Tag Archive for 'astronomy'
Though I printed it a while ago, my PhD thesis was submitted yesterday. Thanks for three years of tax-free employment Australia!(0)
Curious, my photo of the nifty moon-jupiter-venus configuration generated half as many visits as my most popular blog entry, but in only a few days. It appears the title “smiley moon” was what everyone would be googling…(0)
Go out and look at the moon tonight. Venus and Jupiter are nearby making a smiley face. Maybe it will cheer the world up some…
“It is clear, however, that there are a lot of open questions but we believe that we have disclosed a thinkable strategy how to survive the Red Giant catastrophe of our Sun without violating known laws of Nature. To our best knowledge this is the first time that somebody speculated about such a kind of Planetary Engineering.”-Â Taube & Seifritz (2008)
Now that’s thinking ahead… though given the mess we’ve made in 150 years of industrialisation, perhaps ensuring our planet is habitable in 100 years would be more of a priority, rather than problems that will arise in 1,000,000,000 years.
This is part of one of the old burnt out telescopes at Mt Stromlo.
The ASA conference ended nicely. Well worth the trip over to check the place out.
Apparently someone said “He always looks like he just got out of bed, but seems to know what he’s talking about” when I got up to advertise my poster. Best praise from a stranger I’ve had for ages…
The weather was rubbish all night, so I had nothing to do. I took a photo just before bed time when I was refilling the dewar…
More photos here…
I stayed up a wee bit later this morning to watch the sun come up. Well worth it.
More photos here.
At the end of last night we were taking a few images of a supernova. In the second image we managed to get a passing satellite in the frame, pretty unusual but it happens. The third appeared to have something like a plane, but it wasn’t flashing. The reason? We think the ‘plane’ was a meteor from the eta Aquarids, pieces of Halley’s comet. It went straight through the middle of the supernova’s host galaxy! Well it did from our vantage point anyway…
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.
So I found this old perl module Astro::IRAF::CL.pm which is a perl interface to the IRAF cl. It’s rather old and doesn’t work because the ecl is too high tech for the old module. I fixed this by changing the CL.pm file on line 127:
my $t = Expect->spawn('cl') || croak "Cannot spawn CL: $!";
my $t = Expect->spawn('cl -old') || croak "Cannot spawn CL: $!";
so that the module uses the old cl rather than the extended one. I also changed the maximum line length allowed in the
_break_into_strings subroutine to stop error messages. I ran into trouble with too long lines (help pages say see hconfig$iraf.h, mine is a binary however) so put it back. All seems to work fine….
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, the SKARPS survey of planet-hosting stars, looking for warm dust with WISE and LBTI, theoretical aspects, etc. This work could be split into the (related) aspects of i) trying to understand debris disks as an intrinsically interesting outcome of planet formation processes, ii) using debris disks as a tool to learn about planetary systems in general, and iii) characterising warm debris disks and their evolution as a potential barrier to the future discovery of Earth-like planets around other stars. This page is an up to date astro-related CV.
- Evolution from protoplanetary to debris discs: The transition disc around HD 166191, Kennedy et al 2013, submitted
- Discovery of the [tbc...] debris disk, Kennedy et al 2013, MNRAS in press
- Resolved imaging of the HR 8799 debris disk with Herschel, Matthews, Kennedy, et al 2013, ApJ in press [ ADS | PDF ]
- Herschel Observations of Debris Discs Orbiting Planet-hosting Subgiants, Bonsor, Kennedy, et al 2013, MNRAS in press [ ADS | PDF ]
- Alignment in star-debris disc systems seen by Herschel, Greaves, Kennedy, et al 2013, MNRAS in press [ ADS | PDF ]
- Imaged sub-stellar companions: not as eccentric as they appear? The effect of an unseen inner mass on derived orbits, Pearce, Wyatt, & Kennedy 2013, MNRAS in press [ ADS | PDF ]
- Star – Planet – Debris Disk Alignment in the HD 82943 system: Is planetary system coplanarity actually the norm?, Kennedy et al 2013, MNRAS [ ADS | PDF ]
- First results of the SONS survey: submillimetre detections of debris discs, Panic et al 2013, MNRAS [ ADS | PDF]
- The bright end of the exo-Zodi luminosity function: Disk evolution and implications for exo-Earth detectability, Kennedy & Wyatt 2013, MNRAS [ ADS | PDF ]
- Spatially Resolved Images of Dust Belt(s) Around the Planet-hosting Subgiant Kappa CrB, Bonsor, Kennedy et al 2013, MNRAS [ ADS | PDF | 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 | PDF ]
- 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 ]
- The [tbc...] Debris Disk and implications for the [tbc...] system, SCUBA2 Director’s Discretionary Time, 2013
- 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)
- SpiKeS, Spitzer IRAC survey of the Kepler field, PI: M. Werner, 2013
- Constraining the structure of the Kappa Cr B planetary system, a unique subgiant, orbited by two companions and a debris disc, PI: A. Bonsor, HST, 2013
- Finding low-mass planets in debris-disk systems: searching for correlations, PI: E. Di Folco, RV Survey, 2013
- Small SpiKeS, Spitzer IRAC pilot survey of one Kepler tile, PI: M. Werner, 2012
- LBTI exo-zodi key science team, PI: M. Wyatt, 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
- exo-Zodi and exo-Earths, IAU Symposium 299, Victoria, June 2013 [ slides ]
- 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 ]
- exo-Zodi and prospects for exo-Earth detection at PPVI, 2013 [ poster ]
- A Circumbinary Polar-ring Debris Disk at Herschel’s View of Star and Planet Formation, 2012 [ poster ]
- A Circumbinary Polar-ring Debris Disk at Signposts of Planet Formation Conference, 2011 [ 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, 2007 [ poster ]
- Super-earth poster at the Astronomical Society of Australia Annual Meeting, 2006 [ poster ]
- Monthly Notices of the Royal Astronomical Society (MNRAS)
- Astronomy & Astrophysics (A&A)
- The Astrophysical Journal (ApJ)
- James Clerk Maxwell Telescope TAG
- Supervision of Cambridge summer and part III students (2009-) and co-supervision of a Cambridge PhD student (2013-)
- Supervising for Astrophysical Fluid Dynamics (third year course at University of Cambridge), 2013
- Graduate student lectures, Nov 2012, IoA [ slides ]
- Winner of I’m a scientist, get me out of here! (online interaction with UK school kids, £500 prize, March 2013)
- Co-founder of Mt Stromlo student outreach programme (2006)
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 ]
I think April the first is probably a bad day to publish a serious paper. Anyone looking at astro-ph today will be busy enjoying this paper, rather than looking at your paper. Reference number 6 in that paper is also worth a look…(0)
So I’ve made a half-assed resolution to try and take a nice photo every day. Today I was working on the resonances set up when planets migrate and shepherd others, and stole this image out of the excellent book ‘Solar System Dynamics.’
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.
So I imagine people wondering, what is a typical day at Harvard-CfA like for Grant? Here is my ‘typical’ day…
So after wandering down to school through a crisp morning with patches of snow, I find there are some people I know passing through. I go and meet Anna who lives in Texas, and also see Martin and Ken from Australia. I then go to a talk by a guy from Caltech who does cool theoretical planet work, and later to a talk by another guy who does cool observational planet work. Finally I go out to dinner with more people who do things I’m interested in. And the best thing: dinner was free, thanks ITC!
Meeting three or four people in a day who do research directly related to what I do is very cool, and hasn’t even come close to happening in two years in Australia.
Of course some days I just sit at my desk at play with my computer…
A comet discovered by Rob McNaught at Siding Spring Observatory is nearing the sun in about a week. It will be at its brightest around the 15th Jan, when it will appear as in the image below (though a little later when the sun has set!). More information can be found on this page.
Three years later the burnt out domes are getting repainted, they look very white!
Work is well underway on rebuilding the Commonwealth Solar Observatory (CSO), where people here used to have bbq’s every second week. The painted silver domes have been unveiled recently, and look very shiny!
The 4th annual Stromlo Student Seminars were held Thursday and Friday last week, and were a resounding success.
Thanks to all those who made the effort to come from elsewhere and contribute to a great couple of days of student science.
See this post for notes on the social side of things…
We have recently had our new Advanced Instrumentation and Technology Center (AITC) opened. I’ve been watching it come together from my office window, and put together a little time lapse animation of photos taken with my phone.
Have a look at the animation here (19Mb).
On Monday an ANU press release went out and all hell broke loose. Well I did three radio interviews and made it onto PM, Radio National’s evening news which is quite an achievement aparrently.
My 15 minutes of fame is now over. There are a bunch of links to how my story got pasted over the internet on my PhD publications page.
It even made it into Nature’s research highlights!
The Harvard-Smithsonian Center for Astrophysics (CfA) have put out a press release relating to our recently accepted ‘super-Earth’ paper (astro-ph/0609140, ApJL). It’s also on Universe today which is very cool.
This blog has rewritten what happens and makes some good points about what a super-Earth really is, and about disk masses which do have a wide range. Our model uses a disk that is reasonably massive, for this and dynamical reasons we don’t expect planets much larger than ~5 Earth masses to form in this manner.
It seems a tad unfortunate that today a light plane crashed into an apartment building in Manhattan. It’s probably best when press releases go out on ‘no news’ days… (because this is obviously front page news)
In case you’re wondering, below is an artists image of a super-Earth, an icy planet several times further away from a dim ‘red dwarf’ star than the Earth is from the Sun.
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
I thought the Astronomy Picture of the Day today looked like the face of a cat when it turned up in my google desktop plugin.
Upon opening the real APOD page it turned out to be ‘the unusual stone mesas of the Cydonia region on Mars’.
This is the last thing I’ll add while I’m at Parkes, I promise.
I got an excellent tour of the Dish this morning. We climbed on the edge of the dish and took a ride up to zenith, and then climbed up to the focus cabin. The view from up there is spectacular. I’ve never taken so many photos…
Oh yeah I’m at the dish, in Parkes NSW. The telescope of the movie is every bit as impressive as it was made to look in the movie. I have proven that by taking amazing photos of it.
Since it’s a radio telescope it can work during the day, which unfortunately we aren’t taking advantage of. Our runs are from 5pm to 8am which leaves one feeling a little tired on occasion.
Nevertheless it has been totally worth the paltry 4 hour drive here from Canberra. Thanks Ken!
I’ve spent the last three nights at SSO on the 40″ telescope with Daniel Bayliss looking at the galactic plane. The surrounding national park is beautiful, and there are plenty of walks one can do to pass the daytime hours not spent sleeping, see this entry for the one I did. The trip was a a great learning experience. I now feel the urge to dream up a few observational projects of my own..