Integral-field spectroscopy of molecular hydrogen in the optical wavelength region and complementary long-slit near-infrared spectroscopy are presented towards HH91A.The detection of some 200 H_2 lines arising from ro-vibrational levels up to v'=8 ranging between 7700A and 2.3 microns is reported. The emission arises from thermally excited gas where the bulk of the material is at 2750 K and where 1% is at 6000 K. The total column density of shocked gas is N(H_2) = 10^{18} cm^{-2}. Non-thermal excitation scenarios such as UV-fluorescence do not contribute to the excitation of H_2 towards HH91A. The emission is explained in terms of a slow non-dissociative J-shock which propagates into a low-density medium which has been swept-up by previous episodes of outflows which have occurred in the evolved HH90/91 complex.
We have analysed the infrared hydrogen recombination lines of a sample of well studied hot massive stars observed with the Infrared Space Observatory. Our sample contains stars from several classes of objects, whose circumstellar environment is believed to be dominated by an ionized stellar wind (the Luminous Blue Variables) or by a dense disk-like geometry (Be stars and B[e] stars). We show that hydrogen infrared recombination lines can be used as a diagnostic tool to constrain the geometry of the ionized circumstellar material. The line strengths are sensitive to the density of the emitting …
We combine data from our recent FUSE survey of interstellar molecular hydrogen absorption toward 50 high-latitude AGN with COBE-corrected IRAS 100 micron emission maps to study the correlation of infrared cirrus with H2. A plot of the H2 column density vs. IR cirrus intensity shows the same transition in molecular fraction, f_H2, as seen with total hydrogen column density, N_H. This transition is usually attributed to H2 self-shielding, and it suggests that many diffuse cirrus clouds contain H2 in significant fractions, f_H2 = 1-30%. These clouds cover approximately 50% of the northern sky at …
Mass accretion rate determinations are fundamental for an understanding of the evolution of pre-main sequence star circumstellar disks. Magnetospheric accretion models are used to derive values of the mass accretion rates in objects of very different properties, from brown dwarfs to intermediate-mass stars; we test the validity of these models in the brown dwarf regime, where the stellar mass and luminosity, as well as the mass accretion rate, are much lower than in T Tauri stars. We have measured simultaneously two infrared hydrogen lines, Pab and Brg, in a sample of 16 objects in the star-fo…
We present near-infrared spectroscopy of fluorescent molecular hydrogen (H_2) emission from NGC 1333, NGC 2023, NGC 2068, and NGC 7023 and derive the physical properties of the molecular material in these reflection nebulae. Our observations of NGC 2023 and NGC 7023 and the physical parameters we derive for these nebulae are in good agreement with previous studies. Both NGC 1333 and NGC 2068 have no previously-published analysis of near-infrared spectra. Our study reveals that the rotational-vibrational states of molecular hydrogen in NGC 1333 are populated quite differently from NGC 2023 and …
Context: Molecular hydrogen (H2) is the most abundant molecule in the circumstellar (CS) environments of young stars, and is a key element in giant planet formation. The measurement of the H2 content provides the most direct probe of the total amount of CS gas, especially in the inner warm planet-forming regions of the disks. Aims: Most Herbig Be stars (HBes) are distant from the Sun and their nature and evolution are still debated. We therefore conducted mid-infrared observations of H2 as a tracer of warm gas around HBes known to have gas-rich CS environments. Methods: We report a search for …
A possible formation mechanism of hydrogen molecules on a galactic scale is examined. We are interested especially in the role of hydrogen molecules for formation and evolution of primordial galaxies. Then, formation process of hydrogen molecules in a very low-metallicity galaxy (I Zw 18; the most typical metal-deficient galaxy) is studied. Adopting a recent observational result of absorption lines of hydrogen molecule in I Zw 18, we obtain the upper limit for the ionization degree in the case where hydrogen molecules can form via the H$^{-}$-process, although they are generally believed to fo…
Photometric maps, obtained with Spitzer's Infrared Array Camera (IRAC), can provide a valuable probe of warm molecular hydrogen within the interstellar medium. IRAC maps of the supernova remnant IC443, extracted from the Spitzer archive, are strikingly similar to spectral line maps of the H2 pure rotational transitions that we obtained with the Infrared Spectrograph (IRS) instrument on Spitzer. IRS spectroscopy indicates that IRAC Bands 3 and 4 are indeed dominated by the H2 v=0-0 S(5) and S(7) transitions, respectively. Modeling of the H2 excitation suggests that Bands 1 and 2 are dominated b…
We have conducted a survey of Ultra-luminous Infrared Galaxies (ULIRGs) with the Infrared Spectrograph on the Spitzer Space Telescope, obtaining spectra from 5.0-38.5um for 77 sources with 0.02<z <0.93. Observations of the pure rotational H2 lines S(3) 9.67um, S(2) 12.28um, and S(1) 17.04um are used to derive the temperature and mass of the warm molecular gas. We detect H2 in 77% of the sample, and all ULIRGs with F(60um)>2Jy. The average warm molecular gas mass is ~2x10^8solar-masses. High extinction, inferred from the 9.7um silicate absorption depth, is not observed along the line of site to…
High-resolution near-infrared images and moderate resolution spectra were obtained of the bipolar nebulae M~2--9 and AFGL 2688. The ability to spatially and spectrally resolve the various components of the nebulae has proved to be important in determining their physical structure and characteristics. In M~2--9, the lobes are found to have a double-shell structure. Analysis of \h2\ line ratios indicates that the \h2\ emission is radiatively excited. A well-resolved photodissociation region is observed in the lobes. The spectrum of the central source is dominated by H recombination lines and a s…
We report medium resolution VLT ISAAC K-band spectroscopy of the nuclei of seven ultraluminous infrared galaxies. After accounting for stellar absorption features, we have detected several molecular hydrogen (H_2) v=1-0, 2-1, and 3-2 vibrational emission lines, as well as the HI Brγand HeI 2^1P-2^1S recombination lines. The relative H_2 line intensities show little variation between the objects, suggesting that the H_2 excitation mechanisms in the nuclei are similar in all the objects. The 1-0 emissions appear thermalised at temperatures T\sim1000K. However, the 2-1 and 3-2 emissions show evid…
We have observed a large sample of compact planetary nebulae in the near-infrared to determine how the 2^1P-2^1S HeI line at 2.058um varies as a function of stellar effective temperature, Teff. The ratio of this line with HI Br g at 2.166um has often been used as a measure of the highest Teff present in a stellar cluster, and hence on whether there is a cut-off in the stellar initial mass function at high masses. However, recent photoionisation modelling has revealed that the behaviour of this line is more complex than previously anticipated. Our work shows that in most aspects the photoionisa…
We report on near-infrared medium-resolution spectroscopy of a sample of luminous and ultra luminous infrared galaxies (LIRGs-ULIRGs), carried out with SOFI at the ESO 3.5m New Technology Telescope. Because of wavelength dependence of the attenuation, the detection of the Pa_alfa or Br_gamma line in the Ks band should provide relevant constraints on SFR and the contribution of an AGN. We find, however, that the intensities of the Pa_alfa and Br_gamma lines, even corrected for slit losses, are on average only 10% and 40%, respectively, of that expected from a normal starburst of similar bolomet…
We have used the LONGSP spectrometer on the 1.5-m TIRGO telescope to obtain long slit spectra in the J, H, and K wavelength bands towards two positions along the Orion bar. These data have been supplemented with images made using the ARNICA camera mounted on TIRGO as well as with an ESO NTT observation carried out by Dr A. Moorwood. We detect a variety of transitions of hydrogen, helium, OI, FeII, FeIII, and H_2 . From our molecular hydrogen data, we conclude that densities are moderate (3-6 10^4 cm^-3) in the layer responsible for the molecular hydrogen emission and give no evidence for the p…
We report on an infrared 1 to 17 micron study of the nearby (cz = 4600 km/s) interacting spiral galaxy system, UGC 12914/12915, using the ground-based Palomar 200" telescope and PFIRCAM near-infrared detector and space-based mid-infrared imaging and spectral observations using ISOCAM and Phot-S on the Infrared Space Observatory (ISO). Strong line emission from aromatic band features at 6.2, 7.7 and 11.3 microns are seen in both the mid-IR imaging and Phot-S spectro-photometry centered on the nuclei. In the connecting bridge, the mid-infrared imaging reveals dust grains intermixed with the atom…
We investigate the observability of hydrogen molecules in absorption. The absorption efficiency of the hydrogen molecules become comparable with or larger than that of the dust grains in the metal-poor condition expected in the early Universe. If we can use bright infrared continuum sources behind the molecular gas clouds, the absorption measurement of the hydrogen molecules will be an important technique to explore the primordial gas clouds that are contracting into first-generation objects.
The central regions of many interacting and early-type spiral galaxies are actively forming stars. This process affects the physical and chemical properties of the local interstellar medium as well as the evolution of the galaxies. We observed near-infrared H2 emission lines: v=1-0 S(1), 3-2 S(3), 1-0 S(0), and 2-1 S(1) from the central ~1 kpc regions of the archetypical starburst galaxies, M82 and NGC 253, and the less dramatic but still vigorously star-forming galaxies, NGC 6946 and IC 342. Like the far-infrared continuum luminosity, the near-infrared H2 emission luminosity can directly trac…
We present NIR observations of a sample of mainly interacting ULIRGs, comprising H and K band spectra. Our main aims are to investigate the power source of these extremely luminous objects and the various excitation mechanisms of the strong molecular hydrogen emission often seen in such objects. Broadened emission lines were only detected in one object, IRAS 23498, consistent with previous results for this galaxy. The [SiVI] emission line was detected in IRAS17179 and IRAS20210, both classified as Sy2s. Two of the sample were unclassified, IRAS00150 and IRAS23420, which exhibit neither [SiVI] …
We present the first medium-resolution ($R\sim 600$) mid-infrared (8-13.3\micron) spectra of 11 Be stars. A large number of lines are observed and identified in these spectra, including, as an example, 39 hydrogen recombination lines in the spectrum of $γ$ Cas. In the majority of our spectra, all of the observed lines are attributable to hydrogen recombination. Two of the sources, $β$ Lyr and MWC 349 also show emission from other species. Both of these objects show evidence of [Ne II] emission, and $β$ Lyr also shows evidence of He I emission. We tabulate the effective line strength and line w…
We have modeled self-consistently the density and temperature profiles of gas and dust in protoplanetary disks, taking into account irradiation from a central star. Making use of this physical structure, we have calculated the level populations of molecular hydrogen and the line emission from the disks. As a result, we can reproduce the observed strong line spectra of molecular hydrogen from protoplanetary disks, both in the ultraviolet (UV) and the near-infrared, but only if the central star has a strong UV excess radiation.
Here, we present near-infrared spectroscopic observations of 15 helium atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope Facility. While a connection has been demonstrated between the most highly polluted, hydrogen atmosphere white dwarfs and the presence of warm circumstellar dust and gas, their frequency at the helium atmosphere variety is poorly constrained. None of our targets show excess near-infrared radiation consistent with warm orbiting material. Adding these near-infrared constraints to previous near- and mid-infrared observations, the frequency of warm circ…
We present near-infrared spectroscopy for a complete sample of 33 ultraluminous infrared galaxies at a resolution of R\approx 1000. Most of the wavelength range from 1.80-2.20 microns in the rest frame is covered, including the Pa-alpha and Br-gamma hydrogen recombination lines, and the molecular hydrogen vibration-rotation 1-0 S(1) and S(3) lines. Other species, such as He I, [Fe II], and [Si VI] appear in the spectra as well, in addition to a number of weaker molecular hydrogen lines. Nuclear extractions for each of the individual galaxies are presented here, along with spectra of secondary …
This paper continues our study of the behaviour of near infrared helium recombination lines in planetary nebula. We find that the 1.7007um 4^3D-3^3P HeI line is a good measure of the HeI recombination rate, since it varies smoothly with the effective temperature of the central star. We were unable to reproduce the observed data using detailed photoionisation models at both low and high effective temperatures, but plausible explanations for the difference exist for both. We therefore conclude that this line could be used as an indicator of the effective temperature in obscured nebula. We also c…
We present high resolution spectroscopic mid-infrared observations of the circumstellar disk around the Herbig Ae star HD97048 with the VLT Imager and Spectrometer for the mid-InfraRed (VISIR). We detect the S(1) pure rotational line of molecular hydrogen (H2) at 17.035 microns arising from the disk around the star. This detection reinforces the claim that HD97048 is a young object surrounded by a flared disk at an early stage of evolution. The emitting warm gas is located within the inner 35 AU of the disk. The line-to-continuum flux ratio is much higher than expected from models of disks at …
Molecular hydrogen clouds can contribute substantially to the galactic halo< dark matter and may lead to the birth of massive halo objects (MHOs) observed indirectly by microlensing. We present a method to detect these molecular clouds in the halo of M31 using the Doppler shift effect. We also consider the possibility to directly observe MHOs in the halo of M31 via their infrared emission.
We have taken K-band spectra covering 7 cooling flow clusters. The spectra show many of the 1-0S transitions of molecular Hydrogen, as well as some of the higher vibrational transitions, and some lines of ionized Hydrogen. The line ratios allow us to conclude that the rotational states of the first excited vibrational state are in approximate LTE, so that densities above 10^5/ cm^3 are likely, but there is evidence that the higher vibrational states are not in LTE. The lack of pressure balance between the molecular gas and the ionized components emphasizes the need for dynamic models of the ga…
Infrared Space Observatory 3 - 25 $μ$m spectra of the R Coronae Borealis stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp emission features coincident in wavelengths with the well known Unidentified Emission Features are present in the spectrum of V854 Cen but not of R CrB or RY Sgr. Since V854 Cen is not particularly H-poor and has a 1000 times more H than the other stars, the emission features are probably from a carrier containing hydrogen. There is a correspondence between the features and emission from laboratory samples of hydrogenated amorphous carbon. A search for C…
We report the detection of crystalline water ice on the surface of 2003 EL61. Reflectance spectra were collected from Gemini North telescope from 1.0 to 2.4 micron wavelength range, and from the Keck telescope across the 1.4 to 2.4 micron wavelength range. The signature of crystalline water ice is obvious in all data collected. Like the surfaces of many outer solar system bodies, the surface of 2003 EL61 is rich in crystalline water ice, which is energetically less favored than amorphous water ice at low temperatures, suggesting that resurfacing processes may be taking place. The near infrared…
(abridged) B[e] supergiants are known to possess geometrically thick dusty disks. Disk-forming wind models have, however, been found to be insufficient in reproducing the observed dust emission. This problem arises due to the severe assumption that, as for classical Be stars, the near-infrared excess emission originates in the disk. Modeling of the free-free and free-bound emission therefore results in an upper limit for the disk mass loss rate, hampering dust condensation in the disk. We propose a revised scenario for the non-spherical winds of B[e] supergiants: a normal B-type line-driven po…
Knots are commonly found in nearby planetary nebulae (PNe) and star forming regions. Within PNe, knots are often found to be associated with the brightest parts of the nebulae and understanding the physics involved in knots may reveal the processes dominating in PNe. As one of the closest PNe, the Helix Nebula (NGC 7293) is an ideal target to study such small-scale (~300 AU) structures. We have obtained infrared integral spectroscopy of a comet-shaped knot in the Helix Nebula using SINFONI on the Very Large Telescope at high spatial resolution (50-125 mas). With spatially resolved 2 micron spe…
Near-infrared spectroscopy using the new Palomar Integral Field Spectrograph indicates the presence of an AGN (active galactic nucleus) in the ultraluminous infrared galaxy IRAS 08311-2459. The high-velocity wings of the Paschen-alpha hydrogen recombination line are seen to be spatially unresolved, and with no positional offset between red and blue high velocity emission. The [Si VI] coronal line, with a 167 eV excitation potential, is also spatially unresolved with a velocity width comparable to that of the broad component of the Pa-alpha emission. The low velocity component of the Pa-alpha e…
We present near infrared ISAAC VLT observations of nine (0.01<z<0.06) Active Galactic Nuclei selected from the Hamburg/ESO Survey and the Veron-Cetty & Veron catalog. Hydrogen recombination lines Pa$α$ and Br$γ$ are observed in seven of the nine sources of which five show a broad component. In three sources, extended 1-0S(1) rotational-vibrational molecular hydrogen emission is detected. Stellar CO absorption is seen in four sources. In one of these objects, an upper limit of the central mass can be determined from the stellar velocity field. H- and Ks-band imaging allow us to determine the mo…
The Cepheid period-luminosity (P-L) relation is regarded as a linear relation (in log[P]) for a wide period range from ~2 to ~100 days. However, several recent controversial works have suggested that the P-L relation derived from the Large Magellanic Cloud (LMC) Cepheids exhibits a non-linear feature with a break period around 10 days. Here we review the evidence for linear/non-linear P-L relations from optical to near infrared bands. We offer a possible theoretical explanation to account for the nonlinear P-L relation from the idea of stellar photosphere - hydrogen ionization front interactio…
The luminosity of the central source in ionizing radiation is an essential parameter in a photoionized environment, and one of the most fundamental physical quantities one can measure. We outline a method of determining luminosity for any emission-line region using only infrared data. In dusty environments, grains compete with hydrogen in absorbing continuum radiation. Grains produce infrared emission, and hydrogen produces recombination lines. We have computed a very large variety of photoionization models, using ranges of abundances, grain mixtures, ionizing continua, densities, and ionizati…
We present the discovery of strong mid-infrared emission lines of molecular hydrogen of apparently high velocity dispersion (~870 km/s) originating from a group-wide shock wave in Stephan's Quintet. These Spitzer Space Telescope observations reveal emission lines of molecular hydrogen and little else. this is the first time an almost pure H_2 line spectrum has been seen in an extragalactic object. Along with the absence of PAH features and very low excitation ionized gas tracers, the spectra resemble shocked gas seen in Galactic supernova remnants, but on a vast scale. The molecular emission e…
Recent observations of nearby star forming regions have offered evidence that young brown dwarfs undergo a period of mass accretion analogous to the T Tauri phase observed in young stars. Brown dwarf analogs to stellar protostars, however, have yet to be definitively observed. These young, accreting objects would shed light on the nature of the dominant brown dwarf formation process, as well as provide ideal laboratories to investigate the dependence of the accretion mechanism on protostellar mass. Recent near infrared surveys have identified candidate proto-brown dwarfs and characterized low …
We report the first observation of Ly$α$ pumped molecular hydrogen emission lines in planetary nebulae. The H$_{2}$ emission observed in the ultraviolet spectra of NGC 6853 and NGC 3132 can be explained by excitation of vibrationally hot H$_{2}$ by Ly$α$ photons. Constraints are placed on the nebular Ly$α$ emission profile, as well as the molecular hydrogen temperature, column density and turbulent motion. These parameters are similar for the two nebulae, pointing to similar physical conditions in these objects. The ro-vibrational cascade following Ly$α$ pumping is predicted to have low surfac…
We investigate the possibility to search for metal-poor high column density (> 10^{23} cm^{-2}) clouds at high redshift (z) by using gamma ray burst (GRB) afterglows. Such clouds could be related to primeval galaxies which may cause a burst of star formation. We show that a large part of hydrogen is in molecular form in such a high column density environment. Therefore, hydrogen molecules (H2) rather than hydrogen atoms should be searched for. Then we show that infrared H2 lines are detectable for metal-poor (< 0.01 solar metallicity) high column density (log NH [cm^{-2}] > 23.5) systems at hi…
Results of an SiO maser survey for the late-type stars selected by the IRTS (Infrared Telescope in Space) are presented. We have detected SiO J=1-0, v=1 and/or v=2 lines in 27 stars out of 59 stars. The maser intensity increases with the depth of the H2O absorption in the infrared spectra and redness of the 2.2 and 12 micron color. The column densities of the water vapor in the target stars are estimated from the depth of the water absorption in the IRTS spectra. We found that the SiO maser was detected mostly in the stars with the column density of water vapor higher than 3x10^19-3x10^20 cm^-…
We present Spitzer IRAC and IRS observations of the dark cloud L1287. The mid-infrared (MIR) IRAC images show deeply embedded infrared sources in the vicinity of the FU Orionis objects RNO 1B and RNO 1C suggesting their association with a small young stellar cluster. For the first time we resolve the MIR point source associated with IRAS 00338+6312 which is a deeply embedded intermediate-mass protostar driving a known molecular outflow. The IRAC colors of all objects are consistent with young stars ranging from deeply embedded Class 0/I sources to Class II objects, part of which appear to be l…
