Organic Chemistry of Southern Sources: Microwave Spectroscopy of Cha-MMS1 and IRAS 15194-5115

We report new spectra of molecule-rich sources in the southern hemisphere obtained using the 22-meter Mopra telescope. Spectra and maps are presented of organic molecules detected between 30 and 50 GHz in the young Class 0 protostar Chamaeleon MMS-1. The large abundances of polyynes, cyanopolyynes and methanol may be indicative of a warm carbon chemistry in the dense gas surrounding this protostar. Spectra are also presented from a 78-96 GHz scan of the carbon-rich AGB star IRAS 15194-5115, including new detections of HC5N, CCS and C13CH

Externally heated protostellar cores in the Ophiuchus star-forming region

We present APEX 218 GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H$_2$CO and c-C$_3$H$_2$ rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H$_2$CO temperatures range between 16 K and 124 K, with the highest H$_2$CO temperatures toward the hot corino source IRAS 16293-2422 (69-124 K) and the sources in the $\rho$ Oph A cloud (23-49 K) located close to the luminous Herbig Be star S 1, which externally irradiates the $\rho$ Oph A cores. On the other hand, the c-C$_3$H$_2$ rotational temperature is consistently low (7-17 K) in all sources. Our results indicate that the c-C$_3$H$_2$ emission is primarily tracing more shielded parts of the envelope whereas the H$_2$CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS 16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.Comment: 19 pages, 9 figures, accepted for publication in Ap

Diffuse interstellar bands and the structure of the ISM

Results are presented of three different studies into the nature of the diffuse interstellar bands, their carriers and the environments in which they are located. 1. Optical observations of small-scale structure in the distribution of large molecules and/or dust grains in the ISM are examined in the first dedicated study of its type. Evidence is presented for variation in the strengths of fifteen out of sixteen measured narrow diffuse interstellar bands, over spatial scales from ~ < 370 AU to ~ < 20000 AU, observed towards the component members of nearby (< 1.5 kpc distant) early-type binary and multiple star systems. Variations in diffuse interstellar band (DIB) equivalent widths of about five to ten percent are found between the sightlines towards rho Oph A and B (separated by approximately 370 AU in the plane of the sky). The lambda 5780, lambda 5797, lambda 5850, lambda 6376, lambda 6379, lambda 6439, lambda 6614 and lambda 6660 DIBs are found to be significantly stronger towards rho Oph B by an amount comparable to the differences in the column densities of interstellar K I and Ca II in these sightlines. The upper limit on the variability of the lambda 6284 DIB is approximately 1.5%. Different DIBs are subject to different degrees of variation, and in some cases different signs of variation, for example the lambda 5850 DIB is stronger towards rho Oph C than rho Oph A, whereas lambda 6614 is stronger towards A than C, proving the existence of chemical differences between the DIB carriers. The lambda 6614 DIB is found to show a variation in its pattern of sub-structure between rho Oph A and C, which, interpreted within the `Webster hypothesis' (Webster 1996), is consistent with a- 4% enhancement in the interstellar [12C]/[13C] ratio towards rho Oph A relative to C. In other star systems observed: The lambda 5780, lambda 6196 and lambda 6614 diffuse interstellar bands are found to be stronger towards ß2 Sco than ß1 Sco (sightlines separated by ~ 2200 AU). The lambda 6614 DIB is found to be stronger towards HD 150136 than HD 150135 (~ 12,500 AU separation) but no significant variation is found in the strengths of any other DIBs in the spectra of this binary system. The lambda 5780, lambda 6196 and lambda 6614 DIBs are detected in the lightly-reddened sightlines towards the two members of the mu Cru system, and are found to be approximately 50 to 200% stronger towards mu2 Cru than mu1 Cru. Weak interstellar K I absorption is detected and is found to be 122 ± 80% stronger (at 1delta- confidence) towards mu2 Cru than mu1 Cru. The lambda 5780, lambda 6196, lambda 6203 and lambda 6614 diffuse interstellar bands are detected in the well-known `time-variable' sightline towards kappa Vel. Spectra are presented that show the interstellar K I column density in this sightline to be N(K I) = 3.43 ±0.13 x 1010 cm-2 in June 2004, corresponding to approximately a 35% increase in N(K I) since the time of the last measurement in March 2002 by Crawford (2002). During this period, the sightline moved ~<5 AU. DIB strengths towards kappa Vel are compared between observations made in January 1995 and June 2004, during which time the sightline moved ~< 25 AU across the interstellar medium (ISM) and the neutral potassium column density approximately doubled. No significant variation in the strength of lambda 5780 is found, with an upper limit on the change in equivalent width of ±41 %. The variation of diffuse interstellar band strengths over small spatial scales is interpreted as due to variations in the abundances of the carriers. Possible causes of small-scale DIB variability are discussed, including the degree of ionisation and excitation of the carriers. 2. The hypothesis that the cyanomethyl anion CH2CN- is responsible for the relatively narrow diffuse interstellar band at 8037.8 ± 0.15 angstrem is examined. The absorption spectrum arising from the 1B1 <-- 1A' origin band transition from the ground electronic state to the first dipole-bound state of the anion is calculated. Assuming that the distribution of ground state rotational level populations is in thermal equilibrium with the 2.74 K cosmic microwave background radiation, the transition results in a rotational contour with a peak wavelength of 8037.78 angstrem. CH2CN- is found to be a plausible candidate for the carrier of the lambda 8037 diffuse interstellar band provided a mechanism exists by which the rotational contour is broadened by an approximately Gaussian dispersion function with a width characterised by a Doppler b parameter between 16 and 33 km s-1 depending on the specific sightline in which the DIB is observed. Doppler broadening is found to be sufficient to cause such a dispersion in heavily-reddened sightlines, as demonstrated by the velocity structure of the interstellar gas in the sightline towards HD 183143, which is examined for K I, Na I, Ca I, Ca II, Ti II, CH, CH+ and CN. Convolution of the calculated CH2CN- transitions with the optical depth profile of either Ca n or Ti n successfully reproduces the profile of the narrow lambda 8037 DIB observed towards HD 183143. The 2.74 K thermal distribution of ground-state rotational level populations may be modified by the nuclear spin statistics of the molecule. This situation is modelled and results in the appearance of additional strong spectral features at around 8024.8 angstrem and 8049.6 angstrem that are not seen in the observed interstellar spectra. If (a) no chemical mechanisms exist for the conversion of `ortho' CH2CN- (hydrogen nuclear spins parallel) to `para' CH2CN' (hydrogen nuclear spins antiparallel) or (b) the CH2CN- formation mechanisms do not result in a distribution of Kä levels approaching a 2.74 K Boltzmann distribution, then it is found that CH2CN' cannot be the carrier of the A8037 diffuse interstellar band. 3. The strengths of diffuse interstellar bands and atomic lines in the ISM of the Large Magellanic Cloud (LMC) are analysed and compared with Galactic data. Using optical spectra obtained along six reddened sightlines towards early-type stars in the LMC, at a resolution of -3 km s'1 and a signal-to-noise of - 200, the velocity structure and column densities of interstellar K I, Na I, Ca II and Ti II are derived. Evidence is presented that the spectrum of diffuse interstellar bands in the LMC is similar (in strength and structure) to that found in the Galaxy, with the measurement of the equivalent widths of eleven DIBs at the Doppler-shifted wavelengths expected for the radial velocity of the LMC, including lambda 4430, lambda 5705, lambda 5780, lambda 5797, lambda 5850, lambda 6196 lambda 6203, lambda 6284, lambda 6376, lambda 6379 and lambda 6614. The observation of lambda 5705, lambda 5850, lambda 6196 and lambda 6203 constitutes the first reported detection of these DIBs in the LMC, and for lambda 5850, in any location outside of the Galaxy. All of the expected DIBs were observed towards the 30 Dor targets Sk -69°223 and Sk -69°243, and with strengths approximately equal to, or only slightly weaker than, those in Galactic `v-type' (strongly UV irradiated) sightlines with similar reddenings and neutral potassium column densities. This result shows that there are interstellar clouds in the vicinity of 30 Dor that provide favourable environments for the existence of DIB carriers. The velocities of the carriers of the lambda 5780, lambda 5797, lambda 5850, lambda 6196, lambda 6379 and lambda 6614 diffuse interstellar bands in the LMC are found to be coincident with the velocities of the peaks of the atomic column density distributions at radial velocities of between 240 and 300 km s-1 relative to the local standard of rest. The least-squares fitted velocity of the A6614 DIB is found to be shifted by - +5 km s-1 relative to the other DIBs in three out of four sightlines. This may be interpreted as evidence that the profile of sub-structure of the lambda 6614 DIB is skewed towards the red in these three sightlines (Sk -68°135, Sk -69°223 and Sk -69°243) to a greater degree than that found in the Galactic ISM. Compared to Galactic trends, the LMC DIBs are found to be weak with respect to the reddening and neutral potassium column density towards Sk -67°2 and Sk -68°135. This may be attributable to a combination of the high UV flux and reduced shielding of interstellar clouds due to the low metallicity of the interstellar gas of the LMC, and results in the destruction of DIB carriers by photodissociation and/or photoionisation. Relative to N(H I) the lambda 6284 DIB observed in four LMC sightlines is shown to be approximately 1/5 to 1/2 of its average strength in the Milky Way. This supports the idea that the metallicity and/or dust-to-gas ratio of the ISM is closely linked with the chemistry that governs the abundance of DIB carriers relative to N(H I). Variations in the N(Ca II)/N(Ti II) ratio are found over at least an order of magnitude in the LMC ISM, and are taken as evidence for significant variation in the Ca n/Ca m ionisation balance. Derived logarithmic titanium depletions are found to be relatively low in the six LMC sightlines studied, with values between approximately -0.8 and -1.9, which are similar to the levels of depletion generally seen in the warm, shocked interstellar medium of the Galaxy

Measurement of CH3_3D on Titan at Submillimeter Wavelengths

We present the first radio/submillimeter detection of monodeuterated methane (CH$_3$D) in Titan's atmosphere, using archival data from of the Atacama Large Millimeter/submillimeter Array (ALMA). The $J_K=2_1-1_1$ and $J_K=2_0-1_0$ transitions at 465.235 and 465.250 GHz ($\sim0.644$ mm) were measured at significance levels of $4.6\sigma$ and $5.7\sigma$, respectively. These two lines were modeled using the Non-linear optimal Estimator for MultivariatE spectral analySIS (NEMESIS) radiative transfer code to determine the disk-averaged CH$_3$D volume mixing ratio = $6.157\times10^{-6}$ in Titan's stratosphere (at altitudes $\gt130$ km). By comparison with the CH$_4$ vertical abundance profile measured by Cassini-Huygens mass spectrometry, the resulting value for D/H in CH$_4$ is $(1.033\pm0.081)\times10^{-4}$. This is consistent with previous ground-based and in-situ measurements from the Cassini-Huygens mission, though slightly lower than the average of the previous values. Additional CH$_3$D observations at higher spatial resolution will be required to determine a value truly comparable with the Cassini-Huygens CH$_4$ measurements, by measuring CH$_3$D with ALMA close to Titan's equator. In the post-Cassini era, spatially resolved observations of CH$_3$D with ALMA will enable the latitudinal distribution of methane to be determined, making this an important molecule for further studies.Comment: 9 pages, 4 figure

Molecular Anions in Protostars, Prestellar Cores and Dark Clouds

From our recent survey work using the Green Bank Telescope, microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H have been detected in six new sources. Using HC3N = 10(exp -9) emission maps, we targeted the most carbon-chain-rich sources for our anion survey, which included the low-mass Class 0 protostar L1251A-IRS3, the prestellar cores L1389-SMM1 and L1512, and the interstellar clouds Ll172A, TMC-1C and L1495B. Derived [C6H(-)]/[C6H] anion-to-neutral ratios are approximately 1-10. The greatest C6H(-) column densities are found in the quiescent clouds TMC-1C and L1495B, but the anion-to-neutral ratios are greatest in the prestellar cores and protostars. These results are interpreted in terms of the physical and chemical properties of the sources, and the implications for molecular cloud chemistry are discussed

A survey of diffuse interstellar bands in the Andromeda galaxy: optical spectroscopy of M31 OB stars

We present the largest sample to-date of intermediate-resolution blue-to-red optical spectra of B-type supergiants in M31 and undertake the first survey of diffuse interstellar bands (DIBs) in this galaxy. Spectral classifications, radial velocities and interstellar reddenings are presented for 34 stars in three regions of M31. Radial velocities and equivalent widths are given for the 5780 and 6283 DIBs towards 11 stars. Equivalent widths are also presented for the following DIBs detected in three sightlines in M31: 4428, 5705, 5780, 5797, 6203, 6269, 6283, 6379, 6613, 6660, and 6993. All of these M31 DIB carriers reside in clouds at radial velocities matching those of interstellar Na I and/or H I. The relationships between DIB equivalent widths and reddening (E(B-V)) are consistent with those observed in the local ISM of the Milky Way. Many of the observed sightlines show DIB strengths (per unit reddening) which lie at the upper end of the range of Galactic values. DIB strengths per unit reddening are found (with 68% confidence), to correlate with the interstellar UV radiation field strength. The strongest DIBs are observed where the interstellar UV flux is lowest. The mean Spitzer 8/24 micron emission ratio in our three fields is slightly lower than that measured in the Milky Way, but we identify no correlation between this ratio and the DIB strengths in M31. Interstellar oxygen abundances derived from the spectra of three M31 H II regions in one of the fields indicate that the average metallicity of the ISM in that region is 12 + log[O/H] = 8.54 +- 0.18, which is approximately equal to the value in the solar neighbourhood

15N Fractionation in Star-Forming Regions and Solar System Objects

A central issue for understanding the formation and evolution of matter in the early Solar System is the relationship between the chemical composition of star-forming interstellar clouds and that of primitive Solar System materials. The pristinemolecular content of comets, interplanetary dust particles and carbonaceous chondrites show significant bulk nitrogen isotopic fractionation relative to the solar value, 14N15N 440. In addition, high spatial resolution measurements in primitive materials locally show even more extreme enhancements of 14N15N 100