Circumstellar Regions Research Articles

Atomic Alignment and Diagnostics of Magnetic Fields in Diffuse Media

We continue our studies of atomic alignment in diffuse media, in particularly, in interstellar and circumstellar media, with the goal of developing new diagnostics of magnetic fields in these environments. We understand atomic alignment as alignment of atoms or ions in their ground state. Such atoms are sensitive to weak magnetic fields. In particular, we provide predictions of the polarization that arises from astrophysically important aligned atoms (ions) with fine structure of the ground level, namely, OI and SII and Ti II. Unlike our earlier papers which dealt with weak fields only, a substantial part of our current paper is devoted to the studies of atomic alignment when magnetic fields get strong enough to affect the emission from the excited level, i.e. with the regime when the magnetic splitting is comparable to the line-width. This is a regime of Hanle effect modified by the atomic alignment. Using an example of emission and absorption lines of SII ion we demonstrate how polarimetric studies can probe magnetic fields in circumstellar regions and accretion disks. In addition, we show that atomic alignment induced by anisotropic radiation can induce substantial variations of magnetic dipole transitions within the ground state, thus affecting abundance studies based on this emission. Moreover, the radio emission is polarized, provides a new way to study magnetic fields, e.g. at the epoch of Universe reionization.

The inner magnetized regions of circumstellar accretion discs

In this lecture, I will briefly address several phenomena expected when magnetic fields are present in the innermost regions of circumstellar accretion discs: (i) the magneto-rotational instability and related “dead zones”; (ii) the formation of magnetically-driven jets and the observational constraints derived from Classical T Tauri stars; (iii) the magnetic star–disc interactions and their expected role in the stellar spin down. It should be noted that the magnetic fields invoked here are organized large scale magnetic fields, not turbulent small scale ones. I will therefore first argue why one can safely expect these fields to be present in circumstellar accretion discs. Objects devoid of such large scale fields would not be able to drive jets. A global picture is thus gradually emerging where the magnetic flux is an important control parameter of the star formation process as a whole. High angular resolution technics, by probing the innermost circumstellar disc regions should provide valuable constraints.

Submillimeter Array Imaging of the Maser Emission from the H30α Radio Recombination Line in MWC 349A

We used the Submillimeter Array to map the angular distribution of the H30α recombination line (231.9 GHz) in the circumstellar region of the peculiar star MWC 349A. The resolution was 1.2'', but because of high signal-to-noise ratio we measured the positions of all maser components to accuracies better than 0.01'', at a velocity resolution of 1 km s−1. The two strongest maser components (called high-velocity components) at velocities near –14 and 32 km s−1 are separated by 0.048'' ± 0.001'' (60 AU) along a position angle of 102° ± 1°. The distribution of maser emission at velocities between and beyond these two strongest components were also provided. The continuum emission lies at the center of the maser distribution to within 10 mas. The masers appear to trace a nearly edge-on rotating disk structure, reminiscent of the water masers in Keplerian rotation in the nuclear accretion disk of the galaxy NGC 4258. However, the maser components in MWC 349A do not follow a simple Keplerian kinematic prescription with v ∼ r−1/2, but have a larger power-law index. We explore the possibility that the high-velocity masers trace spiral density or shock waves. We also emphasize caution in the interpretation of relative centroid maser positions where the maser is not clearly resolved in position or velocity, and we present simulations that illustrate the range of applicability of the centroiding method.

Crystallization Experiments on Amorphous Silicates with Chondritic Composition: Quantitative Formulation of the Crystallization

In order to make clear crystallization process of silicates in circumstellar environments of oxygen-rich young stars, we have performed laboratory experiments on crystallization of a silicate material by use of a synthetic sample with the chondritic composition for the first time. The aim of this work is to analyze the crystallization process quantitatively using the amorphous material with the chondritic composition. The starting amorphous material was synthesized by the sol-gel method. The sample was heated at 660°-1200°C for 0.5-12 hr to investigate the temperature and time dependence of the crystallization. The run products were analyzed using infrared absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Olivine [(Mg, Fe)2SiO4] was mainly crystallized from the starting amorphous material. We performed infrared spectral fittings of the heated samples using individual spectra of olivine and amorphous silicate, and estimated the degree of crystallization quantitatively. The time-dependent crystallization process could be formulated using the Johnson-Mehl-Avrami equation with the power of about 1.2, which is consistent with theoretical crystallization model of three-dimensional diffusion-controlled growth from a state that a number of nuclei is constant. The constant number of nuclei corresponds to the starting material, which contains crystallites of magnetite (Fe3O4) and ferrihydrite (5Fe2O3 9H2O) as nucleation sites of olivine crystals. From the quantitative analyses, we suggest that crystallization processes in circumstellar regions should depend on properties of the interstellar amorphous silicates such as existence of crystallites and/or FeO content.

The Mid‐Infrared Spectral Energy Distribution, Surface Brightness, and Color Profiles in Elliptical Galaxies

We describe photometry at mid-infrared passbands (1.2 - 24 microns) for a sample of 18 elliptical galaxies. All surface brightness distributions resemble de Vaucouleurs profiles, indicating that most of the emission arises from the photospheres or circumstellar regions of red giant stars. The spectral energy distribution peaks near 1.6 microns, but the half-light or effective radius has a pronounced minimum near the K band (2.15 microns). Apart from the 24 micron passband, all sample-averaged radial color profiles have measurable slopes within about twice the (K band) effective radius. Evidently this variation arises because of an increase in stellar metallicity toward the galactic cores. For example, the sampled-averaged color profile (K - 5.8 microns) has a positive slope although no obvious absorption feature is observed in spectra of elliptical galaxies near 5.8 microns. This, and the minimum in the effective radius, suggests that the K band may be anomalously luminous in metal-rich stars in galaxy cores. Unusual radial color profiles involving the 24 micron passband may suggest that some 24 micron emission comes from interstellar not circumstellar dust grains.

On the circumstellar environment of SS433

We present new 8200-8900 A high-resolution spectroscopic observations of the unusual accreting source SS433. The spectra are highly variable on a night-to-night basis, and are dominated by emission from the Paschen series and O iemission. Differences in line profiles between the two species suggest that they arise in kinematically distinct and highly variable circumstellar regions. Moreover, the strength of O iemission argues against identifying the mass donor as a Wolf-Rayet star since we might expect oxygen to be depleted by the CNO cycle in such a star. Weak N iabsorption lines are present, which, if arising in the photosphere of the mass donor would imply a spectral type of B5 or later. However, no evidence was found for orbital modulation in their radial velocity curves suggesting that they too arise in the accretion-driven outflow. Finally, by analogy to the massive close binary RY Scuti, we suggest that the recent detection of a mid-infrared excess attributed to warm dust may arise in a circumbinary disc, implying that SS433 hosts a rich, highly structured circumstellar environment driven by the high mass-transfer rate from the mass donor.

The inner gaseous accretion disk around a Herbig Be star revealed by near- and mid-infrared spectro-interferometry

AbstractHerbig Ae/Be stars are pre-main-sequence stars of intermediate mass, which are still accreting material from their environment, probably via a disk composed of gas and dust. Here we present a recent study of the geometry of the inner (AU-scale) circumstellar region around the Herbig Be star MWC 147 using long-baseline interferometry. By combining for the first time near- and mid-infrared spectro-interferometry on a Herbig star, our VLTI/AMBER and VLTI/MIDI data constrain not only the geometry of the brightness distribution, but also the radial temperature distribution in the disk. The emission from MWC 147 is clearly resolved and has a characteristic physical size of ∼1.3 AU and ∼9 AU at 2.2 μm and 11 μm respectively. This increase in apparent size towards longer wavelengths is much steeper than predicted by analytic disk models assuming power-law radial temperature distributions. For a detailed modeling of the interferometric data and the spectral energy distribution of MWC 147, we employ 2-D frequency-dependent radiation transfer simulations. This analysis shows that passive irradiated Keplerian dust disks can easily fit the SED, but predict much lower visibilities than observed, so these models can clearly be ruled out. Models of a Keplerian disk with emission from an optically thick inner gaseous accretion disk (inside the dust sublimation zone), however, yield a good fit of the SED and simultaneously reproduce the observed near- and mid-infrared visibilities. We conclude that the near-infrared continuum emission from MWC 147 is dominated by accretion luminosity emerging from an optically thick inner gaseous disk, while the mid-infrared emission also contains strong contributions from the passive irradiated dust disk.

The implications of close binary stars for star-disk interactions

AbstractThe presence of close (≲ 0.1 AU) stellar companions must greatly alter the circumstellar environment of classical T Tauri stars, including severe truncation if not elimination of circumstellar disks. It is thus remarkable how little impact the presence of a close companion has on our observable diagnostics for accretion and outflow. Emission line shapes, degrees of continuum veiling, and spectral energy distributions are all indistinguishable between single classical T Tauri stars and classical T Tauri close binaries. Some of the most classical T Tauri stars that laid the foundation for our single-star accretion-disk paradigm have turned out to have close companions. Periodicities in spectral signatures are suggestive of the presence of accretion flows from circumbinary disks to the circumstellar regions; the subsequent flow of material through the circumstellar region to the stellar surface in the presence of a stellar magnetosphere is unstudied. Observations of stellar rotation distributions in close binaries suggest that inner disk regions may act to regulate stellar angular momentum.

A snapshot of the inner dusty regions of a R CrB-type variable

Context. R Coronae Borealis (R CrB) variable stars are suspected to sporadically eject optically thick dust clouds causing, when one of them lies on the line-of-sight, a huge brightness decline in visible light. Direct detections with 8-m class adaptive optics of such clouds located at about 0.2–0.3 arcsec from the center (∼1000 stellar radii) were recently reported for RY Sgr, the brightest R CrB of the southern hemisphere. Aims. Mid-infrared interferometric observations of RY Sgr allowed us to explore the circumstellar regions much closer to the central star (∼20–40 mas) to look for the signature of any heterogeneities and to characterize them. Methods. Using the VLTI/MIDI instrument, five dispersed visibility curves in the N-band were recorded in May and June 2005 with different projected baselines oriented towards two roughly perpendicular directions. The large spatial frequencies’ visibility curves exhibit a sinusoidal shape, whereas, at shorter spatial frequencies’ visibility curves follow a Gaussian decrease. These observations are well interpreted with a geometrical model consisting of a central star surrounded by an extended circumstellar envelope in which one bright cloud is embedded. Results. Within this simple geometrical scheme, the inner 110 AU dusty environment of RY Sgr is dominated at the time of observations by a single dusty cloud, which at 10 µm represents ∼10% of the total flux of the whole system, slightly less that the star flux. The cloud is located at about 100 stellar radii (or ∼30 AU) from the center toward the East-North-East direction (or the symmetric direction with respect to center) within a circumstellar envelope whose FWHM is about 120 stellar radii. This first detection of a cloud so close to the central star supports the classical scenario of the R CrB brightness variations in the optical spectral domain and demonstrates the feasibility of a temporal monitoring of the dusty environment of this star on a monthly scale.

Polarization from Aligned Atoms as a Diagnostic of Circumstellar, Active Galactic Nuclei, and Interstellar Magnetic Fields. II. Atoms with Hyperfine Structure

We show that atomic alignment presents a reliable way to study the topology of astrophysical magnetic fields. The effect of atomic alignment arises from modulation of the relative population of the sublevels of the atomic ground state pumped by anisotropic radiation flux. As such aligned atoms precess in the external magnetic field, this affects the properties of the polarized radiation arising from both scattering and absorption by the atoms. As a result, the polarizations of emission and absorption lines depend on the three-dimensional (3D) geometry of the magnetic field as well as the direction and anisotropy of incident radiation. We consider a subset of astrophysically important atoms with hyperfine structure. For emission lines, we obtain the dependencies of the direction of linear polarization on the directions of the magnetic field and the incident pumping radiation. For the absorption lines we establish when the polarization is perpendicular and parallel to the magnetic field. For both emission and absorption lines we find the dependence on the degree of polarization on the 3D geometry of the magnetic field. We claim that atomic alignment provides a unique tool for studying magnetic fields in circumstellar regions, active galactic nuclei (AGNs), and the interplanetary and interstellar media. This tool allows one to study the 3D topology of magnetic fields and establish other important astrophysical parameters. We consider polarization arising from both atoms in the steady state and also those undergoing individual scattering of photons. We demonstrate the utility of atomic alignment for studies of astrophysical magnetic fields by considering a case of sodium alignment in a comet wake.

Tracing magnetic fields with aligned grains

Magnetic fields play a crucial role in various astrophysical processes, including star formation, accretion of matter, transport processes (e.g., transport of heat), and cosmic rays. One of the easiest ways to determine the magnetic field direction is via polarization of radiation resulting from extinction or/and emission by aligned dust grains. Reliability of interpretation of the polarization maps in terms of magnetic fields depends on how well we understand the grain-alignment theory. Explaining what makes grains aligned has been one of the big issues of the modern astronomy. Numerous exciting physical effects have been discovered in the course of research undertaken in this field. As both the theory and observations matured, it became clear that the grain-alignment phenomenon is inherent not only in diffuse interstellar medium or molecular clouds but also is a generic property of the dust in circumstellar regions, interplanetary space and cometary comae. Currently the grain-alignment theory is a predictive one, and its results nicely match observations. Among its predictions is a subtle phenomenon of radiative torques. This phenomenon, after having stayed in oblivion for many years after its discovery, is currently viewed as the most powerful means of alignment. In this article, I shall review the basic physical processes involved in grain alignment, and the currently known mechanisms of alignment. I shall also discuss possible niches for different alignment mechanisms. I shall dwell on the importance of the concept of grain helicity for understanding of many properties of grain alignment, and shall demonstrate that rather arbitrarily shaped grains exhibit helicity when they interact with gaseous and radiative flows.

Scattering of electromagnetic waves by charged spheres and some physical consequences

Effect of electromagnetic radiation scattering on homogeneous spherical dust particle which carries excess surface electric charge is investigated. Numerical calculations are presented for the cases of (i) charged spherical particles present in the interplanetary space of the Solar System, and (ii) charged water droplets and ice grains in the Earth's atmosphere. The results show that the surface charge may influence optical properties of very small particles with size parameter x less than 0.01 (astronomical materials like amorphous carbon and silicate are affected also at x ≈ 0.03 ). Slightly absorbing charged particles may attenuate the electromagnetic radiation more than 10 times efficiently than equivalent non-charged particles. The effect of temperature on efficiency factors for scattering Q sca , absorption Q abs , and radiation pressure Q pr is evaluated for astronomical amorphous carbon, as cosmic dust particles may undergo large temperature changes during their motion in the circumstellar regions. The ratios Q x charged / Q x neutral (for x = abs , ext , or pr) increase with decreasing grain temperature.

Simultaneous X-ray, radio, near-infrared, and optical monitoring of young stellar objects in theCoronetcluster

Context. Multi-wavelength (X-ray to radio) monitoring of Young Stellar Objects (YSOs) can provide important information about physical processes at the stellar surface, in the stellar corona, and/or in the inner circumstellar disk regions. While coronal processes should mainly cause variations in the X-ray and radio bands, accretion processes may be traced by time-correlated variability in the X-ray and optical/infrared bands. Several multi-wavelength studies have been successfully performed for field stars and ~$1{-}10$ Myr old T Tauri stars, but so far no such study succeeded in detecting simultaneous X-ray to radio variability in extremely young objects like class I and class 0 protostars. Aims. Here we present the first simultaneous X-ray, radio, near-infrared, and optical monitoring of YSOs, targeting the Coronet cluster in the Corona Australis star-forming region, which harbors at least one class 0 protostar, several class I objects, numerous T Tauri stars, and a few Herbig AeBe stars. Methods. In August 2005, we obtained five epochs of Chandra X-ray observations on nearly successive days accompanied by simultaneous radio observations at the NRAO Very Large Array during four epochs, as well as by simultaneous optical and near-infrared observations from ground-based telescopes in Chile and South Africa. Results. Seven objects are detected simultaneously in the X-ray, radio, and optical/infrared bands; they constitute our core sample. While most of these sources exhibit clear variability in the X-ray regime and several also display optical/infrared variability, none of them shows significant radio variability on the timescales probed. We also do not find any case of clearly time-correlated optical/infrared and X-ray variability. Remarkable intra-band variability is found for the class I protostar IRS 5 which shows much lower radio fluxes than in previous observations, and the Herbig Ae star R CrA, which displays enhanced X-ray emission during the last two epochs, but no time-correlated variations are seen for these objects in the other bands. The two components of S CrA vary nearly synchronously in the I band. Conclusions. The absence of time-correlated multi-wavelength variability suggests that there is no direct link between the X-ray and optical/infrared emission and supports the notion that accretion is not an important source for the X-ray emission of these YSOs. No significant radio variability was found on timescales of days.

Fe II emission lines in Be stars

Aims. The Fell emission lines formed in the circumstellar envelopes (CE) of classical Be stars are studied in order to determine whether they are optically thin or optically thick. We also aim at deriving both average Fell line excitation temperatures and the extent of their formation region in the CE. Methods. We simultaneously observed several series of Fell emission lines in the λλAA4230-7712 A wavelength interval and the first members of the hydrogen Balmer series of 18 southern classical Be stars. The optical depth regime that controls the formation of the observed Fell lines and the physical parameters of their CE formation region were studied using the empirical self-aborption-curve (SAC) method. Results. Our calculations give an average value of To = 2.4 ± 0.9 for the optical depth of the studied Fell lines, which implies that these lines are optically thick in the CE of Be stars. Qualitative indications that Fe II emission lines should be formed in circumstellar regions close to the central star are inferred from the correlations between Fe II emission line widths and V sin The application of the SAC method to Fe II emission lines confirms this result, which gives R e = 2.0R * ± 0.8 for the extension of the line-forming region. The proximity of the line-forming region to the central star is also supported by the behavior of the source function of Fell lines, which rapidly decreases with radii. This prevents the lines from being formed over extended regions and/or far from the star. Finally, the correlations of the central depression in the Balmer emission lines with V sin are consistent with the flattened geometrical shapes or CEs.

Interstellar chemistry

In the past half century, radioastronomy has changed our perception and understanding of the universe. In this issue of PNAS, the molecular chemistry directly observed within the galaxy is discussed. For the most part, the description of the molecular transformations requires specific kinetic schemes rather than chemical thermodynamics. Ionization of the very abundant molecular hydrogen and atomic helium followed by their secondary reactions is discussed. The rich variety of organic species observed is a challenge for complete understanding. The role and nature of reactions involving grain surfaces as well as new spectroscopic observations of interstellar and circumstellar regions are topics presented in this special feature.

Bringing VY Canis Majoris Down to Size: An Improved Determination of Its Effective Temperature

The star VY CMa is a late-type M supergiant with many peculiarities, mostly related to the intense circumstellar environment due to the star's high mass-loss rate. Claims have been made that would imply that this star is considerably more luminous (L ~ 5 × 105 L☉) and larger (R ~ 2800 R☉) than other Galactic red supergiants (RSGs). Indeed, such a location in the H-R diagram would be well within the Hayashi forbidden zone, where stars cannot be in hydrostatic equilibrium. These extraordinary properties, however, rest on an assumed effective temperature of 2800-3000 K, far cooler than recent work has shown RSGs to be. To obtain a better estimate, we fit newly obtained spectrophotometry in the optical and NIR with the same MARCS models used for our recent determination of the physical properties of other RSGs; we also use V - K and V - J from the literature to derive an effective temperature. We find that the star likely has a temperature of 3650 K, a luminosity L ~ 6 × 104 L☉, and a radius of ~600 R☉. These values are consistent with VY CMa being an ordinary, evolved 15 M☉ RSG and agree well with the Geneva evolutionary tracks. We find that the circumstellar dust region has a temperature of 760 K, and an effective radius of ~130 AU, if spherical geometry is assumed for the latter. What causes this star to have such a high mass loss and large variations in brightness (but with little change in color) remains a mystery at present, although we speculate that perhaps this star and NML Cyg are simply normal RSGs caught during an unusually unstable time.

R Coronae Borealis at the 2003 light minimum

A set of five high-resolution optical spectra of R CrB obtained in 2003 March is discussed. At the time of the first spectrum (March 8) the star was at V = 12.6, a decline of more than six magnitudes. By March 31, the date of the last observation, the star at V = 9.3 was on the recovery to maximum light (V = 6). The 2003 spectra are compared with the extensive collection of spectra from the 1995-1996 minimum presented previously. Spectroscopic features common to the two minima include the familiar ones also seen in spectra of other RCBs in decline: sharp emission lines of neutral and singly-ionized atoms, broad emission lines including He i, [N ii] 6583 u Na D, and Ca ii H & K lines, and blueshifted aborption lines of Na D, and K i resonance lines. Prominent differences between the 2003 and 1995-1996 spectra are seen. The broad Na D and Ca H & K lines in 2003 and 1995-1996 are centred approximately on the mean stellar velocity. The 2003 profiles are fit by a single Gaussian but in 1995-1996 two Gaussians separated by about 200 km s 1 were required. However, the He i broad emission lines are fit by a single Gaussian at all times; the emitting He and Na-Ca atoms are probably not colocated. The C2 Phillips 2-0 lines are detected as sharp absorption lines and the C2 Swan band lines as sharp emission lines in 2003 but in 1995-1996 the Swan band emission lines were broad and the Phillips lines were undetected. The 2003 spectra show C i sharp emission lines at minimum light with a velocity changing in five days by about 20 km s 1 when the velocity of ‘metal’ sharp lines is unchanged; the C i emission may arise from shock-heated gas. Reexamination of spectra obtained at maximum light in 1995 shows extended blue wings to strong lines with the extension dependent on a line’s lower excitation potential; this is the signature of a stellar wind, also revealed by published observations of the He i 10830 u line at maximum light. Changes in the cores of the resonance lines of Al i and Na D (variable blue shifts) and the Ca ii IR lines (variable blue and red shifts) suggest complex flow patterns near the photosphere. The spectroscopic differences at the two mimima show the importance of continued scrutiny of the declines of R CrB (and other RCBs). Thorough understanding of the outer atmosphere and circumstellar regions of R CrB will require such continued scrutiny.

Constraining Disk Parameters of Be Stars using Narrowband Hα Interferometry with the Navy Prototype Optical Interferometer

Abstract : Interferometric observations of two well-known Be stars, gamma Cas and phi Per, were collected and analyzed to determine the spatial characteristics of their circumstellar regions. The observations were obtained using the Navy Prototype Optical Interferometer equipped with custom-made narrowband filters. The filters isolate the H(alpha) emission line from the nearby continuum radiation, which results in an increased contrast between the interferometric signature due to the H(alpha)-emitting circumstellar region and the central star. Because the narrowband filters do not significantly attenuate the continuum radiation at wavelengths 50 nm or more away from the line, the interferometric signal in the H(alpha) channel is calibrated with respect to the continuum channels. The observations used in this study represent the highest spatial resolution measurements of the H -emitting regions of Be stars obtained to date. These observations allow us to demonstrate for the first time that the intensity distribution in the circumstellar region of a Be star cannot be represented by uniform disk or ringlike structures, whereas a Gaussian intensity distribution appears to be fully consistent with our observations.

Chemical self-enrichment of HII regions by the Wolf-Rayet phase of an 85 M$_{\odot}$ star

It is clear from stellar evolution and from observations of WR stars that massive stars are releasing metal-enriched gas through their stellar winds in the Wolf-Rayet phase. Although Hii region spectra serve as diagnostics to determine the present-day chemical composition of the interstellar medium, it is far from being understood to what extent the Hii gas is already contaminated by chemically processed stellar wind. Therefore, we analyzed our models of radiative and wind bubbles of an isolated $85~{M}_{\odot}$ star with solar metallicity (Kroger et al. 2006, A&A, in preparation) with respect to the chemical enrichment of the circumstellar Hii region. Plausibly, the hot stellar wind bubble (SWB) is enriched with $^{14}\mbox{N}$ during the WN phase and even much higher with $^{12}\mbox{C}$ and $^{16}\mbox{O}$ during the WC phase of the star. During the short period that the $85~{M}_{\odot}$ star spends in the WC stage enriched SWB material mixes with warm Hii gas of solar abundances and thus enhances the metallicity in the Hii region. However, at the end of the stellar lifetime the mass ratios of the traced elements N and O in the warm ionized gas are insignificantly higher than solar, whereas an enrichment of $22\%$ above solar is found for C. Important issues from the presented study comprise a steeper radial gradient of C than O and a decreasing effect of self-enrichment for metal-poor galaxies.

Temperature effects on the mid-and far-infrared spectra of olivine particles

The absorption spectra of the olivine particles of different Mg/Fe content were measured in the infrared spectral region between 5 and 100 μm, while the particles were continuously cooled down to 10 K. Measurements independently carried out on different samples of synthetic forsterite, natural olivine, and synthetic fayalite at laboratories in Kyoto and Jena. The positions of the olivine infrared bands were measured for these samples in detail at up to seven individual temperatures in the interval between 300 K and 10 K. According to the different widths of the olivine bands in different wavelength regions, spectral resolutions of 2, 1, 0.5, 0.25, 0.2, and 0.125 were used in order to measure the band positions with high accuracy. While in general the band positions and their temperature-dependent shift agree very well for the Kyoto and Jena samples, the positions of some very strong bands differ, which is probably a consequence of different particle shapes. For the two long-wavelength forsterite bands at 49 and 69 μm, the sharpening and strengthening of the bands were quantified. The widths of these bands differ for the Kyoto and Jena samples, which is discussed in terms of different crystal quality and particle coagulation of the samples. Our new data can be used to derive dust temperatures from the observed peak positions for crystalline silicate dust in circumstellar regions.