H2d+ observations give an age of at least one million years for a cloud core forming sun-like stars

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 collapse1,2,

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, H2, which decreases monotonically with age4,5,6. This has been done for the dense

cloud core L183, for which the deuterium fractionation of diazenylium (N2H+) was used as a chemical clock to infer7 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 H2 (refs 8,

9, 10, 11, 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 laboratory13, and recent

progress in instrumentation technology14,15. 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+ work7 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. Access through your institution Buy or subscribe This is a preview of subscription content,

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ACKNOWLEDGEMENTS GREAT is a development by the MPI für Radioastronomie and the KOSMA/Universität zu Köln, in cooperation with the MPI für Sonnensystemforschung and the DLR Institut für

Planetenforschung. SOFIA is jointly operated by the Universities Space Research Association, Inc. (USRA), under NASA contract NAS2-97001, and the Deutsches SOFIA Institut (DSI) under DLR

contract 50 OK 0901 to the University of Stuttgart. APEX, the Atacama Pathfinder Experiment, is a collaboration between the Max Planck Institut für Radioastronomie (MPIfR), the Onsala Space

Observatory (OSO), and the European Southern Observatory (ESO). This work has been supported by the Collaborative Research Centre 956, funded by the Deutsche Forschungsgemeinschaft (DFG).

O.S. and J.H. acknowledge support from the Academy of Finland grants 132291 and 250741. P.C. acknowledges the financial support of the European Research Council (ERC; project PALs 320620).

AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany, Sandra Brünken, Edward T. Chambers, Oskar Asvany, 

Cornelia E. Honingh, Jürgen Stutzki & Stephan Schlemmer * Department of Physics, PO Box 64, 00014 University of Helsinki, Finland Olli Sipilä & Jorma Harju * Max-Planck Institut für

Extraterrestrische Physik, Gießenbachstraße 1, 85741 Garching bei München, Germany, Olli Sipilä & Paola Caselli * School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK,

Paola Caselli * Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, Tomasz Kamiński & Karl M. Menten Authors * Sandra Brünken View author publications You

can also search for this author inPubMed Google Scholar * Olli Sipilä View author publications You can also search for this author inPubMed Google Scholar * Edward T. Chambers View author

publications You can also search for this author inPubMed Google Scholar * Jorma Harju View author publications You can also search for this author inPubMed Google Scholar * Paola Caselli

View author publications You can also search for this author inPubMed Google Scholar * Oskar Asvany View author publications You can also search for this author inPubMed Google Scholar *

Cornelia E. Honingh View author publications You can also search for this author inPubMed Google Scholar * Tomasz Kamiński View author publications You can also search for this author

inPubMed Google Scholar * Karl M. Menten View author publications You can also search for this author inPubMed Google Scholar * Jürgen Stutzki View author publications You can also search

for this author inPubMed Google Scholar * Stephan Schlemmer View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS S.S., S.B., O.A., P.C., J.H.,

O.S. and J.S. jointly designed the study and proposed the SOFIA observations. E.T.C. performed the calibration and the analysis of the SOFIA data. C.E.H. was instrumental in developing the

GREAT receiver. T.K. and K.M.M. made the APEX observations and analysed these data. O.S. carried out the chemistry and radiative transfer modelling with help from J.H. The paper was jointly

written by S.B., J.H., O.S., P.C. and S.S. All authors discussed the results and commented on the manuscript. CORRESPONDING AUTHORS Correspondence to Sandra Brünken or Stephan Schlemmer.

ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. EXTENDED DATA FIGURES AND TABLES EXTENDED DATA FIGURE 1 TEMPERATURE AND DENSITY DISTRIBUTION OF

THE SOURCE MODEL. Physical model of IRAS 16293-2422 A/B, consisting of a widely used core model22 and a low-density ambient cloud. A, The number density _n_(H2) as a function of radius. B,

The radial profile of the kinetic temperature, _T_. The ambient cloud is assumed to have _n_(H2) = 104 cm−3 and _T_ = 10 K. The shaded interval, between a radius of 3,000 and 6,100 au,

represents the outer envelope of the core, which dominates the observed para-H2D+ absorption and ortho-H2D+ emission. EXTENDED DATA FIGURE 2 THE RELATIONSHIP BETWEEN ORTHO/PARA-H2D+ AND

ORTHO/PARA-H2. The ortho/para-H2D+ ratio as a function of ortho/para-H2 resulting from chemistry simulations for different values of the kinetic temperature _T_, indicated with colours. The

dashed curves represent the approximation given by the analytical formula from Hugo _et al._10. EXTENDED DATA FIGURE 3 N2D+/N2H+ AND ORTHO/PARA-H2D+ AS FUNCTIONS OF ORTHO/PARA-H2, FOR

DIFFERENT VALUES OF _T_ AND _N_(H2). A, The N2D+/N2H+ abundance ratio versus the ortho/para H2 ratio for selected values of the kinetic temperature, _T_, and the H2 number density, _n_(H2).

B: The ortho/para H2D+ ratio versus the ortho/para H2 ratio for different temperatures and densities. One can see that this relationship depends on _T_ but not on _n_(H2). EXTENDED DATA

FIGURE 4 N2D+/N2H+ AND ORTHO/PARA-H2D+ AS FUNCTIONS OF ORTHO/PARA-H2, FOR DIFFERENT VALUES OF _T_ AND _Ζ_. A, The N2D+/N2H+ abundance ratio versus the ortho/para H2 ratio for selected values

of the kinetic temperature, _T_, and the cosmic ray ionization rate, _ζ_. B, The same for the ortho/para H2D+ ratio versus the ortho/para H2 ratio for different temperatures and densities

_n_(H2). Hardly any dependence on _ζ_ is seen except at the lowest temperatures. EXTENDED DATA FIGURE 5 THE H2 SPIN TEMPERATURE. Variation of the H2 spin temperature _T_spin as a function of

kinetic temperature and time in a dark cloud according to our gas-grain chemistry model. The corresponding ortho/para-H2 is indicated on the right. The gas density, _n_(H2) = 105 cm−3, and

the visual extinction, _A_V = 10 mag, are kept constant. Ortho/para-H2 tends for long evolutionary times towards the thermal values (dashed line) above _T_kin ≈ 12 K. The blue-hatched region

indicates the _T_ range applicable to the dense core surrounding IRAS 16293-2422 A/B (between a radius of 3,000 and 6,100 au). POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE

FOR FIG. 2 RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Brünken, S., Sipilä, O., Chambers, E. _et al._ H2D+ observations give an age of at least one

million years for a cloud core forming Sun-like stars. _Nature_ 516, 219–221 (2014). https://doi.org/10.1038/nature13924 Download citation * Received: 07 July 2014 * Accepted: 06 October

2014 * Published: 17 November 2014 * Issue Date: 11 December 2014 * DOI: https://doi.org/10.1038/nature13924 SHARE THIS ARTICLE Anyone you share the following link with will be able to read

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