Planets or soap bubbles? these photos are beautiful…(0)
Tag Archive for 'planets'
I’m at Siding Spring Observatory near Coonabarabran in NSW this week. I’m looking for planets via the transit technique for my friend Dan. The observatory is situated in a national park, with great views of the park and surrounding terrain.
There are more photos here.
We have received the excellent news that my third paper has been accepted to ApJ. The paper is about possible mechanisms by which Earth-Neptune (low-)mass planets can reach very close orbits. Using standard models we find trends that might be found by future discoveries, and think about what we can learn from them.
Discovery of low-mass planets (which don’t have large Juipter-like atmospheres) will be particularly interesting, because they may be habitable due to (maybe) having solid surfaces. Unfortunately planets are much easier to find when they’re orbiting very close to their parent stars, and too hot to be habitable. Therefore, if they exist, the first decent sample of low mass planets will be discovered in short-period, close-in orbits.
It’s unlikely that planets in these orbits would form there, because it’s hard to form anything at all close to the star. Therefore, from a formation point of view, there are two main ways these planets
could get to close-in orbits after forming further out: by scattering off other planets, or by migrating through the disk out of which they form. In our paper, we show that planets that scatter will be hard to detect, and that migration is a better mechanism.
At present, very little is known about migration of planets in the “super-Earth” mass range, so discovery of these planets should tell us something about how migration works. Alternatively, we might not find any low-mass planets in short-period orbits, which would tell us that migration doesn’t work how current wisdom says. So either way we learn something!
The paper is posted on astro-ph for now, until the journal publishes it.
Thanks to a nice referees report, and some simulations finally finishing, I submitted a revised version of our “Hot super-Earths” paper this morning. Hopefully all will be well and that will be number three!(0)
I am currently at the IoA in Cambridge, UK. I work with many collaborators on various debris-disk like things, including the Herschel DEBRIS survey, the SCUBA-2 SONS survey, looking for warm dust with WISE and LBTI, theoretical aspects, etc. This page is a reasonably up to date astro-related CV.
- The bright end of the exo-Zodi luminosity function: Disk evolution and implications for exo-Earth detectability, Kennedy & Wyatt, MNRAS, in press
- Spatially Resolved Images of Dust Belt(s) Around the Planet-hosting Subgiant Kappa CrB, Bonsor, Kennedy et al 2013, MNRAS [ ADS | press ]
- Resolved debris disks around A stars in the Herschel DEBRIS survey, Booth, Kennedy et al 2013, MNRAS [ ADS | PDF ]
- Millimeter Emission Structure in the first ALMA Image of the AU Mic Debris Disk, MacGregor et al 2013, ApJL [ ADS | PDF ]
- The Debris Disk around gamma Doradus Resolved with Herschel, Broekhoven-Fiene, Matthews, Kennedy et al 2013, ApJ [ ADS | PDF ]
- A DEBRIS Disk Around The Planet Hosting M-star GJ 581 Spatially Resolved with Herschel, Lestrade et al 2012 [ ADS | PDF | press ]
- Coplanar circumbinary debris disks, Kennedy et al 2012 [ ADS | PDF ]
- Confusion limited surveys: using WISE to quantify the rarity of warm dust around Kepler stars, Kennedy & Wyatt 2012 [ ADS | PDF ]
- Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems, Wyatt, Kennedy et al 2012 [ ADS | PDF | press ]
- A peculiar class of debris disks from Herschel/DUNES – Steep spectral energy distributions, Ertel et al 2012 [ ADS | PDF ]
- 99 Herculis: Host to a circumbinary polar ring debris disk, Kennedy et al 2012 [ ADS | PDF ]
- Searching for Saturn’s Dust Swarm: Limits on the size distribution of Irregular Satellites from km to micron sizes, Kennedy et. al. 2011 [ ADS | PDF ]
- Multi-Wavelength Modelling of the Beta Leo Debris Disc: 1, 2 or 3 planetesimal populations? Churcher et al 2011 [ ADS | PDF ]
- Planet Formation Around M-dwarfs: From Young Disks to Planets, Pascucci et al 2011, Cool Stars 16 Splinter Session [ ADS ]
- Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets, Kennedy & Wyatt 2011 [ ADS | PDF ]
- Resolving debris discs in the far-infrared: early highlights from the DEBRIS survey, Matthews et al 2010 [ ADS | PDF ]
- Are Debris Disks Self-Stirred? Kennedy & Wyatt 2010 [ ADS | PDF]
- Planet formation around stars of various masses: Hot super-Earths, Kennedy & Kenyon 2008 [ ADS | blog | PDF ]
- Planet formation around stars of various masses: The snow line and the frequency of gas giants, Kennedy & Kenyon 2008 [ ADS | blog | PDF ]
- Planet formation around M Dwarfs: The moving snow line and super-Earths, Kennedy, Kenyon, & Bromley 2007 [ ADS | blog | PDF ]
- Planet formation around low-mass stars: The moving snow line and super-Earths, Kennedy, Kenyon, & Bromley 2006 [ ADS | blog | PDF | press ]
Observing programmes (as PI)
- Herschel imaging of a candidate warm debris disk, Herschel Director’s Discretionary Time, 2012
- Debris Disks as a Tracer of Star and Planet Formation in Binaries, Herschel OT2, 2011
- An Irregular Dust Cloud around Uranus, Herschel OT1, 2010
Observing programmes (as Co-I)
- Small SpiKeS, Spitzer IRAC pilot survey of one Kepler tile, PI: M. Werner, 2012
- LBTI exo-zodi key science team, 2012
- DEBRIS, PI: B. Matthews & J. Greaves, Herschel Key Programme, 2009
- SONS, PI: B. Matthews, SCUBA2 Legacy survey, 2012
- Imaging the Birth Ring of the AU Mic Debris Disk, PI: D. Wilner, ALMA Cycle 0, 2011
- Confirmation and characterisation of two debris disks around low-mass stars, PI: J-F Lestrade, Herschel OT2, 2011
- Debris Disks around Low-Mass Planet-Bearing Stars, PI: G. Bryden, Herschel OT2, 2011
- Debris Disks around Planet-Bearing Stars, PI: G. Bryden, Herschel OT1, 2010
- Search for a correlation between planets and debris discs around retired A stars, PI: A. Bonsor, Herschel OT1, 2010
- Testing Planetary Dynamics and Evolutionary History in the HR 8799 Planet/Disc System, PI: B. Matthews, Herschel OT1, 2010
- RAS Undergraduate Bursary for a summer student, March 2013
- Debris disks and planets, and vice versa, IoA, Cambridge, Feb 2013 [ slides ]
- Debris disks and their relation to planets, UNSW, Sydney, Dec 2012
- Debris disks and their relation to planets, Mt Stromlo, Australian Exoplanet Workshop, Dec 2012 [ slides ]
- Debris disks and their relation to planets, Mt Stromlo, Australian National University, Dec 2012
- Debris disks and their relation to planets, CAR, Uni of Hertfordshire, Nov 2012 [ slides ]
- Dust from Saturn’s Irregular Satellites, UK NAM, Mar 2011 [ pdf ]
- Irregular Satellite Swarms, Mt Stromlo, Feb 2011 [ pdf ]
- Evolution of Irregular Satellites, Cambridge DAMTP, Feb 2011
- Herschel DEBRIS Survey, RAS Early Impact of Herschel meeting, January 2011 [ pdf ]
- Theory of Disk Dispersal around M-Dwarfs, Invited review, August 2010, Cool Stars Splinter on M-Dwarf Planet Formation [ keynote | pdf ]
- IoA Theory Grant talks, August 2010
- IoA Star and Planet Formation group, March 2010
- INI Dynamics of Disks and Planets Final Workshop, Dec 2009
- IoA Theory Grant talks, Nov 2009
- Final talk at RSAA [ slides (main) (side) | blog ]
- Super-Earth talk at ASA 2008 [ slides | blog ]
- Mid-term review at RSAA [ slides ]
- Super-earth talk at the Fifth Stromlo Symposium [ slides ]
- A Circumbinary Polar-ring Debris Disk at Herschel’s View of Star and Planet Formation [ poster ]
- A Circumbinary Polar-ring Debris Disk at Signposts of Planet Formation Conference [ poster ]
- Are debris disks self-stirred? posters at Newton Institute workshops in Cambridge and Edinburgh late 2009 [ poster ]
- Gas giant frequency poster at ASA 2008 [ poster ]
- Gas giant frequency poster at Origins of Solar Systems Gordon Conference [ poster ]
- Super-earth poster at the Astronomical Society of Australia Annual Meeting [ poster ]
- Monthly Notices of the Royal Astronomical Society (MNRAS)
- Astronomy & Astrophysics (A&A)
- The Astrophysical Journal (ApJ)
- James Clerk Maxwell Telescope TAG
- Supervising for Astrophysical Fluid Dynamics (third year course at University of Cambridge), 2013
- Graduate student lectures, Nov 2012, IoA [ slides ]
My PhD involved thinking about how planet formation depends on the star the planets form around, and what we might learn as more planets orbiting a range of different stars are discovered. I worked with Scott Kenyon of Smithsonian Astrophysical Observatory, part of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA in the USA. This link has a copy of my thesis as submitted (no corrections), though the body is just the first four papers listed here outlined a bit more in blog posts, links below.
- Stellar mass dependent disk dispersal in the Astrophysical Journal in April 2009 (ApJ v695 p1210) [ ADS ]
- Planet formation around stars of various masses: Hot super-Earths in the Astrophysical Journal in August 2008 (ApJ v682 p1264) [ ADS | blog entry ]
- Planet formation around stars of various masses: The snow line and the frequency of gas giants appeared in the Astrophysical Journal in January 2008 (ApJ v673 p502) [ ADS | blog entry ]
- Planet formation around M Dwarfs: The moving snow line and super-Earths appeared in Astrophysics and Space Science in August 2007 (Ap&SS v311 p9) [ ADS | blog entry ] (this paper is basically a clearer version of the one below)
- Planet formation around low-mass stars: The moving snow line and super-Earths appeared in the Astrophysical Journal Letters in October 2006 (ApJL v650 p139) [ ADS | blog entry ]
So any complaints from referees aside, I’ve submitted a paper today, which gives me something to show for my time here in Boston!(0)
After four revisions and seven months of extra (part time) work, my second planet formation paper has been accepted, finally! To sum up the paper in a few sentences…
We think that the likelihood of a star forming at least one gas giant planet increases with the mass of the star. There are two reasons for this: Firstly, the mass of the disks surrounding these stars seems to increase with the mass of the star, and therefore so do the masses of protoplanets that form. Secondly, there is probably a threshold protoplanet mass at which gas accretion occurs and giant planets form. Higher mass stars can therefore form protoplanets above the gas giant forming threshold (and therefore gas giants) more easily, because on average they have more material to do so.
The preprint can be found here.
This paper was just accepted to the Astrophysical Journal. It considers a simple disk and snow line model, and uses this to predict the likelihood of stars of different masses harbouring gas giants. We think gas giant frequency increases with stellar mass, which is consistent with observations at present.
In summary, observations indicate that disk mass changes roughly with stellar mass, with a wide distribution of masses at a given stellar mass. Therefore more massive stars on average have more material available for planet formation. In addition, there appears to be a threshold protoplanet mass for forming gas giants of about ten Earth masses. Around more massive stars, a higher fraction of the disks can form protoplanets greater than ten Earth masses, so these stars are more likely to form gas giants.
Recent observations by John Johnson indicate a trend of increasing planet frequency with stellar mass, as our paper predicts. Future observations will improve statistics to solidify this result. In the more distant future, planet discoveries will find how processes like migration and scattering have influenced the distribution of planets we can see now.
This paper, just accepted to the 5SS conference proceedings, is similar to the ApJ letter here. It uses a smaller increase in surface density at the snow line, based on modern Solar abundance figures for oxygen. A brief comment on type I migration has also been added.
Our first paper is about how the snow-line in a protoplanetary disk can move due to evolution of the central star, and how it helps the formation of super-Earth mass planets around M Dwarfs. Kennedy, Kenyon & Bromley (2006) uses a simple disk evolution model, with which we are starting to link formation of planets with that of their parent stars.
As a low-mass red dwarf is born it contracts to its main sequence size over hundreds of millions of years. This contraction limits the radiating area of the star, and so it becomes fainter, and the surrounding disk in which planets form becomes cooler.
The cooling of the star means that the distance where ices condense (known as the ‘snow line’) moves inward. In the same way that it is easier to build a snowman above the snow line on a mountain, the presence of ices in the planet forming disk makes it easier to build planets. These planets can be several times larger than our Earth, and are largely made up of ice, roughly similar in structure to Neptune.
The paper had an associated press release, and subsequently generated a bunch of media attention
ANU Press release | CfA Press Release | Uni of Utah press release | Universe Today | Spaceflight Now | Space Daily | Centauri Dreams | PhysOrg | Unexplained Mysteries | Astrobiology Magazine | SciFi Source Book | AstroFind.net | Science Alert | ABC Radio National | ABC Canberra | Nature