Multi-epoch Ultraviolet HST Observations of Accreting Low-mass Stars

Abstract

Variability is a defining characteristic of young low-mass stars that are still accreting material from their primordial protoplanetary disk. Here we present the largest \textit{HST} variability study of Classical T Tauri stars (CTTS) to date. For 5 of these objects, we obtained a total of 25 spectra with the Space Telescope Imaging Spectrograph (STIS). Mass accretion rates and the fraction of the star covered by accretion columns (i.e., filling factors) were inferred using 1D NLTE physical models whose parameters were fit within a Bayesian framework. On week long timescales, typical changes in the mass accretion rates range up to a factor of $\sim 2$, while changes of up to a factor of $\sim 5$ are inferred for the filling factors. In addition to this, we observed a possible accretion burst in the transitional disk system GM Aur, and an incident we interpret as a chance alignment of an accretion column and the undisturbed photosphere along our line of sight in the full disk system VW Cha. We also measure correlations between mass accretion rate and line luminosities for use as secondary tracers of accretion. We place our objects in context with recent high-cadence photometric surveys of low-mass star formation regions and highlight the need for more broad-wavelength, contemporaneous data to better understand the physical mechanisms behind accretion variability in CTTS.

arXiv comment27 pages, 10 figures, 7 tables

References in corpus (62)

• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• Resolved Images of Large Cavities in Protoplanetary Transition Disks
• Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga
• Ringed Substructure and a Gap at 1 AU in the Nearest Protoplanetary Disk
• Evidence for a developing gap in a 10 Myr old protoplanetary disk
• The Cosmic Origins Spectrograph
• CSI 2264: Simultaneous optical and infrared light curves of young disk-bearing stars in NGC 2264 with CoRoT and Spitzer-- evidence for multiple origins of variability
• Accretion in Brown Dwarfs: an Infrared View
• Discovery of seven T Tauri stars and a brown dwarf candidate in the nearby TW Hydrae Association
• Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra
• Eclipses by circumstellar material in the T Tauri star AA Tau. II. Evidence for non-stationary magnetospheric accretion
• A Millimeter Continuum Size-Luminosity Relationship for Protoplanetary Disks
• Accretion to Magnetized Stars through the Rayleigh-Taylor Instability: Global Three-Dimensional Simulations
• Results of the ROTOR-program. I. The long-term photometric variability of classical T Tauri stars
• A Spatially Resolved Inner Hole in the Disk around GM Aurigae
• A Spitzer IRS Study of Infrared Variability in Transitional and Pre-Transitional Disks around T Tauri Stars
• X-Shooter study of accretion in Chamaeleon I: II. A steeper increase of accretion with stellar mass for very low mass stars?
• Unstable Disk Accretion to Magnetized Stars: First Global 3D MHD Simulations
• On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds
• Molecular Hydrogen Emission from Protoplanetary Disks II. Effects of X-ray Irradiation and Dust Evolution
• Accretion dynamics and disk evolution in NGC 2264: a study based on the Corot photometric observations
• Magnetospheric accretion and spin-down of the prototypical classical T Tauri star AATau
• X-Shooter study of accretion in Chamaeleon I
• CSI 2264: Characterizing Accretion-Burst Dominated Light Curves for Young Stars in NGC 2264
• Measuring Protoplanetary Disk Accretion with H I Pf-beta
• The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya
• AA Tau's sudden and long-lasting deepening: enhanced extinction by its circumstellar disk
• A Far-ultraviolet Atlas of Low-resolution Hubble Space Telescope Spectra of T Tauri Stars
• A New Probe of the Planet-Forming Region in T Tauri Disks
• The many-faceted light curves of young disk-bearing stars in Upper Sco and $\rho$ Oph observed by $K2$ Campaign 2
• Hot Gas Lines in T Tauri Stars
• CSI 2264: Characterizing Young Stars in NGC 2264 with Short-Duration, Periodic Flux Dips in their Light Curves
• CSI 2264: Investigating rotation and its connection with disk accretion in the young open cluster NGC 2264
• Spectroscopy of Candidate Members of the Eta Cha and MBM12 Young Associations
• SpectRes: A Fast Spectral Resampling Tool in Python
• The close classical T Tauri binary V4046 Sgr: Complex magnetic fields & distributed mass accretion
• Photometric variability of the T Tauri star TW Hya on time scales of hours to years
• UV variability and accretion dynamics in the young open cluster NGC 2264
• Modeling the Halpha line emission around classical T Tauri stars using magnetospheric accretion and disk wind models
• Multi-wavelength diagnostics of accretion in an X-ray selected sample of CTTSs
• Spitzer Infrared Spectrograph survey of young stars in the Chamaeleon I star-forming region
• MRI-driven Accretion on to Magnetized stars: Global 3D MHD Simulations of Magnetospheric and Boundary Layer Regimes
• Evolution of X-ray and FUV Disk-Dispersing Radiation Fields
• Multiple rings in the transitional disk of GM Aurigae revealed by VLA and ALMA
• TW Hya: Spectral Variability, X-Rays, and Accretion Diagnostics
• On Sunspot and Starspot Lifetimes
• Magnetically Controlled Accretion Flows onto Young Stellar Objects
• The double population of Chamaeleon I detected by Gaia DR2
• Photometric variability of TW~Hya from seconds to years as seen from space and the ground in 2013-2017
• Using FUV to IR Variability to Probe the Star-Disk Connection in the Transitional Disk of GM Aur
• The 1600 Angstrom Emission Bump in Protoplanetary Disks: A Spectral Signature of H${}_2$O Dissociation
• Analysis of variability of TW Hya as observed by MOST and ASAS in 2009
• Multi-epoch monitoring of the AA Tau like star V354 Mon - Indications for a low gas-to-dust ratio in the inner disk warp
• Discovery of a New Companion and Evidence of a Circumprimary Disk: Adaptive Optics Imaging of the Young Multiple System VW Cha
• A stable quasi-periodic 4.18 d oscillation and mysterious occultations in the 2011 MOST light curve of TWHya
• Dynamical star-disk interaction in the young stellar system V354 Mon
• Analysis of MOST light curves of five young stars in Taurus-Auriga and Lupus 3 Star Forming Regions
• Time Dependent Models of Magnetospheric Accretion onto Young Stars
• The Evolution of Protoplanetary Disks: Probing the Inner Disk of Very Low Accretors

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• PENELLOPE: the ESO data legacy program to complement the Hubble UV Legacy Library of Young Stars (ULLYSES) I. Survey presentation and accretion properties of Orion OB1 and $\sigma$-Orionis
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• Molecules with ALMA at Planet-forming Scales (MAPS) XI: CN and HCN as Tracers of Photochemistry in Disks
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• Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around Star
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• Towards a comprehensive view of accretion, inner disks, and extinction in classical T Tauri stars: an ODYSSEUS study of the Orion OB1b association
• Measuring the Density Structure of an Accretion Hot Spot
• The ODYSSEUS Survey. Motivation and First Results: Accretion, Ejection, and Disk Irradiation of CVSO 109
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• The Giant Accreting Protoplanet Survey (GAPlanetS) -- Results from a Six Year Campaign to Image Accreting Protoplanets
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• Synthetic Light Curves of Accretion Variability in T Tauri Stars
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• Interferometric study on the temporal variability of the brightness distributions of protoplanetary disks
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• Correlation between the optical veiling and accretion properties: A case study of the classical T Tauri star DK Tau
• Testing the Potential for Radio Variability in Disks around T Tauri Stars with Observations and Chemical Modeling
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• Molecules with ALMA at Planet-forming Scales (MAPS) XIX. Spiral Arms, a Tail, and Diffuse Structures Traced by CO around the GM Aur Disk
• Understanding Accretion Variability Through TESS Observations of Taurus
• Continuum And Line Emission From Accretion Shocks at T Tauri Stars I. Correlations With Shock Parameters