7.5 Earth masses in the habitable zone, e.g.). The Red Dots project is bound to find out!

Thank you. Could you direct me towards any articles or papers speculating on the origins of the debris disk around Tau Ceti?

 

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