Universität zu Köln

Bruenken, Sandra, Sipilae, Olli, Chambers, Edward T., Harju, Jorma ORCID: 0000-0002-1189-9790, Caselli, Paola ORCID: 0000-0003-1481-7911, Asvany, Oskar, Honingh, Cornelia E., Kaminski, Tomasz ORCID: 0000-0001-8541-8024, Menten, Karl M., Stutzki, Juergen and Schlemmer, Stephan ORCID: 0000-0002-1421-7281 (2014). H2D+ observations give an age of at least one million years for a cloud core forming Sun-like stars. Nature, 516 (7530). S. 219 - 230. LONDON: NATURE PUBLISHING GROUP. ISSN 1476-4687

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Abstract

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse(1,2), whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H-2, which decreases monotonically with age(4-6). This has beendone for the dense cloud core L183, for which the deuterium fractionation of diazenylium(N2H+) was used as a chemical clock to infer(7) that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D+ and para-H2D+, have the most direct chemical connections to H-2 (refs 8-12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D+ is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory(13), and recent progress in instrumentation technology(14,15). Here we report observations of ortho-and para-H2D+ emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H+ work(7) arises because that chemical clock turns off sooner than the H2D+ clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bruenken, Sandra UNSPECIFIED UNSPECIFIED UNSPECIFIED Sipilae, Olli UNSPECIFIED UNSPECIFIED UNSPECIFIED Chambers, Edward T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Harju, Jorma UNSPECIFIED orcid.org/0000-0002-1189-9790 UNSPECIFIED Caselli, Paola UNSPECIFIED orcid.org/0000-0003-1481-7911 UNSPECIFIED Asvany, Oskar UNSPECIFIED UNSPECIFIED UNSPECIFIED Honingh, Cornelia E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kaminski, Tomasz UNSPECIFIED orcid.org/0000-0001-8541-8024 UNSPECIFIED Menten, Karl M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutzki, Juergen UNSPECIFIED UNSPECIFIED UNSPECIFIED Schlemmer, Stephan UNSPECIFIED orcid.org/0000-0002-1421-7281 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-420300
DOI:	10.1038/nature13924
Journal or Publication Title:	Nature
Volume:	516
Number:	7530
Page Range:	S. 219 - 230
Date:	2014
Publisher:	NATURE PUBLISHING GROUP
Place of Publication:	LONDON
ISSN:	1476-4687
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language HETERODYNE INSTRUMENT; CHEMISTRY; H-3(+); ORTHO-H-2; RATIO; APEX; CONSTRAINTS; DEPLETION; SOFIA; WATER Multiple languages Multidisciplinary Sciences Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/42030