F. Lahuis - Academia.edu (original) (raw)

Papers by F. Lahuis

EAS Publications Series, 2011

ABSTRACT Here we present the results of a 3 mm survey of 23 galaxies, obtained with the EMIR rece... more ABSTRACT Here we present the results of a 3 mm survey of 23 galaxies, obtained with the EMIR receiver at the IRAM 30 m telescope. Emission of the main molecular species is compared with existing chemical models, in order to find and test molecular signatures of galaxy evolution and to compare them to IR evolutionary tracers.

The Astrophysical Journal, 2007

We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary i... more We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the ''Cores to Disks'' Spitzer Legacy Program from mid-infrared, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5Y35 m spectrum taken with the IRS, and it shows strong 10 and 20 m silicate features with high feature-to-continuum ratios and clear crystalline features out to 33 m. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot ($300 K) dust responsible for the 10 m feature consists of a roughly equal mix of small ($0.1 m) and large ($1.5 m) grains, whereas the cold ($70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (>1 m). Since the cold dust emission arises from deeper layers in the inner (<3 AU) disk as well as from the surface layers of the outer (3Y5 AU) disk, this provides direct evidence for combined grain growth and settling in the disk. The inferred crystalline mass fractions in the two components are comparable. Since only the inner 0.02 AU of the disk is warm enough to anneal the amorphous silicate grains, even the lowest fraction of 15% of crystalline material requires either very efficient mixing or other formation mechanisms. Subject headingg s: circumstellar matter -stars: individual (SST-Lup3-1) -stars: low-mass, brown dwarfs Online material: color figures 1 Based partly on observations obtained at the ESO NTT at La Silla (Chile) for program 276.C5031.

The Astrophysical Journal, 2007

We present spectroscopy data for a sample of 14 FUors and 2 TTauri stars observed with the Spitze... more We present spectroscopy data for a sample of 14 FUors and 2 TTauri stars observed with the Spitzer Space Telescope or with the Infrared Space Observatory (ISO). Based on the appearance of the 10 µm silicate feature we define 2 categories of FUors. Objects showing the silicate feature in absorption (Category 1) are still embedded in a dusty and icy envelope. The shape of the 10 µm silicate absorption bands is compared to typical dust compositions of the interstellar medium and found to be in general agreement. Only one object (RNO 1B) appears to be too rich in amorphous pyroxene dust, but a superposed emission feature can explain the observed shape. We derive optical depths and

The Astrophysical Journal, 2007

High-resolution spectra of the Spitzer Space Telescope show vibration-rotation absorption bands o... more High-resolution spectra of the Spitzer Space Telescope show vibration-rotation absorption bands of gaseous C 2 H 2 , HCN, and CO 2 molecules toward a sample of deeply obscured (U )LIRG nuclei. The observed bands reveal the presence of dense (n k 10 7 cm À3 ), warm (T ex ¼ 200Y700 K) molecular gas with high column densities of these molecules ranging from a few 10 15 to 10 17 cm À2 . Abundances relative to H 2 , inferred from the silicate optical depth, range from $10 À7 to 10 À6 and show no correlation with temperature. Theoretical studies show that the high abundances of both C 2 H 2 and HCN exclude an X-ray dominated region (XDR) associated with the toroid surrounding an AGN as the origin of this dense warm molecular gas. Galactic massive protostars in the so-called hot-core phase have similar physical characteristics with comparable high abundances of C 2 H 2 , HCN, and CO 2 in the hot phase. However, the abundances of C 2 H 2 and HCN and the C 2 H 2 /CO 2 and HCN/CO 2 ratios are much higher toward the (U)LIRGs in the cooler (T ex P 400 K) phase. We suggest that the warm dense molecular gas revealed by the mid-IR absorption lines is associated with a phase of deeply embedded star formation, where the extreme pressures and densities of the nuclear starburst environment have inhibited the expansion of H ii regions and the global disruption of the starforming molecular cloud cores and have ''trapped'' the star formation process in an ''extended'' hot-core phase. 11 The IRS SH slit width is 4.7 00 , equal to the size of the point-spread function at 19.5 m.

Star Formation with …, 1998

Astronomy and 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 and Astrophysics, 2009

Aims. Polycyclic Aromatic Hydrocarbons (PAHs) have been detected toward molecular clouds and some... more Aims. Polycyclic Aromatic Hydrocarbons (PAHs) have been detected toward molecular clouds and some young stars with disks, but have not yet been associated with embedded young stars. We present a sensitive mid-infrared spectroscopic survey of PAH features toward a sample of low-mass embedded young stellar objects (YSOs). The aim is to put constraints on the PAH abundance in the embedded phase of star formation using radiative transfer modeling. Methods. VLT-ISAAC L-band spectra for 39 sources and Spitzer IRS spectra for 53 sources are presented. Line intensities are compared to recent surveys of Herbig Ae/Be and T Tauri stars. The radiative transfer codes RADMC and RADICAL are used to model the PAH emission from embedded YSOs consisting of a pre-main-sequence star with a circumstellar disk embedded in an envelope. The dependence of the PAH feature on PAH abundance, stellar radiation field, inclination and the extinction by the surrounding envelope is studied. Results. The 3.3 µm PAH feature is undetected for the majority of the sample (97%), with typical upper limits of 5 ×10 −16 W m −2 . One source originally classified as class I, IRS 48, shows a strong 3.3 µm feature from a disk. Compact 11.2 µm PAH emission is seen directly towards 1 out of the 53 Spitzer Short-High spectra, for a source that is borderline embedded. For all 12 sources with both VLT and Spitzer spectra, no PAH features are detected in either. In total, PAH features are detected toward at most 1 out of 63 (candidate) embedded protostars ( 2%), even lower than observed for class II T Tauri stars with disks (11-14%). Models predict the 7.7 µm feature as the best tracer of PAH emission, while the 3.3 µm feature is relatively weak. Assuming typical class I stellar and envelope parameters, the absence of PAHs emission is most likely explained by the absence of emitting carriers through a PAH abundance at least an order of magnitude lower than in molecular clouds but similar to that found in disks. Thus, most PAHs likely enter the protoplanetary disks frozen out in icy layers on dust grains and/or in coagulated form.

Astronomy & Astrophysics, 2013

Context. Over the last few years, the chemistry of molecules other than CO in the planet-forming ... more Context. Over the last few years, the chemistry of molecules other than CO in the planet-forming zones of disks is starting to be explored with Spitzer and high-resolution ground-based data. However, these studies have focused only on a few simple molecules. Aims. The aim of this study is to put observational constraints on the presence of more complex organic and sulfurbearing molecules predicted to be abundant in chemical models of disks. Methods. High S/N Spitzer spectra at 10-30 µm of the near edge-on disks IRS 46 and GV Tau are used to search for mid-infrared absorption bands of various molecules. These disks are good laboratories because absorption studies do not suffer from low line/continuum ratios that plague emission data. Simple LTE slab models are used to infer column densities and excitation temperatures for detected lines and upper limits for non-detections. Results. Mid-infrared bands of HCN, C2H2 and CO2 are clearly detected toward both sources. As found previously for IRS 46 by , the HCN and C2H2 absorption arises in warm gas with excitation temperatures of 400-700 K, whereas the CO2 absorption originates in cooler gas of ∼250 K. Absolute column densities and their ratios are comparable for the two sources. No other absorption features are detected at the 3σ level. Column density limits of the majority of molecules predicted to be abundant in the inner disk -C2H4, C2H6, C3H4, C4H2, CH3, HNC, HC3N, CH3CN, NH3 and SO2-are determined. Simulations are also performed for future higher spectral resolution instruments such as on JWST, SOFIA, SPICA or ELTs. Conclusions. The inferred abundance ratios and limits with respect to C2H2 and HCN are roughly consistent with models of the chemistry in high temperature gas. Models of UV irradiated disk surfaces generally agree better with the data than pure X-ray models. The limit on NH3/HCN implies that evaporation of NH3-containing ices is only a minor contributor. The inferred abundances and their limits also compare well with those found in comets, suggesting that part of the cometary material derives from warm inner disk gas. Future higher resolution data will provide up to an order of magnitude deeper tests of the models.

We present SWS and LWS observations of the Cas A SNR. Broad [O III] 52 and 88um and [O I] 63um em... more We present SWS and LWS observations of the Cas A SNR. Broad [O III] 52 and 88um and [O I] 63um emission lines extending over ~10000 kms-1 are detected. The SWS observations reveal narrower, ~3000 kms-1, blueshifted [O IV] 26um,[Ar II] 7um [Ar III] 9um, [S IV] 10.5 um, [S III] 19 um, [Ne II] 12.8um and [Ne III] 15.5um

Astronomy and …, 1996

Astron. Astrophys. 315, L49-L54 (1996) ASTRONOMY AND ASTROPHYSICS Observing with the ISO Short-Wa... more Astron. Astrophys. 315, L49-L54 (1996) ASTRONOMY AND ASTROPHYSICS Observing with the ISO Short-Wavelength Spectrometer* Th. de Graauw1'5, LN Haser2, DA Beintema1'3'5, PR Roelfsema1'3'5, H. van Agthoven'°, L. Ban2, OH Bauer2, HEG Bekenkamp' , AJ. ...

EAS Publications Series, 2011

ABSTRACT Here we present the results of a 3 mm survey of 23 galaxies, obtained with the EMIR rece... more ABSTRACT Here we present the results of a 3 mm survey of 23 galaxies, obtained with the EMIR receiver at the IRAM 30 m telescope. Emission of the main molecular species is compared with existing chemical models, in order to find and test molecular signatures of galaxy evolution and to compare them to IR evolutionary tracers.

The Astrophysical Journal, 2007

We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary i... more We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the ''Cores to Disks'' Spitzer Legacy Program from mid-infrared, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5Y35 m spectrum taken with the IRS, and it shows strong 10 and 20 m silicate features with high feature-to-continuum ratios and clear crystalline features out to 33 m. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot ($300 K) dust responsible for the 10 m feature consists of a roughly equal mix of small ($0.1 m) and large ($1.5 m) grains, whereas the cold ($70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (>1 m). Since the cold dust emission arises from deeper layers in the inner (<3 AU) disk as well as from the surface layers of the outer (3Y5 AU) disk, this provides direct evidence for combined grain growth and settling in the disk. The inferred crystalline mass fractions in the two components are comparable. Since only the inner 0.02 AU of the disk is warm enough to anneal the amorphous silicate grains, even the lowest fraction of 15% of crystalline material requires either very efficient mixing or other formation mechanisms. Subject headingg s: circumstellar matter -stars: individual (SST-Lup3-1) -stars: low-mass, brown dwarfs Online material: color figures 1 Based partly on observations obtained at the ESO NTT at La Silla (Chile) for program 276.C5031.

The Astrophysical Journal, 2007

We present spectroscopy data for a sample of 14 FUors and 2 TTauri stars observed with the Spitze... more We present spectroscopy data for a sample of 14 FUors and 2 TTauri stars observed with the Spitzer Space Telescope or with the Infrared Space Observatory (ISO). Based on the appearance of the 10 µm silicate feature we define 2 categories of FUors. Objects showing the silicate feature in absorption (Category 1) are still embedded in a dusty and icy envelope. The shape of the 10 µm silicate absorption bands is compared to typical dust compositions of the interstellar medium and found to be in general agreement. Only one object (RNO 1B) appears to be too rich in amorphous pyroxene dust, but a superposed emission feature can explain the observed shape. We derive optical depths and

The Astrophysical Journal, 2007

High-resolution spectra of the Spitzer Space Telescope show vibration-rotation absorption bands o... more High-resolution spectra of the Spitzer Space Telescope show vibration-rotation absorption bands of gaseous C 2 H 2 , HCN, and CO 2 molecules toward a sample of deeply obscured (U )LIRG nuclei. The observed bands reveal the presence of dense (n k 10 7 cm À3 ), warm (T ex ¼ 200Y700 K) molecular gas with high column densities of these molecules ranging from a few 10 15 to 10 17 cm À2 . Abundances relative to H 2 , inferred from the silicate optical depth, range from $10 À7 to 10 À6 and show no correlation with temperature. Theoretical studies show that the high abundances of both C 2 H 2 and HCN exclude an X-ray dominated region (XDR) associated with the toroid surrounding an AGN as the origin of this dense warm molecular gas. Galactic massive protostars in the so-called hot-core phase have similar physical characteristics with comparable high abundances of C 2 H 2 , HCN, and CO 2 in the hot phase. However, the abundances of C 2 H 2 and HCN and the C 2 H 2 /CO 2 and HCN/CO 2 ratios are much higher toward the (U)LIRGs in the cooler (T ex P 400 K) phase. We suggest that the warm dense molecular gas revealed by the mid-IR absorption lines is associated with a phase of deeply embedded star formation, where the extreme pressures and densities of the nuclear starburst environment have inhibited the expansion of H ii regions and the global disruption of the starforming molecular cloud cores and have ''trapped'' the star formation process in an ''extended'' hot-core phase. 11 The IRS SH slit width is 4.7 00 , equal to the size of the point-spread function at 19.5 m.

Star Formation with …, 1998

Astronomy and 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 and Astrophysics, 2009

Aims. Polycyclic Aromatic Hydrocarbons (PAHs) have been detected toward molecular clouds and some... more Aims. Polycyclic Aromatic Hydrocarbons (PAHs) have been detected toward molecular clouds and some young stars with disks, but have not yet been associated with embedded young stars. We present a sensitive mid-infrared spectroscopic survey of PAH features toward a sample of low-mass embedded young stellar objects (YSOs). The aim is to put constraints on the PAH abundance in the embedded phase of star formation using radiative transfer modeling. Methods. VLT-ISAAC L-band spectra for 39 sources and Spitzer IRS spectra for 53 sources are presented. Line intensities are compared to recent surveys of Herbig Ae/Be and T Tauri stars. The radiative transfer codes RADMC and RADICAL are used to model the PAH emission from embedded YSOs consisting of a pre-main-sequence star with a circumstellar disk embedded in an envelope. The dependence of the PAH feature on PAH abundance, stellar radiation field, inclination and the extinction by the surrounding envelope is studied. Results. The 3.3 µm PAH feature is undetected for the majority of the sample (97%), with typical upper limits of 5 ×10 −16 W m −2 . One source originally classified as class I, IRS 48, shows a strong 3.3 µm feature from a disk. Compact 11.2 µm PAH emission is seen directly towards 1 out of the 53 Spitzer Short-High spectra, for a source that is borderline embedded. For all 12 sources with both VLT and Spitzer spectra, no PAH features are detected in either. In total, PAH features are detected toward at most 1 out of 63 (candidate) embedded protostars ( 2%), even lower than observed for class II T Tauri stars with disks (11-14%). Models predict the 7.7 µm feature as the best tracer of PAH emission, while the 3.3 µm feature is relatively weak. Assuming typical class I stellar and envelope parameters, the absence of PAHs emission is most likely explained by the absence of emitting carriers through a PAH abundance at least an order of magnitude lower than in molecular clouds but similar to that found in disks. Thus, most PAHs likely enter the protoplanetary disks frozen out in icy layers on dust grains and/or in coagulated form.

Astronomy & Astrophysics, 2013

Context. Over the last few years, the chemistry of molecules other than CO in the planet-forming ... more Context. Over the last few years, the chemistry of molecules other than CO in the planet-forming zones of disks is starting to be explored with Spitzer and high-resolution ground-based data. However, these studies have focused only on a few simple molecules. Aims. The aim of this study is to put observational constraints on the presence of more complex organic and sulfurbearing molecules predicted to be abundant in chemical models of disks. Methods. High S/N Spitzer spectra at 10-30 µm of the near edge-on disks IRS 46 and GV Tau are used to search for mid-infrared absorption bands of various molecules. These disks are good laboratories because absorption studies do not suffer from low line/continuum ratios that plague emission data. Simple LTE slab models are used to infer column densities and excitation temperatures for detected lines and upper limits for non-detections. Results. Mid-infrared bands of HCN, C2H2 and CO2 are clearly detected toward both sources. As found previously for IRS 46 by , the HCN and C2H2 absorption arises in warm gas with excitation temperatures of 400-700 K, whereas the CO2 absorption originates in cooler gas of ∼250 K. Absolute column densities and their ratios are comparable for the two sources. No other absorption features are detected at the 3σ level. Column density limits of the majority of molecules predicted to be abundant in the inner disk -C2H4, C2H6, C3H4, C4H2, CH3, HNC, HC3N, CH3CN, NH3 and SO2-are determined. Simulations are also performed for future higher spectral resolution instruments such as on JWST, SOFIA, SPICA or ELTs. Conclusions. The inferred abundance ratios and limits with respect to C2H2 and HCN are roughly consistent with models of the chemistry in high temperature gas. Models of UV irradiated disk surfaces generally agree better with the data than pure X-ray models. The limit on NH3/HCN implies that evaporation of NH3-containing ices is only a minor contributor. The inferred abundances and their limits also compare well with those found in comets, suggesting that part of the cometary material derives from warm inner disk gas. Future higher resolution data will provide up to an order of magnitude deeper tests of the models.

We present SWS and LWS observations of the Cas A SNR. Broad [O III] 52 and 88um and [O I] 63um em... more We present SWS and LWS observations of the Cas A SNR. Broad [O III] 52 and 88um and [O I] 63um emission lines extending over ~10000 kms-1 are detected. The SWS observations reveal narrower, ~3000 kms-1, blueshifted [O IV] 26um,[Ar II] 7um [Ar III] 9um, [S IV] 10.5 um, [S III] 19 um, [Ne II] 12.8um and [Ne III] 15.5um

Astronomy and …, 1996

Astron. Astrophys. 315, L49-L54 (1996) ASTRONOMY AND ASTROPHYSICS Observing with the ISO Short-Wa... more Astron. Astrophys. 315, L49-L54 (1996) ASTRONOMY AND ASTROPHYSICS Observing with the ISO Short-Wavelength Spectrometer* Th. de Graauw1'5, LN Haser2, DA Beintema1'3'5, PR Roelfsema1'3'5, H. van Agthoven'°, L. Ban2, OH Bauer2, HEG Bekenkamp' , AJ. ...