A simple analytical formulation for periodic orbits in binary stars

An analytical approximation to periodic orbits in the circular restricted three-body problem is provided. The formulation given in this work is based on calculations known from classical mechanics, but with the addition of certain terms necessary to give a reasonably good approximation. The results are compared with simulations. The derived simple set of analytical expressions gives periodic orbits on the discs of binary systems without the need to solve the equations of motion by numerical integratio

Modeling of CoRoT and Spitzer lightcurves in NGC 2264 caused by an optically thick warp

Aims: We present an analysis of simultaneously observed CoRoT and Spitzer lightcurves for $4$ systems in the stellar forming region NGC 2264: Mon-660, Mon-811, Mon-1140 and Mon-1308. These objects share in common a high resemblance between the optical and infrared lightcurves, such that the mechanism responsible to produce them is the same. The aim of this paper is to explain both lightcurves simultaneously with only one mechanism. Methods: We have modeled the infrared emission as coming from a warp composed of an optically thick wall and an optically thick asymmetric disk beyond this location. We have modeled the optical emission mainly by partial stellar occultation by the warp. Results: The magnitude amplitude of the CoRoT and Spitzer observations for all the objects can be described with the emission coming from the system components. The difference between them is the value of the disk flux compared with the wall flux and the azimuthal variations of the former. This result points out the importance of the hydrodynamical interaction between the stellar magnetic field and the disk. Conclusions: CoRoT and Spitzer lightcurves for the stellar systems Mon-660, Mon-811, Mon-1140 and Mon-1308 can be simultaneously explained using the emission coming from an asymmetric disk and emission with stellar occultation by an optically thick wall.Comment: 17 pages, 10 figure

The dipper light curve of V715 Per: is there dust in the magnetosphere?

The dipper optical light curves in young stellar objects are commonly interpreted as partial or total occultation of the stellar radiation by dust surrounding the star. In this work, we analyze the amplitude of the optical light curve of V715 Per, located in the young star forming region IC 348. Observations gathered over the years suggest that the light curve can be explained by dust extinction events. In our model, the dust is distributed inside the magnetosphere according to the strength of the stellar magnetic field. The dust distribution is modulated by the vertical component of the field, whose axis is misaligned with respect to the rotational axis. We include a model for the evaporation of the dust reaching the magnetosphere in order to consistently calculate its distribution. For V715 Per, there is dust in the optically thick warp at the disk truncation radius. We suggest that the optical light curve is explained by extinction caused by dust reaching inside the magnetosphere. The dust distribution is optically thin and due to the high temperature and low density, it cannot survive for a long time. However because the grains rapidly move towards the stellar surface and the sublimation is not instantaneous, there is a layer of dust covering the magnetosphere responsible for the extinction. Dust surviving the harsh conditions of the magnetospheric accretion flow may be responsible for some of the dipper light curves.Comment: Accepted for publication in Astronomy & Astrophysics 20 pages, 7 figure

A Simple Analytical Formulation for Periodic Orbits in Binary Stars

An analytical approximation to periodic orbits in the circular restricted three-body problem is provided. The formulation given in this work is based in calculations known from classical mechanics, but with the addition of the necessary terms to give a fairly good approximation that we compare with simulations, resulting in a simple set of analytical expressions that solve periodic orbits on discs of binary systems without the need of solving the motion equations by numerical integrations.Comment: Accepted on MNRAS. 29 pages including 6 Figures and 4 table

Early science with the Large Millimetre Telescope:New mm-wave detections of circumstellar discs in IC 348 from LMT/AzTEC

We present the most complete sample of mm measurements of protoplanetary discs in the star-forming region IC 348 to date. New observations from the Large Millimetre Telescope and the 1.1 mm camera AzTEC are combined with literature results in order to characterize the disc population as relating to both stellar properties within the IC 348 region and across other star-forming regions. In addition to detecting 28 of 116 observed known infrared-excess sources, we detected emission from two previously unknown candidate transition discs in the region. When combined with literature results, we find evidence for a steeper-than-expected slope, on average, in disc spectral energy distributions at millimetre wavelengths in the IC 348 region. We show that the presence or absence of high mass discs is a sensitive indicator of regional evolution, both among star-forming regions and within IC 348. In contrast, low mass discs exhibit almost no apparent evolution within the first ∼5 Myr when compared among regions

Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm

We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ~25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ~40 to ~70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (mm/cm sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron- sized) dust grains. We model the broad-band spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ~0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.Comment: Accepted by ApJ Letters, 16 pages, 3 figures, ApJ Letters 201

Wall emission in circumbinary disks: the case of CoKu Tau/4

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 ~10 AU. Based on the 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. 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. 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~8AU). A small amount of optically thin dust in the hole (<0.01 lunar masses) helps to improve the fit to the 10microns silicate band. Also, we find that water ice should be absent or have a very small abundance (a dust to gas mass ratio 0, the model predicts mid-IR variability with periods similar to orbital timescales, assuming that thermal equilibrium is reached instantaneously.Comment: 42 pages, 15 Postscript figure

Mid-infrared variability of the binary system CS Cha

CS Cha is a binary system surrounded by a circumbinary disk. We construct a model for the inner disk regions and compare the resulting synthetic SED with IRS spectra of CS Cha taken at two different epochs. For our model we adopt a non-axisymmetric mass distribution from results of published numerical simulations of the interaction between a circumbinary disk and a binary system, where each star is surrounded by a disk. In particular, we approximate the streams of mass from which the inner circumstellar disks accrete from the circumbinary disk. This structure is due to the gravitational interaction of the stars with the disk, in which an array of disks and streams are formed in an inner hole. We calculate the temperature distribution of the optically thin dust in these inner regions considering the variable impinging radiation from both stars and use the observations to estimate the mass variations in the streams. We find that the SEDs for both epochs can be explained with emission from an optically thick inner edge of the circumbinary disk and from the optically thin streams that connect the circumbinary disk with the two smaller circumstellar disks. To the best of our knowledge, this is the first time that the emission from the optically thin material in the hole, suggested by the theory, is tested against observations of a binary system.Comment: 32 pages, 9 figures, 3 tables, accepted for publication in the Astrophysical Journa