Monday was the first day of the conference. I gave my talk and didn’t pay attention to much else until I did so…
Tag Archive for 'phd'
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!
My PhD involves 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 am working with Scott Kenyon of Smithsonian Astrophysical Observatory, part of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA in the USA.
Pieces of my PhD in Astronomy and Astrophysics at ANU in Australia are scattered around the place. For temporal things such as paper acceptances and slightly less academic stuff, take a look at blog entries filed under school. More permanent or slowly changing things (like papers) are on this page…
Papers
We have so far published two papers, with a third accepted and to be published soon. There is also a conference proceedings article from the Fifth Stromlo Symposium. These are outlined a bit more in blog posts, links below.
- 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 ]
Talks
I have given a number of talks and posters.
- Super-Earth talk at ASA 2008 [ slides | blog entry ]
- Mid-term review at RSAA [ slides ]
- Super-earth talk at the Fifth Stromlo Symposium [ slides ]
- 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 ]
Links
These are for me really… anyone | passworded | phd
So any complaints from referees aside, I’ve submitted a paper today, which gives me something to show for my time here in Boston!
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.
The paper can be found through the NASA Astrophysics Data System. For more information on my PhD have a look at the main PhD page.
I’m not sure whether to claim this one, I spent a week near Springfield at an enjoyable Gordon conference in western Mass this week so have ventured out of Boston.
Maybe I’ll wait until I’ve been to Walden Pond to claim it…
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.
The paper can be found through the NASA Astrophysics Data System. For more information on my PhD have a look at the main PhD page.
