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H4-1 is a planetary nebula (PN) located in the Galactic halo, and is notably carbon-rich and one of the most metal-deficient PNe in the Milky Way. To unveil its progenitor evolution through the accurate measurement of the gas mass, we conducted a comprehensive investigation of H4-1, using the newly obtained Seimei/KOOLS-IFU spectra and multiwavelength spectro-photometry data. The emission line images generated from the KOOLS-IFU datacube successfully resolve the ellipsoidal nebula and the equatorial flattened disk that are frequently seen in bipolar PNe evolved from massive progenitors. By a fully data-driven method, we directly derived the seven elemental abundances, the gas-to-dust mass ratio, and the gas and dust masses based on our own distance scale. By comparing the observed quantities with both the photoionization model and the binary nucleosynthesis model, we conclude that the progenitors of an initial mass of 1.87 Msun and 0.82 Msun are second generation stars formed ~4 Gyrs after the Big Bang, and underwent mass-transfers, binary merger, and ultimately evolved into a PN showing unique chemical abundances. Our binary model successfully reproduces the observed abundances and also explains evolutionary time scale of H4-1., Comment: 19 pages, 5 figures, 11 tables, accepted for publication in PASJ

Recent abrupt changes of CW Leonis may indicate that we are witnessing the moment that the central carbon star is evolving off the Asymptotic Giant Branch (AGB) and entering into the pre-planetary nebula (PPN) phase. The recent appearance of a red compact peak at the predicted stellar position is possibly an unveiling event of the star, and the radial beams emerging from the stellar position resemble the feature of the PPN Egg Nebula. The increase of light curve over two decades is also extraordinary, and it is possibly related to the phase transition. Decadal-period variations are further found in the residuals of light curves, in the relative brightness of radial beams, and in the extended halo brightness distribution. Further monitoring of the recent dramatic and decadal-scale changes of this most well-known carbon star CW Leonis at the tip of AGB is still highly essential, and will help us gain a more concrete understanding on the conditions for transition between the late stellar evolutionary phases., Comment: 6 pages, 4 figures, Winds of Stars and Exoplanets. Proceedings of the International Astronomical Union, Volume 370, pp. 78-83

Planetary nebulae (PNe), the ejected envelopes of red giant stars, provide us with a history of the last, mass-losing phases of 90 percent of stars initially more massive than the Sun. Here, we analyse James Webb Space Telescope (JWST) Early Release Observation (ERO) images of the PN NGC3132. A structured, extended H2 halo surrounding an ionised central bubble is imprinted with spiral structures, likely shaped by a low-mass companion orbiting the central star at 40-60 AU. The images also reveal a mid-IR excess at the central star interpreted as a dusty disk, indicative of an interaction with another, closer companion. Including the previously known, A-type visual companion, the progenitor of the NGC3132 PN must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionisation and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Further, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star to date with excellent precision: 2.86+/-0.06 Mo. These results serve as path finders for future JWST observations of PNe providing unique insight into fundamental astrophysical processes including colliding winds, and binary star interactions, with implications for supernovae and gravitational wave systems., Comment: 32 pages, 5 figures for the main article. 12 pages 8 figures for the supplementary material

Plasma diagnostics are the bases of investigation into the physical and chemical properties of line-emitting gaseous systems. To perform plasma diagnostics properly, it is essential to correct the input spectrum for extinction properly. This is simply because determining the degree of extinction is dependent on the physical properties of the line-emitting gas. Hence, both extinction correction and plasma diagnostics have to be performed simultaneously and self-consistently. By comparing the results of analyses performed for a sample of nine bright planetary nebulae in M 31 with and without the proper extinction correction and plasma diagnostics, we demonstrate how initial assumptions for the physical conditions of the line-emitting gas in extinction correction would compromise the results of the entire analyses. While the electron density/temperature are relatively immune to the imposed inconsistent assumptions, the compromised extinction would cause systematic offsets in the extinction-corrected line strengths, which consequently would impose adverse effects on the resulting ionic and elemental abundances, and other inferences made from the incorrect results. We find that this M 31 PN sample simply represents those around the high-mass end of the mass range for low-mass planetary nebula progenitor stars as expected from the existing theoretical models. It appears that the suspicion raised in the previous study - these PNe being anomalously nitrogen overabundant - is simply caused by the apparent underestimate in extinction that originates from the imposed inconsistent assumptions in extinction correction. In a larger context, the results of plasma diagnostics in the literature without seeking simultaneous self-consistency with extinction correction have to be handled cautiously. Ideally, such previous results should be re-evaluated by seeking simultaneous self-consistency., Comment: 5 pages (main text with 2 tables) plus 5 supplemental pages (5 tables in Appendix); to be published in Astronomy and Astrophysics Letter to the Editor

To understand the physical conditions of various gaseous systems, plasma diagnostics must be performed properly. To that end, it is equally important to have extinction correction performed properly. This means that the physical conditions of the target sources -- the very quantities to be derived via plasma diagnostics -- must be known even before performing extinction correction, because the degree of extinction is usually determined by comparing the observed spectra of the target sources with their theoretically predicted counterparts. One way to resolve this conundrum is to perform both extinction correction and plasma diagnostics together by iteratively seeking a converged solution. In fact, if these analyses are performed self-consistently, a converged solution can be found based solely on well-calibrated line intensities, given the adopted extinction law and the R_V value. However, it is still rare to find these analyses done numerically rigorously from start to finish. In this contribution for the APN 8e conference, we would like to review this convoluted problem and sort out critical issues based on the results of our recent experiments. It appears that the convoluted theoretical and observational progresses exacerbated by the highly numerical nature of these analyses necessitated a number of analytical simplifications to make the problem analytically tractable in the pre-computer era and that such analytical simplifications still remain rampant in the literature today even after ample computational resources became readily available. Hence, the community is encouraged to do away with this old habit of sidestepping numerical calculations, which may have been a necessary evil in the past. This is especially true in the context of spatially-resolved 2-D spectroscopy, which obviously conflicts with the uniformity assumption often blindly inherited from 1-D spectroscopy., Comment: 8 pages; This article belongs to the Special Issue Asymmetric Planetary Nebulae 8e (https://www.mdpi.com/journal/galaxies/special_issues/asymmetric_planetary_nebulae)

In this work, we propose a proper plasma analysis practice (PPAP), an updated procedure of plasma diagnostics in the era of spatially-resolved spectroscopy. In particular, we emphasize the importance of performing both of the extinction correction and the direct method of plasma diagnostics simultaneously as an integrated process. This approach is motivated by the reciprocal dependence between critical parameters in these analyses, which can be resolved by iteratively seeking a converged solution. The use of PPAP allows us to eliminate unnecessary assumptions that prevent us from obtaining an exact solution at each element of the spectral imaging data. Using a suite of HST/WFC3 narrowband images of the planetary nebula, NGC 6720, we validate PPAP by (1) simultaneously and self-consistently deriving the extinction, c(Hb), and electron density/temperature distribution, (n_e, T_e), maps that are consistent with each other, and (2) obtaining identical metal abundance distribution maps, (n(N^+)/n(H^+), n(S^+)/n(H^+)), from multiple emission line maps at different wavelengths/transition energies. We also determine that the derived c(Hb) consists both of the ISM and circumsource components and that the ionized gas-to-dust mass ratio in the main ring is at least 437 and as high as about 1600. We find that, unless we deliberately seek self-consistency, uncertainties at tens of per cent can easily arise in outcomes, making it impossible to discern actual spatial variations that occurs at the same level, defeating the purpose of conducting spatially resolved spectroscopic observations., Comment: 27 pages, 18 figures, to be published as a Tutorial in the Publication of the Astronomical Society of the Pacific

Six images of IRC+10216 taken by the Hubble Space Telescope at three epochs in 2001, 2011, and 2016 are compared in the rest frame of the central carbon star. An accurate astrometry has been achieved with the help of Gaia Data Release 2. The positions of the carbon star in the individual epochs are determined using its known proper motion, defining the rest frame of the star. In 2016, a local brightness peak with compact and red nature is detected at the stellar position. A comparison of the color maps between 2016 and 2011 epochs reveals that the reddest spot moved along with the star, suggesting a possibility of its being the dusty material surrounding the carbon star. Relatively red, ambient region is distributed in an $\Omega$ shape and well corresponds to the dusty disk previously suggested based on near-infrared polarization observations. In a larger scale, differential proper motion of multiple ring-like pattern in the rest frame of the star is used to derive the average expansion velocity of transverse wind components, resulting in $\sim$ 12.5 km s$^{-1}$ ($d$/123 pc), where $d$ is the distance to IRC+10216. Three dimensional geometry is implied from its comparison with the line-of-sight wind velocity determined from half-widths of submillimeter emission line profiles of abundant molecules. Uneven temporal variations in brightness for different searchlight beams and anisotropic distribution of extended halo are revisited in the context of the stellar light illumination through a porous envelope with postulated longer-term variations for a period of $\lesssim10$ years., Comment: 20 pages, 12 figures, 1 table, accepted for publication in The Astrophysical Journal

Non-variable OH/IR stars are thought to have just left the asymptotic giant branch (AGB) phase. In this conventional picture, they must still show strong circumstellar extinction caused by the dust ejected during the AGB phase, and the extinction is expected to decrease over time because of the dispersal of the circumstellar dust after the cessation of the stellar mass loss. The reduction of the extinction makes the stars become apparently brighter and bluer with time especially in the near-infrared (NIR) range. We look for such long-term brightening of non-variable OH/IR stars by using 2MASS, UKIDSS, and OAOWFC survey data. As a result, we get multi-epoch NIR data taken over a 20-year period (1997-2017) for 6 of 16 non-variable OH/IR stars, and all six objects are found to be brightening. The K-band brightening rate of five objects ranges from 0.010 to 0.130 mag yr$^{-1}$, which is reasonably explained with the conventional picture. However, one OH/IR star, OH31.0-0.2, shows a rapid brightening, which cannot be explained only by the dispersal of the dust shell. Multi-color (J-, H-, and K-band) data are obtained for three objects, OH25.1-0.3, OH53.6-0.2, and OH77.9+0.2. Surprisingly, none of them appears to have become bluer, and OH53.6-0.2 is found to have been reddened with a rate of 0.013 mag yr$^{-1}$ in (J-K). Our findings suggest other mechanisms such as rapid changes in stellar properties (temperature or luminosity) or a generation of a new batch of dust grains., Comment: 26 pages, 14 figures, 4 tables, published in ApJ

We performed a far-IR imaging survey of the circumstellar dust shells of 144 evolved stars as a mission programme of the AKARI infrared astronomical satellite using the Far-Infrared Surveyor (FIS) instrument. With this survey, we deliver far-IR surface brightness distributions of roughly 10' x 40' or 10' x 20' areas of the sky around the target evolved stars in the four FIS bands at 65, 90, 140, and 160 microns. Our objectives are to characterize the far-IR surface brightness distributions of the cold dust component in the circumstellar dust shells, from which we derive the amount of cold dust grains as low as 20 K and empirically establish the history of the early mass loss history. In this first installment of the series, we introduce the project and its aims, describe the observations, data reduction, and surface brightness correction process, and present the entire data set along with the results of integrated photometry measurements (i.e., the central source and circumstellar dust shell altogether). We find that (1) far-IR emission is detected from all but one object at the spatial resolution about 30" - 50" in the corresponding bands, (2) roughly 60 - 70 % of the target sources show some extension, (3) previously unresolved nearby objects in the far-IR are now resolved around 28 target sources, (4) the results of photometry measurements are reasonable with respect to the entries in the AKARI/FIS Bright Source Catalogue, despite the fact that the targets are assumed to be point-sources when catalogue flux densities were computed, and (5) an IR two-color diagram would place the target sources in a roughly linear distribution that may correlate with the age of the circumstellar dust shell and can potentially be used to identify which targets are more extended than others., Comment: To be published in PASJ AKARI Special Issue: 25 pages, 5 figures, 5 tables (and 28 supplementary figures available only in PASJ on-line)

We observed two proto-planetary nebulae, HD 56126 representing a source with an elliptical circumstellar shell and IRAS 16594-4656 representing a source with a bipolar circumstellar shell, with ALMA in the 12CO and 13CO J=3-2 lines and neighboring continuum to see how the morpho-kinematics of CO gas and dust emission properties in their circumstellar environments differ., Comment: 2 pages, 2 figures; contribution to Proceedings of IAU Symp 343

The AKARI Infrared Astronomical Satellite produced the all-sky survey (AFASS) maps in the far-IR at roughly arc-minute spatial resolution, enabling us to investigate the whole sky in the far-IR for objects having surface brightnesses greater than a few to a couple of dozen MJy/sr. While the AFASS maps are absolutely calibrated against large-scale diffuse emission, it was uncertain whether or not an additional flux correction for point sources was necessary. Here, we verify that calibration for point-source photometry in the AFASS maps is proper. With the aperture correction method based on the empirical point-spread-function templates derived directly from the AFASS maps, fluxes in the AKARI bright source catalogue (BSC) are reproduced. The AKARI BSC fluxes are also satisfactorily recovered with the 1 sigma aperture, which is the empirical equivalent of an infinite aperture. These results confirm that in the AFASS maps far-IR photometry can be properly performed by using the aperture correction method for point sources and by summing all pixel values within an appropriately defined aperture of the intended target (i.e., the aperture photometry method) for extended sources., Comment: 8 pages, 3 figures, to be published on PASJ (AKARI Special Issue)

The bipolar nebula Menzel 3 (Mz 3) was observed as part of the \textit{Herschel} Planetary Nebula Survey (\textit{HerPlaNS}), which used the PACS and SPIRE instruments aboard the \textit{Herschel Space Observatory} to study a sample of planetary nebulae (PNe). In this paper, one of the series describing \textit{HerPlaNS} results, we report the detection of H I recombination lines (HRLs) in the spectrum of Mz 3. Inspection of the spectrum reveals the presence of 12 HRLs in the 55 to 680 $\mu$m range covered by the PACS and SPIRE instruments (H11$\alpha$ to H21$\alpha$ and H14$\beta$). The presence of HRLs in this range is unusual for PNe and has not been reported in Mz 3 before. Our analysis indicates that the HRLs we observed are enhanced by laser effect occurring in the core of Mz 3. Our arguments for this are: (i) the available Mz 3 optical to submillimetre HRL $\alpha$ line intensity ratios are not well reproduced by the spontaneous emission of optically thin ionized gas, as would be typical for nebular gas in PNe; (ii) the compact core of Mz 3 is responsible for a large fraction of the Herschel HRLs emission; (iii) the line intensity ratios for Mz 3 are very similar to those in the core emission of the well known star MWC 349A, where laser effect is responsible for the enhancement of HRLs in the Herschel wavelength range; (iv) the physical characteristics relevant to cause laser effect in the core of MWC 349A are very similar to those in the core of Mz 3., Comment: Published in MNRAS. ESA Portal Story. 13 Pages, 7 figures

We perform a comprehensive analysis of the planetary nebula (PN) NGC6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object's evolution, based on panchromatic observational data ranging from UV to radio. Empirical nebular elemental abundances, compared with theoretical predictions via nucleosynthesis models of asymptotic giant branch (AGB) stars, indicate that the progenitor is a solar-metallicity, 2.25-3.0 Msun initial-mass star. We derive the best-fit distance of 0.46 kpc by fitting the stellar luminosity (as a function of the distance and effective temperature of the central star) with the adopted post-AGB evolutionary tracks. Our excitation energy diagram analysis indicate high excitation temperatures in the photodissociation region (PDR) beyond the ionized part of the nebula, suggesting extra heating by shock interactions between the slow AGB wind and the fast PN wind. Through iterative fitting using the Cloudy code with empirically-derived constraints, we find the best-fit dusty photoionization model of the object that would inclusively reproduce all of the adopted panchromatic observational data. The estimated total gas mass (0.41 Msun) corresponds to the mass ejected during the last AGB thermal pulse event predicted for a 2.5 Msun initial-mass star. A significant fraction of the total mass (about 70 percent) is found to exist in the PDR, demonstrating the critical importance of the PDR in PNe that are generally recognized as the hallmark of ionized/H+ regions., Comment: 34 pages, 13 Figures and 16 Tables, accepted for publication in the Astrophysical Journal Supplement Series

We present a general surface brightness correction method for compact extended sources imaged in the slow-scan pointed observation mode of the Far-Infrared Surveyor (FIS) aboard the AKARI Infrared Astronomical Satellite. Our method recovers correct surface brightness distribution maps by re-scaling archived raw FIS maps using the surface-brightness-dependent inverse FIS response function. The flux of a target source is then automatically corrected for as the simple sum of surface brightnesses within the adopted contour encircling the perimeter of the target (i.e., contour photometry). This correction method is contrasted to the previous aperture photometry method for point sources, which directly corrects for the target flux with a flux-dependent scaling law. The new surface brightness correction scheme is applicable to objects of any shape from unresolved point sources to resolved extended objects, as long as the target is not deemed diffuse, i.e., the total extent of the target source does not exceed too much more than a single FIS scan width of 10 arcmin. The new correction method takes advantage of the well-defined shape (i.e., the scale invariance) of the point-spread function, which enables us to adopt a power-law FIS response function. We analyze the point-source photometric calibrator data using the FIS AKARI Slow-scan Tool (FAST) and constrained the parameters of the adopted power-law FIS response function. We conclude that the photometric accuracy of the new correction method is better than 10% error based on comparisons with the expected fluxes of the photometric calibrators and that resulting fluxes without the present correction method can lead up to 230% overestimates or down to 50% underestimates., Comment: accepted for publication in PASJ

We present the results of differential proper-motion analyses of the Egg Nebula (RAFGL 2688, V1610 Cyg) based on the archived two-epoch optical data taken with the Hubble Space Telescope. First, we determined that the polarization characteristics of the Egg Nebula is influenced by the higher optical depth of the central regions of the nebula (i.e., the "dustsphere" of about 1000 AU radius), causing the nebula illuminated in two steps -- the direct starlight is first channeled into bipolar cavities and then scattered off to the rest of the nebula. We then measured the amount of motion of local structures and the signature concentric arcs by determining their relative shifts over the 7.25 yr interval. Based on our analysis, which does not rely on the single-scattering assumption, we concluded that the lobes have been excavated by a linear expansion along the bipolar axis for the past 400 yr, while the concentric arcs have been generated continuously and moving out radially at about 10 km/s for the past 5,500 yr, and there appears to be a colatitudinally-increasing trend in the radial expansion velocity field of the concentric arcs. There exist numerical investigations into the mass-loss modulation by the central binary system, which predict such a colatitudinally-increasing expansion velocity field in the spiral-shock trails of the mass-loss ejecta. Therefore, the Egg Nebula may represent a rare edge-on case of the binary-modulated circumstellar environs, corroborating the previous theoretical predictions., Comment: to appear in the Astrophysical Journal

We report mid-infrared (MIR) imaging observations of the carbon star U Ant made with the Infrared Camera (IRC) on board AKARI. Subtraction of the artifacts and extended PSF of the central star reveals the detached dust shell around the carbon star at MIR wavelengths (15 and 24{\mu}m) for the first time. The observed radial brightness profiles of the MIR emission are well explained by two shells at 43" and 50" from the central star detected in optical scattered light observations. Combining Herschel/PACS, AKARI/FIS, and AKARI/IRC data, we obtain the infrared spectral energy distribution (SED) of the thermal emission from the detached shell of U Ant in a wide infrared spectral range of 15- 160 {\mu}m. Thermal emission of amorphous carbon grains with a single temperature cannot account for the observed SED from 15 to 160 {\mu}m: it underestimates the emission at 15 {\mu}m. Alternatively, the observed SED is fitted by the model that amorphous carbon grains in the two shells have different temperatures of 60 and 104 K, which allocates most dust mass in the shell at 50". This supports previous suggestion that the 43" shell is gas-rich and the 50" one is dust-rich. We suggest a possibility that the segregation of the gas and dust resulting from the drift motion of submicron-sized dust grains relative to the gas and that the hot dust component associated with the gas-rich shell is composed of very small grains that are strongly coupled with the gas., Comment: 19 pages, 3 figures, accepted for publication in ApJL

HD179821 is an enigmatic evolved star that possesses characteristics of both a post-asymptotic giant branch star and a yellow hyper-giant, and there has been no evidence that unambiguously defines its nature. These two hypotheses are products of an indeterminate distance, presumed to be 1 kpc or 6 kpc. We have obtained the two-epoch Hubble Space Telescope WFPC2 data of its circumstellar shell, which shows multiple concentric arcs extending out to about 8 arcsec. We have performed differential proper-motion measurements on distinct structures within the circumstellar shell of this mysterious star in hopes of determining the distance to the object, and thereby distinguishing the nature of this enigmatic stellar source. Upon investigation, rather than azimuthal radially symmetric expansion, we discovered a bulk motion of the circumstellar shell of (2.41+-0.43, 2.97+-0.32) mas/yr. This corresponded to a translational ISM flow of (1.28+-0.95, 7.27+-0.75) mas/yr local to the star. This finding implies that the distance to HD 179821 should be rather small in order for its circumstellar shell to preserve its highly intact spherical structure in the presence of the distorting ISM flow, therefore favoring the proposition that HD 179821 is a post-AGB object., Comment: Accepted for publication in ApJL

We report here on the discovery of an extended far-infrared shell around the AGB star, R Cassiopeia, made by AKARI and Spitzer. The extended, cold circumstellar shell of R Cas spans nearly 3 arcmin and is probably shaped by interaction with the interstellar medium. This report is one of several studies of well-resolved mass loss histories of AGB stars under AKARI and Spitzer observing programs labeled "Excavating Mass Loss History in Extended Dust Shells of Evolved Stars (MLHES)"., Comment: Poster contribution, to be published in the proceedings of the conference "AKARI, a light to illuminate the misty Universe" held at University of Tokyo, Japan, 16-19 February 2009

Recent far-infrared mapping of mass-losing stars by the AKARI Infrared Astronomy Satellite and Spitzer Space Telescope have suggested that far-infrared bow shock structures are probably ubiquitous around these mass-losing stars, especially when these stars have high proper motion. Higher spatial resolution data of such far-infrared bow shocks now allow detailed fitting to yield the orientation of the bow shock cone with respect to the heliocentric space motion vector of the central star, using the analytical solution for these bow shocks under the assumption of momentum conservation across a physically thin interface between the stellar winds and interstellar medium (ISM). This fitting analysis of the observed bow shock structure would enable determination of the ambient ISM flow vector, founding a new technique to probe the 3-D ISM dynamics that are local to these interacting systems. In this review, we will demonstrate this new technique for three particular cases, Betelgeuse, R Hydrae, and R Cassiopeiae., Comment: Invited Talk, to be published in the proceedings of the conference "AKARI, a light to illuminate the misty Universe" held at University of Tokyo, Japan, 16-19 February 2009

Evolved mass-losing stars such as Mira enrich the interstellar medium (ISM) significantly by their dust-rich molecular wind. When these stars move fast enough relative to the ISM, the interaction between the wind and ISM generates the structure known as the astropause (a stellar analog of the heliopause), which is a cometary stellar wind cavity bounded by the contact discontinuity surface between the wind and ISM. Far-infrared observations of Mira spatially resolve the structure of its astropause for the first time, distinguishing the contact surface between Mira's wind and the ISM and the termination shock due to Mira's wind colliding with the ISM. The physical size of the astropause and the estimated speed of the termination shock suggest the age of the astropause to be about 40,000 yr, confirming a theoretical prediction of the shock re-establishment time after Mira has entered the Local Bubble., Comment: 9 pages including 2 figures. To appear in the Astrophysical Journal Letters

We present 10' x 50' scan maps around an M supergiant Alpha Ori at 65, 90, 140 and 160 microns obtained with the AKARI Infrared Astronomy Satellite. Higher spatial resolution data with the exact analytic solution permit us to fit the de-projected shape of the stellar wind bow shock around Alpha Ori to have the stand-off distance of 4.8', position angle of 55 degrees and inclination angle of 56 degrees. The shape of the bow shock suggests that the peculiar velocity of Alpha Ori with respect to the local medium is v_* = 40 (n_H)^(-1/2), where n_H is the hydrogen nucleus density at Alpha Ori. We find that the local medium is of n_H = 1.5 to 1.9 cm^(-3) and the velocity of the local flow is at 11 km s^(-1) by using the most recent astrometric solutions for Alpha Ori under the assumption that the local medium is moving away from the Orion OB 1 association. AKARI images may also reveal a vortex ring due to instabilities on the surface of the bow shock as demonstrated by numerical models. This research exemplifies the potential of AKARI All-Sky data as well as follow-up observations with Herschel Space Telescope and Stratospheric Observatory for Infrared Astronomy for this avenue of research in revealing the nature of interaction between the stellar wind and interstellar medium., Comment: 8 pages, 2 figures, to be published in PASJ Vol. 60 Special Issue on Recent Results from AKARI

The structure of the dusty circumstellar envelopes (CSEs) of proto-planetary nebulae (PPNs) reveals the mass-loss history of these sources and how such histories may differ for elliptical (SOLE) and bipolar (DUPLEX) PPNs. To study the PPN structures via dust-scattered linearly polarized starlight, we have compiled the imaging-polarimetric data for all 18 evolved stars that have been obtained to date with NICMOS on-board the Hubble Space Telescope (HST). This alternative imaging technique provides a unique way to probe the distribution of dust grains that scatter light around evolved stars. The new perspective gained from the imaging-polarimetric data has revealed several new aspects to the structures of PPNs. Point-symmetry is a prevalent imaging-polarimetric characteristic resulting from the azimuthal density gradient in the CSEs. Among these point-symmetric nebulae, three detailed morphological types can be differentiated by their polarized intensity, I_pol, and polarization strength, P. While the azimuthal density gradient is reversed above and below the equatorial plane in optically thicker bipolar nebulae, there is no gradient reversal in optically thinner elliptical nebulae. The equatorial plane of the system defined by the integrated angle of polarization is not necessarily orthogonal to the axis of the apparent bipolar structure in the total intensity data., Comment: 27 pages, 14 figures, 3 tables; to appear in the Astronomical Journal March 2007 issue

New Spitzer imaging observations have revealed the structure around the Mira variable star R Hya to be a one-sided parabolic arc 100 arcsec to the West stretching from North to South. We successfully model R Hya and its surroundings in terms of an interaction of the stellar wind from an asymptotic giant branch (AGB) star with the interstellar medium (ISM) the star moves through. Our three-dimensional hydrodynamic simulation reproduces the structure as a bow shock into the oncoming ISM. We propose this as another explanation of detached shells around such stars which should be considered alongside current theories of internal origin. The simulation predicts the existence of a tail of ram-pressure-stripped AGB material stretching downstream. Indications for such a tail behind R Hya are seen in IRAS maps., Comment: 5 pages, 3 colour figures, submitted to MNRAS letters, revised version after referee's comments

We present the far-infrared (IR) maps of a bipolar planetary nebula (PN), NGC 650, at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) on-board the Spitzer Space Telescope. While the two-peak emission structure seen in all MIPS bands suggests the presence of a near edge-on dusty torus, the distinct emission structure between the 24 micron map and the 70/160 micron maps indicates the presence of two distinct emission components in the central torus. Based on the spatial correlation of these two far-IR emission components with respect to various optical line emission, we conclude that the 24 micron emission is largely due to the [O IV] line at 25.9 micron arising from highly ionized regions behind the ionization front, whereas the 70 and 160 micron emission is due to dust continuum arising from low-temperature dust in the remnant asymptotic giant branch (AGB) wind shell. The far-IR nebula structure also suggests that the enhancement of mass loss at the end of the AGB phase has occurred isotropically, but has ensued only in the equatorial directions while ceasing in the polar directions. The present data also show evidence for the prolate spheroidal distribution of matter in this bipolar PN. The AGB mass loss history reconstructed in this PN is thus consistent with what has been previously proposed based on the past optical and mid-IR imaging surveys of the post-AGB shells., Comment: 9 pages in the emulated ApJ format with 6 figures, to appear in ApJ

We are performing a uniform and unbiased, ~7x7 degrees imaging survey of the Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the Spitzer Space Telescope in order to survey the agents of a galaxy's evolution (SAGE), the interstellar medium (ISM) and stars in the LMC. The detection of diffuse ISM with column densities >1.2x10^21 H cm^-2 permits detailed studies of dust processes in the ISM. SAGE's point source sensitivity enables a complete census of newly formed stars with masses >3 solar masses that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass loss rates >1x10^-8 solar masses per year will quantify the rate at which evolved stars inject mass into the ISM of the LMC. The observing strategy includes two epochs in 2005, separated by three months, that both mitigate instrumental artifacts and constrain source variability. The SAGE data are non-proprietary. The data processing includes IRAC and MIPS pipelines and a database for mining the point source catalogs, which will be released to the community in support of Spitzer proposal cycles 4 and 5. We present initial results on the epoch 1 data with a special focus on the N79 and N83 region. The SAGE epoch 1 point source catalog has ~4 million sources. The point source counts are highest for the IRAC 3.6 microns band and decrease dramatically towards longer wavelengths consistent with the fact that stars dominate the point source catalogs and that the dusty objects, e.g. young stellar objects and dusty evolved stars that detected at the longer wavelengths, are rare in comparison. We outline a strategy for identifying foreground MW stars, that may comprise as much as 18% of the source list, and background galaxies, that may comprise ~12% of the source list., Comment: Accepted by the Astronomical Journal

We present the results of proper-motion measurements of the dust shell structure in the Egg Nebula (AFGL 2688, CRL 2688, V1610 Cyg), based on the archived two-epoch imaging-polarimetry data in the 2 micron band taken with NICMOS on-board the Hubble Space Telescope. We measured the amount of motions of local structures in the nebula by determining their relative shifts over an interval of 5.5 years. The dynamical age of the nebula is found to be roughly 350 years based on the overall motion of the nebula that exhibits a Hubble-law-esque linear relation between the measured proper motion and the projected radial distance from the origin of the expansion. By adopting the de-projected velocity of 45 km/s at the tips of the bipolar lobes, our proper-motion measurements indicate that the distance to the Egg Nebula is about 420 pc and that the lobes are inclined at 7.7 degrees with respect to the plane of the sky. The refined distance estimate yields the luminosity of the central star of 3.3 x 10^3 L_sun, the total shell mass of 1.2 M_sun, and the mass loss rate (the upper limit) of 3.6 x 10^(-3) M_sun/yr. Assuming 0.6 M_sun central post-AGB stellar mass, the initial mass of the Egg is 1.8 M_sun. Upon analysis, we also discovered that the central star of the Egg Nebula has proper motion of its own at the rate of (14, -10) mas/yr., Comment: To appear in ApJ in April 2006. 11 ApJ emulated pages including 2 tables and 4 figures

Using NICMOS on HST, we have performed imaging polarimetry of proto-planetary nebulae. Our objective is to study the structure of optically thin circumstellar shells of post-asymptotic giant branch stars by separating dust-scattered, linearly polarized star light from unpolarized direct star light. This unique technique allows us to probe faint reflection nebulae around the bright central star, which can be buried under the point-spread-function of the central star in conventional imaging. Our observations and archival search have yielded polarimetric images for five sources: IRAS 07134+1005 (HD 56126), IRAS 06530-0213, IRAS 04296+3429, IRAS (Z)02229+6208, and IRAS 16594-4656. These images have revealed the circumstellar dust distribution in an unprecedented detail via polarized intensity maps, providing a basis to understand the 3-D structure of these dust shells. We have observationally confirmed the presence of the inner cavity caused by the cessation of AGB mass loss and the internal shell structures which is strongly tied to the progenitor star's mass loss history on the AGB. We have also found that equatorial enhancement in these circumstellar shells comes with various degrees of contrast, suggesting a range of optical depths in these optically thin shells. Our data support the interpretation that the dichotomy of PPN morphologies is due primarily to differences in optical depth and secondary to the inclination effect. The polarization maps reveal a range of inclination angles for these optically thin reflection nebulae, dispelling the notion that elliptical nebulae are pole-on bipolar nebulae., Comment: 17 pages in emulateapj format, 12 figures. To be published in the March 2005 issue of The Astronomical Journal

Past imaging observations of a post-AGB star, HD 161796, have probed different parts of its circumstellar shell which correspond to different epochs of the star's AGB mass loss history. While the overall structure of the shell can be described by an axisymmetric model consisting of three layers of characteristic structure, the mass distribution in the shell appears to rotate its axis of symmetry in a continuous manner. It is thus interesting to observe the halo region of the shell using from far-IR to sub-mm wavelengths and increase the ``time resolution'' during this critical epoch of the star's mass loss history., Comment: 4 pages, 3 figures; to appear in "Asymmetrical Planetary Nebulae III" editors M. Meixner, J. Kastner, N. Soker, & B. Balick (ASP Conf. Series)

We present the preliminary results from our HST/NICMOS imaging polarimetry on optically thin PPNs. The data show the dust distribution in an unprecedented detail. The structure of these faint PPNs is revealed via polarization properties of the dust-scattered light without much interference from the bright central star, proving the unique advantages of the technique over simple imaging., Comment: 2 pages, 1 figure; to appear in "Asymmetrical Planetary Nebulae III" editors M. Meixner, J. Kastner, N. Soker, & B. Balick (ASP Conf. Series)

We present JHK' photometric measurements of 78 objects mostly consisting of proto-planetary nebula candidates. Photometric magnitudes are determined by means of imaging and aperture photometry. Unlike the observations with a photometer with a fixed-sized beam, the method of imaging photometry permits accurate derivation of photometric values because the target sources can be correctly identified and confusion with neighboring sources can be easily avoided. Of the 78 sources observed, we report 10 cases in which the source seems to have been misidentified or confused by nearby bright sources. We also present nearly two dozen cases in which the source seems to have indicated a variability which prompts a follow-up monitoring. There are also a few sources that show previously unreported extendedness. In addition, we present H band finding charts of the target sources., Comment: 3 tables, 1 figure

We have developed a general purpose dust radiative transfer code for an axisymmetric system, 2-Dust, motivated by the recent increasing availability of high-resolution images of circumstellar dust shells at various wavelengths. This code solves the equation of radiative transfer following the principle of long characteristic in a 2-D polar grid while considering a 3-D radiation field at each grid point. A solution is sought through an iterative scheme in which self-consistency of the solution is achieved by requiring a global luminosity constancy throughout the shell. The dust opacities are calculated through Mie theory from the given size distribution and optical properties of the dust grains. The main focus of the code is to obtain insights on (1) the global energetics of dust grains in the shell (2) the 2-D projected morphologies that are strongly dependent on the mixed effects of the axisymmetric dust distribution and inclination angle of the shell. Here, test models are presented with discussion of the results. The code can be supplied with a user-defined density distribution function, and thus, is applicable to a variety of dusty astronomical objects possessing the axisymmetric geometry., Comment: To be published in ApJ, April 2003 issue; 13 pages, 4 tables, 17 figures, 5-page appendix (no figures for the main text included in this preprint). For the complete preprint and code distribution, contact the authors

We present high-sensitivity near-IR images of a carbon-rich proto-planetary nebula, AFGL 618, obtained with the Subaru Telescope. These images have revealed ``bullets'' and ``horns'' extending farther out from the edges of the previously known bipolar lobes. The spatial coincidence between these near-IR micro-structures and the optical collimated outflow structure, together with the detection of shock-excited, forbidden IR lines of atomic species, strongly suggests that these bullets and horns represent the locations from which [\ion{Fe}{2}] IR lines arise. We have also discovered CO clumps moving at $> 200$ km s$^{-1}$ at the positions of the near-IR bullets by re-analyzing the existing $^{12}$CO $J=1-0$ interferometry data. These findings indicate that the near-IR micro-structures represent the positions of shocked surfaces at which fast-moving molecular clumps interface with the ambient circumstellar shell., Comment: 2 figures. To appear in the ApJ Letters

We will review our mid-infrared and HST imaging surveys of the circumstellar dust shells of proto-planetary nebulae. While optical imaging indirectly probes the dust distribution via dust-scattered starlight, mid-IR imaging directly maps the distribution of warm dust grains. Both imaging surveys revealed preferencially axisymmetric nature of PPN dust shells, suggesting that axisymmetry in planetary nebulae sets in by the end of the asymptotic giant branch phase, most likely by axisymmetric superwind mass loss. Moreover, both surveys yielded two morphological classes which have one-to-one correspondence between the two surveys, indicating that the optical depth of circumstellar dust shells plays an equally important role as the inclination angle in determining the morphology of the PPN shells., Comment: 6 pages + 8 figures, to appear in the proceedings of the conference, "Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution", Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorny. Figures have been degraded to minimize the total file size

We investigate spatial distributions of specific dust components in the circumstellar shells of a proto-planetary nebula candidate, HD 179821, and a planetary nebula, BD$+30^{\circ}$3639, by means of spectral imaging. With high-resolution ground-based images and ISO spectra in the mid-infrared, we can derive ``dust feature only'' maps by subtracting synthesized continuum maps from the observed images at the feature wavelength. Such spatially detailed information will help to develop models for the evolution of dust grains around evolved stars., Comment: 4 pages + 7 figures, to appear in the proceedings of the conference, "Post-AGB Objects (proto-planetary nebulae) as a Phase of Stellar Evolution", Torun, Poland, July 5-7, 2000, eds. R. Szczerba, R. Tylenda, and S.K. Gorny. Figures have been degraded to minimize the total file size

We report detection of an extended mid-infrared emission from \iras 18576+0341 (AFGL 2298). The object shows a dusty circumstellar shell that has diameter of $\age 7\arcsec$ at 10.3 and 18.0 $\um$. The dust nebula shows two emission peaks concentrically elongated and symmetrically oriented on the opposite sides of the third, central peak, which appears to be the central star of the system. The observed mid-infrared morphology indicates that the circumstellar dust shell has an equatorially-enhanced material distribution, which is a common signature of stellar objects that have experienced mass loss. Radiative transfer model calculations suggest that the central star is an extremely bright ($\lstar = 10^{6.4} \lsun$) star at a distance of about 10 kpc: this object is best described as a new luminous blue variable candidate. The circumstellar dust shell seems to have been generated by an equatorially-enhanced mass loss process with ${\dot M} \ge 6.8 \times 10^{-6} \msun$ yr$^{-1}$ and ${\dot M}_{\rm pole}/{\dot M}_{\rm eq} \sim 0.5$., Comment: 21 pages, 4 figures, to appear in ApJ

We summarize results of our {\it HST} imaging survey of proto-planetary nebula (PPN) candidates, in which we discovered two types of axisymmetric reflection nebulosities. The Star-Obvious Low-level-Elongated (SOLE) nebulae show a bright central star embedded in a smooth, faint extended nebulosity, whereas the DUst-Prominent Longitudinally-EXtended (DUPLEX) nebulae have remarkable bipolar structure with a completely or partially obscured central star. The intrinsic axisymmetry of the PPN reflection nebulosities demonstrates that the axisymmetry often found in planetary nebulae predates the PPN phase. We suggest that the major cause for the apparent dual morphology is the optical depth difference in the circumstellar dust shell rather than the inclination angle effect., Comment: To appear in ``Asymmetrical Planetary Nebulae II: from Origins to Microstructures,'' ASP Conference Series, Vol. 199, 2000; J.H. Kastner, N. Soker, & S.A. Rappaport, eds

We report the results from an optical imaging survey of proto-planetary nebula candidates using the HST. We exploited the high resolving power and wide dynamic range of HST and detected nebulosities in 21 of 27 sources. All detected reflection nebulosities show elongation, and the nebula morphology bifurcates depending on the degree of the central star obscuration. The Star-Obvious Low-level-Elongated (SOLE) nebulae show a bright central star embedded in a faint, extended nebulosity, whereas the DUst-Prominent Longitudinally-EXtended (DUPLEX) nebulae have remarkable bipolar structure with a completely or partially obscured central star. The intrinsic axisymmetry of these proto-planetary nebula reflection nebulosities demonstrates that the axisymmetry frequently found in planetary nebulae predates the proto-planetary nebula phase, confirming previous independent results. We suggest that axisymmetry in proto-planetary nebulae is created by an equatorially enhanced superwind at the end of the asymptotic giant branch phase. We discuss that the apparent morphological dichotomy is caused by a difference in the optical thickness of the circumstellar dust/gas shell with a differing equator-to-pole density contrast. Moreover, we show that SOLE and DUPLEX nebulae are physically distinct types of proto-planetary nebulae, with a suggestion that higher mass progenitor AGB stars are more likely to become DUPLEX proto-planetary nebulae., Comment: 27 pages (w/ aaspp4.sty), 6 e/ps figures, 4 tables (w/ apjpt4.sty). Data images are available via ADIL (http://imagelib.ncsa.uiuc.edu/document/99.TU.01) To be published in ApJ

We present the data from a mid-infrared imaging survey of 66 proto-planetary nebula candidates using two mid-IR cameras (MIRAC2 and Berkcam) at the NASA Infrared Telescope Facility and the United Kingdom Infrared Telescope. The goal of this survey is to determine the size, flux, and morphology of the mid-IR emission regions, which sample the inner regions of the circumstellar dust shells of proto-planetary nebulae. We imaged these proto-planetary nebulae with narrow-band filters ($\Delta\lambda / \lambda \sim 10%$) at wavelengths of notable dust features. With our typical angular resolution of 1\arcsec, we resolve 17 sources, find 48 objects unresolved, and do not detect 1 source. For several sources, we checked optical and infrared associations and positions of the sources. In table format, we list the size and flux measurements for all the detected objects and show figures of all the resolved sources. Images for all the detected objects are available on line in FITS format from the Astronomy Digital Image Library at the National Center for Supercomputing Application. The proto-planetary nebula candidate sample includes, in addition to the predominant proto-planetary nebulae, extreme asymptotic giant branch stars, young planetary nebulae, a supergiant, and a luminous blue variable. We find that dust shells which are cooler ($\rm T \sim 150$ K) and brighter in the infrared are more easily resolved. Eleven of the seventeen resolved sources are extended and fall into one of two types of mid-IR morphological classes: core/elliptical or toroidal. Core/elliptical structures show unresolved cores with lower surface brightness elliptical nebulae. Toroidal structures show limb-brightened peaks suggesting equatorial density enhancements. We argue that core/ellipticals have denser dust shells than toroidals., Comment: 32 pages, 5 tables, 2 e/ps figures (fig3 is available through ADIL [see text]), to be published in ApJS May 1999 issue