THE INITIAL CONDITIONS OF CLUSTERED STAR FORMATION. III. THE DEUTERIUM FRACTIONATION OF THE OPHIUCHUS B2 CORE
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville VA 22903 (United States)
- Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, STN CSC, Victoria, British Columbia V8W 3P6 (Canada)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Max-Planck Institut fuer Radioastronomie, Auf dem Huegel 69, 53121 Bonn (Germany)
- Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)
- Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d'Astrophysique, C.E. Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette (France)
We present N{sub 2}D{sup +} 3-2 (IRAM), and H{sub 2}D{sup +} 1{sub 11}-1{sub 10} and N{sub 2}H{sup +} 4-3 (JCMT) maps of the small cluster-forming Ophiuchus B2 core in the nearby Ophiuchus molecular cloud. In conjunction with previously published N{sub 2}H{sup +} 1-0 observations, the N{sub 2}D{sup +} data reveal the deuterium fractionation in the high-density gas across Oph B2. The average deuterium fractionation R{sub D} = N(N{sub 2}D{sup +})/N(N{sub 2}H{sup +}) {approx} 0.03 over Oph B2, with several small scale R{sub D} peaks and a maximum R{sub D} = 0.1. The mean R{sub D} is consistent with previous results in isolated starless and protostellar cores. The column density distributions of both H{sub 2}D{sup +} and N{sub 2}D{sup +} show no correlation with total H{sub 2} column density. We find, however, an anticorrelation in deuterium fractionation with proximity to the embedded protostars in Oph B2 to distances {approx}>0.04 pc. Destruction mechanisms for deuterated molecules require gas temperatures greater than those previously determined through NH{sub 3} observations of Oph B2 to proceed. We present temperatures calculated for the dense core gas through the equating of non-thermal line widths for molecules (i.e., N{sub 2}D{sup +} and H{sub 2}D{sup +}) expected to trace the same core regions, but the observed complex line structures in B2 preclude finding a reasonable result in many locations. This method may, however, work well in isolated cores with less complicated velocity structures. Finally, we use R{sub D} and the H{sub 2}D{sup +} column density across Oph B2 to set a lower limit on the ionization fraction across the core, finding a mean x{sub e,lim} {approx}> few x 10{sup -8}. Our results show that care must be taken when using deuterated species as a probe of the physical conditions of dense gas in star-forming regions.
- OSTI ID:
- 21455106
- Journal Information:
- Astrophysical Journal, Vol. 718, Issue 2; Other Information: DOI: 10.1088/0004-637X/718/2/666; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
AMMONIA
DEUTERIUM
DISTRIBUTION
FRACTIONATION
HYDROGEN
IONIZATION
LINE WIDTHS
PROTOSTARS
STAR EVOLUTION
STARS
ELEMENTS
EVOLUTION
HYDRIDES
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NONMETALS
NUCLEI
ODD-ODD NUCLEI
SEPARATION PROCESSES
STABLE ISOTOPES