Wind-blown Bubble Research Articles

Simulated X-ray emission from a single-explosion model for a supernova remnant 3C 400.2

We present a single-explosion model study of the 3C 400.2 supernova remnant (SNR), made with two-dimensional axisymmetric simulations. The numerical simulations were made with the adaptive grid code YGUAZU-A. Several initial scenarios have been tested in order to reproduce the centrally peaked X-ray emission observed for this remnant. This study reveals that the explosion of the SN inside a pre-existing stellar wind bubble successfully generates the observed morphology, when thermal conduction is included in the model. The best morphological fit is obtained at an evolution time of 21 000 yr, when the total luminosity is 1.2 x 10 34 erg s -1 .

Chemical self-enrichment of HII regions by the Wolf-Rayet phase of an 85 M$_{\odot}$ star

It is clear from stellar evolution and from observations of WR stars that massive stars are releasing metal-enriched gas through their stellar winds in the Wolf-Rayet phase. Although Hii region spectra serve as diagnostics to determine the present-day chemical composition of the interstellar medium, it is far from being understood to what extent the Hii gas is already contaminated by chemically processed stellar wind. Therefore, we analyzed our models of radiative and wind bubbles of an isolated $85~{M}_{\odot}$ star with solar metallicity (Kroger et al. 2006, A&A, in preparation) with respect to the chemical enrichment of the circumstellar Hii region. Plausibly, the hot stellar wind bubble (SWB) is enriched with $^{14}\mbox{N}$ during the WN phase and even much higher with $^{12}\mbox{C}$ and $^{16}\mbox{O}$ during the WC phase of the star. During the short period that the $85~{M}_{\odot}$ star spends in the WC stage enriched SWB material mixes with warm Hii gas of solar abundances and thus enhances the metallicity in the Hii region. However, at the end of the stellar lifetime the mass ratios of the traced elements N and O in the warm ionized gas are insignificantly higher than solar, whereas an enrichment of $22\%$ above solar is found for C. Important issues from the presented study comprise a steeper radial gradient of C than O and a decreasing effect of self-enrichment for metal-poor galaxies.

Two new Perseus arm supernova remnants discovered in the Canadian Galactic Plane Survey

We report the discovery of two new second-quadrant supernova remnants, G96.0+2.0 and G113.0+0.2, in the data of the Canadian Galactic Plane Survey. The two SNRs are residents of the Perseus spiral arm at distances of 4.0 kpc and 3.1 kpc, respectively. The distances were determined kinematically by associating the objects with neutral hydrogen and molecular material. G96.0+2.0 is most likely located at the edge of a large stellar wind bubble with a systemic velocity of about −44 km s −1 . It consists of a relatively bright shell where the shock is encountering the wall of H i and slowly fades away towards the interior of the stellar wind bubble. The visible part of the remnant has a diameter of about 30 pc and a radio spectral index of α ≈− 0.66 (S ∼ ν α ), indicating that it is a shell-type remnant in an early stage of development. The SNR is most likely the remnant of a type Ib/c supernova explosion. G113.0+0.2 is located in an area of confusing thermal emission not far from the radio-bright supernova remnant Cassiopeia A. It has an unusual elongated structure consisting of a long polarized filament and a more complex head structure that is interacting with a small molecular cloud; it resides in a butterfly-shaped H i cavity, probably a stellar wind bubble. It is about 36 pc long and 15 pc wide at a position angle of 70 ◦ with the Galactic Plane. A pulsar with a relatively low period derivative, giving it a characteristic age of 10 million years, is located close to the centre of the radio continuum emission at a Perseus arm distance. Whether the pulsar is the result of the same supernova explosion that created G113.0+0.2 or if it was left behind by an earlier supernova that also shaped the stellar wind bubble remains uncertain.

X‐Ray Emission from Wind‐blown Bubbles. III.ASCASIS Observations of NGC 6888

We present ASCA SIS observations of the wind-blown bubble NGC 6888. Owing to the higher sensitivity of the SIS for higher energy photons compared to the ROSAT PSPC, we are able to detect a T ~ 8 × 106 K plasma component in addition to the T ~ 1.3 × 106 K component previously detected in PSPC observations. No significant temperature variations are detected within NGC 6888. Garcia-Segura & Mac Low's analytical models of WR bubbles constrained by the observed size, expansion velocity, and mass of the nebular shell underpredict the stellar wind luminosity and cannot reproduce simultaneously the observed X-ray luminosity, spectrum, surface brightness profile, and SIS count rate of NGC 6888's bubble interior. The agreement between observations and expectations from models may be improved if one or more of the following ad hoc assumptions are made: (1) the stellar wind luminosity was weaker in the past, (2) the bubble is at a special evolutionary stage and the nebular shell has recently been decelerated to of its previous expansion velocity, and (3) the heat conduction between the hot interior and the cool nebular shell is suppressed. Chandra and XMM-Newton observations with high spatial resolution and high sensitivity are needed to accurately determine the physical conditions of NGC 6888's interior hot gas for critical comparisons with bubble models.

The Galactic plane region near $\ell$ = 93°

New Canadian Galactic Plane Survey radio continuum, ROSAT X-ray, and optical line observations of supernova remnant (SNR) 3C 434.1 (G94.0+1.0) are presented. A radio spectrum of index $\alpha=0.4$ (where $S\propto \nu ^{-\alpha }$) confirms this SNR's emission signature as predominantly synchrotron, and suggests the SNR is in the Sedov expansion phase. The morphology of the remnant is compared in X-ray, optical, and radio continuum, and the brightest emission in all three wavelength regimes is from the eastern hemisphere of 3C 434.1, which marks where the SNR shock is interacting with the inside wall of its stellar wind bubble (SWB) home. The system is determined to be 4.5 kpc distant, residing in the Perseus Arm Spiral shock. From a deep H α mosaic of the region, $\lambda $656 nm H α line emission is observed that correlates well with radio synchrotron emission and anticorrelates with X-ray emission from the SNR. The origin of this optical emission is likely dense ($n_{\rm e}=40$ cm -3 ) cooling $\ion{H}{ii}$ from the wall of the SWB, where the SNR shock has penetrated and become radiative ($v_{\rm s}\sim 100$ km s -1 ). The X-ray spectrum of this SNR between 0.5 and 2.4 keV is well modelled by a single-temperature thermal plasma ($T_{\rm e}=4.5\times10^{6}$ K, $n_{\rm e}=0.2$ cm -3 ). The magnetic field of the bright radio synchrotron emission region is found (under the assumption of near equipartition) to be $B\sim 15$ μ G, a factor of 3 compression of the ambient ISM field (5 μ G). The westward extension of 3C 434.1 is the result of ongoing free expansion of the shock into the lower density interior of the SWB. I use multiwavelength observations to arrive at a unique solution for an interaction model of 3C 434.1 with the SWB, from which the age ($t=25\,000$ yr) and mass ejected in the explosion ($M_{\rm ej}=15.5$ $M_{\odot }$) are determined. I also find an initial blast-wave velocity of 1350 km s -1 , typical of type 1b SNe.

The Evolution of Supernovae in Circumstellar Wind‐Blown Bubbles. I. Introduction and One‐Dimensional Calculations

Mass loss from massive stars (≳8 M☉) can result in the formation of circumstellar wind-blown cavities surrounding the star, bordered by a thin, dense, cold shell. When the star explodes as a core-collapse supernova (SN), the resulting shock wave will interact with this modified medium around the star, rather than the interstellar medium. In this work we first explore the nature of the circumstellar medium around massive stars in various evolutionary stages. This is followed by a study of the evolution of SNe within these wind-blown bubbles. The evolution depends primarily on a single parameter Λ, the ratio of the mass of the dense shell to that of the ejected material. We investigate the evolution for different values of this parameter. We also plot approximate X-ray surface brightness plots from the simulations. For very small values Λ ≪ 1 the effect of the shell is negligible, as one would expect. Values of Λ ≲ 1 affect the SN evolution, but the SN "forgets" about the existence of the shell in about 10 doubling times or so. The remnant density profile changes, and consequently the X-ray emission from the remnant will also change. The initial X-ray luminosity of the remnant is quite low, but interaction of the shock wave with the dense circumstellar shell can increase the luminosity by 2-3 orders of magnitude. As the reflected shock begins to move inward, X-ray images will show the presence of a double-shelled structure. Larger values result in more SN energy being expended to the shell. The resulting reflected shock moves quickly back to the origin, and the ejecta are thermalized rapidly. The evolution of the remnant is speeded up, and the entire remnant may appear bright in X-rays. If Λ ≫ 1, then a substantial amount of energy may be expended in the shell. In the extreme case the SN may go directly from the free expansion to the adiabatic stage, bypassing the Sedov stage. Our results show that in many cases the SNR spends a significant amount of time within the bubble. The low density within the bubble can delay the onset of the Sedov stage and may end up reducing the amount of time spent in the Sedov stage. The complicated density profile within the bubble makes it difficult to infer the mass-loss properties of the pre-SN star by studying the evolution of the resulting SNR.

Evolution and Fragmentation of Wide-Angle Wind Driven Molecular Outflows

We present two dimensional cylindrically symmetric hydrodynamic simulations and synthetic emission maps of a stellar wind propagating into an infalling, rotating environment. The resulting outflow morphology, collimation and stability observed in these simulations have relevance to the study of young stellar objects, Herbig-Haro jets and molecular outflows. Our code follows hydrogen gas with molecular, atomic and ionic components tracking the associated time dependent molecular chemistry and ionization dynamics with radiative cooling appropriate for a dense molecular gas. We present tests of the code as well as new simulations which indicate the presence of instabilities in the wind-blown bubble’s swept-up shell.

SpitzerIRAC Observations of Star Formation in N159 in the Large Magellanic Cloud

We present observations of the giant H II region complex N159 in the LMC using IRAC on the Spitzer Space Telescope. One of the two objects previously identified as protostars in N159 has a spectral energy distribution (SED) consistent with classification as a Class I young stellar object (YSO), and the other is probably a Class I YSO as well, making these two stars the youngest stars known outside the Milky Way. We identify two other sources that may also be Class I YSOs. One component, N159AN, is completely hidden at optical wavelengths but is very prominent in the infrared. The integrated luminosity of the entire complex is L ≈ 9 × 106 L☉, consistent with the observed radio emission, assuming a normal Galactic initial mass function (IMF). There is no evidence for a red supergiant population indicative of an older burst of star formation. The N159 complex is 50 pc in diameter, larger in physical size than typical H II regions in the Milky Way with comparable luminosity. We argue that all of the individual components are related in their star formation history. The morphology of the region is consistent with a wind-blown bubble ≈1-2 Myr old that has initiated star formation now taking place at the rim. Other than its large physical size, star formation in N159 appears to be indistinguishable from star formation in the Milky Way.

A Stellar Wind Bubble Coincident with the Anomalous X-Ray Pulsar 1E 1048.1-5937: Are Magnetars Formed from Massive Progenitors?

We present 21 cm H I observations from the Southern Galactic Plane Survey of the field around the anomalous X-ray pulsar 1E 1048.1-5937, a source whose X-ray properties imply that it is a highly magnetized neutron star (a magnetar). These data reveal an expanding hydrogen shell, GSH 288.3-0.5-28, centered on 1E 1048.1-5937, with a diameter of 35 × 23 pc (for a distance of 2.7 kpc) and an expansion velocity of ≈7.5 km s-1. We interpret GSH 288.3-0.5-28 as a wind bubble blown by a 30-40 M☉ star, but no such central star can be readily identified. We suggest that GSH 288.3-0.5-28 is the wind bubble blown by the massive progenitor of 1E 1048.1-5937 and consequently propose that magnetars originate from more massive progenitors than do radio pulsars. This may be evidence that the initial spin period of a neutron star is correlated with the mass of its progenitor and implies that the magnetar birthrate is only a small fraction of that for radio pulsars.

SUPERBUBBLES AS SPACE BAROMETERS

High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous ob-served growth-rate discrepancy for supernova-driven super bubbles and stellar wind bubbles. Pressures of P / k K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic ISM localizations. We demonstrate the sensitivity of shell growth to the ambient pressure, and suggest that super bubbles ultimately might serve as ISM barometers.

Triggered massive star formation in the vicinity of WR 48a

We utilise Midcourse Space Experiment mid-IR imaging and published data to discuss the (massive) star formation region at galactic longitude ∼305 ◦ , apparently associated with the Wolf Rayet WR 48a and the attendant clusters Danks 1 and 2. A spectacular three lobed wind blown bubble surrounds the aforementioned sources, for which we may infer a minimum age of ∼3 Myr from the presence of the WCL star. Near IR data reveals the presence of numerous embedded sources on the periphery of the wind blown bubble. The presence of coincindent H2O, OH and methanol maser emission is suggestive of ongoing massive star formation, which is suppported by the fluxes of the associated IR sources, and the requisite LyC flux required to support the emission from the subset that have associated ucH  regions. Consideration of the integrated radio flux of the complex implies that a minimum of 31 O7V stars must be present, under the assumption of no photon leakage. Given the age and morphology of the complex and in particular the observation that the central exciting clusters have entirely cleared their natal material, we expect this assumption will be violated, and hence that the true population of massive stars is likely to be significantly larger. If confirmed, the G305 complex represents one of the most massive regions of ongoing triggered star formation currently identified in the galaxy.

Ambient Interstellar Pressure and Superbubble Evolution

High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous observed growth rate discrepancy for supernova-driven superbubbles and stellar wind bubbles. Pressures of P/k ~ 105 cm-3 K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic midplane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic interstellar medium (ISM) localizations. We demonstrate the sensitivity of shell growth to the ambient pressure and suggest that superbubbles ultimately might serve as ISM barometers.

NGC 604, the Scaled OB Association (SOBA) Prototype. I. Spatial Distribution of the Different Gas Phases and Attenuation by Dust

We have analyzed HST and ground-based data to characterize the different gas phases and their interaction with the MYC in NGC 604, a GHR in M33. The warm ionized gas is made out of two components: a high-excitation, high-surface brightness H II surface located at the faces of the molecular clouds directly exposed to the ionizing radiation of the central SOBA; and a low-excitation, low-surface brightness halo that extends to much larger distances from the ionizing stars. The cavities created by the winds and SN explosions are filled with X-ray-emitting coronal gas. The nebular lines emitted by the warm gas experience a variable attenuation as a consequence of the dust distribution, which is patchy in the plane of the sky and with clouds interspersed among emission-line sources in the same line of sight. The optical depth at H alpha as measured from the ratio of the thermal radio continuum to H alpha shows a very good correlation with the total CO (1-0) column, indicating that most of the dust resides in the cold molecular phase. The optical depth at H alpha as measured from the ratio of H alpha to H beta also correlates with the CO emission but not as strongly as in the previous case. We analyze the difference between those two measurements and we find that <=11% of the H II gas is hidden behind large-optical-depth molecular clouds. We detect two candidate compact H II regions embedded inside the molecular cloud; both are within short distance of WR/Of stars and one of them is located within 16 pc of a RSG. We estimate the age of the main stellar generation in NGC 604 to be approx. 3 Myr from the ionization structure of the H II region. The size of the main cavity is smaller than the one predicted by extrapolating from single-star wind-blown bubbles.

Confronting the Superbubble Model with X‐Ray Observations of 30 Doradus C

We present an analysis of XMM-Newton observations of the superbubble 30 Dor C and compare the results with the predictions from the standard wind-blown bubble model. We find that the observed X-ray spectra cannot be fitted satisfactorily with the model alone and that there is evidence for nonthermal X-ray emission, which is particularly important at > 4 keV. The total unabsorbed 0.1-10 keV luminosities of the eastern and western parts of the bubble are ~3 10^36 erg/s and ~5 10^36 erg/s, respectively. The unabsorbed 0.1-10 keV luminosity of the bubble model is 4 10^36 erg/s and so the power-law component contributes between 1/3 and 1/2 to the total unabsorbed luminosity in this energy band. The nature of the hard nonthermal emission is not clear, although recent supernovae in the bubble may be responsible. We expect that about one or two core-collapse supernovae could have occured and are required to explain the enrichment of the hot gas, as evidenced by the overabundance of alpha-elements by a factor of 3, compared to the mean value of 0.5 solar for the interstellar medium in the Large Magellanic Cloud. As in previous studies of various superbubbles, the amount of energy currently present in 30 Dor C is significantly less than the expected energy input from the enclosed massive stars over their lifetime. We speculate that a substantial fraction of the input energy may be radiated in far-infrared by dust grains, which are mixed with the hot gas because of the thermal conduction and/or dynamic mixing.

XMM-Newtonobservations of the giant H II region N 11 in the LMC

Using the sensitive XMM-Newton observatory, we have observed the giant H  region N 11 in the LMC for ∼30 ks. We have detected several large areas of soft diffuse X-ray emission along with 37 point sources. One of the most interesting results is the possible association of a faint X-ray source with BSDL 188, a small extended object of uncertain nature. The OB associations in the field-of-view (LH9, LH10 and LH13) are all detected with XMM-Newton, but they appear very different from one another. The diffuse soft X-ray emission associated with LH9 peaks near HD 32228, a dense cluster of massive stars. The combined emission of all individual massive stars of LH9 and of the superbubble they have created is not sufficient to explain the high level of emission observed: hidden SNRs, colliding-wind binaries and the numerous pre-main sequence stars of the cluster are most likely the cause of this discrepancy. The superbubble may also be leaking some hot gas in the ISM since faint, soft emission can be observed to the south of the cluster. The X-ray emission from LH10 consists of three pointlike sources and a soft extended emission of low intensity. The two brightest point sources are clearly associated with the fastest expanding bubbles blown by hot stars in the SW part of the cluster. The total X-ray emission from LH10 is rather soft, although it presents a higher temperature than the other soft emissions of the field. The discrepancy between the combined emission of the stars and the observed luminosity is here less severe than for LH9 and could be explained in terms of hot gas filling the wind-blown bubbles. On the other hand, the case of LH13 is different: it does not harbour any extended emission and its X-ray emission could most probably be explained by the Sk −66 ◦ 41 cluster alone. Finally, our XMM-Newton observation included simultaneous observations with the OM camera that provide us with unique UV photometry of more than 6000 sources and enable the discovery of the UV emission from the SNR N11L.

The Galactic Plane region near $\mathsf{\ell = 93\degr}$

New Canadian Galactic Plane Survey λ21 cm H  line observations towards supernova remnant (SNR) 3C 434.1 (G94.0+1.0) are presented. We find a fragmented and thin-walled atomic hydrogen shell inside which the SNR is seen to be contained at v �− 80 km s −1 , which we report to be a highly evolved stellar wind bubble (SWB) associated with the remnant. A dark area in the midst of otherwise bright line emission is also seen near −71 km s −1 . An absorption profile to the extragalactic continuum source 4C 51.45 (superimposed on the shell's north face) allows us to probe the shell's optical depth, kinetic temperature and expansion velocity. The material in the dark area has the same properties as material in the fragmented shell, suggesting that the dark area is actually the far-side cap of the shell seen absorbing emission from warm background gas, the first instance of H  Self Absorption (HISA) seen in such a structure. We show that the kinematic distance of 10 kpc derived from a flat Galactic rotation model is highly improbable, and that this bubble/SNR system is most likely resident in the Perseus Spiral Arm, lying 5.2 kpc distant. We model the SWB shell in three dimensions as a homologously expanding ellipsoid. Physical and dynamical characteristics of the bubble are determined, showing its advanced evolutionary state. Finally, from a photometric search for one or more stars associated with the SWB, we determine that three B0V stars and one O4V star currently inhabit this bubble, and that the progenitor of 3C 434.1 was at latest also an O4 type star.

GSH 23.0−0.7+117: A Neutral Hydrogen Shell in the Inner Galaxy

GSH 23.0-0.7+117 is a well-defined neutral hydrogen shell discovered in the Very Large Array (VLA) Galactic Plane Survey (VGPS). Only the blueshifted side of the shell was detected. The expansion velocity and systemic velocity were determined through the systematic behavior of the H I emission with velocity. The center of the shell is at (l, b, v) = (2305, - 077, + 117 km s-1). The angular radius of the shell is 68, or 15 pc at a distance of 7.8 kpc. The H I mass divided by the volume of the half-shell implies an average density nH = 11 ± 4 cm-3 for the medium in which the shell expanded. The estimated age of GSH 23.0-0.7+117 is 1 Myr, with an upper limit of 2 Myr. The modest expansion energy of 2 × 1048 ergs could have been provided by the stellar wind of a single O4-O8 star over the age of the shell. The 3 σ upper limit to the 1.4 GHz continuum flux density (S1.4 < 248 mJy) is used to derive an upper limit to the Lyman continuum luminosity generated inside the shell. This upper limit implies a maximum of one O9 star (i.e., O8-O9.5, taking into account the error in the distance) inside the H I shell, unless most of the incident ionizing flux leaks through the H I shell. To allow this, the shell should be fragmented on scales smaller than the beam (2.3 pc). If the stellar wind bubble is not adiabatic or the bubble has burst (as suggested by the H I channel maps), agreement between the energy and ionization requirements is even less likely. The limit set by the nondetection in the continuum provides a significant challenge for the interpretation of GSH 23.0-0.7+117 as a stellar wind bubble. A similar analysis may be applicable to other Galactic H I shells that have not been detected in the continuum.

On the origin of the system PSR B 1757$\mathsf{-}$24/SNR G 5.4$\mathsf{-}$1.2

A scenario for the origin of the system PSR B 1757-24/supernova remnant (SNR) G5.4-1.2 is proposed. It is suggested that both objects are the remnants of a supernova (SN) that exploded within a pre-existing bubble blown-up by a runaway massive star (the SN progenitor) during the final (Wolf-Rayet) phase of its evolution. This suggestion implies that (a) the SN blast centre was significantly offset from the geometric centre of the wind-blown bubble (i.e. from the centre of the future SNR), (b) the bubble was surrounded by a massive wind-driven shell, and (c) the SN blast wave was drastically decelerated by the interaction with the shell. Therefore, one can understand how the relatively young and low-velocity pulsar PSR B 1757-24 was able to escape from the associated SNR G 5.4-1.2 and why the inferred vector of pulsar transverse velocity does not point away from the geometric centre of the SNR. A possible origin of the radio source G 5.27-0.9 (located between PSR B 1757-24 and the SNR G 5.4-1.2) is proposed. It is suggested that G 5.27-0.9 is a lobe of a low Mach number (≃1.7) jet of gas outflowing from the interior of G5.4-1.2. through the hole bored in the SNR's shell by the escaping pulsar. It is also suggested that the non-thermal emission of the comet-shaped pulsar wind nebula originates in the vicinity of the termination shock and in the cylindric region of subsonically moving shocked pulsar wind. The role of magnetized wind-driven shells (swept-up during the Wolf-Rayet phase from the ambient interstellar medium with the regular magnetic field) in formation of elongated axisymmetric SNRs is discussed.

Mass-loaded spherical accretion flows

We have calculated the evolution of spherical accretion flows undergoing mass-loading from embedded clouds through either conduction or hydrodynamical ablation. We have observed the effect of varying the ratios of the mass-loading timescale and the cooling timescale to the ballistic crossing timescale through the mass-loading region. We have also varied the ratio of the potential energy of a particle injected into the flow near the outer region of mass-loading to the temperature at which a minimum occurs in the cooling curve. The two types of mass-loading produce qualitatively different types of behaviour in the accretion flow, since mass-loading through conduction requires the ambient gas to be hot, whereas mass ablation from clumps occurs throughout the flow. Higher ratios of injected to accreted mass typically occur with hydrodynamical ablation, in agreement with previous work on wind-blown bubbles and supernova remnants. We find that mass-loading damps the radiative overstability of such flows, in agreement with our earlier work. If the mass-loading is high enough it can stabilize the accretion shock at a constant radius, yielding an almost isothermal subsonic post-shock flow. Such solutions may be relevant to cooling flows onto massive galaxies. Mass-loading can also lead to the formation of isolated shells of high temperature material, separated by gas at cooler temperatures.

Small Magellanic Cloud–Type Interstellar Dust in the Milky Way

It is well known that the sight line toward HD 204827 in the cluster Trumpler 37 shows a UV extinction curve that does not follow the average Galactic extinction relation. However, when a dust component, foreground to the cluster, is removed, the residual extinction curve is identical to that found in the SMC within the uncertainties. The curve is very steep and has little or no 2175 A bump. The position of HD 204827 in the sky is projected onto the edge of the Cepheus IRAS bubble. In addition, HD 204827 has an IRAS bow shock, indicating that it may be embedded in dust swept up by the supernova that created the IRAS bubble. Shocks due to the supernova may have led to substantial processing of this dust. The HD 204827 cloud is dense and rich in carbon molecules. The 3.4 μm feature indicating a C-H grain mantle is present in the dust toward HD 204827. The environment of the HD 204827 cloud dust may be similar to the dust associated with HD 62542, which lies on the edge of a stellar wind bubble and is also dense and rich in molecules. This sight line may be a Rosetta Stone if its environment can be related to those in the SMC having similar dust.