A survey of SiO 5 → 4 emission towards outflows from massive young stellar objects (original) (raw)
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A survey of SiO 5-4 emission towards outflows from low-luminosity protostellar candidates
2003
SiO abundances of 10^(-8) to 8x10^(-7) are derived from LTE analysis. For 2 sources we have additional transitions which we use to conduct statistical equilibrium modeling to estimate the gas density in the SiO-emitting regions. For HH25MMS these results suggest that the SiO emission arises in a higher-density region than the methanol previously observed. We find that the most likely explanation for the preferential detection of SiO emission towards class 0 sources is the greater density of those environments, reinforced by higher shock velocities. We conclude that while not all class 0 sources exhibit SiO emission, SiO emission is a good signpost for the presence of class 0 sources.
A Survey of SiO 5 → 4 Emission toward Outflows from Low‐Luminosity Protostellar Candidates
The Astrophysical Journal, 2004
We have observed the SiO J=5→4 line towards a sample of 25 low-luminosity (L * < 10 3 L ⊙ ) protostellar outflow systems. The line was detected towards 7 of the 25 sources, a detection rate of 28 per cent. The majority (5 out of 7) of sources detected were of class 0 status. We detected a higher fraction of class 0 sources compared with the class I and II sources, although given the small numbers involved the significance of this result should be regarded as tentative. Most of the detected sources showed emission either at or close to the central position, coincident with the protostar. In four cases (HH 211, HH 25MMS, V-380 Ori NE and HH 212) emission was also detected at positions away from the center, and was stronger than that observed at the centre position.
A survey of SiO emission towards interstellar masers
Astronomy and Astrophysics Supplement Series, 1998
We have conducted a survey of SiO emission towards galactic H 2 O and OH masers and ultracompact HII regions using the 15-m SEST and the 20-m Onsala telescope. With the SEST the transitions (v = 0, J = 2 − 1) and (v = 0, J = 3−2) of SiO at 3 and 2 mm were measured simultaneously. With Onsala only the (v = 0, J = 2 − 1) line was accessible. Altogether 369 objects were observed and SiO was detected towards 137 of them. The detection rate is highest towards the most intense H 2 O masers, which probably require powerful shocks to be excited. The SiO detection rate correlates also with the integrated farinfrared flux density and the FIR luminosity of the associated IRAS point source, indicating that the occurrence of shocks is related to the amount of radiation from the central stellar source(s). For flux and luminosity limited samples the SiO detection rate is higher in the inner 7 kpc from the galactic centre than elsewhere. This suggests that dense cores belonging to the so called "molecular ring" provide particularly favourable conditions for the production of gaseous SiO. The full widths above 2σ of the SiO(J = 2 − 1) lines, which are likely to be related to the associated shock velocities, range from 2 to 60 km s −1 except for the line in Ori KL which has a full width of about 100 km s −1. The median of our sample is 19 km s −1. The SiO lines are singlepeaked and the peak velocities are always close to the ambient cloud velocity as determined from published CS observations. These line characteristics are compared with the predictions of kinematical bow-shock models. The SiO line shapes correspond with the model of Raga & Cabrit (1993) where the emission arises from turbulent wakes behind bow-shocks. However, the number of symmetric, rel-Send offprint requests to: J. Harju The entire Tables B.1 and B.2 and the spectra of all the detected SiO sources are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html atively narrow profiles indicates that at least in some of the observed sources SiO emission arises also from the quiescent gas component. We suggest that this is due to evaporation of silicon compounds from grain mantles and their reprocessing to SiO in dense quiescent gas according to the model of McKay (1995, 1996). These reactions may be initiated and sustained by ionizing radiation from shocks, in the same way as the enhancement of HCO + near Herbig-Haro objects has been explained in the model of Wolfire & Königl (1993). The excitation temperatures of SiO(J = 2 − 1) and (J = 3 − 2) transitions were determined towards three strong sources using measurements in isotopically substituted SiO. In all three sources the transitions are clearly subthermally excited, implying moderate densities (< 3 10 6 cm −3) in the SiO emission regions.
Observations of high-J SiO emission along the HH211 outflow
Astronomy and Astrophysics, 2002
Spectra of the pure rotational SiO J = 11-10 and J = 8-7 lines, at 477.5 GHz and 347.3 GHz respectively, have been obtained along the HH211 protostellar jet. Bright emission has been observed localized inside about 15 of projected distance from the central source, where a compact and collimated SiO jet was previously discovered by means of SiO J = 1-0 interferometric observations (Chandler & Richer 2001). The detection of the high-J lines testifies for the extreme conditions of density and temperature of the SiO emission. Values of T > 250 K and n H2 ∼ 2−5×10 6 cm −3 are inferred from the observed line ratios, while a SiO abundance in the range ∼10 −7 −10 −6 has been estimated through a comparison with the CO rotational lines at J > 14 observed by the ISO Long Wavelength Spectrometer. Both the estimated physical conditions and abundance are in agreement with a picture in which the observed SiO emission directly arises at the front of a C-type shock with v s < 35 km s −1 , where all the silicon released from the grains by sputtering and/or grain-grain collisions is converted into gas-phase SiO.
SiO Outflows as Tracers of Massive Star Formation in Infrared Dark Clouds
The Astrophysical Journal, 2021
To study the early phases of massive star formation, we present ALMA observations of SiO(5-4) emission and VLA observations of 6 cm continuum emission towards 32 Infrared Dark Cloud (IRDC) clumps, which are spatially resolved down to 0.05 pc. Out of the 32 clumps observed, we have detected SiO emission in 20 clumps, and in 11 of them it is relatively strong and likely tracing protostellar outflows. Some SiO outflows are collimated, while others are less well ordered. There is evidence for episodic ejection events, as well as multiple outflows originating from scales of 0.1 pc. For the six strongest SiO outflows, we estimate basic outflow properties. We do not see clear dependence of the degree of collimation of the outflows on core mass, luminosity and evolutionary stage. In our entire sample, where there is SiO emission, we always find 1.3 mm continuum emission and some infrared emission nearby, but not vice versa. We build the spectral energy distributions (SEDs) of all the cores with 1.3 mm continuum emission and fit them with radiative transfer (RT) models. The low luminosities and stellar masses returned by SED fitting suggest these are early stage protostars. We see a slight trend of increasing SiO line luminosity with bolometric luminosity, which suggests more powerful shocks in the vicinity of more massive YSOs. However, we do not see a clear relation between the SiO luminosity and the evolutionary stage indicated by L/M. We conclude that as a protostar approaches a bolometric luminosity of ∼ 10 2 L , the shocks in the outflow are generally strong enough to form SiO emission. The VLA 6 cm observations toward the 15 clumps with the strongest SiO emission detect emission in four clumps, which is likely to be shock ionized jets associated with the more massive of these protostellar cores.
SiO in G34.26: Outflows and shocks in a high mass star forming region
Astronomy and Astrophysics, 2001
We have looked for SiO emission as evidence of shocks in the high mass star formation region G34.26+0.15. JCMT, VLA and FCRAO observations show that SiO emission is widespread across the region. The SiO emission highlights a massive, collimated outflow and other regions where stellar winds are interacting with molecular clumps. As in other star forming regions, there is also SiO at ambient velocities which is related to the outflow activity. No strong SiO abundance enhancement was measured in either the outflow or the low velocity gas, though abundances up to 10 −8 are possible if the SiO is locally enhanced in clumps and optically thick. SiO emission is not detected from the hot core itself, indicating either that SiO is not strongly enhanced in the hot core or that column densities in the region where grain mantle evaporation has taken place are low. In line of sight spiral arm clouds, we measure a SiO abundance of 0.4-2 × 10 −10 , consistent with previous estimates for quiescent clouds.
SiO outflows in high-mass star forming regions: A potential chemical clock?
Astronomy & Astrophysics, 2011
Context. Some theoretical models propose that O-B stars form via accretion, in a similar fashion to low-mass stars. Jet-driven molecular outflows play an important role in this scenario, and their study can help to understand the process of high-mass star formation and the different evolutionary phases involved. Aims. Observations towards low-mass protostars so far favour an evolutionary picture in which jets are always associated with Class 0 objects while more evolved Class I/II objects show less evidence of powerful jets. The present study aims at checking whether an analogous picture can be found in the high-mass case. Methods. The IRAM 30-m telescope (Spain) has been used to perform single-pointing SiO(2-1) and (3-2) observations towards a sample of 57 high-mass molecular clumps in different evolutionary stages. Continuum data at different wavelengths, from mid-IR to 1.2 mm, have been gathered to build the spectral energy distributions of all the clumps and estimate their bolometric luminosities. Results. SiO emission at high velocities, characteristic of molecular jets, is detected in 88% of our sources, a very high detection rate indicating that there is ongoing star formation activity in most of the sources of our sample. The SiO(2-1) luminosity drops with L bol /M, which suggests that jet activity declines as time evolves. This represents the first clear evidence of a decrease of SiO outflow luminosity with time in a homogeneous sample of high-mass molecular clumps in different evolutionary stages. The SiO(3-2) to SiO(2-1) integrated intensity ratio shows only minor changes with evolutionary state.
SiO and CH 3 CCH abundances and dust emission in high-mass star-forming cores
Astronomy and Astrophysics, 2006
Aims. The main goal of the present study is to determine the fractional SiO abundance in high-mass star-forming cores, and to investigate its dependence on the physical conditions. In this way we wish to provide constraints on the chemistry models concerning the formation of SiO in the gas phase or via grain mantle evaporation. The work addresses also CH 3 CCH chemistry as the kinetic temperature is determined using this molecule. Methods. We estimate the physical conditions of 15 high-mass star-forming cores and derive the fractional SiO and CH 3 CCH abundances in them by using spectral line and dust continuum observations with the SEST.
The Astrophysical Journal, 2016
NGC 2264-C is a high-mass protocluster where several star-formation events are known to have occurred. To investigate whether past protostellar activity has left a chemical imprint in this region, we mapped it in SiO(J = 2 − 1), a shock tracer, and several other molecular lines with the Nobeyama 45 m telescope. Our observations show the presence of a complex network of protostellar outflows. The strongest SiO emission lies beyond a radius of ∼ 0.1 pc with respect to the center of the clump, and is characterized by broad (> 10 km s −1) lines and abundances of ∼ 1.4 × 10 −8 with respect to H 2. Interestingly, SiO appears relatively depleted (χ SiO ∼ 4 × 10 −9) within this radius, despite it being affected by molecular outflow activity. We attribute this to fast condensation of SiO back onto dust grains and/or rapid gas-phase destruction of SiO, favored by the high density present in this area (> 10 6 cm −3). Finally, we identify a peripheral, narrow-line (∼ 2 km s −1) component, where SiO has an abundance of a few times 10 −11. After considering different options, we conclude that this weak emission may be tracing protostellar shocks from the star formation episode that preceded the current one, which have decelerated over time and eventually resulted in SiO being largely depleted/destroyed. Alternatively, a population of unresolved low-mass protostars may be responsible for the narrow SiO emission. Highangular resolution observations are necessary to distinguish between these two possibilities and thus understand the role of SiO as a chemical tracer of past star-formation episodes in massive protoclusters.