scholarly journals Testing the Wind-shock Paradigm for B-Type Star X-Ray Production with θ Car

2016 ◽  
Vol 12 (S329) ◽  
pp. 395-395
Author(s):  
T. F. Doyle ◽  
V. Petit ◽  
D. Cohen ◽  
M. Leutenegger
Keyword(s):  
Mass Loss Rate ◽  
Low Density ◽  
X Rays ◽  
Wind Regime ◽  
X Ray ◽  
Wind Theory ◽  
Stellar Photosphere ◽  
Hydrodynamical Simulations ◽  
Grating Spectroscopy ◽  
Weak Wind

AbstractWe present Chandra X-ray grating spectroscopy of the B0.2V star, θ Carina. θ Car is in a critical transition region between the latest O-type and earliest B-type stars, where some stars are observed to have UV-determined wind densities much lower than theoretically expected (e.g., Marcolino et al. 2009). In general, X-ray emission in this low-density wind regime should be less prominent than for O-stars (e.g., Martins et al. 2005), but observations suggest a higher than expected X-ray emission filling factor (Lucy 2012; Huenemoerder et al. 2012); if a larger fraction of the wind is shock-heated, it could explain the weak UV wind signature seen in weak wind stars, but this might severely challenge predictions of radiatively-driven wind theory.We measured the line widths of several He-, H-like and Fe ions and the f/i ratio of He-like ions in the X-ray spectrum, which improves upon the results from Nazé et al. (2008) (XMM-Newton RGS) with additional measurements (Chandra HETG) of Mgxi and Sixiii by further constraining the X-ray emission location. The f/i ratio is modified by the proximity to the UV-emitting stellar photosphere, and is therefore a diagnostic of the radial location of the X-ray emitting plasma. The measured widths of X-ray lines are narrow, <300 km s−1 and the f/i ratios place the X-rays relatively close to the surface, both implying θ Car is a weak wind star. The measured widths are also consistent with other later-type stars in the weak wind regime, β Cru (Cohen et al. 2008), for example, and are smaller on average than earlier weak wind stars such as μ Col (Huenemoerder et al. 2012). This could point to a spectral type divide, where one hypothesis, low density, works for early-B type stars and the other hypothesis, a larger fraction of shock-heated gas, explains weak winds in late-O type stars. Archival IUE data still needs to be analyzed to determine the mass loss rate and hydrodynamical simulations will be compared with observations to determine which hypothesis works for θ Car.

scholarly journals Chandra grating spectroscopy of embedded wind shock X-ray emission from O stars shows low plasma temperatures and significant wind absorption

2021 ◽  
Author(s):  
David H Cohen ◽  
Vanessa Vaughn Parts ◽  
Graham M Doskoch ◽  
Jiaming Wang ◽  
Véronique Petit ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Mass Loss ◽  
Mass Loss Rate ◽  
Emission Measure ◽  
X Rays ◽  
X Ray ◽  
Hot Plasma ◽  
Similar Temperature ◽  
Grating Spectroscopy ◽  
X Ray Absorption

Abstract We present a uniform analysis of six examples of embedded wind shock (EWS) O star X-ray sources observed at high resolution with the Chandra grating spectrometers. By modeling both the hot plasma emission and the continuum absorption of the soft X-rays by the cool, partially ionized bulk of the wind we derive the temperature distribution of the shock-heated plasma and the wind mass-loss rate of each star. We find a similar temperature distribution for each star’s hot wind plasma, consistent with a power-law differential emission measure, $\frac{d\log EM}{d\log T}$, with a slope a little steeper than -2, up to temperatures of only about 107 K. The wind mass-loss rates, which are derived from the broadband X-ray absorption signatures in the spectra, are consistent with those found from other diagnostics. The most notable conclusion of this study is that wind absorption is a very important effect, especially at longer wavelengths. More than 90 per cent of the X-rays between 18 and 25 Å produced by shocks in the wind of ζ Pup are absorbed, for example. It appears that the empirical trend of X-ray hardness with spectral subtype among O stars is primarily an absorption effect.

scholarly journals What Do We Really Know About the Winds of Massive Stars?

2007 ◽  
Vol 3 (S250) ◽  
pp. 89-96
Author(s):  
D. John Hillier
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Standard Theory ◽  
Stellar Winds ◽  
X Rays ◽  
X Ray ◽  
Stellar Photosphere ◽  
Weak Winds ◽  
Ionization Balance ◽  
Loss Rates

AbstractThe standard theory of radiation driven winds has provided a useful framework to understand stellar winds arising from massive stars (O stars, Wolf-Rayet stars, and luminous blue variables). However, with new diagnostics, and advances in spectral modeling, deficiencies in our understanding of stellar winds have been thrust to the forefront of our research efforts. Spectroscopic observations and analyses have shown the importance of inhomogeneities in stellar winds, and revealed that there are fundamental discrepancies between predicted and theoretical mass-loss rates. For late O stars, spectroscopic analyses derive mass-loss rates significantly lower than predicted. For all O stars, observed X-ray fluxes are difficult to reproduce using standard shock theory, while observed X-ray profiles indicate lower mass-loss rates, the potential importance of porosity effects, and an origin surprisingly close to the stellar photosphere. In O stars with weak winds, X-rays play a crucial role in determining the ionization balance, and must be taken into account.

scholarly journals Variability in X-ray line ratios in helium-like ions of massive stars: the wind-driven case

2019 ◽  
Vol 625 ◽  
pp. A86 ◽  
Author(s):  
R. Ignace ◽  
Z. Damrau ◽  
K. T. Hole
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Variable Mass ◽  
Line Ratio ◽  
High Spectral Resolution ◽  
X Rays ◽  
Wind Integration ◽  
X Ray ◽  
Wind Variability

Context. High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths. Aims. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R = f∕i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability. Methods. This contribution is the second to explore how variability in the line ratio can provide new diagnostic information about distributed X-rays in a massive star wind. We focus on wind integration for total line luminosities, taking account of radiative pumping and stellar occultation. While the case of a variable stellar radiation field was explored in the first paper, the effects of wind variability are emphasized in this work. Results. We formulate an expression for the ratio of line luminosities f∕i that closely resembles the classic expression for the on-the-spot result. While there are many ways to drive variability in the line ratio, we use variable mass loss as an illustrative example for wind integration, particularly since this produces no variability for the on-the-spot case. The f∕i ratio can be significantly modulated owing to evolving wind properties. The extent of the variation depends on how the timescale for the wind flow compares to the timescale over which the line emissivities change. Conclusions. While a variety of factors can ellicit variable line ratios, a time-varying mass-loss rate serves to demonstrate the range of amplitude and phased-dependent behavior in f∕i line ratios. Importantly, we evaluate how variable mass loss might bias measures of f∕i. For observational exposures that are less than the timescale of variable mass loss, biased measures (relative to the time-averaged wind) can result; if exposures are long, the f∕i ratio is reflective of the time-averaged spherical wind.

scholarly journals Massive star mass-loss revealed by X-ray observations of young supernovae

2018 ◽  
Vol 14 (S346) ◽  
pp. 83-87
Author(s):  
Vikram V. Dwarkadas
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Ambient Medium ◽  
Mass Loss Rate ◽  
Stellar Mass ◽  
X Rays ◽  
X Ray ◽  
The Common ◽  
Almost All ◽  
Loss Rates

AbstractMassive stars lose a considerable amount of mass during their lifetime. When the star explodes as a supernova (SN), the resulting shock wave expands in the medium created by the stellar mass-loss. Thermal X-ray emission from the SN depends on the square of the density of the ambient medium, which in turn depends on the mass-loss rate (and velocity) of the progenitor wind. The emission can therefore be used to probe the stellar mass-loss in the decades or centuries before the star’s death.We have aggregated together data available in the literature, or analysed by us, to compute the X-ray lightcurves of almost all young supernovae detectable in X-rays. We use this database to explore the mass-loss rates of massive stars that collapse to form supernovae. Mass-loss rates are lowest for the common Type IIP supernovae, but increase by several orders of magnitude for the highest luminosity X-ray SNe.

scholarly journals Dust entrainment in photoevaporative winds: The impact of X-rays

2020 ◽  
Vol 635 ◽  
pp. A53 ◽  
Author(s):  
R. Franz ◽  
G. Picogna ◽  
B. Ercolano ◽  
T. Birnstiel
Keyword(s):  
Extreme Ultraviolet ◽  
Mass Loss Rate ◽  
Disk Surface ◽  
Maximum Height ◽  
X Rays ◽  
X Ray ◽  
T Tauri ◽  
Dust Entrainment ◽  
Disk Evolution ◽  
The Impact

Context. X-ray- and extreme ultraviolet (XEUV) driven photoevaporative winds acting on protoplanetary disks around young T Tauri stars may crucially impact disk evolution, affecting both gas and dust distributions. Aims. We investigate the dust entrainment in XEUV-driven photoevaporative winds and compare our results to existing magnetohydrodynamic and EUV-only models. Methods. We used a 2D hydrodynamical gas model of a protoplanetary disk irradiated by both X-ray and EUV spectra from a central T Tauri star to trace the motion of passive Lagrangian dust grains of various sizes. The trajectories were modelled starting at the disk surface in order to investigate dust entrainment in the wind. Results. For an X-ray luminosity of LX = 2 × 1030 erg s−1 emitted by a M* = 0.7 M⊙ star, corresponding to a wind mass-loss rate of Ṁw ≃ 2.6 × 10−8 M⊙ yr−1, we find dust entrainment for sizes a0 ≲ 11 μm (9 μm) from the inner 25 AU (120 AU). This is an enhancement over dust entrainment in less vigorous EUV-driven winds with Ṁw ≃ 10−10 M⊙ yr−1. Our numerical model also shows deviations of dust grain trajectories from the gas streamlines even for μm-sized particles. In addition, we find a correlation between the size of the entrained grains and the maximum height they reach in the outflow. Conclusions. X-ray-driven photoevaporative winds are expected to be dust-rich if small grains are present in the disk atmosphere.

scholarly journals Precessing AGN jets, bubbles and cooling flows

2010 ◽  
Vol 6 (S275) ◽  
Author(s):  
D. Falceta-Gonçalves ◽  
A. Caproni ◽  
Z. Abraham ◽  
E. M. de Gouveia Dal Pino ◽  
D. M. Teixeira
Keyword(s):  
Galaxy Clusters ◽  
Flow Problem ◽  
X Rays ◽  
Intracluster Medium ◽  
X Ray ◽  
Cooling Flows ◽  
Cooling Flow ◽  
Central Regions ◽  
Multiple Bubbles ◽  
Hydrodynamical Simulations

AbstractSeveral galaxy clusters are known to present multiple and misaligned pairs of cavities seen in X-rays, as well as twisted kiloparsec-scale jets at radio wavelengths. It suggests that the AGN precessing jets play a role in the formation of the misaligned bubbles. Also, X-ray spectra reveal that typically these systems are also able to supress cooling flows, predicted theoretically. The absence of cooling flows in galaxy clusters has been a mistery for many years since numerical simulations and analytical studies suggest that AGN jets are highly energetic, but are unable to redistribute it at all directions. We performed 3D hydrodynamical simulations of the interaction between a precessing AGN jet and the warm intracluster medium plasma, in which dynamics is coupled to a NFW dark matter gravitational potential. Radiative cooling has been taken into account and the cooling flow problem was studied. We found that precession is responsible for multiple pairs of bubbles, as observed. The misaligned bubbles rise up to scales of tens of kiloparsecs, where the thermal energy released by the jets are redistributed. After ~150 Myrs, the temperature of the gas within the cavities is kept of order of ~107 K, while the denser plasma of the intracluster medium at the central regions reaches T ~ 105 K. The existence of multiple bubbles, at diferent directions, results in an integrated temperature along the line of sight much larger than the simulations of non-precessing jets. This result is in agreement with the observations. The simulations reveal that the cooling flows cessed ~50–70 Myr after the AGN jets are started.

scholarly journals Ion fractions and the weak wind problem

2010 ◽  
Vol 6 (S272) ◽  
pp. 600-601
Author(s):  
Matthew J. Austin ◽  
Raman K. Prinja
Keyword(s):  
X Rays ◽  
Late Type ◽  
Hot Stars ◽  
Wind Theory ◽  
Weak Winds ◽  
Weak Wind ◽  
Bulk Plasma

AbstractSome late-type O stars display anomalously weak winds, possibly due to decoupling of the main driving ions from the bulk plasma. This issue and the uncertainty about the nature of wind clumping are a challenge to line-driven wind theory and need resolving in order to fully understand hot stars. We describe the results from the computation of ion fractions for the various elements in O star winds using non-LTE code CMFGEN, including parameterisation of microclumping and X-rays.

scholarly journals Optical spectroscopy and X-ray observations of the D-type symbiotic star EF Aql

2020 ◽  
Vol 495 (1) ◽  
pp. 1461-1467
Author(s):  
K A Stoyanov ◽  
K Iłkiewicz ◽  
G J M Luna ◽  
J Mikołajewska ◽  
K Mukai ◽  
...  
Keyword(s):  
High Resolution ◽  
Optical Spectroscopy ◽  
Chemical Elements ◽  
Mass Loss Rate ◽  
X Rays ◽  
Symbiotic Star ◽  
Optical Telescope ◽  
X Ray ◽  
V Band ◽  
Periodogram Analysis

ABSTRACT We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with the Southern African Large Telescope (SALT), we determine the temperature (∼55 000 K) and the luminosity (∼5.3 L⊙) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10−12 erg cm−2 s−1, which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise we detected it with the UltraViolet and Optical Telescope (UVOT) instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4 ± 0.3 d caused by the pulsations of the Mira-type donor star.

scholarly journals Mass loss and the Eddington parameter: a new mass-loss recipe for hot and massive stars

2020 ◽  
Vol 493 (3) ◽  
pp. 3938-3946 ◽  
Author(s):  
Joachim M Bestenlehner
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Gamma Ray ◽  
Massive Stars ◽  
Dominant Role ◽  
Mass Loss Rate ◽  
Large Magellanic Cloud ◽  
Wind Regime ◽  
Wind Theory

ABSTRACT Mass loss through stellar winds plays a dominant role in the evolution of massive stars. In particular, the mass-loss rates of very massive stars ($\gt 100\, M_{\odot}$) are highly uncertain. Such stars display Wolf–Rayet spectral morphologies (WNh), whilst on the main sequence. Metal-poor very massive stars are progenitors of gamma-ray bursts and pair instability supernovae. In this study, we extended the widely used stellar wind theory by Castor, Abbott & Klein from the optically thin (O star) to the optically thick main-sequence (WNh) wind regime. In particular, we modify the mass-loss rate formula in a way that we are able to explain the empirical mass-loss dependence on the Eddington parameter (Γe). The new mass-loss recipe is suitable for incorporation into current stellar evolution models for massive and very massive stars. It makes verifiable predictions, namely how the mass-loss rate scales with metallicity and at which Eddington parameter the transition from optically thin O star to optically thick WNh star winds occurs. In the case of the star cluster R136 in the Large Magellanic Cloud we find in the optically thin wind regime $\dot{M} \propto \Gamma _{\rm e}^{3}$, while in the optically thick wind regime $\dot{M} \propto 1/ (1 - \Gamma _{\rm e})^{3.5}$. The transition from optically thin to optically thick winds occurs at Γe, trans ≈ 0.47. The transition mass-loss rate is $\log \dot{M}~(\mathrm{M}_{\odot } \, \mathrm{yr}^{-1}) \approx -4.76 \pm 0.18$, which is in line with the prediction by Vink & Gräfener assuming a volume filling factor of $f_{\rm V} = 0.23_{-0.15}^{+0.40}$.

scholarly journals X-ray spectral diagnostics of activity in massive stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 348-353 ◽  
Author(s):  
David H. Cohen ◽  
Emma E. Wollman ◽  
Maurice A. Leutenegger
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Broad Band ◽  
Variable Structure ◽  
Spectral Energy ◽  
X Rays ◽  
X Ray ◽  
Spectral Diagnostics ◽  
Loss Rates

AbstractX-rays give direct evidence of instabilities, time-variable structure, and shock heating in the winds of O stars. The observed broad X-ray emission lines provide information about the kinematics of shock-heated wind plasma, enabling us to test wind-shock models. And their shapes provide information about wind absorption, and thus about the wind mass-loss rates. Mass-loss rates determined from X-ray line profiles are not sensitive to density-squared clumping effects, and indicate mass-loss rate reductions of factors of 3 to 6 over traditional diagnostics that suffer from density-squared effects. Broad-band X-ray spectral energy distributions also provide mass-loss rate information via soft X-ray absorption signatures. In some cases, the degree of wind absorption is so high, that the hardening of the X-ray SED can be quite significant. We discuss these results as applied to the early O stars ζ Pup (O4 If), 9 Sgr (O4 V((f))), and HD 93129A (O2 If*).

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