Methanol and Silicon Monoxide Observations toward Bipolar Outflows Associated with Class 0 Objects (original) (raw)

A survey of SiO 5 → 4 emission towards outflows from massive young stellar objects

Monthly Notices of the Royal Astronomical Society, 2007

Results are presented of a survey of SiO 5→4 emission observed with the James Clerk Maxwell Telescope (JCMT) towards a sample of outflows from massive young stellar objects. The sample is drawn from a single-distance study by Ridge & Moore and allows the reasons that govern the detectability of SiO to be explored without the bias introduced by observing sources at different distances. This is the first such unbiased survey of SiO emission from massive outflows. In a sample of 12 sources, the 5→4 line was detected in 5, a detection rate of 42 per cent. This detection rate is higher than that found for a sample of low-luminosity outflow sources, although for sources of comparable luminosity, it is in good agreement with the results of a previous survey of high luminosity sources. For most of the detected sources, the 5→4 emission is compact or slightly extended along the direction of the outflow. NGC 6334I shows a clear bipolar flow in the 5→4 line. Additional data were obtained for W3-IRS5, AFGL 5142 and W75N for the 2→1 transition of SiO using the Berkeley-Illinois-Maryland Association (BIMA) millimetre interferometer. There is broad agreement between the appearance of the SiO emission in both lines, though there are some minor differences. The 2→1 emission in AFGL 5142 is resolved into two outflow lobes which are spatially coincident on the sky, in good agreement with previous observations. In general the SiO emission is clearly associated with the outflow. Simple analysis and radiative transfer modelling of the detected sources yield similar SiO column densities. The abundance of SiO is ∼ 0.1-7.0 × 10 −9 , and the H 2 number density is within a factor of two of 10 5 cm −3 . However, the temperature is not constrained over the range 50-150 K. The primary indicator of SiO 5→4 detectability is the outflow velocity, i.e. the presence of SiO is an indicator of a high velocity outflow. This result is consistent with the existence of a critical shock velocity required to disrupt dust grains and subsequent SiO formation in post-shock gas. There is also weak evidence that higher luminosity sources and denser outflows are more likely to be detected.

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.

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.

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 emission from the Galactic Center Molecular Clouds

1997

We have mapped the J=1 → 0 line of SiO in a 1 ◦ ×12 ′ (l×b) region around the Galactic center (GC) with an angular resolution of 2 ′ (∼4 pc). In contrast to the spatial distribution of other high dipole moment molecules like CS, whose emission is nearly uniform, the SiO emission is very fragmented and it is only associated with some molecular clouds. In particular, it is remarkable that the SiO emission closely follows the non-thermal radio arc in the GC. The SiO clouds are more extended than the beam with typical sizes between 4 and 20 pc. High angular resolution (26 ′ ′ ) mapping in the J=2 → 1 line of SiO toward the molecular clouds in Sgr B2 and Sgr A shows that the SiO emission is relatively smooth with structures of typically 2 pc. From the line intensities of the J=2 → 1, J=3 → 2 and J=5 → 4 transitions of SiO we derive H2 densities for these clouds of a few 10 4 cm −3. The SiO fractional abundances are ∼ 10 −9 for the SiO clouds and < ∼ 10−10 for the other molecular cloud...

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.

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 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.

Detection of a dense SiO jet in the evolved protostellar phase

2021

Jets and outflows trace the accretion history of protostars. High-velocity molecular jets have been observed from several protostars in the early Class 0 phase of star formation, detected with the highdensity tracer SiO. Until now, no clear jet has been detected with SiO emission from isolated evolved Class I protostellar systems. We report a prominent dense SiO jet from a Class I source G205S3 (HOPS 315: Tbol ∼ 180 K, spectral index ∼ 0.417), with a moderately high mass-loss rate (∼ 0.59 × 10−6 M yr−1) estimated from CO emission. Together, these features suggest that G205S3 is still in a high accretion phase, similar to that expected of Class 0 objects. We compare G205S3 to a representative Class 0 system G206W2 (HOPS 399) and literature Class 0/I sources to explore the possible explanations behind the SiO emission seen at the later phase. We estimate a high inclination angle (∼ 40◦) for G205S3 from CO emission, which may expose the infrared emission from the central core and misle...