Fred Lahuis | SRON, Netherlands Institute for Space Research (original) (raw)

Papers by Fred Lahuis

The Astrophysical Journal, 2008

CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have... more CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH 4 toward low-mass star-forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH 4 abundance toward a large sample of low-mass young stellar objects. A total of 25 out of 52 ice sources in the ''Cores to Disks'' (c2d) Legacy program have an absorption feature at 7.7 m, attributed to the bending mode of solid CH 4 . The solid CH 4 /H 2 O abundances are 2%Y8%, except for three sources with abundances as high as 11%Y13%. The latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H 2 O column densities above 2 ; 10 18 cm À2 , the CH 4 abundances (20 out of 25) are nearly constant at 4:7% AE 1:6%. Correlation plots with solid H 2 O, CH 3 OH, CO 2 , and CO column densities and abundances relative to H 2 O reveal a closer relationship of solid CH 4 with CO 2 and H 2 O than with solid CO and CH 3 OH. The inferred solid CH 4 abundances are consistent with models where CH 4 is formed through sequential hydrogenation of C on grain surfaces. Finally, the equal or higher abundances toward low-mass young stellar objects compared with high-mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH 3 OH and formation in gas phase with subsequent freezeout.

The Astrophysical Journal Supplement Series, 2004

Sensitive 5-38 µm Spitzer Space Telescope (SST) and ground based 3-5 µm spectra of the embedded l... more Sensitive 5-38 µm Spitzer Space Telescope (SST) and ground based 3-5 µm spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO 2 bending mode at 15 µm is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN − bands, however. The observed CO 2 profile indicates an intimate mixture with H 2 O, but not necessarily with CH 3 OH, in contrast to some high mass protostars. This is consistent with the low CH 3 OH abundance derived from the ground based L band spectra. The CO 2 /H 2 O column density ratios are high in both B5 IRS1 and HH46 IRS (∼ 35%). Clearly, the SST spectra are essential to study ice evolution in low mass protostellar environments, and to eventually determine the relation between interstellar and solar system ices.

The Astrophysical Journal, 2008

CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have... more CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have previously been determined mostly toward high mass star forming regions. Spitzer/IRS now provides a unique opportunity to probe solid CH 4 toward low mass star forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH 4 abundance toward a large sample of low mass young stellar objects. 25 out of 52 ice sources in the c2d (cores to disks) legacy have an absorption feature at 7.7 µm, attributed to the bending mode of solid CH 4 . The solid CH 4 / H 2 O abundances are 2-8%, except for three sources with abundances as high as 11-13%. These latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H 2 O column densities above 2×10 18 cm −2 , the CH 4 abundances (20 out of 25) are nearly constant at 4.7±1.6%. Correlation plots with solid H 2 O, CH 3 OH, CO 2 and CO column densities and abundances relative to H 2 O reveal a closer relationship of solid CH 4 with CO 2 and H 2 O than with solid CO and CH 3 OH. The inferred solid CH 4 abundances are consistent with models where CH 4 is formed through sequential hydrogenation of C on grain surfaces. Finally the equal or higher abundances toward low mass young stellar objects compared with high mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH 3 OH and formation in gas phase with subsequent freeze-out.

Astronomy & Astrophysics, 1996

The Short-Wavelength Spectrometer (SWS) is one of the four instruments on-board ESA's Infrared Sp... more The Short-Wavelength Spectrometer (SWS) is one of the four instruments on-board ESA's Infrared Space Observatory (ISO), launched on November 17, 1995. The spectrometer covers the wavelength range of 2.38 to 45.2 m with a spectral resolution ranging from 1000 to 2000. By inserting Fabry-Perot filters the resolution can be enhanced by a factor 20 for the wavelength range from 11.4 to 44.5 m. An overview is given of the instrument, its in-orbit calibration, performance, observing modes and off-line processing software.

Astrophysical Journal Supplement Series, 2004

Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded l... more Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO2 bending mode at 15 um is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN- bands, however. The observed CO2 profile indicates an intimate mixture with H2O, but not necessarily with CH3OH, in contrast to some high mass protostars. This is consistent with the low CH3OH abundance derived from the ground based L band spectra. The CO2/H2O column density ratios are high in both B5 IRS1 and HH46 IRS (~35%). Clearly, the SST spectra are essential to study ice evolution in low mass protostellar environments, and to eventually determine the relation between interstellar and solar system ices.

We present a summary of all ground based SWS instrument tests and calibrations together with a de... more We present a summary of all ground based SWS instrument tests and calibrations together with a description of test equipment and environment. The contents and results of the SWS ground calibration are discussed and their value for the in-flight calibration of SWS is demonstrated.

Astronomy & Astrophysics, 1996

We report absorption features of solid CO 2 stretching and bending modes in several lines of sigh... more We report absorption features of solid CO 2 stretching and bending modes in several lines of sight, including embedded young stellar objects and the Galactic Center source Sgr A*. The overall CO 2 abundance in ices is 15% relative to H 2 O. Profile shapes are consistent with the presence of grain mantles with distinct polar (H 2 O-rich) and nonpolar (CO or CO 2 -rich) layers. In addition to the normal isotopic form, we report detection of the stretching mode of 13 CO 2 ; the 12 C/ 13 C ratio is consistent with terrestrial and interstellar values.

Astronomy & Astrophysics, 1996

We give an overview of the photometric calibration of the Short Wavelength Spectrometer (SWS) thr... more We give an overview of the photometric calibration of the Short Wavelength Spectrometer (SWS) through the Performance Verification phase. The basic strategy for deriving absolute flux densities from detector output for the grating and Fabry-Perot sections of SWS is reviewed, and the results are demonstrated with 2.4 -45 m spectra of representative standards Dra, Lyr, and Cru. The effects of in-orbit changes in the relative spectral response function (RSRF) and ISO pointing are discussed. The systematic continuum flux level uncertainties (1 ) are within the pre-launch specification of 30%. Further improvements depend on characterization of the in-orbit RSRF, improved performance of ISO pointing, and new data processing techniques.

Astronomy & Astrophysics, 1996

We present SWS full-scan observations of three objects that are thought to be in a stage of evolu... more We present SWS full-scan observations of three objects that are thought to be in a stage of evolution between the youngest, embedded, Herbig Ae/Be stars and Beta Pictoris, a young main-sequence star with a circumstellar disk. The 8-12 m spectra of all three stars cannot be understood in terms of purely amorphous silicates, but require the presence of crystalline silicates in different amounts. Around two objects both oxygen-rich and carbon-rich dust particles are present: the spectrum of HD 100546 displays the full set of UIR features; in the spectrum of HD 142527 both the 3.29 and 3.42 m emission features are observed, as well as a strong 3.51 m feature. The spectrum of HD 100546 is extremely rich in silicate features in the spectral range from 20 to 45 m; some of these features strongly suggest the presence of appreciable amounts of crystalline silicates.

Astronomy & Astrophysics, 1996

The laboratory wavelength calibration of the SWS has been succesfully transferred to the in orbit... more The laboratory wavelength calibration of the SWS has been succesfully transferred to the in orbit situation. The achieved accuracies for the grating sections are = 10000.

Astrophysical Journal, 2008

With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spect... more With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]

Icarus, 1995

Page 1. Icarus 114, 197-202 (1995) IRAS LRS Spectra of Comets Tempel 1 and Tempel 2* David K. Lyn... more Page 1. Icarus 114, 197-202 (1995) IRAS LRS Spectra of Comets Tempel 1 and Tempel 2* David K. Lynch, John A. Hackwell, and David Edelsohn Space and Environment Technology Center, Aerospace Corporation M2I266 ...

We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on dif... more We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on different hardware platforms. The IA 2 system design ) has been reviewed and major parts of the concept have been changed for the operating IA 3 system.

Astronomy & Astrophysics, 2002

We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolutio... more We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolution (λ/δ λ ≈ 1500-2000). The spectra were recorded using the Short-Wavelength Spectrometer aboard the Infrared Space Observatory (ISO-SWS). The bulk of the observations were performed during a dedicated observation campaign after the liquid helium depletion of the ISO satellite, the so-called post-helium programme. This programme was aimed at extending the MK-classification to the nearinfrared. Therefore the programme covers a large range of spectral types and luminosity classes. The 2.36 µm-4.05 µm region is a valuable spectral probe for both hot and cool stars. H I lines (Bracket, Pfund and Humphreys series), He I and He II lines, atomic lines and molecular lines (CO, H 2 O, NH, OH, SiO, HCN, C 2 H 2 , ...) are sensitive to temperature, gravity and/or the nature of the outer layers of the stellar atmosphere (outflows, hot circumstellar discs, etc.). Another objective of the programme was to construct a homogeneous dataset of near-infrared stellar spectra that can be used for population synthesis studies of galaxies. At near-infrared wavelengths these objects emit the integrated light of all stars in the system. In this paper we present the dataset of post-helium spectra completed with observations obtained during the nominal operations of the ISO-SWS. We discuss the calibration of the SWS data obtained after the liquid helium boil-off and the data reduction. We also give a first qualitative overview of how the spectral features in this wavelength range change with spectral type. The dataset is scrutinised in two papers on the quantitative classification of near-infrared spectra of early-type stars and late-type stars (Vandenbussche et al., in prep).

Astronomy & Astrophysics, 1996

The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode ... more The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode (2.4-45 m) shows a wealth of features never seen before in previous observations. These include ro-vibrational lines of H 2 O at 2.7 and 6.2 m, of OH between 3 and 3.5 m and a deep absorption band of CO 2 at 4.26 m. We also report on the detection of pure rotational emission lines of H 2 O between 35 and 45 m and of the 34.6 m absorption line of OH which is thought to pump the well known 1612 MHz OH maser line. There are two, as yet, unidentified features at 33 and 40 m which may be related to silicate dust.

We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on dif... more We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on different hardware platforms. The IA 2 system design ) has been reviewed and major parts of the concept have been changed for the operating IA 3 system.

Astronomy & Astrophysics, 2002

We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolutio... more We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolution (λ/δ λ ≈ 1500-2000). The spectra were recorded using the Short-Wavelength Spectrometer aboard the Infrared Space Observatory (ISO-SWS). The bulk of the observations were performed during a dedicated observation campaign after the liquid helium depletion of the ISO satellite, the so-called post-helium programme. This programme was aimed at extending the MK-classification to the nearinfrared. Therefore the programme covers a large range of spectral types and luminosity classes. The 2.36 µm-4.05 µm region is a valuable spectral probe for both hot and cool stars. H I lines (Bracket, Pfund and Humphreys series), He I and He II lines, atomic lines and molecular lines (CO, H 2 O, NH, OH, SiO, HCN, C 2 H 2 , ...) are sensitive to temperature, gravity and/or the nature of the outer layers of the stellar atmosphere (outflows, hot circumstellar discs, etc.). Another objective of the programme was to construct a homogeneous dataset of near-infrared stellar spectra that can be used for population synthesis studies of galaxies. At near-infrared wavelengths these objects emit the integrated light of all stars in the system. In this paper we present the dataset of post-helium spectra completed with observations obtained during the nominal operations of the ISO-SWS. We discuss the calibration of the SWS data obtained after the liquid helium boil-off and the data reduction. We also give a first qualitative overview of how the spectral features in this wavelength range change with spectral type. The dataset is scrutinised in two papers on the quantitative classification of near-infrared spectra of early-type stars and late-type stars (Vandenbussche et al., in prep).

Astronomy & Astrophysics, 1996

The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode ... more The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode (2.4-45 m) shows a wealth of features never seen before in previous observations. These include ro-vibrational lines of H 2 O at 2.7 and 6.2 m, of OH between 3 and 3.5 m and a deep absorption band of CO 2 at 4.26 m. We also report on the detection of pure rotational emission lines of H 2 O between 35 and 45 m and of the 34.6 m absorption line of OH which is thought to pump the well known 1612 MHz OH maser line. There are two, as yet, unidentified features at 33 and 40 m which may be related to silicate dust.

The Astrophysical Journal, 2008

CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have... more CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH 4 toward low-mass star-forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH 4 abundance toward a large sample of low-mass young stellar objects. A total of 25 out of 52 ice sources in the ''Cores to Disks'' (c2d) Legacy program have an absorption feature at 7.7 m, attributed to the bending mode of solid CH 4 . The solid CH 4 /H 2 O abundances are 2%Y8%, except for three sources with abundances as high as 11%Y13%. The latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H 2 O column densities above 2 ; 10 18 cm À2 , the CH 4 abundances (20 out of 25) are nearly constant at 4:7% AE 1:6%. Correlation plots with solid H 2 O, CH 3 OH, CO 2 , and CO column densities and abundances relative to H 2 O reveal a closer relationship of solid CH 4 with CO 2 and H 2 O than with solid CO and CH 3 OH. The inferred solid CH 4 abundances are consistent with models where CH 4 is formed through sequential hydrogenation of C on grain surfaces. Finally, the equal or higher abundances toward low-mass young stellar objects compared with high-mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH 3 OH and formation in gas phase with subsequent freezeout.

The Astrophysical Journal Supplement Series, 2004

Sensitive 5-38 µm Spitzer Space Telescope (SST) and ground based 3-5 µm spectra of the embedded l... more Sensitive 5-38 µm Spitzer Space Telescope (SST) and ground based 3-5 µm spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO 2 bending mode at 15 µm is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN − bands, however. The observed CO 2 profile indicates an intimate mixture with H 2 O, but not necessarily with CH 3 OH, in contrast to some high mass protostars. This is consistent with the low CH 3 OH abundance derived from the ground based L band spectra. The CO 2 /H 2 O column density ratios are high in both B5 IRS1 and HH46 IRS (∼ 35%). Clearly, the SST spectra are essential to study ice evolution in low mass protostellar environments, and to eventually determine the relation between interstellar and solar system ices.

The Astrophysical Journal, 2008

CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have... more CH 4 is proposed to be the starting point of a rich organic chemistry. Solid CH 4 abundances have previously been determined mostly toward high mass star forming regions. Spitzer/IRS now provides a unique opportunity to probe solid CH 4 toward low mass star forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH 4 abundance toward a large sample of low mass young stellar objects. 25 out of 52 ice sources in the c2d (cores to disks) legacy have an absorption feature at 7.7 µm, attributed to the bending mode of solid CH 4 . The solid CH 4 / H 2 O abundances are 2-8%, except for three sources with abundances as high as 11-13%. These latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H 2 O column densities above 2×10 18 cm −2 , the CH 4 abundances (20 out of 25) are nearly constant at 4.7±1.6%. Correlation plots with solid H 2 O, CH 3 OH, CO 2 and CO column densities and abundances relative to H 2 O reveal a closer relationship of solid CH 4 with CO 2 and H 2 O than with solid CO and CH 3 OH. The inferred solid CH 4 abundances are consistent with models where CH 4 is formed through sequential hydrogenation of C on grain surfaces. Finally the equal or higher abundances toward low mass young stellar objects compared with high mass objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH 3 OH and formation in gas phase with subsequent freeze-out.

Astronomy & Astrophysics, 1996

The Short-Wavelength Spectrometer (SWS) is one of the four instruments on-board ESA's Infrared Sp... more The Short-Wavelength Spectrometer (SWS) is one of the four instruments on-board ESA's Infrared Space Observatory (ISO), launched on November 17, 1995. The spectrometer covers the wavelength range of 2.38 to 45.2 m with a spectral resolution ranging from 1000 to 2000. By inserting Fabry-Perot filters the resolution can be enhanced by a factor 20 for the wavelength range from 11.4 to 44.5 m. An overview is given of the instrument, its in-orbit calibration, performance, observing modes and off-line processing software.

Astrophysical Journal Supplement Series, 2004

Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded l... more Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO2 bending mode at 15 um is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN- bands, however. The observed CO2 profile indicates an intimate mixture with H2O, but not necessarily with CH3OH, in contrast to some high mass protostars. This is consistent with the low CH3OH abundance derived from the ground based L band spectra. The CO2/H2O column density ratios are high in both B5 IRS1 and HH46 IRS (~35%). Clearly, the SST spectra are essential to study ice evolution in low mass protostellar environments, and to eventually determine the relation between interstellar and solar system ices.

We present a summary of all ground based SWS instrument tests and calibrations together with a de... more We present a summary of all ground based SWS instrument tests and calibrations together with a description of test equipment and environment. The contents and results of the SWS ground calibration are discussed and their value for the in-flight calibration of SWS is demonstrated.

Astronomy & Astrophysics, 1996

We report absorption features of solid CO 2 stretching and bending modes in several lines of sigh... more We report absorption features of solid CO 2 stretching and bending modes in several lines of sight, including embedded young stellar objects and the Galactic Center source Sgr A*. The overall CO 2 abundance in ices is 15% relative to H 2 O. Profile shapes are consistent with the presence of grain mantles with distinct polar (H 2 O-rich) and nonpolar (CO or CO 2 -rich) layers. In addition to the normal isotopic form, we report detection of the stretching mode of 13 CO 2 ; the 12 C/ 13 C ratio is consistent with terrestrial and interstellar values.

Astronomy & Astrophysics, 1996

We give an overview of the photometric calibration of the Short Wavelength Spectrometer (SWS) thr... more We give an overview of the photometric calibration of the Short Wavelength Spectrometer (SWS) through the Performance Verification phase. The basic strategy for deriving absolute flux densities from detector output for the grating and Fabry-Perot sections of SWS is reviewed, and the results are demonstrated with 2.4 -45 m spectra of representative standards Dra, Lyr, and Cru. The effects of in-orbit changes in the relative spectral response function (RSRF) and ISO pointing are discussed. The systematic continuum flux level uncertainties (1 ) are within the pre-launch specification of 30%. Further improvements depend on characterization of the in-orbit RSRF, improved performance of ISO pointing, and new data processing techniques.

Astronomy & Astrophysics, 1996

We present SWS full-scan observations of three objects that are thought to be in a stage of evolu... more We present SWS full-scan observations of three objects that are thought to be in a stage of evolution between the youngest, embedded, Herbig Ae/Be stars and Beta Pictoris, a young main-sequence star with a circumstellar disk. The 8-12 m spectra of all three stars cannot be understood in terms of purely amorphous silicates, but require the presence of crystalline silicates in different amounts. Around two objects both oxygen-rich and carbon-rich dust particles are present: the spectrum of HD 100546 displays the full set of UIR features; in the spectrum of HD 142527 both the 3.29 and 3.42 m emission features are observed, as well as a strong 3.51 m feature. The spectrum of HD 100546 is extremely rich in silicate features in the spectral range from 20 to 45 m; some of these features strongly suggest the presence of appreciable amounts of crystalline silicates.

Astronomy & Astrophysics, 1996

The laboratory wavelength calibration of the SWS has been succesfully transferred to the in orbit... more The laboratory wavelength calibration of the SWS has been succesfully transferred to the in orbit situation. The achieved accuracies for the grating sections are = 10000.

Astrophysical Journal, 2008

With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spect... more With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]

Icarus, 1995

Page 1. Icarus 114, 197-202 (1995) IRAS LRS Spectra of Comets Tempel 1 and Tempel 2* David K. Lyn... more Page 1. Icarus 114, 197-202 (1995) IRAS LRS Spectra of Comets Tempel 1 and Tempel 2* David K. Lynch, John A. Hackwell, and David Edelsohn Space and Environment Technology Center, Aerospace Corporation M2I266 ...

We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on dif... more We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on different hardware platforms. The IA 2 system design ) has been reviewed and major parts of the concept have been changed for the operating IA 3 system.

Astronomy & Astrophysics, 2002

We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolutio... more We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolution (λ/δ λ ≈ 1500-2000). The spectra were recorded using the Short-Wavelength Spectrometer aboard the Infrared Space Observatory (ISO-SWS). The bulk of the observations were performed during a dedicated observation campaign after the liquid helium depletion of the ISO satellite, the so-called post-helium programme. This programme was aimed at extending the MK-classification to the nearinfrared. Therefore the programme covers a large range of spectral types and luminosity classes. The 2.36 µm-4.05 µm region is a valuable spectral probe for both hot and cool stars. H I lines (Bracket, Pfund and Humphreys series), He I and He II lines, atomic lines and molecular lines (CO, H 2 O, NH, OH, SiO, HCN, C 2 H 2 , ...) are sensitive to temperature, gravity and/or the nature of the outer layers of the stellar atmosphere (outflows, hot circumstellar discs, etc.). Another objective of the programme was to construct a homogeneous dataset of near-infrared stellar spectra that can be used for population synthesis studies of galaxies. At near-infrared wavelengths these objects emit the integrated light of all stars in the system. In this paper we present the dataset of post-helium spectra completed with observations obtained during the nominal operations of the ISO-SWS. We discuss the calibration of the SWS data obtained after the liquid helium boil-off and the data reduction. We also give a first qualitative overview of how the spectral features in this wavelength range change with spectral type. The dataset is scrutinised in two papers on the quantitative classification of near-infrared spectra of early-type stars and late-type stars (Vandenbussche et al., in prep).

Astronomy & Astrophysics, 1996

The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode ... more The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode (2.4-45 m) shows a wealth of features never seen before in previous observations. These include ro-vibrational lines of H 2 O at 2.7 and 6.2 m, of OH between 3 and 3.5 m and a deep absorption band of CO 2 at 4.26 m. We also report on the detection of pure rotational emission lines of H 2 O between 35 and 45 m and of the 34.6 m absorption line of OH which is thought to pump the well known 1612 MHz OH maser line. There are two, as yet, unidentified features at 33 and 40 m which may be related to silicate dust.

We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on dif... more We describe the ISO SWS Pipeline software and ISO SWS Interactive Analysis system ( IA 3 ) on different hardware platforms. The IA 2 system design ) has been reviewed and major parts of the concept have been changed for the operating IA 3 system.

Astronomy & Astrophysics, 2002

We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolutio... more We present an atlas of near-infrared spectra (2.36 µm-4.1 µm) of ∼300 stars at moderate resolution (λ/δ λ ≈ 1500-2000). The spectra were recorded using the Short-Wavelength Spectrometer aboard the Infrared Space Observatory (ISO-SWS). The bulk of the observations were performed during a dedicated observation campaign after the liquid helium depletion of the ISO satellite, the so-called post-helium programme. This programme was aimed at extending the MK-classification to the nearinfrared. Therefore the programme covers a large range of spectral types and luminosity classes. The 2.36 µm-4.05 µm region is a valuable spectral probe for both hot and cool stars. H I lines (Bracket, Pfund and Humphreys series), He I and He II lines, atomic lines and molecular lines (CO, H 2 O, NH, OH, SiO, HCN, C 2 H 2 , ...) are sensitive to temperature, gravity and/or the nature of the outer layers of the stellar atmosphere (outflows, hot circumstellar discs, etc.). Another objective of the programme was to construct a homogeneous dataset of near-infrared stellar spectra that can be used for population synthesis studies of galaxies. At near-infrared wavelengths these objects emit the integrated light of all stars in the system. In this paper we present the dataset of post-helium spectra completed with observations obtained during the nominal operations of the ISO-SWS. We discuss the calibration of the SWS data obtained after the liquid helium boil-off and the data reduction. We also give a first qualitative overview of how the spectral features in this wavelength range change with spectral type. The dataset is scrutinised in two papers on the quantitative classification of near-infrared spectra of early-type stars and late-type stars (Vandenbussche et al., in prep).

Astronomy & Astrophysics, 1996

The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode ... more The high resolution spectrum of NML Cyg observed with the ISO-SWS in its slow-speed grating mode (2.4-45 m) shows a wealth of features never seen before in previous observations. These include ro-vibrational lines of H 2 O at 2.7 and 6.2 m, of OH between 3 and 3.5 m and a deep absorption band of CO 2 at 4.26 m. We also report on the detection of pure rotational emission lines of H 2 O between 35 and 45 m and of the 34.6 m absorption line of OH which is thought to pump the well known 1612 MHz OH maser line. There are two, as yet, unidentified features at 33 and 40 m which may be related to silicate dust.