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FN Tau: Small Planets Emerging?

We have a long way to go in the study of circumstellar disks, especially around smaller stars. Given the difficulty of making such observations, work at the Subaru Telescope has focused on stars more massive than the Sun in hopes of studying the more apparent structure of the disks around such stars. But FN Tauri is an exception. The young star is a tenth of the Sun’s mass, its disk seven times lighter than the lowest mass disk previously imaged, which was around the star TW Hydrae. The hope is to extend our knowledge of planetary formation more broadly across stellar types to learn what kind of worlds they form and where.

FN Tauri

The team of Japanese researchers performing this work used the Coronagraphic Imager with Adaptive Optics (CIAO) at the Subaru Telescope. What they’ve learned about FN Tauri is that the thick, roughly circular disk, with a radius of 260 AU, is relatively featureless at this point in the star’s evolution (FN Tauri is thought to be a mere 100,000 years old). Thus far it seems that the more massive protostellar disks are those more likely to show asymmetries. With a mass estimated at 6 percent of the star, the FN Tauri disk becomes thicker with increasing distance, making it appear brighter than expected.

Image: FN Tauri captured by CIAO instrument mounted on the Subaru Telescope. This infrared image taken at 1.6 micron shows an almost face-on circular disk structure. The light from the central star FN Tauri itself is blocked by the coronagraph mask. Somewhat symmetrical darker areas are the blocking by the secondary mirror support. Credit: Subaru Telescope/NAOJ.

In the class of stars known as T Tauri, FN Tauri is powered by the contraction of its disk as it moves toward the main sequence and thus offers a look at early stellar formation. Based on current models, the protoplanetary disk around the star could produce no planets larger than Earth and could form smaller worlds within 30 AU. New adaptive optics at the Subaru site (located on the summit of Mauna Kea in Hawaii) should make still more detailed observations of disk structures possible, along with analysis of the material within them. That makes work like this valuable not only in itself, but also in terms of target gathering for the more powerful telescopes planned for next generation exoplanet hunting.

The paper is Kudo et al., “Discovery of a Scattering Disk around the Low‐Mass T Tauri Star FN Tauri,” Astrophysical Journal 673 (January 20, 2008), L67-L70 (abstract).

Comments on this entry are closed.

  • James M. Essig February 14, 2008, 8:51

    Hi Folks;

    The ability to study protoplanetary disks and solar systems around small stars is going to be real interesting. Given that Red Drawfs have a predicted lifetime of upwards of 10 EXP 15 years, or about 100,000 times the age of our universe, such stars offer potential habitats for ETI lifeforms to evolve for a quadrillion years before possibly moving onto a new star.

    Mankind may too find future homes around red dwarfs all ready formed and yet to be formed. We see how far we have come in just 200 years; from fireplaces and coal burning stoves to modern nuclear power plants, from hourse drawn carriages to maglev trains, 787 dreamliner jet aircraft and space shuttles, from crude home remedies to the plethora of modern pharmacological agents, PET scans, MRI scans, Functional MRI scans, CAT scans, magnetic beam encephelography scans, and the list goes on and on.

    Imagine what we can accomplish in another 100 years! another 1,000 years! another million years! another billion years! another quadrillion years!…

    Just a thought.

    Your Friend Jim

  • ljk February 22, 2008, 11:31

    Orbits and Masses in the T Tauri System

    Authors: Rainer Köhler, Thorsten Ratzka, T. M. Herbst, Markus Kasper

    (Submitted on 21 Feb 2008)

    Abstract: We investigate the binary star T Tauri South, presenting the orbital parameters of the two components and their individual masses. We combined astrometric positions from the literature with previously unpublished VLT observations. Model fits yield the orbital elements of T Tau Sa and Sb. We use T Tau N as an astrometric reference to derive an estimate for the mass ratio of Sa and Sb. Although most of the orbital parameters are not well constrained, it is unlikely that T Tau Sb is on a highly elliptical orbit or escaping from the system. The total mass of T Tau S is rather well constrained to 3.0 +0.15/-0.24 M_sun. The mass ratio Sb:Sa is about 0.4, corresponding to individual masses of M_Sa = 2.1+/-0.2 M_sun and M_Sb = 0.8+/-0.1 M_sun. This confirms that the infrared companion in the T Tauri system is a pair of young stars obscured by circumstellar material.

    Comments: 10 pages, 11 figures, accepted by Astronomy and Astrophysics

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.3178v1 [astro-ph]

    Submission history

    From: Rainer Koehler [view email]

    [v1] Thu, 21 Feb 2008 18:03:36 GMT (704kb)


  • ljk February 25, 2008, 11:16

    A coagulation-fragmentation model for the turbulent growth and destruction of preplanetesimals

    Authors: Anders Johansen, Frithjof Brauer, Cornelis Dullemond, Hubert Klahr, Thomas Henning

    (Submitted on 22 Feb 2008)

    Abstract: To treat the problem of growing protoplanetary disc solids across the meter barrier, we consider a very simplied two-component coagulation-fragmentation model that consists of macroscopic boulders and smaller dust grains, the latter being the result of catastrophic collisions between the boulders. Boulders in turn increase their radii by sweeping up the dust fragments. An analytical solution to the dynamical equations predicts that growth by coagulation-fragmentation can be efficient and allow agglomeration of 10-meter-sized objects within the time-scale of the radial drift. These results are supported by computer simulations of the motion of boulders and fragments in 3-D time-dependent magnetorotational turbulence. Allowing however the fragments to diffuse freely out of the sedimentary layer of boulders reduces the density of both boulders and fragments in the mid-plane, and thus also the growth of the boulder radius, drastically. The reason is that the turbulent diffusion time-scale is so much shorter than the collisional time-scale that dust fragments leak out of the mid-plane layer before they can be swept up by the boulders there.

    Our conclusion that coagulation-fragmentation is not an efficient way to grow across the meter barrier in fully turbulent protoplanetary discs confirms recent results by Brauer, Dullemond, & Henning who solved the coagulation equation in a parameterised turbulence model with collisional fragmentation, cratering, radial drift, and a range of particle sizes. We find that a relatively small population of boulders in a sedimentary mid-plane layer can populate the entire vertical extent of the disc with small grains and that these grains are not first generation dust, but have been through several agglomeration-destruction cycles during the simulations.

    Comments: 17 pages, 8 figures. Submitted to A&A, first referee report
    received, comments welcome

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.3331v1 [astro-ph]

    Submission history

    From: Anders Johansen [view email]

    [v1] Fri, 22 Feb 2008 15:10:57 GMT (647kb)


  • ljk February 29, 2008, 8:48

    Planet Formation by Concurrent Collapse

    Authors: Michael Wilkinson, Bernhard Mehlig

    (Submitted on 27 Feb 2008)

    Abstract: We discuss the difficulties faced by the conventional theory of planet formation, which involves aggregation of microscopic dust particles. We describe an alternative hypothesis, termed ‘concurrent collapse’, in which planets form by gravitational collapse at the same time as the star about which they orbit.

    This mechanism avoids theoretical difficulties associated with the conventional model and suggests satisfying explanations for various poorly understood phenomena. We introduce new explanations for FU Orionis outbursts seen in young stars, the discovery of exoplanets with eccentric orbits and the existence of small rocky objects such as chondrules in the solar system.

    Comments: 6 pages

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.4099v1 [astro-ph]

    Submission history

    From: Michael Wilkinson [view email]

    [v1] Wed, 27 Feb 2008 22:10:40 GMT (12kb)


  • ljk February 29, 2008, 8:54

    SPH simulations of star/planet formation triggered by cloud-cloud collisions

    Authors: Spyridon Kitsionas (AIP, Potsdam, Germany), Anthony P. Whitworth (School of Physics & Astronomy, Cardiff University, U.K.), Ralf S. Klessen (ITA, University of Heidelberg, Germany)

    (Submitted on 28 Feb 2008)

    Abstract: We present results of hydrodynamic simulations of star formation triggered by cloud-cloud collisions. During the early stages of star formation, low-mass objects form by gravitational instabilities in protostellar discs. A number of these low-mass objects are in the sub-stellar mass range, including a few objects of planetary mass. The disc instabilities that lead to the formation of low-mass objects in our simulations are the product of disc-disc interactions and/or interactions between the discs and their surrounding gas.

    Comments: 8 pages, 7 figures; accepted for publication in the proceedings of IAU Symposium 249: Exoplanets: Detection, Formation and Dynamics, Y.-S. Sun, S. Ferraz-Mello & J.-L. Zhou (eds.), Cambridge University Press

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.4146v1 [astro-ph]

    Submission history

    From: Spyridon Kitsionas [view email]

    [v1] Thu, 28 Feb 2008 09:05:01 GMT (379kb)


  • ljk February 29, 2008, 8:56

    The dusty disk around VV Ser

    Authors: T. Alonso-Albi, A. Fuente, R. Bachiller, R. Neri, P. Planesas, L. Testi

    (Submitted on 28 Feb 2008)

    Abstract: We have carried out observations at millimeter and centimeter wavelengths towards VV Ser using the Plateau de Bure Interferometer and the Very Large Array. This allows us to compute the SED from near infrared to centimeter wavelengths. The modeling of the full SED has provided insight into the dust properties and a more accurate value of the disk mass.

    The mass of dust in the disk around VV Ser is found to be about 4 10^(-5) Msun, i.e. 400 times larger than previous estimates. Moreoever, the SED can only be accounted for assuming dust stratification in the vertical direction across the disk. The existence of small grains (0.25–1 micron) in the disk surface is required to explain the emission at near- and mid-infrared wavelengths. The fluxes measured at millimeter wavelengths imply that the dust grains in the midplane have grown up to very large sizes, at least to some centimeters.

    Comments: To appear in ApJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.4152v1 [astro-ph]

    Submission history

    From: Tom\’as Alonso [view email]

    [v1] Thu, 28 Feb 2008 09:27:35 GMT (441kb)


  • ljk March 3, 2008, 10:12

    Turbulent transport and its effect on the dead zone in protoplanetary discs

    Authors: Martin Ilgner, Richard P. Nelson

    (Submitted on 29 Feb 2008)

    Abstract: Protostellar accretion discs have cool, dense midplanes where externally originating ionisation sources such as X-rays or cosmic rays are unable to penetrate. This suggests that for a wide range of radii, MHD turbulence can only be sustained in the surface layers where the ionisation fraction is sufficiently high. A dead zone is expected to exist near the midplane, such that active accretion only occurs near the upper and lower disc surfaces. Recent work, however, suggests that under suitable conditions the dead zone may be enlivened by turbulent transport of ions from the surface layers into the dense interior.

    In this paper we present a suite of simulations that examine where, and under which conditions, a dead zone can be enlivened by turbulent mixing. We use three-dimensional, multifluid shearing box MHD simulations, which include vertical stratification, ionisation chemistry, ohmic resistivity, and ionisation due to X-rays from the central protostar. We compare the results of the MHD simulations with a simple reaction-diffusion model.

    The simulations show that in the absence of gas-phase heavy metals, such as magnesium, turbulent mixing has essentially no effect on the dead zone. The addition of a relatively low abundance of magnesium, however, increases the recombination time and allows turbulent mixing of ions to enliven the dead zone completely beyond a distance of 5 AU from the central star, for our particular disc model. During the late stages of protoplanetary disc evolution, when small grains have been depleted and the disc surface density has decreased below its high initial value, the structure of the dead zone may be significantly altered by the action of turbulent transport.

    Comments: 20 pages, 11 figures, accepted for publication in A&A, high resolution pdf available at this http URL

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0802.4409v1 [astro-ph]

    Submission history

    From: Martin Ilgner [view email]

    [v1] Fri, 29 Feb 2008 15:17:22 GMT (2511kb,D)


  • ljk March 10, 2008, 23:48

    Constraining the Earliest Circumstellar Disks and their Envelopes

    Authors: Hsin-Fang Chiang, Leslie W. Looney, Konstantinos Tassis, Lee G. Mundy, Telemachos Ch. Mouschovias

    (Submitted on 9 Mar 2008)

    Abstract: Using interferometric data from BIMA observations, combined with detailed modeling in Fourier space of the physical structures predicted by models, we constrain the circumstellar envelope parameters for four Class 0 young stellar objects, as well as their embedded circumstellar disks. The envelopes of these objects are still undergoing collapse, and theoretical collapse models can be compared to the observations. Since it has been suggested in a previous study that both the Larson-Penston and Shu similarity solutions underestimate the age of the system, we adopt Tassis & Mouschovias’ model of the collapse process, which includes all relevant magnetic fields effects.

    The results of the model fitting show a good consistency between theory and data; furthermore, no age problem exists since the Tassis & Mouschovias’ model is age independent for the first 255 kyr. Although the majority of the continuum dust emission arises from the circumstellar envelopes, these objects have well known outflows, which suggest the presence of circumstellar disks. At the highest resolution, most of the large-scale envelope emission is resolved out by interferometry, but the small-scale residual emission remains, making it difficult to observe only the compact disk component. By modeling the emission of the envelope and subtracting it from the total emission, we constrain the disk masses in our four systems to be comparable to or smaller than the typical disk masses for T Tauri systems.

    Comments: 23 pages, 4 figures, accepted for publication in the Astrophysical Journal

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0803.1272v1 [astro-ph]

    Submission history

    From: Hsin-Fang Chiang [view email]

    [v1] Sun, 9 Mar 2008 00:49:30 GMT (59kb)


  • ljk March 13, 2008, 12:39

    Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk

    Authors: William Herbst, Catrina M. Hamilton, Katherine LeDuc, Joshua N. Winn, Christopher M. Johns-Krull, Reinhard Mundt, Mansur Ibrahimov

    (Submitted on 12 Mar 2008)

    Abstract: We show that grains have grown to ~mm size (sand sized) or larger in the terrestrial zone (within ~3 AU) of the protoplanetary disk surrounding the 3 Myr old binary star KH 15D. We also argue that the reflected light in the system reaches us by back scattering off the far side of the same ring whose near side causes the obscuration.

    Comments: 22 pages, 5 figures. To be published in Nature, March 13, 2008. Contains a Supplement

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0803.1782v1 [astro-ph]

    Submission history

    From: Bill Herbst [view email]

    [v1] Wed, 12 Mar 2008 18:04:49 GMT (887kb)