The Nature of Class I Sources: Periodic Variables in Orion

Abstract

We present a quantitative, empirically based argument that at least some Class I sources are low-mass, pre-main-sequence stars surrounded by spatially extended envelopes of dusty gas. The source luminosity arises principally from stellar gravitational contraction, as in optically visible pre-main-sequence stars that lack such envelopes. We base our argument on the fact that some Class I sources in Orion and other star-forming regions have been observed by Spitzer to be periodic variables in the mid-infrared, and with periods consistent with T Tauri rotation rates. Using a radiative transfer code, we construct a variety of dust envelopes surrounding rotating, spotted stars, to see if an envelope that produces a Class I SED at least broadly matches the observed modulations in luminosity. Acceptable envelopes can either be spherical or flattened, and may or may not have polar cavities. The key requirement is that they have a modest equatorial optical depth at the Spitzer waveband of 3.6 $\mu$m, typically ${\tau }_{3.6}$ $\approx$ 0.6. The total envelope mass, based on this limited study, is at most about 0.1 ${\text{M}}_{\odot }$, less than a typical stellar mass. Future studies should focus on the dynamics of the envelope, to determine whether material is actually falling onto the circumstellar disk.

17 pages, 16 figures. Additional light curve figures and associated data table referred to in Appendix B available as online data

References in corpus (11)

• Monte Carlo radiative transfer in protoplanetary disks
• Spitzer IRS Spectra and Envelope Models of Class I Protostars in Taurus
• Far-infrared to millimeter data of protoplanetary disks: dust growth in the Taurus, Ophiuchus, and Chamaeleon I star-forming regions
• Doppler Images and Chromospheric Variability of TWA 6
• YSOVAR: Mid-IR variability in the star forming region Lynds 1688
• Characterizing the Youngest Herschel-detected Protostars I. Envelope Structure Revealed by CARMA Dust Continuum Observations
• Multiwavelength studies of the gas and dust disc of IRAS 04158+2805
• Investigating the Nature of Variable Class I and Flat Spectrum Protostars Using 2-4$\mu$m Spectroscopy
• The Taurus Boundary of Stellar/Substellar (TBOSS) Survey I: far-IR disk emission measured with Herschel
• Stellar and Circumstellar Properties of Class I Protostars
• A Model for (Quasi-)Periodic Multi-wavelength Photometric Variability in Young Stellar Objects

Cited by in corpus (2)

• A protostellar system fed by a streamer of 10,500 au length
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