Herschel PACS and SPIRE imaging of CW Leonis

Cox

Royer

et al. 2012

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Context. The interaction between stellar winds and the interstellar medium (ISM) can create complex bow shocks. The photometers on board the Herschel Space Observatory are ideally suited to studying the morphologies of these bow shocks. Aims. We aim to study the circumstellar environment and wind-ISM interaction of the nearest red supergiant, Betelgeuse. Methods. Herschel PACS images at 70, 100, and 160 μm and SPIRE images at 250, 350, and 500 μm were obtained by scanning the region around Betelgeuse. These data were complemented with ultraviolet GALEX data, near-infrared WISE data, and radio 21 cm GALFA-HI data. The observational properties of the bow shock structure were deduced from the data and compared with hydrodynamical simulations. Results. The infrared Herschel images of the environment around Betelgeuse are spectacular, showing the occurrence of multiple arcs at ∼6-7 from the central target and the presence of a linear bar at ∼9 . Remarkably, no large-scale instabilities are seen in the outer arcs and linear bar. The dust temperature in the outer arcs varies between 40 and 140 K, with the linear bar having the same colour temperature as the arcs. The inner envelope shows clear evidence of a non-homogeneous clumpy structure (beyond 15 ), probably related to the giant convection cells of the outer atmosphere. The non-homogeneous distribution of the material even persists until the collision with the ISM. A strong variation in brightness of the inner clumps at a radius of ∼2 suggests a drastic change in mean gas and dust density ∼32 000 yr ago. Using hydrodynamical simulations, we try to explain the observed morphology of the bow shock around Betelgeuse. Conclusions. Different hypotheses, based on observational and theoretical constraints, are formulated to explain the origin of the multiple arcs and the linear bar and the fact that no large-scale instabilities are visible in the bow shock region. We infer that the two main ingredients for explaining these phenomena are a non-homogeneous mass-loss process and the influence of the Galactic magnetic field. The hydrodynamical simulations show that a warm interstellar medium, reflecting a warm neutral or partially ionized medium, or a higher temperature in the shocked wind also prevent the growth of strong instabilities. The linear bar is probably an interstellar structure illuminated by Betelgeuse itself.

Section: Galex Observationsmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed byHerschel

Cox

Royer

et al. 2012

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“…Applying aperture photometry on the azimuthally averaged deconvolved PACS images and using a modified blackbody of the form B ν · λ −β , as expected for a grain emissivity Q abs ∼ λ −β with β equal to 1.2 (representing amorphous carbon, Mennella et al 1998), we derived a dust temperature between 108 ± 5 K at 20 and 40 ± 5 K at 180 . The temperature of the bowshock at 480 is 25 ± 3 K (Ladjal et al 2010).…”

Section: Resultsmentioning

confidence: 99%

“…The PACS 160 μm data were already presented by Ladjal et al (2010), who discussed the detection of a bowshock at ∼585 when measured from the nearest focus of an ellipse fit to the shape of the bowshock, or at 480 when measured from the central star.…”

Section: Introductionmentioning

confidence: 96%

Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC +10216 usingHerschel/PACS

Royer

Cox

et al. 2011

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We present new Herschel/PACS images at 70, 100, and 160 μm of the well-known, nearby, carbon-rich asymptotic giant branch star IRC+10216 revealing multiple dust shells in its circumstellar envelope. For the first time, dust shells (or arcs) are detected until 320 . The almost spherical shells are non-concentric and have an angular extent between ∼40• and ∼200• . The shells have a typical width of 5 -8 , and the shell separation varies in the range of ∼10 -35 , corresponding to ∼500 -1 700 yr. Local density variations within one arc are visible. The shell/intershell density contrast is typically ∼4, and the arcs contain some 50% more dust mass than the smooth envelope. The observed (nested) arcs record the mass-loss history over the past 16 000 yr, but Rayleigh-Taylor and Kelvin-Helmholtz instabilities in the turbulent astropause and astrosheath will erase any signature of the mass-loss history for at least the first 200 000 yr of mass loss. Accounting for the bowshock structure, the envelope mass around IRC+10216 contains >2 M of gas and dust mass. It is argued that the origin of the shells is related to non-isotropic mass-loss events and clumpy dust formation.

“…However, the relative calibration is much better, hence it is possible to estimate the contribution of the most abundant species to the lines of HCl by using adjacent lines of these species. PACS and SPIRE photometry observations are presented in Ladjal et al (2010).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Detection of anhydrous hydrochloric acid, HCl, in IRC +10216 with the HerschelSPIRE and PACS spectrometers

Cernicharo¹,

Barlow

et al. 2010

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We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine, HCl) in the carbon-rich star IRC +10216 using the spectroscopic facilities onboard the Herschel satellite. Lines from J = 1−0 up to J = 7−6 have been detected. From the observed intensities, we conclude that HCl is produced in the innermost layers of the circumstellar envelope with an abundance relative to H 2 of 5 × 10 −8 and extends until the molecules reach its photodissociation zone. Upper limits to the column densities of AlH, MgH, CaH, CuH, KH, NaH, FeH, and other diatomic hydrides have also been obtained.