H2 Emission Features Research Articles

NIR spectroscopic survey of protostellar jets in the star-forming region IC 1396N

Context. The bright-rimmed cloud IC 1396N, associated with an intermediate-mass star-forming region, hosts a number of CO, molecular hydrogen, and Herbig-Haro (HHs) outflows powered by a set of millimetre compact sources. Aims. The aim of this work is to characterise the kinematics and physical conditions of the H2 emission features spread throughout the IC 1396N region. The features appear as chains of knots with a jet-like morphology and trace different H2 outflows. We also obtain further information about (and an identification of) the driving sources. Methods. Low-resolution, long-slit near-infrared spectra were acquired with the NICS camera at the TNG telescope, using grisms KB (R ~ 1200), HK, and JH (R ~ 500). Several slit pointings and position angles were used throughout the IC 1396N region in order to sample a number of the H2 knots that were previously detected in deep H2 2.12 μm images. Results. The knots exhibit rich ro–vibrational spectra of H2, consistent with shock-excited excitation, from which radial velocities and relevant physical conditions of the IC 1396N H2 outflows were derived. These also allowed estimating extinction ranges towards several features. [Fe ii] emission was only detected towards a few knots that also display unusually high H2 1–0 S(3)/S(1) flux ratios. The obtained radial velocities confirm that most of the outflows are close to the plane of the sky. Nearby knots in the same chain often display different radial velocities, both blue–shifted and red–shifted, which we interpret as due to ubiquitous jet precession in the driving sources or the development of oblique shocks. One of the chains (strand A, i.e. knots A1 to A15) appears as a set of features trailing a leading bow-shock structure consistent with the results of 3D magneto-hydrodynamical models. The sides of the leading bow shock (A15) exhibit different radial velocities. We discuss possible explanations. Our data cannot confirm whether strands A and B have both originated in the intermediate mass young stellar object [BGE2002] BIMA 2 because a simple model of a precessing jet cannot account for their locations. Conclusions. Near-infrared spectroscopy has confirmed that most of the H2 ro-vibrational emission in IC 1396N is shock-excited rather than uv-excited in photon-dominated regions. It has shown a complex kinematical structure in most strands of emitting knots as well.

The Near-stellar Environment of Class 0 Protostars: A First Look with Near-infrared Spectroscopy

Abstract We present near-infrared K-band spectra for a sample of seven Class 0 protostars in the Perseus and Orion star-forming regions. We detect Brγ, CO overtone, and H2 emission, features that probe the near-circumstellar environment of the protostar and reveal evidence of magnetospheric accretion, a hot inner disk atmosphere, and outflows, respectively. Comparing the properties of these features with those of Class I sources from the literature, we find that their Brγ emission and CO emission are generally consistent in strength and velocity width. The Brγ line profiles are broad and centrally peaked, with FWHMs of ∼200 km s−1 and wings extending to ∼300 km s−1. The line ratios of our H2 emission features, which are spatially extended for some sources, are consistent with shock excitation and indicate the presence of strong jets or a disk wind. Within our small sample, the frequency of CO band emission (∼67%) is high relative to that of Class I samples (∼15%), indicating that Class 0 sources have high inner disk accretion rates, similar to those of the most actively accreting Class I sources. Collectively, our results suggest that Class 0 sources have similar accretion mechanisms to the more evolved classes, with strong organized stellar magnetic fields established at the earliest observable stage of evolution.

High-resolution Near-infrared Spectroscopic Study of Galactic Supernova Remnants. I. Kinematic Distances

Abstract We have carried out high-resolution near-infrared spectroscopic observations toward 16 Galactic supernova remnants (SNRs) showing strong H2 emission features. A dozen bright H2 emission lines are clearly detected for individual SNRs, and we have measured their central velocities, line widths, and fluxes. For all SNRs except one (G9.9−0.8), the H2 line ratios are well consistent with that of thermal excitation at T ∼ 2000 K, indicating that the H2 emission lines are most likely from shock-excited gas and therefore that they are physically associated with the remnants. The kinematic distances to the 15 SNRs are derived from the central velocities of the H2 lines using a Galactic rotation model. We derive for the first time the kinematic distances to four SNRs: G13.5+0.2, G16.0−0.5, G32.1−0.9, and G33.2−0.6. Among the remaining 11 SNRs, the central velocities of the H2 emission lines for six SNRs are well consistent (±5 ) with those obtained in previous radio observations, while for the other five SNRs (G18.1−0.1, G18.9−1.1, Kes 69, 3C 396, W49B) they are significantly different. We discuss the velocity discrepancies in these five SNRs. In G9.9−0.8, the H2 emission shows nonthermal line ratios and narrow line width (∼4 ), and we discuss its origin.

Near-infrared [Fe ii] and H2 Emission-line Study of Galactic Supernova Remnants in the First Quadrant

Abstract We report the detection of near-infrared (NIR) [Fe ii] (1.644 μm) and H2 1–0 S(1) (2.122 μm) line features associated with Galactic supernova remnants (SNRs) in the first quadrant using two narrowband imaging surveys, UWIFE and UWISH2. Among the total of 79 SNRs fully covered by both surveys, we found 19 [Fe ii]-emitting and 19 H2-emitting SNRs, giving a detection rate of 24% for each. Eleven SNRs show both emission features. The detection rate of [Fe ii] and H2 peaks at the Galactic longitude (l) of 40°–50° and 30°–40°, respectively, and gradually decreases toward smaller/larger l. Five out of the eleven SNRs emitting both emission lines clearly show an “[Fe ii]–H2 reversal,” where H2 emission features are found outside the SNR boundary in [Fe ii] emission. Our NIR spectroscopy shows that the H2 emission originates from collisionally excited H2 gas. The brightest SNR in both [Fe ii] and H2 emissions is W49B, contributing more than 70% and 50% of the total [Fe ii] 1.644 μm (2.0 × 104 L ⊙ ) and H2 2.122 μm (1.2 × 103 L ⊙ ) luminosities of the detected SNRs. The total [Fe ii] 1.644 μm luminosity of our Galaxy is a few times smaller than that expected from the SN rate using the correlation found in nearby starburst galaxies. We discuss possible explanations for this.

UNTANGLING THE NEAR-IR SPECTRAL FEATURES IN THE PROTOPLANETARY ENVIRONMENT OF KH 15D

ABSTRACT We report on Gemini/GNIRS observations of the binary T Tauri system V582 Mon (KH 15D) at three orbital phases. These spectra allow us to untangle five components of the system: the photosphere and magnetosphere of star B, the jet, scattering properties of the ring material, and excess near-infrared (near-IR) radiation previously attributed to a possible self-luminous planet. We confirm an early-K subgiant classification for star B and show that the magnetospheric He i emission line is variable, possibly indicating increased mass accretion at certain times. As expected, the H2 emission features associated with the inner part of the jet show no variation with orbital phase. We show that the reflectance spectrum for the scattered light has a distinctive blue slope and spectral features consistent with scattering and absorption by a mixture of water and methane ice grains in the 1–50 μm size range. This suggests that the methane frost line is closer than ∼5 au in this system, requiring that the grains be shielded from direct radiation. After correcting for features from the scattered light, jet, magnetosphere, and photosphere, we confirm the presence of leftover near-IR light from an additional source, detectable near minimum brightness. A spectral emission feature matching the model spectrum of a 10 M J, 1 Myr old planet is found in the excess flux, but other expected features from this model are not seen. Our observations, therefore, tentatively support the picture that a luminous planet is present within the system, although they cannot yet be considered definitive.

CANDIDATES FOR THE YOUNG STELLAR OUTFLOWS: WATER AND METHANOL MASERS FROM YOUNG STELLAR OBJECTS

We conducted simultaneous 22 GHz water maser and 44 GHz class I methanol maser surveys of newly identified 282 H2 emission features from the 2.122 μ mH 2 narrowband image survey in the Galactic plane (UWISH2 project) using Korean VLBI Network 21 m radio telescopes. We detected 16 and 13 new water and methanol maser sources, respectively. This result indicates that at least ∼5% of the H2 emission features originate from young stellar objects (YSOs) that are in the right physical condition to produce the water and methanol masers. The masers are closely related to the current outflow activities in the Galactic plane. The power sources of these 23 diffused/collimated H2 emission features (six sources are detected for both masers) are likely to be intermediate- to high-mass YSOs, based on a comparison with the maser luminosities of other well-studied YSOs. Both maser velocities are mostly close to their own systemic velocities within 5k m s −1 , even though water masers generally show larger variabilities in the intensity, velocity, and shape than methanol masers. We also discovered three new water maser sources with high-velocity components: ∼25 km s −1 redshifted CMHO 019, ∼50 km s −1 blueshifted CMHO 132, and ∼120 km s −1 blueshifted CMHO 182. In particular, we propose that the dominant blueshifted water maser of CHMO 182 can be a unique laboratory for the study of the high-mass young stellar jet and its acceleration.

WIDE-FIELD NEAR-INFRARED IMAGING OF THE L1551 DARK CLOUD

We present wide-field near-infrared images of the densest part of the L1551 dark cloud taken with the narrow-band filters for [Fe II] λ 1.644 μm and H2 v = 1-0 S(1) lines, together with the broadband H and K s filters. Numerous [Fe II] and H2 emission features were detected from the regions around HL/XZ Tau, HH 30, HH 262, L1551 NE, and L1551 IRS 5. Most of the [Fe II] features are compact or jet-like, suggesting that the emission arises from fast shocks occurring in the ejecta of jets. The H2 features are more diffuse and widely distributed in outflow lobes, with none of the H2 features showing the well-collimated emission associated with jets. This implies that the H2 emission originates from slower shocks where the ejecta interacts with ambient material. The outflow structure in the vicinity of the deeply embedded object L1551 NE is revealed, featuring a well-collimated, spatially continuous [Fe II] jet penetrating a fan-shaped infrared reflection nebula. The tangential velocities of knots in the L1551 NE jet are estimated to be 140-190 km s–1 from their proper motions, implying an inclination of 45°-60° for the jet axis. A counter-jet from L1551 IRS 5 is detected for the first time in [Fe II]; this probably corresponds to the northern-most of the two jets on the blueshifted side. The relative brightness of the counter-jet suggests a visual extinction of 20-30 mag. The [Fe II] emissions from collimated jets are relatively strong toward L1551 NE and L1551 IRS 5 compared to those toward HL Tau and HH 30. This implies that the jets from the former objects, which are more embedded, have a higher shock velocity and/or a larger gas density than the latter, more revealed objects. The results presented here show that the near-infrared [Fe II] emission is a useful probe of well-collimated jets from deeply embedded sources, in much the same way that optical [S II] emission is used for relatively revealed objects.

Variability of the NGC 1333 IRAS 4A Outflow: Molecular Hydrogen and Silicon Monoxide Images

The NGC 1333 region was observed in the H2 1-0 S(1) line. The H2 images cover a 5' × 7' region around IRAS 4. Numerous H2 emission features were detected. The northeast-southwest bipolar outflow driven by IRAS 4A was studied by combining the H2 images with SiO maps published previously. The SiO-H2 outflows are continuous on the southwestern side but show a gap on the northeastern side. The southwestern outflow lobe curves smoothly, and the position angle increases with the distance from the driving source. The base and the outer tip of the northeastern outflow lobe are located at positions opposite to the corresponding parts of the southwestern lobe. This point symmetry suggests that the outflow axis may be drifting or precessing clockwise in the plane of the sky and that the cause of the axis drift may be intrinsic to the outflow engine. The axis drift model is supported by the asymmetric lateral intensity profile of the SiO outflow. The axis drift rate is ~0011 yr-1. The middle part of the northeastern outflow does not exactly follow the point symmetry because of the superposition of two different kinds of directional variability: the axis drift of the driving source and the deflection by a dense core. The axis drift model provides a good explanation for the large deflection angle of the northeastern outflow. Other H2 emission features around the IRAS 4 region are discussed briefly. Some of them are newly found outflows, and some are associated with outflows already known before.

Collimated molecular jets from high-mass young stars: IRAS 18151-1208

Recent near-IR images of massive star forming regions have revealed two collimated jets in the IRAS 18151-1208 region, one of which is almost a parsec in length (Varricatt et al.). Follow-up high-spectral-resolution echelle spectroscopy and 2-dimensional “integral field” spectroscopy of the associated molecular shock features are presented here. From these data kinematic information and excitation maps are extracted, which show that the two jets are morphologically, kinematically and energetically similar to their counterparts from low mass protostars. The close association between the H2 emission features and the high-velocity CO emission presented by Beuther et al. also suggests that the CO represents gas entrained by these two very collimated jets. From the mass and momentum of the molecular gas, and the luminosity of the H2 features, it is clear that the flows must be powered by massive sources. To all intents and purposes, the molecular jets appear to be scaled-up versions of low-mass YSO jets. Collectively, the observations add further support to the idea that massive stars are formed through vigorous disk accretion, and that, while in their earliest stages of evolution, massive protostars drive collimated jets.

Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912

Near-infrared images and K-band spectroscopy of the massive star-forming region IRAS 23151+5912 are presented. The JHK' images reveal an embedded infrared cluster associated with infrared nebula, and the H2 (2.12 µm) narrow-band image provides for the first time evidence of outflow activity associated with the cluster. That the cluster is young can be shown by the high percentage of infrared excess sources and the outflow activity. We suggest an age of the cluster of ∼ 106 yr. Eight young stars are found in the bright nebular core around IRAS 23151+5912. By the color-magnitude diagrams of the cluster, we found five high-mass YSOs and four intermediate-mass YSOs in the cluster. Eight H2 emission features are discovered in the region with a scattered and non-axisymmetric distribution, indicating the existence of multiple outflows driven by the cluster. Diffuse H2 emission detected to the north and to the west of the cluster may result from UV leakage of the cluster. Brγ, H2, and CIV emission lines are found in the K-band spectrum of the brightest source, NIRS 19, indicating the presence of envelope, stellar wind, and shock in the circumstellar environment. We have estimated an O7–O9 spectral type for the central massive YSO (20 ∼ 30 M☉), with an age of less than 1×106 yr.

The unusual morphology of molecular hydrogen emission in the planetary nebula J900

view Abstract Citations (11) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Unusual Morphology of Molecular Hydrogen Emission in the Planetary Nebular J900 Shupe, D. L. ; Armus, L. ; Matthews, K. ; Soifer, B. T. Abstract We report new high-resolution near-infrared imaging observations of the planetary nebula J900, in broadband J, H, and K, and narrowband 2.122 micrometers (for H2 1-0 S(1)), Brackett-gamma, and continuum filters. The H2 images reveal a remarkable set of outward-extending features not detected in any previous observations of theis object. In the northwest lobe of the inner bipolar region, the H2 emission, Brackett-gamma emission, and underlying continuum are spatially resolved. The relative positions of the peaks of the line emission suggest an ionization front seen edge-on. The continuum emission, apparently located nearer to the central star, is likely due to transiently heated small dust grains. The extended H2 emission features are probably excited either by oblique shocks caused by material ejected from the nebula, or by radiation leaking from holes in the opacity surrounding the ionized shell. Publication: The Astronomical Journal Pub Date: March 1995 DOI: 10.1086/117350 Bibcode: 1995AJ....109.1173S Keywords: Hydrogen; Infrared Imagery; Morphology; Planetary Nebulae; Stellar Envelopes; Stellar Winds; Vibrational Spectra; Flux Density; Image Analysis; Ionization; Shock Fronts; Spatial Resolution; Stellar Spectrophotometry; Astronomy; PLANETARY NEBULAE: INDIVIDUAL: J900; ISM: JETS AND OUTFLOWS full text sources ADS | data products SIMBAD (5)