skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The census of complex organic molecules in the solar-type protostar IRAS16293-2422

Abstract

Complex organic molecules (COMs) are considered to be crucial molecules, since they are connected with organic chemistry, at the basis of terrestrial life. More pragmatically, they are molecules which in principle are difficult to synthesize in harsh interstellar environments and, therefore, are a crucial test for astrochemical models. Current models assume that several COMs are synthesized on lukewarm grain surfaces (≳30-40 K) and released in the gas phase at dust temperatures of ≳100 K. However, recent detections of COMs in ≲20 K gas demonstrate that we still need important pieces to complete the puzzle of COMs formation. Here, we present a complete census of the oxygen- and nitrogen-bearing COMs, previously detected in different Interstellar Medium (ISM) regions, toward the solar-type protostar IRAS16293-2422. The census was obtained from the millimeter-submillimeter unbiased spectral survey TIMASSS. Of the 29 COMs searched for, 6 were detected: methyl cyanide, ketene, acetaldehyde, formamide, dimethyl ether, and methyl formate. Multifrequency analysis of the last five COMs provides clear evidence that they are present in the cold (≲30 K) envelope of IRAS16293-2422, with abundances of 0.03-2 × 10{sup –10}. Our data do not allow us to support the hypothesis that the COMs abundance increases with increasing dust temperaturemore » in the cold envelope, as expected if COMs were predominately formed on lukewarm grain surfaces. Finally, when also considering other ISM sources, we find a strong correlation over five orders of magnitude between methyl formate and dimethyl ether, and methyl formate and formamide abundances, which may point to a link between these two couples of species in cold and warm gas.« less

Authors:
; ;  [1];  [2]
  1. Université Grenoble Alpes, IPAG, F-38000 Grenoble (France)
  2. Université de Toulouse, UPS-OMP, IRAP, F-31400 Toulouse (France)
Publication Date:
OSTI Identifier:
22365397
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 791; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACETALDEHYDE; CORRELATIONS; COSMOLOGICAL MODELS; CYANIDES; DETECTION; DUSTS; ELEMENT ABUNDANCE; FORMAMIDE; HYPOTHESIS; INTERSTELLAR SPACE; KETENES; METHYL ETHER; MOLECULES; NITROGEN; OXYGEN; PROTOSTARS; STARS; SURFACES

Citation Formats

Jaber, Ali A., Ceccarelli, C., Kahane, C., and Caux, E. The census of complex organic molecules in the solar-type protostar IRAS16293-2422. United States: N. p., 2014. Web. doi:10.1088/0004-637X/791/1/29.
Jaber, Ali A., Ceccarelli, C., Kahane, C., & Caux, E. The census of complex organic molecules in the solar-type protostar IRAS16293-2422. United States. doi:10.1088/0004-637X/791/1/29.
Jaber, Ali A., Ceccarelli, C., Kahane, C., and Caux, E. Sun . "The census of complex organic molecules in the solar-type protostar IRAS16293-2422". United States. doi:10.1088/0004-637X/791/1/29.
@article{osti_22365397,
title = {The census of complex organic molecules in the solar-type protostar IRAS16293-2422},
author = {Jaber, Ali A. and Ceccarelli, C. and Kahane, C. and Caux, E.},
abstractNote = {Complex organic molecules (COMs) are considered to be crucial molecules, since they are connected with organic chemistry, at the basis of terrestrial life. More pragmatically, they are molecules which in principle are difficult to synthesize in harsh interstellar environments and, therefore, are a crucial test for astrochemical models. Current models assume that several COMs are synthesized on lukewarm grain surfaces (≳30-40 K) and released in the gas phase at dust temperatures of ≳100 K. However, recent detections of COMs in ≲20 K gas demonstrate that we still need important pieces to complete the puzzle of COMs formation. Here, we present a complete census of the oxygen- and nitrogen-bearing COMs, previously detected in different Interstellar Medium (ISM) regions, toward the solar-type protostar IRAS16293-2422. The census was obtained from the millimeter-submillimeter unbiased spectral survey TIMASSS. Of the 29 COMs searched for, 6 were detected: methyl cyanide, ketene, acetaldehyde, formamide, dimethyl ether, and methyl formate. Multifrequency analysis of the last five COMs provides clear evidence that they are present in the cold (≲30 K) envelope of IRAS16293-2422, with abundances of 0.03-2 × 10{sup –10}. Our data do not allow us to support the hypothesis that the COMs abundance increases with increasing dust temperature in the cold envelope, as expected if COMs were predominately formed on lukewarm grain surfaces. Finally, when also considering other ISM sources, we find a strong correlation over five orders of magnitude between methyl formate and dimethyl ether, and methyl formate and formamide abundances, which may point to a link between these two couples of species in cold and warm gas.},
doi = {10.1088/0004-637X/791/1/29},
journal = {Astrophysical Journal},
number = 1,
volume = 791,
place = {United States},
year = {Sun Aug 10 00:00:00 EDT 2014},
month = {Sun Aug 10 00:00:00 EDT 2014}
}
  • A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly formed stars, for example, to identify the presence of rotation and infall. IRAS 16293–2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.''46 × 0.''29, i.e., ∼55 × 35 AU) images of compact emission from the C{sup 17}O (3-2) and C{sup 34}S (7-6) transitions at 337 GHz (0.89 mm). To recover the more extended emission wemore » have combined the eSMA data with SMA observations of the same molecules. The emission of C{sup 17}O (3-2) and C{sup 34}S (7-6) both show a velocity gradient oriented along a northeast-southwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS 16293A. Our combined eSMA and SMA observations show that the velocity field on the 50-400 AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293–2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.« less
  • Formamide (NH{sub 2}CHO), the simplest possible amide, has recently been suggested to be a central species in the synthesis of metabolic and genetic molecules, the chemical basis of life. In this Letter, we report the first detection of formamide in a protostar, IRAS 16293-2422, which may be similar to the Sun and solar system progenitor. The data combine spectra from the millimeter and submillimeter TIMASSS survey with recent, more sensitive observations at the IRAM 30 m telescope. With an abundance relative to H{sub 2} of {approx}10{sup -10}, formamide appears as abundant in this solar-type protostar as in the two high-massmore » star-forming regions, Orion-KL and SgrB2, where this species has previously been detected. Given the largely different UV-illuminated environments of the three sources, the relevance of UV photolysis of interstellar ices in the synthesis of formamide is therefore questionable. Assuming that this species is formed in the gas phase via the neutral-neutral reaction between the radical NH{sub 2} and H{sub 2}CO, we predict an abundance in good agreement with the value derived from our observations. The comparison of the relative abundance [NH{sub 2}CHO]/[H{sub 2}O] in IRAS 16293-2422 and in the coma of the comet Hale-Bopp supports the similarity between interstellar and cometary chemistry. Our results thus suggest that the abundance of some cometary organic volatiles could reflect gas phase rather than grain-surface interstellar chemistry.« less
  • Glycolaldehyde (HCOCH{sub 2}OH) is the simplest sugar and an important intermediate in the path toward forming more complex biologically relevant molecules. In this Letter we present the first detection of 13 transitions of glycolaldehyde around a solar-type young star, through Atacama Large Millimeter Array (ALMA) observations of the Class 0 protostellar binary IRAS 16293-2422 at 220 GHz (6 transitions) and 690 GHz (7 transitions). The glycolaldehyde lines have their origin in warm (200-300 K) gas close to the individual components of the binary. Glycolaldehyde co-exists with its isomer, methyl formate (HCOOCH{sub 3}), which is a factor 10-15 more abundant towardmore » the two sources. The data also show a tentative detection of ethylene glycol, the reduced alcohol of glycolaldehyde. In the 690 GHz data, the seven transitions predicted to have the highest optical depths based on modeling of the 220 GHz lines all show redshifted absorption profiles toward one of the components in the binary (IRAS 16293B) indicative of infall and emission at the systemic velocity offset from this by about 0.''2 (25 AU). We discuss the constraints on the chemical formation of glycolaldehyde and other organic species-in particular, in the context of laboratory experiments of photochemistry of methanol-containing ices. The relative abundances appear to be consistent with UV photochemistry of a CH{sub 3}OH-CO mixed ice that has undergone mild heating. The order of magnitude increase in line density in these early ALMA data illustrates its huge potential to reveal the full chemical complexity associated with the formation of solar system analogs.« less
  • Gas-phase complex organic molecules have been detected toward a range of high- and low-mass star-forming regions at abundances which cannot be explained by any known gas-phase chemistry. Recent laboratory experiments show that UV irradiation of CH{sub 3}OH-rich ices may be an important mechanism for producing complex molecules and releasing them into the gas phase. To test this ice formation scenario, we mapped the B1-b dust core and nearby protostar in CH{sub 3}OH gas using the IRAM 30 m telescope to identify locations of efficient non-thermal ice desorption. We find three CH{sub 3}OH abundance peaks tracing two outflows and a quiescentmore » region on the side of the core facing the protostar. The CH{sub 3}OH gas has a rotational temperature of {approx}10 K at all locations. The quiescent CH{sub 3}OH abundance peak and one outflow position were searched for complex molecules. Narrow, 0.6-0.8 km s{sup -1} wide, HCOOCH{sub 3} and CH{sub 3}CHO lines originating in cold gas are clearly detected, CH{sub 3}OCH{sub 3} is tentatively detected, and C{sub 2}H{sub 5}OH and HOCH{sub 2}CHO are undetected toward the quiescent core, while no complex molecular lines were found toward the outflow. The core abundances with respect to CH{sub 3}OH are {approx}2.3% and 1.1% for HCOOCH{sub 3} and CH{sub 3}CHO, respectively, and the upper limits are 0.7%-1.1%, which is similar to most other low-mass sources. The observed complex molecule characteristics toward B1-b and the pre-dominance of HCO-bearing species suggests a cold ice (below 25 K, the sublimation temperature of CO) formation pathway followed by non-thermal desorption through, e.g., UV photons traveling through outflow cavities. The observed complex gas composition together with the lack of any evidence of warm gas-phase chemistry provides clear evidence of efficient complex molecule formation in cold interstellar ices.« less
  • Analysis of published data on the physical conditions in the Taurus star-formation complex show that stars are being formed with very low efficiency, only roughly-equal1%. This low value is attributable to the action of the gravitational field and rotation of the complex in halting gravitational contraction of its material. Both factors also affect the formation of wide binary systems, as evidenced by the orientation of binary components along preferred position angles.