arXiv subjects

P. Royer

Publications and source records attributed to P. Royer.

At least 37 records · Page 2Linked to original sources

arXiv2018

The perturbed sublimation rim of the dust disk around the post-AGB binary IRAS08544-4431

Context: Post-Asymptotic Giant Branch (AGB) binaries are surrounded by stable dusty and gaseous disks similar to the ones around young stellar objects. Whereas significant effort is spent on modeling observations of disks around young stellar objects, the disks around post-AGB binaries receive significantly less attention, even though they pose significant constraints on theories of disk physics and binary evolution. Aims: We want to examine the structure of and phenomena at play in circumbinary disks around post-AGB stars. We continue the analysis of our near-infrared interferometric image of the inner rim of the circumbinary disk around IRAS08544-4431. We want to understand the physics governing this inner disk rim. Methods: We use a radiative transfer model of a dusty disk to reproduce simultaneously the photometry as well as the near-infrared interferometric dataset on IRAS08544-4431. The model assumes hydrostatic equilibrium and takes dust settling self-consistently into account. Results: The best-fit radiative transfer model shows excellent agreement with the spectral energy distribution up to mm wavelengths as well as with the PIONIER visibility data. It requires a rounded inner rim structure, starting at a radius of 8.25 au. However, the model does not fully reproduce the detected over-resolved flux nor the azimuthal flux distribution of the inner rim. While the asymmetric inner disk rim structure is likely to be the consequence of disk-binary interactions, the origin of the additional over-resolved flux remains unclear. Conclusions: As in young stellar objects, the disk inner rim of IRAS08544-4431 is ruled by dust sublimation physics. Additional observations are needed to understand the origin of the extended flux and the azimuthal perturbation at the inner rim of the disk.

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arXiv2016

Evolutionary status of the Of?p star HD148937 and of its surrounding nebula NGC6164/5

Aims. The magnetic star HD148937 is the only Galactic Of?p star surrounded by a nebula. The structure of this nebula is particularly complex and is composed, from the center out outwards, of a close bipolar ejecta nebula (NGC6164/5), an ellipsoidal wind-blown shell, and a spherically symmetric Stromgren sphere. The exact formation process of this nebula and its precise relation to the star's evolution remain unknown. Methods. We analyzed infrared Spitzer IRS and far-infrared Herschel/PACS observations of the NGC6164/5 nebula. The Herschel imaging allowed us to constrain the global morphology of the nebula. We also combined the infrared spectra with optical spectra of the central star to constrain its evolutionary status. We used these data to derive the abundances in the ejected material. To relate this information to the evolutionary status of the star, we also determined the fundamental parameters of HD148937 using the CMFGEN atmosphere code. Results. The H$α$ image displays a bipolar or "8"-shaped ionized nebula, whilst the infrared images show dust to be more concentrated around the central object. We determine nebular abundance ratios of N/O = 1.06 close to the star, and N/O = 1.54 in the bright lobe constituting NGC6164. Interestingly, the parts of the nebula located further from HD148937 appear more enriched in stellar material than the part located closer to the star. Evolutionary tracks suggest that these ejecta have occured $\sim$1.2-1.3 and $\sim$0.6 Myrs ago, respectively. In addition, we derive abundances of argon for the nebula compatible with the solar values and we find a depletion of neon and sulfur. The combined analyses of the known kinematics and of the new abundances of the nebula suggest either a helical morphology for the nebula, possibly linked to the magnetic geometry, or the occurrence of a binary merger.

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arXiv2016

A test field for Gaia. Radial velocity catalogue of stars in the South Ecliptic Pole

Gaia is a space mission currently measuring the five astrometric parameters as well as spectrophotometry of at least 1 billion stars to G = 20.7 mag with unprecedented precision. The sixth parameter in phase space (radial velocity) is also measured thanks to medium-resolution spectroscopy being obtained for the 150 million brightest stars. During the commissioning phase, two fields, one around each ecliptic pole, have been repeatedly observed to assess and to improve the overall satellite performances as well as the associated reduction and analysis software. A ground-based photometric and spectroscopic survey was therefore initiated in 2007, and is still running in order to gather as much information as possible about the stars in these fields. This work is of particular interest to the validation of the Radial Velocity Spectrometer (RVS) outputs. The paper presents the radial velocity measurements performed for the Southern targets in the 12 - 17 R magnitude range on high- to mid-resolution spectra obtained with the GIRAFFE and UVES spectrographs.

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arXiv2016

The mass-loss rates of red supergiants at low metallicity: Detection of rotational CO emission from two red supergiants in the Large Magellanic Cloud

Using the PACS and SPIRE spectrometers on-board the Herschel Space Observatory, we obtained spectra of two red supergiants (RSGs) in the Large Magellanic Cloud (LMC). Multiple rotational CO emission lines (J=6-5 to 15-14) and 15 H2O lines were detected from IRAS 05280-6910, and one CO line was detected from WOH G64. This is the first time CO rotational lines have been detected from evolved stars in the LMC. Their CO line intensities are as strong as those of the Galactic RSG, VY CMa. Modelling the CO lines and the spectral energy distribution results in an estimated mass-loss rate for IRAS 05280-6910 of 3x10^-4 Msun per yr. The model assumes a gas-to-dust ratio and a CO-to-H2 abundance ratio is estimated from the Galactic values scaled by the LMC metallicity ([Fe/H]~-0.3), i.e., that the CO-to-dust ratio is constant for Galactic and LMC metallicities within the uncertainties of the model. The key factor determining the CO line intensities and the mass-loss rate found to be the stellar luminosity.

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arXiv2016

Tracing back the evolution of the candidate LBV HD168625

Aims. We obtained Herschel/PACS imaging and spectroscopic observations of the nebula surrounding the candidate LBV HD168625. By combining these data with optical spectra of the star, we want to constrain the abundances in the nebula and in the star and compare them to trace back its evolution. Methods. We use CMFGEN to determine the fundamental parameters and the CNO abundances of the central star whilst the abundances of the nebula are derived from the emission lines present in the Herschel/PACS spectrum. Result. The FIR images show a nebula composed of an elliptical ring/torus of ejecta with a ESE-WNW axis and of a second perpendicular bipolar structure composed of empty caps/rings. We detect equatorial shells composed of dust and ionized material with different sizes when observed at different wavelengths, and bipolar caps more of less separated from the central star in H$α$ and mid-IR images. This complex global structure seems to show 2 different inclinations: 40° for the equatorial torus and 60° for the bipolar ejections. From the Herschel/PACS spectrum, we determine nebular abundances of $\mathrm{N/H} = 4.1 \pm 0.8 \times~10^{-4}$ and $\mathrm{C/H} \sim 1.6_{-0.35}^{+1.16} \times~10^{-4}$, as well as a mass of ionized gas of $0.17\pm 0.04$M$_{\odot}$ and a neutral hydrogen mass of about $1.0\pm 0.3$M$_{\odot}$ which dominates. Analysis of the central star reveals Teff = 14000K, log g = 1.74 and log (L/L$_{\odot}$) = 5.58. We derive stellar abundances of about $\mathrm{N/H} = 5.0 \pm 1.5 \times~10^{-4}$, $\mathrm{C/H} = 1.4 \pm 0.5 \times~10^{-4}$ and $\mathrm{O/H} = 3.5 \pm 1.0\times~10^{-4}$. All these measurements taken together are compatible with the evolutionary tracks of a star with an initial mass between $28$ and $33$M$_{\odot}$ and with a crit. rotational rate between 0.3 and 0.4 that has lost its material during or just after the BSG phase.

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arXiv2016

A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling

We aim to constrain the temperature and velocity structures, and H2O abundances in the winds of a sample of M-type AGB stars. We further aim to determine the effect of H2O line cooling on the energy balance in the inner circumstellar envelope. We use two radiative-transfer codes to model molecular emission lines of CO and H2O towards four M-type AGB stars. We focus on spectrally resolved observations of CO and H2O from HIFI. The observations are complemented by ground-based CO observations, and spectrally unresolved CO and H2O observations with PAC. The observed line profiles constrain the velocity structure throughout the circumstellar envelopes (CSEs), while the CO intensities constrain the temperature structure in the CSEs. The H2O observations constrain the o-H2O and p-H2O abundances relative to H2. Finally, the radiative-transfer modelling allows to solve the energy balance in the CSE, in principle including also H2O line cooling. The fits to the line profiles only set moderate constraints on the velocity profile, indicating shallower acceleration profiles in the winds of M-type AGB stars than predicted by dynamical models, while the CO observations effectively constrain the temperature structure. Including H2O line cooling in the energy balance was only possible for the low-mass-loss-rate objects in the sample, and required an ad hoc adjustment of the dust velocity profile in order to counteract extreme cooling in the inner CSE. H2O line cooling was therefore excluded from the models. The constraints set on the temperature profile by the CO lines nevertheless allowed us to derive H2O abundances. The derived H2O abundances confirm previous estimates and are consistent with chemical models. However, the uncertainties in the derived abundances are relatively large, in particular for p-H2O, and consequently the derived o/p-H2O ratios are not well constrained.

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arXiv2016

Herschel detects oxygen in the beta Pictoris debris disk

The young star beta Pictoris is well known for its dusty debris disk, produced through the grinding down by collisions of planetesimals, kilometre-sized bodies in orbit around the star. In addition to dust, small amounts of gas are also known to orbit the star, likely the result from vaporisation of violently colliding dust grains. The disk is seen edge on and from previous absorption spectroscopy we know that the gas is very rich in carbon relative to other elements. The oxygen content has been more difficult to assess, however, with early estimates finding very little oxygen in the gas at a C/O ratio 20x higher than the cosmic value. A C/O ratio that high is difficult to explain and would have far-reaching consequences for planet formation. Here we report on observations by the far-infrared space telescope Herschel, using PACS, of emission lines from ionised carbon and neutral oxygen. The detected emission from C+ is consistent with that previously reported being observed by the HIFI instrument on Herschel, while the emission from O is hard to explain without assuming a higher-density region in the disk, perhaps in the shape of a clump or a dense torus, required to sufficiently excite the O atoms. A possible scenario is that the C/O gas is produced by the same process responsible for the CO clump recently observed by ALMA in the disk, and that the re-distribution of the gas takes longer than previously assumed. A more detailed estimate of the C/O ratio and the mass of O will have to await better constraints on the C/O gas spatial distribution.

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arXiv2016

Herschel observations of the nebula M1-67 around the Wolf-Rayet star WR 124

Infrared Herschel imaging and spectroscopic observations of the nebula M1-67 around the Wolf-Rayet star WR 124 have been obtained along with optical imaging observations. The infrared images reveal a clumpy dusty nebula that extends up to 1 pc. The comparison with the optical images shows that the ionized gas nebula coincides with the dust nebula, the dust and the gas being mixed together. A photodissociation region is revealed from the infrared spectroscopic analysis. The analysis of the infrared spectrum of the nebula, where forbidden emission lines of ionized elements were detected, showed that the nebula consists of mildly processed material with the calculated abundance number ratios being N/O = 1.0 +/- 0.5 and C/O = 0.46 +/- 0.27. Based on a radiative transfer model, the dust mass of the nebula was estimated to be 0.22 Msun with a population of large grains being necessary to reproduce the observations. The comparison of the mass-loss rate and the abundance ratios to theoretical models of stellar evolution led to the conclusion that the nebular ejection took place during a RSG/YSG evolutionary phase of a central star with an initial mass of 32 Msun.

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arXiv2016

Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars

Context. The recent detection of warm H$_2$O vapor emission from the outflows of carbon-rich asymptotic giant branch (AGB) stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H$_2$O vapor formation. In the first, periodic shocks passing through the medium immediately above the stellar surface lead to H$_2$O formation. In the second, penetration of ultraviolet interstellar radiation through a clumpy circumstellar medium leads to the formation of H$_2$O molecules in the intermediate wind. Aims. We aim to determine the properties of H$_2$O emission for a sample of 18 carbon-rich AGB stars and subsequently constrain which of the above mechanisms provides the most likely warm H$_2$O formation pathway. Methods, Results, and Conclusions. See paper.

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arXiv2015

Herschel observations of extreme OH/IR stars - the isotopic ratios of oxygen as a sign-post for the stellar mass

Aim: The late stages of stellar evolution are mainly governed by the mass of the stars. Low- and intermediate-mass stars lose copious amounts of mass during the asymptotic giant branch (AGB) which obscure the central star making it difficult to study the stellar spectra and determine the stellar mass. In this study, we present observational data that can be used to determine lower limits to the stellar mass. Method: Spectra of nine heavily reddened AGB stars taken by the Herschel Space Observatory display numerous molecular emission lines. The strongest emission lines are due to H2O. We search for the presence of isotopologues of H2O in these objects. Result: We detected the 16O and 17O isotopologues of water in these stars, but lines due to H2^{18}O are absent. The lack of 18O is predicted by a scenario where the star has undergone hot-bottom burning which preferentially destroys 18O relative to 16O and 17O. From stellar evolution calculations, this process is thought to occur when the stellar mass is above 5 Msun for solar metallicity. Hence, observations of different isotopologues of H2O can be used to help determine the lower limit to the initial stellar mass. Conclusion: From our observations, we deduce that these extreme OH/IR stars are intermediate-mass stars with masses of >= 5 Msun. Their high mass-loss rates of ~ 1.0e-4 Msun/yr may affect the enrichment of the interstellar medium and the overall chemical evolution of our Galaxy.

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arXiv2015

H2O vapor excitation in dusty AGB envelopes. A PACS view of OH 127.8+0.0

Context: AGB stars lose a large percentage of their mass in a dust-driven wind. This creates a circumstellar envelope, which can be studied through thermal dust emission and molecular emission lines. In the case of high mass-loss rates, this study is complicated by the high optical depths and the intricate coupling between gas and dust radiative transfer characteristics. An important aspect of the physics of gas-dust interactions is the strong influence of dust on the excitation of several molecules, including H2O. Aims: The dust and gas content of the envelope surrounding the high mass-loss rate OH/IR star OH 127.8+0.0, as traced by Herschel observations, is studied, with a focus on the H2O content and the dust-to-gas ratio. We report detecting a large number of H2O vapor emission lines up to J = 9 in the Herschel data, for which we present the measured line strengths. Methods: The treatments of both gas and dust species are combined using two numerical radiative transfer codes. The method is illustrated for both low and high mass-loss-rate sources. Specifically, we discuss different ways of assessing the dust-to-gas ratio: 1) from the dust thermal emission spectrum and the CO molecular gas line strengths; 2) from the momentum transfer from dust to gas and the measured gas terminal velocity; and 3) from the determination of the required amount of dust to reproduce H2O lines for a given H2O vapor abundance. These three diagnostics probe different zones of the outflow, for the first time allowing an investigation of a possible radial dependence of the dust-to-gas ratio. Results: ... Continued in article.

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arXiv2015

The Herschel view of the nebula around the luminous blue variable star AG Carinae

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter. In the infrared light, the nebula appears as a clumpy ring shell that extends up to 1.2 pc with an inner radius of 0.4 pc. It coincides with the Halpha nebula, but extends further out. Dust modeling of the nebula was performed and indicates the presence of large grains. The dust mass is estimated to be ~ 0.2 Msun. The infrared spectrum of the nebula consists of forbidden emission lines over a dust continuum. Apart from ionized gas, these lines also indicate the existence of neutral gas in a photodissociation region that surrounds the ionized region. The abundance ratios point towards enrichment by processed material. The total mass of the nebula ejected from the central star amounts to ~ 15 Msun, assuming a dust-to-gas ratio typical of LBVs. The abundances and the mass-loss rate were used to constrain the evolutionary path of the central star and the epoch at which the nebula was ejected, with the help of available evolutionary models. This suggests an ejection during a cool LBV phase for a star of ~ 55 Msun with little rotation.

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arXiv2014

A stubbornly large mass of cold dust in the ejecta of Supernova 1987A

We present new Herschel photometric and spectroscopic observations of Supernova 1987A, carried out in 2012. Our dedicated photometric measurements provide new 70 micron data and improved imaging quality at 100 and 160 micron compared to previous observations in 2010. Our Herschel spectra show only weak CO line emission, and provide an upper limit for the 63 micron [O I] line flux, eliminating the possibility that line contaminations distort the previously estimated dust mass. The far-infrared spectral energy distribution (SED) is well fitted by thermal emission from cold dust. The newly measured 70 micron flux constrains the dust temperature, limiting it to nearly a single temperature. The far-infrared emission can be fitted by 0.5+-0.1 Msun of amorphous carbon, about a factor of two larger than the current nucleosynthetic mass prediction for carbon. The observation of SiO molecules at early and late phases suggests that silicates may also have formed and we could fit the SED with a combination of 0.3 Msun of amorphous carbon and 0.5 Msun of silicates, totalling 0.8 Msun of dust. Our analysis thus supports the presence of a large dust reservoir in the ejecta of SN 1987A. The inferred dust mass suggests that supernovae can be an important source of dust in the interstellar medium, from local to high-redshift galaxies.

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arXiv2014

The wind of W Hya as seen by Herschel. II. The molecular envelope of W Hya

The evolution of low- and intermediate-mass stars on the asymptotic giant branch (AGB) is mainly controlled by the rate at which these stars lose mass in a stellar wind. Understanding the driving mechanism and strength of the stellar winds of AGB stars and the processes enriching their surfaces with products of nucleosynthesis are paramount to constraining AGB evolution and predicting the chemical evolution of galaxies. In a previous paper we have constrained the structure of the outflowing envelope of W Hya using spectral lines of the $^{12}$CO molecule. Here we broaden this study by modelling an extensive set of H$_{2}$O and $^{28}$SiO lines observed by the three instruments on board Herschel using a state-of-the-art molecular excitation and radiative transfer code. The oxygen isotopic ratios and the $^{28}$SiO abundance profile can be connected to the initial stellar mass and to crucial aspects of dust formation at the base of the stellar wind, respectively. The modelling of H$_{2}$O and $^{28}$SiO confirms the properties of the envelope model of W Hya derived from $^{12}$CO lines. We find an H$_2$O ortho-to-para ratio of 2.5\,$^{+2.5}_{-1.0}$, consistent with what is expected for an AGB wind. The O$^{16}$/O$^{17}$ ratio indicates that W Hya has an initial mass of about 1.5 M$_\odot$. Although the ortho- and para-H$_{2}$O lines observed by HIFI appear to trace gas of slightly different physical properties, a turbulence velocity of $0.7\pm0.1$ km s$^{-1}$ fits the HIFI lines of both spin isomers and those of $^{28}$SiO well. The ortho- and para-H$_2^{16}$O and $^{28}$SiO abundances relative to H$_{2}$ are $(6^{+3}_{-2}) \times 10^{-4}$, $(3^{+2}_{-1}) \times 10^{-4}$, and $(3.3\pm 0.8)\times 10^{-5}$, respectively. Assuming a solar silicon-to-carbon ratio, the $^{28}$SiO line emission model is consistent with about one-third of the silicon atoms being locked up in dust particles.

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arXiv2014

Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae

S-type AGB stars have a C/O ratio which suggests that they are transition objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such, their circumstellar compositions of gas and dust are thought to be sensitive to their precise C/O ratio, and it is therefore of particular interest to examine their circumstellar properties. We present new Herschel HIFI and PACS sub-millimetre and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances. We used radiative transfer codes to model the circumstellar dust and molecular line emission to determine circumstellar properties and molecular abundances. We assumed a spherically symmetric envelope formed by a constant mass-loss rate driven by an accelerating wind. Our model includes fully integrated H2O line cooling as part of the solution of the energy balance. We detect circumstellar molecular lines from CO, H2O, SiO, HCN, and, for the first time in an S-type AGB star, NH3. The radiative transfer calculations result in an estimated mass-loss rate for W Aql of 4.0e-6 Msol yr-1 based on the 12CO lines. The estimated 12CO/13CO ratio is 29, which is in line with ratios previously derived for S-type AGB stars. We find an H2O abundance of 1.5e-5, which is intermediate to the abundances expected for M and C stars, and an ortho/para ratio for H2O that is consistent with formation at warm temperatures. We find an HCN abundance of 3e-6, and, although no CN lines are detected using HIFI, we are able to put some constraints on the abundance, 6e-6, and distribution of CN in W Aql's circumstellar envelope using ground-based data. We find an SiO abundance of 3e-6, and an NH3 abundance of 1.7e-5, confined to a small envelope.

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arXiv2014

Herschel spectral-mapping of the Helix Nebula (NGC 7293): Extended CO photodissociation and OH+ emission

The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it is an ideal template for photochemical studies at small spatial scales in planetary nebulae. We aim to study the spatial distribution of the atomic and the molecular gas, and the structure of the photodissociation region along the western rims of the Helix Nebula as seen in the submillimeter range with Herschel. We use 5 SPIRE FTS pointing observations to make atomic and molecular spectral maps. We analyze the molecular gas by modeling the CO rotational lines using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model. For the first time, we have detected extended OH+ emission in a planetary nebula. The spectra towards the Helix Nebula also show CO emission lines (from J= 4 to 8), [NII] at 1461 GHz from ionized gas, and [CI] (2-1), which together with the OH+ lines, trace extended CO photodissociation regions along the rims. The estimated OH+ column density is (1-10)x1e12 cm-2. The CH+ (1-0) line was not detected at the sensitivity of our observations. Non-LTE models of the CO excitation were used to constrain the average gas density (n(H2)=(1-5)x1e5 cm-3) and the gas temperature (Tk= 20-40 K). The SPIRE spectral-maps suggest that CO arises from dense and shielded clumps in the western rims of the Helix Nebula whereas OH+ and [CI] lines trace the diffuse gas and the UV and X-ray illuminated clumps surface where molecules reform after CO photodissociation. [NII] traces a more diffuse ionized gas component in the interclump medium.

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arXiv2014

Herschel/PACS observations of the 69 $μm$ band of crystalline olivine around evolved stars

We present 48 Herschel/PACS spectra of evolved stars in the wavelength range of 67-72 $μ$m. This wavelength range covers the 69 $μ$m band of crystalline olivine ($\text{Mg}_{2-2x}\text{Fe}_{(2x)}\text{SiO}_{4}$). The width and wavelength position of this band are sensitive to the temperature and composition of the crystalline olivine. Our sample covers a wide range of objects: from high mass-loss rate AGB stars (OH/IR stars, $\dot M \ge 10^{-5}$ M$_\odot$/yr), through post-AGB stars with and without circumbinary disks, to planetary nebulae and even a few massive evolved stars. The goal of this study is to exploit the spectral properties of the 69 $μ$m band to determine the composition and temperature of the crystalline olivine. Since the objects cover a range of evolutionary phases, we study the physical and chemical properties in this range of physical environments. We fit the 69 $μ$m band and use its width and position to probe the composition and temperature of the crystalline olivine. For 27 sources in the sample, we detected the 69 $μ$m band of crystalline olivine ($\text{Mg}_{(2-2x)}\text{Fe}_{(2x)}\text{SiO}_{4}$). The 69 $μ$m band shows that all the sources produce pure forsterite grains containing no iron in their lattice structure. The temperature of the crystalline olivine as indicated by the 69 $μ$m band, shows that on average the temperature of the crystalline olivine is highest in the group of OH/IR stars and the post-AGB stars with confirmed Keplerian disks. The temperature is lower for the other post-AGB stars and lowest for the planetary nebulae. A couple of the detected 69 $μ$m bands are broader than those of pure magnesium-rich crystalline olivine, which we show can be due to a temperature gradient in the circumstellar environment of these stars. continued...

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arXiv2014

The wind of W Hya as seen by Herschel - I. The CO envelope

Asymptotic giant branch (AGB) stars lose their envelopes by means of a stellar wind whose driving mechanism is not understood well. Characterizing the composition and thermal and dynamical structure of the outflow provides constraints that are essential for understanding AGB evolution, including the rate of mass loss and isotopic ratios. We modeled the CO emission from the wind of the low mass-loss rate oxygen-rich AGB star W Hya using data obtained by the HIFI, PACS, and SPIRE instruments onboard the Herschel Space Observatory and ground-based telescopes. $^{12}$CO and $^{13}$CO lines are used to constrain the intrinsic $^{12}$C/$^{13}$C ratio from resolved HIFI lines. The acceleration of the outflow up to about 5.5 km/s is quite slow and can be represented by a beta-type velocity law with index 5. Beyond this point, acceleration up the terminal velocity of 7 km/s is faster. Using the J=10-9, 9-8, and 6-5 transitions, we find an intrinsic $^{12}$C/$^{13}$C ratio of $18\pm10$ for W Hya, where the error bar is mostly due to uncertainties in the $^{12}$CO abundance and the stellar flux around 4.6 $μ$m. To match the low-excitation CO lines, these molecules need to be photo-dissociated at about 500 stellar radii. The radial dust emission intensity profile measured by PACS images at 70 $μ$m shows substantially stronger emission than our model predicts beyond 20 arcsec. The initial slow acceleration of the wind implies inefficient wind driving in the lower part of the envelope. The final injection of momentum in the wind might be the result of an increase in the opacity thanks to the late condensation of dust species. The derived intrinsic isotopologue ratio for W Hya is consistent with values set by the first dredge-up and suggestive of an initial mass of 2 M$_\odot$ or more. However, the uncertainty in the main-sequence mass derived based on this isotopologic ratio is large.

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