Interesting extrasolar planet discoveries - Page 15

George · #**421** (**permalink**) 06-December-2008, 04:47 AM

Quote:

Originally Posted by timb

No, two days matches 39 km/s if you do the calculations.

Yep, I should have done the math.

I did not know they were so fast. Wow. The 1000 km/s rotators take less than 2 hours to whirl. I assume these are regarded as the youngest.

timb · #**422** (**permalink**) 06-December-2008, 07:03 AM

Quote:

Originally Posted by George

Yep, I should have done the math.

I did not know they were so fast. Wow. The 1000 km/s rotators take less than 2 hours to whirl. I assume these are regarded as the youngest.

Not necessarily. Older stars tend to rotate slower because they have had longer to lose angular momentum, but stars of similar age can have very different rotational periods. The fastest ones would be close to the maximum, ie any faster and they'd start throwing rings.

timb · #**423** (**permalink**) 06-December-2008, 07:05 AM

Quote:

Originally Posted by timb

Good point. My error. That should be hottest fast-rotating main-sequence star yet found to have a planet.

Well according to wiki Fomalhaut has a v.sin(i) of 93 km/s, so I give up and declare shenanigans on that ESO press release.

Romanus · #**424** (**permalink**) 06-December-2008, 04:09 PM

What also makes this later planet interesting is that it's more massive than most of the hot Jupiters we've found thus far.

Sporally · #**425** (**permalink**) 06-December-2008, 05:18 PM

Quote:

Originally Posted by sol_g2v

Isn't Fomalhaut the hottest main-sequence star yet found to have a planet?

That just make it even more amazing that we have now photographed a planet around Formalhaut when it is this hot - yes, i know they obscure the light of Formalhaut, but still amazing. No surprise Formalhaut b is found 115AU from Formalhaut. I guess since the star is this hot, its light intensity in the visible spectrum is relative low. Am i wrong?

George · #**426** (**permalink**) 06-December-2008, 06:13 PM

Quote:

Originally Posted by Sporally

I guess since the star is this hot, its light intensity in the visible spectrum is relative low. Am i wrong?

The higher the temperature of a star, the more light is emitted at all wavelengths. Although the peak temperature shifts in the blue direction the entire spectrum will rise in energy radiated.

Fomalhaut radiates in the visible spectrum about 5 times more energy than the Sun, even though its peak intensity is in the UV (330nm - 340nm). [I get 7x as much @ 400nm, 5x @ 500nm, and 3x @ 700nm. Does anyone have a simple equation for total energy output over a given portion of the spectrum?]

George · #**427** (**permalink**) 06-December-2008, 06:21 PM

Quote:

Originally Posted by timb

Not necessarily. Older stars tend to rotate slower because they have had longer to lose angular momentum, but stars of similar age can have very different rotational periods. The fastest ones would be close to the maximum, ie any faster and they'd start throwing rings.

Yes, I have just begun reading about this sort of thing in a book: "The Birth of Stars and Planets" , Baily & Reipurth (2006). It is believed that the intermediate mass stars are too hot for much of a convective zone so it, apparently, does not have disk brakes no matter how hard it stomps on the pedal.

[The convective zone is believed to be the key to strong magnetic fields that cause disk interaction and braking.]

I'd love to get other recommendations for good reads on star birth, especially more on the Class 0 and Class 1 protostars.

Sporally · #**428** (**permalink**) 06-December-2008, 06:33 PM

Quote:

Originally Posted by George

The higher the temperature of a star, the more light is emitted at all wavelengths. Although the peak temperature shifts in the blue direction the entire spectrum will rise in energy radiated.

Yes, i am aware of the fact that it emits more on all wavelenghts, but as you said, the peak emission is not in the visible light.

Quote:

Originally Posted by George

Fomalhaut radiates in the visible spectrum about 5 times more energy than the Sun, even though its peak intensity is in the UV (330nm - 340nm). [I get 7x as much @ 400nm, 5x @ 500nm, and 3x @ 700nm. Does anyone have a simple equation for total energy output over a given portion of the spectrum?]

What math methods do you use to calculate this?

George · #**429** (**permalink**) 06-December-2008, 07:29 PM

Quote:

Originally Posted by Sporally

Yes, i am aware of the fact that it emits more on all wavelenghts, but as you said, the peak emission is not in the visible light.

I must be misunderstanding your original question.

Quote:

What math methods do you use to calculate this?

I have a spreadsheet that uses Planck's equation for any given range of wavelengths and increments.

However, something may be wrong. In using the inverse square law to calculate Fomalhaut's magnitude at a 1 AU distance, I find that it is about 15 times brighter than the Sun and not the 5x brighter I estimated from the Planck equations (using 8500K for its surface temp. -- an A3 star).

[Added: BTW, I calculate that Fomalhaut b should be around 27.5 in apparent magnitude using a Jupiter radius for its size and a 0.6 albedo.]

timb · #**430** (**permalink**) 06-December-2008, 10:35 PM

Quote:

Originally Posted by George

Yes, I have just begun reading about this sort of thing in a book: "The Birth of Stars and Planets" , Baily & Reipurth (2006). It is believed that the intermediate mass stars are too hot for much of a convective zone so it, apparently, does not have disk brakes no matter how hard it stomps on the pedal.

[The convective zone is believed to be the key to strong magnetic fields that cause disk interaction and braking.]

That doesn't seem 100% right. Isn't the Sun an intermediate mass star? it appears to have had some mechanism for losing its angular momentum. The Sun has a convective zone, but it is not classed as "fully convective". Maybe Baily & Reipurth are referring to stars a little more massive than the Sun. Stars earlier than F7 tend to be rapid rotators. I think F6 corresponds to about 1.2 M_sun, but that's just a guess.

Quote:

Originally Posted by George

I'd love to get other recommendations for good reads on star birth, especially more on the Class 0 and Class 1 protostars.

AFAIK the process is not well understood.

In reply to your earlier question I should have mentioned gyrochronology, the art of dating stars by their rotation. For a given color the rotation rate of a singleton star is a good guide to its age. For example Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics gives an account of the issues and methods used in dating stars.

timb · #**431** (**permalink**) 06-December-2008, 10:51 PM

Quote:

Originally Posted by George

I must be misunderstanding your original question.

I have a spreadsheet that uses Planck's equation for any given range of wavelengths and increments.

However, something may be wrong. In using the inverse square law to calculate Fomalhaut's magnitude at a 1 AU distance, I find that it is about 15 times brighter than the Sun and not the 5x brighter I estimated from the Planck equations (using 8500K for its surface temp. -- an A3 star).

Did you account for the fact Fomalhaut's area is about 3.4 times solar? I think Fomalhaut's bolometric luminosity is about 17 times solar.

Quote:

Originally Posted by George

[Added: BTW, I calculate that Fomalhaut b should be around 27.5 in apparent magnitude using a Jupiter radius for its size and a 0.6 albedo.]

So it could be imaged in reflected light (as opposed to in its own IR emissions), if they were willing to point HST at it for long enough. I've read that the albedo of gas giants varies greatly with their temperature though.

George · #**432** (**permalink**) 07-December-2008, 03:24 AM

Quote:

Originally Posted by timb

That doesn't seem 100% right. Isn't the Sun an intermediate mass star? it appears to have had some mechanism for losing its angular momentum. The Sun has a convective zone, but it is not classed as "fully convective". Maybe Baily & Reipurth are referring to stars a little more massive than the Sun. Stars earlier than F7 tend to be rapid rotators. I think F6 corresponds to about 1.2 M_sun, but that's just a guess.

They are refering to a mass range of 2M_sun to 5M_sun, (typically, B and A class and they mention the Herbig AeBe stars).

Quote:

In reply to your earlier question I should have mentioned gyrochronology, the art of dating stars by their rotation. For a given color the rotation rate of a singleton star is a good guide to its age. For example Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics gives an account of the issues and methods used in dating stars.

Thanks.

Quote:

Did you account for the fact Fomalhaut's area is about 3.4 times solar? I think Fomalhaut's bolometric luminosity is about 17 times solar.

Darn, I knew I should have slept in this morning.

Ok, at 25 lyrs, a visual mag. of 1.16 matches to a 9,075K blackbody with a 1.83 Solar radius star. Both show Fomalhaut to be 17.9 times brighter than the white hot Sun.

Quote:

So it could be imaged in reflected light (as opposed to in its own IR emissions), if they were willing to point HST at it for long enough. I've read that the albedo of gas giants varies greatly with their temperature though.

Guess what!

Fomalhaut b is the very first one found in visible light.

[I still think we need to party about this huge milestone accomplishment.] I was just curious to see if I could determine its apparent magnitude since I had not seen it stated in the few articles I've read.

timb · #**433** (**permalink**) 07-December-2008, 10:04 AM

Quote:

Originally Posted by George

Guess what!

Fomalhaut b is the very first one found in visible light.

[I still think we need to party about this huge milestone accomplishment.] I was just curious to see if I could determine its apparent magnitude since I had not seen it stated in the few articles I've read.

Ok, I was slow too this morning. I think Fomalhaut b was quite a good deal brighter in the optical (600nm) than you calculated. The discovery paper tried to explain this by suggesting the Fomalhaut-light was reflecting off a large circumplanetary disk.

George · #**434** (**permalink**) 07-December-2008, 08:31 PM

Quote:

Originally Posted by timb

Ok, I was slow too this morning. I think Fomalhaut b was quite a good deal brighter in the optical (600nm) than you calculated. The discovery paper tried to explain this by suggesting the Fomalhaut-light was reflecting off a large circumplanetary disk.

Thanks for the paper. I had seen one article saying the 20 to 40 Jupiter radii for the object might be due to moons. The circumplanetary disk seems to be the better answer and the paper states it to be 100x brighter than if it were a Jupiter size object. That seems to put the exoplanet at a 22.5 magnitude.

timb · #**435** (**permalink**) 08-December-2008, 03:32 AM

The HATNet team have reported a new transiting exoplanet HAT-P-8b. Most likely parameters are mass 1.52 M_J, radius 1.5 R_J, P=3.08 days, a=0.049 au, e=0. This is a relatively massive and highly inflated inflated hot Jupiter. The primary is an F star 3.3 times as bright as the Sun.

Sporally · #**436** (**permalink**) 09-December-2008, 08:41 PM

Quote:

Originally Posted by George

I must be misunderstanding your original question.

No, not at all i guess. Did i sound angry in my reply - just wanted to make you know i was (this) stupid

Quote:

Originally Posted by timb

The HATNet team have reported a new transiting exoplanet HAT-P-8b. Most likely parameters are mass 1.52 M_J, radius 1.5 R_J, P=3.08 days, a=0.049 au, e=0. This is a relatively massive and highly inflated inflated hot Jupiter. The primary is an F star 3.3 times as bright as the Sun.

Wasn't it you who said you were bored by the talk of every single exoplanet finding that there wasn't something noticeable in?

George · #**437** (**permalink**) 09-December-2008, 09:10 PM

Quote:

Originally Posted by Sporally

No, not at all i guess. Did i sound angry in my reply - just wanted to make you know i was (this) stupid

Great to see some fall down to my level.

I was curious about your point because bb radiation has been something I think I have some familiarity, perhaps enough to converse with the more luminous members here about it.

[I really never cared, but in determining the Sun's true color it had to get learnt and good.

]

timb · #**438** (**permalink**) 09-December-2008, 09:31 PM

Quote:

Originally Posted by Sporally

Wasn't it you who said you were bored by the talk of every single exoplanet finding that there wasn't something noticeable in?

Now I think every exoplanet is beautiful.

This one is the puffiest, and one of the most massive for its period.

01101001 · #**439** (**permalink**) 09-December-2008, 11:09 PM

NASA: Hubble Finds Carbon Dioxide on an Extrasolar Planet

Quote:

NASA's Hubble Space Telescope has discovered carbon dioxide in the atmosphere of a planet orbiting another star. This breakthrough is an important step toward finding chemical biotracers of extraterrestrial life.

The Jupiter-sized planet, called HD 189733b, is too hot for life. But the Hubble observations are a proof-of-concept demonstration that the basic chemistry for life can be measured on planets orbiting other stars. Organic compounds also can be a by-product of life processes and their detection on an Earthlike planet someday may provide the first evidence of life beyond our planet.

Previous observations of HD 189733b by Hubble and the Spitzer Space Telescope found water vapor. Earlier this year, Hubble found methane in the planet's atmosphere.

Same stuff: Reuters: CO2 found on "hot Jupiter" planet

Jerry · #**440** (**permalink**) 10-December-2008, 05:01 AM

arXiv:0812.1582
Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems
Wright et al
ApJ accepted

Quote:

Originally Posted by abstract

We present the latest velocities for 10 multi-planet systems, including a re-analysis of archival Keck and Lick data, resulting in improved velocities that supersede our previously published measurements. We derive updated orbital fits for ten Lick and Keck systems, including two systems (HD 11964, HD 183263) for which we provide confirmation of second planets only tentatively identified elsewhere, and two others (HD 187123, and HD 217107) for which we provide a major revision of the outer planet's orbit. We compile orbital elements from the literature to generate a catalog of the 28 published multiple-planet systems around stars within 200 pc. From this catalog we find several intriguing patterns emerging: - Including those systems with long-term radial velocity trends, at least 28% of known planetary systems appear to contain multiple planets. - Planets in multiple-planet systems have somewhat smaller eccentricities than single planets. - The distribution of orbital distances of planets in multi-planet systems and single planets are inconsistent: single-planet systems show a pile-up at P ~ 3 days and a jump near 1 AU, while multi-planet systems show a more uniform distribution in log-period. In addition, among all planetary systems we find: - There may be an emerging, positive correlation between stellar mass and giant-planet semi-major axis. - Exoplanets more massive than Jupiter have eccentricities broadly distributed across 0 < e < 0.5, while lower-mass exoplanets exhibit a distribution peaked near e = 0.

My bold.

timb · #**441** (**permalink**) 10-December-2008, 07:01 AM

Quote:

Originally Posted by Jerry

arXiv:0812.1582
Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems
Wright et al
ApJ accepted

My bold.

Big star, big planet, big orbit... Would that be surprising? The HAT-P-8b discovery paper says that planet challenges the hypothesized mass-period relationship, so it may just be due to the small sample size. The explanation for some of the observations in the paper you refer to might have been found in How eccentric orbital solutions can hide planetary systems in 2:1 resonant orbits by Anglada-Escude et al. The apparent lower eccentricity of multi-planet systems is what you would expect if there are multi-planet systems hiding behind single planet solutions, as Anglada-Escude et al. suggest. This possibility is well illustrated by their fig.2 which I have taken the liberty of reproducing here.

This mistaking of multi-planet systems for single planet systems could also contribute to the apparently greater eccentricity of more massive planets.

timb · #**442** (**permalink**) 10-December-2008, 11:35 AM

At the risk of boring Sporally I report the discovery of another five exoplanets in two systems by HARPS consortium. These include a 7.5 M_E (minimum) super-Earth HD 181433b, a=0.08 AU, e=0.4. The K3 primary is 31% as bright as the Sun, so I make the insolation 48 S. I expect some follow-up on this because the reported elements for the other two planets in this system, giants between Saturn and Jupiter in mass, put them in overlapping orbits, which seems unlikely.

timb · #**443** (**permalink**) 11-December-2008, 01:00 PM

The Very Low Albedo of an Extrasolar Planet: MOST Space-based Photometry of HD 209458 reports that observations of the HD 209458 system around secondary eclipse show that the geometric albedo of HD 209458b is 0.038+/-0.045. This is very low, about the same as fresh asphalt. The fact that their standard error implies a ~20% chance that the albedo is negative suggests to me that their analysis might have benefited from a transformation of the data.

Sporally · #**444** (**permalink**) 11-December-2008, 05:25 PM

@ 01101001
That does indeed sound very interesting. Another step closer to find something that is suitable for life. Maybe people say that oxygen is posioness for much expected life. Have we found any interesting planets with something other than oxygen that could be very suitable for life? I know we have found tons of different chemicals floating around in space, but what about on the planets themselves?

Quote:

Originally Posted by Jerry

Wright et al

I've always tried to figure out what this means. I guess Wright is a name of the lead scientist doing the studt, but what does 'et al' mean?

Quote:

Originally Posted by timb

The Very Low Albedo of an Extrasolar Planet: MOST Space-based Photometry of HD 209458 reports that observations of the HD 209458 system around secondary eclipse show that the geometric albedo of HD 209458b is 0.038+/-0.045. This is very low, about the same as fresh asphalt. The fact that their standard error implies a ~20% chance that the albedo is negative suggests to me that their analysis might have benefited from a transformation of the data.

I guess it is possible to find a planet with a negative albedo, but for this study i would suggest that it curve showing the likelyhood of the albedo plums around 0.000.

timb · #**445** (**permalink**) 11-December-2008, 11:22 PM

Quote:

Originally Posted by Sporally

I've always tried to figure out what this means. I guess Wright is a name of the lead scientist doing the studt, but what does 'et al' mean?

"et al" is an abbreviation for et alia, which is Latin for "and others".

Quote:

Originally Posted by Sporally

I guess it is possible to find a planet with a negative albedo,

No, that would be impossible.

AndreasJ · #**446** (**permalink**) 11-December-2008, 11:31 PM

Quote:

Originally Posted by timb

"et al" is an abbreviation for et alia, which is Latin for "and others".

To be entirely pedantic, the full form is "et alia" for things, "et aliae" for women, and "et alii" for men or mixed gender groups. The abbreviation neatly avoids this issue.

Sporally · #**447** (**permalink**) 13-December-2008, 02:52 PM

Quote:

Originally Posted by timb

No, that would be impossible.

No? Imaging a planet that has a surface giving it a very low albedo. What is needed to make it negative is that it is a very newly formed planet with a great inner heat making the albedo negative. Unless i am mixing it up what a planet with albedo 0 and albedo 1 is...

George · #**448** (**permalink**) 13-December-2008, 02:56 PM

Albedo is the ratio of reflected light to incident light. There can be no negative albedo, unless the object could somehow suck light out of the observer.

Sporally · #**449** (**permalink**) 13-December-2008, 02:59 PM

OK, i mixed it one - thx for clearing it out for me, i can never remember this but i will try now that i've got an explanation of it. Just need to think of 1 being positive and 0 being negative. Amazing they can find a planet with this low albedo!

timb · #**450** (**permalink**) 18-December-2008, 12:22 AM

In The multiplicity of exoplanet host stars the authors report the discovery of binary companions to stars already known to host planets, HD125612 and HD212301. The companions are red dwarfs at separations of ~4750 AU and ~230 AU (projected) respectively. This boosts the proportion of known planetary systems hosted by binary stars to 17%.

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