A 3-5 mu m VLT spectroscopic survey of embedded young low mass stars II - Solid OCN-

F A van Broekhuizen, K M Pontoppidan, H J Fraser, E F van Dishoeck

Research output: Contribution to journalArticle

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Abstract

The 4.62 mu m (2164.5 cm(-1)) "XCN" band has been detected in the M-band spectra of 34 deeply embedded young stellar objects (YSO's), observed with high signal-to-noise and high spectral resolution with the VLT-ISAAC spectrometer, providing the first opportunity to study the solid OCN- abundance toward a large number of low-mass YSO's. It is shown unequivocally that at least two components, centred at 2165.7 cm(-1) (FWHM=26 cm(-1)) and 2175.4 cm(-1) (FWHM=15 cm(-1)), underlie the XCN band. Only the 2165.7-component can be ascribed to OCN-, embedded in a strongly hydrogen-bonding, and possibly thermally annealed, ice environment based on laboratory OCN- spectra. In order to correct for the contribution of the 2175.4-component to the XCN band, a phenomenological decomposition into the 2165.7- and the 2175.4-components is used to fit the full band profile and derive the OCN- abundance for each line-of-sight. The same analysis is performed for 5 high-mass YSO's taken from the ISO-SWS data archive. Inferred OCN- abundances are <= 0.85% toward low-mass YSO's and <= 1% toward high-mass YSO's, except for W33A. Abundances are found to vary by at least a factor of 10-20 and large source-to-source abundance variations are observed within the same star-forming cloud complex on scales down to 400 AU, indicating that the OCN- formation mechanism is sensitive to local conditions. The inferred abundances allow quantitatively for photochemical formation of OCN-, but the large abundance variations are not easily explained in this scenario unless local radiation sources or special geometries are invoked. Surface chemistry should therefore be considered as an alternative formation mechanism.

LanguageEnglish
Pages249-260
Number of pages12
JournalAstronomy and Astrophysics
Volume441
Issue number1
DOIs
Publication statusPublished - Oct 2005

Fingerprint

stars
formation mechanism
ice environments
young
radiation sources
spectral resolution
line of sight
spectrometer
hydrogen
spectrometers
decomposition
chemistry
ice
geometry
high resolution
profiles

Keywords

  • astrochemistry
  • line identification
  • line profiles
  • molecular data
  • abundances
  • lines and bands
  • molecular clouds
  • absorption
  • grain mantles
  • dense clouds

Cite this

van Broekhuizen, F. A., Pontoppidan, K. M., Fraser, H. J., & van Dishoeck, E. F. (2005). A 3-5 mu m VLT spectroscopic survey of embedded young low mass stars II - Solid OCN-. Astronomy and Astrophysics, 441(1), 249-260. https://doi.org/10.1051/0004-6361:20041711
van Broekhuizen, F A ; Pontoppidan, K M ; Fraser, H J ; van Dishoeck, E F . / A 3-5 mu m VLT spectroscopic survey of embedded young low mass stars II - Solid OCN-. In: Astronomy and Astrophysics. 2005 ; Vol. 441, No. 1. pp. 249-260.
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abstract = "The 4.62 mu m (2164.5 cm(-1)) {"}XCN{"} band has been detected in the M-band spectra of 34 deeply embedded young stellar objects (YSO's), observed with high signal-to-noise and high spectral resolution with the VLT-ISAAC spectrometer, providing the first opportunity to study the solid OCN- abundance toward a large number of low-mass YSO's. It is shown unequivocally that at least two components, centred at 2165.7 cm(-1) (FWHM=26 cm(-1)) and 2175.4 cm(-1) (FWHM=15 cm(-1)), underlie the XCN band. Only the 2165.7-component can be ascribed to OCN-, embedded in a strongly hydrogen-bonding, and possibly thermally annealed, ice environment based on laboratory OCN- spectra. In order to correct for the contribution of the 2175.4-component to the XCN band, a phenomenological decomposition into the 2165.7- and the 2175.4-components is used to fit the full band profile and derive the OCN- abundance for each line-of-sight. The same analysis is performed for 5 high-mass YSO's taken from the ISO-SWS data archive. Inferred OCN- abundances are <= 0.85{\%} toward low-mass YSO's and <= 1{\%} toward high-mass YSO's, except for W33A. Abundances are found to vary by at least a factor of 10-20 and large source-to-source abundance variations are observed within the same star-forming cloud complex on scales down to 400 AU, indicating that the OCN- formation mechanism is sensitive to local conditions. The inferred abundances allow quantitatively for photochemical formation of OCN-, but the large abundance variations are not easily explained in this scenario unless local radiation sources or special geometries are invoked. Surface chemistry should therefore be considered as an alternative formation mechanism.",
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van Broekhuizen, FA, Pontoppidan, KM, Fraser, HJ & van Dishoeck, EF 2005, 'A 3-5 mu m VLT spectroscopic survey of embedded young low mass stars II - Solid OCN-' Astronomy and Astrophysics, vol. 441, no. 1, pp. 249-260. https://doi.org/10.1051/0004-6361:20041711

A 3-5 mu m VLT spectroscopic survey of embedded young low mass stars II - Solid OCN-. / van Broekhuizen, F A ; Pontoppidan, K M ; Fraser, H J ; van Dishoeck, E F .

In: Astronomy and Astrophysics, Vol. 441, No. 1, 10.2005, p. 249-260.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A 3-5 mu m VLT spectroscopic survey of embedded young low mass stars II - Solid OCN-

AU - van Broekhuizen, F A

AU - Pontoppidan, K M

AU - Fraser, H J

AU - van Dishoeck, E F

PY - 2005/10

Y1 - 2005/10

N2 - The 4.62 mu m (2164.5 cm(-1)) "XCN" band has been detected in the M-band spectra of 34 deeply embedded young stellar objects (YSO's), observed with high signal-to-noise and high spectral resolution with the VLT-ISAAC spectrometer, providing the first opportunity to study the solid OCN- abundance toward a large number of low-mass YSO's. It is shown unequivocally that at least two components, centred at 2165.7 cm(-1) (FWHM=26 cm(-1)) and 2175.4 cm(-1) (FWHM=15 cm(-1)), underlie the XCN band. Only the 2165.7-component can be ascribed to OCN-, embedded in a strongly hydrogen-bonding, and possibly thermally annealed, ice environment based on laboratory OCN- spectra. In order to correct for the contribution of the 2175.4-component to the XCN band, a phenomenological decomposition into the 2165.7- and the 2175.4-components is used to fit the full band profile and derive the OCN- abundance for each line-of-sight. The same analysis is performed for 5 high-mass YSO's taken from the ISO-SWS data archive. Inferred OCN- abundances are <= 0.85% toward low-mass YSO's and <= 1% toward high-mass YSO's, except for W33A. Abundances are found to vary by at least a factor of 10-20 and large source-to-source abundance variations are observed within the same star-forming cloud complex on scales down to 400 AU, indicating that the OCN- formation mechanism is sensitive to local conditions. The inferred abundances allow quantitatively for photochemical formation of OCN-, but the large abundance variations are not easily explained in this scenario unless local radiation sources or special geometries are invoked. Surface chemistry should therefore be considered as an alternative formation mechanism.

AB - The 4.62 mu m (2164.5 cm(-1)) "XCN" band has been detected in the M-band spectra of 34 deeply embedded young stellar objects (YSO's), observed with high signal-to-noise and high spectral resolution with the VLT-ISAAC spectrometer, providing the first opportunity to study the solid OCN- abundance toward a large number of low-mass YSO's. It is shown unequivocally that at least two components, centred at 2165.7 cm(-1) (FWHM=26 cm(-1)) and 2175.4 cm(-1) (FWHM=15 cm(-1)), underlie the XCN band. Only the 2165.7-component can be ascribed to OCN-, embedded in a strongly hydrogen-bonding, and possibly thermally annealed, ice environment based on laboratory OCN- spectra. In order to correct for the contribution of the 2175.4-component to the XCN band, a phenomenological decomposition into the 2165.7- and the 2175.4-components is used to fit the full band profile and derive the OCN- abundance for each line-of-sight. The same analysis is performed for 5 high-mass YSO's taken from the ISO-SWS data archive. Inferred OCN- abundances are <= 0.85% toward low-mass YSO's and <= 1% toward high-mass YSO's, except for W33A. Abundances are found to vary by at least a factor of 10-20 and large source-to-source abundance variations are observed within the same star-forming cloud complex on scales down to 400 AU, indicating that the OCN- formation mechanism is sensitive to local conditions. The inferred abundances allow quantitatively for photochemical formation of OCN-, but the large abundance variations are not easily explained in this scenario unless local radiation sources or special geometries are invoked. Surface chemistry should therefore be considered as an alternative formation mechanism.

KW - astrochemistry

KW - line identification

KW - line profiles

KW - molecular data

KW - abundances

KW - lines and bands

KW - molecular clouds

KW - absorption

KW - grain mantles

KW - dense clouds

U2 - 10.1051/0004-6361:20041711

DO - 10.1051/0004-6361:20041711

M3 - Article

VL - 441

SP - 249

EP - 260

JO - Astronomy and Astrophysics

T2 - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

IS - 1

ER -