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Title: A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS

Abstract

Protostellar systems, ranging from low-luminosity classical T Tauri and Herbig Ae stars to high-luminosity Herbig Be stars, exhibit a near-infrared (NIR) excess in their spectra that is dominated by a bump in the monochromatic luminosity with a peak near 3 {mu}m. The bump can be approximated by a thermal emission component of temperature {approx}1500 K that is of the order of the sublimation temperature of interstellar dust grains. In the currently popular 'puffed-up rim' scenario, the bump represents stellar radiation that propagates through the optically thin inner region of the surrounding accretion disk and is absorbed and reemitted by the dust that resides just beyond the dust sublimation radius r {sub sub}. However, this model cannot account for the strongest bumps measured in these sources, and it predicts a pronounced secondary bounce in the interferometric visibility curve that is not observed. In this paper we present an alternative interpretation, which attributes the bump to reemission of stellar radiation by dust that is uplifted from the disk by a centrifugally driven wind. Winds of this type are a leading candidate for the origin of the strong outflows associated with protostars, and there is observational evidence for disk winds originating on scalesmore » {approx}r {sub sub}. Using a newly constructed Monte Carlo radiative transfer code and focusing on low-luminosity sources, we show that this model can account for the NIR excess emission even in bright Herbig Ae stars such as AB Auriga and MWC 275, and that it successfully reproduces the basic features of the visibilities measured in these protostars. We argue that a robust dusty outflow in these sources could be self-limiting-through shielding of the stellar FUV photons-to a relatively narrow launching region between r {sub sub} and {approx}2 r {sub sub}. We also suggest that the NIR and scattered-light variability exhibited by a source like MWC 275 can be attributed in this picture to the uplifting of dust clouds from the disk.« less

Authors:
;  [1]
  1. Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)
Publication Date:
OSTI Identifier:
22086511
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 758; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ASTRONOMY; ASTROPHYSICS; COSMIC DUST; COSMIC PHOTONS; EMISSION SPECTRA; INTERSTELLAR GRAINS; LUMINOSITY; MAGNETOHYDRODYNAMICS; MONOCHROMATIC RADIATION; MONTE CARLO METHOD; NEAR INFRARED RADIATION; PHOTON EMISSION; PROTOPLANETS; PROTOSTARS; RADIANT HEAT TRANSFER; STARS; STELLAR RADIATION; SUBLIMATION; VISIBLE RADIATION

Citation Formats

Bans, Alissa, and Koenigl, Arieh, E-mail: abans@uchicago.edu, E-mail: akonigl@uchicago.edu. A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS. United States: N. p., 2012. Web. doi:10.1088/0004-637X/758/2/100.
Bans, Alissa, & Koenigl, Arieh, E-mail: abans@uchicago.edu, E-mail: akonigl@uchicago.edu. A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS. United States. doi:10.1088/0004-637X/758/2/100.
Bans, Alissa, and Koenigl, Arieh, E-mail: abans@uchicago.edu, E-mail: akonigl@uchicago.edu. Sat . "A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS". United States. doi:10.1088/0004-637X/758/2/100.
@article{osti_22086511,
title = {A DISK-WIND MODEL FOR THE NEAR-INFRARED EXCESS EMISSION IN PROTOSTARS},
author = {Bans, Alissa and Koenigl, Arieh, E-mail: abans@uchicago.edu, E-mail: akonigl@uchicago.edu},
abstractNote = {Protostellar systems, ranging from low-luminosity classical T Tauri and Herbig Ae stars to high-luminosity Herbig Be stars, exhibit a near-infrared (NIR) excess in their spectra that is dominated by a bump in the monochromatic luminosity with a peak near 3 {mu}m. The bump can be approximated by a thermal emission component of temperature {approx}1500 K that is of the order of the sublimation temperature of interstellar dust grains. In the currently popular 'puffed-up rim' scenario, the bump represents stellar radiation that propagates through the optically thin inner region of the surrounding accretion disk and is absorbed and reemitted by the dust that resides just beyond the dust sublimation radius r {sub sub}. However, this model cannot account for the strongest bumps measured in these sources, and it predicts a pronounced secondary bounce in the interferometric visibility curve that is not observed. In this paper we present an alternative interpretation, which attributes the bump to reemission of stellar radiation by dust that is uplifted from the disk by a centrifugally driven wind. Winds of this type are a leading candidate for the origin of the strong outflows associated with protostars, and there is observational evidence for disk winds originating on scales {approx}r {sub sub}. Using a newly constructed Monte Carlo radiative transfer code and focusing on low-luminosity sources, we show that this model can account for the NIR excess emission even in bright Herbig Ae stars such as AB Auriga and MWC 275, and that it successfully reproduces the basic features of the visibilities measured in these protostars. We argue that a robust dusty outflow in these sources could be self-limiting-through shielding of the stellar FUV photons-to a relatively narrow launching region between r {sub sub} and {approx}2 r {sub sub}. We also suggest that the NIR and scattered-light variability exhibited by a source like MWC 275 can be attributed in this picture to the uplifting of dust clouds from the disk.},
doi = {10.1088/0004-637X/758/2/100},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 758,
place = {United States},
year = {2012},
month = {10}
}