James Clerk Maxwell Telescope Data Research Articles

No evidence of phosphine in the atmosphere of Venus from independent analyses

The detection of phosphine (PH3) in the atmosphere of Venus has been recently reported based on millimeter-wave radio observations (Greaves et al. 2020), and its re-analyses (Greaves et al. 2021a/b). In this Matters Arising we perform an independent reanalysis, identifying several issues in the interpretation of the spectroscopic data. As a result, we determine sensitive upper-limits for PH3 in Venus' atmosphere (>75 km, above the cloud decks) that are discrepant with the findings in G2020 and G2021a/b. The measurements target the fundamental first rotational transition of PH3 (J=1-0) at 266.944513 GHz, which was observed with the James Clerk Maxwell Telescope (JCMT) in June 2017 and with the Atacama Large Millimeter/submillimeter Array (ALMA) in March 2019. This line's center is near the SO2 (J=309,21-318,24) transition at 266.943329 GHz (only 1.3 km/s away from the PH3 line) which represents a potential source of contamination. The JCMT and ALMA data, as presented in G2020, are at spectral resolutions comparable to the frequency separation of the two lines. Moreover, the spectral features identified are several km/s in width, and therefore do not permit distinct spectroscopic separation of the candidate spectral lines of PH3 and SO2. We present the radiative transfer modelling we have performed and then discuss the ALMA and JCMT analyses in turn.

C+ distribution around S 1 in ρ Ophiuchi

We analyze a [C II] 158 μm map obtained with the L2 GREAT receiver on SOFIA of the reflection nebula illuminated by the early B star S 1 in the ρ Oph A cloud core. This data set has been complemented with maps of CO(3–2), 13CO(3–2), and C18O(3–2), observed as a part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey, with archival HCO+(4–3) JCMT data, as well as with [O I] 63 and 145 μm imaging with Herschel/PACS. The [C II] emission is completely dominated by the strong emission from the photon dominated region (PDR) in the nebula surrounding S 1 expanding into the dense Oph A molecular cloud west and south of S 1. The [C II] emission is significantly blueshifted relative to the CO spectra and also relative to the systemic velocity, particularly in the northwestern part of the nebula. The [C II] lines are broader toward the center of the S 1 nebula and narrower toward the PDR shell. The [C II] lines are strongly self-absorbed over an extended region in the S 1 PDR. Based on the strength of the [13C II] F = 2–1 hyperfine component, [C II] is significantly optically thick over most of the nebula. CO and 13CO(3–2) spectra are strongly self-absorbed, while C18O(3–2) is single peaked and centered in the middle of the self-absorption. We have used a simple two-layer LTE model to characterize the background and foreground cloud contributing to the [C II] emission. From this analysis we estimated the extinction due to the foreground cloud to be ~9.9 mag, which is slightly less than the reddening estimated toward S 1. Since some of the hot gas in the PDR is not traced by low-J CO emission, this result appears quite plausible. Using a plane parallel PDR model with the observed [O I](145)/[C II] brightness ratio and an estimated FUV intensity of 3100–5000 G0 suggests that the density of the [C II] emitting gas is ~3–4 × 103 cm−3.

H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION

HII regions are particularly interesting because they can generate dense layers of gas and dust, elongated columns or pillars of gas pointing towards the ionizing sources, and cometary globules of dense gas, where triggered star formation can occur. Understanding the interplay between the ionizing radiation and the dense surrounding gas is very important to explain the origin of these peculiar structures, and hence to characterize triggered star formation. G46.5-0.2 (G46), a poorly studied galactic HII region located at about 4 kpc, is an excellent target to perform this kind of studies. Using public molecular data extracted from the Galactic Ring Survey (13CO J=1-0) and from the James Clerk Maxwell Telescope data archive (12CO, 13CO, C18O J=3-2, HCO+ and HCN J=4-3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a complete study of G46, its molecular environment and the young stellar objects placed around it. We found that G46, probably excited by an O7V star, is located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It presents a horse-shoe morphology opening in direction of the cloud. We observed a filamentary structure in the molecular gas likely related to G46 and not considerable molecular emission towards its open border. We found that about 10' towards the southwest of G46 there are some pillar-like features, shining at 8 um and pointing towards the HII region open border. We propose that the pillar-like features were carved and sculpted by the ionizing flux from G46. We found several young stellar objects likely embedded in the molecular cloud grouped in two main concentrations: one, closer to the G46 open border consisting of Class II type sources, and other one mostly composed by Class I type YSOs located just ahead the pillars-like features, strongly suggesting an age gradient in the YSOs distribution.

GROUND-BASED MULTIWAVELENGTH OBSERVATIONS OF COMET 103P/HARTLEY 2

The Jupiter-family comet 103P/Hartley 2 (103P) was the target of the NASA EPOXI mission. In support of this mission, we conducted observations from radio to submillimeter wavelengths of comet 103P in the three weeks preceding the spacecraft rendezvous on UT 2010 November 4.58. This time period included the passage at perihelion and the closest approach of the comet to the Earth. Here we report detections of HCN, H2CO, CS, and OH and upper limits for HNC and DCN towards 103P, using the Arizona Radio Observatory Kitt Peak 12m telescope (ARO 12m) and submillimeter telescope (SMT), the James Clerk Maxwell Telescope (JCMT) and the Greenbank Telescope (GBT). The water production rate, QH2O = (0.67 - 1.07) x 10^28 s^-1, was determined from the GBT OH data. From the average abundance ratios of HCN and H2CO relative to water (0.13 +/- 0.03 % and 0.14 +/- 0.03 %, respectively), we conclude that H2CO is depleted and HCN is normal with respect to typically-observed cometary mixing ratios. However, the abundance ratio of HCN with water shows a large diversity with time. Using the JCMT data we measured an upper limit for the DCN/HCN ratio <0.01. Consecutive observations of ortho- H2CO and para-H2CO on November 2 (from data obtained at the JCMT), allowed us to derive an ortho : para ratio (OPR) ~ 2.12 +/- 0.59 (1sigma), corresponding to Tspin > 8 K (2sigma).

OMC-1: A Cool Arching Filament in a Hot Gaseous Cavity: Geometry, Kinematics, Magnetic Vectors, and Pressure Balance

We have assembled data on large (Galactic shell), middle (filament), and small (protostar) scales. OMC-1 is embedded in a hot cavity. Here we have made multiconstituent (gas/dust/field) homogeneous maps of the central part of the OMC-1 filament, covering an area of 2' ? 2'. We find here that the vertical filament has a turbulent pressure about equal to the magnetic pressure; its total pressure roughly equals that in the surrounding medium. The magnetic field crosses the filament with an estimated strength of 300-350 ?G in the sky plane. It could be an externally wrapped U-shaped magnetic field going around the filament (due to a large shock front traveling in the cavity), or else an internally generated helical field (of unknown origin). Near the OMC-1 map center, we map the low-velocity outflow near IRc2-source I, with a pattern of blue south-southwest gas and red north-northeast gas. Our James Clerk Maxwell Telescope data yield a plane-of-sky field of 2.4-2.6 mG across the outflow; this strength nearly equals the published Zeeman line-of-sight data. Farther out, the Zeeman data show a negative magnetic field, possibly suggesting a pole-on dipolar field.

Rotation of the pre-stellar core L1689B

The search for the onset of star formation in pre-stellar cores has focused on the identification of an infall signature in the molecular line profiles of tracer species. The classic infall signature is a double-peaked line profile with an asymmetry in the strength of the peaks such that the blue peak is stronger. L1689B is a pre-stellar core and infall candidate, but new James Clerk Maxwell Telescope (JCMT) HCO+ line profile data, presented here, confirm that both blue and red asymmetric line profiles are present in this source. Moreover, a dividing line can be drawn between the locations where each type of profile is found. It is argued that it is unlikely that the line profiles can be interpreted with simple models of infall or outflow, and that rotation of the inner regions is the most likely explanation. A rotational model is developed in detail with a new three-dimensional molecular line transport code, and it is found that the best type of model is one in which the rotational velocity profile is in between solid-body and Keplerian. It is first shown that red and blue asymmetric line profiles can be generated with a rotation model entirely in the absence of any infall motion. The model is then quantitively compared with the JCMT data, and an iteration over a range of parameters is performed to minimize the difference between the data and the model. The results indicate that rotation can dominate the line profile shape even before the onset of infall.

The circumstellar environment of IRAS 16293–2422

We present far-infrared (FIR) continuum observations of the deeply embedded source IRAS 16293-2422 performed with the Long Wavelength Spectrometer (LWS) on-board the Infrared Space Observatory (ISO). We also report 450 and 850 μm mapping observations done with the Submillimetre Common-User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT). We combined these observations with IRAS and other JCMT data available in the literature to construct a complete spectral energy distribution (SED) of the source. A spherically symmetric dusty envelope model was used to reproduce the SED and to characterize the circumstellar matter around the object. We call attention to the fact that when using models such as the one presented here, one needs spatial information about the object to distinguish between different possible fits to the SED. A comparison between the intensity profiles at 450 and 850 μm obtained from the SCUBA observations and the profiles predicted by the model allowed us to constrain the size of the envelope and its density distribution. The SED and the 850 μm intensity profile of the source are consistent with a centrally peaked power law dust density distribution of the form p(r) r -p with p = 1.5-2, with a radius R env = 3000-3250 AU, defining a very compact circumstellar envelope. We estimate a bolometric luminosity L bol = 36 L ○. , an envelope mass M env = 3.4 M ○. , and a submillimetre to bolometric luminosity ratio L submm /L bol = 1.9%, confirming that the source shows a submillimetre excess characteristic of Class 0 sources.

JCMT Observations of Cometary Clouds in the Galactic Chimney near W4

Recently, Normandeau and coworkers reported the discovery of a Galactic chimney emerging out of the Galactic plane above a cluster of O stars associated with the W4 H II region. Two compact molecular clouds have survived the evacuation of the chimney and show evidence of dynamical effects from the energetic radiation of the nearby O stars. The age of the star cluster indicates that the clouds have been subject to intense UV radiation for several Myr. We have obtained high-resolution images of the compact heads of these clouds in the CO (2-1) line using the James Clerk Maxwell Telescope (JCMT). We have also obtained CO (3-2) over a more limited area for one of the clouds. Our observations reveal a striking arrow-shaped CO globule, with the symmetry axis of the pointing toward the most luminous cluster star. A large velocity gradient analysis, carried out using both the JCMT data and CO (1-0) observations from the Five College Radio Astronomy Observatory, yields a temperature of 30 K and a density of 104 cm−3 for the molecular gas at the apex. The total mass of molecular hydrogen in the region surveyed in C18O (5.3 pc2) is ~800 M☉. The velocity gradients about the symmetry axis of the arrow are well represented by a simple model of symmetric advance about the cloud center of an ionization front driven by the UV radiation of the nearby O star. The overall morphology and kinematics of the globule are in good agreement with the hydrodynamical simulations of photoevaporation of cometary globules, although for our more massive cloud the survival timescale is much longer.