SCUBA polarization observations of the magnetic fields in the pre-stellar cores L1498 and L1517B

We have mapped linearly polarized dust emission from the pre-stellar cores L1498 and L1517B with the James Clerk Maxwell Telescope (JCMT) using the Submillimetre Common User Bolometer Array (SCUBA) and its polarimeter (SCUBAPOL) at a wavelength of 850 μm. We use these measurements to determine the plane-of-sky magnetic field orientation in the cores. In L1498, we see a magnetic field across the peak of the core that lies at an offset of ∼19°± 12° to the short axis of the core. This is similar to the offsets seen in previous observations of pre-stellar cores. To the south-east of the peak, in the filamentary tail of the core, we see that the magnetic field has rotated to lie almost parallel to the long axis of the filament. We hypothesize that the field in the core may have decoupled from the field in the filament that connects the core to the rest of the cloud. We use the Chandrasekhar–Fermi (CF) method to measure the plane-of-sky field strength in the core of L1498 to be ∼10 ± 7 μG.
In L1517B, we see a more gradual turn in the field direction from the northern part of the core to the south. This appears to follow a twist in the filament in which the core is buried, with the field staying at a roughly constant ∼25°± 6° offset to the short axis of the filament, consistent with previous observations of pre-stellar cores. Hence these two clouds in an apparently similar evolutionary state, that exhibit similar masses, morphologies and densities, have very different magnetic field configurations. We again use the CF method and calculate the magnetic field strength in L1517B to be ∼30 ± 10 μG. Both cores appear to be roughly virialized. Comparison with our previous work on somewhat denser cores shows that, for the denser cores, thermal and non-thermal (including magnetic) support are approximately equal, while for the lower density cores studied here, thermal support dominates.     

A SCUBA survey of L1689 – the dog that didn't bark

We present submillimetre data for the L1689 cloud in the ρ Ophiuchi molecular cloud complex. We detect a number of starless and pre-stellar cores and protostellar envelopes. We also detect a number of filaments for the first time in the submillimetre continuum that are parallel both to each other, and to filaments observed in the neighbouring L1688 cloud. These filaments are also seen in the ¹³CO observations of L1689. The filaments contain all of the star-formation activity in the cloud. L1689 lies next to the well-studied L1688 cloud that contains the ρ Oph-A core. L1688 has a much more active star-formation history than L1689 despite their apparent similarity in ¹³CO data. Hence, we label L1689 as the dog that didn't bark. We endeavour to explain this apparent anomaly by comparing the total mass of each cloud that is currently in the form of dense material such as pre-stellar cores. We note firstly that L1688 is more massive than L1689, but we also find that when normalized to the total mass of each cloud, the L1689 cloud has a much lower percentage of mass in dense cores than L1688. We attribute this to the hypothesis of Loren that the star formation in the ρ Ophiuchi complex is being affected and probably dominated by the external influence of the nearby Upper Scorpius OB association and predominantly by σ Sco. L1689 is further from σ Sco and is therefore less active. The influence of σ Sco appears none the less to have created the filaments that we observe in L1689.     

Ultra-high-resolution observations of CH in Southern Molecular Cloud envelopes

We present a mini-survey of ultrahigh-resolution spectroscopy (UHRS) of CH towards three southern molecular cloud envelopes. The sightlines are selected to probe physically similar gas in different Galactic environments. With a velocity resolution of ∼0.5 km s⁻¹  ( R =575 000)  these observations resolve most kinematic components of the absorption lines. We do, however, detect one line component in the Lupus region, which is not resolved and for which an upper limit of   b <0.3 km s^-1  is found. We find a correlation between distance of the absorbing gas from the Galactic mid-plane and the fractional abundance of CH. We show that this correlation can be explained as being a result of a fall-off in the ultraviolet radiation field intensity and propose that CH observations in carefully selected sightlines might allow a mapping of the variations in the interstellar radiation field.     

Complex organic molecules in an early stage of protostellar evolution

We have detected the rotational lines of HCOOCH₃ toward a Class 0 low-mass protostar, NGC1333 IRAS4B, which is reported to be extremely young according to the dynamical age of the molecular outflow (a few 100 yr). This suggests that the complex organic molecules appear from the very early stage of protostellar evolution. On the other hand, the complex organic molecules are not detected in a more evolved protostar, L1527. We have also found a similar trend in a massive star forming region, NGC2264. The HCOOCH₃ emission is almost absent toward IRS1, whereas it is concentrated near MMS3, which is younger than IRS1. In addition, the HCOOCH₃ intensity peak is slightly shifted from the dust emission peak, as is seen in the Orion KL Compact Ridge, giving an important clue to solve its origin.     

Dense cores in the L1630 molecular cloud: discovering new protostars with SCUBA

Maps of the 450- and 850-μm dust continuum emission from three star-forming condensations within the Lynds 1630 molecular cloud, made with the SCUBA bolometer array, reveal the presence of four new submillimetre sources, each of a few solar masses (two of which are probably class I and two of which are class 0), as well as several sources the existence of which was previously known. The sources are located in filaments and appear elongated when observed at 450 μm. They probably have dust temperatures in the range 10 to 20 K, in good agreement with previous ammonia temperature estimates. Attempts to fit their structures with power-law and Gaussian density distributions suggest that the central distribution is flatter than expected for a simple singular isothermal sphere.
Although the statistics are poor, our results suggest that the ratio of 'protostellar core' mass to total virial mass may be similar for both large and small condensations.     

Spitzer discovery of very low luminosity objects

The Spitzer Space Telescope allows for the .rst time to search systematically for very low luminosity (≲0.1 L_⊙) objects (VeLLOs) associated with dense molecular cores. They may be the .rst candidate Class 0 sources with sub‐stellar masses. We describe such a source in the dense molecular core L1148. VeLLO natal cores show properties that are unusual for star‐forming cores. The low luminosity and in some cases the lack of prominent out.ow could be the result of the small gas supply near the VeLLO. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A search for propylene oxide and glycine in Sagittarius B2 (LMH) and Orion

We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have been able to put sensitive upper limits on the abundances of both molecules. The 3σ upper limits derived for glycine conformer I are  3.7 × 10¹⁴ cm⁻²  in both Orion-KL and Sgr B2 (LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3σ upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of  7.7 × 10¹² cm⁻²  in both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results have ruled out the detection of glycine (both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of  3.0 × 10¹⁴ cm⁻²  in Orion-KL and  6.7 × 10¹⁴ cm⁻²  in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the interstellar medium, but have not been able to plausibly assign these transitions to any carrier.     

A search for absorption of Mg and Ca compounds in molecular clouds towards Galactic continuum sources

Absorption lines of MgH and CaH N  = 1 − 0 transitions were searched for in foreground molecular clouds towards the continuum sources associated with Sgr B2 (M) and W49A (N). None of these lines was detected with our sensitivity level of ∼20 mK. Millimetric absorption lines of MgO, MgOH, CaO and CaOH were also searched for towards Sgr B2 (M) without success. The fractional abundances relative to molecular hydrogen are ≲ 1.0 × 10⁻¹¹ for MgH, ≲ 7.9 × 10⁻¹³ for MgO, ≲ 1.6 × 10⁻¹⁰ for MgOH, ≲ 1.6 × 10⁻⁹ for CaH, ≲ 2.0 × 10⁻¹² for CaO, and ≲ 2.5 × 10⁻¹⁰ for CaOH, respectively. The low abundances measured in absorption indicate that a significant fraction of interstellar magnesium and calcium cannot be tied up in their monohydrides, monoxides and monohydroxides. The low abundance of MgH also implies that grain-surface chemistry involving magnesium is not efficient and that magnesium is depleted on to grains to a factor of ≳ 10^2.5 in well-shielded molecular clouds.     

C~(18)O Observations of the Dark Molecular Cloud L134 and Gas Depletion onto Dust

We map the dark molecular cloud core of L134 in the C18O (J = 1 - 0) emission line using the PMO 13.7m telescope, and present a contour map of integrated intensity of C18O (J = 1 - 0) emission. The C18O cloud is inside the distribution of extinction AB, the visual extinction of blue light, as well as inside the 13CO cloud in the L134 region. The depletion factors in this C18O cloud are generally greater than unity, which means there is gas depletion onto dust. Since only a minimum AB = 9.7 mag is available, and our observations measure both undepleted and depleted regions along the line of sight, the depletion factors could very likely be larger in the central core than the calculated value. So we conclude that depletion does occur in the bulk of the C18O cloud through a comparison between the C18O and blue extinction maps in the L134 region. There is no direct evidence as yet for star formation in L134, and so cores on the verge of collapse will not be visible in CO and other gas molecules.     

Molecular cores of the high-latitude cloud MBM 40

Towards the high-latitude cloud MBM 40, we identify 3 dense molecular cores of M0.2–0.5 M, and sizes of 0.2 pc in diameter embedded in the H I cloud of 8 M which is observed to be extended along the northeast–southwest direction. The molecular cloud is located almost perpendicularly to the H I emission. We confirm the previous result of Magnani et al. that MBM 40 is not a site for new star formations. We found a very poor correlation between the H I and the IRAS 100 μm emissions, but the CO (1–0) and 100 μm emissions show a better correlation of W_CO/I₁₀₀=1±0.2 K km s⁻¹ (MJy sr⁻¹)⁻¹. This ratio is larger by a factor of ≥5 than in dense dark clouds, which may indicate that the CO is less depleted in MBM 40 than in dense dark clouds.     

Revealing the “fingerprints” of the magnetic precursor of C-shocks

We present the first C-shock and radiative transfer model that calculates the evolution of the line profiles of neutral and ion species like SiO, H¹³CO⁺ and HN¹³C for different flow times along the propagation of the shock through the unperturbed gas. We find that the line profiles of SiO characteristic of the magnetic precursor stage have very narrow linewidths and are centered at velocities close to the ambient cloud velocity, as observed toward the young shocks in the L1448-mm outflow. Consistently with previous works, our model also reproduces the broad SiO emission detected in the high velocity gas in this outflow, for the downstream postshock gas in the shock. This implies that the different velocity components observed in L1448-mm are due to the coexistence of different shocks at different evolutionary stages.     

L 43: the late stages of a molecular outflow

Our new 21-arcsec resolution CO J  = 2 → 1 map of the L 43 dark cloud shows a poorly collimated molecular outflow, with little evidence for wings at velocities 10 km s⁻¹. The outflow appears not to be currently driven by a jet: its structure can instead be modelled as a slowly expanding shell. The shell may be compressed either by a wide-angled wind catching up with an existing shell (as in the case of planetary nebulæ), or by the thermal pressure of a hot low-emissivity medium interior to the shell. The outflow is most probably in a late stage of evolution, and appears to be in the process of blowing away its molecular cloud. We also present a 45-arcsec resolution CO J  = 1 → 0 map of the whole molecular cloud, showing that the outflow structure is clearly visible even in the integrated intensity of this low excitation line, and suggesting that rapid mapping may prove useful as a way of finding regions of outflow activity. We also examine the immediate surroundings of the driving source with 450 μm imaging: this confirms that the outflow has already evacuated a bay in the vicinity of the young stellar object.     

CO abundances in a protostellar cloud: freeze-out and desorption in the envelope and outflow of L483

CO isotopes are able to probe the different components in protostellar clouds. These components, core, envelope and outflow have distinct physical conditions, and sometimes more than one component contributes to the observed line profile. In this study, we determine how CO isotope abundances are altered by the physical conditions in the different components. We use a 3D molecular line transport code to simulate the emission of four CO isotopomers, ¹²CO   J = 2 → 1, ¹³CO J = 2 → 1  , C¹⁸O   J = 2 → 1  and C¹⁷O   J = 2 → 1  from the Class 0/1 object L483, which contains a cold quiescent core, an infalling envelope and a clear outflow. Our models replicate James Clerk Maxwell Telescope (JCMT) line observations with the inclusion of freeze-out, a density profile and infall. Our model profiles of ¹²CO and ¹³CO have a large linewidth due to a high-velocity jet. These profiles replicate the process of more abundant material being susceptible to a jet. C¹⁸O and C¹⁷O do not display such a large linewidth as they trace denser quiescent material deep in the cloud.