Icy planets common around A-type stars

A Spitzer Study of Debris Disks In The Young Nearby Cluster NGC 2232: Icy Planets Are Common Around ~ 1.5--3 Solar-Mass Stars
http://arxiv.org/abs/0807.2056

Abstract wrote:

We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr-old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify 1 A-type star, HD 45435, with definite excess emission at 4.5--24 micron indicative of debris from terrestrial planet formation. We also identify 2--4 late-type stars with possible 8 micron excesses, and 8 early-type stars with definite 24 micron excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears correlated with 24 micron excess, a result expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters. The frequency of debris disks around A-type stars appears to increase from ~ 25% at 5 Myr to ~ 50--60% at 20--25 Myr. Older A-type stars have smaller debris disk frequencies: ~ 20% at 50--100 Myr. For these ages, the typical level of debris emission rises from 5--20 Myr and then declines. Because 24 micron dust emission probes icy planet formation around A-type stars, our results suggest that the frequency of icy planet formation is eta(i) > 0.5--0.6. Thus, most A-type stars (approx. 1.5--3 Msun) produce icy planets.

This is very interesting, but no survey has suceeded to really detect any kind of certain planetary companion so far, neither in Jovian regime (see Beta Pictoris, Vega, Fomalhaut...)

Another paper relevant to this:
Variations on Debris Disks: Icy Planet Formation at 30-150 AU for 1-3 Solar Mass Main Sequence Stars
Icy planets around 1.5-3 solar mass stars proceeds faster than for 1 solar mass stars and results in planets which are on average slightly larger at a given age and distance from the star, but not by much. The largest icy planets produced in both cases are predicted to be about ~50% larger in radius than Pluto.

Edasich wrote:

This is very interesting, but no survey has suceeded to really detect any kind of certain planetary companion so far, neither in Jovian regime (see Beta Pictoris, Vega, Fomalhaut...)

True, but we know Jovian planets around A stars must exist, as planets have been found around stars that have evolved out of type A and into G or K.

Lazarus wrote:

The largest icy planets produced in both cases are predicted to be about ~50% larger in radius than Pluto.

What about planets such as Neptune and Uranus? Aren't they considered "ice giants"? Does this mean that we can expect a lack of Neptune-mass "ice giants" around type A stars?

Sirius_Alpha wrote:

What about planets such as Neptune and Uranus? Aren't they considered "ice giants"? Does this mean that we can expect a lack of Neptune-mass "ice giants" around type A stars?

The paper in question was about planet formation by accretion in the 30-150 AU region. In our solar system Neptune is located at 30 AU, but it is believed to have migrated to this distance from closer in. It may also be possible to form large (Jovian-mass) planets in the outer regions of a protoplanetary disc by gravitational instability.

And looking at this in the light of certain recent discoveries...

heh. heh.

Edasich wrote:

This is very interesting, but no survey has suceeded to really detect any kind of certain planetary companion so far, neither in Jovian regime (see Beta Pictoris, Vega, Fomalhaut...)

I have to retract this.

Yeah, it's interesting to look back on our state of knowledge before, and after the fact.

Here's a 1952 paper proposing the existence of Hot Jupiters.
Link (pdf -- didn't see an abstract).

Quote :

...Hence, there may be many objects of planet-like character in the galaxy. But how should we proceed to detect them? ... There seems to be at present no way to discover objects the size and mass of Jupiter...

Quote :

...But there seems to be no compelling reason why the hypothetical stellar planets should not, in some instances, be closer to their parent stars than is the case in the solar system. It would be of interest to test whether there are any such planets...

Quote :

...It is not unreasonable that a planet might exist at a distance 1/50 AU, or about 3,000,000 km. Its period around a star of solar mass would then be 1 day...

Yet more on what happens in the outer planetary systems...

Variations on Debris Disks II. Icy Planet Formation as a Function of the Bulk Properties and Initial Sizes of Planetesimals
Predictions of ice worlds up to about 1.5 Earth masses, but mainly concentrating on production of Pluto-analogues.