scholarly journals The impact of winds on the spectral appearance of red supergiants

2021 ◽  
Author(s):  
Ben Davies ◽  
Bertrand Plez
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Mass Loss Rate ◽  
Far Infrared ◽  
Evolutionary Stage ◽  
Spectral Variability ◽  
Near Ir ◽  
Red Supergiants ◽  
Preliminary Study ◽  
The Impact

Abstract The rate at which mass is lost during the Red Supergiant evolutionary stage may strongly influence how the star appears. Though there have been many studies discussing how RSGs appear in the mid and far-infrared (IR) as a function of their mass-loss rate, to date there have been no such investigations at optical and near-IR wavelengths. In a preliminary study we construct model atmospheres for RSGs which include a wind, and use these models to compute synthetic spectra from the optical to the mid-infrared. The inclusion of a wind has two important effects. Firstly, higher mass-loss rates result in stronger absorption in the TiO bands, causing the star to appear as a later spectral type despite its effective temperature remaining constant. This explains the observed relation between spectral type, evolutionary stage and mid-IR excess, as well as the mismatch between temperatures derived from the optical and infrared. Secondly, the wind mimics many observed characteristics of a ‘MOLsphere’, potentially providing an explanation for the extended molecular zone inferred to exist around nearby RSGs. Thirdly, we show that wind fluctuations can explain the spectral variability of Betelgeuse during its recent dimming, without the need for dust.

scholarly journals A new mass-loss rate prescription for red supergiants

2020 ◽  
Vol 492 (4) ◽  
pp. 5994-6006 ◽  
Author(s):  
Emma R Beasor ◽  
Ben Davies ◽  
Nathan Smith ◽  
Jacco Th van Loon ◽  
Robert D Gehrz ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Substantial Effect ◽  
Evolutionary Models ◽  
Total Mass Loss ◽  
Red Supergiants ◽  
Current Mass ◽  
The Impact ◽  
Loss Rates

ABSTRACT Evolutionary models have shown the substantial effect that strong mass-loss rates ($\dot{M}$s) can have on the fate of massive stars. Red supergiant (RSG) mass-loss is poorly understood theoretically, and so stellar models rely on purely empirical $\dot{M}$–luminosity relations to calculate evolution. Empirical prescriptions usually scale with luminosity and effective temperature, but $\dot{M}$ should also depend on the current mass and hence the surface gravity of the star, yielding more than one possible $\dot{M}$ for the same position on the Hertzsprung–Russell diagram. One can solve this degeneracy by measuring $\dot{M}$ for RSGs that reside in clusters, where age and initial mass (Minit) are known. In this paper we derive $\dot{M}$ values and luminosities for RSGs in two clusters, NGC 2004 and RSGC1. Using newly derived Minit measurements, we combine the results with those of clusters with a range of ages and derive an Minit-dependent $\dot{M}$ prescription. When comparing this new prescription to the treatment of mass-loss currently implemented in evolutionary models, we find models drastically overpredict the total mass-loss, by up to a factor of 20. Importantly, the most massive RSGs experience the largest downward revision in their mass-loss rates, drastically changing the impact of wind mass-loss on their evolution. Our results suggest that for most initial masses of RSG progenitors, quiescent mass-loss during the RSG phase is not effective at removing a significant fraction of the H-envelope prior to core-collapse, and we discuss the implications of this for stellar evolution and observations of SNe and SN progenitors.

scholarly journals A radio census of the massive stellar cluster Westerlund 1

2019 ◽  
Vol 632 ◽  
pp. A38
Author(s):  
H. Andrews ◽  
D. Fenech ◽  
R. K. Prinja ◽  
J. S. Clark ◽  
L. Hindson
Keyword(s):  
Radio Emission ◽  
Mass Loss ◽  
Stellar Wind ◽  
Massive Stars ◽  
Mass Loss Rate ◽  
Evolutionary Stage ◽  
Spectral Indices ◽  
Stellar Cluster ◽  
The Impact ◽  
Loss Rates

Context. Massive stars and their stellar winds are important for a number of feedback processes. The mass lost in the stellar wind can help determine the end-point of the star as a neutron star (NS) or a black hole (BH). However, the impact of mass loss on the post-main sequence evolutionary stage of massive stars is not well understood. Westerlund 1 is an ideal astrophysical laboratory in which to study massive stars and their winds in great detail over a large range of different evolutionary phases. Aims. We aim to study the radio emission from Westerlund 1, in order to measure radio fluxes from the population of massive stars, and determine mass-loss rates and spectral indices where possible. Methods. Observations were carried out in 2015 and 2016 with the Australia Telescope Compact Array (ATCA) at 5.5 and 9 GHz using multiple configurations, with maximum baselines ranging from 750 m to 6 km. Results. Thirty stars are detected in the radio from the fully concatenated dataset, ten of which are Wolf-Rayet stars (WRs) (predominantly late type WN stars), five yellow hypergiants (YHGs), four red supergiants (RSGs), one luminous blue variable (LBV), the sgB[e] star W9, and several OB supergiants. New source detections in the radio are found for five WR stars, and five OB supergiants. These detections lead to evidence for three new OB supergiant binary candidates, which is inferred from derived spectral index limits. Conclusions. Spectral indices and index limits were determined for massive stars in Westerlund 1. For cluster members found to have partially optically thick emission, mass-loss rates were calculated. Under the approximation of a thermally emitting stellar wind and a steady mass-loss rate, clumping ratios were then estimated for eight WRs. Diffuse radio emission was detected throughout the cluster. Detections of knots of radio emission with no known stellar counterparts indicate the highly clumped structure of this intra-cluster medium, likely shaped by a dense cluster wind.

scholarly journals ENHANCED MASS LOSS RATES IN RED SUPERGIANTS AND THEIR IMPACT ON THE CIRCUMSTELLAR MEDIUM

2019 ◽  
Vol 55 (2) ◽  
pp. 161-175
Author(s):  
L. Hernández-Cervantes ◽  
B. Pérez-Rendón ◽  
A. Santillán ◽  
G. García-Segura ◽  
C. Rodríguez-Ibarra
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Gas Dynamics ◽  
Numerical Experiments ◽  
Evolutionary Models ◽  
Solar Composition ◽  
Red Supergiants ◽  
The Impact ◽  
Circumstellar Medium ◽  
Loss Rates

In this work, we present models of massive stars between 15 and 23 M⊙ , with enhanced mass loss rates during the red supergiant phase. Our aim is to explore the impact of extreme red supergiant mass-loss on stellar evolution and on their circumstellar medium. We computed a set of numerical experiments, on the evolution of single stars with initial masses of 15, 18, 20 and, 23 M⊙ , and solar composition (Z = 0.014), using the numerical stellar code BEC. From these evolutionary models, we obtained time-dependent stellar wind parameters, that were used explicitly as inner boundary conditions in the hydrodynamical code ZEUS-3D, which simulates the gas dynamics in the circumstellar medium (CSM), thus coupling the stellar evolution to the dynamics of the CSM. We found that stars with extreme mass loss in the RSG phase behave as a larger mass stars.

scholarly journals Warm CO in evolved stars from the THROES catalogue

2019 ◽  
Vol 622 ◽  
pp. A123 ◽  
Author(s):  
J. M. da Silva Santos ◽  
J. Ramos-Medina ◽  
C. Sánchez Contreras ◽  
P. García-Lario
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Asymptotic Giant Branch ◽  
Strong Line ◽  
Order Estimate ◽  
Evolved Stars ◽  
Flux Variability ◽  
The Impact ◽  
Loss Rates

Context. This is the second paper of a series making use of Herschel/PACS spectroscopy of evolved stars in the THROES catalogue to study the inner warm regions of their circumstellar envelopes (CSEs). Aims. We analyse the CO emission spectra, including a large number of high-J CO lines (from J = 14–13 to J = 45–44, ν = 0), as a proxy for the warm molecular gas in the CSEs of a sample of bright carbon-rich stars spanning different evolutionary stages from the asymptotic giant branch to the young planetary nebulae phase. Methods. We used the rotational diagram (RD) technique to derive rotational temperatures (Trot) and masses (MH2) of the envelope layers where the CO transitions observed with PACS arise. Additionally, we obtained a first order estimate of the mass-loss rates and assessed the impact of the opacity correction for a range of envelope characteristic radii. We used multi-epoch spectra for the well-studied C-rich envelope IRC+10216 to investigate the impact of CO flux variability on the values of Trot and MH2. Results. The sensitivity of PACS allowed for the study of higher rotational numbers than before indicating the presence of a significant amount of warmer gas (∼200 − 900 K) that is not traceable with lower J CO observations at submillimetre/millimetre wavelengths. The masses are in the range MH2 ∼ 10−2 − 10−5 M⊙, anticorrelated with temperature. For some strong CO emitters we infer a double temperature (warm T¯rot ∼ 400 K and hot T¯rot ∼ 820 K) component. From the analysis of IRC+10216, we corroborate that the effect of line variability is perceptible on the Trot of the hot component only, and certainly insignificant on MH2 and, hence, the mass-loss rate. The agreement between our mass-loss rates and the literature across the sample is good. Therefore, the parameters derived from the RD are robust even when strong line flux variability occurs, and the major source of uncertainty in the estimate of the mass-loss rate is the size of the CO-emitting volume.

scholarly journals The luminosity distribution of RSGs to test their mass-loss rate

2015 ◽  
Vol 11 (A29B) ◽  
pp. 454-454 ◽  
Author(s):  
Cyril Georgy ◽  
Sylvia Ekström
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Star ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Red Supergiants ◽  
Loss Rates

AbstractThe red supergiant phase is an important phase of the evolution of massive star, as it mostly determines its final stages. One of the most important driver of the evolution during this phase is mass loss. However, the mass-loss rates prescription used for red supergiants in current stellar evolution models are still very inaccurate.Varying the mass-loss rate makes the star evolve for some time in yellow/blue regions of the HRD, modifying the number of RSGs in some luminosity ranges. Figure 1 shows how the luminosity distribution of RSGs is modified for various mass-loss prescriptions. This illustrates that it is theoretically possible to determine at least roughly what is the typical mass loss regime of RSGs in a stellar evolution perspective.

scholarly journals The theory of winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 125-130 ◽  
Author(s):  
A.G. Hearn
Keyword(s):  
Mass Loss ◽  
Spectral Type ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Optical Measurements ◽  
Early Type ◽  
Large Uncertainty ◽  
Early Type Stars ◽  
Loss Rates

I assume that the purpose of this review of the theory of winds from early type stars is to summarize the way in which the mass loss rate of a star may be included in a calculation of stellar evolution. Let me summarize my conclusions. It is not possible. One can only use estimates of mass loss rates obtained from the observations. Even these give a large uncertainty. The observed mass loss rates for different stars of the same spectral type vary. Further the mass loss rates obtained by different methods for the same star differ. An extreme example of this is 9 Sgr. The mass loss rate derived from the radio observations is forty times greater than that derived from the U.V. and optical measurements (Abbott et al. 1980).

scholarly journals Surface brightness fluctuations, tracers of stellar mass-loss?

2009 ◽  
Vol 5 (S262) ◽  
pp. 48-51
Author(s):  
Rosa A. González-Lópezlira ◽  
Gustavo Bruzual-A. ◽  
Stéphane Charlot ◽  
Javier Ballesteros-Paredes ◽  
Laurent Loinard
Keyword(s):  
Mass Loss ◽  
Stellar Population ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Broad Band ◽  
Global Changes ◽  
Agb Stars ◽  
Near Ir ◽  
Surface Brightness Fluctuations ◽  
Order Of Magnitude

AbstractWe present optical and IR integrated colors and SBF magnitudes, computed from stellar population synthesis models that include emission from the dusty envelopes surrounding mass-loosing TP-AGB stars. We explore the effects of varying the mass-loss rate by one order of magnitude around the fiducial value, modifying accordingly both the stellar parameters and the output spectra of the TP-AGB stars plus their dusty envelopes. We compare these models to optical and near-IR data of single AGB stars and Magellanic star clusters. Neither broad-band colors nor SBF measurements in the optical or the near-IR can discern global changes in the mass-loss rate of a stellar population. However, we predict that mid-IR SBF measurements can pick out such changes, and actually resolve whether a relation between metallicity and mass-loss exists.

scholarly journals Evolved massive stars at low metallicity

2020 ◽  
Vol 639 ◽  
pp. A116
Author(s):  
Ming Yang ◽  
Alceste Z. Bonanos ◽  
Bi-Wei Jiang ◽  
Jian Gao ◽  
Panagiotis Gavras ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Dust Emission ◽  
Evolutionary Model ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Near Ir ◽  
Low Metallicity ◽  
Bolometric Correction ◽  
Giant Branch Stars

We present the most comprehensive red supergiant (RSG) sample for the Small Magellanic Cloud (SMC) to date, including 1239 RSG candidates. The initial sample was derived based on a source catalog for the SMC with conservative ranking. Additional spectroscopic RSGs were retrieved from the literature, and RSG candidates were selected based on the inspection of Gaia and 2MASS color-magnitude diagrams (CMDs). We estimate that there are in total ∼1800 or more RSGs in the SMC. We purify the sample by studying the infrared CMDs and the variability of the objects, though there is still an ambiguity between asymptotic giant branch stars (AGBs) and RSGs at the red end of our sample. One heavily obscured target was identified based on multiple near-IR and mid-IR (MIR) CMDs. The investigation of color-color diagrams shows that there are fewer RSGs candidates (∼4%) showing PAH emission features compared to the Milky Way and LMC (∼15%). The MIR variability of RSG sample increases with luminosity. We separate the RSG sample into two subsamples (risky and safe), and identify one M5e AGB star in the risky subsample based on simultaneous inspection of variabilities, luminosities, and colors. The degeneracy of mass loss rate (MLR), variability, and luminosity of the RSG sample is discussed, indicating that most of the targets with high variability are also the bright ones with high MLR. Some targets show excessive dust emission, which may be related to previous episodic mass loss events. We also roughly estimate the total gas and dust budget produced by entire RSG population as ∼1.9−1.1+2.4 × 10−6 M⊙ yr−1 in the most conservative case, according to the derived MLR from IRAC1–IRAC4 color. Based on the MIST models, we derive a linear relation between Teff and observed J − KS color with reddening correction for the RSG sample. By using a constant bolometric correction and this relation, the Geneva evolutionary model is compared with our RSG sample, showing a good agreement and a lower initial mass limit of ∼7 M⊙ for the RSG population. Finally, we compare the RSG sample in the SMC and the LMC. Despite the incompleteness of LMC sample in the faint end, the result indicates that the LMC sample always shows redder color (except for the IRAC1–IRAC2 and WISE1–WISE2 colors due to CO absorption) and higher variability than the SMC sample, which is likely due to a positive relation between MLR, variability and the metallicity.

scholarly journals Probing the hidden atomic gas in Class I jets with SOFIA

2020 ◽  
Vol 642 ◽  
pp. A216
Author(s):  
T. Sperling ◽  
J. Eislöffel ◽  
C. Fischer ◽  
B. Nisini ◽  
T. Giannini ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Far Infrared ◽  
Class I ◽  
Ejection Rate ◽  
Almost Everywhere ◽  
Atomic Gas ◽  
Protostellar Outflows ◽  
Mass Ejection ◽  
Loss Rates

Context. We present SOFIA/FIFI-LS observations of five prototypical, low-mass Class I outflows (HH111, SVS13, HH26, HH34, HH30) in the far-infrared [O I]63μm and [O I]145μm transitions. Aims. Spectroscopic [O I]63μm,145μm maps enable us to study the spatial extent of warm, low-excitation atomic gas within outflows driven by Class I protostars. These [O I] maps may potentially allow us to measure the mass-loss rates (Ṁjet) of this warm component of the atomic jet. Methods. A fundamental tracer of warm (i.e. T ~ 500–1500 K), low-excitation atomic gas is the [O I]63μm emission line, which is predicted to be the main coolant of dense dissociative J-type shocks caused by decelerated wind or jet shocks associated with protostellar outflows. Under these conditions, the [O I]63μm line can be directly connected to the instantaneous mass ejection rate. Thus, by utilising spectroscopic [O I]63μm maps, we wish to determine the atomic mass flux rate Ṁjet ejected from our target outflows. Results. Strong [O I]63μm emission is detected at the driving sources HH111IRS, HH34IRS, SVS13, as well as at the bow shock region, HH7. The detection of the [O I]63μm line at HH26A and HH8/HH10 can be attributed to jet deflection regions. The far-infrared counterpart of the optical jet is detected in [O I]63μm only for HH111, but not for HH34. We interpret the [O I]63μm emission at HH111IRS, HH34IRS, and SVS13 to be coming primarily from a decelerated wind shock, whereas multiple internal shocks within the HH111 jet may cause most of the [O I]63μm emission seen there. At HH30, no [O I]63μm,145μm was detected. The [O I]145μm line detection is at noise level almost everywhere in our obtained maps. The observed outflow rates of our Class I sample are to the order of Ṁjet ~ 10−6M⊙ yr−1, if proper shock conditions prevail. Independent calculations connecting the [O I]63μm line luminosity and observable jet parameters with the mass -loss rate are consistent with the applied shock model and lead to similar mass-loss rates. We discuss applicability and caveats of both methods. Conclusions. High-quality spectroscopic [O I]63μm maps of protostellar outflows at the jet driving source potentially allow a clear determination of the mass ejection rate.

scholarly journals Constraining red supergiant mass-loss prescriptions through supernova radio properties

2021 ◽  
Vol 503 (1) ◽  
pp. L28-L32
Author(s):  
Takashi J Moriya
Keyword(s):  
Mass Loss ◽  
Rise Time ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Strong Dependence ◽  
Core Collapse ◽  
Type Ii ◽  
Red Supergiants ◽  
Circumstellar Environment ◽  
Peak Luminosity

ABSTRACT Supernova (SN) properties in radio strongly depend on their circumstellar environment and they are an important probe to investigate the mass-loss of SN progenitors. Recently, core-collapse SN observations in radio have been assembled and the rise time and peak luminosity distribution of core-collapse SNe at 8.4 GHz has been estimated. In this paper, we constrain the mass-loss prescriptions for red supergiants (RSGs) by using the rise time and peak luminosity distribution of Type II SNe in radio. We take the de Jager and van Loon mass-loss rates for RSGs, calculate the rise time and peak luminosity distribution based on them, and compare the results with the observed distribution. We found that the de Jager mass-loss rate explains the widely spread radio rise time and peak luminosity distribution of Type II SNe well, while the van Loon mass-loss rate predicts a relatively narrow range for the rise time and peak luminosity. We conclude that the mass-loss prescriptions of RSGs should have strong dependence on the luminosity as in the de Jager mass-loss rate to reproduce the widely spread distribution of the rise time and peak luminosity in radio observed in Type II SNe.

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