Author Topic: Astronomy & Planetary Science Thread  (Read 439141 times)

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #160 on: 08/18/2017 07:23 pm »
Scientists improve brown dwarf weather forecasts

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To make sense of the ups and downs of brightness, scientists had to rethink their assumptions about what was going on in the brown dwarf atmospheres. The best model to explain the variations involves large waves, propagating through the atmosphere with different periods. These waves would make the cloud structures rotate with different speeds in different bands.

University of Arizona researcher Theodora Karalidi used a supercomputer and a new computer algorithm to create maps of how clouds travel on these brown dwarfs.

“When the peaks of the two waves are offset, over the course of the day there are two points of maximum brightness,” Karalidi said. “When the waves are in sync, you get one large peak, making the brown dwarf twice as bright as with a single wave.”

The results explain the puzzling behavior and brightness changes that researchers previously saw. The next step is to try to better understand what causes the waves that drive cloud behavior.

https://astronomynow.com/2017/08/17/scientists-improve-brown-dwarf-weather-forecasts/

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #161 on: 08/18/2017 09:50 pm »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #162 on: 08/18/2017 11:16 pm »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #163 on: 08/18/2017 11:19 pm »
Only in as far as most stars are believed to have planets. Most of the nearest stars to 16.3 ly* still don't even have candidate planets yet.

*To 21 ly, as Wikipedia doesn't seem to have a list of stars from 16.3 - 20 ly.

Offline redliox

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Re: Exoplanets And Stars Thread
« Reply #164 on: 08/19/2017 05:30 am »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Only in as far as most stars are believed to have planets. Most of the nearest stars to 16.3 ly* still don't even have candidate planets yet.

*To 21 ly, as Wikipedia doesn't seem to have a list of stars from 16.3 - 20 ly.

Although fortunately we have TESS and the JWST coming up, I'd like to see an effort to catalog specifically our neighboring stars.  I don't expect it to be easy, but it would be worth it.
"Let the trails lead where they may, I will follow."
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Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #165 on: 08/19/2017 08:14 am »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Aren't Pale Red Dot now studying all our local red dwarfs for planets?

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #166 on: 08/19/2017 11:38 am »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Only in as far as most stars are believed to have planets. Most of the nearest stars to 16.3 ly* still don't even have candidate planets yet.

*To 21 ly, as Wikipedia doesn't seem to have a list of stars from 16.3 - 20 ly.

Although fortunately we have TESS and the JWST coming up, I'd like to see an effort to catalog specifically our neighboring stars.  I don't expect it to be easy, but it would be worth it.


ESPRESSO
should also be helpful with that. It's an order of magnitude more sensitive than HARPS and should be online this year (if not already, it saw first light nearly a year ago).

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #167 on: 08/19/2017 02:24 pm »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Aren't Pale Red Dot now studying all our local red dwarfs for planets?

AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #168 on: 08/19/2017 02:25 pm »
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Aren't Pale Red Dot now studying all our local red dwarfs for planets?

AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.

Out of interest what was the criteria for choosing those three out of all the red dwarfs near Sol?

Offline Alpha_Centauri

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Re: Exoplanets And Stars Thread
« Reply #169 on: 08/19/2017 02:42 pm »
Because they are visible from La Silla at this time of year and are bright enough for high-res spectroscopy.
« Last Edit: 08/19/2017 02:46 pm by Alpha_Centauri »

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #170 on: 08/19/2017 03:21 pm »
There is a candidate for a Super Earth around Lalande 21185, the 6th closest main sequence star / 4th closest star system (it's missing from CuddlyRocket's list).

Offline Hungry4info3

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Re: Exoplanets And Stars Thread
« Reply #171 on: 08/19/2017 05:33 pm »
Aren't Pale Red Dot now studying all our local red dwarfs for planets?
AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.
Out of interest what was the criteria for choosing those three out of all the red dwarfs near Sol?
Because they are visible from La Silla at this time of year and are bright enough for high-res spectroscopy.
To add to that, there has been a shift in in strategy in recent years for radial velocity surveys away from "Sample numerous stars a few times each" to "Sample a few stars numerous times each." The first one easily catches your intermediate- and long-period giant planets, but to get down to low-mass planets, you have to really drill a star to get enough data to overcome statistical noise. Detecting low-mass planets in the solar neighborhood is now finally feasible, so rather than observing all the local M dwarfs in the sky, we're focusing on hitting a few nearby, bright systems.
« Last Edit: 08/19/2017 05:34 pm by Hungry4info3 »

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #172 on: 08/19/2017 05:45 pm »
Aren't Pale Red Dot now studying all our local red dwarfs for planets?
AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.
Out of interest what was the criteria for choosing those three out of all the red dwarfs near Sol?
Because they are visible from La Silla at this time of year and are bright enough for high-res spectroscopy.
To add to that, there has been a shift in in strategy in recent years for radial velocity surveys away from "Sample numerous stars a few times each" to "Sample a few stars numerous times each." The first one easily catches your intermediate- and long-period giant planets, but to get down to low-mass planets, you have to really drill a star to get enough data to overcome statistical noise. Detecting low-mass planets in the solar neighborhood is now finally feasible, so rather than observing all the local M dwarfs in the sky, we're focusing on hitting a few nearby, bright systems.

Thank you all. I am constantly amazed that we are able to make such fine measurements of objects so far, it almost seems remarkable.

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #173 on: 08/20/2017 08:27 pm »
There is a candidate for a Super Earth around Lalande 21185, the 6th closest main sequence star / 4th closest star system (it's missing from CuddlyRocket's list).

I didn't include Lalande 21185 in my list because I was listing those stars not known to have a planet and this star has a pretty solid candidate. But then I forgot to adjust the ordinal numbering (Sirius should be the 7th nearest etc.)!  :-[

Offline Bynaus

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Re: Exoplanets And Stars Thread
« Reply #174 on: 08/22/2017 07:50 am »
Dynamics of a Probable Earth-mass Planet in the GJ 832 System

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The stability of planetary orbits around the GJ 832 star system, which contains inner (GJ 832c) and outer (GJ 832b) planets, is investigated numerically and a detailed phase-space analysis is performed. Special attention is given to the existence of stable orbits for a planet less than 15 M ⊕ that is injected between the inner and outer planets. Thus, numerical simulations are performed for three and four bodies in elliptical orbits (or circular for special cases) by using a large number of initial conditions that cover the selected phase-spaces of the planet's orbital parameters. The results presented in the phase-space maps for GJ 832c indicate the least deviation of eccentricity from its nominal value, which is then used to determine its inclination regime relative to the star–outer planet plane. Also, the injected planet is found to display stable orbital configurations for at least one billion years. Then, the radial velocity curves based on the signature from the Keplerian motion are generated for the injected planets with masses 1 M ⊕ to 15 M ⊕ in order to estimate their semimajor axes and mass limits. The synthetic RV signal suggests that an additional planet of mass ≤15 M ⊕ with a dynamically stable configuration may be residing between 0.25 and 2.0 au from the star. We have provided an estimated number of RV observations for the additional planet that is required for further observational verification.

http://iopscience.iop.org/article/10.3847/1538-4357/aa80e2/meta

I have to say I find that article a bit weird. Its not like they have detected anything, not even that there is a hint in the data for the presence of an additional planet. All they have is "if there is a planet here, its orbit would be stable". Oh well - a super-Earth way inside Mercury would also be on a stable orbit, but that doesn't mean there is one. But still, you have news sites like this one running with headlines suggesting a planet has been found...
More of my thoughts: www.final-frontier.ch (in German)

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #175 on: 08/22/2017 04:30 pm »
New Findings on Brown Dwarf Atmospheres

Interesting tidbit from this article.

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I often think of brown dwarfs in terms of the planets that might form around them, and the question of whether even these small ‘failed stars’ may be capable of sustaining life. Have a look, for example, at Luhman 16AB, two brown dwarfs in the Sun’s immediate neighborhood. There are some indications of a planet here which, if it were ever confirmed, would make it the second closest known exoplanet to the Earth, at least for now. We can rule out planets of Neptune mass or greater with a period of between one and two years, but future Hubble observations, already approved for August of next year, may tell us more.

https://www.centauri-dreams.org/?p=38327

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #176 on: 08/22/2017 07:12 pm »
On reflection this seems more appropriate in this area.

Likely Transiting Exocomets Detected by Kepler

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We present the first good evidence for exocomet transits of a host star in continuum light in data from the Kepler mission. The Kepler star in question, KIC 3542116, is of spectral type F2V and is quite bright at Kp=10. The transits have a distinct asymmetric shape with a steeper ingress and slower egress that can be ascribed to objects with a trailing dust tail passing over the stellar disk. There are three deeper transits with depths of ≃0.1% that last for about a day, and three that are several times more shallow and of shorter duration. The transits were found via an exhaustive visual search of the entire Kepler photometric data set, which we describe in some detail. We review the methods we use to validate the Kepler data showing the comet transits, and rule out instrumental artifacts as sources of the signals. We fit the transits with a simple dust-tail model, and find that a transverse comet speed of ∼35-50 km s−1 and a minimum amount of dust present in the tail of ∼1016 g are required to explain the larger transits. For a dust replenishment time of ∼10 days, and a comet lifetime of only ∼300 days, this implies a total cometary mass of ≳3×1017 g, or about the mass of Halley's comet. We also discuss the number of comets and orbital geometry that would be necessary to explain the six transits detected over the four years of Kepler prime-field observations. Finally, we also report the discovery of a single comet-shaped transit in KIC 11084727 with very similar transit and host-

https://arxiv.org/abs/1708.06069

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #177 on: 08/24/2017 12:34 am »
The META detections. Somewhat before my time so I had never heard of these before. Useful links in the description to further reading as well.


Offline Star One

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Exoplanets And Stars Thread
« Reply #178 on: 08/24/2017 09:59 pm »
The CGI in the video makes it look like it has a malevolent face, with two huge staring eyes it even has pupils!

Best Ever Image of a Star’s Surface and Atmosphere

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First map of motion of material on a star other than the Sun

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Using ESO’s Very Large Telescope Interferometer astronomers have constructed the most detailed image ever of a star — the red supergiant star Antares. They have also made the first map of the velocities of material in the atmosphere of a star other than the Sun, revealing unexpected turbulence in Antares’s huge extended atmosphere. The results were published in the journal Nature.

http://www.eso.org/public/news/eso1726/

« Last Edit: 08/24/2017 10:08 pm by Star One »

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #179 on: 08/29/2017 07:29 pm »
Likely Transiting Exocomets Detected by Kepler by Visual Lightcurve Inspection

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In January 2017, amateur astronomer Tom Jacobs proposed the idea of visually surveying the complete Q1-Q17 Kepler lightcurve archive spanning 201,250 target stars for Data Release 25 (Thompson et al. 2016) with professional astronomers Saul Rappaport and Andrew Vanderburg along with amateur astronomer Daryll LaCourse. "The survey was conducted using the LcTools software system (Kipping et al. 2015), a publicly available Windows-based set of applications designed for processing lightcurves in a fast and efficient manner. Two primary components from the system were utilized; LcGenerator for building lightcurves in bulk and LcViewer for visually inspecting plots of the lightcurve for signals of interest."

The team has worked on similar projects with the K2 campaigns. The survey lasted five months with one person (TJ) individually inspecting each lightcurve for interesting objects that were non periodic in nature. There were no predetermined search parameters. Everything was on the table and numerous flagged objects turned out to be data breaks and data processing anomalies (data glitches) upon subsequent analysis by Saul Rappaport and Andrew Vanderburg. Both veterans were indefatigable in supporting the search effort. On March 18th, KIC 35421116 was initially flagged for its three aperiodic transits and subsequently labeled and analyzed as exocomet candidates.

http://keplerlightcurves.blogspot.co.uk/2017/08/likely-transiting-exocomets-detected-by.html?m=1

 

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