Absorption features in the 3 micron spectra of protostars

Smith, Robert G.; Sellgren, K.; Tokunaga, A. T.

doi:10.1086/167809

Cited by 193 publications

(213 citation statements)

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“…However, if the long wavelength wing of the 3.1 µm band is attributed to absorption by H 2 O ice, the 6.0 µm and 3.1 µm column densities are more consistent with each other. All sources are best fitted by a cold (T ≤ 50 K) laboratory amorphous H 2 O ice, except Mon R2:IRS3 which is fitted by an 80 K profile, which is consistent with previous work (Smith et al 1989). …”

Section: Discussionsupporting

confidence: 89%

“…Since the laboratory spectrum of amorphous H 2 O does not vary much upon warm-up to 50 K, it is very difficult to distinguish between the profile of a colder ice (10 K) and that of a warmer ice (50 K). The presence of warmed-up H 2 O ice in space is well known from studies of the 3.1 µm H 2 O band (Smith et al 1989) and the derived temperatures agree well for those sources in common between these two samples. Thermal processing of interstellar ice is also apparent from the profiles of the various solid CO 2 modes Boogert et al 2000a).…”

Section: H 2 O Icesupporting

confidence: 63%

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Ice absorption features in the 5-8μm region toward embedded protostars

Keane¹,

Tielens

Boogert

et al. 2001

A&A

239

295

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Abstract.We have obtained 5-8 µm spectra towards 10 embedded protostars using the Short Wavelength Spectrometer on board the Infrared Space Observatory (ISO-SWS) with the aim of studying the composition of interstellar ices. The spectra are dominated by absorption bands at 6.0 µm and 6.85 µm. The observed peak positions, widths and relative intensities of these bands vary dramatically along the different lines of sight. On the basis of comparison with laboratory spectra, the bulk of the 6.0 µm absorption band is assigned to amorphous H2O ice. Additional absorption, in this band, is seen toward 5 sources on the short wavelength wing, near 5.8 µm, and the long wavelength side near 6.2 µm. We attribute the short wavelength absorption to a combination of formic acid (HCOOH) and formaldehyde (H2CO), while the long wavelength absorption has been assigned to the C-C stretching mode of aromatic structures. From an analysis of the 6.85 µm band, we conclude that this band is composed of two components: a volatile component centered near 6.75 µm and a more refractory component at 6.95 µm. From a comparison with various temperature tracers of the thermal history of interstellar ices, we conclude that the two 6.85 µm components are related through thermal processing. We explore several possible carriers of the 6.85 µm absorption band, but no satisfactory identification can be made at present. Finally, we discuss the possible implications for the origin and evolution of interstellar ices that arise from these new results.

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Section: Discussionsupporting

confidence: 89%

Section: H 2 O Icesupporting

confidence: 63%

Ice absorption features in the 5-8μm region toward embedded protostars

Keane¹,

Tielens

Boogert

et al. 2001

A&A

239

295

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“…This suggests that the sources with higher H 2 O gas/solid ratios are more evolved than sources with low gas/solid ratios. The sources with the higher gasphase H 2 O abundances and gas/solid ratios also show evidence for thermal processing of the ices (Smith et al 1989;Boogert et al 2000;Gerakines et al 1999). Similarly, other evolutionary tracers, such as gas-phase HCN, C 2 H 2 , CH 3 OH, and CO 2 show their highest abundances and/or gas/solid ratios for the same sources as gas-phase H 2 O and the lowest values for those sources where no gas-phase H 2 O has been detected (Lahuis & van Dishoeck 2000;van der Tak et al 2000a;Boonman et al 2003a).…”

Section: H 2 O As An Evolutionary Tracermentioning

confidence: 83%

Abundant gas-phase H₂O in absorption toward massive protostars

Boonman

Dishoeck

2003

A&A

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Abstract. We present infrared spectra of gas-phase H 2 O around 6 µm toward 12 deeply embedded massive protostars obtained with the Short Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The ν 2 ro-vibrational band has been detected toward 7 of the sources and the excitation temperatures indicate an origin in the warm gas at T ex > ∼ 250 K. Typical derived gas-phase H 2 O abundances are ∼5 × 10 −6 −6 × 10 −5 , with the abundances increasing with the temperature of the warm gas. The inferred gas/solid ratios show a similar trend with temperature and suggest that grain-mantle evaporation is important. The increasing gas/solid ratio correlates with other indicators of increased temperatures. If the higher temperatures are due to a larger ratio of source luminosity to envelope mass, this makes gas-phase H 2 O a good evolutionary tracer. Comparison with chemical models shows that three different chemical processes, ice evaporation, high-T chemistry, and shocks, can reproduce the high inferred gas-phase H 2 O abundances. In a forthcoming paper each of these processes are investigated in more detail in comparison with data from the Long Wavelength Spectrometer on board ISO and the Submillimeter Wave Astronomy Satellite (SWAS). Comparison with existing SWAS data indicates that a jump in the H 2 O abundance is present and that the observed ν 2 ro-vibrational band traces primarily the warm inner envelope.

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“…In addition, the 3 μm absorption feature (the width and the position of the bottom of the feature) depends on the dust temperature and the grain size (e.g. Smith et al 1989;Pendleton et al 1990). If we assume Chiang & Goldreich's double-layered disk (Chiang & Goldreich 1997), we may derive the grain properties on the surface layer more than in the midplane.…”

Section: Generalized Scattering Modelmentioning

confidence: 99%

Polarization disks in near-infrared high-resolution imaging

Murakawa

2010

A&A

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A polarization disk is a characteristic feature of optical and near-infrared (NIR) polarimetric images of young stellar objects (YSOs) and is regarded as convincing evidence that a dust disk is present. We analyze high-resolution linear polarization maps of a sample of low-mass YSO disk models by means of radiative transfer calculations to investigate the effects of the disk geometry and grain sizes on polarization properties. Our modeling assumes spherical grains with a power-law size distribution of n (a) ∝ a −3.5 ; 0.005 μm ≤ a ≤ a max and with a fixed a max of 0.25 μm for the outer envelope and a different a max for the disk. The parameters to examine are the disk height (i.e. the ratio of the disk height to the outer disk radius H of 0.1 to 1.0) and the dust sizes in the disk (i.e. a max of 0.25 to 1000.0 μm). In a near pole-on view, the polarization vectors are centro-symmetrically aligned even towards the disk, but the degree of polarization can be different from the envelope. We predict that the pole-on disk can be distinguished from the envelope. In contrast, the model images show a bipolar nebulosity and a polarization disk with a vector alignment in edge-on view. The polarization is low (<10%) for large grains or low H values and high (up to ∼80%) for small grains and high H values. In contrast, comparably constant polarizations (20-40%) are obtained in the optical. The wavelength dependence in low NIR polarization cases is often detected in many T Tauri stars, suggesting that grain growth or an advanced disk accretion is expected in these objects. The opposite trend in high NIR polarization cases, which is found in some low-mass protostars, is reproduced with spherical grain models. To understand our results, we developed a generalized scattering model, which is an extension of the vector alignment mechanism. In the lowmass star disk case, multiple-scattered light behaves as if it chooses paths of comparably low optical density region (e.g. the disk surface), avoiding a high density, equatorial region, which we call the roundabout effect. The single-scattered light does not reach the observer, and the double-scattered light contributes the most flux. However, the effect of the first scattering still appears in the final polarization status. The higher the disk height in our models, the closer to 90 • the scattering angle on the disk surface, resulting in a higher polarization. The variety of the wavelength dependence on the polarization is also an example of the roundabout effect. In the optical, only stray light passed through the envelope reaches the observer. Thus, the optical polarization is characterized by scattering by small grains in the envelope. On the other hand, since the NIR photons can pass through a somewhat inner part of the disk, the NIR polarization can still offer information on the dust and geometry of the disk. We expect that a polarization disk analysis in high-resolution data, such as the one we present, offers opportunities to investigate the grain growth and dust se...

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Absorption features in the 3 micron spectra of protostars

Cited by 193 publications

References 1 publication

Ice absorption features in the 5-8μm region toward embedded protostars

Ice absorption features in the 5-8μm region toward embedded protostars

Abundant gas-phase H₂O in absorption toward massive protostars

Polarization disks in near-infrared high-resolution imaging

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Absorption features in the 3 micron spectra of protostars

Cited by 193 publications

References 1 publication

Ice absorption features in the 5-8μm region toward embedded protostars

Ice absorption features in the 5-8μm region toward embedded protostars

Abundant gas-phase H2O in absorption toward massive protostars

Polarization disks in near-infrared high-resolution imaging

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Abundant gas-phase H₂O in absorption toward massive protostars