WALL EMISSION IN CIRCUMBINARY DISKS: THE CASE OF CoKu TAU/4

Journal Article · Fri Jan 01 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/708/1/38· OSTI ID:21392505

Nagel, Erick; D'Alessio, Paola ^[1]; Calvet, Nuria ^[2]; Espaillat, Catherine ^[3]; Sargent, Ben ^[4]; Hernandez, Jesus ^[5]

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1. Centro de RadioastronomIa y AstrofIsica, UNAM, Morelia, Michoacan, Mexico 58089 (Mexico)
2. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)
3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States)
4. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
5. Centro de Investigaciones de AstronomIa, Merida 5101-A (Venezuela, Bolivarian Republic of)

A few years ago, the mid-IR spectrum of a Weak Line T Tauri Star, CoKu Tau/4, was explained as emission from the inner wall of a circumstellar disk, with the inner disk truncated at approx10 AU. Based on the spectral energy distribution (SED) shape and the assumption that it was produced by a single star and its disk, CoKu Tau/4 was classified as a prototypical transitional disk, with a clean inner hole possibly carved out by a planet, some other orbiting body, or by photodissociation. However, recently it has been discovered that CoKu Tau/4 is a close binary system. This implies that the observed mid-IR SED is probably produced by the circumbinary disk. The aim of the present paper is to model the SED of CoKu Tau/4 as arising from the inner wall of a circumbinary disk, with parameters constrained by what is known about the central stars and by a dynamical model for the interaction between these stars and their surrounding disk. We lack a physical prescription for the shape of the wall, thus, here we use a simplified and unrealistic assumption: the wall is vertical. In order to fit the Spitzer IRS SED, the binary orbit should be almost circular, implying a small mid-IR variability (10%) related to the variable distances of the stars to the inner wall of the circumbinary disk. In the context of the present model, higher eccentricities would imply that the stars are farther from the wall, the latter being too cold to explain the observed SED. Our models suggest that the inner wall of CoKu Tau/4 is located at 1.7a, where a is the semi-major axis of the binary system (a approx 8 AU). A small amount of optically thin dust in the hole (approx<0.01 lunar masses) helps to improve the fit to the 10 mum silicate band. Also, we find that water ice should be absent or have a very small abundance (a dust to gas mass ratio approx<5.6 x 10{sup -5}). In general, for a binary system with eccentricity e>0, the model predicts mid-IR variability with periods similar to orbital timescales, assuming that thermal equilibrium is reached instantaneously.

• OSTI ID: 21392505
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 708; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
BINARY STARS
CHEMICAL REACTIONS
DECOMPOSITION
DUSTS
EMISSION
ENERGY SPECTRA
EQUILIBRIUM
ERUPTIVE VARIABLE STARS
HYDROGEN COMPOUNDS
ICE
INFRARED SPECTRA
MASS
MATTER
ORBITS
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PLANETS
SILICATES
SILICON COMPOUNDS
SPECTRA
STARS
T TAURI STARS
THERMAL EQUILIBRIUM
VARIABLE STARS
WATER