SiO Observations Research Articles

Numerical simulations for the interaction of the NGC 1333 IRAS 4A outflow and an ambient cloud

NGC 1333 contains numerous young stellar objects and outflows and is a well-studied star formation region. High resolution SiO observations of the NGC 1333 IRAS 4A region showed a highly collimated outflow with a substantial deflection angle. It was also suggested by the observations that the deflection was due to the interaction of the outflow and a dense cloud core (Choi 2005a, 2005b). In order to make a detailed model of the deflected outflow, we have carried out three-dimensional hydrodynamic simulations of outflow/cloud interactions with a hydrodynamic code based on the TVD scheme. In our models, an initial outflow with number density 10 cm−3 and temperature 104 K interacts with a spherical cloud with a power-law density distribution. The cloud has a uniform temperature of 10 K and is surrounded by a homogeneous gas of density 100 cm−3 and temperature 10 K. The radius of the cloud is 0.02 pc, and the outflow has a sectional radius 300 AU. Through the numerical experiments, we found that the deflection angle is mainly determined by the impact parameter and the density ratio between the outflow and the impact zone of the cloud. The deflection angle is, however, not sensitive to the velocity of outflow. Using initial conditions and parameters which are particularly suitable for NGC 1333 IRAS 4A, we can reproduce its bent morphology. We therefore confirm that the northeastern deflected outflow of the NGC 1333 IRAS 4A may be colliding with a dense cloud core and deflected as a result.

Time Monitoring Observations of SiO J = 2–1 and J = 3–2 Maser Emission toward Late‐Type Stars

We present the results of simultaneous time monitoring observations of SiO J = 2-1 and J = 3-2 maser emission for 10 late-type stars (8 Mira variables, 1 OH/IR star, and 1 supergiant) with the 14 m radio telescope at Taeduk Radio Astronomy Observatory from 1999 January to 2001 February. The SiO v = 1, J = 2-1 and J = 3-2 maser emission was detected at almost all observational epochs. The SiO v = 2, J = 2-1 maser was detected from 4 late-type stars (VY CMa, R Cas, χ Cyg, R Leo) and the v = 2, J = 3-2 maser was detected from 7 stars (R Aqr, TX Cam, R Cas, χ Cyg, W Hya, R Leo, IK Tau). The v = 3, J = 2-1 and J = 3-2 masers were also detected from χ Cyg and TX Cam, respectively. Based on these observational data, line profile and peak velocity variations with respect to stellar velocity, antenna temperatures, and their ratio variations as a function of optical phase of central star were investigated. As main results, the line profile and the peak velocity variation of the v = 1, J = 3-2 maser with pulsation phase was found to differ from the v = 1, J = 2-1 transition. Similarly, the J = 2-1 and J = 3-2 transitions also differ between rovibrational transitions at a given pulsation phase. However, it is difficult to find significant correlations between the peak velocity variation relative to the stellar velocity of either the J = 3-2 or J = 2-1 transitions over pulsation phase, due to limited time sampling in these data. The peak and integrated antenna temperature (PT and IT) ratios among rotational ladders and vibrational states are investigated. These ratios between rotational ladders of the v = 1, J = 2-1, and J = 3-2 masers are averaged to be the peak antenna temperature ratio, PT(v = 1, J = 3-2)/PT(v = 1, J = 2-1) ≈ 0.29, and the integrated antenna temperature ratio, IT(v = 1, J = 3-2)/IT(v = 1, J = 2-1) ≈ 0.21, respectively. In the v = 2 state, these ratios are PT(v = 2, J = 3-2)/PT(v = 2, J = 2-1) ≈ 7.94 and IT(v = 2, J = 3-2)/IT(v = 2, J = 2-1) ≈ 8.50, respectively. The peak and integrated antenna temperature ratios between vibrational states are also averaged to be PT(v = 2, J = 3-2)/PT(v = 1, J = 3-2) ≈ 1.29, IT(v = 2, J = 3-2)/IT(v = 1, J = 3-2) ≈ 1.02, PT(v = 2, J = 2-1)/PT(v = 1, J = 2-1) ≈ 0.06, and IT(v = 2, J = 2-1)/IT(v = 1, J = 2-1) ≈ 0.05, respectively. These intensity ratios for the v = 2, J = 2-1 and v = 2, J = 3-2 masers suggest that line overlaps operating in the v = 2, J = 2-1 transition do not similarly affect the v = 2, J = 3-2 transition.

Kinematics of SiOJ = 8–7 Emission towards the HH 212 Jet

Abstract We present SiO $J = 8 \hbox{--} 7$ (347.3 GHz) observations towards HH 212 (Herbig-Haro object 212) using the ASTE (Atacama Submillimeter Telescope Experiment) telescope. Our observations with a $22^{\prime\prime}$-diameter beam show that the SiO emission is highly concentrated within $1'$ of the driving source. We carefully compare the SiO observations with archival $\mathrm{H}_2$ 1–0 S(1) images and published $\mathrm{H}_2$ echelle spectra. We find that, although the SiO velocities closely match the radial velocities seen in $\mathrm{H}_2$, the distributions of $\mathrm{H}_2$ and SiO emission differ markedly. We attribute the latter to the different excitation conditions required for $\mathrm{H}_2$ and SiO emission, particularly the higher critical density ($n_{\mathrm{H}_2} \sim 10^8 \,\mathrm{cm}^{-3}$) of the SiO $J = 8 \hbox{--} 7$ emission. The kinematic similarities imply that the $\mathrm{H}_2$ and SiO are associated with the same internal working surfaces. We conclude that the SiO $J = 8 \hbox{--} 7$ emission has a potential for probing the jet/wind launching region through interferometric observations in the future, particularly for the youngest, most deeply embedded protostars where IR observations are not possible.

Molecular abundance variations near our galactic center

Millimeter-wave observations of CO, HCO+, HNCO, and SiO molecular lines toward Sgr A show that the prominent gas condensations in this region differ significantly in their chemical properties, which may be a result of gradients in the physical conditions as a function of location. HNCO and SiO observations suggest that M−0.13−0.08 (the +20kms−1 cloud) appears to consist of two different components, M−0.13−0.08a and M−0.13−0.08b, with LSR velocities of about +25 and +5kms−1, respectively. The clump M−0.13−0.08a (the +25kms−1 cloud) seems to be located very close to Sgr A East and the observed enhancement of HNCO and SiO may result from the interaction with Sgr A East. The molecular gas clump M−0.02−0.07 (the +50kms−1 cloud) shows the strongest 13CO emission among the identified clouds in this region, and is the most massive condensation (⩾3×105M⊙), but may be located closer to us than other clouds, since it appears to be chemically quiescent and shade the “inter-cloud region” where the HCO+/13CO ratio is enhanced. The −30kms−1 component shows a similar morphology to the HCO+ enhanced “inter-cloud” region. M+0.07−0.08 and M+0.11−0.08 show strong HCO+ 1–0 emission, and appear to consist of one cloud (the HCO+ cloud) in this observation. The HCO+/13CO abundance ratio is enhanced by a factor of 2–3 toward this HCO+ cloud and the inter-cloud region between l=0.1° and 0° near to Sgr A East, compared to other clouds observed in this region. This relative enhancement of HCO+ is thought to result from interaction with Sgr A East.

The structure of the Onsala 1 star forming region

We present new high-sensitivity high-resolution mm-wave observations of the Onsala 1 ultra-compact HII region that bring to light the internal structure of this massive star forming cloud. The 1.2 mm continuum map obtained with the IRAM 30-m radiotelescope (~11″ resolution) shows a centrally peaked condensation of 1´ size (~0.5 pc at the assumed distance of 1.8 kpc) which has been further investigated at higher resolution in the 3 mm continuum and in the emission lines of H13CO+ 1–0 and SiO 2–1 with the IRAM Plateau de Bure interferometer. The 3 mm data, with a resolution of ~5″ 4″, display an unresolved continuum source at the peak of the extended 1.2 mm emission and closely associated with the ultra-compact HII region. The H13CO+ map traces the central condensation in good agreement with previous NH3 maps of Zheng et al. ([CITE]). However, the velocity field of this central condensation, which was previously thought to arise in a rapidly rotating structure, is better explained in terms of the dense and compact component of a bipolar outflow. This interpretation is confirmed by SiO and CO observations of the full region. In fact, our new SiO data unveil the presence of multiple (at least 4) outflows in the region. In particular, there is an important center of outflow activity in the region about 1′ north of the UCHII region. Indeed the different outflows are related to different members of the Onsala 1 cluster. The data presented here support a scenario in which massive star formation begin much later in the evolution of a cluster and/or the phases of UCHII regions last for much longer than 105 yr.

Massive Molecular Outflows at High Spatial Resolution

We present high-spatial resolution Plateau de Bure Interferometer CO(2-1) and SiO(2-1) observations of one intermediate-mass and one high-mass star-forming region. The intermediate-mass region IRAS20293+3952 exhibits four molecular outflows, one being as collimated as the highly collimated jet-like outflows observed in low-mass star formation sources. Furthermore, comparing the data with additional infrared H2 and cm observations we see indications that the nearby ultracompact HII region triggers a shock wave interacting with the outflow. The high-mass region IRAS19217+1651 exhibits a bipolar outflow as well and the region is dominated by the central driving source. Adding two more sources from the literature, we compare position-velocity diagrams of the intermediate- to high-mass sources with previous studies in the low-mass regime. We find similar kinematic signatures, some sources can be explained by jet-driven outflows whereas other are better constrained by wind-driven models. The data also allow to estimate accretion rates varying from a few times 10^{-5}Msun/yr for the intermediate-mass sources to a few times 10^{-4}Msun/yr for the high-mass source, consistent with models explaining star formation of all masses via accretion processes.

SiO as a chemical signature of outflows from bright, compact sources in MSX IR-dark clouds

The line profiles of dense cores in infrared-dark clouds indicate the presence of young stellar objects (YSOs), but the youth of the YSOs and the large distances to the clouds make it difficult to distinguish the outflows that normally accompany star formation from turbulence within the cloud. We report here the first unambiguous identification of a bipolar outflow from a young stellar object (YSO) in an infrared-dark cloud, using observations of SiO to distinguish the relatively small amounts of gas in the outflow from the rest of the ambient cloud. Key words: infrared-dark clouds, star formation, bipolar outflows, SiO, G81.56+0.10.

Dimerlike positional correlation and resonant transmission of electromagnetic waves in aperiodic dielectric multilayers

In this paper, we investigate transmission of electromagnetic wave through aperiodic dielectric multilayers. A generic feature shown is that the mirror symmetry in the system can induce the resonant transmission, which originates from the positional correlations ~for example, presence of dimers! in the system. Furthermore, the resonant transmission can be manipulated at a specific wavelength by tuning aperiodic structures with internal symmetry. The theoretical results are experimentally proved in the optical observation of aperiodic SiO 2 /TiO2 multilayers with internal symmetry. We expect that this feature may have potential applications in optoelectric devices such as the wavelength division multiplexing system.

Thermal SiO observations of a shell attached to the nonthermal filaments in Sgr A

The CS observations with NRO 45 m telescope reveal that a dense molecular shell is located between Sgr A and the nonthermal filaments of the radio arc, and that the shell shows an interacting feature with the nonthermal filaments (Tsuboi et al. 1997). The shell is associated with X-ray emission observed with ASCA and Chandra (Yusef-Zadah et al. 2002). These result suggests the shell is formed by a shock. The SiO lines in the v = 0 state are thermally excited and are thought to be a shock tracer. They are good probes to investigate the physical property of the shell. We observed the shell in SiO (J = 1 − 0, v = 0) and SiO (J = 2 − 1, v = 0) using the NRO 45 m telescope. Features associated with the shell clearly appear in both the SiO lines. The morphology of the shell in both SiO lines after adjusting the beamsize effect is similar in l − b − v 3-dimensional space. The intensity ratio of the two SiO lines (J = 2 − 1 over J = 1 − 0) is uniform over the shell, suggesting the shell is uniform in density. We estimate the average value of the ratio R2−1/1−0 ≈ 0.9, which means the molecular gas density is about 105 cm−3 using multi-level population analysis with the LVG approximation. The morphology of the shell in SiO lines is quite similar to in the CS line in l − b − v 3-dimensional space. The intensity ratio of SiO (J = 1 − 0) to CS (J = 1 − 0) is almost uniform over the shell and RSiO/CS ≈ 0.24. The ratio of the SiO (J = 1− 0) line over the CS (J = 1− 0) line is about 0.24, which means the relative abundance of SiO over CS, X(SiO)/X(CS) ≈ 0.05 − 0.13 using multi-level population analysis with the LVG approximation. It is close to the value found in an SNR shell.

Looking for dust and molecules in Nova V4743 Sagittarii

We present 1.2 mm continuum images and spectral line observations of CO(1--0) and SiO(3--2) rotational transitions of the recent nova V4743 Sgr. The nova is detected at 1.2 mm showing a variable millimetre emission. Only upper limits of T_A* = 0.06 K for CO and T_A* = 0.03 K for SiO could be derived. We discuss the results in terms the nature of the millimetre emission favouring dust from a phase before the recent outburst as the likely radiating source. We also comment on the possibility of free-free emission from the ionised shell as the source of the measured millimetre radiation.

Circular polarization of water masers in the circumstellar envelopes of late type stars

We present circular polarization measurements of circumstellar H2O masers. The magnetic fields in circumstellar envelopes are generally examd. by polarization observations of SiO and OH masers. SiO masers C probe the high temp. and d. regime close to the central star. OH masers are found at much lower densities and temps., generally much further out in the circumstellar envelope. The circular polarization detected in the (616-523) rotational transition of the H2O maser can be attributed to Zeeman splitting in the intermediate temp. and d. regime. The magnetic fields are derived using a general, LTE Zeeman anal. as well as a full radiative transfer method (non-LTE), which includes a treatment of all hyperfine components simultaneously as well as the effects of satn. and unequal populations of the magnetic substates. The differences and relevances of these interpretations are discussed extensively. We also address a non-Zeeman interpretation as the cause for the circular polarization, but this is found to be unlikely. We favor the non-LTE anal. The H2O masers are shown to be unsatd., on the basis of their line widths and the lack of linear polarization. The field strengths are compared with previous detections of the magnetic field on the SiO and OH masers. Assuming a r-2 dependence of the magnetic field on the distance to the star, similar to a solar-type magnetic field, our results seem to indicate that we are probing the highest d. maser clumps at the inner edge of the H2O maser region. This allows us to est. the d. of the clumps, and the extent of the H2O maser region. We show that the magnetic pressure dominates the thermal pressure by a factor of 20 or more. We also give an order of magnitude est. of the magnetic field on the surface of the stars. In particular we discuss the differences between supergiants and Mira variable stars. [on SciFinder (R)]

Circular polarization of circumstellar water masers around S Per

We present the first circular polarization measurements of circumstellar H2O masers. Previously the magnetic field in circumstellar envelopes has been estimated using polarization observations of SiO and OH masers. SiO masers are probes of the high temperature and density regime close to the central star. OH masers are found at much lower densities and temperatures, generally much further out in the circumstellar envelope. The detection of the circular polarization of the (6_16 - 5_23) rotational transition of the H2O maser could be attributed to Zeeman splitting due to the magnetic field in the intermediate temperature and density regime. The fields inferred here agree well with predicted values for a combination of the r^{-2} dependence of a solar-type magnetic field, and the coupling of the field to the high density masing regions. We also discuss the unexpected narrowing of the circular polarization spectrum.

Observations of SiO towards photon dominated regions

We report observations with the IRAM 30-m telescope of SiO(2-1), (3-2), and (5-4) towards the Orion Bar, S 140, NCC 2023 and NGC 7023. We detect SiO towards the Orion Bar and the S 140 photon dominated region (PDR) with an abundance of order 10-11 relative to . Towards the Orion Bar, SiO is extended and is not confined to a layer close to the ionization front. We put limits of 2- on [SiO]/[ ] towards several positions in NGC 2023 and NGC 7023. In order to interpret these data, we present model calculations of the SiO abundance in PDRs as a function of the incident radiation field and consider also the expected Si+ 35 fine structure line intensity. Our data suggest that silicon is very highly depleted onto dust grains within the molecular cloud but that a fraction of the order of ten percent of the silicon comes back into the gas phase in a layer close to the ionization front. We attempted to estimate whether the observed silicon fine structure line emission could originate in fully ionized gas and conclude that in the case of the Orion Bar, it is quite likely. Finally, a by-product of our observations was the detection of the 86773.43 MHz component of the line of HCO in all four sources confirming that this species is relatively abundant in PDRs.

AFM investigation of selective etching mechanism of nanostructured silica

We have developed the atomic force microscope (AFM) for in situ observation of SiO 2 etching in the HF aqueous solution. This work is devoted to the AFM investigation of etching of the SiO 2 surface layer modified by high-dose Fe + ion bombardment. Such samples have a two-phase nanostructure (SiO 2 containing buried Fe nanoparticles). Formation and dissociation of nanorelief during etching was observed in situ with AFM. The computer animation of this phenomenon was made with morphing of the experimental AFM images. The additional in situ registration of the optical absorption of Fe nanoparticles during etching, ex situ AFM and ferromagnetic resonance measurements enable us to propose that observed morphology transformation takes place because the etching rate of Fe nanoparticles is much higher than the SiO 2 etching rate. This etching mechanism was used for computer simulation of the AFM image transformation during etching of the model samples with buried nanoparticles. Good correlation of simulated and experimental AFM images and the corresponding surface roughness parameters vs. etching time confirms that this structural model and the mechanism of selective etching are correct.

Near-IR Observations of IRAS Sources with SiO Masers at the Inner Galactic Bulge

Near-infrared photometric observations in the J-, H-, and K-bands have been made for 86 IRAS sources toward the inner Galactic bulge ($\vert l\vert \lt 3{{}^{\mathrm{\circ}}}$ and $\vert b\vert \lt 3{{}^{\mathrm{\circ}}}$). SiO maser emission has previously been detected in all of these sources; they are well-confirmed, mass-losing, late-type stars having accurate radial velocities derived from SiO observations. For 78 sources, single, unambiguous near-infrared counterparts were found within the errors of the IRAS positions; for the other 8 sources, multiple candidates, candidates with a low confidence level, or candidates overlapped with other stars were found. From the J-, H-, K-band and IRAS 12 and 25 ${\mu \mathrm {m}}$ intensities, we estimated the spectral energy distributions of the sources, and obtained the distances, assuming a constant luminosity. The derived distances of the IRAS/SiO sources are consistent with the current bar model of the Galactic bulge, where the near side of the bar is located in the first quadrant of the galactic longitude. We also reanalyzed the radial velocity shift with distance, and confirmed the presence of streaming motions of stars in the bar-like bulge.

Near-Infrared Observations of IRAS Sources with SiO Masers in the Direction of the Near End of the Galactic Bar

In order to investigate the kinematics of stars in the direction of the near end of the galactic bar, J, H, and K photometric observations were made for 67 IRAS sources in the galactic plane $(15^\circ\lt l\lt 25^\circ$ and $|b| \lt 3^\circ)$. SiO maser emission has previously been detected for all of these sources; they are well-confirmed, mass-losing, late-type stars having accurate radial velocities derived from the SiO observations. For 61 sources, single near-infrared counterparts are found within the $\sim 20^{\prime\prime}$ error ellipse of the IRAS positions, and for the other 6 sources, multiple candidates or candidates with a low confidence level are found. From the J, H, K-band and IRAS 12 and 25 μm intensities, we estimated the spectral energy distributions of the 61 sources. After correcting for interstellar extinction, the bolometric corrections to the 12 μm fluxes of the sources were calculated. The distances from the Sun have been obtained assuming a constant stellar luminosity $(L=8000 L_\odot)$ for the sources. The stars with a large deviation of motion from the galactic rotation are found to fall at a distance of ∼ 5.5 kpc from the Sun. This fact might indicate that the stellar motion deviates strongly from smooth galactic rotation near to the tip of the bar.

In situ observation of discrete glassy SiO 2 formation and quantitative evaluation of glassy SiO 2 in MoSi 2 compacts

Properties, distribution and quantity of grain boundary glassy SiO 2 are very important factors to determine the mechanical properties of MoSi 2 sintered bodies. The formation mechanism of discrete glassy SiO 2 in MoSi 2, and sintering mechanism of a MoSi 2 powder were clarified by in situ SEM observation method using a new type of direct heating stage with small thermal drift. Furthermore, the glassy SiO 2 in sintered MoSi 2 was quantitatively evaluated by the cryogenic specific heat measurements, which has been developed for Si 3N 4 based materials. Combining these method enables precise evaluation of sintered MoSi 2 based material.

Full polarization structure of the OH main-line maser envelopes of W Hydrae

Simultaneous MERLIN observations of the OH 1665- and 1667-MHz maser lines in the circumstellar envelope of the semiregular star W Hya have been taken in all Stokes parameters. The 1665-MHz emission comes from two elongated clusters located 80 au from the star. The 1667-MHz emission arises in an incomplete shell of radius 130 au, with the blueshifted features located in the northern part of the envelope and the redshifted components clustered south of the centre. The circularly polarized maser components exhibit spatial separation along the north–south direction. The linearly polarized components were found from the near side of the envelope. Their polarization position angles indicate that the projected axis of the magnetic field at PA ≃ −20° is consistent with spatial segregation of circular polarization. The intensity of the magnetic field, estimated from a tentative measurement of Zeeman splitting, is about 0.6 mG at the location of the 1667-MHz emission, with the field pointing away from the observer. A small change of position angles of linear polarization observed in both maser lines is interpreted as a weak Faraday effect in the maser regions with an electron density of about 2 cm−3. The overall polarization structure of the envelope suggests an ellipsoidal or weak bipolar geometry. In such a configuration, the circumstellar magnetic field may exert a non-negligible influence on mass loss. The velocity field in the circumstellar envelope recovered from observations of SiO, H2O, OH and CO lines at five radial distances reveals a logarithmic velocity gradient of 0.25 and 0.21 in the 1665- and 1667-MHz maser regions respectively. The acceleration within tens of stellar radii cannot be explained by the classical model of radiation pressure on dust.

Observations of SiO ( v = 0, 1, 2) J = 3–2 and J = 2–1 Emission in Late‐Type Stars

Observations of SiO v = 0, 1, 2, J = 3-2 transitions were carried out for 42 late-type stars containing SiO v = 1, J = 2-1 maser emission with the 14 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO) during 1995 February and 1996 February. Observations of the v = 0, 1, 2, J = 2-1 transitions in the same objects were performed within 40 days of the former observations using the same telescope. For SiO v = 1, J = 3-2 masers, the line was detected in 23 stars giving a detection rate of 55%. Seventeen of them were new detections. For SiO v = 2, J = 3-2 masers, the line was detected in seven stars, four of them being new detections. The v = 2, J = 3-2 line intensities were found at the expected intensity, unlike the anomalously weak emission seen previously in the rare v = 2, J = 2-1 maser. We also report the intensity ratios observed within the vibrational and rotational states.

Enhanced Chemical Abundances in the L1157 Outflow: SiO and CH 3OH Observations

Enhanced Chemical Abundances in the L1157 Outflow: SiO and CH 3OH Observations