Young "Dipper" Stars in Upper Sco and $\rho$ Oph Observed by K2

Abstract

We present ten young ($\lesssim$10 Myr) late-K and M dwarf stars observed in K2 Campaign 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show $\sim$10-20 dips in flux over the 80-day observing campaign with durations of $\sim$0.5-2 days and depths of up to $\sim$40%. These stars are all members of the $\rho$ Ophiuchus ($\sim$1 Myr) or Upper Scorpius ($\sim$10 Myr) star-forming regions. To investigate the nature of these "dippers" we obtained: optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. The spectra reveal Li I absorption and H$\alpha$ emission consistent with stellar youth (<50 Myr), but also accretion rates spanning those of classical and weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary disks extending to within $\sim$10 stellar radii in most cases; however, the sub-mm observations imply disk masses that are an order of magnitude below those of typical protoplanetary disks. We find a positive correlation between dip depth and WISE-2 excess, which we interpret as evidence that the dipper phenomenon is related to occulting structures in the inner disk, although this is difficult to reconcile with the weakly accreting aperiodic dippers. We consider three mechanisms to explain the dipper phenomenon: inner disk warps near the co-rotation radius related to accretion; vortices at the inner disk edge produced by the Rossby Wave Instability; and clumps of circumstellar material related to planetesimal formation.

Accepted to ApJ, 19 pages, 10 figures

References in corpus (22)

• The Dartmouth Stellar Evolution Database
• The K2 Mission: Characterization and Early results
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission
• A Submillimeter View of Circumstellar Dust Disks in $\rho$ Ophiuchus
• Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
• Protoplanetary disk lifetimes vs stellar mass and possible implications for giant planet populations
• How to form planetesimals from mm-sized chondrules and chondrule aggregates
• Probing T Tauri Accretion and Outflow with 1 Micron Spectroscopy
• Planets Around Low-Mass Stars (PALMS). IV. The Outer Architecture of M Dwarf Planetary Systems
• On the Stability of Elliptical Vortices in Accretion Discs
• CSI 2264: Probing the inner disks of AA Tau-like systems in NGC 2264
• Effects of dust feedback on vortices in protoplanetary disks
• Large Impacts around a Solar Analog Star in the Era of Terrestrial Planet Formation
• CSI 2264: Characterizing Young Stars in NGC 2264 with Short-Duration, Periodic Flux Dips in their Light Curves
• New Pre-main-Sequence Stars in the Upper Scorpius Subgroup of Sco-Cen
• Revised Filter Profiles and Zero Points for Broadband Photometry
• An ALMA Continuum Survey of Circumstellar Disks in the Upper Scorpius OB Association
• The Masses of Transition Circumstellar Disks: Observational Support for Photoevaporation Models
• High Precision Photometry for K2 Campaign 1
• Search for associations containing young stars (SACY). VI. Is multiplicity universal? Stellar multiplicity in the range 3-1000 au from adaptive-optics observations
• Probing the presence of planets in transition discs' cavities via warps: the case of TW Hya

Cited by in corpus (97)

• BANYAN. XI. The BANYAN $\Sigma$ multivariate Bayesian algorithm to identify members of young associations within 150 pc
• Planet Hunters X. KIC 8462852 - Where's the Flux?
• Zodiacal Exoplanets in Time (ZEIT) III: A short-period planet orbiting a pre-main-sequence star in the Upper Scorpius OB Association
• Rotation of Low-Mass Stars in Upper Scorpius and Rho Ophiuchus with K2
• A Multi-Ringed, Modestly-Inclined Protoplanetary Disk around AA Tau
• Magnetospheric Truncation, Tidal Inspiral, and the Creation of Short and Ultra-Short Period Planets
• Signatures of broken protoplanetary discs in scattered light and in sub-millimetre observations
• Refining the Census of the Upper Scorpius Association with Gaia
• The many-faceted light curves of young disk-bearing stars in Upper Sco and $\rho$ Oph observed by $K2$ Campaign 2
• Age Determination in Upper Scorpius with Eclipsing Binaries
• Zodiacal Exoplanets in Time (ZEIT) VI: a three-planet system in the Hyades cluster including an Earth-sized planet
• Dippers and Dusty Disks Edges: A Unified Model
• Orbiting Clouds of Material at the Keplerian Co-Rotation Radius of Rapidly Rotating Low Mass WTTs in Upper Sco
• Annular substructures in the transition disks around LkCa 15 and J1610
• Are Inner Disc Misalignments Common? ALMA Reveals an Isotropic Outer Disc Inclination Distribution for Young Dipper Stars
• A Census of the Stellar Populations in the Sco-Cen Complex
• New Young Stars and Brown Dwarfs in the Upper Scorpius Association
• The SEEDS High Contrast Imaging Survey of Exoplanets around Young Stellar Objects
• Scattered light shadows in warped protoplanetary discs
• A precise asteroseismic age and metallicity for HD 139614: a pre-main-sequence star with a protoplanetary disc in Upper-Centaurus Lupus
• Families of Plausible Solutions to the Puzzle of Boyajian's Star
• A WISE Survey of Circumstellar disks in the Upper Scorpius Association
• Complex Rotational Modulation of Rapidly Rotating M-Stars Observed with TESS
• A Compact Multi-Planet System With A Significantly Misaligned Ultra Short Period Planet
• Dipper disks not inclined towards edge-on orbits
• As the Worlds Turn: Constraining Spin Evolution in the Planetary-Mass Regime
• Relentless and Complex Transits from a Planetesimal Debris Disk
• Three-dimensional Simulations of Magnetospheric Accretion in a T Tauri Star: Accretion and Wind Structures Just Around Star
• Identification of Young Stellar Variables with KELT for K2 I: Campaign 13 Taurus Dippers and Rotators
• A Survey for New Stars and Brown Dwarfs in the Ophiuchus Star-forming Complex
• ALMA Reveals a Misaligned Inner Gas Disk inside the Large Cavity of a Transitional Disk
• Modelling the KIC8462852 light curves: compatibility of the dips and secular dimming with an exocomet interpretation
• The Many-Faceted Light Curves of Young Disk-bearing Stars in Taurus as Seen by K2
• Star-disc (mis-)alignment in Rho Oph and Upper Sco: insights from spatially resolved disc systems with K2 rotation periods
• Photometric variability of TW~Hya from seconds to years as seen from space and the ground in 2013-2017
• A PSF-based Approach to TESS High quality data Of Stellar clusters (PATHOS) -- III. Exploring the properties of young associations through their variables, dippers, and candidate exoplanets
• A giant planet transiting a 3-Myr protostar with a misaligned disk
• The transiting dust clumps in the evolved disk of the Sun-like UXor RZ Psc
• Multicolor Variability of Young Stars in the Lagoon Nebula: Driving Causes and Intrinsic Timescales
• Rotational evolution of solar-type protostars during the star-disk interaction phase
• Subaru/HiCIAO $H{K}_{\mathrm{s}}$ imaging of LkH$\alpha$ 330 - multi-band detection of the gap and spiral-like structures
• The Rotational Evolution of Young, Binary M Dwarfs
• Deep Long Asymmetric Occultation in EPIC 204376071
• Discovery of New Dipper Stars with K2: A Window into the Inner Disk Region of T Tauri Stars
• Extinction and the Dimming of KIC 8462852
• The peculiar dipping events in the disk-bearing young-stellar object EPIC 204278916
• Spitzer Observations of Long Term Infrared Variability Among Young Stellar Objects in Chamaeleon I
• Star-disk interactions in multi-band photometric monitoring of the classical T Tauri star GI Tau
• The Random Transiter -- EPIC 249706694/HD 139139
• Periodic Eclipses of the Young Star PDS 110 Discovered with WASP and KELT Photometry
• A ZTF Look at Optical Variability of Young Stellar Objects in the North America and Pelican Nebulae Complex
• A Transient Transit Signature Associated with the Young Star RIK-210
• The Little Dippers: Transits of Star-grazing Exocomets?
• The ASAS-SN Catalog of Variable Stars VIII: "Dipper" Stars in the Lupus Star-Forming Region
• The dipper population of Taurus seen with K2
• Using the Gaia excess uncertainty as a proxy for stellar variability and age
• A UV-to-NIR Study of Molecular Gas in the Dust Cavity Around RY Lupi
• Identification of Young Stellar Variables with KELT for K2 II: The Upper Scorpius Association
• Planetesimals Around Stars with TESS (PAST): I. Transient Dimming of a Binary Solar Analog at the End of the Planet Accretion Era
• A survey for variable young stars with small telescopes: First results from HOYS-CAPS
• A Population of Dipper Stars from the Transiting Exoplanet Survey Satellite Mission
• NGTS clusters survey -- II. White-light flares from the youngest stars in Orion
• Variability of young stellar objects in the star-forming region Pelican Nebula
• Dust Accumulation near the Magnetospheric Truncation of Protoplanetary Discs around T Tauri Stars
• Prospects from TESS and Gaia to constrain the flatness of planetary systems
• Planetesimals Around Stars with TESS (PAST): II. An M Dwarf "Dipper" Star with a Long-Lived Disk in the TESS Continuous Viewing Zone
• VVV-WIT-08: the giant star that blinked
• A survey for variable young stars with small telescopes: II -- Mapping a protoplanetary disk with stable structures at 0.15 AU
• Millimeter Observations of the disk around GW Ori
• Can Large-Scale Migration Explain the Giant Planet Occurrence Rate?
• The Rotation-Disk Connection in Young Brown Dwarfs: Strong Evidence for Early Rotational Braking
• The PDS 110 observing campaign - photometric and spectroscopic observations reveal eclipses are aperiodic
• Effects of disc asymmetries on astrometric measurements - Can they mimic planets?
• The Structure and Stability of Extended, Inclined Circumplanetary Disk or Ring Systems
• Quantitative polarimetry for the transition disk in RX J1604.3-213010
• Evidence for Centrifugal Breakout around the Young M Dwarf TIC 234284556
• A survey for variable young stars with small telescopes: IV -- Rotation Periods of YSOs in IC5070
• A low-mass stellar companion to the young variable star RZ Psc
• Evidence for planetary hypothesis for PTFO 8-8695b with five-year optical/infrared monitoring observations
• Variability of Young Stellar Objects in the Perseus Molecular Cloud
• Spectroscopy of Candidate Members of the Sco-Cen Complex
• Spectroscopic classification of X-ray sources in the Galactic Bulge Survey
• Clumpy dust rings around non-accreting young stars
• Observations of UX Ori in deep minima with the Nordic Optical Telescope. I. Analysis of spectral lines
• One of Everything: The Breakthrough Listen Exotica Catalog
• Wavelength-Dependent Extinction and Grain Sizes in Dippers
• On the diversification and dissipation of protoplanetary disks
• K2 Discovery of a Circumsecondary Disk Transiting EPIC 220208795
• NGTS clusters survey IV. Search for Dipper stars in the Orion Nebular Cluster
• Climate Change in Hell: Long-Term Variation in Transits of the Evaporating Planet K2-22b
• Flickers, Bursts, and Dips: Detecting Rapid Variability with the g(2) Autocorrelation Function
• On The Unusual Variability of 2MASS J06195260-2903592: A Long-Lived Disk around a Young Ultracool Dwarf
• Dippers from TESS Full-frame Images. II. Spectroscopic Characterization of Four Young Dippers
• $COD:$ An Algorithm for Shape Reconstruction of Transiting Celestial Bodies through Topological Optimization
• The nature of ASASSN-24fw's occultation: modelling the event as dimming by optically thick rings around a sub-stellar companion
• The Visual Survey Group: A Decade of Hunting Exoplanets and Unusual Stellar Events with Space-Based Telescopes
• Twinkle Twinkle Little Star, Roman Sees Where You Are: Predicting Exoplanet Transit Yields in the Rosette Nebula with the Nancy Grace Roman Space Telescope