Author Topic: Astronomy Thread  (Read 96972 times)

Offline Star One

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Astronomy Thread
« Reply #280 on: 12/13/2017 08:01 PM »
Amongst the 86 official star names allocated by the IAU Barnard’s Star officially gains that name 100 years after its discovery by Edward Emerson Barnard.

https://www.iau.org/news/pressreleases/detail/iau1707/
« Last Edit: 12/13/2017 08:02 PM by Star One »

Offline Dao Angkan

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Re: Astronomy Thread
« Reply #281 on: 12/13/2017 08:40 PM »
Extragalactic exoplanets could be detected by the Large Synoptic Survey Telescope. 

Can gravitational microlensing detect extragalactic exoplanets? Self-lensing models of the Small Magellanic Cloud

Also, ESPRESSO sees first light. It should achieve precision of at least an order of magnitude over HARPS.
« Last Edit: 12/13/2017 08:55 PM by Dao Angkan »

Offline redliox

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Re: Astronomy Thread
« Reply #282 on: 12/13/2017 10:22 PM »
Extragalactic exoplanets could be detected by the Large Synoptic Survey Telescope. 

Can gravitational microlensing detect extragalactic exoplanets? Self-lensing models of the Small Magellanic Cloud

Also, ESPRESSO sees first light. It should achieve precision of at least an order of magnitude over HARPS.

Every time I hear about the discovery of some planet 1,000 light years away...I can't help thinking "And we still don't know how many planets are around Alpha Centauri yet."  At least Proxima b makes a start...

I will say finding exoplanets in an entirely different galaxy is impressive.
"Let the trails lead where they may, I will follow."
-Tigatron

Offline Dao Angkan

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Re: Astronomy Thread
« Reply #283 on: 12/14/2017 04:16 PM »
Detection by radial velocity is probably the best bet for discovering more planets around the Alpha Centauri system and other relatively nearby stars. ESPRESSO and EXPRES should help with this in the near term.

Microlensing is great for distant stars, currently several exoplanets have been discovered at over 20,000 LY distance. The Small Magellanic Cloud is ~200,000 LY away.
« Last Edit: 12/14/2017 04:19 PM by Dao Angkan »

Offline the_other_Doug

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Re: Astronomy Thread
« Reply #284 on: 12/14/2017 10:45 PM »
Has anyone come up with what our own sun's radial velocity perturbations would look like from a variety of distances and with a variety of viewing "resolutions"?

In other words, how easy would it be from 30 light-years away, for example, to examine Sol and state that it has four inner rocky planets and four outer gas / ice giants?  How easy from 300?  From 3,000?  Et cetera...
-Doug  (With my shield, not yet upon it)

Online Alpha_Centauri

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Re: Astronomy Thread
« Reply #285 on: 12/15/2017 12:05 PM »
Typical angular resolution isn't the problem with RV as you only need an unresolved blob of light. The main limiting factors are things like getting enough photons to flesh out the spectrum (either use a big enough light bucket / telescope / array, or viewing brighter stars), a high enough spectrograph resolution to separate out absorption lines, and the intrinsic "noise" largely due to stellar activity.

Our Sun has a decent luminosity so would be viewable for spectrographs like ours for quite some distance. It is also pretty quiet in comparison to many stars, so I think it would be on any alien astronomers target list. I don't know about exact figures. Of course on the other hand our solar system has one rather big downside; compared with many other systems most of our planets are quite some distance from our star and so have long orbital periods, so monitoring to get large enough orbital arcs to improve S/N would take some time.

I believe radial velocity observations of sunlight were conducted in the past, especially back when people were first thinking about finding planets using RV in the 90s. There will be papers on it somewhere. Obviously our instruments have inmproved significantly since then.

Online jebbo

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Re: Astronomy Thread
« Reply #286 on: 12/18/2017 11:24 AM »
Two interesting exoplanet papers today

First, more detail of the "Fulton gap" in planet radii:

Exoplanet Radius Gap Dependence on Host Star Type
Quote
Exoplanets smaller than Neptune are numerous, but the nature of the planet populations in the 1-4 Earth radii range remains a mystery. The complete Kepler sample of Q1-Q17 exoplanet candidates shows a radius gap at ~ 2 Earth radii, as reported by us in January 2017 in LPSC conference abstract #1576 (Zeng et al. 2017). A careful analysis of Kepler host stars spectroscopy by the CKS survey allowed Fulton et al. (2017) in March 2017 to unambiguously show this radius gap. The cause of this gap is still under discussion (Ginzburg et al. 2017; Lehmer & Catling 2017; Owen & Wu 2017). Here we add to our original analysis the dependence of the radius gap on host star type.
https://arxiv.org/abs/1712.05458

Second, a study of tidal heating in the TRAPPIST-1 system:

Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
Quote
With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H2O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H2O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳ 0.3. Determining the planet's masses within ∼0.1 to 0.5 Earth masses would confirm or rule out the presence of H2O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.
https://arxiv.org/abs/1712.05641

I'm still dubious of the density measurements in this system ... they'll be much more certain once we get RV data from instruments like SPIROU

--- Tony




Offline Star One

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Re: Astronomy Thread
« Reply #287 on: 12/18/2017 07:55 PM »
Two interesting exoplanet papers today

First, more detail of the "Fulton gap" in planet radii:

Exoplanet Radius Gap Dependence on Host Star Type
Quote
Exoplanets smaller than Neptune are numerous, but the nature of the planet populations in the 1-4 Earth radii range remains a mystery. The complete Kepler sample of Q1-Q17 exoplanet candidates shows a radius gap at ~ 2 Earth radii, as reported by us in January 2017 in LPSC conference abstract #1576 (Zeng et al. 2017). A careful analysis of Kepler host stars spectroscopy by the CKS survey allowed Fulton et al. (2017) in March 2017 to unambiguously show this radius gap. The cause of this gap is still under discussion (Ginzburg et al. 2017; Lehmer & Catling 2017; Owen & Wu 2017). Here we add to our original analysis the dependence of the radius gap on host star type.
https://arxiv.org/abs/1712.05458

Second, a study of tidal heating in the TRAPPIST-1 system:

Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
Quote
With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H2O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H2O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳ 0.3. Determining the planet's masses within ∼0.1 to 0.5 Earth masses would confirm or rule out the presence of H2O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.
https://arxiv.org/abs/1712.05641

I'm still dubious of the density measurements in this system ... they'll be much more certain once we get RV data from instruments like SPIROU

--- Tony

First paper listed above comes under criticism for being an example of ‘flag planting’, half finished and not the appropriate forum for discussing the topic.

https://mobile.twitter.com/chrislintott/status/942831019161538561

Online jebbo

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Re: Astronomy Thread
« Reply #288 on: 12/19/2017 06:27 AM »
First paper listed above comes under criticism for being an example of ‘flag planting’, half finished and not the appropriate forum for discussing the topic.

Yes, I saw that ... it was a discussion over the purpose of the (extremely new) "Research Notes" rather than a critique of the paper (don't think anyone questioned the data).  To me, leaving aside the flag-planting issue, it seems in the spirit of RN: small contributions that either need follow-up or are not worth a paper in their own right.

The wider discussion surrounding this bit was more interesting: when should effects be named after people.

--- Tony

Offline Star One

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Re: Astronomy Thread
« Reply #289 on: 12/19/2017 06:37 AM »
First paper listed above comes under criticism for being an example of ‘flag planting’, half finished and not the appropriate forum for discussing the topic.

Yes, I saw that ... it was a discussion over the purpose of the (extremely new) "Research Notes" rather than a critique of the paper (don't think anyone questioned the data).  To me, leaving aside the flag-planting issue, it seems in the spirit of RN: small contributions that either need follow-up or are not worth a paper in their own right.

The wider discussion surrounding this bit was more interesting: when should effects be named after people.

--- Tony

Yes I noticed the naming issue. I know Twitter isn’t a very good basis for judging these things but the consensus seemed to be against the naming in this case

Online jebbo

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Re: Astronomy Thread
« Reply #290 on: 12/19/2017 07:00 AM »
Yes I noticed the naming issue. I know Twitter isn’t a very good basis for judging these things but the consensus seemed to be against the naming in this case

Yes ... hardly surprising as the whole "Fulton gap" name was really just a bit of a running gag on Twitter.  Photo-evaporation valley is short and descriptive enough.

--- Tony

Offline as58

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Re: Astronomy Thread
« Reply #291 on: 12/19/2017 07:59 AM »
I must admit that I don't see the point of RNAAS when everything is put on arxiv anyway. To me it seems like a flag-planting operation by AAS...

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Re: Astronomy Thread
« Reply #292 on: 12/20/2017 08:41 AM »
Predictions of planet detections with near infrared radial velocities in the up-coming SPIRou Legacy Survey-Planet Search
Quote
The SPIRou near infrared spectro-polarimeter is destined to begin science operations at the Canada-France-Hawaii Telescope in mid-2018. One of the instrument's primary science goals is to discover the closest exoplanets to the Solar System by conducting a 3-5 year long radial velocity survey of nearby M dwarfs at an expected precision of ∼1 m s−1; the SPIRou Legacy Survey-Planet Search (SLS-PS). In this study we conduct a detailed Monte-Carlo simulation of the SLS-PS using our current understanding of the occurrence rate of M dwarf planetary systems and physical models of stellar activity. From simultaneous modelling of planetary signals and activity, we predict the population of planets detected in the SLS-PS. With our fiducial survey strategy and expected instrument performance over a nominal survey length of ∼3 years, we expect SPIRou to detect 85.3+29.3−12.4 planets including 20.0+16.8−7.2 habitable zone planets and 8.1+7.6−3.2 Earth-like planets from a sample of 100 M1-M8.5 dwarfs out to 11 pc. By studying mid-to-late M dwarfs previously inaccessible to existing optical velocimeters, SPIRou will put meaningful constraints on the occurrence rate of planets around those stars including the value of η⊕ at an expected level of precision of ≲45%. We also predict a subset of 46.7+16.0−6.0 planets may be accessible with dedicated high-contrast imagers on the next generation of ELTs including 4.9+4.7−2.0 potentially imagable Earth-like planets. Lastly, we compare the results of our fiducial survey strategy to other foreseeable survey versions to quantify which strategy is optimized to reach the SLS-PS science goals. The results of our simulations are made available to the community on github.
https://arxiv.org/abs/1712.06673

I'm looking forward to the results from this one!  First, it should give us much better masses for Proxima b and the TRAPPIST-1 planets; second, it should yield a few direct imaging targets for the forthcoming 30m class telescopes.

--- Tony

Offline Star One

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Astronomy Thread
« Reply #293 on: 12/20/2017 08:07 PM »
Giant Bubbles on Red Giant Star’s Surface

Quote
Astronomers using ESO’s Very Large Telescope have for the first time directly observed granulation patterns on the surface of a star outside the Solar System — the ageing red giant π1 Gruis. This remarkable new image from the PIONIER instrument reveals the convective cells that make up the surface of this huge star, which has 350 times the diameter of the Sun. Each cell covers more than a quarter of the star’s diameter and measures about 120 million kilometres across. These new results are being published this week in the journal Nature.

http://www.eso.org/public/news/eso1741/

« Last Edit: 12/20/2017 08:09 PM by Star One »

Offline Star One

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Astronomy Thread
« Reply #294 on: 12/22/2017 07:24 PM »
The cool and distant formation of Mars

Quote
With approximately one ninth of Earth's mass, Mars is widely considered to be a stranded planetary embryo that never became a fully-grown planet. A currently popular planet formation theory predicts that Mars formed near Earth and Venus and was subsequently scattered outwards to its present location. In such a scenario, the compositions of the three planets are expected to be similar to each other. However, bulk elemental and isotopic data for martian meteorites demonstrate that key aspects of Mars' composition are markedly different from that of Earth. This suggests that Mars formed outside of the terrestrial feeding zone during primary accretion. It is therefore probable that Mars always remained significantly farther from the Sun than Earth; its growth was stunted early and its mass remained relatively low. Here we identify a potential dynamical pathway that forms Mars in the asteroid belt and keeps it outside of Earth's accretion zone while at the same time accounting for strict age and compositional constraints, as well as mass differences. Our uncommon pathway (approximately 2% probability) is based on the Grand Tack scenario of terrestrial planet formation, in which the radial migration by Jupiter gravitationally sculpts the planetesimal disc at Mars' current location. We conclude that Mars' formation requires a specific dynamical pathway, while this is less valid for Earth and Venus. We further predict that Mars' volatile budget is most likely different from Earth's and that Venus formed close enough to our planet that it is expected to have a nearly identical composition from common building blocks.

http://www.sciencedirect.com/science/article/pii/S0012821X1730184X?via%3Dihub#!

https://arxiv.org/pdf/1704.00184.pdf
« Last Edit: 12/22/2017 07:25 PM by Star One »

Offline Star One

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Astronomy Thread
« Reply #295 on: 12/28/2017 05:05 PM »
The origins of our solar system?

Triggered Star Formation inside the Shell of a Wolf–Rayet Bubble as the Origin of the Solar System

Quote
A critical constraint on solar system formation is the high ${}^{26}\mathrm{Al}$/27Al abundance ratio of $5\times {10}^{-5}$ at the time of formation, which was about 17 times higher than the average Galactic ratio, while the 60Fe/56Fe value was about $2\times {10}^{-8}$, lower than the Galactic value. This challenges the assumption that a nearby supernova (SN) was responsible for the injection of these short-lived radionuclides into the early solar system. We show that this conundrum can be resolved if the solar system was formed by a triggered star formation at the edge of a Wolf–Rayet (W–R) bubble. 26Al is produced during the evolution of the massive star, released in the wind during the W–R phase, and condenses into dust grains that are seen around W–R stars. The dust grains survive passage through the reverse shock and the low-density shocked wind, reach the dense shell swept-up by the bubble, detach from the decelerated wind, and are injected into the shell. Some portions of this shell subsequently collapse to form the dense cores that give rise to solar-type systems. The subsequent aspherical SN does not inject appreciable amounts of ${}^{60}\mathrm{Fe}$ into the proto–solar system, thus accounting for the observed low abundance of ${}^{60}\mathrm{Fe}$. We discuss the details of various processes within the model and conclude that it is a viable model that can explain the initial abundances of ${}^{26}\mathrm{Al}$ and ${}^{60}\mathrm{Fe}$. We estimate that 1%–16% of all Sun-like stars could have formed in such a setting of triggered star formation in the shell of a W–R bubble.

http://iopscience.iop.org/article/10.3847/1538-4357/aa992e/meta
« Last Edit: 12/28/2017 05:06 PM by Star One »

Offline ExoExplorer

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Re: Astronomy Thread
« Reply #296 on: 01/03/2018 05:29 PM »
Predictions of planet detections with near infrared radial velocities in the up-coming SPIRou Legacy Survey-Planet Search
Quote
The SPIRou near infrared spectro-polarimeter is destined to begin science operations at the Canada-France-Hawaii Telescope in mid-2018. One of the instrument's primary science goals is to discover the closest exoplanets to the Solar System by conducting a 3-5 year long radial velocity survey of nearby M dwarfs at an expected precision of ∼1 m s−1; the SPIRou Legacy Survey-Planet Search (SLS-PS). In this study we conduct a detailed Monte-Carlo simulation of the SLS-PS using our current understanding of the occurrence rate of M dwarf planetary systems and physical models of stellar activity. From simultaneous modelling of planetary signals and activity, we predict the population of planets detected in the SLS-PS. With our fiducial survey strategy and expected instrument performance over a nominal survey length of ∼3 years, we expect SPIRou to detect 85.3+29.3−12.4 planets including 20.0+16.8−7.2 habitable zone planets and 8.1+7.6−3.2 Earth-like planets from a sample of 100 M1-M8.5 dwarfs out to 11 pc. By studying mid-to-late M dwarfs previously inaccessible to existing optical velocimeters, SPIRou will put meaningful constraints on the occurrence rate of planets around those stars including the value of η⊕ at an expected level of precision of ≲45%. We also predict a subset of 46.7+16.0−6.0 planets may be accessible with dedicated high-contrast imagers on the next generation of ELTs including 4.9+4.7−2.0 potentially imagable Earth-like planets. Lastly, we compare the results of our fiducial survey strategy to other foreseeable survey versions to quantify which strategy is optimized to reach the SLS-PS science goals. The results of our simulations are made available to the community on github.
https://arxiv.org/abs/1712.06673

I'm looking forward to the results from this one!  First, it should give us much better masses for Proxima b and the TRAPPIST-1 planets; second, it should yield a few direct imaging targets for the forthcoming 30m class telescopes.

--- Tony
SLS-PS is unlikely to detect the radial velocity of TRAPPIST-1 (mv = 19). It's just simply too faint for Doppler spectroscopy.
« Last Edit: 01/03/2018 05:30 PM by ExoExplorer »

Online jebbo

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Re: Astronomy Thread
« Reply #297 on: 01/03/2018 05:39 PM »
SLS-PS is unlikely to detect the radial velocity of TRAPPIST-1 (mv = 19). It's just simply too faint for Doppler spectroscopy.

Yes, it is very dim in the V band, but it is much brighter in IR. Also, I didn't post that blind, I asked them ages ago:

Quote
with IR mags of J=11, H=10.7 and K=10.3, Trappist-1 is in reach of SPIRou_astro. no doubt SPIRou_astro will look at it once on CFHT


https://twitter.com/SPIRou_astro/status/836515528474755072

Quote
W/ expected RV amplitudes of 0.9 to 3.5m/s, Trappist-1 planets b to h may be better characterized in mass & density w/ SPIRou_astro


--- Tony

« Last Edit: 01/03/2018 05:43 PM by jebbo »

Offline ExoExplorer

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Re: Astronomy Thread
« Reply #298 on: 01/03/2018 05:53 PM »
Typical angular resolution isn't the problem with RV as you only need an unresolved blob of light. The main limiting factors are things like getting enough photons to flesh out the spectrum (either use a big enough light bucket / telescope / array, or viewing brighter stars), a high enough spectrograph resolution to separate out absorption lines, and the intrinsic "noise" largely due to stellar activity.

Our Sun has a decent luminosity so would be viewable for spectrographs like ours for quite some distance. It is also pretty quiet in comparison to many stars, so I think it would be on any alien astronomers target list. I don't know about exact figures. Of course on the other hand our solar system has one rather big downside; compared with many other systems most of our planets are quite some distance from our star and so have long orbital periods, so monitoring to get large enough orbital arcs to improve S/N would take some time.

I believe radial velocity observations of sunlight were conducted in the past, especially back when people were first thinking about finding planets using RV in the 90s. There will be papers on it somewhere. Obviously our instruments have inmproved significantly since then.
The orbital inclination of the alien Earth would also limit the measurable amplitude of wobble. For example, if the inclination is close to 0°, the planet would be undetectable by RV regardless of how precise.
« Last Edit: 01/03/2018 06:23 PM by ExoExplorer »

Offline ExoExplorer

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Re: Astronomy Thread
« Reply #299 on: 01/03/2018 06:23 PM »
SLS-PS is unlikely to detect the radial velocity of TRAPPIST-1 (mv = 19). It's just simply too faint for Doppler spectroscopy.

Yes, it is very dim in the V band, but it is much brighter in IR. Also, I didn't post that blind, I asked them ages ago:

Quote
with IR mags of J=11, H=10.7 and K=10.3, Trappist-1 is in reach of SPIRou_astro. no doubt SPIRou_astro will look at it once on CFHT


https://twitter.com/SPIRou_astro/status/836515528474755072

Quote
W/ expected RV amplitudes of 0.9 to 3.5m/s, Trappist-1 planets b to h may be better characterized in mass & density w/ SPIRou_astro


--- Tony
How surprising. I thought it would be impossible in the short-term, but the outer three planets are hardly achievable since low-density materials like ice probably make up a significant part of their masses. Combination of RV and TTV would constrain the whole system with better precision I believe.
« Last Edit: 01/03/2018 06:24 PM by ExoExplorer »