revealing H{sub 2}D{sup +} depletion and compact structure in starless and protostellar cores with ALMA
- Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St George Street, Toronto, ON M5S 3H4 (Canada)
- National Research Council Canada, Radio Astronomy Program, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
- Radio and Geoastronomy Division, Harvard Smithsonian Center for Astrophysics, MS-42, Cambridge, MA 02138 (United States)
- Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching (Germany)
- Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Ø. (Denmark)
- Institute for Astronomy, ETH Zürich, Wolfgang-Pauli-Strasse 27, CH-8093 Zürich (Switzerland)
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the submillimeter dust continuum and H{sub 2}D{sup +} 1{sub 10}-1{sub 11} emission toward two evolved, potentially protostellar cores within the Ophiuchus molecular cloud, Oph A SM1 and SM1N. The data reveal small-scale condensations within both cores, with mass upper limits of M ≲ 0.02 M {sub ☉} (∼20 M {sub Jup}). The SM1 condensation is consistent with a nearly symmetric Gaussian source with a width of only 37 AU. The SM1N condensation is elongated and extends 500 AU along its major axis. No evidence for substructure is seen in either source. A Jeans analysis indicates that these sources are unlikely to fragment, suggesting that both will form single stars. H{sub 2}D{sup +} is only detected toward SM1N, offset from the continuum peak by ∼150-200 AU. This offset may be due to either heating from an undetected, young, low-luminosity protostellar source or first hydrostatic core, or HD (and consequently H{sub 2}D{sup +}) depletion in the cold center of the condensation. We propose that SM1 is protostellar and that the condensation detected by ALMA is a warm (T ∼ 30-50 K) accretion disk. The less concentrated emission of the SM1N condensation suggests that it is still starless, but we cannot rule out the presence of a low-luminosity source, perhaps surrounded by a pseudodisk. These data observationally reveal the earliest stages of the formation of circumstellar accretion regions and agree with theoretical predictions that disk formation can occur very early in the star formation process, coeval with or just after the formation of a first hydrostatic core or protostar.
- OSTI ID:
- 22370077
- Journal Information:
- Astrophysical Journal, Vol. 797, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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