High-velocity Component Research Articles

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.

Water Maser and Ammonia Survey toward IRAS Sources in the Galaxy I. H$_{2}$O Maser Data

Abstract We present H $_{2}$ O maser data from a survey toward IRAS sources in the Galaxy with the Nobeyama 45 m telescope. This survey had a 1$\sigma$ noise level as small as 0.24 Jy, resulting in one of the most sensitive water-maser surveys. The maximum distance of the masers to be detected by our survey is estimated to be 3 kpc for sources with $F_{\nu, \mathrm{1\,kpc}} <$ 10 Jy and 10 kpc for those with 10 Jy $\le F_{\nu, \mathrm{1\,kpc}} <$ 100 Jy, where $F_{\nu, \mathrm{1\,kpc}}$ is the maser flux density converted at a distance of 1 kpc. For strong masers with $F_{\nu, \mathrm{1\,kpc}} \ge$ 100 Jy, our survey could detect all sources in the Galaxy. We carried out a total of 2229 observations toward 1563 sources and detected water-maser emission toward 222 sources. Our survey newly found masers from 75 of the 222 sources. The maser spectra of the new sources are shown in addition to the line parameters of all the detected sources. Furthermore, we discovered an extremely high-velocity component with $V_\mathrm{LSR} = -146$kms$^{-1}$ toward a well-known source, NGC 7538 IRS 11. For the three sources of NGC 1333 IRAS 4A/B, IRAS 05329$-$0512, and 06053$-$0622, we succeeded to spatially separate multiple-velocity components.

Submillimeter Array Observation of the Proto-Planetary Nebula CRL 618 in the CO J = 6-5 Line

We report on the results of a Submillimeter Array interferometric observation of the proto-planetary nebula CRL 618 in the 12CO J=6-5 line. With the new capability of SMA enabling us to use two receivers at a time, we also observed simultaneously in the 12CO J=2-1 and 13CO J=2-1 lines. The 12CO J=6-5 and 13CO J=2-1 lines were first interferometrically observed toward CRL 618. The flux of the high velocity component of the 12CO J=6-5 line is almost fully recovered, while roughly 80% of the flux of the low velocity component is resolved out. The low recovery rate suggests that the emission region of the low velocity component of the 12CO J=6-5 line is largely extended. Continuum emission is detected both at 230 and 690 GHz. The flux of the 690 GHz continuum emission seems to be partially resolved out, suggesting dust emission partly contaminates the 690 GHz continuum flux. The cavity structure, which has been confirmed in a previous observation in the 12CO J=2-1 line, is not clearly detected in the 12CO J=6-5 line, and only the south wall of the cavity is detected. This result suggests that the physical condition of the molecular envelope of CRL 618 is not exactly axial symmetric.

Spectropolarimetry of the Type Ib/c SN 2005bf*

We present spectropolarimetric observations of the peculiar Type Ib/c SN 2005bf, in MCG+0027-005, from 3600‐8550 A. The SN was observed on 2005 April 30.9, 18 d after the first B-band light-curve maximum and 6 d before the second B-band light-curve maximum. The degree of the interstellar polarization (ISP), determined from depolarized emission lines in the spectrum, is found to be large with pmax(ISP) = 1.6 per cent and θ(ISP) = 149. ◦ 7 ± 4. ◦ 0, but this may be an upper limit on the real value of the ISP. After ISP subtraction, significant polarization is observed over large wavelength regions, indicating a significant degree of global asymmetry, � 10 per cent. Polarizations of 3.5 and 4 per cent are observed for absorption components of Ca II H& K and infrared triplet, and 1.3 per cent for He I 5876 A and Fe II .O n theQ‐U plane clear velocity-dependent loop structure is observed for the He I 5876 A line, suggestive of departures from an axial symmetry and possible clumping of the SN ejecta. Weak highvelocity components of Hα ,H β and Hγ are observed, with velocities of −15 000 km s −1 . The low degree of polarization observed at Hβ suggests that the polarization observed for the other Balmer lines (∼0.4 per cent above the background polarization) may rather be due to blending of Hα and Hγ with polarized Si II and Fe II lines, respectively. We suggest a model in which a jet of material, that is rich in 56 Ni, has penetrated the C‐O core, but not the He mantle. The jet axis is tilted with respect to the axis of the photosphere. This accounts for the lack of significant polarization of O I 7774 A, the delayed excitation and, hence, observability of He I and, potentially, the varied geometries of He and Ca.

Further Indications of Jet Rotation in New Ultraviolet and OpticalHubble Space TelescopeSTIS Spectra

We present survey results which suggest rotation signatures at the base of T-Tauri jets. Observations were conducted with the Hubble Space Telescope Imaging Spectrograph at optical and near ultraviolet wavelengths (NUV). Results are presented for the approaching jet from DG Tau, CW Tau, HH 30 and the bipolar jet from TH 28. Systematic asymmetries in Doppler shift were detected across the jet, within 100 AU from the star. At optical wavelengths, radial velocity differences were typically 10 to 25 (+/-5) km/s, while differences in the NUV range were consistently lower at typically 10 (+/-5) km/s. Results are interpreted as possible rotation signatures. Importantly, there is agreement between the optical and NUV results for DG Tau. Under the assumption of steady magnetocentrifugal acceleration, the survey results lead to estimates for the distance of the jet footpoint from the star, and give values consistent with earlier studies. In the case of DG Tau, for example, we see that the higher velocity component appears to be launched from a distance of 0.2 to 0.5 AU from the star along the disk plane, while the lower velocity component appears to trace a wider part of the jet launched from as far as 1.9 AU. The results for the other targets are similar. Therefore, if indeed the detected Doppler gradients trace rotation within the jet then, under the assumption of steady MHD ejection, the derived footpoint radii support the existence of magnetized disk winds. However, since we do not resolved the innermost layers of the flow, we cannot exclude the possibility that there also exists an X-wind or stellar wind component.

Ionization effect to plasma expansion study during nanosecond pulsed laser deposition

The dynamic characteristic and effects of plasma play an important role in film growth process of pulsed laser deposition (PLD). Based on numerical hydrodynamic modeling, supposed the laser radiation and partial ionization of the plasma as a dynamic source, we deduce a set of new plasma expansion dynamics equations. Based on which, as an example of carbon target, using finite difference method, the plasma flow dynamics evolvement in vacuum is investigated. Our results show the dynamic partial ionization increases the expansion in all directions, which changes into a new dynamic source for plasma expansion. In the axial direction, because of the collisional interactions between particles, the plume density peak is in the vicinity of the target surface and the acceleration of plasma occurs mainly near the target surface too. In the transverse direction, the plume peak is not near the target, but at the surface. The space expansion distance is far less than the axial direction because there is no high initial velocity component in this direction. The predictions of the plasma expansion action based on the proposed dynamics source assumption are found to be in agreement with the experimental observation.

Highly ionized plasma in the Large Magellanic Cloud: evidence for outflows and a possible galactic wind

Based on an analysis of the interstellar highly ionised species C IV, Si IV, N V, and O VI observed in the FUSE and HST/STIS E140M spectra of four hot stars in the Large Magellanic Cloud (LMC), we find evidence for a hot LMC halo fed by energetic outflows from the LMC disk and even possibly an LMC galactic wind. Signatures for such outflows are the intermediate and high-velocity components (v_LSR>100 km/s) relative to the LMC disk observed in the high- and low-ion absorption profiles. The stellar environments produce strong, narrow (T<20,000 K) components of C IV and Si IV associated with the LMC disk; in particular they are likely signatures of H II regions and expanding shells. Broad components are observed in the profiles of C IV, Si IV, and O VI with their widths implying hot, collisionally ionised gas at temperatures of a few times 100,000 K. There is a striking similarity in the O VI/C IV ratios for the broad LMC and high-velocity components, suggesting much of the material at v_LSR>100 km/s is associated with the LMC. The velocity of the high-velocity component is large enough to escape altogether the LMC, polluting the intergalactic space between the LMC and the Milky Way. The observed high-ion ratios of the broad LMC and high-velocity components are consistent with those produced in conductive interfaces; such models are also favored by the apparent kinematically coupling between the high and the weakly ionised species.

Spectroscopic diagnostics of T Tauri inner winds

AbstractThe role of the star-disk interaction region in launching the high velocity component of accretion-driven outflows is examined. Spectroscopic indicators of high velocity inner winds have been recognized in T Tauri stars for decades, but identifying the wind launch site and the accompanying mass loss rates has remained elusive. A promising new diagnostic is He I λ10830, whose metastable lower level results in a powerful probe of the geometry of the outflowing gas in the interaction region. This, together with other atomic and molecular spectral diagnostics covering a wide range of excitation and ionization states, suggests that more than one launch site of the innermost wind is operational in most accreting stars.

On the orbital period of the magnetic cataclysmic variable HS 0922+1333

Context: The object HS 0922+1333 was visited briefly in 2002 in a mini survey of low accretion rate polars (LARPs) in order to test if they undergo high luminosity states similar to ordinary polars. On the basis of that short observation the suspicion arose that the object might be an asynchronous polar (Tovmassian et al. 2004). The disparity between the presumed orbital and spin period appeared to be quite unusual. Aims: We performed follow-up observations of the object to resolve the problem. Methods: New simultaneous spectroscopic and photometric observations spanning several years allowed measurements of radial velocities of emission and absorption lines from the secondary star and brightness variations due to synchrotron emission from the primary. Results: New observations show that the object is actually synchronous and its orbital and spin period are equal to 4.04 hours. Conclusions: We identify the source of confusion of previous observations to be a high velocity component of emission line arousing from the stream of matter leaving L1 point.

Anatomy of HH 111 from CO Observations: A Bow‐Shock‐driven Molecular Outflow

We present single-dish and interferometric millimeter line observations of the HH 111 outflow and its driving source. The physical conditions of the core have been determined from the emission of the millimeter line of CO and its isotopomers and CS with the IRAM 30 m telescope, and the CO J = 7 → 6 line with the Caltech Submillimeter Observatory. The emission reveals a small condensation of cold (T = 20-25 K) and dense gas [n(H2) = 3 × 105 cm-3]. The outflow has been mapped with the IRAM Plateau de Bure interferometer (PdBI). The cold gas is distributed in a hollow cylinder surrounding the optical jet. The formation of this cavity and its kinematics are well accounted for in the frame of outflow gas entrainment by jet bow shocks. Evidence of gas acceleration is found along the cavity walls, correlated with the presence of optical bow shocks. The separation of the inner walls reaches 8''-10'', which matches the transverse size of the wings in the bow shock. CSO observations of the J = 7 → 6 line show evidence of a high-velocity and hot gas component (T = 300-1000 K) with a low filling factor. This emission probably arises from shocked gas in the jet. Observations of the 3P2-3P1 [C I] line are consistent with C-type nondissociative shocks. Mapping of the high-velocity molecular bullets B1-B3, located beyond the optical jet, reveals small structures of 3'' × 7'' flattened perpendicular to the flow direction. They are made of cold (T ~ 30 K), moderate density gas [n(H2) = (0.5-1.0) × 104 cm-3], expanding into the low-density surrounding medium. Their properties are consistent with their being shocked gas knots resulting from past time-variable ejections in the jet.

The Earth’s ‘hum’ is driven by ocean waves over the continental shelves

Observations show that the seismic normal modes of the Earth at frequencies near 10 mHz are excited at a nearly constant level in the absence of large earthquakes. This background level of excitation has been called the 'hum' of the Earth, and is equivalent to the maximum excitation from a magnitude 5.75 earthquake. Its origin is debated, with most studies attributing the forcing to atmospheric turbulence, analogous to the forcing of solar oscillations by solar turbulence. Some reports also predicted that turbulence might excite the planetary modes of Mars to detectable levels. Recent observations on Earth, however, suggest that the predominant excitation source lies under the oceans. Here I show that turbulence is a very weak source, and instead it is interacting ocean waves over the shallow continental shelves that drive the hum of the Earth. Ocean waves couple into seismic waves through the quadratic nonlinearity of the surface boundary condition, which couples pairs of slowly propagating ocean waves of similar frequency to a high phase velocity component at approximately double the frequency. This is the process by which ocean waves generate the well known 'microseism peak' that dominates the seismic spectrum near 140 mHz (refs 11, 12), but at hum frequencies, the mechanism differs significantly in frequency and depth dependence. A calculation of the coupling between ocean waves and seismic modes reproduces the seismic spectrum observed. Measurements of the temporal correlation between ocean wave data and seismic data have confirmed that ocean waves, rather than atmospheric turbulence, are driving the modes of the Earth.

The Nature of Optical Features in the Inner Region of the 3C 48 Host Galaxy

The well-known quasar 3C48 is the most powerful compact steep-spectrum radio-loud QSO at low redshifts. It also has two unusual optical features within the radius of the radio jet (~1"): (1) an anomalous, high-velocity narrow-line component, having several times as much flux as does the narrow-line component coinciding with the broad-line redshift; and (2) a bright continuum peak (3C48A) ~1" northeast of the quasar. Both of these optical features have been conjectured to be related to the radio jet. Here we explore these suggestions. We have obtained Gemini North GMOS integral-field-unit (IFU) spectroscopy of the central region around 3C48. We use the unique features of the IFU data to remove unresolved emission at the position of the quasar. The resolved emission at the wavelength of the high-velocity component is peaked <~0.25" north of the quasar, at virtually the same position angle as the base of the radio jet. These observations appear to confirm that this high-velocity gas is connected with the radio jet. However, most of the emission comes from a region where the jet is still well collimated, rather than from the regions where the radio maps indicate strong interaction with an external medium. We also present the results of HST STIS spectroscopy of 3C48A. We show that 3C48A is dominated by stars with a luminosity-weighted age of ~1.4 X 10^8 years, substantially older than any reasonable estimate for the age of the radio source. Our IFU data indicate a similar age. Thus, 3C48A almost certainly cannot be attributed to jet-induced star formation. The host galaxy of 3C48 is clearly the result of a merger, and 3C48A seems much more likely to be the distorted nucleus of the merging partner, in which star formation was induced during the previous close passage.

High‐Resolution Imaging of Molecular Outflows in Massive Young Stars

We present high angular resolution observations toward two massive star-forming regions, IRAS 18264-1152 and IRAS 23151+5912, with the Plateau de Bure Interferometer (PdBI) in the SiO(J = 2-1) and H13CO+(J = 1-0) lines and at 1.3 and 3.4 mm continuum, and with the Very Large Array (VLA) in the NH3(J,K) = (1,1), (2, 2) lines. The NH3(1, 1) and (2, 2) emission is detected toward IRAS 18264-1152 only. For IRAS 18264-1152, the SiO observations reveal at least two quasi-perpendicular outflows with high collimation factors, and the most dominant feature is a redshifted jetlike outflow with very high velocities up to about Δv = 60 km s-1 with respect to the systemic velocity. The very high velocity component (Δv = 22-60 km s-1) of this outflow is spatially offset from its high-velocity (Δv = 3-21 km s-1) component. The SiO line profiles and position-velocity characteristics of these two components suggest that this outflow could be driven by an underlying precessing jet. For IRAS 23151+5912, the bipolar but mainly blueshifted SiO outflow coincides with the inner parts of the single-dish CO outflow. In particular, the quasi-parabolic shape of the blueshifted outflow coincides with the near-infrared nebulosity and is consistent with entrainment of the gas by an underlying wide-angle wind. The analysis of the molecular outflow data of the two luminous sources further supports high-mass stars forming via a disk-mediated accretion process similar to that in low-mass stars.

The Molecular Envelope around the Red Supergiant VY CMa

We present millimeter interferometric observations of the molecular envelope around the red supergiant VY CMa with the Submillimeter Array (SMA). The high angular resolution (<2'') allows us to derive the structure of the envelope as observed in the 1.3 mm continuum, 12CO(2-1), 13CO(2-1), and SO(65-54) lines emission. The circumstellar envelope is resolved into three components: (1) a dense, compact, and dusty central component, embedded in (2) a more diffuse and extended envelope, and (3) a high-velocity component. We construct a simple model, consisting of a spherically symmetric slowly expanding envelope and bipolar outflows with a wide opening angle (~120°) viewed close to the line of sight (i = 15°). Our model can explain the main features of the SMA data and previous single-dish CO multiline observations. An episode of enhanced mass loss along the bipolar direction is inferred from our modeling. The SMA data provide a better understanding of the complicated morphology seen in the optical/IR high-resolution observations.

Adaptive Optics Spectroscopy of the [Feii] Outflows from HL Tauri and RW Aurigae

We present new results of [Fe II] λ1.644 μm spectroscopy toward the jets from HL Tau and RW Aur carried out with the Subaru Telescope combined with the adaptive optics system. We observed the regions within 2''-3'' from the stars with the subarcsecond resolutions of 05 and 02 for HL Tau and RW Aur, respectively. In addition to the strong high-velocity component (HVC) extended along each jet, we detected a blueshifted low-velocity component (LVC) seen as a wing or shoulder of the HVC at each stellar position. The position velocity diagrams of the two objects show a characteristic similar to those of the cold disk wind and X-wind models in that the [Fe II] line width is broad close to the stellar position and narrower at the extended jet. A closer comparison suggests, however, that the disk wind model tends to have too large a line width at the HVC, while the X-wind model has excess redshifted emission at the stellar position. The narrow velocity width with symmetric line profiles of the observed HVC supports an X-wind-type model, while the LVC, located away from the star, favors the presence of a disk wind. The [Fe II] emission shows a gap of 08 for HL Tau and a marked drop of Y ~ -02 for RW Aur between the redshifted jet and the star, which indicate optically thick disks of ~160 and <40 AU in radius, respectively. Part of the Br12 emission of HL Tau originates from the jet itself because its normalized line profile shows a signigicantly large deviation from the normalized continuum in spatial profile.

Inside the large globule CB205: YSOs feeding multiple outflows

Context. The molecular and continuum surveys at NIR and (sub-)mmwavelengths recently performed in the large and distant ( ≥ 1 kpc) Bok globules CB3 and CB34 are the framework of the present paper. With this multi-wavelength approach, it is possible to trace the hot jets and cold outflows driven by the (proto-)stars, to investigate how they interact with the surrounding medium, and to assess that in these globules star formation is a continuous process and not a unique event. Aims. With the present work we continue our survey of a sample of large globules by investigating CB205. The aim is to carefully map the outflow motions and to locate the driving sources. The occurrence of outflows is used to identify the earliest star-forming regions. Methods. Our analysis has been performed through JCMT observations at (sub)millimeter wavelengths of the continuum (850 and 450 μ m) and CO(2–1) and (3–2) line emission. Results. The continuum maps reveal three Class 0 candidates located in the western region of the globule, without NIR counterparts. The line maps show a complex scenario for the high velocity components with different clumps at different velocities. The outflow activity is concentrated around the Class 0 candidates. On the other hand, the NIR objects are associated with lower velocity outflow clumps. Conclusions. The present results confirm that for CB205, star formation is propagating through the globule. The western part hosts the latest formation episode with Class 0 candidates feeding multiple outflows. We suggest that the eastern region, which is associated with a NIR cluster, reflects a later evolutionary phase, when the outflow is fading.

H$\mathsf{\alpha}$ line profiles for a sample of supergiant HII regions

We analyze the broad, low intensity, high velocity components that are seen in the H line profiles for a sample of HII regions. These HII regions are chosen from among the brightest and most isolated in a sample of spiral galaxies for which we have photometric and spectroscopic data: NGC 157, NGC 3631, NGC 6764, NGC 3344, NGC 4321, NGC 5364, NGC 5055, NGC 5985, and NGC 7479. We confirm that the line profiles of most of these bright, giant extragalactic HII regions contain broad kinematic components of low intensity, but high velocity, that we denote as wings. We analyze these components, deriving emission measures, central velocities, and velocity dispersions of the blue and red features, which are similar. We interpret these components as expanding shells within the HII regions and produced by the stellar winds from the ionizing stars. We compare the kinetic energies of these expanding shells with the kinetic energy available from the stellar winds. If we allow for the hypothesis that the brightest HII regions are density bounded, we show that, for these HII regions, the stellar wind mechanism can explain the observed shell kinetic energies.

Hαline profiles for a sample of supergiant HII regions

We present an analysis of the Hα emission line profiles of a sample of giant extragalactic HII regions, selected from among the brightest and most isolated in a group of spiral galaxies for which we have photometric and spectroscopic data: NGC 157, NGC 3631, NGC 6764, NGC 3344, NGC 4321, NGC 5364, NGC 5055, NGC 5985, NGC 7479. Our study confirms that the majority of the line profiles are composed of a bright, main component and two fainter, high velocity components that we denominate wings. Here, we analyze the kinematics of the principal components, finding a relation between the Hα luminosity, LHα, and the turbulent velocity dispersion, σnt. A linear fit to the relation between these quantities yields log LHα = (35.6 ± 0.4) + (2.87 ± 0.2) log σnt, in agreement with previous studies. We compute the mass of each HII region using both the virial theorem and the Hα luminosity, confirming that, though these estimates do not coincide exactly, they are comparable within the uncertainties and consequently that the HII regions in our sample are approximately virialized.

Does the Milky Way Produce a Nuclear Galactic Wind?

We detect high-velocity absorbing gas using Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer medium resolution spectroscopy along two high-latitude AGN sight lines (Mrk 1383 and PKS 2005-489) above and below the Center (GC). These absorptions are most straightforwardly interpreted as a wind emanating from the GC which does not escape from the Galaxy's gravitational potential. Spectra of four comparison B stars are used to identify and remove foreground velocity components from the absorption-line profiles of O VI, N V, C II, C III, C IV, Si II, Si III, and Si IV. Two high-velocity (HV) absorption components are detected along each AGN sight line, three redshifted and one blueshifted. Assuming that the four HV features trace a large-scale wind emanating from the GC, the blueshifted absorber is falling toward the GC at a velocity of 250 +/- 20 km/s, which can be explained by Galactic fountain material that originated in a bound wind. The other three absorbers represent outflowing material; the largest derived outflow velocity is +250 +/- 20 km/s, which is only 45% of the velocity necessary for the absorber to escape from its current position in the gravitational potential. All four HV absorbers are found to reach the same maximum height above the plane (|z_max| = 12 +/- 1 kpc), implying that they were all ejected from the GC with the same initial velocity. The derived metallicity limits of >10-20% Solar are lower than expected for material recently ejected from the GC unless these absorbers also contain significant amounts of hotter gas in unseen ionization stages.

A Slowly Expanding Disk and Fast Bipolar Outflow from the S Star π1Gruis

We study the molecular outflow of the nearby evolved S star π1 Gru. We imaged the outflow in CO J = 2-1 and dust continuum with the Submillimeter Array. The CO emission was detected over a very broad velocity width of ~90 km s-1. Our high-resolution images show that the outflow at low velocities (≤15 km s-1) is elongated east-west and at high velocities (≥25 km s-1) is displaced north (at redshifted velocities) and south (blueshifted velocities) of center as defined by the dust continuum source. We model the spatial-kinematic structure of the low-velocity outflow as a flared disk with a central cavity of radius 200 AU and an expansion velocity of 11 km s-1, inclined by 55° to our line of sight. We attribute the high-velocity component to a bipolar outflow that emerges perpendicular to this disk with a velocity of up to ~45 km s-1. This high-velocity outflow may play an important role in shaping the gas envelope previously ejected by the AGB star and thus produce a bipolar morphology when the object evolves into a proto-planetary nebula.