APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)
Post by APOD Robot » Wed Feb 01, 2017 5:06 am
Four Planets Orbiting Star HR 8799
Explanation: Does life exist outside our Solar System? To help find out, NASA has created the Nexus for Exoplanet System Science (NExSS) to better locate and study distant star systems that hold hope of harboring living inhabitants. A new observational result from a NExSS collaboration is the featured time-lapse video of recently discovered planets orbiting the star HR 8799. The images for the video were taken over seven years from the Keck Observatory in Hawaii. Four exoplanets appear as white dots partially circling their parent star, purposefully occluded in the center. The central star HR 8799 is slightly larger and more massive than our Sun, while each of the planets is thought to be a few times the mass of Jupiter. The HR 8799 system lies about 130 light years away toward the constellation of the Flying Horse (Pegasus). Research will now continue on whether any known or potential planets -- or even moons of these planets -- in the HR 8799 star system could harbor life.
Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)
Post by Ann » Wed Feb 01, 2017 8:31 am
And once again, it is an A-type star that provides really spectacular images. (HR 8799 is an A5V-type star, aout five times more luminous than the Sun and bluer in color.)
Click to view full size image
Fomalhaut and planet.
Beta Pictoris and planet.
M. Bonnefoy et al., published in Astronomy & Astrophysics, 2011, vol. 528, L15
Other A-type stars with spectacular planets are Fomalhaut, spectral class A3V, some 17 times more luminous than the Sun, and Beta Pictoris, also spectral class A3V, 9 times brighter than the Sun.
It seems "intuitively correct" that more massive stars should have more massive planets, although I have no idea if this is really the case. Nevertheless, it seems certain that A-type stars are becoming a treasure trove when it comes to offering up spectacular planets that can be actually imaged rather than just inferred.
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Location: Auburn, Washington, USA
Post by ta152h0 » Wed Feb 01, 2017 10:20 am
and sometimes i cannot find my glasses, even when stuck on my face
Wolf Kotenberg
RedFishBlueFish
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Post by RedFishBlueFish » Wed Feb 01, 2017 10:44 am
Gobsmacked am I > amazing images!
Am sure that Galileo Galilei - whose defence and advocation of heliocentrism and was found by the Inquisitors of the Catholic Church to be "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture." - would take satisfaction in this view of a distant star and its planets which so resembles his own view of Jupiter and its moons.
Post by Roger » Wed Feb 01, 2017 1:12 pm
This star is of visual magnitude 6.0, detectable with the unaided eye from a dark site, and with binoculars from all but the brightest cities. It is approximately along a line between the western two stars of the Great Square of Pegasus, halfway between those two stars. It's amazing that such a dramatic demonstration of exoplanets involves a naked-eye star!
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Post by darksky2500@gmail.com » Wed Feb 01, 2017 1:20 pm
Hats off to the astronomers and scientists responsible for an image like this. Actually catching the images of the planets over a significant time period to animate the arcs of their orbits - amazing! A great nerd-gasm start to the day.
FrankTKO
Post by FrankTKO » Wed Feb 01, 2017 2:36 pm
And here I was thinking that all exoplanets had been inferred and never been imaged directly, duh! I see from the first comment that an exoplanet was imaged as early as 2003 - what was the first exoplanet imaged ever?
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Post by Case » Wed Feb 01, 2017 2:38 pm
Roger wrote: It is approximately along a line between the western two stars of the Great Square of Pegasus, halfway between those two stars.
Post by neufer » Wed Feb 01, 2017 2:43 pm
Ann wrote:
And once again, it is an A-type star that provides really spectacular images. (HR 8799 is an A5V-type star, aout five times more luminous than the Sun and bluer in color.) Other A-type stars with spectacular planets are Fomalhaut, spectral class A3V, some 17 times more luminous than the Sun, and Beta Pictoris, also spectral class A3V, 9 times brighter than the Sun.
I think the key is that they are all young stars with young hot planets which show up well with infrared adaptive optics.
(Although the A-type star's own infrared light might also be concentrated
in hydrogen emission lines which could be filtered out if necessary.)
https://en.wikipedia.org/wiki/Beta_Pictoris wrote:
Beta Pictoris (β Pic, β Pictoris) is 1.75 times as massive and 8.7 times as luminous as the Sun. The Beta Pictoris system is very young, only 20 to 26 million years old, although it is already in the main sequence stage of its evolution.
https://en.wikipedia.org/wiki/HR_8799 wrote:
HR 8799 is a young (~30 million-year-old) main-sequence star with roughly 1.5 times the Sun's mass and 4.9 times its luminosity.
On 13 November 2008, Christian Marois and his team announced they had directly observed three planets orbiting the star with the Keck and Gemini telescopes in Hawaii, in both cases employing adaptive optics to make observations in the infrared. The 4 planets are still glowing red hot due to their young age.
https://en.wikipedia.org/wiki/Fomalhaut wrote:
Fomalhaut is a young star, for many years thought to be only 100 to 300 million years old, with a potential lifespan of a billion years. A 2012 study gave a slightly higher age of 440±40 million years. Fomalhaut's mass is about 1.92 times that of the Sun, its luminosity is about 16.6 times greater, and its diameter is roughly 1.84 times as large.
mudkip177
Post by mudkip177 » Wed Feb 01, 2017 3:15 pm
The orbits are apparently much longer compared to earth years. Does that imply these are outer planets? What else is implied? TY -- B
Post by Chris Peterson » Wed Feb 01, 2017 3:18 pm
Ann wrote: And once again, it is an A-type star that provides really spectacular images. (HR 8799 is an A5V-type star, aout five times more luminous than the Sun and bluer in color.)
Strictly speaking, this is not an A-type star. Based on its hydrogen emission lines and temperature, it is best classified as F0 V. However, its heavy element absorption line spectrum suggests a classification of A5 V. It is a member of a special class of low metallicity pulsating stars called Lambda Boötis stars. Its formal spectral classification is kA5 hF0 mA5 V; λ Boo. This breaks down to
A5 characteristics, spectra with interstellar absorption features;
F0 characteristics, WR star with emission lines due to hydrogen;
A5 characteristics, enhanced metal features;
Lambda Boötis class.
A spectral mess, for sure!
neufer wrote: I think the key is that they are all young stars with young hot planets which show up well with infrared adaptive optics.
In some cases, perhaps. However, the IR band used with ground-based adaptive optics only slightly enhances thermal IR emissions, which are largely blocked by the Earth's atmosphere. In this case (HR 8799) we are seeing the planets by the reflected light of the star, not by their own IR emission. The outer planets can be imaged in visible light using small (meter-class) telescopes without adaptive optics.
Post by Ann » Wed Feb 01, 2017 3:37 pm
Chris Peterson wrote:
I believe you. I thought a luminosity of 5 times solar seemed puny for an A5-type star, although admittedly very young stars are often fainter than those that are well into their main sequence. The color of HR 8799 is a little bit red, but still pretty okay for an A5V-type star, particularly if we see it from its "fat" side, the equator.
But I'm not protesting if you call it an F0V-type star with A5V-type features, or a Lambda Boötis class star.
However, the star Lambda Boötis itself is much bluer than HR 8799 (with a B-V index of around 0.10, versus about 0.27 for HR 8799), and Lambda Boötis is about three times brighter than HR 8799, some 16 times solar, versus about 5 times solar for the star of today's APOD.
Ah, stellar classifications, what a fascinating subject!
EDIT: No, stop! I just checked what Bright Star Catalog said about Lambda Boötis, and it said, Prototype of Lambda Boo stars, dwarfs with very weak metallic lines.
So if HR 8799 has enhanced metal lines, it doesn't sound much like a Lambda Boo star to me!
Last edited by Ann on Wed Feb 01, 2017 3:45 pm, edited 1 time in total.
mudkip177 wrote: The orbits are apparently much longer compared to earth years. Does that imply these are outer planets? What else is implied? TY -- B
Note the distance scale on the video. These planets are roughly equivalent to planets in our solar system lying outwards from Neptune, and have similar orbital periods to those outer planets. (Neptune is about 30 AU from the Sun with a 165 y period; Pluto is about 40 AU from the Sun with a 250 y period.)
neufer wrote:
In some cases, perhaps. However, the IR band used with ground-based adaptive optics only slightly enhances thermal IR emissions, which are largely blocked by the Earth's atmosphere. In this case (HR 8799) we are seeing the planets by the reflected light of the star, not by their own IR emission.
Did you miss the part about HR 8799's 4 planets still glowing red hot due to their young age.
Keck's adaptive optics run from 1 micron to 5 microns (i.e., 3,000K to 600K 'thermal' IR).
Last edited by neufer on Wed Feb 01, 2017 3:47 pm, edited 1 time in total.
Ann wrote: However, the star Lambda Boötis itself is much bluer than HR 8799 (with a B-V index of around 0.10, versus about 0.27 for HR 8799), and Lambda Boötis is about three times brighter than HR 8799, some 16 times solar, versus about 5 times solar for the star of today's APOD.
Ah, stellar classifications, what a fascinating subject! :D
Lambda Boötis has a much simpler stellar classification, pA0, which means it's an A0 star with some peculiar spectral characteristics. The kA5 hF0 mA5 V; λ Boo classification of HR 8799 is certainly the most complex designation I've ever seen!
Chris Peterson wrote: In some cases, perhaps. However, the IR band used with ground-based adaptive optics only slightly enhances thermal IR emissions, which are largely blocked by the Earth's atmosphere. In this case (HR 8799) we are seeing the planets by the reflected light of the star, not by their own IR emission.
Did you miss the part about HR 8799's 4 planets still glowing red hot due to their young age. :?:
No. Did you miss the discussions in the linked references that explain that we can these planets by the reflected light of the star, and that they have also been imaged in visible light using small telescopes without adaptive optics? (I understand that the highest resolution images, made with the GPI, do record some thermal emissions. But this system is visible by reflected light as well.)
If one knows where to look I suppose one could do that...but these things are first discovered using near IR adaptive optics thermal emissions as shown here. Note that these are all approximately Jupiter sized planets. If reflected light was the dominant factor here then the 3rd planet should be ~7 times dimmer than the first.
Thank you for helping me understand (even though it was obvious
SaraBiga
Post by SaraBiga » Wed Feb 01, 2017 8:20 pm
Were the images featured in the animation resolved from reflected light in the ultraviolet range like the examples in the article that Ann linked to? Or am I misreading it? If so, is there a reason for reflected light from exoplanets to be best captured in the ultraviolet?
Also, I think that the method used for getting the images (reflected light, wavelength range) should have been included in the caption, as I genuinely believed we could only 'infer' exoplanets, not 'see' them (of course if you know where to look for from some other method, as it was sensibly pointed out in another comment), but also as a general good rule for educating us 'profanes'...
SaraBiga wrote:
Also, I think that the method used for getting the images (reflected light, wavelength range) should have been included in the caption,
http://asterisk.apod.com/viewtopic.php? ... 06#p266669
Post by Ann » Wed Feb 01, 2017 11:56 pm
SaraBiga wrote: Were the images featured in the animation resolved from reflected light in the ultraviolet range like the examples in the article that Ann linked to? Or am I misreading it? If so, is there a reason for reflected light from exoplanets to be best captured in the ultraviolet?
No, the pictures I linked to were in all probability not captured in the ultraviolet. Ultraviolet light is mostly blocked by the Earth's atmosphere. You really need a space telescope to take good pictures of deep space objects in ultraviolet, but the ultraviolet capabilities of existing space telescopes are limited. Hubble is your best option, but Hubble is a very "busy" telescope, and if Hubble is indeed used there is no reason why it should search in the ultraviolet if an object is comfortably visible at longer wavelengths. The two "standard filters" most often used by Hubble are 606 nm (centered in the orange part of the visible spectrum) and 814 nm (infrared).
Also, if there is dust in the vicinity of the star and the planet, any ultraviolet light reflecting off the planet may be completely blocked by the dust. Infrared light will make it through, and some visible light, particularly red light, may penetrate. It would be folly to search for a planet of dusty Beta Pictoris in the ultraviolet.
So you should never just assume that a picture of a deep space object is an ultraviolet image, because that is most likely not the case. So why does today's APOD look blue, and why does the Beta Pictoris image look blue? It's because they are false color images, and red and blue are very popular colors to use for false color images (which are also called mapped color images). False color images were often photographed in such a way that the finished photograph would look black and white. But black and white photographs are unpopular, and therefore they are often colored red or blue instead.
Today's APOD, by the way, was taken by the Earth-based Keck telescope. Since neither ultraviolet nor infrared light penetrates the Earth's atmosphere very well, we should assume that today's APOD was taken at a visible wavelength.
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Post by saturno2 » Thu Feb 02, 2017 12:21 am
Very very interesting, indeed!!
Post by Chris Peterson » Thu Feb 02, 2017 12:41 am
Ann wrote: Today's APOD, by the way, was taken by the Earth-based Keck telescope. Since neither ultraviolet nor infrared light penetrates the Earth's atmosphere very well, we should assume that today's APOD was taken at a visible wavelength.
The instrument that was probably used images in the near IR, between one and five micrometers. I have not seen any details regarding which filters were used, however, so it's unclear what the actual wavelength or wavelength range is, except that it's somewhere in the near IR.
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Post by Boomer12k » Thu Feb 02, 2017 3:23 am
fantastic... typing with one hand... other is in a splint..car accident... I saw Moon, Mars and Venus the other night though with binocs.... I have always believed in other planets around stars...life or no...