Infrared Emission Lines Research Articles

L-Band Spectra of 13 Outbursting Be Stars

ABSTRACTWe present new L-band spectra of 13 outbursting Be stars obtained with ISAAC at the ESO Paranal Observatory. These stars can be classified in three groups depending on the presence or absence of emission lines and the strength of Brα and Pfγ emission lines relative to those of Humphreys lines from transitions 6–14 to the end of the series. These groups are representative of circumstellar envelopes with different optical depths. For the group showing Brα and Pfγ lines stronger than Humphreys lines, the Humphreys decrement roughly follows the Menzel case-B for optically thin conditions. For the group showing comparable Brα, Pfγ, and Humphreys emission-line strengths, the Humphreys decrements moves from an optically thin to an optically thick regime at a transition wavelength that is characteristic for each star but typically is located around 3.65–3.75 μm (transitions 6–19 and 6–17). Higher-order Humphreys lines probe optically thin inner regions even in the optically thicker envelopes. We find evidence of larger broadening in the infrared emission lines compared with optical lines, probably reflecting larger vertical velocity fields near the star. The existence of the aforementioned groups is in principle consistent with the description recently proposed by de Wit et al. for Be star outbursts in terms of the ejection of an optically thick disk that expands and becomes optically thin before dissipation into the interstellar medium. Time-resolved L-band spectroscopy sampling the outburst cycle promises to be an unique tool for testing Be star disk evolution.

Infrared spectroscopic diagnostics for Active Galactic Nuclei

Infrared spectroscopy in the mid- and far-infrared provides powerful diagnostics for studying the emission regions in active galaxies. The large variety of ionic fine structure lines can probe gas conditions in a variety of physical conditions, from highly ionized gas excited by photons originated by black hole accretion to gas photoionized by young stellar systems. The critical density and the ionization potential of these transitions allow to fully cover the density-ionization parameter space. Some examples of line ratios diagrams using both mid-infrared and far-infrared ionic fine structure lines are presented. The upcoming space observatory Herschel will be able to observe the far-infrared spectra of large samples of local active galaxies. Based on the observed near-to-far infrared emission line spectrum of the template galaxy NGC 1068, are presented the predictions for the line fluxes expected for galaxies at high redshift. To observe spectroscopically large samples of distant galaxies, we will have to wait for the future space missions, like SPICA and, ultimately, FIRI.

Synthesis and spectroscopic properties of neodymium doped lead chloride

The crystal growth and infrared spectroscopic properties of Nd doped lead chloride (Nd:PbCl2) are reported. Lead halide based materials have recently emerged as laser hosts with low maximum phonon energies. In this work, Nd:PbCl2 crystals were grown by a self-seeded Bridgman technique. Following optical pumping at 750 and 808nm, Nd:PbCl2 exhibited several infrared (IR) emission lines between 800 and 1600nm as well as a broad mid-IR band centered at ∼5.19μm. It was found that for Nd3+ concentrations larger than ∼1×1019cm−3, the mid-IR emission is predominantly due to the transition I11∕24→I9∕24. From a Judd-Ofelt analysis, the radiative quantum efficiency of the 5.19μm emission was determined to be ∼27%. The multiphonon decay rates of several closely spaced Nd3+ transitions were modeled using the well known energy-gap law and the host dependent parameters B and β were determined to be 9.5×109s−1 and 1.26×10−2cm, respectively. The obtained energy-gap law parameters were subsequently used to describe the temperature dependence of the 5.19μm mid-IR emission lifetime for a range from 77to450K.

Toward Mapping the Detailed Density Structure of Classical Be Circumstellar Disks

The first results from a near-contemporaneous optical and infrared spectroscopic observing program designed to probe the detailed density structure of classical Be circumstellar disks are presented. We report the discovery of asymmetrical infrared emission lines of He I, O I, Fe II, and the Brackett, Paschen, and Pfund series lines of H I which exhibit an opposite V/R orientation (V $>$ R) to that observed for the optical Balmer H$\alpha$ line (V $<$ R) in the classical Be star $\zeta$ Tau. We interpret these data as evidence that the density wave which characterizes $\zeta$ Tau's disk has a significantly different average azimuthal morphology in the inner disk region as compared to the outer disk region. A follow-up multi-wavelength observational campaign to trace the temporal evolution of these line profile morphologies, along with detailed theoretical modeling, is suggested to test this hypothesis.

Infrared single mode chalcogenide glass fiber for space

An important measuring technique under study for the DARWIN planet finding mission, is nulling interferometry, enabling the detection of the weak infrared emission lines of an orbiting planet. This technique requires a perfect wavefront of the light beams to be combined in the interferometer. By using a single mode waveguide before detection, wavefront errors are filtered and a virtually perfect plane wavefront is obtained. In this paper the results on the development and the optical characterisation of suitable infrared transmitting chalcogenide glasses and mid-IR guiding optical fibers are reported. Two different perform techniques for manufacturing core-cladding chalcogenide fibers are described. Two types of step index fibers, prepared with Te(2)As(3)Se(5) chalcogenide glasses, offer single mode guidance at 10.6 mum.

Molecular line emission in HH54: a coherent view from near to far infrared

Aims. We present a detailed study of the infrared line emission (1–200 µm) in the Herbig-Haro object HH54. Our database comprises: high- (R ∼ 9000) and low- (R ∼ 600) resolution spectroscopic data in the near-infrared band (1–2.5 µm); mid-infrared spectrophotometric images (5–12 µm); and, far-IR (45–200 µm, R ∼ 200) spectra acquired with the ISO satellite. As a result, we provide the detection of and the absolute fluxes for more than 60 molecular features (mainly from H2 in the near- and mid-infrared and from H2O, CO and OH in the far-infrared) and 23 ionic lines. Methods. The H2 lines, coming from levels from v = 0t ov = 4 have been interpreted in the context of a state-of-the-art shock code, whose output parameters are adopted as input to a Large Velocity Gradient computation in order to interpret the FIR emission of CO, H2O and OH. Results. The H2 emission can be interpreted as originating in either steady-state J-type shocks or in quasi-steady J-type shocks with magnetic precursor. However, our multi-species analysis shows that only a model of a J-type shock with magnetic precursor (vshock = 18 km s −1 , nH = 10 4 cm −3 , B = 100 µG, age = 400 yr) can account for both the observed H2 emission and the CO and H2O lines. Such a model predicts a H2O abundance of ∼7 × 10 −5 , in agreement with estimations from other shock models of outflows associated with low mass protostars. We can exclude the possibility that the observed atomic lines arise in the same shock as the molecular lines, and give arguments in favour of the presence of a further high-velocity, fully dissociative shock component in the region. Finally, in view of the forthcoming spectroscopic facilities on board of the Herschel satellite, we provide predictions for H2O lines considered to be the most suitable for diagnostic purposes.

Synthesis and 1.5μm emission properties of Nd3+ activated lead bromide and lead iodide crystals

We report on the purification, synthesis, and infrared emission properties of Nd doped PbBr2 and PbI2 crystals. Under optical excitation at ∼0.8μm, characteristic Nd3+ emission lines arising from the F3∕24 level were observed. In addition, near infrared emission lines were also observed at ∼0.97, ∼1.2, and ∼1.5μm arising from the F5∕24,H9∕22 states of Nd3+. The emission efficiency at 1.5μm was determined to be 74% for Nd:PbBr2 and 64% for Nd:PbI2 with peak emission cross sections in the range of (0.2–0.5)×10−20cm2. These cross sections are comparable to those of Er3+ doped materials employed in optical communications and eye-safe lasers.

Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in HD 105

We report infrared spectroscopic observations of HD 105, a nearby (~40 pc) and relatively young (~30 Myr) G0 star with excess infrared continuum emission, which has been modeled as arising from an optically thin circumstellar dust disk with an inner hole of size 13 AU. We have used the high spectral resolution mode of the Infrared Spectrometer (IRS) on the Spitzer Space Telescope to search for gas emission lines from the disk. The observations reported here provide upper limits to the fluxes of H2 S(0) 28 μm, H2 S(1) 17 μm, H2 S(2) 12 μm, [Fe II] 26 μm, [Si II] 35 μm, and [S I] 25 μm infrared emission lines. The H2 line upper limits place direct constraints on the mass of warm molecular gas in the disk: M(H2) < 4.6, 3.8 × 10-2, and 3.0 × 10-3 MJ at T = 50, 100, and 200 K, respectively. We also compare the line flux upper limits to predictions from detailed thermal/chemical models of various gas distributions in the disk. These comparisons indicate that if the gas distribution has an inner hole with radius ri,gas, the surface density at that inner radius is limited to values ranging from 3 g cm-2 at ri,gas = 0.5 AU to 0.1 g cm-2 at ri,gas = 5-20 AU. These values are considerably below the value for a minimum mass solar nebula, and suggest that less than 1 Jupiter mass (MJ) of gas (at any temperature) exists in the 1-40 AU planet-forming region. Therefore, it is unlikely that there is sufficient gas for gas giant planet formation to occur in HD 105 at this time.

Infrared Emission Lines of [Fe ii ] as Diagnostics of Shocked Gas in Stellar Jets

We predict fluxes for the brightest lines of [Fe II] at wavelengths longer than 8000 A for several radiative shocks whose parameters resemble those typically present in stellar jets. The models show that the brightest lines are those at 1.257, 1.643, 5.340, 17.94, and 25.99 μm. Depending on the model, these lines typically have comparable fluxes and are usually brighter than the [O I] 63.3 μm and [Si II] 34.8 μm lines. We call attention to the 5.34 μm line of Fe II, which cannot be seen from the ground but should be easily observable with the Spitzer satellite and SOFIA for many sources. This line should be an excellent probe of outflows from the youngest stars; at mid-IR wavelengths, it penetrates through most dusty regions of star formation, yet has a short enough wavelength to retain good spatial resolution in diffraction-limited images obtainable from space.

ISO spectroscopy of star formation and active nuclei in the luminous infrared galaxy NGC 6240

We present Infrared Space Observatory mid- and far-infrared spectroscopy of the merging galaxy NGC 6240, an object presenting many aspects of importance for the role of star formation and AGN activity in [ultra]luminous infrared galaxies. The mid-infrared spectrum shows starburst indicators in the form of low excitation fine-structure line emission and aromatic `PAH' features. A strong high excitation [OIV] line is observed which most likely originates in the Narrow Line Region of an optically obscured AGN. NGC 6240 shows extremely powerful emission in the pure rotational lines of molecular hydrogen. We argue that this emission is mainly due to shocks in its turbulent central gas component and its starburst superwind. The total shock cooling in infrared emission lines accounts for ~0.6% of the bolometric luminosity, mainly through rotational H_2 emission and the [OI] 63micron line. We analyse several ways of estimating the luminosities of the starburst and the AGN in NGC 6240 and suggest that the contributions to its bolometric luminosity are most likely in the range 50-75% starburst and 25-50% AGN.

Clustered Star Formation in W75 N

We present 2 to 7 resolution 3 mm continuum and CO(J=1-0) line emission and near infrared Ks, H2, and [FeII] images toward the massive star forming region W75 N. The CO emission uncovers a complex morphology of multiple, overlapping outflows. A total flow mass of greater than 255 Msun extends 3 pc from end-to-end and is being driven by at least four late to early-B protostars. More than 10% of the molecular cloud has been accelerated to high velocities by the molecular flows (> 5.2 km/s relative to v{LSR}) and the mechanical energy in the outflowing gas is roughly half the gravitational binding energy of the cloud. The W75 N cluster members represent a range of evolutionary stages, from stars with no apparent circumstellar material to deeply embedded protostars that are actively powering massive outflows. Nine cores of millimeter-wavelength emission highlight the locations of embedded protostars in W75 N. The total mass of gas & dust associated with the millimeter cores ranges from 340 Msun to 11 Msun. The infrared reflection nebula and shocked H2 emission have multiple peaks and extensions which, again, suggests the presence of several outflows. Diffuse H2 emission extends about 0.6 parsecs beyond the outer boundaries of the CO emission while the [FeII] emission is only detected close to the protostars. The infrared line emission morphology suggests that only slow, non-dissociative J-type shocks exist throughout the pc-scale outflows. Fast, dissociative shocks, common in jet-driven low-mass outflows, are absent in W75 N. Thus, the energetics of the outflows from the late to early B protostars in W75 N differ from their low-mass counterparts -- they do not appear to be simply scaled-up versions of low-mass outflows.

The instability of fast shocks in molecular clouds

We report on the discovery that moderately fast shocks in dense molecular clouds with low transverse magnetic fields are likely to be unstable. The instability is triggered by the promoted cooling that results from the formation of carbon monoxide and water molecules in an extended warm shock section. Numerical methods are employed to demonstrate that, in the absence of magnetic fields, the instability regime is restricted to densities above n0= 104 cm−3, velocities between 30–70 km s−1, and O or C abundances above ∼10−4, so that cooling from reforming molecules dominates in the warm gas without being suppressed by ultraviolet dissociation. The result is either a quasi-periodic or chaotic collapse and re-establishment of the warm shock layer on a typical time-scale of 106 cm−3/n0 yr with variations on shorter time-scales and changes in period being possible. Infrared emission lines from the unstable region, including the H2 lines, exhibit orders of magnitude variability. Atomic lines such as Hα display constant fluxes but undergo rapid radial velocity variations.

Spectroscopic Studies of the Solar Corona – V. Physical Properties of Coronal Structures

Spectra around the 6374 A [Fe x] and 7892 A [Fe xi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200′ ′×500′ ′ of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4′ ′×4′ ′) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 A emission line increases with height above the limb with an average value of 1.02 mA arc sec−1. The FWHM of the 7892 A line also increases with height but at a smaller average value of 0.55 mA arc sec−1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures.

H2infrared line emission across the bright side of theρOphiuchi main cloud

We present imaging and spectroscopic observations of dust and gas (H2) emission, obtained with ISO, from the western edge of the ρ Ophiuchi molecular cloud illuminated by the B2 star HD147889 (χ ∼ 400). This photodissociation region (PDR) is one of the nearest PDRs to the Sun (d = 135 ± 15 pc from the stellar parallax) and the layer of UV light penetration and of H2 emission is spatially resolved. It is therefore an ideal target to test the prediction of models on the integrated fluxes but also on the spatial distribution. The emission from dust heated by the external UV radiation, from collisionally excited and fluorescent H2 are observed to coincide spatially. The spectroscopic data, obtained with ISO-SWS, allows us to estimate the gas temperature to be 300-345 K in the H2 emitting layer, in which the ortho-to-para H2 ratio is about 1 or significantly smaller than the equilibrium ratio (∼3 at that temperature). We interpret this data with an equilibrium PDR model. In this low excitation PDR, the gas heat budget is dominated by the contribution of the photoelectric heating from very small grains and polycyclic aromatic hydrocarbons (PAHs). With the standard PAH abundance ((C/H)PAH � 5 × 10 −5 ), we find that the H2 formation rate Rf must be high in warm gas (∼6 times the rate derived by Jura, 1975), in order to account for the observed H2 emission. This result and the spatial coincidence between the PAHs and H2 emission suggest that H2 forms efficiently by chemisorption on the PAHs surface. If the latter interpretation is correct, the enhancement in Rf may also result from an increased PAH abundance: assuming that Rf scales with the PAH abundance, the observed H2 excitation is well explained with Rf � 1 × 10 −16 cm 3 s −1 at Tgas = 330 K (∼3 times the rate derived by Jura 1975) and (C/H)PAH � 7.5 × 10 −5 .

Temporal Behavior of Stratospheric Ammonia Abundance and Temperature Following the SL9 Impacts

Infrared emission lines of stratospheric ammonia (NH 3) were observed following the collisions of the fragments of Comet Shoemaker–Levy 9 with Jupiter in July of 1994 at the impact sites of fragments G and K. Infrared heterodyne spectra near 10.7 μm were obtained by A. Betz et al. (in Abstracts for Special Sessions on Comet Shoemaker-Levy 9, The 26th Meeting of the Division for Planetary Sciences, Washington DC, 31 Oct.–4 Nov. 1994, p. 25) using one of the Infrared Spatial Interferometer telescope systems on Mount Wilson. Lineshapes of up to three different NH 3 emission lines were measured at a resolving power of ∼10 7 at multiple times following the impacts. We present here our radiative transfer analysis of the fully resolved spectral lineshapes of the multiple rovibrational lines. This analysis provides information on temperature structure and NH 3 abundance distributions and their temporal changes up to 18 days after impact. These results are compared to photochemical models to determine the role of photochemistry and other mechanisms in the destruction and dilution of NH 3 in the jovian stratosphere after the SL9 impacts. One day following the G impact, the inferred temperature above 0.001 mbar altitude is 283±13 K, consistent with a recent plume splashback model. Cooling of the upper stratosphere to 204 K by the fourth day and to quiescence after a week is consistent with a simple gray atmosphere radiative flux calculation and mixing with cold jovian air. During the first 4 days after impact, NH 3 was present primarily at altitudes above 1 mbar with a column density of (7.7±1.6)×10 17 cm −2 after 1 day and (3.7±0.8)×10 17 cm −2 after 4 days. (Errors represent precision.) We obtained >2.5 times more NH 3 than can be supplied by nitrogen from a large cometary fragment, suggesting a primarily jovian source for the NH 3. By 18 days postimpact, a return to quiescent upper stratospheric temperature is retrieved for the G region, with an NH 3 column density of 7.3×10 17 cm −2 or more in the lower stratosphere, possibly supplied by NH 3 upwelling across an impact-heated and turbulent tropopause, which may have been masked by initial dust and haze. Above the 1-mbar level, the maximum retrieved column density decreased to 6.5×10 16 cm −2. Comparison to photochemical models indicates that photolysis alone is not sufficient to account for the loss of NH 3 above 1 mbar by that time, even when chemical reformation of NH 3 is ignored. We speculate that the dispersion of plume material at high altitudes (above 1 mbar) is responsible for the change in the spectra observed a few days postimpact. Data on the K impact region provide qualitatively consistent results.

Deficiency of molecular hydrogen in the disk of beta Pictoris.

Molecular hydrogen (H2) is by far the most abundant material from which stars, protoplanetary disks and giant planets form, but it is difficult to detect directly. Infrared emission lines from H2 have recently been reported towards beta Pictoris, a star harbouring a young planetary system. This star is surrounded by a dusty 'debris disk' that is continuously replenished either by collisions between asteroidal objects or by evaporation of ices on Chiron-like objects. A gaseous disk has also been inferred from absorption lines in the stellar spectrum. Here we present the far-ultraviolet spectrum of beta Pictoris, in which H2 absorption lines are not seen. This allows us to set a very low upper limit on the column density of H2: N(H2) </= 1018 cm-2. This non-detection is puzzling when compared to the quantity of H2 inferred from the infrared observations, but it does show that H2 is not in the disk on the direct line of sight. Carbon monoxide (CO) has been seen in absorption against the star, yielding a ratio of CO/H2 > 6 x 10-4. As CO would be destroyed under ambient conditions in about 200 years (refs 9, 11), our result demonstrates that the CO in the disk arises from evaporation of planetesimals.

Infrared Line Emission in the Interacting Region of Arp 244 (the Antennae): Colliding Molecular Cloud Complexes?

We report velocity-resolved spectroscopy of infrared hydrogen recombination lines in the interacting region of the Antennae galaxies (NGC 4038/4039). It generally has been assumed that the active star formation found there is due to the interaction of the disks of the two galaxies and indeed two molecular cloud complexes, separated in velocity by $\sim$100 km s$^{-1}$, have been observed in the southern part of this region. Our measurements imply that the two cloud complexes are moving away from each other. This result poses interesting questions about the physical mechanisms leading to starbursts in Arp 244 and other interacting galaxies.

Near-infrared line imaging of the starburst galaxies NGC 520, NGC 1614 and NGC 7714

We present high spatial resolution (0: 00 6) near{infrared broad{band JHK images and Br 2.1661 m and H2 1{0 S(1) 2.122 m emission line images of the nuclear regions in the interacting starburst galaxies NGC 520, NGC 1614 and NGC 7714. The near{infrared emission line and radio morphologies are in general agreement, although there are dierences in details. In NGC 1614, we detect a nuclear double structure in Br, in agreement with the radio double structure. We derive average extinctions of AK =0 .41 andAK =0 .18 toward the nuclear regions of NGC 1614 and NGC 7714, respectively. For NGC 520, the extinction is much higher, AK =1 :2 1:6. The observed H2/Br ratios indicate that the main excitation mechanism of the molecular gas is fluorescence by intense UV radiation from clusters of hot young stars, while shock excitation can be ruled out. The starburst regions in all galaxies exhibit small Br equivalent widths. Assuming a constant star formation model, even with a lowered upper mass cuto of Mu =3 0M, results in rather old ages (10 40 Myr), in disagreement with the clumpy near{infrared morphologies. We prefer a model of an instantaneous burst of star formation with Mu = 100 M, occurring6{7 Myr ago, in agreement with previous determinations and with the detection of W{R features in NGC 1614 and NGC 7714. Finally, we note a possible systematic dierence in the amount of hot molecular gas between starburst and Seyfert galaxies.

Investigating the structure of the accretion disc in WZ Sge from multiwaveband time-resolved spectroscopic observations — I

We present the first of two papers describing an in-depth study of multiwaveband phase-resolved spectroscopy of the unusual dwarf nova WZ Sge. In this paper we present an extensive set of Doppler maps of WZ Sge covering optical and infrared emission lines, and describe a new technique for studying the accretion discs of cataclysmic variables using ratioed Doppler maps. Applying the ratioed Doppler map technique to our WZ Sge data shows that the radial temperature profile of the disc is unlike that predicted for a steady state α disc. Time-averaged spectra of the accretion disc line flux (with the bright spot contribution removed) show evidence in the shapes of the line profiles for the presence of shear broadening in a quiescent non-turbulent accretion disc. From the positions of the bright spots in the Doppler maps of different lines, we conclude that the bright spot region is elongated along the ballistic stream, and that the density of the outer disc is low. The velocity of the outer edge of the accretion disc measured from the Hα line is found to be 723±23 km s−1. Assuming that the accretion disc reaches to the 3:1 tidal resonance radius, we derive a value for the primary star mass of 0.82 M⊙. We discuss the implications of our results on the present theories of WZ Sge type dwarf nova outbursts.

Chromium centers in stoichiometric LiNbO 3

The nature of Cr 3+ center in LiNbO 3 has been the subject of intense discussions in recent years. Partly, contradictory assignments of the centers resulted from intrinsic defects in the so-called congruent samples. More recently, stoichiometric samples, produced via the VTE process, have become available and show a largely reduced number of Cr sites. In this paper we present new spectroscopic data on a stoichiometric LiNbO 3 : Cr 3+ sample produced using the HTTSSG process. This sample shows an even further reduced number of lines in the so-called R-line region. In addition, the study of this sample sheds new light on the origin of near infrared emission lines first discovered in LiNbO 3 : Cr : Mg, which might be due to Cr 3+–Nb 4+ pairs. All emission lines show an unprecedented small line width, which allows high-resolution studies on this fascinating system.