We have detected [Fe II] 17.94 um and 24.52 um emission from a sample of M supergiants using TEXES on the IRTF. These low opacity emission lines are resolved at R = 50, 000 and provide new diagnostics of the dynamics and thermodynamics of the stellar wind acceleration zone. The [Fe II] lines, from the first excited term, are sensitive to the warm plasma where energy is deposited into the extended atmosphere to form the chromosphere and wind outflow. These diagnostics complement previous KAO and ISO observations which were sensitive to the cooler and more extended circumstellar envelopes. The turbulent velocities, Vturb is about 12 to 13 km/s, observed in the [Fe II] forbidden lines are found to be a common property of our sample, and are less than that derived from the hotter chromospheric C II] 2325 Angstrom lines observed in alpha Ori, where Vturb is about 17 to 19 km/s. For the first time, we have dynamically resolved the motions of the dominant cool atmospheric component discovered in alpha Ori from multi-wavelength radio interferometry by Lim et al. (1998). Surprisingly, the emission centroids are quite Gaussian and at rest with respect to the M supergiants. These constraints combined with model calculations of the infrared emission line fluxes for alpha Ori imply that the warm material has a low outflow velocity and is located close to the star. We have also detected narrow [Fe I] 24.04 um emission that confirms that Fe II is the dominant ionization state in alpha Ori's extended atmosphere.
We introduce the first synthetic light-curve model set of Type IIP supernovae exploded within circumstellar media in which the acceleration of the red supergiant winds is taken into account. Because wind acceleration makes the wind velocities near the progenitors low, the density of the immediate vicinity of the red supergiant supernova progenitors can be higher than that extrapolated by using a constant terminal wind velocity. Therefore, even if the mass-loss rate of the progenitor is relatively low, it can have a dense circumstellar medium at the immediate stellar vicinity and the early ligh…
Wind-fed high-mass X-ray binaries are powered by accretion of the radiatively driven wind on the compact star. Accretion-generated X-rays alter the ionization state of the wind. Because higher ionization states drive the wind less effectively, X-ray ionization may brake acceleration of the wind. This causes a decrease in the wind terminal velocity and mass flux in the direction toward the X-ray source. We study the effect of X-ray ionization on the stellar wind of B supergiants. We determine the binary parameters for which the X-ray irradiation significantly influences the stellar wind. This c…
What causes the large extensions of red-supergiant atmospheres? Comparisons of interferometric observations with 1-D hydrostatic, 3-D convection, and 1-D pulsating model atmospheres
Hot massive stars present strong stellar winds that are driven by absorption, scattering and re\-emission of photons by the ions of the atmosphere (\textit{line-driven winds}). A better comprehension of this phenomenon, and a more accurate calculation of hydrodynamics and radiative acceleration is required to reduce the number of free parameters in spectral fitting, to determine accurate wind parameters such as mass-loss rates and velocity profiles. We use the non-LTE model-atmosphere code CMFGEN to numerically solve the radiative transfer equation in the stellar atmosphere and to calculate th…
We examine flash spectroscopy of a circumstellar medium (CSM) ionized by the hard radiation pulse produced by the emerging shock of a supernova (SN). We first find that the rise and fall times of the Halpha emission constrains the location of the CSM with a peak at tpeak=Rstar sqrt(2/c vshock) for a star of radius Rstar and a shock velocity of vshock. The dropping temperature of the transient emission naturally reproduces the evolution of lines with different ionization energies. Second, for red supergiants (RSGs), the shock break out radiatively accelerates the CSM to produce broad, early-tim…
Universidad Técnica Federico Santa María（费德里科·圣玛丽亚理工大学）；Universidad de Valparaíso（瓦尔帕莱索大学）；Universidad Mayor（市长大学）；CONICET（国家科学技术研究委员会）；Universidad Nacional de La Plata（拉普拉塔国立大学）；Instituto de Astrofísica de La Plata（拉普拉塔天体物理研究所）
We fit a new line shape model to \textit{Chandra} X-ray spectra of the O supergiant $ζ$ Puppis to test the robustness of mass-loss rates derived from X-ray wind line profiles against different assumed heating models. Our goal is to track the hot gas by replacing the common assumption that it is proportional to the cool gas emission measure. Instead of assuming a turn-on radius for the hot gas (as appropriate for the line-deshadowing instability internal to the wind), we parametrize the hot gas in terms of a mean-free path for accelerated low-density gas to encounter slower high-density materia…
This overview paper presents ATOMIUM, a Large Programme in Cycle 6 with the Atacama Large Millimeter-submillimeter Array (ALMA). The goal of ATOMIUM is to understand the dynamics and the gas phase and dust formation chemistry in the winds of evolved asymptotic giant branch (AGB) and red supergiant (RSG) stars. A more general aim is to identify chemical processes applicable to other astrophysical environments. 17 oxygen-rich AGB and RSG stars spanning a range in (circum)stellar parameters and evolutionary phases were observed in a homogeneous observing strategy allowing for an unambiguous compa…
