The Disk Around CoKu Tauri/4: Circumbinary, Not Transitional

“This routine was implemented using the ALLSTAR routine in the IRAF package DAOPHOT (Stetson 1987), and based on previous experience with NIRC2 imaging, we chose to model the PSF using a Gaussian core with Lorentzian wings.”

“To estimate the reddening, we used the following data: intrinsic colors reported in Bessell & Brett (1988) and Bessell (1990) interpolating between giants (log(g) ∼ 1) and dwarfs (log(g) ∼ 5) at an assumed log(g) of 3.7, JHK photometry from 2MASS, V-band photometry averaged between Cohen & Kuhi…”

“In this geometry, Artymowicz & Lubow (1994) calculate that the 3:1 orbital resonance at RD ∼ 2.08a is opened for all but improbably small eccentricities (e & 0.03).”

“5 spectral classification from Cohen & Kuhi (1979) with an assumed 1 sub-class uncertainty.”

“In addition to this method, we used a recursive-phase algorithm (e.g Lohmann et al. 1983) to reconstruct Fourier Phase from bispectrum phase, and then fitted a binary model to the reconstructed phase of the image.”

“This inner hole could be caused by natural processes of grain growth and/or photo-evaporation (Alexander et al. 2006), or truncation of the disk due to dynamical interactions with companions (Lin & Papaloizou 1979).”

“This inner hole could be caused by natural processes of grain growth and/or photo-evaporation (Alexander et al. 2006), or truncation of the disk due to dynamical interactions with companions (Lin & Papaloizou 1979).”

“Simon et al. (2000) used resolved CO 2-1 observations of disks around several T Tauri stars to measure their masses directly.”

“Radial velocity monitoring is most applicable to DM Tau, where the cleared inner hole is expected to have only a 3AU radius (Calvet et al. 2005).”

“5 stars (Luhman 1999), the stars are 4MYr old and are of mass ∼0.52 and ∼0.62M⊙.”

“Most young stars have disks that are optically thick at all wavelengths or have no observable disk at all, while a small subset of young stars are in an intermediate state, thought to be in “transition” (Skrutskie et al. 1990).”

“An uncertainty in distance due to the depth of Taurus (e.g. Torres et al. 2007) can not reconcile this discrepancy, as both RD determined from radiative transfer modeling and the minimum RD determined by dynamical considerations both increase linearly with the distance estimate.”

“The observational scatter in the Taurus HR diagram (e.g Luhman 2004) is consistent with CoKu Tau/4 being either single as assumed by previous authors or an equal brightness double.”

“Many of these intermediate objects have optically thick “cold disks” as seen by large excesses at ∼30µm, but much smaller or nonexistent near- and mid- infrared excesses (Brown et al. 2007).”

“An uncertainty in distance due to the depth of Taurus (e.g. Torres et al. 2007) can not reconcile this discrepancy, as both RD determined from radiative transfer modeling and the minimum RD determined by dynamical considerations both increase linearly with the distance estimate.”

“Aperturemasking interferometry (e.g. Tuthill et al. 2000) is a well established technique for achieving the full diffraction limit of a single telescope, recently applied to observations behind adaptive optics systems (e.g. Lloyd et al. 2006; Kraus et al. 2008).”

“The disk has been modeled as having an inner hole of radius ∼10AU (D’Alessio et al. 2005), with suggestions that this hole is due to a giant planet (Quillen et al. 2004).”

“An example of this is CS Cha, which was announced as a transitional disk (Espaillat et al. 2007) shortly after its discovery as a circumbinary disk (Guenther et al. 2007).”

“Although the most exciting interpretation for the development of gaps is arguably truncation due to planetary formation, it is also possible to dynamically truncate disks due to stellar companions (e.g Jensen & Mathieu 1997; Beust & Dutrey 2005; White & Hillenbrand 2005).”

“CoKu Tau/4 was discovered to have a large ∼20-30µm excess and no excess at wavelengths < 8µm through Spitzer Space Telescope Infrared Spectrograph observations (Forrest et al. 2004).”

“An example of this is CS Cha, which was announced as a transitional disk (Espaillat et al. 2007) shortly after its discovery as a circumbinary disk (Guenther et al. 2007).”

“We extracted photometry and astrometry from the direct AO imaging of these sources using the PSF reconstruction technique described in Kraus & Hillenbrand (2007b), which iteratively fits a template PSF to the primary and then subtracts the secondary to fit an im- proved estimate of the primary.”

“Some authors (e.g. Furlan et al. 2007) have considered the term “transitional” to be an observational term that means the spectral signature of a cleared inner disk rather than an evolutionary term that implicitly applies to single stars.”

“Although the most exciting interpretation for the development of gaps is arguably truncation due to planetary formation, it is also possible to dynamically truncate disks due to stellar companions (e.g Jensen & Mathieu 1997; Beust & Dutrey 2005; White & Hillenbrand 2005).”

“Aperturemasking interferometry (e.g. Tuthill et al. 2000) is a well established technique for achieving the full diffraction limit of a single telescope, recently applied to observations behind adaptive optics systems (e.g. Lloyd et al. 2006; Kraus et al. 2008).”

“Beust & Dutrey (2005) predict a gap size of > 2.6a for eccentricities > 0.1 for GG Tau, which has a similar mass ratio to CoKu Tau/4 (and find this not to be large enough for that system).”

“…Bessell & Brett (1988) and Bessell (1990) interpolating between giants (log(g) ∼ 1) and dwarfs (log(g) ∼ 5) at an assumed log(g) of 3.7, JHK photometry from 2MASS, V-band photometry averaged between Cohen & Kuhi (1979) and Hanson et al. (2004) with an assumed 0.1mag overall uncertainty, and an M1.”

“We extracted photometry and astrometry from the direct AO imaging of these sources using the PSF reconstruction technique described in Kraus & Hillenbrand (2007b), which iteratively fits a template PSF to the primary and then subtracts the secondary to fit an im- proved estimate of the primary.”

“UY Aur (Duvert et al. 1998) and CoKu Tau 4 (Ireland & Kraus 2008) are additional examples of primordial circumbinary disks but they appear to be rare exceptions rather than the rule.”

“…to explain observations of transition disks, including extensive particle growth (Tanaka et al. 2005; Dullemond & Dominik 2005), photoevaporative massloss in winds (Clarke et al. 2001; Alexander et al. 2006a), and tidal interactions with companions (e.g., Rice et al. 2003a; Ireland & Kraus 2008).”

“Some outliers may be expected from this relationship for circumbinary disks, such as the disk around CoKu Tau 4 (D’Alessio et al. 2005; Ireland & Kraus 2008).”

“This approach has been quite fruitful, resulting in the discovery of companions within these gaps spanning the stellar (CoKu Tau 4: Ireland & Kraus 2008; HD 142527: Biller et al. 2012, Close et al. 2014, Rodigas et al. 2014, Lacour et al. 2015), brown dwarf (HD 169142: Biller et al. 2014, Reggiani…”

“Taurus members that are known to harbor transitional disks include CoKu Tau/4, GM Aur, and DM Tau (Rice et al. 2003; Forrest et al. 2004; Quillen et al. 2004; Calvet et al. 2005; D’Alessio et al. 2005), although the inner hole in the disk of CoKu Tau/4 was probably produced by a stellar companion rather than processes…”