Polarisation observations of VY Canis Majoris H_2O 5_(32)–4_(41) 620.701 GHz maser emission with HIFI

Context. Water vapour maser emission from evolved oxygen-rich stars remains poorly understood. Additional observations, including polarisation studies and simultaneous observation of different maser transitions may ultimately lead to greater insight. Aims. We have aimed to elucidate the nature and structure of the VY CMa water vapour masers in part by observationally testing a theoretical prediction of the relative strengths of the 620.701 GHz and the 22.235 GHz maser components of ortho H_2O. Methods. In its high-resolution mode (HRS) the Herschel Heterodyne Instrument for the Far Infrared (HIFI) offers a frequency resolution of 0.125 MHz, corresponding to a line-of-sight velocity of 0.06 km s^(-1), which we employed to obtain the strength and linear polarisation of maser spikes in the spectrum of VY CMa at 620.701 GHz. Simultaneous ground based observations of the 22.235 GHz maser with the Max-Planck-Institut für Radioastronomie 100-m telescope at Effelsberg, provided a ratio of 620.701 GHz to 22.235 GHz emission. Results. We report the first astronomical detection to date of H_2O maser emission at 620.701 GHz. In VY CMa both the 620.701 and the 22.235 GHz polarisation are weak. At 620.701 GHz the maser peaks are superposed on what appears to be a broad emission component, jointly ejected from the star. We observed the 620.701 GHz emission at two epochs 21 days apart, both to measure the potential direction of linearly polarised maser components and to obtain a measure of the longevity of these components. Although we do not detect significant polarisation levels in the core of the line, they rise up to approximately 6% in its wings

High-Resolution 4.7 Micron Keck/NIRSPEC Spectroscopy of the CO Emission from the Disks Surrounding Herbig Ae Stars

We explore the high-resolution (λ/Δλ = 25,000; Δv = 12 km s^(-1)) M-band (4.7-5.1 μm) spectra of several disk-dominated Herbig Ae (HAe) systems: AB Aur, MWC 758, MWC 480, HD 163296, and VV Ser. All five objects show ^(12)CO v = 1-0 emission lines up to J = 42, but there is little or no evidence of moderate-J, v = 2-1 transitions despite their similar excitation energies. AB Aur shows ^(13)CO emission as well. The line/continuum ratios and intensity profiles are well correlated with inclination, and they trace collisionally driven emission from the inner disk (R_(th) ≾ 0.5-1 AU) as well as resonance fluorescence to much larger radii (R_(hν) ≾ 50-100 AU for J ≾ 10). The temperature, density, and radiation field profiles required to fit the CO emission are in good agreement with models of HAe disks derived from their spectral energy distributions. High-resolution and high dynamic range infrared spectroscopy of CO, and future observations of less abundant species, thus provide direct access to the physicochemical properties and surface structure of disks in regions where planet formation likely occurs

Methane Abundance Variations toward the Massive Protostar NGC 7538 : IRS9

Absorption and emission lines originating from the nu3 C-H stretching manifold of gas phase CH4 were discovered in the high resolution (R=25,000) infrared L band spectrum along the line of sight toward NGC 7538 : IRS9. These observations provide a diagnostic of the complex dynamics and chemistry in a massive star forming region. The line shapes resemble P Cygni profiles with the absorption and emission components shifted by ~7 km/s with respect to the systemic velocity. Similar velocity components were observed in CO at 4.7 um, but in contrast to CH4, the CO shows deep absorption due to a high velocity outflow as well as absorption at the systemic velocity due to the cold outer envelope. It is concluded that the gas phase CH4 abundance varies by an order of magnitude in this line of sight: it is low in the envelope and the outflow (X[CH4]<0.4e-6), and at least a factor of 10 larger in the central core. The discovery of solid CH4 in independent ground and space based data sets shows that methane is nearly entirely frozen onto grains in the envelope. It thus appears that CH4 is formed by grain surface reactions, evaporates into the gas phase in the warm inner regions of protostellar cores and is efficiently destroyed in shocks related to outflows.Comment: Scheduled for publication in ApJ 615, 01 Nov. 2004. 11 page

High-Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars. II. Detection of the ^(13)CO Isotope in Icy Grain Mantles

The high-resolution (R = 25,000) infrared M-band spectrum of the massive protostar NGC 7538 IRS 9 shows a narrow absorption feature at 4.779 μm (2092.3 cm^(-1)) that we attribute to the vibrational stretching mode of the ^(13)CO isotope in pure CO icy grain mantles. This is the first detection of ^(13)CO in icy grain mantles in the interstellar medium. The ^(13)CO band is a factor of 2.3 narrower than the apolar component of the ^(12)CO band. With this in mind, we discuss the mechanisms that broaden solid-state absorption bands. It is shown that ellipsoidally shaped pure CO grains fit the bands of both isotopes at the same time. Slightly worse but still reasonable fits are also obtained by CO embedded in N_2-rich ices and thermally processed O_2-rich ices. In addition, we report new insights into the nature and evolution of interstellar CO ices by comparing the very high resolution multicomponent solid ^(12)CO spectrum of NGC 7538 IRS 9 with that of the previously studied low-mass source L1489 IRS. The narrow absorption of apolar CO ices is present in both spectra but much stronger in NGC 7538 IRS 9. It is superposed on a smooth broad absorption feature well fitted by a combination of CO_2 and H_2O-rich laboratory CO ices. The abundances of the latter two ices, scaled to the total H_2O ice column, are the same in both sources. We thus suggest that thermal processing manifests itself as evaporation of apolar ices only and not the formation of CO_2 or polar ices. Finally, the decomposition of the ^(12)CO band is used to derive the ^(12)CO/^(13)CO abundance ratio in apolar ices. A ratio of ^(12)CO/^(13)CO = 71 ± 15 (3 σ) is deduced, in good agreement with gas-phase CO studies (~77) and the solid ^(12)CO_2/^(13)CO_2 ratio of 80 ± 11 found in the same line of sight. The implications for the chemical path along which CO_2 is formed are discussed

CO Rovibrational Emission as a Probe of Inner Disk Structure

We present an analysis of CO emission lines from a sample of T Tauri, Herbig Ae/Be, and transitional disks with known inclinations in order to study the structure of inner disk molecular gas. We calculate CO inner radii by fitting line profiles with a simple parameterized model. We find that, for optically thick disks, CO inner radii are strongly correlated with the total system luminosity (stellar plus accretion) and consistent with the dust sublimation radius. Transitional disk inner radii show the same trend with luminosity, but are systematically larger. Using rotation diagram fits, we derive, for classical T Tauri disks, emitting areas consistent with a ring of width ~0.15 AU located at the CO inner radius; emitting areas for transitional disks are systematically smaller. We also measure lower rotational temperatures for transitional disks, and disks around Herbig Ae/Be stars, than for those around T Tauri stars. Finally, we find that rotational temperatures are similar to, or slightly lower than, the expected temperature of blackbody grains located at the CO inner radius, in contrast to expectations of thermal decoupling between gas and dust

Detection of Extremely Broad Water Emission from the molecular cloud interacting Supernova Remnant G349.7+0.2

We performed Herschel HIFI, PACS and SPIRE observations towards the molecular cloud interacting supernova remnant G349.7+0.2. An extremely broad emission line was detected at 557 GHz from the ground state transition 1_{10}-1_{01} of ortho-water. This water line can be separated into three velocity components with widths of 144, 27 and 4 km/s. The 144 km/s component is the broadest water line detected to date in the literature. This extremely broad line width shows importance of probing shock dynamics. PACS observations revealed 3 additional ortho-water lines, as well as numerous high-J carbon monoxide (CO) lines. No para-water lines were detected. The extremely broad water line is indicative of a high velocity shock, which is supported by the observed CO rotational diagram that was reproduced with a J-shock model with a density of 10^4 cm^{-3} and a shock velocity of 80 km/s. Two far-infrared fine-structure lines, [O~I] at 145 micron and [C~II] line at 157 micron, are also consistent with the high velocity J-shock model. The extremely broad water line could be simply from short-lived molecules that have not been destroyed in high velocity J-shocks; however, it may be from more complicated geometry such as high-velocity water bullets or a shell expanding in high velocity. We estimate the CO and H2O densities, column densities, and temperatures by comparison with RADEX and detailed shock models. Detection of Extremely Broad Water Emission from the molecular cloud interacting Supernova Remnant G349.7+0.

Animal cognition: the benefits of remembering

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.How cognitive abilities evolve through natural selection is poorly understood. Two new studies show that a good spatial memory helps birds that hide their food to survive and produce more offspring

The methanol lines and hot core of OMC2-FIR4, an intermediate-mass protostar, with Herschel/HIFI

In contrast with numerous studies on the physical and chemical structure of low- and high-mass protostars, much less is known about their intermediate-mass counterparts, a class of objects that could help to elucidate the mechanisms of star formation on both ends of the mass range. We present the first results from a rich HIFI spectral dataset on an intermediate-mass protostar, OMC2-FIR4, obtained in the CHESS (Chemical HErschel Survey of Star forming regions) key programme. The more than 100 methanol lines detected between 554 and 961 GHz cover a range in upper level energy of 40 to 540 K. Our physical interpretation focusses on the hot core, but likely the cold envelope and shocked regions also play a role in reality, because an analysis of the line profiles suggests the presence of multiple emission components. An upper limit of 10^(-6) is placed on the methanol abundance in the hot core, using a population diagram, large-scale source model and other considerations. This value is consistent with abundances previously seen in low-mass hot cores. Furthermore, the highest energy lines at the highest frequencies display asymmetric profiles, which may arise from infall around the hot core