Spectropolarimetry and Modeling of the Eclipsing T Tauri Star KH 15D

Abstract

KH 15D is a strongly variable T Tauri star in the young star cluster NGC 2264 that shows a decrease in flux of 3.5 magnitudes lasting for 18 days and repeating every 48 days. The eclipsing material is likely due to orbiting dust or rocky bodies in a partial ring or warped disk that periodically occults the star. We measured the polarized spectrum in and out of eclipse at the Keck and Palomar observatories. Outside of the eclipse, the star exhibited low polarization consistent with zero. During eclipse, the polarization increased dramatically to ~2% across the optical spectrum, while the spectrum had the same continuum shape as outside of eclipse and exhibited emission lines of much larger equivalent width, as previously seen. From the data, we conclude that (a) the scattering region is uneclipsed; (b) the scattering is nearly achromatic; (c) the star is likely completely eclipsed so that the flux during eclipse is entirely due to scattered light, a conclusion also argued for by the shape of the ingress and egress. We argue that the scattering is not due to electrons, but may be due to large dust grains of size ~10 micron, similar to the interplanetary grains which scatter the zodiacal light. We construct a warped-disk model with an extended dusty atmosphere which reproduces the main features of the lightcurve, namely (a) a gradual decrease before ingress due to extinction in the atmosphere (similar for egress); (b) a sharper decrease within ingress due to the optically-thick base of the atmosphere; (c) a polarized flux during eclipse which is 0.1% of the total flux outside of eclipse, which requires no fine-tuning of the model. (abridged)

9 pages, 7 figures, accepted for publication in ApJ, MPEG simulation available at http://www.astro.washington.edu/agol/scatter2.mpg

References in corpus (6)

• MC3D - 3D Continuum Radiative Transfer, Version 2
• Fine Structure in the Circumstellar Environment of a Young, Solar-like Star: the Unique Eclipses of KH 15D
• Natural Coronagraphic Observations of the Eclipsing T Tauri System KH 15D: Evidence for Accretion and Bipolar Outflow in a WTTS
• Constraints on the disk geometry of the T Tauri star AA Tau from linear polarimetry
• Limits on eclipses of the pre-main-sequence star KH 15D in the first half of the 20th century
• KH15D: a star eclipsed by a large scale dusty vortex?

Cited by in corpus (25)

• The Planetary Mass Companion 2MASS1207-3932 B: Temperature, Mass and Evidence for an Edge-On Disk
• The Circumbinary Ring of KH 15D
• KH 15D: Gradual Occultation of a Pre-Main-Sequence Binary
• A Spitzer View of the Young Open Cluster NGC 2264
• The Orbit and Occultations of KH 15D
• Wave-like warp propagation in circumbinary discs II. Application to KH 15D
• Locating the Trailing Edge of the Circumbinary Ring in the KH 15D System
• KH 15D: A Spectroscopic Binary
• Reflected Light from Sand Grains in the Terrestrial Zone of a Protoplanetary Disk
• The History of the Mysterious Eclipses of KH 15D: Asiago Observatory, 1967-1982
• The Disappearing Act of KH 15D: Photometric Results from 1995 to 2004
• The Light Curve of the Weakly-Accreting T Tauri Binary KH 15D from 2005-10: Insights into the Nature of its Protoplanetary Disk
• Spectroscopy of Molecular Hydrogen Emission from KH 15D
• H${}_2$ Emission Nebulosity Associated with KH 15D
• The History of the Mysterious Eclipses of KH 15D II. Asiago, Kiso, Kitt Peak, Mt. Wilson, Palomar, Tautenburg and Rozhen Observatories, 1954-97
• Near-Infrared Photometric Monitoring of a Pre-Main-Sequence Object KH 15D
• Complex Variability of the H$\alpha$ Emission Line Profile of the T Tauri Binary System KH 15D: The Influence of Orbital Phase, Occultation by the Circumbinary Disk, and Accretion Phenomenae
• Optical and Radio Observations of the T Tauri Binary KH 15D (V582 Mon): Stellar Properties, Disk Mass Limit and Discovery of a CO Outflow
• Multi-Wavelength Photometry of the T Tauri Binary V582 Mon (KH 15D): A New Epoch of Occultations
• Blue and IR Light Curves of the Mysterious Pre-Main Sequence Star V582 Mon (KH 15D) from 1955 to 1970
• X-ray Emission from the Weak-lined T Tauri Binary System KH 15D
• Seeing Through the Ring: Near-Infrared Photometry of V582 Mon (KH 15D)
• Extending the Model of KH 15D: Estimating the Effects of Forward Scattering and Curvature of the Occulting Ring Edge
• Untangling the Near-IR Spectral Features in the Protoplanetary Environment of KH 15D
• Gas Absorption in the KH 15D System: Further Evidence for Dust Settling in the Circumbinary Disk