What also makes this later planet interesting is that it's more massive than most of the hot Jupiters we've found thus far.
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?]
I'd love to get other recommendations for good reads on star birth, especially more on the Class 0 and Class 1 protostars.
I have a spreadsheet that uses Planck's equation for any given range of wavelengths and increments.What math methods do you use to calculate this?
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.]
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.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.
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.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.
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.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.
discovery paper tried to explain this by suggesting the Fomalhaut-light was reflecting off a large circumplanetary disk.
The HATNet team have reported a new transiting exoplanet HAT-P-8b. Most likely parameters are mass 1.52 MJ, radius 1.5 RJ, 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.
Last edited by George; 2008-Dec-09 at 09:12 PM. Reason: gramm
NASA: Hubble Finds Carbon Dioxide on an Extrasolar Planet
Same stuff: Reuters: CO2 found on "hot Jupiter" planetNASA'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.
Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems
Wright et al
My bold.Originally Posted by abstract
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.
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 ME (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.
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.
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?
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.
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!
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%.