From Molecular Cores to Planet‐forming Disks: An SIRTF Legacy Program Author(s): Neal J. Evans II, Lori E. Allen, Geoffrey A. Blake, A. C. A. Boogert, Tyler Bourke, Paul M. Harvey, J. E. Kessler, David W. Koerner, Chang Won Lee, Lee G. Mundy, Philip C. Myers, Deborah L. Padgett, K. Pontoppidan, Anneila I. Sargent, Karl R. Stapelfeldt, Ewine F. van Dishoeck, Chadwick H. Young, and Kaisa E. Young Reviewed work(s): Source: Publications of the Astronomical Society of the Pacific, Vol. 115, No. 810 (August 2003), pp. 965-980 Published by: The University of Chicago Press on behalf of the Astronomical Society of the Pacific Stable URL: http://www.jstor.org/stable/10.1086/376697 . Accessed: 17/09/2012 17:23 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press and Astronomical Society of the Pacific are collaborating with JSTOR to digitize, preserve and extend access to Publications of the Astronomical Society of the Pacific. http://www.jstor.org Publications of the Astronomical Society of the Pacific, 115:965–980, 2003 August ᭧ 2003. The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A. From Molecular Cores to Planet-forming Disks: An SIRTF Legacy Program Neal J. Evans II,1 Lori E. Allen,2 Geoffrey A. Blake,3 A. C. A. Boogert,4 Tyler Bourke,2 Paul M. Harvey,1 J. E. Kessler,5 David W. Koerner,6 Chang Won Lee,7 Lee G. Mundy,8 Philip C. Myers,2 Deborah L. Padgett,9 K. Pontoppidan,10 Anneila I. Sargent,4 Karl R. Stapelfeldt,11 Ewine F. van Dishoeck,10 Chadwick H. Young,1 and Kaisa E. Young1 Received 2003 March 6; accepted 2003 April 18 ABSTRACT. Crucial steps in the formation of stars and planets can be studied only at mid- to far-infrared wavelengths, where the Space Infrared Telescope (SIRTF) provides an unprecedented improvement in sensitivity. We will use all three SIRTF instruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for SIRTF [MIPS], and Infrared Spectrograph [IRS]) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star- forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6–70 mm) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation (ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet-forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 deg2 of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground-based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow-up studies with ground-based telescopes, as well as with SIRTF itself and other space missions such as SIM, JWST, Herschel, and TPF/Darwin. 1. INTRODUCTION Our Legacy program, “From Molecular Cores to Planet- Stars and planets form in a closely coupled process that is forming Disks,” uses 400 hr of SIRTF observations to study generally accessible to study only at relatively long wave- the process of star and planet formation from the earliest stages lengths, from infrared to radio. Observational studies of this of molecular cores to the epoch of planet-forming disks. This process have generally suffered from one or more of the fol- program, hereafter referred to simply as “Cores to Disks” (c2d), lowing problems: biased samples, inadequate sensitivity, in- is closely coordinated with the Legacy program on “Formation adequate spatial resolution, or incomplete data across the wave- and Evolution of Planetary Systems” (FEPS), which carries the length ranges of interest. The Space Infrared Telescope Facility age sequence to later times. Our program uses all three SIRTF (SIRTF) offers a singular opportunity for a major advance in instruments: the Infrared Array Camera (IRAC), covering 3.6–8 this area of research. The SIRTF mission has been described mm (Fazio et al. 1998); the Multiband Imaging Photometer for by Gallagher, Irace, & Werner (2003). SIRTF (MIPS), covering 24–160 mm (Engelbracht et al. 2000); and the Infrared Spectrometer (IRS), supplying spectroscopy from 5.3 to 40 mm with resolving powerR p 60 –120 and from 10 to 37 mm withR p 600 (Houck et al. 2000). 1 Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712–0259; [email protected], [email protected] 6 Department of Physics and Astronomy, Northern Arizona University, Box .utexas.edu, [email protected], [email protected]. 6010, Flagstaff, AZ 86011-6010; [email protected]. 2 Smithsonian Astrophysical Observatory, 60 Garden Street, MS42, Cam- 7 Taeduk Radio Astronomy Observatory, Korea Astronomy Observatory, bridge, MA 02138; [email protected], [email protected], 36-1 Hwaam-dong, Yusung-gu, Taejon 305-348, Korea; [email protected]. [email protected]. 8 Department of Astronomy, University of Maryland, College Park, MD 3 Division of Geological and Planetary Sciences, MS 150-21, California 20742; [email protected]. Institute of Technology, Pasadena, CA 91125; [email protected]. 9 SIRTF Science Center, MC 220-6, Pasadena, CA 91125; 4 Division of Physics, Mathematics, and Astronomy, MS 105-24, California [email protected]. Institute of Technology, Pasadena, CA 91125; [email protected], 10 Leiden Observatory, Postbus 9513, 2300 RA Leiden, Netherlands; [email protected]. [email protected], [email protected]. 5 Division of Chemistry and Chemical Engineering, California Institute of 11 Jet Propulsion Laboratory, MS 183-900, California Institute of Technol- Technology, Pasadena, CA 91125; [email protected]. ogy, 4800 Oak Grove Drive, Pasadena, CA 91109; [email protected]. 965 966 EVANS ET AL. The observational programs, described in greater detail in will differ from past studies of disk incidence in its greater the individual sections, include unbiased mapping of five large sensitivity to faint objects, in its unbiased coverage of large nearby molecular clouds and about 150 compact molecular cloud areas, and in its inclusion of isolated cores not in cores (§ 2), photometry of about 190 stars with ages up to complexes. about 10 Myr (§ 3), and spectroscopy of at least 170 objects 3. Do “starless” isolated cores harbor faint protostars? Star- in a wide range of evolutionary states (§ 4). In these sections, less or “pre-protostellar” cores have no pointlike infrared emis- we discuss the scientific questions, the sample selection, the sion, according to ground-based near-infrared observations and planned observations, and the expected results. The data prod- far-infrared observations by the IRAS and ISO satellites. These ucts are summarized in § 5. We also describe ancillary data, cores are prime targets for studies of the initial conditions of which are part of the c2d data products, and complementary isolated star formation, and some such cores have associated data, which are being obtained by us or others to provide a internal motions suggestive of the early stages of star formation. more complete picture. The SIRTF and ancillary data will be SIRTF’s sensitivity will allow detection of extremely young available to the broader community from the SIRTF Science protostars and proto–brown dwarfs missed by earlier obser- Center (SSC) via their Infrared Sky Archive (IRSA). Comple- vations. Identification of such objects would stimulate more mentary data products will be made available, as far as possible, detailed studies and so would advance our understanding of through either IRSA or public Web sites. Further information the earliest stage of star formation. on the program can be found at the c2d Web site.12 4. What are the statistical lifetimes of various stages? Our survey covers a large area and will catalog a large number of 2. A SURVEY OF NEARBY MOLECULAR young and embedded systems. These data will allow the first CLOUDS AND CORES unbiased statistical studies of the complete stellar content of five large clouds. In addition, systems that are statistically rare 2.1. Scientific Questions and systems in rapid phases of evolution will be present in the The SIRTF mission offers an unprecedented opportunity to sample. We may, for example, find systems in the short-lived determine the stellar content of the nearest star-forming mo- phase in which the first hydrostatic core forms, a crucial, but lecular clouds, the distributions of their youngest stars and so far unobserved stage of star formation (Boss & Yorke 1995). substellar objects, and the properties of their circumstellar en- 5. Do isolated cores with associated stars preferentially har- velopes and disks. Just as IRAS and ISO revealed many prop- bor single stars or small stellar groups? Observations by IRAS erties of isolated and clustered star-forming regions, SIRTF will and ISO led to the idea of “one core, one star”: an isolated yield new insights into how stars and brown dwarfs are born.