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Lack of PAH emission toward low-mass embedded young stellar objects

Geers, V. C. and van Dishoeck, E. F. and Pontoppidan, K. M. and Lahuis, F. and Crapsi, A. and Dullemond, C. P. and Blake, G. A. (2009) Lack of PAH emission toward low-mass embedded young stellar objects. Astronomy and Astrophysics, 495 (3). pp. 837-846. ISSN 0004-6361. http://resolver.caltech.edu/CaltechAUTHORS:20090611-152310756

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Abstract

Aims. Polycyclic aromatic hydrocarbons (PAHs) have been detected toward molecular clouds and some young stars with disks, but have not yet been associated with embedded young stars. We present a sensitive mid-infrared spectroscopic survey of PAH features toward a sample of low-mass embedded young stellar objects (YSOs). The aim is to put constraints on the PAH abundance in the embedded phase of star formation using radiative transfer modeling. Methods. VLT-ISAAC L-band spectra for 39 sources and Spitzer IRS spectra for 53 sources are presented. Line intensities are compared to recent surveys of Herbig Ae/Be and T Tauri stars. The radiative transfer codes RADMC and RADICAL are used to model the PAH emission from embedded YSOs consisting of a pre-main-sequence star with a circumstellar disk embedded in an envelope. The dependence of the PAH feature on PAH abundance, stellar radiation field, inclination and the extinction by the surrounding envelope is studied. Results. The 3.3 µm PAH feature is undetected for the majority of the sample (97%), with typical upper limits of 5 10-16 Wm^(-2). One source originally classified as class I, IRS 48 , shows a strong 3.3 µm feature from a disk. Compact 11.2 m PAH emission is seen directly towards 1 out of the 53 Spitzer Short-High spectra, for a source that is borderline embedded. For all 12 sources with both VLT and Spitzer spectra, no PAH features are detected in either. In total, PAH features are detected toward at most 1 out of 63 (candidate) embedded protostars (≤2%), even lower than observed for class II T Tauri stars with disks (11–14%). Models predict the 7.7 m feature as the best tracer of PAH emission, while the 3.3 m feature is relatively weak. Assuming typical class I stellar and envelope parameters, the absence of PAH emission is most likely explained by the absence of emitting carriers through a PAH abundance at least an order of magnitude lower than in molecular clouds but similar to that found in disks. Thus, most PAHs likely enter the protoplanetary disks frozen out in icy layers on dust grains and/or in coagulated form.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1051/0004-6361:200811001DOIArticle
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361:200811001PublisherArticle
ORCID:
AuthorORCID
van Dishoeck, E. F.0000-0001-7591-1907
Pontoppidan, K. M.0000-0001-7552-1562
Blake, G. A.0000-0003-0787-1610
Additional Information:© ESO 2009. Received 19 September 2008; accepted 2 December 2008. The authors thank R. Visser for his models and comments. Support for this work, part of the Spitzer Legacy Science Program, was provided by NASA through contracts 1224608, 1230779 and 1256316 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. A.C. was supported by a fellowship from the European Research Training Network ``The Origin of Planetary Systems'' (PLANETS, contract number HPRN-CT-2002-00308) at Leiden Observatory and by a Marie Curie Intra-European Fellowship from the European Community (contract number FP6-024227) at Observatorio Astronómico Nacional. Astrochemistry in Leiden is supported by a NWO Spinoza grant and a NOVA grant.
Funders:
Funding AgencyGrant Number
NASA1224608
NASA1230779
NASA1256316
European Research Training NetworkHPRN-CT-2002-00308
Marie Curie FellowshipFP6-024227
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Nederlandse Onderzoekschool voor de Astronomie (NOVA)UNSPECIFIED
Subject Keywords:stars: pre-main sequence - stars: planetary systems: protoplanetary disks; stars: circumstellar matter; astrochemistry
Issue or Number:3
Record Number:CaltechAUTHORS:20090611-152310756
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20090611-152310756
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14395
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:25 Jun 2009 21:19
Last Modified:22 Aug 2017 20:08

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