Pedro Garcia-Lario

The Infrared Astronomical Mission AKARI

AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from mid- to far-infrared. The instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180 mu m in the pointed observation mode, occasionally inserted into a continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90% of the whole sky with a higher spatial resolution and a wider wavelength coverage than that of the previous IRAS all-sky survey. Point-source catalogues of the All-Sky Survey will be released to the astronomical community. Pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission.

MESS (Mass-loss of Evolved StarS), a Herschel key program

MESS (Mass-loss of Evolved StarS) is a guaranteed time key program that uses the PACS and SPIRE instruments on board the Herschel space observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of order 150 objects are observed in imaging and about 50 objects inspectroscopy. This paper describes the target selection and target list, and the observing strategy. Key science projects are described, and illustrated using results obtained during Herschel’s science demonstration phase. Aperture photometry is given for the 70 AGB and post-AGB stars observed up to October 17, 2010, which constitutes the largest single uniform database of far-IR and sub-mm fluxes for late-type stars.

A high-resolution line survey of IRC+10216 with Herschel/HIFI. First results: Detection of warm silicon dicarbide (SiC2)

We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901 GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5 − 636.5 GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal–to– noise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and, surprisingly, silicon dicarbide (SiC2). We identified 55 SiC2 transitions involving energy levels between 300 and 900 K. By analysing these rotational lines, we conclude that SiC2 is produced in the inner dust formation zone, with an abundance of ∼2×10−7 relative to molecular hydrogen. These SiC2 lines have been observed for the first time in space and have been used to derive an SiC2 rotational temperature of ∼204 K and a source-averaged column density of ∼6.4×1015 cm−2. Furthermore, the high quality of the HIFI data set was used to improve the spectroscopic rotational constants of SiC2.We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901 GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5−636.5 GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal-tonoise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and, surprisingly, silicon dicarbide (SiC2). We identified 55 SiC2 transitions involving energy levels between 300 and 900 K. By analysing these rotational lines, we conclude that SiC2 is produced in the inner dust formation zone, with an abundance of ∼2 × 10 −7 relative to molecular hydrogen. These SiC2 lines have been observed for the first time in space and have been used to derive an SiC2 rotational temperature of ∼204 K and a source-averaged column density of ∼6.4 × 10 15 cm −2 . Furthermore, the high quality of the HIFI data set was used to improve the spectroscopic rotational constants of SiC2.

THE NATURE OF DUST IN COMPACT GALACTIC PLANETARY NEBULAE FROM SPITZER SPECTRA

We present the Spitzer/Infrared Spectrograph (IRS) spectra of 157 compact Galactic planetary nebulae (PNe). These young PNe provide insight on the effects of dust in early post-asymptotic giant branch evolution, before much of the dust is altered or destroyed by the hardening stellar radiation field. Most of the selected targets have PN-type IRS spectra, while a few turned out to be misclassified stars. We inspected the group properties of the PN spectra and classified them based on the different dust classes (featureless or F, carbon-rich dust or CRD, oxygen-rich dust or ORD, mixed-chemistry dust or MCD) and subclasses (aromatic and aliphatic, and crystalline and amorphous). All PNe are characterized by dust continuum and more than 80% of the sample shows solid-state features above the continuum, in contrast with the Magellanic Cloud sample where only ~40% of the entire sample displays solid-state features; this is an indication of the strong link between dust properties and metallicity. The Galactic PNe that show solid-state features are almost equally divided among the CRD, ORD, and MCD. We analyzed dust properties together with other PN properties and found that (1) there is an enhancement of MCD PNe toward the Galactic center, in agreement with studies of Galactic bulge PNe; (2) CRD PNe could be seen as defining an evolutionary sequence, contrary to the ORD and MCD PNe, which are scattered in all evolutionary diagrams; (3) carbon-rich and oxygen-rich grains retain different equilibrium temperatures, as expected from models; and (4) ORD PNe are highly asymmetric, i.e., bipolar or bipolar core, and CRD PNe highly symmetric, i.e., round or elliptical; point symmetry is statistically more common in MCD than in other dust class PNe. By comparing the sample of this paper to that of Magellanic Cloud PNe, we find that the latter sample does not include MCD PNe, and the other dust classes are differently populated, with continuity of the fraction of F, CRD, ORD, and MCD populations from high to low metallicity environments. We also find similar sequences for CRD PNe in the Galactic disk and the Magellanic Clouds, except that the Magellanic Cloud PNe seem to attain higher dust temperatures at similar evolutionary stages, in agreement with the observational findings of smaller dust grains (i.e., lower radiation efficiency) in low metallicity interstellar environments.

Distinguishing between HII regions and planetary nebulae with Hi-GAL, WISE, MIPSGAL, and GLIMPSE ,

Context. HII regions and planetary nebulae (PNe) both emit at radio and infrared (IR) wavelengths, and angularly small H II regions can be mistaken for PNe. This problem of classification is most severe for HII regions in an early evolutionary stage, those that are extremely distant, or those that are both young and distant. Previous work has shown that HII regions and PNe can be separated based on their infrared colors. Aims. Using data from the Herschel Hi-GAL survey, as well as WISE and the Spitzer MIPSGAL and GLIMPSE surveys, we wish to establish characteristic IR colors that can be used to distinguish between HII regions and PNe. Methods. We perform aperture photometry measurements for a sample of 126 HII regions and 43 PNe at wavelengths from 8.0 mu m to 500 mu m. Results. We find that H II regions and PNe have distinct IR colors. The most robust discriminating color criteria are [F-12/F-8] \textless 0.3, [F-160/F-12] \textgreater 1.3, and [F-160/F-24] \textgreater 0.8 (or alternately [F-160/F-22] \textgreater 0.8), where the brackets indicate the log of the flux ratio. All three of these criteria are individually satisfied by over 98% of our sample of HII regions and by similar to 10% of our sample of PNe. Combinations of these colors are more robust in separating the two populations; for example all HII regions and no PNe satisfy [F-12/F-8] \textless 0.4 and [F-160/F-22] \textgreater 0.8. When applied to objects of unknown classification, these criteria prove useful in separating the two populations. The dispersion in color is relatively small for HII regions; this suggests that any evolution in these colors with time for HII regions must be relatively modest. The spectral energy distributions (SEDs) of HII regions can be separated into “warm” and “cold” components. The “cold” component is well-fit by a grey-body of temperature 25 K. The SEDs of nearly two-thirds of our sample of HII regions peak at 160 mu m and one third peak at 70 mu m. For PNe, 67% of the SEDs peak at 70 mu m, 23% peak at either 22 mu m or 24 mu m, and 9% (two sources) peak at 160 mu m.

Discovery of Time Variation of the Intensity of Molecular Lines in IRC+10216 in The Submillimeter and Far Infrared Domains

We report on the discovery of strong intensity variations in the high rotational lines of abundant molecular species towards the archetypical circumstellar envelope of IRC+10216. The observations have been carried out with the HIFI instrument on board Herschel and with the IRAM 30-m telescope. They cover several observing periods spreading over 3 years. The line intensity variations for molecules produced in the external layers of the envelope most probably result from time variations in the infrared pumping rates. We analyze the main implications this discovery has on the interpretation of molecular line emission in the envelopes of Mira-type stars. Radiative transfer calculations have to take into account both the time variability of infrared pumping and the possible variation of the dust and gas temperatures with stellar phase in order to reproduce the observation of molecular lines at different epochs. The effect of gas temperature variations with stellar phase could be particularly important for lines produced in the innermost regions of the envelope. Each layer of the circumstellar envelope sees the stellar light radiation with a different lag time (phase). Our results show that this effect must be included in the models. The sub-mm and FIR lines of AGB stars cannot anymore be considered as safe intensity calibrators.

The high-velocity outflow in the proto-planetary nebula Hen 3-1475

The proto-planetary nebula Hen 3-1475 shows a remarkable highly collimated optical jet with an S-shaped string of three pairs of knots and extremely high velocities. We present here a detailed analysis of the overall morphology, kinematic structure and the excitation conditions of these knots based on deep ground-based high dispersion spectroscopy complemented with high spatial resolution spectroscopy obtained with STIS onboard HST, and WFPC2 (N II) images. The spectra obtained show double-peaked, extremely wide emission line profiles, and a decrease of the radial velocities with distance to the source in a step-like fashion. We find that the emission line ratios observed in the intermediate knots are consistent with a spectrum arising from the recombination region of a shock wave with shock velocities ranging from 100 to 150 km s 1 . We propose that the ejection velocity is varying as a function of time with a quasi-periodic variability (with timescale of the order of 100 years) and the direction of ejection is also varying with a precession period of the order of 1500 years. Some slowing down with distance along the axis of the Hen 3-1475 jet may be due to the entrainment process and/or to the enviromental drag. This scenario is supported by geometric and kinematic evidence: firstly, the decrease of the radial velocities along the Hen 3-1475 jet in a step like fashion; secondly, the kinematic structure observed in the knots; thirdly, the point-symmetric morphology together with the high proper motions shown by several knots; and finally the fact that the shock velocity predicted from the observed spectra of the shocked knots is much slower than the velocities at which these knots move outwards with respect to the central source.

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

Context. We present 48 Herschel/PACS spectra of evolved stars in the wavelength range of 67 72 m. This wavelength range covers the 69 m band of crystalline olivine (Mg 2 2x Fe(2x)SiO4). 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, ˙ M 10 5 M /yr), through post-AGB stars with and without circumbinary disks, to planetary nebulae and even a few massive evolved stars. Aims. The goal of this study is to exploit the spectral properties of the 69 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. Methods. We fit the 69 m band and use its width and position to probe the composition and temperature of the crystalline olivine. Results. For 27 sources in the sample, we detected the 69 m band of crystalline olivine (Mg(2 2x)Fe(2x)SiO4). The 69 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 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 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. The disk sources in our sample with crystalline olivine are very diverse. They show either no 69 m band, a moderately strong band, or a very strong band, together with a temperature for the crystalline olivine in their disk that is either very warm ( 600 K), moderately warm ( 200 K), or cold ( 120 K), respectively.

High-resolution spectroscopy of the high-velocity hot post-AGB star LS III +52°24 (IRAS 22023+5249)

Aims. To investigate the first high resolution optical spectrum of the B−type star, LS III +52 ◦ 24, identified as the optical counterpart of the hot post−AGB candidate IRAS 22023+5249 (I22023). Methods. We carried out detailed identifications of the observed abso rption and emission features in the high resolution spectrum (4290 − 9015A ) of I22023 obtained with the Utrecht Echelle Spectrograph on the 4.2m William Herschel Telescope. Using Kurucz’s WIDTH9 program and the spectrum synthesis code, SYNSPEC, we determined the atmospheric parameters and abundances. The photospheric abundances were derived under the LTE approximation. The NEBULAR package under IRAF was used to estimate the electrontemperature (Te) and the electron density (Ne) from the [N II] and [S II] lines. Results. We estimated Teff=24000 K, log g=3.0, ξt=7 kms −1 . The derived CNO abundances suggest an evolved star with C/O< 1. P−Cygni profiles of hydrogen and helium indicate ongoing post−AGB mass loss. The presence of [N II] and [S II] lines and the non−detection of [O III] indicate that photoionisation has just started. The derived nebular parameters (Te=7000 K, Ne=1.2×10 4 cm −3 ) are comparable to those measured in young compact planetary nebulae (PNe). The nebular expansion velocity was estimated to be 17.5 kms −1 . Conclusions. The observed spectral features, large heliocentric radial velocity (−148.31± 0.60 kms −1 ), atmospheric parameters and chemical composition indicate that I22023, at a distance of 1.95 kpc, is an evolved post−AGB star belonging to the old disk population. The nebular parameters suggest that the central star may be evolving into a compact, young PN, similar to Hen3−1357.

Hi-GAL, the Herschel infrared Galactic Plane Survey: photometric maps and compact source catalogues - First data release for the inner Milky Way: +68° ≥ l ≥ −70°

Aims. We present the first public release of high-quality data products (DR1) from Hi-GAL, the Herschel infrared Galactic Plane Survey. Hi-GAL is the keystone of a suite of continuum Galactic plane surveys from the near-IR to the radio and covers five wavebands at 70, 160, 250, 350 and 500 µm, encompassing the peak of the spectral energy distribution of cold dust for 8 < T < 50 K. This first Hi-GAL data release covers the inner Milky Way in the longitude range 68◦ > t > −70◦ in a |b| ≤ 1◦ latitude strip. ∼ ∼ ∼ ∼ Methods. Photometric maps have been produced with the ROMAGAL pipeline, which optimally capitalizes on the excellent sensitivity and stability of the bolometer arrays of the Herschel PACS and SPIRE photometric cameras. It delivers images of exquisite quality and dynamical range, absolutely calibrated with Planck and IRAS, and recovers extended emission at all wavelengths and all spatial scales, from the point-spread function to the size of an entire 2◦ × 2◦ “tile” that is the unit observing block of the survey. The compact source catalogues were generated with the CuTEx algorithm, which was specifically developed to optimise source detection and extraction in the extreme conditions of intense and spatially varying background that are found in the Galactic plane in the thermal infrared. Results. Hi-GAL DR1 images are cirrus noise limited and reach the 1σ-rms predicted by the Herschel Time Estimators for parallel-mode obser- vations at 6011 s−1 scanning speed in relatively low cirrus emission regions. Hi-GAL DR1 images will be accessible through a dedicated web-based image cutout service. The DR1 Compact Source Catalogues are delivered as single-band photometric lists containing, in addition to source posi- tion, peak, and integrated flux and source sizes, a variety of parameters useful to assess the quality and reliability of the extracted sources. Caveats and hints to help in this assessment are provided. Flux completeness limits in all bands are determined from extensive synthetic source experiments and greatly depend on the specific line of sight along the Galactic plane because the background strongly varies as a function of Galactic longitude. Hi-GAL DR1 catalogues contain 123210, 308509, 280685, 160972, and 85460 compact sources in the five bands.