scholarly journals Bloated Stars as BLR Clouds: Numeric Results

1994 ◽  
Vol 159 ◽  
pp. 437-437
Author(s):  
Tal Alexander ◽  
Hagai Netzer
Keyword(s):  
Mass Loss ◽  
Stellar Population ◽  
Line Emission ◽  
Distribution Functions ◽  
Solar Neighborhood ◽  
High Mass ◽  
Line Spectrum ◽  
Edge Density ◽  
Cloud Models ◽  
Wide Range

The ‘Bloated Stars Scenario’ proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS) (see e.g. Kazanas 1989 and references therein). Its main advantage over BLR cloud models is the gravitational confinement of the gas and its major difficulty the large estimated number of BSs and the resulting high collisional and evolutionary mass loss rates (see e.g. Begelman & Sikura 1991). Previous work on this model did not include detailed calculations of the line spectrum, modeled solar neighborhood super giants (SG) and used very simplified stellar distribution functions for the nucleus. Here (Alexander & Netzer, 1993) we calculate the emission line ratios by applying a detailed numerical photoionization code (Rees, Netzer & Ferland, 1989) to the wind and by assuming a detailed nucleus model (Murphy, Cohn & Durisen, 1990). Allowing for the yet unknown effects of the AGN's extreme conditions on stars and stellar evolution, we study a wide range of simplified wind structures rather than confine ourselves to normal SGs. Our model consists of a spherically symmetric outflowing wind that emanates from the surface of the BS (R∗ = 1013 cm, M∗ = 0.8M⊙, M = 10−6M⊙/yr) whose size and edge density are determined by various processes: Comptonization by the central continuum source (calculated self consistently for our Lion = 1046 erg/s model continuum by the photoionization code), tidal disruption by the black hole (Mbh = 8 × 107M⊙) and the limit set by the assumption that the wind's mass ≤ 0.2M⊙. This results in a large range of wind sizes, from 1013 to 1016 cm. We find that the line emission spectrum is mainly determined by the conditions at the edge of the wind rather than by its internal structure. Comptonization results in a very high ionization parameter at the edge which produces an excess of unobserved broad high excitation forbidden lines. The finite mass constraint limits the wind's size, increases the edge density and thus improves the results. Studying power-law wind structures (v(R) = v∗(R/R∗)−α where v∗ is the wind's base velocity at the BS's surface), we find that slow, decelerating, mass-constrained flows (v∗ = 50 m/s, α = 0.5) with high gas densities (108 to 1012 cm−3) are as successful as cloud models in reproducing the overall observed line spectrum. The Mg II λ2798 and N V λ1240 lines are however under-produced in our models. The denser the winds, the more efficient they are as BLR clouds. By calculating the Lα emission from the wind we adjust the number of BSs so as to obtain the BLR's observed EW(Lα). We find that only ∼ 5 × 104 BSs with dense winds (v∗ = 50 m/s, α = 0.5) are required in the inner 1/3 pc (∼ 0.005 of the total stellar population). This small fraction approaches that of SGs in the solar neighborhood. The calculated mass loss from such a small number of BSs is consistent with the observational constraints. We find that the required number of BSs, and consequently their mass loss rate, are a very sensitive functions of the wind's density structure (a ∼ 104 factor between the slow v∗ = 50 m/s, α = 0.5 model and the fast v∗ = 50 km/s, α = −2 model). In particular, high mass loss rules out SG-like BSs (v∗ = 10 km/s, α = 0). We conclude that BSs with dense winds can reproduce the BLR line spectrum and be supported by the stellar population without excessive mass loss and collisional destruction rates. The question whether such hitherto unobserved stars actually exist in the BLR remains open.

scholarly journals Progenitors of early-time interacting supernovae

2020 ◽  
Vol 496 (2) ◽  
pp. 1325-1342 ◽  
Author(s):  
Ioana Boian ◽  
Jose H Groh
Keyword(s):  
Mass Loss ◽  
Large Scale ◽  
Massive Stars ◽  
Early Time ◽  
High Mass ◽  
Single Star ◽  
Circumstellar Material ◽  
Wide Range ◽  
Wind Velocities ◽  
Loss Rates

ABSTRACT We compute an extensive set of early-time spectra of supernovae interacting with circumstellar material using the radiative transfer code cmfgen. Our models are applicable to events observed from 1 to a few days after explosion. Using these models, we constrain the progenitor and explosion properties of a sample of 17 observed interacting supernovae at early times. Because massive stars have strong mass-loss, these spectra provide valuable information about supernova progenitors, such as mass-loss rates, wind velocities, and surface abundances. We show that these events span a wide range of explosion and progenitor properties, exhibiting supernova luminosities in the 108 to 1012 L⊙ range, temperatures from 10 000 to 60 000 K, progenitor mass-loss rates from a few 10−4 up to 1 M⊙ yr−1, wind velocities from 100 to 800 km s−1, and surface abundances from solar-like to H-depleted. Our results suggest that many progenitors of supernovae interacting with circumstellar material have significantly increased mass-loss before explosion compared to what massive stars show during the rest of their lifetimes. We also infer a lack of correlation between surface abundances and mass-loss rates. This may point to the pre-explosion mass-loss mechanism being independent of stellar mass. We find that the majority of these events have CNO-processed surface abundances. In the single star scenario this points to a preference towards high-mass RSGs as progenitors of interacting SNe, while binary evolution could impact this conclusion. Our models are publicly available and readily applicable to analyse results from ongoing and future large-scale surveys such as the Zwicky Transient Factory.

scholarly journals First detection of X-ray line emission from Type IIn supernova 1978K with XMM-Newton’s RGS

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Yuki Chiba ◽  
Satoru Katsuda ◽  
Takashi Yoshida ◽  
Koh Takahashi ◽  
Hideyuki Umeda
Keyword(s):  
Mass Loss ◽  
Surface Composition ◽  
Massive Stars ◽  
Line Emission ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Expansion Velocity ◽  
X Ray ◽  
Elemental Abundances ◽  
High Mass Loss

Abstract We report on robust measurements of elemental abundances of the Type IIn supernova SN 1978K, based on the high-resolution X-ray spectrum obtained with the Reflection Grating Spectrometer (RGS) onboard XMM-Newton. The RGS clearly resolves a number of emission lines, including N Ly$\alpha$, O Ly$\alpha$, O Ly$\beta$, Fe xvii, Fe xviii, Ne He$\alpha$, and Ne Ly$\alpha$ for the first time from SN 1978K. The X-ray spectrum can be represented by an absorbed, two-temperature thermal emission model, with temperatures of $kT \sim 0.6$ keV and 2.7 keV. The elemental abundances are obtained to be N $=$$2.36_{{-0.80}}^{{+0.88}}$, O $=$$0.20 \pm {0.05}$, Ne $=$$0.47 \pm {0.12}$, Fe $=$$0.15_{{-0.02}}^{{+0.01}}$ times the solar values. The low metal abundances except for N show that the X-ray emitting plasma originates from the circumstellar medium blown by the progenitor star. The abundances of N and O are far from the CNO-equilibrium abundances expected for the surface composition of a luminous blue variable, and resemble the H-rich envelope of less massive stars with masses of 10–25$\, M_{\odot }$. Together with other peculiar properties of SN 1978K, i.e., a low expansion velocity of 500–1000 km s$^{-1}$ and SN IIn-like optical spectra, we propose that SN 1978K is a result of either an electron-capture SN from a super asymptotic giant branch star, or a weak Fe core-collapse explosion of a relatively low-mass ($\sim \! \! 10\, M_{\odot }$) or high-mass ($\sim$20–25$\, M_{\odot }$) red supergiant star. However, these scenarios cannot naturally explain the high mass-loss rate of the order of $\dot{M} \sim 10^{-3}\, M_{\odot }\:{\rm yr^{-1}}$ over $\gtrsim$1000 yr before the explosion, which is inferred by this work as well as many other earlier studies. Further theoretical studies are required to explain the high mass-loss rates at the final evolutionary stages of massive stars.

scholarly journals On the nature of OH/IR stars

1985 ◽  
Vol 106 ◽  
pp. 131-132
Author(s):  
Dieter Engels
Keyword(s):  
Mass Loss ◽  
Line Emission ◽  
Optical Emission ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Radial Pulsation ◽  
Intermediate Mass ◽  
Ir Stars ◽  
Loss Rates

OH/IR stars are the infrared counterparts of galactic OH maser sources which show a characteristic double-peaked emission-line profile. Their strong radio emission can be detected at large distances, making them excellent tracers of distribution and kinematics of evolved stars in the Milky Way. The OH maser profile is typical for line emission from an expanding circumstellar shell. The circumstellar shells of OH/IR stars absorb the optical emission of the central star nearly completely and reemit the energy in the infrared. Having luminosities ~ 105 L⊙ and energy distributions peaking around 10μm, they may make a major contribution to the interstellar radiation field beyond 5μm. With mass loss rates of 10-5 to 10-4 M⊙/yr they lose several solar masses in a few hundred thousand years. OH/IR stars are therefore important objects for recycling stellar matter into the interstellar medium.Progress has been made in understanding the nature of OH/IR stars. They are Mira-like large-amplitude variables with periods up to 5 years long. It is proposed that they are stars of intermediate mass (2–10 M⊙) on the asymptotic giant branch (AGB). They have not only larger masses than Mira variables proper, but also longer periods of pulsation and larger mass loss rates. As a result optically thick circumstellar dust shells are formed, which prevent the detection of these more massive Mira-like variables at optical wavelengths. Radial pulsation (Mira variability) is thus thought to occur for all intermediate-mass stars in the course of their evolution on the AGB. In view of their high mass-loss rates, these stars may be key objects in the study of the formation of planetary nebulae.

scholarly journals Study of CS, SiO, and SiS abundances in carbon star envelopes: assessing their role as gas-phase precursors of dust

2019 ◽  
Vol 628 ◽  
pp. A62 ◽  
Author(s):  
S. Massalkhi ◽  
M. Agúndez ◽  
J. Cernicharo
Keyword(s):  
Mass Loss ◽  
Gas Phase ◽  
Mass Loss Rate ◽  
Carbon Star ◽  
High Mass ◽  
Agb Stars ◽  
Dust Grains ◽  
Fractional Abundance ◽  
Wide Range ◽  
Loss Rates

Aims. We aim to determine the abundances of CS, SiO, and SiS in a large sample of carbon star envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in the surroundings of the central AGB star. Methods. We surveyed a sample of 25 carbon-rich AGB stars in the λ 2 mm band, more concretely in the J = 3−2 line of CS and SiO, and in the J = 7−6 and J = 8−7 lines of SiS, using the IRAM 30 m telescope. We performed excitation and radiative transfer calculations based on the large velocity gradient (LVG) method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. We also assessed the effect of infrared pumping in the excitation of the molecules. Results. We detected CS in all 25 targeted envelopes, SiO in 24 of them, and SiS in 17 sources. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10−6 M⊙ yr−1 while it is detected in all envelopes with mass loss rates above that threshold. We found that CS and SiS have similar abundances in carbon star envelopes, while SiO is present with a lower abundance. We also found a strong correlation in which the denser the envelope, the less abundant are CS and SiO. The trend is however only tentatively seen for SiS in the range of high mass loss rates. Furthermore, we found a relation in which the integrated flux of the MgS dust feature at 30 μm increases as the fractional abundance of CS decreases. Conclusions. The decline in the fractional abundance of CS with increasing density could be due to gas-phase chemistry in the inner envelope or to adsorption onto dust grains. The latter possibility is favored by a correlation between the CS fractional abundance and the 30 μm feature, which suggests that CS is efficiently incorporated onto MgS dust around C-rich AGB stars. In the case of SiO, the observed abundance depletion with increasing density is most likely caused by an efficient incorporation onto dust grains. We conclude that CS, SiO (very likely), and SiS (tentatively) are good candidates to act as gas-phase precursors of dust in C-rich AGB envelopes.

scholarly journals The initial luminosity and mass functions of Galactic open clusters

2008 ◽  
Vol 4 (S254) ◽  
pp. 221-226
Author(s):  
Hans Zinnecker ◽  
Anatoly E. Piskunov ◽  
Nina V. Kharchenko ◽  
Siegfried Röser ◽  
Elena Schilbach ◽  
...  
Keyword(s):  
Dynamical Evolution ◽  
Distribution Functions ◽  
Open Clusters ◽  
Solar Neighborhood ◽  
High Mass ◽  
Cluster Mass ◽  
Initial Cluster ◽  
High Infant Mortality ◽  
The Difference ◽  
Mass Functions

AbstractWe have derived a complete magnitude-limited sample of 440 Galactic open clusters in the solar neighborhood, with integrated V-magnitude brighter than 8 mag. This sample can be used to infer the present-day luminosity and mass functions of open clusters up to a given age; it can even be used to construct the initial mass and luminosity function (IMF, ILF) of clusters (defined as visible clusters with age 4 – 8 Myr). The high-mass end of the cluster IMF is a power-law with a slope of −2 or slightly shallower (−1.7) while the luminous cluster ILF has a power-slope of −1, in agreement with what is found for extragalactic clusters. Both distribution functions show a turnover, starting at 300 M⊙ and integrated magnitude −3 mag, respectively. The overall birthrate of clusters is 0.4 clusters per kpc2 and per Myr. The average present-day cluster mass is 700 M⊙, while the average initial cluster mass is 4500 M⊙. The difference of these two average masses indicates the high infant mortality and/or weight loss of Galactic open clusters (due to dynamical evolution).

scholarly journals Mass loss from Luminous Blue Variables

1989 ◽  
Vol 113 ◽  
pp. 135-148 ◽  
Author(s):  
Henny J. G. L. M. Lamers
Keyword(s):  
Mass Loss ◽  
High Mass ◽  
Luminous Blue Variables ◽  
Large Numbers ◽  
Wide Range ◽  
High Mass Loss

Luminous Blue Variables (LBV’s) are losing mass at a rate which is higher than in normal stars of the same luminosity. This high mass loss is evident from the occurrence of P Cygni profiles in the visual spectrum, the large numbers of UV lines which are Doppler shifted or show P Cygni profiles and the large IR excess or radio free-free emission. Mass loss from LBV’s is strongly variable on a wide range of timescales from months to centuries and possibly even millenia. During these variations the mass loss may vary from values as low as 10-6to 10-5M⊙/yr, when the star is quiet, to outbursts of the type observed in P Cygni in AD 1600 and n Car in 1837 (for reviews see Davidson, 1987; Lamers, 1986, 1987).

Discovery of a complex spiral-shell structure around the oxygen-rich AGB star GX Monocerotis

2020 ◽  
Vol 636 ◽  
pp. A123 ◽  
Author(s):  
S. K. Randall ◽  
A. Trejo ◽  
E. M. L. Humphreys ◽  
H. Kim ◽  
M. Wittkowski ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Loss Rate ◽  
Close Binary System ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Close Binary ◽  
Chemical Compositions ◽  
Circumstellar Envelopes ◽  
Wide Range ◽  
High Mass Loss

The circumstellar envelopes of asymptotic giant branch (AGB) stars exhibit a wide range of morphologies and chemical compositions that can be exploited to unravel their mass-loss history as well as binary status. Here, we present ALMA Band 6 observations centred upon the oxygen-rich, high mass-loss rate AGB star GX Mon. The resulting CO (2–1) map reveals an intricate, complex circumstellar spiral-arc structure consistent with hydrodynamical models for an AGB experiencing mass loss in a highly eccentric, close binary system with an orbital period of around 140 years. Several other transitions (including SiO, SiS, SO2, and CS) are detected in the data, however only the SO (5–4) map shows a similar – although much weaker – distribution as imaged for the CO.

scholarly journals Circumstellar environment of the M-type AGB star R Doradus

2018 ◽  
Vol 615 ◽  
pp. A8 ◽  
Author(s):  
E. De Beck ◽  
H. Olofsson
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Line Emission ◽  
Asymptotic Giant Branch ◽  
Emission Lines ◽  
High Mass ◽  
Spectral Features ◽  
High Mass Loss ◽  
Spectral Scan

Context. Our current insights into the circumstellar chemistry of asymptotic giant branch (AGB) stars are largely based on studies of carbon-rich stars and stars with high mass-loss rates. Aims. In order to expand the current molecular inventory of evolved stars we present a spectral scan of the nearby, oxygen-rich star R Dor, a star with a low mass-loss rate (~2 × 10−7 M⊙ yr−1). Methods. We carried out a spectral scan in the frequency ranges 159.0–321.5 GHz and 338.5–368.5 GHz (wavelength range 0.8–1.9 mm) using the SEPIA/Band-5 and SHeFI instruments on the APEX telescope and we compare it to previous surveys, including one of the oxygen-rich AGB star IK Tau, which has a high mass-loss rate (~5 ×10−6 M⊙ yr−1). Results. The spectrum of R Dor is dominated by emission lines of SO2 and the different isotopologues of SiO. We also detect CO, H2O, HCN, CN, PO, PN, SO, and tentatively TiO2, AlO, and NaCl. Sixteen out of approximately 320 spectral features remain unidentified. Among these is a strong but previously unknown maser at 354.2 GHz, which we suggest could pertain to H2SiO, silanone. With the exception of one, none of these unidentified lines are found in a similarly sensitive survey of IK Tau performed with the IRAM 30 m telescope. We present radiative transfer models for five isotopologues of SiO (28SiO, 29SiO, 30SiO, Si17O, Si18O), providing constraints on their fractional abundance and radial extent. We derive isotopic ratios for C, O, Si, and S and estimate that, based on our results for 17O/18O, R Dor likely had an initial mass in the range 1.3–1.6 M⊙, in agreement with earlier findings based on models of H2O line emission. From the presence of spectral features recurring in many of the measured thermal and maser emission lines we tentatively identify up to five kinematical components in the outflow of R Dor, indicating deviations from a smooth, spherical wind.

scholarly journals Kinematics of Nuclei of Sc Galaxies

1980 ◽  
Vol 5 ◽  
pp. 191-191
Author(s):  
V. C. Rubin
Keyword(s):  
High Velocity ◽  
Stellar Population ◽  
Hii Regions ◽  
Emission Lines ◽  
High Luminosity ◽  
Rotation Curves ◽  
Velocity Gradients ◽  
Wide Range ◽  
Central Regions ◽  
Velocity Dispersions

For a sample of 21 Sc galaxies with a wide range of luminosities, of radii, and of masses, W. K. Ford and I have obtained spectra and determined rotation curves. By their kinematical behavior in their central regions, the Sc’s can be separated into two groups. Some galaxies, generally small and of low luminosity, have shallow central velocity gradients, reflecting their low central masses and densities. Other galaxies, most often large ones of high luminosity, have steep central velocity gradients. One reason this separation by central velocity gradients is of interest is because these galaxies exhibit other significant spectral differences which go hand-in-hand with the kinematical differences.The small, low luminosity galaxies show emission lines of Hα and [NII], with nuclear Ha sharp and stronger than [NII], and little or no stellar nuclear continuum, just as conventional HII regions. In contrast, the high luminosity galaxies show broad nuclear emission, with [NII] stronger than Ha. These galaxies have a strong red stellar continuum, arising from a red stellar population. The cause of the Hα[NII] intensity reversal in the nuclei of some galaxies remains unknown. However, the strong [NII] emission in generally high luminosity galaxies with massive nuclei, nuclei which show strong red continua, suggests that [Nil] intensity correlates with nuclear luminosity, and in turn with the density and velocity properties of the nuclear populations. We would expect high velocity dispersions and high bulge luminosities for galaxies with strong nuclear [NII] and steep central velocity gradients.

scholarly journals Water maser and radio continuum emission towards IRAS 23139+5939

2007 ◽  
Vol 3 (S242) ◽  
pp. 180-181
Author(s):  
M. A. Trinidad ◽  
S. Curiel ◽  
J. M. Torrelles ◽  
L. F. Rodríguez ◽  
V. Migenes ◽  
...  
Keyword(s):  
Flux Density ◽  
Line Emission ◽  
The Other ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
Maser Line ◽  
Water Masers ◽  
Water Maser ◽  
The Continuum

AbstractWe present simultaneous observations of continuum (3.5 and 1.3cm) and water maser line emission (1.3cm) carried out with the VLA-A toward the high-mass object IRAS 23139+5939. We detected two radio continuum sources at 3.5cm separated by 0”5 (~2400 AU), I23139 and I23139S. Based on the observed continuum flux density and the spectral index, we suggest that I23139 is a thermal radio jet associated with a high-mass YSO. On the other hand, based on the spatio-kinematical distribution of the water masers, together with the continuum emission information, we speculate that I23139S is also a jet source powering some of the masers detected in the region.

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