The EDIBLES survey

Astronomy and Astrophysics, vol. 662, pp. A24

Abstract

Context. Several diffuse interstellar bands (DIBs) have profiles with resolved sub-peaks that resemble rotational bands of large molecules. Analysis of these profiles can constrain the sizes and geometries of the DIB carriers, especially if the profiles exhibit clear variations along lines of sight probing different physical conditions. Aims. Using the extensive data set from the ESO Diffuse Interstellar Bands Large Exploration Survey we searched for systematic variations in the peak-to-peak separation of these sub-peaks for three well-known DIBs in lines of sight with a single dominant interstellar cloud. Methods. We used the spectra of twelve single-cloud sight lines to examine the λλ5797, 6379, and 6614 DIB profiles. We measured the peak-to-peak separation in the band profile substructures for these DIBs. We adopted the rotational contour formalism for linear or spherical top molecules to infer the rotational constant for each DIB carrier and the rotational excitation temperature in the sight lines. We compared these to experimentally or theoretically obtained rotational constants for linear and spherical molecules to estimate the DIB carrier sizes. Results. All three DIBs have peak separations that vary systematically between lines of sight, indicating correlated changes in the rotational excitation temperatures. The rotational constant B of the λ6614 DIB was determined independently of the rotational excitation temperature; we derived B6614 = (22.2 ± 8.9) x 10−3 cm−1, consistent with previous estimates. Assuming a similar rotational temperature for the λ6614 DIB carrier and assuming a linear carrier, we found B5797linear = (5.1 ± 2.0) × 10−3 cm−1 and B6379linear = (2.3 ± 0.9) × 10−3 cm−1. If the carriers of those DIBs are spherical species, on the other hand, their rotational constants are half that value, B5797spherical = (2.6 ± 1.0) × 10−3 cm−1 and B6379spherical = (1.1 ± 0.4) × 10−3 cm−1. Conclusions. Systematic variations in the DIB profiles provide the means to constrain the molecular properties. We estimate molecule sizes that range from 7–9 carbon atoms (λ6614 carrier, linear) to 77–114 carbon atoms (λ6379, spherical).

Authors 16

1. Heather MacIsaac

   Western University

   Affiliation as printed

   Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 Canada

   Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada

2. J. Cami

   Western University · Search for Extraterrestrial Intelligence

   Affiliation as printed

   Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 Canada

   Institute for Earth and Space Exploration, The University of Western Ontario, London, ON N6A 3K7, Canada

   SETI Institute, 189 Bernardo Ave, Suite 100, Mountain View, CA 94043, USA

3. N. L. J. Cox

   ACRI Group (France)

   Affiliation as printed

   ACRI-ST, 260 route du Pin Montard, 06904 Sophia Antipolis, France

4. Amin Farhang

   Western University · Institute for Research in Fundamental Sciences

   Affiliation as printed

   Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 Canada

   School of Astronomy, Institute for Research in Fundamental Sciences, 19395-5531 Tehran, Iran

5. Jonathan V. Smoker

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory, Alonso de Cordova 3107 Vitacura, Santiago, Chile

6. M. Elyajouri

   Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Paris Cité · Galaxies, Etoiles, Physique et Instrumentation · Université Paris Diderot

   Affiliation as printed

   GEPI, Observatoire de Paris, PSL Research University, CNRS, Université Paris-Diderot, Sorbonne Paris Cité, Place Jules Janssen, 92195 Meudon, France

7. Rosine Lallement

   Centre National de la Recherche Scientifique · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Paris Cité · Galaxies, Etoiles, Physique et Instrumentation · Université Paris Diderot

   Affiliation as printed

   GEPI, Observatoire de Paris, PSL Research University, CNRS, Université Paris-Diderot, Sorbonne Paris Cité, Place Jules Janssen, 92195 Meudon, France

8. Peter J. Sarre

   University of Nottingham

   Affiliation as printed

   School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK

9. Martin Cordiner

   Goddard Space Flight Center · Catholic University of America

   Affiliation as printed

   Astrochemistry Laboratory, NASA Goddard Space Flight Center, Code 691, 8800 Greenbelt Road, Greenbelt, MD 20771, USA

   Department of Physics, The Catholic University of America, Washington, DC 20064, USA

10. Haoyu Fan

    Western University

    Affiliation as printed

    Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 Canada

11. Klay Kulik

    Western University

    Affiliation as printed

    Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 Canada

12. H. Linnartz Aachen Laboratory for Astrophysics, Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

13. Bernard H. Foing

    European Space Research and Technology Centre

    Affiliation as printed

    ESTEC, ESA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

14. Jacco Th. van Loon

    Keele University

    Affiliation as printed

    Lennard-Jones Laboratories, Keele University, ST5 5BG UK

15. G. Mulas

    Osservatorio Astronomico di Cagliari

    Affiliation as printed

    INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius, Italy

16. Keith T. Smith
    Affiliation as printed

    AAAS Science International, Clarendon House, Clarendon Road, Cambridge CB2 8FH, UK