Search

This is the first of a series of investigations into far-IR characteristics of 11 planetary nebulae (PNs) under the Herschel Space Observatory Open Time 1 program, Herschel Planetary Nebula Survey (HerPlaNS). Using the HerPlaNS data set, we look into the PN energetics and variations of the physical conditions within the target nebulae. In the present work, we provide an overview of the survey, data acquisition and processing, and resulting data products. We perform (1) PACS/SPIRE broadband imaging to determine the spatial distribution of the cold dust component in the target PNs and (2) PACS/SPIRE spectral-energy-distribution (SED) and line spectroscopy to determine the spatial distribution of the gas component in the target PNs. For the case of NGC 6781, the broadband maps confirm the nearly pole-on barrel structure of the amorphous carbon-richdust shell and the surrounding halo having temperatures of 26-40 K. The PACS/SPIRE multi-position spectra show spatial variations of far-IR lines that reflect the physical stratification of the nebula. We demonstrate that spatially-resolved far-IR line diagnostics yield the (T_e, n_e) profiles, from which distributions of ionized, atomic, and molecular gases can be determined. Direct comparison of the dust and gas column mass maps constrained by the HerPlaNS data allows to construct an empirical gas-to-dust mass ratio map, which shows a range of ratios with the median of 195+-110. The present analysis yields estimates of the total mass of the shell to be 0.86 M_sun, consisting of 0.54 M_sun of ionized gas, 0.12 M_sun of atomic gas, 0.2 M_sun of molecular gas, and 4 x 10^-3 M_sun of dust grains. These estimates also suggest that the central star of about 1.5 M_sun initial mass is terminating its PN evolution onto the white dwarf cooling track., Comment: 27 pages, 16 figures, accepted for publication in A&A

We present medium resolution ($R\approx5300$) $K$-band integral field spectroscopy of six MYSOs. The targets are selected from the RMS survey, and we used the NIFS on the Gemini North telescope. The data show various spectral line features including Br$\gamma$, CO, H$_2$, and \mbox{He\,{\sc i}}. The Br$\gamma$ line is detected in emission in all objects with $v_\mathrm{FWHM}\sim100$ -- 200 kms$^{-1}$. V645 Cyg shows a high-velocity P-Cygni profile between -800 kms$^{-1}$ and -300 kms$^{-1}$. We performed three-dimensional spectroastrometry to diagnose the circumstellar environment in the vicinity of the central stars using the Br$\gamma$ line. We measured the centroids of the velocity components with sub-mas precision. The centroids allow us to discriminate the blueshifted and redshifted components in a roughly east--west direction in both IRAS 18151--1208 and S106 in Br$\gamma$. This lies almost perpendicular to observed larger scale outflows. We conclude, given the widths of the lines and the orientation of the spectroastrometric signature, that our results trace a disc wind in both IRAS 18151--1208 and S106. The CO $\nu=2-0$ absorption lines at low $J$ transitions are detected in IRAS 18151--1208 and AFGL 2136. We analysed the velocity structure of the neutral gas discs. In IRAS 18151--1208, the absorption centroids of the blueshifted and redshifted components are separated in a direction of north-east to south-west, nearly perpendicular to that of the larger scale $H_2$ jet. The position-velocity relations of these objects can be reproduced with central masses of 30 $M_{\sun}$ for IRAS 18151--1208 and 20 $M_{\sun}$ for AFGL 2136. We also detect CO $\nu=2-0$ bandhead emission in IRAS 18151--1208, S106 and V645 Cyg. The results can be fitted reasonably with a Keplerian rotation model, with masses of 15, 20 and 20 $M_{\sun}$ respectively., Comment: 17 pages, 10 figures, accepted by MNRAS

We investigate the circumstellar dust properties of the oxygen-rich bipolar proto-planetary nebula IRAS 18276-1431 by means of two-dimensional radiative transfer simulations of the circumstellar dust shell. The model geometry is assumed to have a torus and an envelope. The parameters of the dust and the dust shell are constrained by comparing the SED and NIR intensity and polarisation data with the models. The polarisation in the envelope reaches 50 -- 60 % and is nearly constant in the H and K_S bands in the observations. This weak wavelength dependence of the polarisation can be reproduced with a grain size distribution function for the torus: 0.05 micron <= a with n(a)=a^{-(p=5.5)}exp(-a/{a_c=0.3 micron}). The power index p is significantly steeper than that for interstellar dust. Similar results have also been found in some other PPNs and suggest that mechanisms that grind down large particles may also have acted when the dust particles formed. The spectral opacity index beta is found to be 0.6+/-0.5 from the millimeter fluxes. This low value indicates the presence of large dust grains in the torus. We discuss two possible dust models for the torus. One has a size distribution function of 1.0 micron <= a <= a_max=5,000.0 micron with n(a)=a^{-(p=2.5)} and the other is 1.0 micron <= a <= a_max=10,000.0 micron with n(a)=a^{-(p=3.5)}. The former has beta of 0.633, but we are not able to find reasonable geometry parameters to fit the SED in the infrared. The latter has beta of 1.12, but reproduces the SED better over a wide wavelength range. With this dust model, the geometric parameters are estimated as follows: the inner and outer radii are 30 AU and 1000 AU and the torus mass is 3.0 M_sun. Assuming an expansion velocity of 15 kms^{-1}, the torus formation time and mass-loss rate are found to be \sim300 yrs and \sim10^{-2}M_sun yr^{-1} respectively., Comment: 9 pages, 5 figures, accepted for publication in MNRAS

We investigate the circumstellar dust shell of the water fountain source IRAS 16342-3814. We performed two-dimensional radiative transfer modeling of the dust shell, taking into account previously observed spectral energy distributions (SEDs) and our new $J$-band imaging and $H$- and $K_S$-band imaging polarimetry obtained using the VLT/NACO instrument. Previous observations expect an optically thick torus in the equatorial plane because of a striking bipolar appearance and a large viewing angle of 30 - 40$\degr$. However, models with such a torus as well as a bipolar lobe and an AGB shell cannot fit the SED and the images simultaneously. We find that an additional optically and geometrically thick disk located inside a massive torus solves this problem. The masses of the disk and the torus are estimated to be 0.01 $M_{\sun}$ at the $a_\mathrm{max}=100 \mu$m dust and 1 $M_{\sun}$ at $a_\mathrm{max}=10 \mu$m dust, respectively. We discuss a possible formation scenario for the disk and torus based on a similar mechanism to the equatorial back flow. IRAS 16342-3814 is expected to undergo mass loss at a high rate. The radiation from the central star is shielded by the dust that was ejected in the subsequent mass loss event. As a result, the radiation pressure on dust particles cannot govern the motion of the particles anymore. The mass loss flow can be concentrated in the equatorial plane by help of an interaction, which might be the gravitational attraction by the companion, if it exists in IRAS 16342-3814. A fraction of the ejecta is captured in a circum-companion or circum-binary disk and the remains are escaping from the central star(s) and form the massive torus., Comment: 8 pages, 6 figures

Cool, evolved stars undergo copious mass loss but the details of how the matter is returned to the ISM are still under debate. We investigated the structure and evolution of the wind at 5 to 50 stellar radii from Asymptotic Giant Branch and Red Supergiant stars. 22-GHz water masers around seven evolved stars were imaged using MERLIN, at sub-AU resolution. Each source was observed at between 2 and 7 epochs (several stellar periods). We compared our results with long-term Pushchino single dish monitoring. The 22-GHz emission is located in ~spherical, thick, unevenly filled shells. The outflow velocity doubles between the inner and outer shell limits. Water maser clumps could be matched at successive epochs separated by <2 years for AGB stars, or at least 5 years for RSG. This is much shorter than the decades taken for the wind to cross the maser shell, and comparison with spectral monitoring shows that some features fade and reappear. In 5 sources, most of the matched features brighten or dim in concert from one epoch to the next. One cloud in W Hya was caught in the act of passing in front of a background cloud leading to 50-fold, transient amplification. The masing clouds are 1-2 orders of magnitude denser than the wind average and contain a substantial fraction of the mass loss in this region, with a filling factor <1%. The RSG clouds are ~10x bigger than those round the AGB stars. Proper motions are dominated by expansion, with no systematic rotation. The maser clouds survive for decades (the shell crossing time) but the masers are not always beamed in our direction. Radiative effects cause changes in flux density throughout the maser shells on short timescales. Cloud size is proportional to parent star size; clouds have a similar radius to the star in the 22-GHz maser shell. Stellar properties such as convection cells must determine the clumping scale., Comment: Accepted by A&A 2012 July 10 Main text 29 pages, 62 figures Appendix 44 pages, 23 figures

We investigate the dust size and dust shell structure of the bipolar proto-planetary nebula M 1--92 by means of radiative transfer modeling. Our models consists of a disk and bipolar lobes that are surrounded by an AGB shell, each component having different dust characteristics. The upper limit of the grain size $a_\mathrm{max}$ in the lobes is estimated to be $0.5 \mu$m from the polarization value in the bipolar lobe. The $a_\mathrm{max}$ value of the disk is constrained with the disk mass (0.2 $M_{\sun}$), which was estimated from a previous CO emission line observation. We find a good model with $a_\mathrm{max}=1000.0 \mu$m, which provides an approximated disk mass of 0.15 $M_{\sun}$. Even taking into account uncertainties such as the gas-to-dust mass ratio, a significantly larger dust of $a_\mathrm{max}>100.0 \mu$m, comparing to the dust in the lobe, is expected. We also estimated the disk inner radius, the disk outer radius, and the envelope mass to be 30 $R_\star$(=9 AU), 4500 AU, and 4 $M_{\sun}$, respectively, where $v_\mathrm{exp}$ is the expansion velocity. If the dust existing in the lobes in large separations from the central star undergoes little dust processing, the dust sizes preserves the ones in the dust formation. Submicron-sized grains are found in many objects besides M 1--92, suggesting that the size does not depend much on the object properties, such as initial mass of the central star and chemical composition of the stellar system. On the other hand, the grain sizes in the disk do. Evidence of large grains has been reported in many bipolar PPNs, including M 1--92. This result suggests that disks play an important role in grain growth., Comment: 8 pages with 3 figures. Accepted for publication in A&A

We obtained near-infrared long-baseline interferometry of IRC+10420 with the AMBER instrument of ESO's Very Large Telescope Interferometer (VLTI) in low and high spectral resolution (HR) mode to probe the photosphere and the innermost circumstellar environment of this rapidly evolving yellow hypergiant. In the HR observations, the visibilities show a noticeable drop across the Brackett gamma (BrG) line on all three baselines, and we found differential phases up to -25 degrees in the redshifted part of the BrG line and a non-zero closure phase close to the line center. The calibrated visibilities were corrected for AMBER's limited field-of-view to appropriately account for the flux contribution of IRC+10420's extended dust shell. We derived FWHM Gaussian sizes of 1.05 +/- 0.07 and 0.98 +/- 0.10 mas for IRC+10420's continuum-emitting region in the H and K bands, respectively, and the BrG-emitting region can be fitted with a geometric ring model with a diameter of 4.18 +0.19/-0.09 mas, which is approximately 4 times the stellar size. The geometric model also provides some evidence that the BrG line-emitting region is elongated towards a position angle of 36 degrees, well aligned with the symmetry axis of the outer reflection nebula. The HR observations were further analyzed by means of radiative transfer modeling using CMFGEN and the 2-D Busche & Hillier codes. Our spherical CMFGEN model poorly reproduces the observed line shape, blueshift, and extension, definitively showing that the IRC+10420 outflow is asymmetric. Our 2-D radiative transfer modeling shows that the blueshifted BrG emission and the shape of the visibility across the emission line can be explained with an asymmetric bipolar outflow with a high density contrast from pole to equator (8-16), where the redshifted light is substantially diminished., Comment: paper accepted for publication in A&A main journal (16 pages, 9 figures); please note that the astro-ph latex compilation shifts Fig. 7 to the very end of the paper

We obtained H-band polarimetric data of IRAS 19312+1950 using the near-infrared camera (CIAO) on the 8 m Subaru telescope. In order to investigate the physical properties of the central star and the nebula, we performed dust radiative transfer modeling and compared the model results with the observed spectral energy distributions (SEDs), the radial profiles of the total intensity image, and the fraction of linear polarization map. The total intensity image shows a nearly spherical core with ~3" radius, an S-shaped arm extending ~10" in the northwest to southeast direction, and an extended lobe towards the southwest. The polarization map shows a centro-symmetric vector alignment in almost the entire nebula and low polarizations along the S-shaped arm. These results suggest that the nebula is accompanied by a central star, and the S-shaped arm has a physically ring-like structure. From our radiative transfer modeling, we estimated the stellar temperature, the bolometric luminosity, and the current mass-loss rate to be 2800 K, 7000 L_sun, and 5.3x10^{-6} M_sun yr^{-1}, respectively. Taking into account previous observational results, such as the detection of SiO maser emissions and silicate absorption feature in the 10 $\mu$m spectrum, our dust radiative transfer analysis based on our NIR imaging polarimetry suggests that (1) the central star of IRAS 19312+1950 is likely to be an oxygen-rich, dust-enshrouded AGB star and (2) most of the circumstellar material originates from other sources (e.g. ambient dark clouds) rather than as a result of mass loss from the central star., Comment: 8 pages with 4 figures

Many observations of late-type M stars show large near-spherical circumstellar envelopes, yet planetary nebulae and supernova remnants are frequently axisymmetric. We present VLBI and MERLIN observations of masers around the red supergiant S Per which show varying degrees of axisymmetry and a dynamically significant magnetic field. There is no evidence for rotation here or in most similar objects. We examine possible origins of the magnetic field., Comment: 4 pages. 4 figures. Proceedings of the 7th European VLBI Network Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R. Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico Nacional), p. 209-212. Needs evn2004.cls

Saturn's largest satellite, Titan, has stratospheric wind speeds that may be up to ~210 m/sec [1], circling Titan in about a day compared to Titan's slow 16-day rotation. Theoretical models to explain such super-rotating winds are not well constrained [2,3,4,5,6] by observations of Titan or a similar slow rotator, Venus. Titan's stratospheric temperature and the abundance of the important constituent ethane (C2H6) should be zonally invariant due to long photochemical and radiative lifetimes and rapid transport and mixing by high zonal winds. Here, we report new measurements of zonal wind in Titan's equatorial region, including the Cassini Huygens probe entry latitude [7]. Prograde zonal winds of 190+/-90 m/sec are found from Doppler-shifted ethane gas infrared emission near 12 micron wavelength, confirming high wind velocity even near the equator. Surprisingly, we find a temperature difference of 6+/-3 K between the East and West hemispheres of Titan at ~240 km altitude. Common direct processes such as diurnal heating by sunlight do not adequately explain the asymmetry, suggesting other processes, such as unknown atmospheric dynamics, may be responsible. The origin of the temperature difference is enigmatic and currently unexplained., Comment: 14 pages, including 2 figures, letter submitted to Nature