HR8799: wrap-up

So we had a rather nice discussion over the recent paper on LBT observations of HR8799. Seemed a good discussion with mostly a few people who work in the field or closely related fields. If you missed it feel free to comment. And there was a question by @LeonBaloo about resonances which got lost. Any good definitions welcome. Start from the bottom when reading.

@Matt_Burleigh: @nialldeacon thanks for organizing Niall. Goodnight from the UK #astrojc

@nialldeacon: @johngizis true, but it says those kind of objects (formed by instability) are rare #astrojc

@Matt_Burleigh: @johngizis yes, which makes it so exciting and gives us all a lot to work on! #astrojc

@johngizis:We are still too much at the tip of the iceberg, only the widest, most massive planets can be detected. right? #astrojc

@nialldeacon: Think probably a good time to wrap up #astrojc will put a review post up soon so others can contribute

@Matt_Burleigh: @astronomerslc25 50-60, late B to early F spectral types #astrojc

@astronomerslc25: @Matt_Burleigh how many in the sample? #astrojc

@Matt_Burleigh: @nialldeacon I guess we just dont have enough information yet. Fascinating system, poses many questions for different areas #astrojc

@nialldeacon: @Matt_Burleigh still would be one of the younger systems but doesn’t explain why it’s the only one #astrojc

@Matt_Burleigh: @nialldeacon @johngizis I think the sample were selected for youth (<~250My) #astrojc

@nialldeacon: @Matt_Burleigh Are all the A stars in the sample of similar age? Maybe others have had planets which were kicked out dynamically? #astrojc

@Matt_Burleigh: @nialldeacon @johngizis I guess HR8799 needed a massive, large (~100AU) disc though #astrojc

@nialldeacon: . @Matt_Burleigh My disk knowledge isn't good enough to know how exceptional the disk is @johngizis any ideas? #astrojc ‏

@Matt_Burleigh: @nialldeacon Maybe. What was special about HR8799 then? Or maybe stats arent yet good enough, #astrojc

@nialldeacon: @Matt_Burleigh so I dunno what it says about formation. That wide massive planets from disk instability are rare #astrojc

@nialldeacon: Retired A stars means ones that evolved off the main sequence so have lines that make RV planet surveys easier #astrojc

@Matt_Burleigh: @nialldeacon yes, some appear to be retired G stars! #astrojc

@nialldeacon:. @Matt_Burleigh there are some around the "retired A stars" although there is debate as to whether the retired A stars are retired #astrojc

@astronomerslc25nialldeacon oh yes. Although not as odd as 2mass1207 #astrojc

@Matt_Burleigh: Jenny Patience revealed at #nam2012 that no other A star in their survey has planets. What does all this say about their formation?#astrojc

@astronomerslc25: @Matt_Burleigh @nialldeacon #astrojc or much else I think. Looks more and more gravity dependent too

@nialldeacon: @astronomerslc25 Planet b being the poster-child for that #astrojc

@astronomerslc25: @nialldeacon #astrojc looks like more evidence for a delayed L-T transition with youth.
In reply to Niall Deacon

@Matt_Burleigh: @nialldeacon @astronomerslc25 the infamous L-T transition – where it seems spectral type does not tell you much about temperature #astrojc

@nialldeacon: @astronomerslc25 #astrojc well they all lie close to the L to T spectral type transition in temperature

@astronomerslc25: @nialldeacon so what makes them patchy? just right combo of teff and grav? #astrojc

@nialldeacon:. @Matt_Burleigh youth makes the clouds thicker hence makes them redder but they still needed patchy clouds to fit #astrojc

@astronomerslc25: @Matt_Burleigh @nialldeacon there was an Akari paper on L dwarfs in 3.3um. They found the spectra was not what was expected. #astrojc

@Matt_Burleigh: @astronomerslc25 @nialldeacon is the low gravity a factor? #astrojc

@astronomerslc25: @Matt_Burleigh probably. Although not much flux there #astrojc

@astronomerslc25: Maybe just effects of youth though? #astrojc

@astronomerslc25: @nialldeacon I suspect so, but the bright 3.3 is odd. #astrojc
In reply to Niall Deacon

@nialldeacon: too simplistic? #astrojc

@nialldeacon: my understanding of patchy clouds, cloudy parts look like L dwarfs, gaps like T dwarfs and the integrated atmosphere mixed #astrojc

@LeonBaloo:.@nialldeacon ok 5:2 means 5 inner = 2 outer orbits. But what defines a resonance? The largest/smallest/innermost/outermost planet? #astrojc

@nialldeacon: @astronomerslc25 so patchy clouds then #astrojc

@astronomerslc25: @nialldeacon hey! I'm in for the atmosphere stuff #astrojc

@nialldeacon: I've seen claims of huge free floating planetary mass things from microlensing, how believable are they? #astrojc

@nialldeacon: So @dh4gan mentioned chaotic orbits lead 2 ejections and would be a source of the population of free floating planetary mass things #astrojc

@LeonBaloo: So, basic planetary question: what’s a 4:2:1 or 5:2 resonance? #astrojc

@LeonBaloo: Hi @nialldeacon; am arriving late to the party – know nothing on planetary science so will mostly be watching and maybe questioning #astrojc

@Matt_Burleigh: Im partcularly interested in orbits and thoughts on formation mecahnism. Hoping @astronomerslc25 will join in to talk about atmos #astrojc

@nialldeacon: Right, the hour has come, let #astrojc begin. Which aspect do you want to talk about? the atmospheres, the AO or the orbits

@dh4gan: Also, ejection of such planets might help explain the apparently large number of free floating planets #astrojc

@dh4gan: HR8799 is poster child of gravitational instability mode of planet formation. Growing realisation that GI systems often unstable #astrojc

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Dusty, young and chaotic – the HR 8799 system with the new LBT AO system

Hi folks, for one week only I’ll be MCing astrojc while Emma is off wedding planning.

This week’s paper is on the HR 8799 system. Three planets were directly imaged around this young star in 2008 with a fourth, closer companion identified in 2010. The system also has a disk inside the orbit of the closest companion (planet e) and a more distant outer disk beyond the orbits of the planets. Spectroscopic observations indicate that the planets are cool, around the temperature of the transition between the L spectral class and the T spectral class. However there are indications of some non-equilibrium chemistry and thicker clouds than field L and T dwarfs (which are often higher mass brown dwarfs).

The paper in question is one of two studying HR 8799 with the new AO system on the LBT. It presents H band photometry of the system along with a companion paper containing 3.3 micron observations.  The papers indicate that the planets are indeed atmospherically strange, showing little methane absorption compared to field brown dwarfs of similar temperatures (the onset of methane in the spectrum is the signature of the L to T transition). As was previously known, planet b is significantly fainter and redder than most known L dwarfs. The paper also models the orbits of the planets indicating that the orbits are not stable on a timescale comparable to the age of the host star.

So what shall we talk about,

1) The LBT AO system and the two instruments used for this detection (PISCES and LBTI)

2) The strange atmospheric chemistry of these objects

3) The dynamics of the system. I’m no expert on this part, what does it mean for formation models?

So come along everyone for #astrojc at 8pm BST on Thursday

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On hiatus

I’m off to get married so I can’t run the astronomy twitter journal club for the next few weeks. If anyone would like to step in and run things whilst I’m away send me an email ( and I’ll initiate you into the mysteries of astrojc (i.e. let you access the twitter account), otherwise things will resume in May.

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Transcript: the pros & cons of pro/am collaboration

The transcript of the 24th Astronomy Twitter Journal Club meeting is now online at Chirpstory: or

You can also download the PDF: Tweet transcript archive.

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This week’s meeting: the pros & cons of pro/am collaboration

Professional / amateur collaboration in science, and astronomy in particular, is the discussion topic for this Thursday’s astronomy twitter journal club, starting at 20:10 GMT. @SamHawkins, who proposed this topic, explains more:

Astronomy is one of the few branches of science to which amateurs regularly contribute significant observations and discoveries. For decades amateurs and professionals have worked together on research projects to compute the orbits of Near-Earth Objects (NEOs), monitor active regions on the Sun, as well as variable stars of various types as they fluctuate in magnitude. We have also long studied the extra-terrestrial storm systems that grow and subside on the gas giants, and more recently amateurs have used relatively inexpensive equipment to discover extra-solar planets. These ‘pro-am’ collaborations can be effective when organised well, but I often wonder what could be done to improve them. Have they ever failed? Why? What areas of astronomy have benefited from such efforts? And do amateurs deserve more recognition? During this Twitter meeting we’ll discuss the pros and cons of pro-am collaboration in astronomy, and then some.

@ThilinaH kindly pointed out these slides from the UNAWE project which give some background to the subject:

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Review: Understanding gamma-ray flares in the Crab Nebula

coming soon…

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Transcript: Understanding gamma-ray flares in the Crab Nebula

The transcript of the 23rd Astronomy Twitter Journal Club meeting is now online at Chirpstory: or

You can also download the PDF: Tweet transcript archive.

Posted in Transcripts | Tagged | Leave a comment