Modeling dust emission in PN IC 418

We investigated the infrared (IR) dust emission from PN IC 418, using a detailed model controlled by a previous determination of the stellar properties and the characteristics of the photoionized nebula, keeping as free parameters the dust types, amounts and distributions relative to the distance of the central star. The model includes the ionized region and the neutral region beyond the recombination front (Photodissociation region, or PDR), where the [OI] and [CII] IR lines are formed. We succeeded in reproducing the observed infrared emission from 2 to 200~\mm. The global energy budget is fitted by summing up contributions from big grains of amorphous carbon located in the neutral region and small graphite grains located in the ionized region (closer to the central star). Two emission features seen at 11.5 and 30~\mm are also reproduced by assuming them to be due to silicon carbide (SiC) and magnesium and iron sulfides (Mg$_x$Fe$_{1-x}$S), respectively. For this, we needed to consider ellipsoidal shapes for the grains to reproduce the wavelength distribution of the features. Some elements are depleted in the gaseous phase: Mg, Si, and S have sub-solar abundances (-0.5 dex below solar by mass), while the abundance of C+N+O+Ne by mass is close to solar. Adding the abundances of the elements present in the dusty and gaseous forms leads to values closer to but not higher than solar, confirming that the identification of the feature carriers is plausible. Iron is strongly depleted (3 dex below solar) and the small amount present in dust in our model is far from being enough to recover the solar value. A remaining feature is found as a residue of the fitting process, between 12 and 25~\mm, for which we do not have identification.Comment: Accepted for publication in Astronomy & Astrophysics. V2: adding reference

New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme

CONTEXT: Asymptotic giant branch (AGB) stars are in one of the latest evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss has a significant effect on the stellar evolution, and is a significant source of heavy elements and dust grains for the interstellar medium. The mass-loss rate can be well traced by carbon monoxide (CO) line emission. AIMS: We present new Herschel HIFI and IRAM 30m telescope CO line data for a sample of 53 galactic AGB stars. The lines cover a fairly large range of excitation energy from the $J=1\to0$ line to the $J=9\to8$ line, and even the $J=14\to13$ line in a few cases. We perform radiative transfer modelling for 38 of these sources to estimate their mass-loss rates. METHODS: We used a radiative transfer code based on the Monte Carlo method to model the CO line emission. We assume spherically symmetric circumstellar envelopes that are formed by a constant mass-loss rate through a smoothly accelerating wind. RESULTS: We find models that are consistent across a broad range of CO lines for most of the stars in our sample, i.e., a large number of the circumstellar envelopes can be described with a constant mass-loss rate. We also find that an accelerating wind is required to fit, in particular, the higher-J lines and that a velocity law will have a significant effect on the model line intensities. The results cover a wide range of mass-loss rates ($\sim 10^{-8}$ to $2\times 10^{-5}~\mathrm{M}_\odot~\mathrm{ yr}^{-1}$) and gas expansion velocities (2 to $21.5$ km s$^{-1}$), and include M-, S-, and C-type AGB stars. Our results generally agree with those of earlier studies, although we tend to find slightly lower mass-loss rates by about 40%, on average. We also present "bonus" lines detected during our CO observations.Comment: 36 page

Diabetes insípida central e hipotiroidismo secundario debidos a un macroadenoma hipofisario en un perro

Se expone el caso de una perra que presentaba inicialmente midriasis unilateral como único signo clínico. A los 12 meses apareció también midriasis en el otro ojo junto con poliuria, polidipsia, letargia y alopecia bilateral troncal. Tras distintas pruebas se diagnosticó diabetes insípida central e hipotiroidismo secundario, presuntamente debidos a un tumor hipofisario posteriormente confirmado mediante necropsia.

Nebular emission lines in IRAS 17347-3139

We report the detection of nebular emission lines in the optical and mid-infrared spectra of IRAS 17347-3139, a heavily obscured OH/IR star which may be rapidly evolving from the AGB to the PN stage. The presence of emission lines is interpreted as a clear indication that the ionization of its circumstellar envelope has already started. This source belongs to the rare class of objects known as `OHPNe' displaying both OH maser and radio continuum emission. However, unlike the rest of stars in this class, prominent C-rich dust features are detected in its mid-infrared spectrum, which makes the analysis of this star particularly interesting.Comment: 2 pages, 2 figures, Proc. IAU Symp. 234, Planetary Nebulae in Our Galaxy and Beyond (3-7 Apr 2006), eds. M.J. Barlow & R.H. Mendez (Cambridge Univ. Press

V2324Cyg - an F-type star with fast wind

For the first time high-resolution optical spectroscopy of the variable star V2324Cyg associated with the IR-source IRAS20572+4919 is made. More than 200 absorption features (mostly FeII, TiII, CrII, YII, BaII, and YII) are identified within the wavelength interval 4549-7880AA. The spectral type and rotation velocity of the star are found to be F0III and Vsini=69km/s, respectively. HI and NaID lines have complex PCyg-type profiles with an emission component. Neither systematic trend of radial velocity Vr with line depth Ro nor temporal variability of Vr have been found. We determined the average heliocentric radial velocity Vr=-16.8\pm 0.6km/s. The radial velocities inferred from the cores of the absorption components of the H$\beta$ and NaI wind lines vary from -140 to -225km/s (and the expansion velocities of the corresponding layers, from about 120 to 210km/s). The maximum expansion velocity is found for the blue component of the split H$\alpha$ absorption: 450km/s for December 12, 1995. The model atmospheres method is used to determine the star's parameters: Teff=7500K, log g=2.0, $\xi_t$=6.0km/s, and metallicity, which is equal to the solar value. The main peculiarity of the chemical abundances pattern is the overabundance of lithium and sodium. The results cast some doubt on the classification of V2324Cyg as a post-AGB star.Comment: 28 pages, 6 figure

New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge

We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates. We find that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the common view of planetary nebulae. In particular, it is challenging to interpret the peculiar gas chemical composition of many analyzed objects in the standard picture of the evolution of planetary nebulae progenitors. We confirm that the dual-dust chemistry phenomenon is not limited to planetary nebulae with emission-line central stars.Comment: 17 pages, 13 figure

Spitzer Infrared Spectrograph Observations of Magellanic Cloud Planetary Nebulae: the nature of dust in low metallicity circumstellar ejecta

We present 5 - 40 micron spectroscopy of 41 planetary nebulae (PNe) in the Magellanic Clouds, observed with the Infrared Spectrograph on board the Spitzer Space Telescope. The spectra show the presence of a combination of nebular emission lines and solid-state features from dust, superimposed on the thermal IR continuum. By analyzing the 25 LMC and 16 SMC PNe in our sample we found that the IR spectra of 14 LMC and 4 SMC PNe are dominated by nebular emission lines, while the other spectra show solid-state features. We observed that the solid-state features are compatible with carbon-rich dust grains (SiC, polycyclic aromatic hydrocarbons (PAHs), etc.) in most cases, except in three PNe showing oxygen-rich dust features. The frequency of carbonaceous dust features is generally higher in LMC than in SMC PNe. The spectral analysis allowed the correlations of the dust characteristics with the gas composition and morphology, and the properties of the central stars. We found that: 1) all PNe with carbonaceous dust features have C/O>1, none of these being bipolar or otherwise highly asymmetric; 2) all PNe with oxygen-rich dust features have C/O<1, with probable high mass progenitors if derived from single-star evolution (these PNe are either bipolar or highly asymmetric); 3) the dust temperature tracks the nebular and stellar evolution; and 4) the dust production efficiency depends on metallicity, with low metallicity environments not favoring dust production.Comment: The Astrophysical Journal, in pres