NUMERICAL SIMULATIONS OF WIND ACCRETION IN SYMBIOTIC BINARIES

International Nuclear Information System (INIS)

De Val-Borro, M.; Karovska, M.; Sasselov, D.

2009-01-01

About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the mass transfer and formation of accretion disks around the secondary in detached systems consisting of an asymptotic giant branch (AGB) mass-losing star and an accreting companion. The presence of mass outflows is studied as a function of mass-loss rate, wind temperature, and binary orbital parameters. A two-dimensional hydrodynamical model is used to study the stability of mass transfer in wind accreting symbiotic binary systems. In our simulations we use an adiabatic equation of state and a modified version of the isothermal approximation, where the temperature depends on the distance from the mass losing star and its companion. The code uses a block-structured adaptive mesh refinement method that allows us to have high resolution at the position of the secondary and resolve the formation of bow shocks and accretion disks. We explore the accretion flow between the components and formation of accretion disks for a range of orbital separations and wind parameters. Our results show the formation of stream flow between the stars and accretion disks of various sizes for certain orbital configurations. For a typical slow and massive wind from an AGB star the flow pattern is similar to a Roche lobe overflow with accretion rates of 10% of the mass loss from the primary. Stable disks with exponentially decreasing density profiles and masses of the order 10 -4 solar masses are formed when wind acceleration occurs at several stellar radii. The disks are geometrically thin with eccentric streamlines and close to Keplerian velocity profiles. The formation of tidal streams and accretion disks is found to be weakly dependent

Properties of the cold components of symbiotic stars

International Nuclear Information System (INIS)

Luud, L.; Leedyarv, L.

1986-01-01

The basic physical parameters of the cold components of symbiotic stars and comparison red giants have been determined from the data of infrared photometry by means of the Blackwell-Shallis method. It is found that the cold components of the symbiotic stars do not differ from normal red giants of the asymptotic branch. The masses of the cold components of the symbiotic stars are close to 3M. The red components of the symbiotic stars do not fill their Roche lobes. Among the cold components of the symbiotic stars, there are approximately ten times as many carbon stars as among the red giants in the neighborhood of the Sun

Symbiotic stars according to IRAS observations

International Nuclear Information System (INIS)

Luud, L.; Tuvikene, T.

1987-01-01

Symbiotic stars contained in Allen's catalog are examined with a view to establishing their coincidence with sources of far infrared radiation in the catalog of point sources observed with the IRAS satellite. Altogether, 72 symbiotic or suspected symbiotic objects have been identified. A list of the identified stars has been compiled, and the energy distributions in the infrared spectra of selected stars are given. It has been found that the presence of dust in symbiotic systems is a more widespread phenomenon than hitherto believed. Almost 40% of them are dust systems. Among them, objects with dust temperature of several tens of degrees kelvin have been found. It is shown that the only useful two-color diagram is the (K - m 12 )-(m 12 - m 25 ) diagram. Finally, attention is drawn to a type of symbiotic stars having cold components of the spectral class G; these require a special investigation

UV line emission of symbiotic stars

International Nuclear Information System (INIS)

Nussbaumer, H.

1982-01-01

General characteristics of emission line spectra from symbiotic stars are outlined. Data from some special line ratios in the 1000 A - 3000 A range, and others connecting the visual and the far UV lines are presented, and their application to symbiotic stars is discussed. Integrated fractional abundances for ions easily observed in the far UV are given to facilitate abundance determinations for nebular conditions. It is found that the physical conditions of the regions emitting the emission line spectra differ considerably among different symbiotic stars. (Auth.)

The symbiotic star H1-36

International Nuclear Information System (INIS)

Allen, D.A.

1983-01-01

Optical and infrared spectrophotometry is presented of the high-excitation emission-line star H1-36. The presence of a variable M giant is established: H1-36 may therefore be classified as a symbiotic star. The observations are interpreted in terms of the usual binary model for symbiotic stars, namely that an unseen star is heated by accretion of gas from its companion M giant. (author)

Near IR spectra of symbiotic stars

International Nuclear Information System (INIS)

Andrillat, Y.

1982-01-01

The author reports on recent observations from the near IR spectra of symbiotic stars. The helium and oxygen lines useful for the construction of theoretical models are identified. Observations for cool stars and novae (nebular phase) are outlined and the spectra of specific symbiotic stars between lambdalambda 8000-11000 are presented and discussed. (Auth./C.F.)

Symbiotic star H1-36

Energy Technology Data Exchange (ETDEWEB)

Allen, D A

1983-01-01

It is suggested that H1-36 should be classified as a symbiotic star rather than a planetary nebula. Evidence of a cool giant now exists and the high-excitation emission-line spectrum resembles the spectra of many symbiotic stars. The optical spectrum, radio spectrum, high spectral index of +0.9 and computed mass-loss rate are among the features discussed.

On the nature of the symbiotic star BF Cygni

International Nuclear Information System (INIS)

Mikolajewska, J.; Mikolajewski, M.; Kenyon, S.J.

1989-01-01

Optical and ultraviolet spectroscopy of the symbiotic binary BF Cyg obtained during 1979-1988 is discussed. This system consists of a low-mass M5 giant filling about 50 percent of its tidal volume and a hot, luminous compact object similar to the central star of a planetary nebula. The binary is embedded in an asymmetric nebula which includes a small, high-density region and an extended region of lower density. The larger nebula is formed by a slow wind ejected by the cool component and ionized by the hot star, while the more compact nebula is material expelled by the hot component in the form of a bipolar wind. The analysis indicates that disk accretion is essential to maintain the nuclear burning shell of the hot star. 84 refs

On the model of symbiotic stars

International Nuclear Information System (INIS)

Tutukov, A.V.; Yungelson, L.R.

1982-01-01

The authors discuss conditions necessary for appearance and discovery of the symbiotic star phenomenon within the model of a binary consisting of a red (super)giant 3 solar masses not filling the Roche lobe and of an accreting hot degenerate CO-dwarf 0.8 solar masses. Within this model ''classical'' symbiotic stars may exist only within a narrow region of mass accretion rates and separations of components: 10 -7 approximately -7 solar masses/y and 3x10 13 approximately 14 cm. The evolutionary status of symbiotic stars and related objects and the mechanisms of their variability are discussed. (Auth.)

Determination of the term symbiotic star

International Nuclear Information System (INIS)

Boyarchuk, A.A.

1982-01-01

The author proposes the following criteria for the use of the term symbiotic star: The symbiotic stars must have a spectrum which simultaneously present the cool star features (TiO bands or G-band, etc.), and the emission lines of HeII and/or [OIII], and/or [NeIII], and lines which require even higher ionization level. He also proposes a classification of symbiotic stars according to different types of observations: according to 1) UBV photometry, 2) infrared observations, 3) radio observations, 4) absorption spectrum, 5) emission spectrum. The limted amount of ultraviolet and X-ray observations prevents any classification. The author thinks that the groups are not independent, one type showing variations belonging to another group. (Auth./C.F.)

SS 383: A NEW S-TYPE YELLOW SYMBIOTIC STAR?

Energy Technology Data Exchange (ETDEWEB)

Baella, N. O.; Pereira, C. B. [Observatório Nacional, Rua José Cristino 77, CEP 20921-400, São Cristóvão, Rio de Janeiro (Brazil); Miranda, L. F. [Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Vigo, E-36310 Vigo (Spain)

2013-11-01

Symbiotic stars are key objects in understanding the formation and evolution of interacting binary systems, and are probably the progenitors of Type Ia supernovae. However, the number of known symbiotic stars is much lower than predicted. We aim to search for new symbiotic stars, with particular emphasis on the S-type yellow symbiotic stars, in order to determine their total population, evolutionary timescales, and physical properties. The Two Micron All Sky Survey (2MASS) (J – H) versus (H – K {sub s}) color-color diagram has been previously used to identify new symbiotic star candidates and show that yellow symbiotics are located in a particular region of that diagram. Candidate symbiotic stars are selected on the basis of their locus in the 2MASS (J – H) versus (H – K {sub s}) diagram and the presence of Hα line emission in the Stephenson and Sanduleak Hα survey. This diagram separates S-type yellow symbiotic stars from the rest of the S-type symbiotic stars, allowing us to select candidate yellow symbiotics. To establish the true nature of the candidates, intermediate-resolution spectroscopy is obtained. We have identified the Hα emission line source SS 383 as an S-type yellow symbiotic candidate by its position in the 2MASS color-color diagram. The optical spectrum of SS 383 shows Balmer, He I, He II, and [O III] emission lines, in combination with TiO absorption bands that confirm its symbiotic nature. The derived electron density (≅10{sup 8-9} cm{sup –3}), He I emission line intensity ratios, and position in the [O III] λ5007/Hβ versus [O III] λ4363/Hγ diagram indicate that SS 383 is an S-type symbiotic star, with a probable spectral type of K7-M0 deduced for its cool component based on TiO indices. The spectral type and the position of SS 383 (corrected for reddening) in the 2MASS color-color diagram strongly suggest that SS 383 is an S-type yellow symbiotic. Our result points out that the 2MASS color-color diagram is a powerful tool in

SS 383: A NEW S-TYPE YELLOW SYMBIOTIC STAR?

International Nuclear Information System (INIS)

Baella, N. O.; Pereira, C. B.; Miranda, L. F.

2013-01-01

Symbiotic stars are key objects in understanding the formation and evolution of interacting binary systems, and are probably the progenitors of Type Ia supernovae. However, the number of known symbiotic stars is much lower than predicted. We aim to search for new symbiotic stars, with particular emphasis on the S-type yellow symbiotic stars, in order to determine their total population, evolutionary timescales, and physical properties. The Two Micron All Sky Survey (2MASS) (J – H) versus (H – K s ) color-color diagram has been previously used to identify new symbiotic star candidates and show that yellow symbiotics are located in a particular region of that diagram. Candidate symbiotic stars are selected on the basis of their locus in the 2MASS (J – H) versus (H – K s ) diagram and the presence of Hα line emission in the Stephenson and Sanduleak Hα survey. This diagram separates S-type yellow symbiotic stars from the rest of the S-type symbiotic stars, allowing us to select candidate yellow symbiotics. To establish the true nature of the candidates, intermediate-resolution spectroscopy is obtained. We have identified the Hα emission line source SS 383 as an S-type yellow symbiotic candidate by its position in the 2MASS color-color diagram. The optical spectrum of SS 383 shows Balmer, He I, He II, and [O III] emission lines, in combination with TiO absorption bands that confirm its symbiotic nature. The derived electron density (≅10 8-9 cm –3 ), He I emission line intensity ratios, and position in the [O III] λ5007/Hβ versus [O III] λ4363/Hγ diagram indicate that SS 383 is an S-type symbiotic star, with a probable spectral type of K7-M0 deduced for its cool component based on TiO indices. The spectral type and the position of SS 383 (corrected for reddening) in the 2MASS color-color diagram strongly suggest that SS 383 is an S-type yellow symbiotic. Our result points out that the 2MASS color-color diagram is a powerful tool in identifying new S

A polarimetric survey of symbiotic stars

International Nuclear Information System (INIS)

Schulte-Ladbeck, R.E.; Magalhaes, A.M.; Magalhaes, A.M.

1990-01-01

We present optical and near-infrared linear polarization observations of 24 symbiotic stars, 14 observed with polarimetry for the first time. In combination with published data, we find that ∼ 50% of the symbiotics observed polarimetrically show evidence for intrinsic polarization. We discuss the results in the light of previous observations and comment on the temporal variability and wavelength dependence of the polarization. Dust scattering is identified as the dominant mechanism producing polarization in symbiotic stars. While we cannot exclude that some symbiotic systems are completely engulfed in their dust shells our data indicate that the Hα emission line may originate from outside of the dust-scattering envelopes in some systems

The first symbiotic stars from the LAMOST survey

International Nuclear Information System (INIS)

Li, Jiao; Chen, Xue-Fei; Han, Zhan-Wen; Mikołajewska, Joanna; Luo, A-Li; Wu, Yue; Yang, Ming; Rebassa-Mansergas, Alberto; Hou, Yong-Hui; Wang, Yue-Fei; Zhang, Yong

2015-01-01

Symbiotic stars are interacting binary systems with the longest orbital periods. They are typically formed by a white dwarf and a red giant that are embedded in a nebula. These objects are natural astrophysical laboratories for studying the evolution of binaries. Current estimates of the population of symbiotic stars in the Milky Way vary from 3000 up to 400 000. However, a current census has found less than 300. The Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) survey can obtain hundreds of thousands of stellar spectra per year, providing a good opportunity to search for new symbiotic stars. We detect four such binaries among 4 147 802 spectra released by LAMOST, of which two are new identifications. The first is LAMOST J12280490–014825.7, considered to be an S-type halo symbiotic star. The second is LAMOST J202629.80+423652.0, a D-type symbiotic star. (paper)

The symbiotic star H1-36

International Nuclear Information System (INIS)

Allen, D.A.

1983-01-01

It is suggested that H1-36 should be classified as a symbiotic star rather than a planetary nebula. Evidence of a cool giant now exists and the high-excitation emission-line spectrum resembles the spectra of many symbiotic stars. The optical spectrum, radio spectrum, high spectral index of +0.9 and computed mass-loss rate are among the features discussed

Symbiotic and VV Cephei stars in the Small Magellanic Cloud

International Nuclear Information System (INIS)

Walker, A.R.

1983-01-01

Three symbiotic stars, including a carbon symbiotic star, are identified in the Small Magellanic Cloud, thus two out of five known symbiotic stars in the Magellanic Clouds have C rather than M components, compared to our own Galaxy where the proportion is much lower. This supports the assertion that the symbiotic phenomenon follows the higher C:M star ratio in the Magellanic Clouds and is not a property of M binaries alone. Two other emission-line stars are discussed; one is the only known VV Cephei star in the SMC while the second is a composite Be + K supergiant system. (author)

Symbiotic stars as an old disk population

Energy Technology Data Exchange (ETDEWEB)

Wallerstein, G [Joint Inst. for Lab. Astrophysics, Boulder, CO (USA)

1981-10-01

A table of all symbiotic stars in the General Catalogue of Variable Stars and its supplements has been assembled and their radial velocities have been discussed. A velocity dispersion of 63 +- 14 km/s is found for all the stars and a value of 58 +- 14 km/s is established if the probable halo star, AG Dra, is omitted. The space distribution is similar to that of an old disk population. Some implications of low masses for the symbiotic stars are discussed, and some suggestions are made regarding possibly useful observations.

AGB stellar evolution and symbiotic stars

International Nuclear Information System (INIS)

Schild, H.

1989-01-01

Published data on the mass loss rates and periods of Miras and OH/IR stars have been compiled. There is a good correlation between mass loss rate and period and a smooth transition from Miras to OH/IR sources. At periods below 600 d. the mass loss increases exponentially but at longer periods it remains constant. As a Mira evolves from short to longer periods, its mass loss rate increases dramatically. Phenomenologically, the object evolves from a classical Mira into a variable OH/IR source. Symbiotic stars cluster in the transition zone where Miras transform into OH/IR stars and mass loss increase is at its steepest. The red star in these symbiotic systems is in the same evolutionary status as short periodic OH/IR stars. (author)

Recent photometry of selected symbiotic stars

Science.gov (United States)

Vrašťák, M.

2018-04-01

A new multicolour (BVRcIc) photometric observations of symbiotic stars UV Aur, YY Her, V443 Her, V1016 Cyg, PU Vul, V407 Cyg, V471 Per and suspected symbiotic stars ZZ CMi, NQ Gem, V934 Her, V335 Vul, V627 Cas is presented. The data were obtained from 2016 October to 2018 January by the metod of classical CCD photometry. The monitoring program is still running, so on this paper partial light curves are presented.

Polarimetry of symbiotic stars

International Nuclear Information System (INIS)

Piirola, V.

1983-01-01

Five symbiotic stars have been observed for linear polarization (UBVRI) in September 1981. Three systems, CH Cyg, CI Cyg and AG Peg show intrinsic polarization while in the case of Z And and AX Per the observed polarization seems to be mostly of interstellar origin. The position angle of polarization of CI Cyg and AG Peg rotates strongly vs. wavelength, as observed also for CH Cyg in 1977-80. The polarization of CH Cyg has decreased since May 1980, especially in the I, R and U bands, so that the maximum polarization is now in the blue (Psub(B) approx. 0.3%). Probably one is monitoring the formation, growth and disappearance of dust particles in the atmosphere of this star. Two related systems, PU Vul (Nova Vul 1979) and R Aql (Mira) have polarization behaviour rather similar to that of symbiotic stars which suggests that the M type giant present in these systems is responsible for most of the intrinsic polarization. (Auth.)

Origin and evolutionary stage of symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Tutukov, A V; Yungel' son, L R [AN SSSR, Moscow. Astronomicheskij Sovet

1976-08-01

Symbiotic stars are considered which best of all are described by the binary star model. An analysis of properties of symbiotic stars shows that their hot components should be either carbon-oxygen dwarfs with thin hydrogen-helium envelopes or helium stars with thin mantles. Cold components are red giants losing matter at the rate of 10/sup -5/-10/sup -6/ M/yr over the period of 10/sup 5/-10/sup 6/ years (M is the Sun mass). Such systems can be formed of wide pairs as a result of loss of envelope of an initially more massive star of the system by way of continuous outflow of matter or expulsion due to dynamic instability at the red giant stage,, and also of closer pairs as a result of exchange of matter between the components. It has been shown that hot components of symbiotic stars can accrete 10/sup -6/-10/sup -9/ M/yr, and some consequencies of accretion on a C-O dwarf have been considered.

TIDALLY ENHANCED STELLAR WIND: A WAY TO MAKE THE SYMBIOTIC CHANNEL TO TYPE Ia SUPERNOVA VIABLE

International Nuclear Information System (INIS)

Chen, X.; Han, Z.; Tout, C. A.

2011-01-01

In the symbiotic (or WD+RG) channel of the single-degenerate scenario for type Ia supernovae (SNe Ia), the explosions occur a relatively long time after star formation. The birthrate from this channel would be too low to account for all observed SNe Ia were it not for some mechanism to enhance the rate of accretion on to the white dwarf. A tidally enhanced stellar wind, of the type which has been postulated to explain many phenomena related to giant star evolution in binary systems, can do this. Compared to mass stripping, this model extends the space of SNe Ia progenitors to longer orbital periods and hence increases the birthrate to about 0.0069 yr -1 for the symbiotic channel. Two symbiotic stars, T CrB and RS Oph, considered to be the most likely progenitors of SNe Ia through the symbiotic channel, are well inside the period-companion mass space predicted by our models.

Radio observations of symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Wright, A E [Commonwealth Scientific and Industrial Research Organization, Epping (Australia). Div. of Radiophysics; Allen, D A

1978-09-01

A search for 2-cm continuum emission from 91 symbiotic stars has been undertaken using the Parkes radio telescope. Nine sources have been detected, four of which are reported for the first time. The radio spectral indices are mostly about + 0.6; these are interpreted in terms of mass loss. In two stars a portion of the radio spectrum has an index of zero, and for one of these stars (RX Puppis) this is plausibly a manifestation of the cessation of symbiotic activity that occurred about two decades ago. There is an extraordinarily good correlation between the detectability at 2cm and the presence of circumstellar dust, but not between the radio and optical domains. The importance of continued radio monitoring of HM Sagittae over the next few years is stressed.

X-ray observations of symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Allen, D A [Anglo-Australian Observatory, Epping (Australia)

1981-11-01

Observations of 19 symbiotic stars made with the image proportional counter of the Einstein Observatory are reported. Three were detected as soft X-ray sources. All three have shown slow-nova eruptions in the past 40 years. The data are interpreted as support for a model for slow novae involving thermonuclear events on white dwarfs which accrete from M giant companions. Symbiotic stars in their steady state, not being detected X-ray sources, are presumed to be powered by the accretion process alone.

X-ray observations of symbiotic stars

International Nuclear Information System (INIS)

Allen, D.A.

1981-01-01

Observations of 19 symbiotic stars made with the image proportional counter of the Einstein Observatory are reported. Three were detected as soft X-ray sources. All three have shown slow-nova eruptions in the past 40 years. The data are interpreted as support for a model for slow novae involving thermonuclear events on white dwarfs which accrete from M giant companions. Symbiotic stars in their steady state, not being detected X-ray sources, are presumed to be powered by the accretion process alone. (author)

The collective radio properties of symbiotic stars

International Nuclear Information System (INIS)

Seaquist, E.R.; Taylor, A.R.

1990-01-01

Radio measurements of symbiotic stars are reported which extend the search for radio emission and provide multifrequency and multiepoch measurements of previously detected stars. The results show no evidence that there are time variations in excess of about 30 percent over a period of several years in the detected stars. The radio flux densities are correlated with brightness in the IR, especially at the longer IR wavelengths where dust emission dominates. It is confirmed that symbiotics with the latest red giant spectral types are the most luminous radio emitters. The D-types are the most radio-luminous. Virtually all detected stars with measurements at more than one frequency exhibit a positive spectral index, consistent with optically thick thermal bremsstrahlung. The binary separation for a number of radio-emitting symbiotics is estimated, and it is found that the distribution of inferred binary separations is dramatically different for IR D-types than for S-types. 37 refs

On origin and evolutionary stage of symbiotic stars

International Nuclear Information System (INIS)

Tutukov, A.V.; Yungel'son, L.R.

1976-01-01

Symbiotic stars are considered which best of all are described by the binary star model. An analysis of properties of symbiotic stars shows that their hot components should be either carbon-oxygen dwarfs with thin hydrogen-helium envelopes or helium stars with thin mantles. Cold components are red giants losing matter with the rate of 10 -5 -10 -6 M/yr over the period of 10 5 -10 6 years (M is the Sun mass). Such systems can be formed of wide pairs as a result of loss of envelope of an initially more massive star of the system by way of continuous outflow of matter or expulsion due to dynamic instability at the stage of red giant, and also of more close pairs as a result of exchange of matter between the components. It has been shown that hot components of symbiotic stars can accrete 10 -6 -10 -9 M/yr and some consequencies of accretion on a C-O dwarf have been considered

Wind accretion and formation of disk structures in symbiotic binary systems

Science.gov (United States)

de Val-Borro, M.; Karovska, M.; Sasselov, D. D.; Stone, J. M.

2015-05-01

We investigate gravitationally focused wind accretion in binary systems consisting of an evolved star with a gaseous envelope and a compact accreting companion. We study the mass accretion and formation of an accretion disk around the secondary caused by the strong wind from the primary late-type component using global 2D and 3D hydrodynamic numerical simulations. In particular, the dependence of the mass accretion rate on the mass loss rate, wind temperature and orbital parameters of the system is considered. For a typical slow and massive wind from an evolved star the mass transfer through a focused wind results in rapid infall onto the secondary. A stream flow is created between the stars with accretion rates of a 2--10% percent of the mass loss from the primary. This mechanism could be an important method for explaining periodic modulations in the accretion rates for a broad range of interacting binary systems and fueling of a large population of X-ray binary systems. We test the plausibility of these accretion flows indicated by the simulations by comparing with observations of the symbiotic variable system CH Cyg.

Properties of symbiotic stars from studies in the optical region

International Nuclear Information System (INIS)

Ciatti, F.

1982-01-01

The author uses observations of symbiotic stars in the optical region to discuss the following aspects: definition, photometric and spectroscopic evolution, the three-component model, evidence for the binary nature, spectroscopic properties and anomalies, single-star interpretations, the ''very slow novae'' and BQ// stars and a comparison of symbiotic stars with other classes. (C.F.)

Broad absorption line symbiotic stars: highly ionized species in the fast outflow from MWC 560

Science.gov (United States)

Lucy, Adrian B.; Knigge, Christian; Sokoloski, J. L.

2018-04-01

In symbiotic binaries, jets and disk winds may be integral to the physics of accretion onto white dwarfs from cool giants. The persistent outflow from symbiotic star MWC 560 (≡V694 Mon) is known to manifest as broad absorption lines (BALs), most prominently at the Balmer transitions. We report the detection of high-ionization BALs from C IV, Si IV, N V, and He II in International Ultraviolet Explorer spectra obtained on 1990 April 29 - 30, when an optical outburst temporarily erased the obscuring `iron curtain' of absorption troughs from Fe II and similar ions. The C IV and Si IV BALs reached maximum radial velocities at least 1000 km s-1 higher than contemporaneous Mg II and He II BALs; the same behaviors occur in the winds of quasars and cataclysmic variables. An iron curtain lifts to unveil high-ionization BALs during the P Cygni phase observed in some novae, suggesting by analogy a temporary switch in MWC 560 from persistent outflow to discrete mass ejection. At least three more symbiotic stars exhibit broad absorption with blue edges faster than 1500 km s-1; high-ionization BALs have been reported in AS 304 (≡V4018 Sgr), while transient Balmer BALs have been reported in Z And and CH Cyg. These BAL-producing fast outflows can have wider opening angles than has been previously supposed. BAL symbiotics are short-timescale laboratories for their giga-scale analogs, broad absorption line quasars (BALQSOs), which display a similarly wide range of ionization states in their winds.

Infrared studies of symbiotic stars

International Nuclear Information System (INIS)

Allen, D.A.

1982-01-01

Infrared photometry and spectroscopy of symbiotic stars is reviewed. It is shown that at wavelengths beyond 1 μm these systems are generally dominated by the cool star's photosphere and, indeed, are indistinguishable from ordinary late-type giants. About 25% of symbiotic stars exhibit additional emission due to circumstellar dust. Most of the dusty systems probably involve Mira variables, the dust forming in the atmospheres of the Miras. In a few cases the dust is much cooler and the cool component hotter; the dust must then form in distant gas shielded from the hot component, perhaps by an accretion disk. Spectroscopy at 2 μm can be used to spectral type the cool components, even in the presence of some dust emission. Distances may thereby be estimated, though with some uncertainty. Spectroscopy at longer wavelengths reveals information about the dust itself. In most cases this dust appears to include silicate grains, which form in the oxygen-rich envelope of an M star. In the case of HD 33036, however, different emission features are found which suggest a carbon-rich environment. (Auth.)

Interacting Winds in Eclipsing Symbiotic Systems

Indian Academy of Sciences (India)

2016-01-27

Jan 27, 2016 ... Interacting Winds in Eclipsing Symbiotic Systems – The Case Study of EG Andromedae ... to obtain the physical parameters of a quiescent eclipsing symbiotic system. ... Articles are also visible in Web of Science immediately.

Late-type components of slow novae and symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Allen, D A [Anglo-Australian Observatory, Epping (Australia); Royal Observatory, Edinburgh (UK))

1980-08-01

It is argued that the various types of symbiotic stars and the slow novae are the same phenomena exhibiting a range of associated time-scales, the slow novae being of intermediate speed. Evidence is summarized showing that both types of object contain normal M giants or mira variables. This fact is at odds with currently fashionable single-star models for slow novae, according to which the M star is totally disrupted before the outburst. Spectral types of the late-type components are presented for nearly 80 symbiotic stars and slow novae, derived from 2 ..mu..m spectroscopy. It is found that both the intensity of the emission spectrum and the electron density of the gas are functions of the spectral type of the late-type star. Explanations for these correlations are given. On the assumption that the late-type components are normal giants, spectroscopic parallaxes are determined; credible distances are derived which indicate that the known symbiotic stars have been sampled as far afield as the Galactic Centre. Hydrogen shell flashes on a white dwarf accreting gas from the late-type components offer an attractive explanation of the phenomena of slow novae and symbiotic stars, and such models are discussed in the concluding section.

A DISCUSSION ON THE CLASSIFICATION AND EVOLUTION OF SYMBIOTIC STARS

NARCIS (Netherlands)

SEAL, P

1990-01-01

A H-R diagram is drawn from the bolometric luminosities and effective temperatures of 24 symbiotic stars and compared with theoretical evolutionary tracks of Population I metal-rich stars. It is shown that the S-type and D-type symbiotic stars are classified very clearly in course of their evolution

SEARCHING FOR NEW YELLOW SYMBIOTIC STARS: POSITIVE IDENTIFICATION OF StHα63

Energy Technology Data Exchange (ETDEWEB)

Baella, N. O. [Unidad de Astronomía, Instituto Geofísico del Perú, Lima, Per (Peru); Pereira, C. B.; Alvarez-Candal, A. [Observatório Nacional/MCTI, Rua Gen. José Cristino, 77, 20921-400, Rio de Janeiro (Brazil); Miranda, L. F., E-mail: nobar.baella@gmail.com, E-mail: claudio@on.br, E-mail: alvarez@on.br, E-mail: lfm@iaa.es [Instituto de Astrofísica de Andalucía- CSIC, C/Glorieta de la Astronomía s/n, E-18008 Granada (Spain)

2016-04-15

Yellow symbiotic stars are useful targets for probing whether mass transfer has happened in their binary systems. However, the number of known yellow symbiotic stars is very scarce. We report spectroscopic observations of five candidate yellow symbiotic stars that were selected by their positions in the 2MASS (J − H) versus (H − K{sub s}) diagram and which were included in some emission-line catalogs. Among the five candidates, only StHα63 is identified as a new yellow symbiotic star because of its spectrum and its position in the [TiO]{sub 1}–[TiO]{sub 2} diagram, which indicates a K4–K6 spectral type. In addition, the derived electron density (∼10{sup 8.4} cm{sup −3}) and several emission-line intensity ratios provide further support for that classification. The other four candidates are rejected as symbiotic stars because three of them actually do not show emission lines and the fourth one only Balmer emission lines. We also found that the WISE W3–W4 index clearly separates normal K-giants from yellow symbiotic stars and therefore can be used as an additional tool for selecting candidate yellow symbiotic stars.

Symbiotic star AG Dra

International Nuclear Information System (INIS)

Ipatov, A.P.; Yudin, B.F.; Moskovskij Gosudarstvennyj Univ.

1986-01-01

The results obtained from photometric (in the UBVRJHKLM system) and spectrophotometric (in the range 0.33-0.75 μm) observations of symbiotic star AG Dra are presented. The cool component of this star is a red giant with approximately constant brightness (ΔJ ≤ 0 m .3) classified as K4-K5. This red giant fills it's Roche loble and probably is on the assymptotic giant branch of the HR diagramm. The presence of IR excess in 5 μm associated with radiation of the gaseous envelope with the mass of M≅ 10 -6 M sun have been detected. Observations of AG Dra indicate that growing of the bolometric flux of a hot component is accompanied with decreasing effective temperature. The hot component of the system is probably an accerting red dwarf with the mass M≅ 0.4 M sun and disk accretion of matter of cool star with the rate M >or ∼ 10 -4 M sun year in equatorial region. Increase of accretion rate during the outburst of AG Dra leads to the increase of stellar wind from the red dwarf surface and the decrease of it's effective temperature. The hot component of AG Dra may also be considered as a white Dwarf with luminosity L 3 L sun and R eff >or approx. 0.2 R sun . In this case gravitational energy of accreting matter M > or ∼ 10 -6 M sun / year would be the source of the hot component outbursts. The luminosity between outbursts is determined by energy generation from the burning hydrogen layer source

The Search for Symbiotic Stars in the IPHAS Survey

Directory of Open Access Journals (Sweden)

Corradi R. L. M.

2012-06-01

Full Text Available We have started a project to search for symbiotic stars using the data from IPHAS, the Hα survey of the Northern Galactic plane. Candidates are selected from the IPHAS photometric catalogue based on their colors, combined with the information in the near-infrared from 2MASS. So far, follow-up spectroscopy allowed us to discover 14 new symbiotic stars, compared to the 10 systems previously known in the IPHAS survey area. Their general characteristics and the most notable cases are briefly presented. the spectroscopic campaign also allowed us to refine the selection criteria for symbiotic stars in IPHAS. Perspectives, which include the extension of the survey in the Southern Galactic plane and a portion of the bulge (VPHAS+, are discussed.

Symbiotic binaries

International Nuclear Information System (INIS)

Mikolajewska, J.; Iijima, T.

1988-01-01

The symbiotic star BF Cyg shows periodic variations in its spectrum. [O3] line intensity changes in antiphase with the blue continuum, H-Balmer and He1 emission line intensity. These variations are interpreted in terms of a hot star moving on an eccentric orbit and ionizing a part of an M-type giant wind. 20 refs., 2 figs., 1 tab. (author)

On the late-type components of slow novae and symbiotic stars

International Nuclear Information System (INIS)

Allen, D.A.

1980-01-01

It is argued that the various types of symbiotic stars and the slow novae are the same phenomena exhibiting a range of associated time-scales, the slow novae being of intermediate speed. Evidence is summarized showing that both types of object contain normal M giants or mira variables. This fact is at odds with currently fashionable single-star models for slow novae, according to which the M star is totally disrupted before the outburst. Spectral types of the late-type components are presented for nearly 80 symbiotic stars and slow novae, derived from 2 μm spectroscopy. It is found that both the intensity of the emission spectrum and the electron density of the gas are functions of the spectral type of the late-type star. Explanations for these correlations are given. On the assumption that the late-type components are normal giants, spectroscopic parallaxes are determined; credible distances are derived which indicate that the known symbiotic stars have been sampled as far afield as the Galactic Centre. Hydrogen shell flashes on a white dwarf accreting gas from the late-type components offer an attractive explanation of the phenomena of slow novae and symbiotic stars, and such models are discussed in the concluding section. (author)

Symbiotic star UV emission and theoretical models

International Nuclear Information System (INIS)

Kafatos, M.

1982-01-01

Observations of symbiotic stars in the far UV have provided important information on the nature of these objects. The canonical spectrum of a symbiotic star, e.g. RW Hya, Z And, AG Peg, is dominated by strong allowed and semiforbidden lines of a variety of at least twice ionized elements. Weaker emission from neutral and singly ionized species is also present. A continuum may or may not be present in the 1200 - 2000 A range but is generally present in the range 2000 - 3200 A range. The suspected hot subdwarf continuum is seen in some cases in the range 1200 - 2000 A (RW Hya, AG Peg, SY Mus). The presence of an accretion disk is difficult to demonstrate and to this date the best candidate for accretion to a main sequence star remains CI Cyg. A number of equations have been derived by the author that can yield the accretion parameters from the observable quantities. Boundary layer temperatures approximately 10 5 K and accretion rates approximately > 10 -5 solar masses/yr are required for accreting main sequence companions. To this date, though, most of the symbiotics may only require the presence of a approximately 10 5 K hot subdwarf. (Auth.)

A new carbon-symbiotic star in the Large Magellanic Cloud

International Nuclear Information System (INIS)

Cowley, A.P.; Hartwick, F.D.A.

1989-01-01

A new carbon-symbiotic star, designated as CH-95, was discovered during a study of the kinematics of CH stars in the LMC. The spectrum of CH-95 is presented. Some of the strong emission lines found include H, He I, He II, forbidden O III, and the broad C III/N III blend at 4640 A, often seen in compact systems such as X-ray binaries. A comparison was made with other C-star symbiotics in the LMC, SMC, and Draco. 12 refs

Radio molecular maser line study of symbiotic stars

International Nuclear Information System (INIS)

Cohen, N.L.; Ghigo, F.D.

1980-01-01

A sample of symbiotic stars has been searched for maser emission from the 1665- and 1667-MHz OH mainlines, the 22-GHz H 2 O line, and the 43-GHz SiO line. R Aqr remains the sole symbiotic for which maser emission has been detected. Its SiO spectrum reveals a pedestal of emission with a narrow superposed peak at V/sub LSR/ -26.4 +- 0.7 km/s. The line's existence and the pedestal feature are both characteristic of SiO lines found in late-type variables by Snyder et al. [Astrophys. J. 224, 512 (1978)]. For the other symbiotic stars, it is possible that conditions favorable for maser emission have been suppressed by the presence of a hot companion. Alternatively our findings may argue against the presence of late-type variables in symbiotic stars. In either case, R Aqr seems to be in a class by itself. We cannot confirm the suggestion that R Aqr is a binary, since the spectral feature has not shifted noticeably in the two years since the observations by Lepine, LeSqueren, and Scalise [Astrophys. J. 225, 869 (1978)]. However, we point out that monitoring the pedestal emission over a number of years is the least ambiguous way to discern any velocity shift that might result from orbital motion

Three-dimensional hydrodynamical models of wind and outburst-related accretion in symbiotic systems

Science.gov (United States)

de Val-Borro, M.; Karovska, M.; Sasselov, D. D.; Stone, J. M.

2017-07-01

Gravitationally focused wind accretion in binary systems consisting of an evolved star with a gaseous envelope and a compact accreting companion is a possible mechanism to explain mass transfer in symbiotic binaries. We study the mass accretion around the secondary caused by the strong wind from the primary late-type component using global three-dimensional hydrodynamic numerical simulations during quiescence and outburst stages. In particular, the dependence of the mass accretion rate on the mass-loss rate, wind parameters and phases of wind outburst development is considered. For a typical wind from an asymptotic giant branch star with a mass-loss rate of 10-6 M⊙ yr-1 and wind speeds of 20-50 km s-1, the mass transfer through a focused wind results in efficient infall on to the secondary. Accretion rates on to the secondary of 5-20 per cent of the mass-loss from the primary are obtained during quiescence and outburst periods where the wind velocity and mass-loss rates are varied, about 20-50 per cent larger than in the standard Bondi-Hoyle-Lyttleton approximation. This mechanism could be an important method for explaining observed accretion luminosities and periodic modulations in the accretion rates for a broad range of interacting binary systems.

Formation of broad Balmer wings in symbiotic stars

International Nuclear Information System (INIS)

Chang, Seok-Jun; Heo, Jeong-Eun; Hong, Chae-Lin; Lee, Hee-Won

2016-01-01

Symbiotic stars are binary systems composed of a hot white dwarf and a mass losing giant. In addition to many prominent emission lines symbiotic stars exhibit Raman scattered O VI features at 6825 and 7088 Å. Another notable feature present in the spectra of many symbiotics is the broad wings around Balmer lines. Astrophysical mechanisms that can produce broad wings include Thomson scattering by free electrons and Raman scattering of Ly,β and higher series by neutral hydrogen. In this poster presentation we produce broad wings around Hα and H,β adopting a Monte Carlo techinique in order to make a quantitative comparison of these two mechanisms. Thomson wings are characterized by the exponential cutoff given by the termal width whereas the Raman wings are dependent on the column density and continuum shape in the far UV region. A brief discussion is provided. (paper)

Ultraviolet properties of the symbiotic stars

International Nuclear Information System (INIS)

Slovak, M.H.; Lambert, D.L.

1982-01-01

This article is an interim report on a survey of the symbiotic stars with the IUE satellite, both at low resolution and, for AG Pegasi and CH Cygni, at high resolution. The UV spectra, including both the emission lines and the continua, are presented and discussed. Since it is somewhat premature to draw general conclusions, the emphasis is biased towards a discussion of individual stars. AG Pegasi is used as an illustrative, albeit atypical, example. (Auth./C.F.)

SIMULTANEOUS OBSERVATIONS OF SiO AND H2O MASERS TOWARD SYMBIOTIC STARS

International Nuclear Information System (INIS)

Cho, Se-Hyung; Kim, Jaeheon

2010-01-01

We present the results of simultaneous observations of SiO v = 1, 2, J = 1-0, 29 SiO v = 0, J = 1-0, and H 2 O 6 16 -5 23 maser lines performed with the KVN Yonsei 21 m radio telescope from 2009 November to 2010 January. We searched for these masers in 47 symbiotic stars and detected maser emission from 21 stars, giving the first time detection from 19 stars. Both SiO and H 2 O masers were detected from seven stars of which six were D-type symbiotic stars and one was an S-type star, WRAY 15-1470. In the SiO maser emission, the 28 SiO v = 1 maser was detected from 10 stars, while the v = 2 maser was detected from 15 stars. In particular, the 28 SiO v = 2 maser emission without the v = 1 maser detection was detected from nine stars with a detection rate of 60%, which is much higher than that of isolated Miras/red giants. The 29 SiO v = 0 maser emission was also detected from two stars, H 2-38 and BF Cyg, together with the 28 SiO v = 2 maser. We conclude that these different observational results between isolated Miras/red giants and symbiotic stars may be related with the presence of hot companions in a symbiotic binary system.

Far-infrared data for symbiotic stars. II. The IRAS survey observations

International Nuclear Information System (INIS)

Kenyon, S.J.; Fernandez-Castro, T.; Stencel, R.E.

1988-01-01

IRAS survey data for all known symbiotic binaries are reported. S type systems have 25 micron excesses much larger than those of single red giant stars, suggesting that these objects lose mass more rapidly than do normal giants. D type objects have far-IR colors similar to those of Mira variables, implying mass-loss rate of about 10 to the -6th solar masses/yr. The near-IR extinctions of the D types indicate that their Mira components are enshrouded in optically thick dust shells, while their hot companions lie outside the shells. If this interpretation of the data is correct, then the very red near-IR colors of D type symbiotic stars are caused by extreme amounts of dust absorption rather than dust emission. The small group of D prime objects possesses far-IR colors resembling those of compact planetary nebulae or extreme OH/IR stars. It is speculated that these binaries are not symbiotic stars at all, but contain a hot compact star and an exasymptotic branch giant which is in the process of ejecting a planetary nebula shell. 42 references

Spectroscopic observations of the symbiotic star AG Draconis

Energy Technology Data Exchange (ETDEWEB)

Smith, S E; Bopp, B W [Toledo Univ., OH (USA)

1981-06-01

Spectroscopic observations, covering the lambdalambda 3500-7000 region, of the symbiotic star AG Draconis are reported. The Balmer and He I line profiles were found to show pronounced blueward asymmetries. Changes in the line profiles of the Balmer lines were observed, and found to be well correlated with the 554-day photometric period of Meinunger, with a second, blueward component being visible in the Balmer emissions at photometric minimum. The weak, blueshifted component in the Balmer emission lines is explained in terms of a stellar wind from the hot secondary at of the order of 60 kms s/sup -1/. The behaviour of the broad emission feature at lambda6380 has been investigated. This feature was found to originate from an ion with an ionization potential in the range 77-101 eV. Various models for AG Dra are discussed.

Physical Structure of Four Symbiotic Binaries

Science.gov (United States)

Kenyon, Scott J. (Principal Investigator)

1997-01-01

Disk accretion powers many astronomical objects, including pre-main sequence stars, interacting binary systems, and active galactic nuclei. Unfortunately, models developed to explain the behavior of disks and their surroundings - boundary layers, jets, and winds - lack much predictive power, because the physical mechanism driving disk evolution - the viscosity - is not understood. Observations of many types of accreting systems are needed to constrain the basic physics of disks and provide input for improved models. Symbiotic stars are an attractive laboratory for studying physical phenomena associated with disk accretion. These long period binaries (P(sub orb) approx. 2-3 yr) contain an evolved red giant star, a hot companion, and an ionized nebula. The secondary star usually is a white dwarf accreting material from the wind of its red giant companion. A good example of this type of symbiotic is BF Cygni: our analysis shows that disk accretion powers the nuclear burning shell of the hot white dwarf and also manages to eject material perpendicular to the orbital plane (Mikolajewska, Kenyon, and Mikolajewski 1989). The hot components in other symbiotic binaries appear powered by tidal overflow from a very evolved red giant companion. We recently completed a study of CI Cygni and demonstrated that the accreting secondary is a solar-type main sequence star, rather than a white dwarf (Kenyon et aL 1991). This project continued our study of symbiotic binary systems. Our general plan was to combine archival ultraviolet and optical spectrophotometry with high quality optical radial velocity observations to determine the variation of line and continuum sources as functions of orbital phase. We were very successful in generating orbital solutions and phasing UV+optical spectra for five systems: AG Dra, V443 Her, RW Hya, AG Peg, and AX Per. Summaries of our main results for these systems appear below. A second goal of our project was to consider general models for the

A search for OH emission from symbiotic stars

International Nuclear Information System (INIS)

Norris, R.P.; Haynes, R.F.; Wright, A.E.

1984-01-01

A search was made for OH maser emission from a sample of 16 symbiotic stars. This sample was selected on the basis of infrared optical depth and variability, so that the stars within it have circumstellar shells similar to those seen in OH/IR and OH/Mira stars. There were no significant detections, except for one unassociated background source, and it is concluded that the presence of a hot binary companion inhibits any possible OH maser action

High resolution infrared spectroscopy of symbiotic stars

International Nuclear Information System (INIS)

Bensammar, S.

1989-01-01

We report here very early results of high resolution (5x10 3 - 4x10 4 ) infrared spectroscopy (1 - 2.5 μm) of different symbiotic stars (T CrB, RW Hya, CI Cyg, PU Vul) observed with the Fourier Transform Spectrometer of the 3.60m Canada France Hawaii Telescope. These stars are usually considered as interacting binaries and only little details are known about the nature of their cool component. CO absorption lines are detected for the four stars. Very different profiles of hydrogen Brackett γ and helium 10830 A lines are shown for CI Cyg observed at different phases, while Pu Vul shows very intense emission lines

Optical flickering of the symbiotic star CH Cyg

Science.gov (United States)

Stoyanov, K. A.; Martí, J.; Zamanov, R.; Dimitrov, V. V.; Kurtenkov, A.; Sánchez-Ayaso, E.; Bujalance-Fernández, I.; Latev, G. Y.; Nikolov, G.

2018-02-01

Here we present quasi-simultaneous observations of the flickering of the symbiotic binary star CH Cyg in U, B and V bands. We calculate the flickering source parameters and discuss the possible reason for the flickering cessation in the period 2010-2013.

Detection of new southern SiO maser sources associated with Mira and symbiotic stars

International Nuclear Information System (INIS)

Allen, D.A.; Hall, P.J.; Norris, R.P.; Troup, E.R.; Wark, R.M.; Wright, A.E.

1989-01-01

In 1987 July the Parkes radio telescope was used to search for 43.12 GHz SiO maser emission from southern late-type stars. We report the discovery of such emission from 12 Mira-like systems, including the symbiotic star H1-36, and discuss the implications of our data for the symbiotic stars. We identify several M-type Mira variables with unusually low SiO/infrared flux ratios, but with present data are not able to discredit the correlation between the two parameters. In addition, we present line profiles for the only other known symbiotic maser, R Aqr, at unprecedented signal-to-noise ratio; these profiles show linearly polarized emission from several components of the source. (author)

Rotation of the Mass Donors in High-mass X-ray Binaries and Symbiotic Stars

Directory of Open Access Journals (Sweden)

K. Stoyanov

2015-02-01

Full Text Available Our aim is to investigate the tidal interaction in High-mass X-ray Binaries and Symbiotic stars in order to determine in which objects the rotation of the mass donors is synchronized or pseudosynchronized with the orbital motion of the compact companion. We find that the Be/X-ray binaries are not synchronized and the orbital periods of the systems are greater than the rotational periods of the mass donors. The giant and supergiant High-mass X-ray binaries and symbiotic stars are close to synchronization. We compare the rotation of mass donors in symbiotics with the projected rotational velocities of field giants and find that the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. We find that the projected rotational velocity of the red giant in symbiotic star MWC 560 is v sin i= 8.2±1.5 km.s−1, and estimate its rotational period to be Prot<>/sub = 144 - 306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e = 0.68 − 0.82.

St 2-22 - Another Symbiotic Star with High-Velocity Bipolar Jets

Science.gov (United States)

Tomov, T.; Zamanov, R.; Gałan, C.; Pietrukowicz, P.

2017-09-01

We report the detection of high-velocity components in the wings of Hα emission line in spectra of symbiotic binary star St 2-22 obtained in 2005. This finding encouraged us to start the present investigation in order to show that this poorly-studied object is a jet-producing system. We have used high-resolution optical and low-resolution near-infrared spectra, as well as available optical and infrared photometry, to evaluate some physical parameters of the St 2-22 components and characteristics of the jets. We confirm that St 2-22 is a S-type symbiotic star. Our results demonstrate that an unnoticed outburst, similar to those in classical symbiotic systems, occurred in the first half of 2005. During the outburst, collimated bipolar jets were ejected by the hot component of St 2-22 with an average velocity of about 1700 km/s.

Su Lyncis, a Hard X-Ray Bright M Giant: Clues Point to a Large Hidden Population of Symbiotic Stars

Science.gov (United States)

Mukai, K.; Luna, G. J. M.; Cusumano, G.; Segreto, A.; Munari, U.; Sokoloski, J. L.; Lucy, A. B.; Nelson, T.; Nunez, N. E.

2016-01-01

Symbiotic star surveys have traditionally relied almost exclusively on low resolution optical spectroscopy. However, we can obtain a more reliable estimate of their total Galactic population by using all available signatures of the symbiotic phenomenon. Here we report the discovery of a hard X-ray source, 4PBC J0642.9+5528, in the Swift hard X-ray all-sky survey, and identify it with a poorly studied red giant, SU Lyn, using pointed Swift observations and ground-based optical spectroscopy. The X-ray spectrum, the optical to UV spectrum, and the rapid UV variability of SU Lyn are all consistent with our interpretation that it is a symbiotic star containing an accreting white dwarf. The symbiotic nature of SU Lyn went unnoticed until now, because it does not exhibit emission lines strong enough to be obvious in low resolution spectra. We argue that symbiotic stars without shell-burning have weak emission lines, and that the current lists of symbiotic stars are biased in favor of shell-burning systems. We conclude that the true population of symbiotic stars has been underestimated, potentially by a large factor.

Spectroscopic confirmation of the first symbiotic star in a globular cluster

Science.gov (United States)

Zurek, David

2013-10-01

We have recently discovered an 18-minute period in the ultraviolet of a star in the globular cluster NGC 1851. In the redder optical bands, this star is red and bright, while it shows a clear UV excess relative to other stars at similar positions in the HR diagram. The system is most likely a symbiotic binary, composed of a cool evolved star and a white dwarf, with an 18 minute spin period, accreting the cool star's wind. The binary would be the first such object ever found in a globular cluster, and only the third in the Galaxy where the white dwarf spin period is measured. The only viable alternatives are that the two components are a chance superposition - something with a nontrivial chance of happening in a globular cluster core. In such a case, the 18 minute period would most likely be the spin period of a magnetic white dwarf in an intermediate polar cataclysmic variable {this would be the first confirmed magnetic CV in a globular cluster}, or the orbital period of a double-degenerate AM CVn binary. Each of these three possibilities show unique {and very different} emission line spectra in the blue wavelength range. Two orbits of HST with STIS/G430L will produce a spectrum of sufficient signal-to-noise to distinguish between these 3 scenarios. The result will be an important constraint on N-body models of globular clusters.

IUE observations of the symbiotic star CH Cygni during an active phase

Energy Technology Data Exchange (ETDEWEB)

Hack, M [Astronomical Observatory, Trieste (Italy)

1979-05-24

The observations of CH Cygni reported here were made to determine whether a symbiotic star is a binary system composed of an M6 giant and a hot subdwarf, or whether it is a cooled star surrounded by a thick corona.

Photographic infrared spectra of symbiotic stars

International Nuclear Information System (INIS)

Andrillat, Y.; Houziaux, L.

1982-01-01

The authors have observed six symbiotic stars during the period 1962-1977 with a grating spectrograph attached to the newtonian focus of the 120-cm telescope at Observatoire de Haute Provence. The reciprocal dispersion is 230 A.mm -1 and the region 5800 to 8800 A has been covered using hypersensitized IN plates. The minimum equivalent width for an emission line to be seen is about 0.5 A. The spectra are displayed and the main spectral characteristics are reviewed briefly. (Auth.)

Infrared spectroscopy of symbiotic stars and the nature of their cool components

International Nuclear Information System (INIS)

Kenyon, S.J.; Gallagher, J.S.

1983-01-01

We present low-resolution 2--4 μm spectroscopy of a small sample of symbiotic stars, in an effort to determine if the giant components of these systems fill their Roche Lobes. A [2.35]-[2.2] color index measures the strength of the CO absorption band and provides a useful discriminant of luminosity class among single M-type giants which separates normal giants from supergiants at the same spectral type. Although interpretation of symbiotic spectra is complicated somewhat by their binary nature, our results suggest the late-type components in these systems range from normal red giants to bright asymptotic giants. The possible presence of non-Roche Lobe filling, low-luminosity giants in some symbiotic stars cannot be understood within the framework of existing theories for these interesting objects, and thus may provide important information for understanding mass transfer in binary systems

SYMBIOTIC STAR BLOWS BUBBLES INTO SPACE

Science.gov (United States)

2002-01-01

A tempestuous relationship between an unlikely pair of stars may have created an oddly shaped, gaseous nebula that resembles an hourglass nestled within an hourglass. Images taken with Earth-based telescopes have shown the larger, hourglass-shaped nebula. But this picture, taken with NASA's Hubble Space Telescope, reveals a small, bright nebula embedded in the center of the larger one (close-up of nebula in inset). Astronomers have dubbed the entire nebula the 'Southern Crab Nebula' (He2-104), because, from ground-based telescopes, it looks like the body and legs of a crab. The nebula is several light-years long. The possible creators of these shapes cannot be seen at all in this Wide Field and Planetary Camera 2 image. It's a pair of aging stars buried in the glow of the tiny, central nebula. One of them is a red giant, a bloated star that is exhausting its nuclear fuel and is shedding its outer layers in a powerful stellar wind. Its companion is a hot, white dwarf, a stellar zombie of a burned-out star. This odd duo of a red giant and a white dwarf is called a symbiotic system. The red giant is also a Mira Variable, a pulsating red giant, that is far away from its partner. It could take as much as 100 years for the two to orbit around each other. Astronomers speculate that the interaction between these two stars may have sparked episodic outbursts of material, creating the gaseous bubbles that form the nebula. They interact by playing a celestial game of 'catch': as the red giant throws off its bulk in a powerful stellar wind, the white dwarf catches some of it. As a result, an accretion disk of material forms around the white dwarf and spirals onto its hot surface. Gas continues to build up on the surface until it sparks an eruption, blowing material into space. This explosive event may have happened twice in the 'Southern Crab.' Astronomers speculate that the hourglass-shaped nebulae represent two separate outbursts that occurred several thousand years apart

IUE observations of the symbiotic star CH Cygni during an active phase

International Nuclear Information System (INIS)

Hack, M.

1979-01-01

The observations of CH Cygni reported here were made to determine whether a symbiotic star is a binary system composed of an M6 giant and a hot subdwarf, or whether it is a cooled star surrounded by a thick corona. (author)

PC 11: Symbiotic star or planetary nebulae?

International Nuclear Information System (INIS)

Gutierrez-Moreno, A.; Moreno, H.; Cortes, G.

1987-01-01

PC 11 is an object listed in Perek and Kohoutek (1967) Catalogue of Galactic Planetary Nebulae as PK 331 -5 0 1. Some authors suggest that it is not a planetary nebula, but that it has some characteristics (though not all) of symbiotic stars. We have made photographic, spectrophotometric and spectroscopic observations of PC 11. The analysis of the results suggests that it is a young planetary nebula. (Author)

THREE FUNDAMENTAL PERIODS IN AN 87 YEAR LIGHT CURVE OF THE SYMBIOTIC STAR MWC 560

Energy Technology Data Exchange (ETDEWEB)

Leibowitz, Elia M.; Formiggini, Liliana, E-mail: elia@astro.tau.ac.il [The Wise Observatory and the School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)

2015-08-15

We construct a visual light curve of the symbiotic star MWC covering the last 87 years of its history. The data were assembled from the literature and from the AAVSO data bank. Most of the periodic components of the system brightness variation can be accounted for by the operation of three basic clocks of the periods P1 = 19,000 days, P2 = 1943 days, and P3 = 722 days. These periods can plausibly, and consistently with the observations, be attributed to three physical mechanisms in the system: the working of a solar-like magnetic dynamo cycle in the outer layers of the giant star of the system, the binary orbit cycle, and the sidereal rotation cycle of the giant star. MWC 560 is the seventh symbiotic star with historical light curves that reveal similar basic characteristics of the systems. The light curves of all these stars are well interpreted on the basis of the current understanding of the physical processes that are the major sources of the optical luminosity of these symbiotic systems.

THREE FUNDAMENTAL PERIODS IN AN 87 YEAR LIGHT CURVE OF THE SYMBIOTIC STAR MWC 560

International Nuclear Information System (INIS)

Leibowitz, Elia M.; Formiggini, Liliana

2015-01-01

We construct a visual light curve of the symbiotic star MWC covering the last 87 years of its history. The data were assembled from the literature and from the AAVSO data bank. Most of the periodic components of the system brightness variation can be accounted for by the operation of three basic clocks of the periods P1 = 19,000 days, P2 = 1943 days, and P3 = 722 days. These periods can plausibly, and consistently with the observations, be attributed to three physical mechanisms in the system: the working of a solar-like magnetic dynamo cycle in the outer layers of the giant star of the system, the binary orbit cycle, and the sidereal rotation cycle of the giant star. MWC 560 is the seventh symbiotic star with historical light curves that reveal similar basic characteristics of the systems. The light curves of all these stars are well interpreted on the basis of the current understanding of the physical processes that are the major sources of the optical luminosity of these symbiotic systems

Unidentified bands lambda lambda 6830, 7088 in symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Allen, D A [Anglo-Australian Observatory, Epping (Australia)

1980-01-01

About 60 stars are known which show broad emission bands centred at wavelengths of 6830 and 7088 A. The stars are all classified as symbiotic, since they combine high-excitation emission and M-type absorption spectra. From the behaviour of the bands in the evolution of slow novae as they approach the symbiotic phase, and from the occurrence of the bands in stars of different excitation, it is concluded that the ions responsible have ionization potentials near 100 eV. The similarity of behaviour and profile of the two suggests that both arise in the same species. No suitable identification appears possible at this time, because of the lack of data on highly ionized species. Arguments are presented which narrow the range of possibilities, the most notable argument being the absence of O VI emission. It is suggested that Fe VII or Fe VI may be responsible. In particular, it is recommended that transitions from the z/sup 3/P/sup 0/ and z/sup 1/F/sup 0/ levels of Fe VII be examined in detail. The differing, and time-varying profiles of the 6830 and 7088 bands in the stars observed are best explained in terms of velocity broadening. Velocities in excess of 1000 km s/sup -1/ are present. Rotation is a more credible form of the mass motion than expansion, because of the tendency to double profiles in these bands. If rotation is responsible, these velocities imply that the objects central to the emission nebulae are more compact than main sequence stars.

Symbiotic Novae

OpenAIRE

Mikolajewska, Joanna

2010-01-01

The symbiotic novae are thermonuclear novae in symbiotic binary systems -- interacting binaries with evolved red giant donors, and the longest orbital periods. This paper aims at presenting physical characteristics of these objects and discussing their place among the whole family of symbiotic stars.

Observations of the symbiotic star AS 296

International Nuclear Information System (INIS)

Gutierrez-Moreno, A.; Moreno, H.

1990-01-01

Observations of the symbiotic star AS 296 are presented. The spectra, obtained during the quiescent phase, are typical of this kind of object. They show strong molecular bands and some forbidden emission lines, including faint forbidden Fe VII and Ca V lines. Measured intensities of the emission lines are given. Some of the physical parameters of the object are derived. Recently this object has been observed in outburst by Heathcote (1988); a copy of one such spectrum is presented with a brief qualitative description of its main features. 28 refs

The X-Ray Evolution of the Symbiotic Star V407 Cygni During Its 2010 Outburst

Science.gov (United States)

Mukai, K.; Nelson, T.; Chomiuk, L.; Donato, D.; Sokoloski, J.

2011-01-01

We present a summary of Swift and Suzaku X-ray observations of the 2010 nova outburst of the symbiotic star, V407 Cyg. The Suzaku spectrum obtained on day 30 indicates the presence of the supersoft component from the white dwarf surface, as well as optically thin component from the shock between the nova ejecta and the Mira wind. The Swift observations then allow us to track the evolution of both components from day 4 to day 150. Most notable is the sudden brightening of the optically think component around day 20. We identify this as the time when the blast wave reached the immediate vicinity of the photosphere of the Mira. We have developed a simplified model of the blast wave-wind interaction that can reproduce the gross features of the X-ray evolution of V407 Cyg. If the model is correct, the binary separation is likely to be large and the mass loss rate of the Mira is likely to be relatively low.

HM Sagittae - a most remarkable star

International Nuclear Information System (INIS)

Kwok, S.

1982-01-01

The author summarises recent observations of HM Sagittae, a symbiotic star that displays activity in every spectral band from X-ray to radio. He concludes that it is best described as a binary system consisting of a late M giant and a hot compact object which is similar to central stars of planetary nebulae. The presence of a wind from the M giant implies that Roche-lobe overflow is not a necessary condition for mass transfer. The complex structure of the circumstellar nebula is possibly the result of wind interactions. The ongoing spectral evolution of HM Sge after its recent outburst makes it an ideal candidate to test models of the symbiotic phenomenon. (Auth.)

High-resolution Optical Spectroscopic Observations of Four Symbiotic Stars: AS 255, MWC 960, RW Hya, and StH α 32

Energy Technology Data Exchange (ETDEWEB)

Pereira, C. B.; Drake, N. A.; Roig, F. [Observatório Nacional/MCTIC, Rua Gen. José Cristino 77, Rio de Janeiro, 20921-400 (Brazil); Baella, N. O. [Unidad de Astronomía, Instituto Geofísico del Perú, Lima, Per (Peru); Miranda, L. F., E-mail: claudio@on.br, E-mail: drake@on.br, E-mail: froig@on.br, E-mail: nobar.baella@gmail.com, E-mail: lfm@iaa.es [Instituto de Astrofísica de Andalucía - CSIC, C/Glorieta de la Astronomía s/n, E-18008 Granada (Spain)

2017-05-20

We report on the analysis of high-resolution optical spectra of four symbiotic stars: AS 255, MWC 960, RW Hya, and StH α 32. We employ the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code moog to analyze the spectra. The abundance of barium and carbon was derived using the spectral synthesis technique. The chemical composition of the atmospheres of AS 255 and MWC 960 show that they are metal-poor K giants with metallicities of −1.2 and −1.7 respectively. StH α 32 is a CH star and also a low-metallicity object (−1.4). AS 255 and MWC 960 are yellow symbiotic stars and, like other previously studied yellow symbiotics, are s -process enriched. StH α 32, like other CH stars, is also an s -process and carbon-enriched object. RW Hya has a metallicity of −0.64, a value in accordance with previous determinations, and is not s -process enriched. Based on its position in the 2MASS diagram, we suggest that RW Hya is at an intermediate position between yellow symbiotics and classical S-type symbiotics. We also discuss whether the dilution effect was the mechanism responsible for the absence of the s -process elements overabundance in RW Hya. The luminosity obtained for StH α 32 is below the luminosity of the asymptotic giant branch (AGB) stars that started helium burning (via thermal pulses) and became self-enriched in neutron-capture elements. Therefore, its abundance peculiarities are due to mass transfer from the previous thermally pulsing AGB star (now the white dwarf) that was overabundant in s -process elements. For the stars AS 255 and MWC 960, the determination of their luminosities was not possible due to uncertainties in their distance and interstellar absorption. AS 255 and MWC 960 have a low galactic latitude and could be bulge stars or members of the inner halo population. The heavy-element abundance distribution of AS 255 and MWC 960 is similar to that of the other yellow symbiotics previously analyzed. Their

High-resolution Optical Spectroscopic Observations of Four Symbiotic Stars: AS 255, MWC 960, RW Hya, and StH α 32

International Nuclear Information System (INIS)

Pereira, C. B.; Drake, N. A.; Roig, F.; Baella, N. O.; Miranda, L. F.

2017-01-01

We report on the analysis of high-resolution optical spectra of four symbiotic stars: AS 255, MWC 960, RW Hya, and StH α 32. We employ the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code moog to analyze the spectra. The abundance of barium and carbon was derived using the spectral synthesis technique. The chemical composition of the atmospheres of AS 255 and MWC 960 show that they are metal-poor K giants with metallicities of −1.2 and −1.7 respectively. StH α 32 is a CH star and also a low-metallicity object (−1.4). AS 255 and MWC 960 are yellow symbiotic stars and, like other previously studied yellow symbiotics, are s -process enriched. StH α 32, like other CH stars, is also an s -process and carbon-enriched object. RW Hya has a metallicity of −0.64, a value in accordance with previous determinations, and is not s -process enriched. Based on its position in the 2MASS diagram, we suggest that RW Hya is at an intermediate position between yellow symbiotics and classical S-type symbiotics. We also discuss whether the dilution effect was the mechanism responsible for the absence of the s -process elements overabundance in RW Hya. The luminosity obtained for StH α 32 is below the luminosity of the asymptotic giant branch (AGB) stars that started helium burning (via thermal pulses) and became self-enriched in neutron-capture elements. Therefore, its abundance peculiarities are due to mass transfer from the previous thermally pulsing AGB star (now the white dwarf) that was overabundant in s -process elements. For the stars AS 255 and MWC 960, the determination of their luminosities was not possible due to uncertainties in their distance and interstellar absorption. AS 255 and MWC 960 have a low galactic latitude and could be bulge stars or members of the inner halo population. The heavy-element abundance distribution of AS 255 and MWC 960 is similar to that of the other yellow symbiotics previously analyzed. Their

INFRARED SPECTROSCOPY OF SYMBIOTIC STARS. VII. BINARY ORBIT AND LONG SECONDARY PERIOD VARIABILITY OF CH CYGNI

International Nuclear Information System (INIS)

Hinkle, Kenneth H.; Joyce, Richard R.; Fekel, Francis C.

2009-01-01

High-dispersion spectroscopic observations are used to refine orbital elements for the symbiotic binary CH Cyg. The current radial velocities, added to a previously published 13 year time series of infrared velocities for the M giant in the CH Cyg symbiotic system, more than double the length of the time series to 29 years. The two previously identified velocity periods are confirmed. The long period, revised to 15.6 ± 0.1 yr, is shown to result from a binary orbit with a 0.7 M sun white dwarf and 2 M sun M giant. Mass transfer to the white dwarf is responsible for the symbiotic classification. CH Cyg is the longest period S-type symbiotic known. Similarities with the longer period D-type systems are noted. The 2.1 year period is shown to be on Wood's sequence D, which contains stars identified as having long secondary periods (LSP). The cause of the LSP variation in CH Cyg and other stars is unknown. From our review of possible causes, we identify g-mode nonradial pulsation as the leading mechanism for LSP variation in CH Cyg. If g-mode pulsation is the cause of the LSPs, a radiative region is required near the photosphere of pulsating asymptotic giant branch stars.

DETECTION OF X-RAYS FROM THE SYMBIOTIC STAR V1329 Cyg

International Nuclear Information System (INIS)

Stute, Matthias; Luna, Gerardo J. M.; Sokoloski, Jennifer L.

2011-01-01

We report the detection of X-ray emission from the symbiotic star V1329 Cyg with XMM-Newton. The spectrum from the EPIC pn, MOS1, and MOS2 instruments consists of a two-temperature plasma with k T 1 = 0.11 +0.02 -0.02 keV and k T 2 = 0.93 +0.12 -0.14 keV. Unlike the vast majority of symbiotic stars detected in X-rays, the soft component of the spectrum seems to be absorbed only by interstellar material. The shock velocities corresponding to the observed temperatures are about 300 km s -1 and about 900 km s -1 . We did not find either periodic or aperiodic X-ray variability, with upper limits on the amplitudes of such variations being 46% and 16% (rms), respectively. We also did not find any ultraviolet variability with an rms amplitude of more than approximately 1%. The derived velocities and the unabsorbed nature of the soft component of the X-ray spectrum suggest that some portion of the high energy emission could originate in shocks within a jet and beyond the symbiotic nebula. The lower velocity is consistent with the expansion velocity of the extended structure present in Hubble Space Telescope observations. The higher velocity could be associated with an internal shock at the base of the jet or with shocks in the accretion region.

SYMBIOTIC STARS IN X-RAYS. III. SUZAKU OBSERVATIONS

Energy Technology Data Exchange (ETDEWEB)

Nuñez, N. E. [Instituto de Ciencias Astronómicas de la Tierra y del Espacio (ICATE-UNSJ, CONICET), Av. España (S) 1512, J5402DSP, San Juan (Argentina); Nelson, T. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN, 55455 (United States); Mukai, K. [CRESST and X-ray Astrophysics Laboratory, (NASA/GSFC), Greenbelt, MD 20 771, USA. (United States); Sokoloski, J. L. [Columbia Astrophysics Lab, 550 W120th St., 1027 Pupin Hall, MC 5247 Columbia University, 10027, New York (United States); Luna, G. J. M., E-mail: nnunez@icate-conicet.gov.ar [Instituto de Astronomía y Física del Espacio (IAFE, CONICET-UBA), Av. Inte. Güiraldes 2620, C1428ZAA, Buenos Aires (Argentina)

2016-06-10

We describe the X-ray emission as observed by Suzaku from five symbiotic stars that we selected for deep Suzaku observations after their initial detection with ROSAT, ASCA , and Swift . We find that the X-ray spectra of all five sources can be adequately fit with absorbed optically thin thermal plasma models, with either single- or multi-temperature plasmas. These models are compatible with the X-ray emission originating in the boundary layer between an accretion disk and a white dwarf. The high plasma temperatures of kT > 3 keV for all five targets were greater than expected for colliding winds. Based on these high temperatures as well as previous measurements of UV variability and UV luminosity and the large amplitude of X-ray flickering in 4 Dra, we conclude that all five sources are accretion-powered through predominantly optically thick boundary layers. Our X-ray data allow us to observe a small optically thin portion of the emission from these boundary layers. Given the time between previous observations and these observations, we find that the intrinsic X-ray flux and the intervening absorbing column can vary by factors of three or more on a timescale of years. However, the location of the absorber and the relationship between changes in accretion rate and absorption are still elusive.

SYMBIOTIC STARS IN X-RAYS. III. SUZAKU OBSERVATIONS

International Nuclear Information System (INIS)

Nuñez, N. E.; Nelson, T.; Mukai, K.; Sokoloski, J. L.; Luna, G. J. M.

2016-01-01

We describe the X-ray emission as observed by Suzaku from five symbiotic stars that we selected for deep Suzaku observations after their initial detection with ROSAT, ASCA , and Swift . We find that the X-ray spectra of all five sources can be adequately fit with absorbed optically thin thermal plasma models, with either single- or multi-temperature plasmas. These models are compatible with the X-ray emission originating in the boundary layer between an accretion disk and a white dwarf. The high plasma temperatures of kT > 3 keV for all five targets were greater than expected for colliding winds. Based on these high temperatures as well as previous measurements of UV variability and UV luminosity and the large amplitude of X-ray flickering in 4 Dra, we conclude that all five sources are accretion-powered through predominantly optically thick boundary layers. Our X-ray data allow us to observe a small optically thin portion of the emission from these boundary layers. Given the time between previous observations and these observations, we find that the intrinsic X-ray flux and the intervening absorbing column can vary by factors of three or more on a timescale of years. However, the location of the absorber and the relationship between changes in accretion rate and absorption are still elusive.

The X-Ray Evolution of the Symbiotic Star V407 Cyg During its 2010 Outburst

Directory of Open Access Journals (Sweden)

Mukai K.

2012-06-01

Full Text Available We present a summary of Swift and Suzaku X-ray observations of the 2010 nova outburst of the symbiotic star, V407 Cyg. the Suzaku spectrum obtained on day 30 indicates the presence of the supersoft component from the white dwarf surface, as well as optically thin component from the shock between the nova ejecta and the Mira wind. the Swift observations then allow us to track the evolution of both components from day 4 to day 150. Most notable is the sudden brightening of the optically thin component around day 20. We identify this as the time when the blast wave reached the immediate vicinity of the photosphere of the Mira. We have developed a simpe model of the blast wave - wind interaction that can reproduce the gross features of the X-ray evolution of V407 Cyg. If the model is correct, the binary separation is likely to be larger than previously suggested and the mass-loss rate of the Mira is likely to be relatively low.

NuSTAR Observation of the Symbiotic System GX 1+4

Science.gov (United States)

Wolff, Michael Thomas; Becker, Peter A.; Enoto, Teruaki; Pottschmidt, Katja; Wood, Kent

2017-08-01

We report on a NuSTAR observation of the symbiotic binary system GX 1+4. GX 1+4 is one of a small number of systems with a red giant mass donor and a magnetic neutron star in orbit around each other. The accreting pulsar in GX 1+4 has a spin period of ~150 seconds with epochs of both spin-up and spin-down. The orbital period that has not been determined. Magnetic accretion theory in such systems suggests that the neutron star has a magnetic field in the range 1013-1014 Gauss although this is not settled because no cyclotron absorption feature has been observed in the X-ray spectrum. The NuSTAR spectrum shows broad Fe-line emission near ~6.5 keV and also shows a broad power law shape detected up to ~60 keV. We analyze and discuss the NuSTAR X-ray data with particular attention to the question of what can the spectrum tell us about the structure of the accretion flow onto the neutron star and the magnetic field strength.

Symbiotic stars: spectrophotometry at 3-4 and 8-13 μm

International Nuclear Information System (INIS)

Roche, P.F.; Aitken, D.K.

1983-01-01

Infrared spectrophotometry of 20 symbiotic stars, mostly of dust-rich variety, is presented. HDE 330036 is unique in showing an emission feature at 11.3 μm. The remainder combine a hot grey component and/or optically thin silicate emission. A model in which the grey component is due to optically thick silicate dust is not consistent with the spectra. It is proposed instead that iron-based grains, expected to form in the ejecta of cool stars, are heated by the ultraviolet radiation field of the hot companion. (author)

Anomalously high intercombination line ratios in symbiotic stars; extreme Bowen pumping?

International Nuclear Information System (INIS)

Kastner, S.O.; Bhatia, A.K.; Feibelman, W.A.

1989-01-01

We assemble International Ultraviolet Explorer observations of the ratio of the O III intercombination lines near 1660 A, showing that the observed ratios in symbiotic stars are significantly higher than the theoretically predicted optically thin limit of 2.5. The presence of an enhancing physical process is thereby indicated. It is suggested that Bowen pumping of the lower level of the 1666.2 A line in an 'external saturation' limit, coupled with appreciable optical depth, could logically explain the high ratios. Some tentative evidence for this is presented and the relevance of far-infrared observations of the O III 51.8 and 88.3 μm lines in symbiotic sources is emphasized. (author)

Investigating mass transfer in symbiotic systems with hydrodynamic simulations

Science.gov (United States)

de Val-Borro, Miguel; Karovska, Margarita; Sasselov, Dimitar D.

2014-06-01

We investigate gravitationally focused wind accretion in binary systems consisting of an evolved star with a gaseous envelope and a compact accreting companion. We study the mass accretion and formation of an accretion disk around the secondary caused by the strong wind from the primary late-type component using global 2D and 3D hydrodynamic numerical simulations. In particular, the dependence on the mass accretion rate on the mass loss rate, wind temperature and orbital parameters of the system is considered. For a typical slow and massive wind from an evolved star the mass transfer through a focused wind results in rapid infall onto the secondary. A stream flow is created between the stars with accretion rates of a 2-10% percent of the mass loss from the primary. This mechanism could be an important method for explaining periodic modulations in the accretion rates for a broad range of interacting binary systems and fueling of a large population of X-ray binary systems. We test the plausibility of these accretion flows indicated by the simulations by comparing with observations of the symbiotic CH Cyg variable system.

Coordinated NuSTAR and Swift observations of SU Lyncis: a hard X-ray bright symbiotic star with weak optical signatures

Science.gov (United States)

Lopes de Oliveira, Raimundo; Mukai, Koji; Luna, Gerardo Juan Manuel; Sokoloski, Jennifer; Nelson, Thomas; Lucy, Adrian B.

2018-01-01

The variable M giant SU Lyncis was recently identified as the optical counterpart of a hard, thermal X-ray source. Also considering the fact that the star displays weak high-excitation emission, it was classified as a symbiotic system purely powered by accretion without accompanying nuclear fusion. This discovery revealed the existence of a subclass of symbiotics which is "invisible" to optical surveys and thus underestimated since these surveys favour the identification of systems with more intense emission lines that arise when shell-burning is present. At the same time, this discovery opens up a new window to investigate accretion and evolution of symbiotic systems. Here we report on the X-ray and UV properties of SU Lyncis derived from simultaneous NuSTAR and Swift observations. The investigation is focused on the strong photometric variability in UV and on the X-ray spectral characterization, which is associated with a hot thermal plasma with sub-solar abundance and suffering the effects of a relatively dense local absorber. The results are discussed in the context of the accretion geometry and mass of the white dwarf, and the imposed limits to the reflection fraction.

Symbiotic star AS 296: optical and infrared photometry in 1982-1983

International Nuclear Information System (INIS)

Taranova, O.G.; Yudin, B.F.

1985-01-01

Photometric UBVRJHK observations of the symbiotic star AS 296 are presented. No light valiations exceeding 0sup(m).2 are found. The cool star is classified as M5III. The color excegss is E(B-V)=sup(m).43+-0sup(m).04. Analysis of the photometric and spectral observations has shown that AS 296 is similar to V1016 Cyg at the moment of low brightness of the hot source. The luminosity of the hot component of AS 296 amounts up to approximately 200 Lsub(Sun) if provided its distance to be 2.2 kpc

A mini atlas of K-band spectra of southern symbiotic stars

Czech Academy of Sciences Publication Activity Database

Marchiano, P.E.; Cidale, L.S.; Arias, M.L.; Borges Fernandes, M.; Kraus, Michaela

2015-01-01

Roč. 57, č. 1 (2015), s. 87-89 E-ISSN 1669-9521 R&D Projects: GA ČR(CZ) GA14-21373S; GA MŠk(CZ) 7AMB14AR017 Institutional support: RVO:67985815 Keywords : binaries * symbiotic * stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics http://www. astronomia argentina.org.ar/b57/2015BAAA...57...87M.pdf

Interacting Winds in Eclipsing Symbiotic Systems - The Case Study of EG Andromedae

Science.gov (United States)

Calabrò, Emanuele

2014-03-01

We report the mathematical representation of the so called eccentric eclipse model, whose numerical solutions can be used to obtain the physical parameters of a quiescent eclipsing symbiotic system. Indeed the nebular region produced by the collision of the stellar winds should be shifted to the orbital axis because of the orbital motion of the system. This mechanism is not negligible, and it led us to modify the classical concept of an eclipse. The orbital elements obtained from spectroscopy and photometry of the symbiotic EG Andromedae were used to test the eccentric eclipse model. Consistent values for the unknown orbital elements of this symbiotic were obtained. The physical parameters are in agreement with those obtained by means of other simulations for this system.

Symbiotic Stars in X-rays. II. Faint Sources Detected with XMM-Newton and Chandra

Science.gov (United States)

Nunez, N. E.; Luna, G. J. M.; Pillitteri, I.; Mukai, K.

2014-01-01

We report the detection from four symbiotic stars that were not known to be X-ray sources. These four object show a ß-type X-ray spectrum, that is, their spectra can be modeled with an absorbed optically thin thermal emission with temperatures of a few million degrees. Photometric series obtained with the Optical Monitor on board XMM-Newton from V2416 Sgr and NSV 25735 support the proposed scenario where the X-ray emission is produced in a shock-heated region inside the symbiotic nebulae.

DO HYDROGEN-DEFICIENT CARBON STARS HAVE WINDS?

International Nuclear Information System (INIS)

Geballe, T. R.; Rao, N. Kameswara; Clayton, Geoffrey C.

2009-01-01

We present high resolution spectra of the five known hydrogen-deficient carbon (HdC) stars in the vicinity of the 10830 A line of neutral helium. In R Coronae Borealis (RCB) stars the He I line is known to be strong and broad, often with a P Cygni profile, and must be formed in the powerful winds of those stars. RCB stars have similar chemical abundances as HdC stars and also share greatly enhanced 18 O abundances with them, indicating a common origin for these two classes of stars, which has been suggested to be white dwarf mergers. A narrow He I absorption line may be present in the hotter HdC stars, but no line is seen in the cooler stars, and no evidence for a wind is found in any of them. The presence of wind lines in the RCB stars is strongly correlated with dust formation episodes so the absence of wind lines in the HdC stars, which do not make dust, is as expected.

Flickering of the symbiotic variable CH Cygni during outburst

Energy Technology Data Exchange (ETDEWEB)

Slovak, M H [Texas Univ., Austin (USA). Dept. of Astronomy; Africano, J

1978-11-01

High-speed and conventional BVRI photometry are reported for the bright symbiotic variable CH Cygni (M6 IIIe), obtained during the course of a recent outburst. Unlike the quiescent symbiotic stars, the presence of flickering similar in nature to that seen in the cataclysmic variables has been confirmed during this active phase. The BVRI photometry for a sample of stars in the field is used to derive the reddening and the distance to CH Cyg. A composite energy distribution is derived from 0.35 to 11.0 ..mu..m which clearly establishes the existence of a variable, blue continuum. The lack of variability in the near infrared suggests that the blue continuum arises from a hot companion. A binary model including a subluminous hot companion accreting material from the stellar wind of an SRa variable is discussed to account for the observed photometric properties.

Infrared spectroscopy of the remnant of Nova Sco 2014: a symbiotic star with too little circumstellar matter to decelerate the ejecta

Science.gov (United States)

Munari, U.; Banerjee, D. P. K.

2018-03-01

Pre-outburst 2MASS and WISE photometry of Nova Sco 2014 (V1534 Sco) has suggested the presence of a cool giant at the location of the nova in the sky. The spectral evolution recorded for the nova did not, however, support a direct partnership because no flash-ionized wind and no deceleration of the ejecta were observed, contrary to the behaviour displayed by other novae which erupted within symbiotic binaries like V407 Cyg or RS Oph. We have therefore obtained 0.8-2.5 μm spectra of the remnant of Nova Sco 2014 in order to ascertain if a cool giant is indeed present and if it is physically associated with the nova. The spectrum shows the presence of a M6III giant, reddened by E(B - V) = 1.20, displaying the typical and narrow emission-line spectrum of a symbiotic star, including He I 1.0830 μm with a deep P-Cyg profile. This makes Nova Sco 2014 a new member of the exclusive club of novae that erupt within a symbiotic binary. Nova Sco 2014 shows that a nova erupting within a symbiotic binary does not always come with a deceleration of the ejecta, contrary to the common belief. Many other similar systems may lay hidden in past novae, especially in those that erupted prior to the release of the 2MASS all-sky infrared survey, which could be profitably cross-matched now against them.

He 2-467 = LT Del - the yellow symbiotic star with a period about 500 days

International Nuclear Information System (INIS)

Arkhipova, V.P.; Noskova, R.I.

1988-01-01

By means of broad and narrow-band photometry in UBV spectral region the variability of the object He 2-467 earlier classified as peculiar cenral star of planetary nebyla has been revealed. The brightness amplitude significantly decreases with the wavelength from 1 m .9 in u-band to 0 m .3 in V. The brightness variations were found to be periodic, with P=488 days. The observations of He2-467 were interpreted using the model of binary consisting of very hot subdwarf and G511-giant. The parameters of both components have been derived. The hot star is probably the evolved low mass nucleus of planetary nebula already dissipated. The periodic variations in U-band may be the result of the reflection effect due to the presence of hot extended region on the side of cold star facing the subdwarf. The subdwarf UV-flux can heat and ionize the upper atmosphere of the giant giving birth to the emission lines and Balmer continuum. The yellow symbiotics to which He 2-467 belong may be predecessors of red symbiotics with M giants

Outbursts in Symbiotic Binaries

Science.gov (United States)

Sonneborn, George (Technical Monitor); Kenyon, Scott J.

2004-01-01

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

A multi-frequency study of symbiotic stars: Pt. 1

International Nuclear Information System (INIS)

Ivison, R.J.; Bode, M.F.; Roberts, J.A.

1991-01-01

The relationship between optical line flux and 5 GHz radio flux is investigated for a sample of 17 northern sky symbiotic stars. Data were obtained near-simultaneously with the Manchester Echelle Spectrograph mounted on the Isaac Newton Telescope, La Palma and the Broad Band Interferometer at Jodrell Bank. Colour excesses, calculated from Balmer hydrogen line fluxes assuming Case B recombination ratios, are compared with other reddening estimates and also combined with extinction maps to provide improved distance estimates. Optical line fluxes are used in combination with radio fluxes to estimate physical parameters of these objects, including mass-loss rates. (author)

Observation of Bowen fluorescence and other phenomena in five symbiotic stars

International Nuclear Information System (INIS)

Wallerstein, G.; Garnavich, P.M.; Schachter, J.; Oke, J.B.

1991-01-01

Wavelength measurements and line identifications in the 3200-3600 A regions are presented for the symbiotic stars AG Dra, HM Sge, V1016 Cyg, V1329 Cyg, Z And, and R Aqr. The O III lines excited via Bowen's mechanism are analyzed in detail, and a shell model yielding reasonable shell thicknesses and electron densities is described. The Ne/Fe ratio is derived for five of the systems, and spectra in the blue region are briefly described. 42 refs

Reconstructing Historical Light Curves of Symbiotic Stars and Novae

Directory of Open Access Journals (Sweden)

Jurdana-Šepić R.

2012-06-01

Full Text Available We reconstructed photometric histories of symbiotic stars and novae from direct inspection and measurement of photographic plates preserved at historical archives. We have completed the digging of the rich Asiago archive, and have started working on the Harvard plate stack, while other plate collections should be added soon. For homogeneity, we use the same UBV RCIC photometric comparison sequences used in current CCD observations. This data harvest has permitted the discovery of past undetected outbursts and secular trends, or to derive previously unknown orbital periods and recurrence times, which are essential to constrain the nature of these capricious and variegated active binaries.

On the nature of the symbiotic binary CI Cygni

International Nuclear Information System (INIS)

Kenyon, S.J.; Oliversen, N.A.; Mikolajewska, J.; Mikolajewski, M.; Stencel, R.E.

1991-01-01

An analysis of ultraviolet and optical spectroscopy is presented for the symbiotic binary CI Cyg. This system contains an M5 II asymptotic branch giant Mg of about 1.5 solar mass, transfering material at a few times 0.00001 solar mass/yr into a large accretion disk surrounding a main-sequence star with Mh of about 0.5 solar mass. A boundary layer at the inner edge of the disk photoionizes a small nebula approximately confined to the Roche volume of the accreting star. An extended, more highly ionized region forms when material ejected from the disk interacts with the red giant wind. 115 refs

Theories for the winds from Wolf Rayet stars

International Nuclear Information System (INIS)

Cassinelli, J.P.

1982-01-01

The massive and fast winds of Wolf Rayet stars present a serious momentum problem for the line-driven wind theories that are commonly used to explain the fast winds of early type stars. It is perhaps possible for the winds to be driven by lines, if multiple scattering occurs and if there are a sufficient number of lines in the spectrum so that large fraction of the continuum is blocked by line opacity in the winds. Several other mechanisms are discussed, in particular two that rely on strong magnetic fields: a) Alfven wave driven wind models like those recently developed by Hartmann and MacGregor for late type supergiants and b) the ''Fast Magnetic Rotator'' model that was developed by Belcher and MacGregor for the winds from pre-main sequence stars. In either model, large magnetic fields (approximately equal to 10 4 gauss) are required to drive the massive and fast winds of Wolf Rayet stars. Smaller fields might be possible if the multiple scattering line radiation force can be relied on to provide a final acceleration to terminal velocity. (Auth.)

Focused Wind Mass Accretion in Mira AB

Science.gov (United States)

Karovska, Margarita; de Val-Borro, M.; Hack, W.; Raymond, J.; Sasselov, D.; Lee, N. P.

2011-05-01

At a distance of about only 100pc, Mira AB is the nearest symbiotic system containing an Asymptotic Giant Branch (AGB) star (Mira A), and a compact accreting companion (Mira B) at about 0.5" from Mira A. Symbiotic systems are interacting binaries with a key evolutionary importance as potential progenitors of a fraction of asymmetric Planetary Nebulae, and SN type Ia, cosmological distance indicators. The region of interaction has been studied using high-angular resolution, multiwavelength observations ranging from radio to X-ray wavelengths. Our results, including high-angular resolution Chandra imaging, show a "bridge" between Mira A and Mira B, indicating gravitational focusing of the Mira A wind, whereby components exchange matter directly in addition to the wind accretion. We carried out a study using 2-D hydrodynamical models of focused wind mass accretion to determine the region of wind acceleration and the characteristics of the accretion in Mira AB. We highlight some of our results and discuss the impact on our understanding of accretion processes in symbiotic systems and other detached and semidetached interacting systems.

Distinguishing between symbiotic stars and planetary nebulae

Science.gov (United States)

Iłkiewicz, K.; Mikołajewska, J.

2017-10-01

Context. The number of known symbiotic stars (SySt) is still significantly lower than their predicted population. One of the main problems in finding the total population of SySt is the fact that their spectrum can be confused with other objects, such as planetary nebulae (PNe) or dense H II regions. This problem is reinforced by the fact that in a significant fraction of established SySt the emission lines used to distinguish them from other objects are not present. Aims: We aim at finding new diagnostic diagrams that could help separate SySt from PNe. Additionally, we examine a known sample of extragalactic PNe for candidate SySt. Methods: We employed emission line fluxes of known SySt and PNe from the literature. Results: We found that among the forbidden lines in the optical region of spectrum, only the [O III] and [N II] lines can be used as a tool for distinguishing between SySt and PNe, which is consistent with the fact that they have the highest critical densities. The most useful diagnostic that we propose is based on He I lines, which are more common and stronger in SySt than forbidden lines. All these useful diagnostic diagrams are electron density indicators that better distinguish PNe and ionized symbiotic nebulae. Moreover, we found six new candidate SySt in the Large Magellanic Cloud and one in M 81. If confirmed, the candidate in M 81 would be the farthest known SySt thus far.

SWIFT OBSERVATIONS OF HARD X-RAY EMITTING WHITE DWARFS IN SYMBIOTIC STARS

International Nuclear Information System (INIS)

Kennea, J. A.; Burrows, D. N.; Mukai, K.; Markwardt, C. B.; Sokoloski, J. L.; Luna, G. J. M.; Tueller, J.

2009-01-01

The X-ray emission from most accreting white dwarfs (WDs) in symbiotic binary stars is quite soft. Several symbiotic WDs, however, produce strong X-ray emission at energies greater than ∼20 keV. The Swift Burst Alert Telescope (BAT) instrument has detected hard X-ray emission from four such accreting WDs in symbiotic stars: RT Cru, T CrB, CD -57 3057, and CH Cyg. In one case (RT Cru), Swift detected X-rays out to greater than 50 keV at >5σ confidence level. Combining data from the X-Ray Telescope (XRT) and BAT detectors, we find that the 0.3-150 keV spectra of RT Cru, T CrB, and CD -57 3057 are well described by emission from a single-temperature, optically thin thermal plasma, plus an unresolved 6.4-6.9 keV Fe line complex. The X-ray spectrum of CH Cyg contains an additional bright soft component. For all four systems, the spectra suffer high levels of absorption from material that both fully and partially covers the source of hard X-rays. The XRT data did not show any of the rapid, periodic variations that one would expect if the X-ray emission were due to accretion onto a rotating, highly magnetized WD. The X-rays were thus more likely from the accretion-disk boundary layer around a massive, non-magnetic WD in each binary. The X-ray emission from RT Cru varied on timescales of a few days. This variability is consistent with being due to changes in the absorber that partially covers the source, suggesting localized absorption from a clumpy medium moving into the line of sight. The X-ray emission from CD -57 3057 and T CrB also varied during the nine months of Swift observations, in a manner that was also consistent with variable absorption.

An Indication of the Enhanced Circumstellar Matter Near the Orbital Plane of the Symbiotic Star EG And

Science.gov (United States)

Shagatova, N.; Skopal, A.

2015-07-01

In this contribution we derive the velocity profile of the material produced by the giant in the symbiotic binary EG And, and the corresponding mass loss rate. Our analysis revealed a significant enhancement of the wind material along the binary plane, which allows a high efficiency of the wind transfer onto the accreting white dwarf.

Stellar Wind Retention and Expulsion in Massive Star Clusters

Science.gov (United States)

Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

2018-05-01

Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

Interactions between exoplanets and the winds of young stars

Directory of Open Access Journals (Sweden)

Vidotto A. A.

2014-01-01

Full Text Available The topology of the magnetic field of young stars is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. Here, we investigate the interaction between winds of young stars and hypothetical planets. For that, we model the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt simplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star, we show that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.

IGR J17329-2731: The birth of a symbiotic X-ray binary

Science.gov (United States)

Bozzo, E.; Bahramian, A.; Ferrigno, C.; Sanna, A.; Strader, J.; Lewis, F.; Russell, D. M.; di Salvo, T.; Burderi, L.; Riggio, A.; Papitto, A.; Gandhi, P.; Romano, P.

2018-05-01

We report on the results of the multiwavelength campaign carried out after the discovery of the INTEGRAL transient IGR J17329-2731. The optical data collected with the SOAR telescope allowed us to identify the donor star in this system as a late M giant at a distance of 2.7-1.2+3.4 kpc. The data collected quasi-simultaneously with XMM-Newton and NuSTAR showed the presence of a modulation with a period of 6680 ± 3 s in the X-ray light curves of the source. This unveils that the compact object hosted in this system is a slowly rotating neutron star. The broadband X-ray spectrum showed the presence of a strong absorption (≫1023 cm-2) and prominent emission lines at 6.4 keV, and 7.1 keV. These features are usually found in wind-fed systems, in which the emission lines result from the fluorescence of the X-rays from the accreting compact object on the surrounding stellar wind. The presence of a strong absorption line around 21 keV in the spectrum suggests a cyclotron origin, thus allowing us to estimate the neutron star magnetic field as 2.4 × 1012 G. All evidencethus suggests IGR J17329-2731 is a symbiotic X-ray binary. As no X-ray emission was ever observed from the location of IGR J17329-2731 by INTEGRAL (or other X-ray facilities) during the past 15 yr in orbit and considering that symbiotic X-ray binaries are known to be variable but persistent X-ray sources, we concluded that INTEGRAL caught the first detectable X-ray emission from IGR J17329-2731 when the source shined as a symbiotic X-ray binary. The Swift XRT monitoring performed up to 3 months after the discovery of the source, showed that it maintained a relatively stable X-ray flux and spectral properties.

Accretion onto hot white dwarfs in relation to symbiotic novae

International Nuclear Information System (INIS)

Livio, M.; Prialnik, D.; Regev, O.

1989-01-01

Numerical calculations are used to study the hydrodynamic evolution of a hot white dwarf with 1 solar mass accreting hydrogen-rich matter at rates between 10 to the -8th and 10 to the -6th solar masses/yr. It is found that for accretion at a rate of about 10 to the -8th solar masses/yr, nova-type outbursts of long duration occur at intervals of about 1500 yr. About half of the accreted envelope is ejected during these outbursts. At a rate of about 10 to the -7th solar masses/yr, the star alternates between comparable periods at a high plateau luminosity and giant dimensions and periods at a low luminosity and white dwarf dimension. At 10 to the -6th solar masses/yr, equilibrium is achieved with a typical red giant luminosity supported by steady hydrogen burning. It is concluded that symbiotic novae are more likely to occur in detached systems involving wind accretors. Thus, the contribution of symbiotic stars to the frequency of type I supernovae is severely constrained. 39 refs

Radiation of the symbiotic star CH Cygni in the period 1982 -July 1984

International Nuclear Information System (INIS)

Skopal, A.

1987-01-01

Spectroscopic behavior is described of the symbiotic star CH Cygni in the period of the activity 1982 - July 1984. Observed variations of the intensities of the emission lines and absorption shell lines are discussed. An analysis of these lines supports the idea that a few different regions of radiation exist in CH Cygni. Drop in brightness and development of jets are interpreted as the consequence of an accretion disk evolution. (author). 4 figs., 10 refs

The infrared variability and nature of symbiotic stars

International Nuclear Information System (INIS)

Feast, M.W.; Catchpole, R.M.; Whitelock, P.A.; Carter, B.S.; Roberts, G.

1983-01-01

Infrared variability and spectra show that the symbiotic systems (He 2-106, He 2-38, He 2-34) contain Mira variable components. The first two also show a longer term infrared variability. It is suggested that this is due to variable dust obscuration (as in R Aqr). The phenomenon is then too frequent for the dust clouds to be confined to the orbital planes of the binary systems. Seven Miras in symbiotics have known periods which range from 370 to 580 days, suggesting a greater frequency of long-period Miras in symbiotics than in the general field. Symbiotic Miras have dust excesses with colour temperatures near 1000 K. Observations of four other symbiotic systems (Pe 2-3, He 2-87, H 2-5, AG Peg) are consistent with their containing non-variable or low amplitude M-type components. (author)

Wind bubbles within H ii regions around slowly moving stars

Science.gov (United States)

Mackey, Jonathan; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert

2015-01-01

Interstellar bubbles around O stars are driven by a combination of the star's wind and ionizing radiation output. The wind contribution is uncertain because the boundary between the wind and interstellar medium is difficult to observe. Mid-infrared observations (e.g., of the H ii region RCW 120) show arcs of dust emission around O stars, contained well within the H ii region bubble. These arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by density gradients and/or stellar motion. We present two-dimensional, radiation-hydrodynamics simulations investigating the evolution of wind bubbles and H ii regions around massive stars moving through a dense (nH = 3000 cm-3), uniform medium with velocities ranging from 4 to 16 km s-1. The H ii region morphology is strongly affected by stellar motion, as expected, but the wind bubble is also very aspherical from birth, even for the lowest space velocity considered. Wind bubbles do not fill their H ii regions (we find filling factors of 10-20 per cent), at least for a main sequence star with mass M⋆ ~ 30 M⊙. Furthermore, even for supersonic velocities the wind bow shock does not significantly trap the ionization front. X-ray emission from the wind bubble is soft, faint, and comes mainly from the turbulent mixing layer between the wind bubble and the H ii region. The wind bubble radiates <1 per cent of its energy in X-rays; it loses most of its energy by turbulent mixing with cooler photoionized gas. Comparison of the simulations with the H ii region RCW 120 shows that its dynamical age is ≲0.4 Myr and that stellar motion ≲4 km s-1 is allowed, implying that the ionizing source is unlikely to be a runaway star but more likely formed in situ. The region's youth, and apparent isolation from other O or B stars, makes it very interesting for studies of massive star formation and of initial mass functions. Movies are available in electronic form at http://www.aanda.org

Symbiotic star CI Cygni: S-process episode or accretion event

Energy Technology Data Exchange (ETDEWEB)

Kenyon, S J; Webbink, R F; Gallagher, J S; Truran, J W

1982-02-01

Evidence that the symbiotic star C I Cygni is an eclipsing binary is reviewed. It is shown that the s-process episode described by Audouze et al. (1981) during its 1975 outburst arises from superposition of normal gM4 absorption features on the continuum of the hot component during eclipse ingress, and not to sudden enhancements of rare earth elements. The peculiar velocity displacements of absorption lines with different excitation potentials during this episode are identified as signatures of an optically thick accretion disk, which dominates the visible spectrum during outburst. The data presented by Audouze et al., and the shape of the light curve thus provide evidence that the outburst is accretion-powered.

On the Symbiotic X-Ray Binary Nature of the Star CGCS 5926

Directory of Open Access Journals (Sweden)

Masetti N.

2012-06-01

Full Text Available We report on multiwavelength (from X-ray to optical follow up observations of a carbon star CGCS 5926, motivated by the fact that it is positionally coincident with a faint X-ray source of the ROSAT catalog, thus suggesting its possible symbiotic X-ray binary (SyXB nature. Our optical spectroscopy confirms that this is a carbon star of type C(6,2. This allows us to infer for CGCS 5926 a distance of ~5 kpc. BVRCIC photometry of the star shows variability of ~0.3 mag with a periodicity of 151 days, which we interpret as due to radial pulsations. the source is not detected with the Swift satellite in X-rays down to a 0.3-10 keV luminosity of ~3 × 1032 erg s−1. This nondetection is apparently in contrast with the ROSAT data; however, the present information does not rule out that CGCS 5926 can be a SyXB. This will be settled by more sensitive observations at high energies.

Galactic Winds and the Role Played by Massive Stars

Science.gov (United States)

Heckman, Timothy M.; Thompson, Todd A.

Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

IR photometry results and dust envelope model for symbiotic Mira star candidate V 335 Vul

Science.gov (United States)

Bogdanov, M. B.; Taranova, O. G.; Shenavrin, V. I.

2017-10-01

We present the results of JHKLM-photometry for the symbiotic Mira star candidate V 335 Vul. Based on the average flux data, supplemented by IRAS, MSX, AKARI, and WISE mid-IR observations, we calculated a model of a spherically symmetric dust envelope of the star, made up of amorphous carbon and silicon carbide particles. The optical depth of the envelope in the visible range with a dust temperature at the inner boundary of T 1 = 1300 K is τ V = 0.58. For an envelope expansion velocity of 26.5 km s-1, the estimated mass loss rate is equal to 5.7 × 10-7 M ⊙ yr-1.

(C III lambda 1909/Si III lambda 1892) ratio as a diagnostic for planetary nebulae and symbiotic stars

International Nuclear Information System (INIS)

Feibelman, W.A.; Aller, L.H.; California Univ., Los Angeles)

1987-01-01

Suitable IUE archival material on planetary nebulae has been examined to determine the log R /F(lambda 1909 C III)/F(lambda 1892 Si III)/ as a discriminant for distinguishing planetary nebulae from symbiotic stars and related objects. The mean value of log R for 73 galactic planetaries is 1.4, while that of extragalactic planetaries appears to be slightly lower, and that for symbiotics is 0.3. The lower value of log R for symbiotics is easily understood as a consequence of their higher densities. A plot of log R versus N-epsilon indicates that 80 percent of the planetaries fall into the range of log R between 1.2 and 1.8, but some of the peculiar and bipolar nebulae fall below log R = 1.2. The corresponding N(C++)/N(Si++) ionic ratio varies over a large range. 53 references

IUE observations of the hot components in two symbiotic stars. [R Agr and RW Hya, 1200 to 3200 A

Energy Technology Data Exchange (ETDEWEB)

Michalitsianos, A G [National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center; Kafatos, M; Hobbs, R W; Maran, S P

1980-03-13

Ultraviolet measurements in the 1,200 - 3,200 A range are reported on two symbiotic stars, R Agr and RW Hya. The results indicate the presence of a hot component in each star, supporting the view that each is a binary system with a luminous red primary and a hot, sub-luminous companion. In the case of RW Hya the hot companion manifests itself by exciting a compact nebulosity while in the case of R Agr it is believed that the continuous spectrum of the hot star is directly detected, while the continuum of nebulosity excited by the hot star is detected at longer wavelengths.

Thermal radio emission from the winds of single stars

International Nuclear Information System (INIS)

Abbott, D.C.

1985-01-01

Observations of thermal emission at radio wavelengths provides a powerful diagnostic of the rate of mass loss and temperature of the winds of early-type stars. Some winds are also strong sources of nonthermal emission. Case studies of known thermal and nonthermal sources provide empirical criteria for classifying the observed radio radiation. Mass loss rates are derived for 37 OB and Wolf-Rayet stars considered definite or probable thermal wind sources by these criteria. The rate of mass loss is strongly linked to stellar luminosity in OB stars and probably linked to stellar mass in Wolf-Rayet stars, with no measurable correlation with any other stellar property. A few late-type giants and supergiants also have detectable thermal emission, which arises from extended, accelerating, partially-ionized chromospheres. (orig.)

The symbiotic star CI Cygni: S-process episode or accretion event

International Nuclear Information System (INIS)

Kenyon, S.J.; Webbink, R.F.; Gallagher, J.S.; Truran, J.W.

1982-01-01

Evidence that the symbiotic star C I Cygni is an eclipsing binary is reviewed. It is shown that the 's-process episode' described by Audouze et al. (1981) during its 1975 outburst arises from superposition of normal gM4 absorption features on the continuum of the hot component during eclipse ingress, and not to sudden enhancements of rare earth elements. The peculiar velocity displacements of absorption lines with different excitation potentials during this episode are identified as signatures of an optically thick accretion disk, which dominates the visible spectrum during outburst. The data presented by Audouze et al., and the shape of the light curve thus provide evidence that the outburst is accretion-powered. (orig.)

Winds of AGB stars: does size matter?

International Nuclear Information System (INIS)

Hoefner, S

2008-01-01

Asymptotic giant branch (AGB) stars are showing clear signs of significant mass loss through cool stellar winds. These outflows are attributed to the combined effects of pulsation-induced shocks and radiation pressure on dust grains formed in the outer atmospheric layers. This paper gives an overview of the current status of radiation-hydrodynamical modelling of these processes, and presents a toy model that allows analysis of certain features of detailed models, such as the influence of grain size dependent opacities and basic differences in winds of C- and M-type AGB stars.

On the Weak-Wind Problem in Massive Stars: X-Ray Spectra Reveal a Massive Hot Wind in mu Columbae

Science.gov (United States)

Huenemoerder, David P.; Oskinova, Lidia M.; Ignace, Richard; Waldron, Wayne L.; Todt, Helge; Hamaguchi, Kenji; Kitamoto, Shunji

2012-01-01

Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind UV/optical spectra--is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.

H α and H β Raman scattering line profiles of the symbiotic star AG Pegasi

Science.gov (United States)

Lee, Seong-Jae; Hyung, Siek

2018-04-01

The H α and H β line profiles of the symbiotic star AG Pegasi, observed in 1998 September (phase ϕ = 10.24), display top narrow double Gaussian components and bottom broad components (FWHM = 200-400 km s-1). The photoionization model indicates that the ionized zone, responsible for the hydrogen Balmer and Lyman lines, is radiation-bounded, with a hydrogen gas number density of nH ˜ 109.85 cm-3 and a gas temperature of Te = 12 000-15 000 K. We have carried out Monte Carlo simulations to fit the Raman scattering broad wings, assuming that the hydrogen Ly β and Ly γ lines emitted within the radiation-bounded H II zone around a white dwarf have the same double Gaussian line profile shape as the hydrogen Balmer lines. The simulation shows that the scattering H I zones are attached to (or located just outside) the inner H II shells. The best fit to the observed broad H I line profiles indicates that the column density of the scattering neutral zone is NH ≃ 3-5 × 1019 cm-2. We have examined whether the geometrical structure responsible for the observed H α and H β line profiles is a bipolar conical shell structure, consisting of the radiation-bounded ionized zone and the outer material bounded neutral zone. The expanding bipolar structure might be two opposite regions of the common envelope or the outer shell of the Roche lobe around the hot white dwarf, formed through the mass inflows from the giant star and pushed out by the fast winds from the hot white dwarf.

Stellar and wind parameters of massive stars from spectral analysis

Science.gov (United States)

Araya, Ignacio; Curé, Michel

2017-11-01

The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

Emission-line widths and stellar-wind flows in T Tauri stars

International Nuclear Information System (INIS)

Sa, C.; Lago, M.T.V.T.

1986-01-01

Spectra are reported of T Tauri stars taken with the IPCS on the Isaac Newton Telescope at the Observatorio del Roque de los Muchachos at a dispersion of l7 A mm -1 . These were taken in order to determine emission-line widths and hence flow velocities in the winds of these stars following the successful modelling of the wind from RU Lupi using such data. Line widths in RW Aur suggest a similar pattern to the wind flow as in RU Lupi with velocities rising in the inner chromosphere of the star and then entering a 'ballistic' zone. The wind from DFTau is also similar but velocities are generally much lower and the lines sharper. (author)

Eclipse in the binary system of the CI Cyg symbiotic star

Energy Technology Data Exchange (ETDEWEB)

Belyakina, T S

1979-01-01

Photoelectric photometry and spectral observations of the symbiotic star CI Cyg were carried out at the Crimean Astrophysical Observatory from April, 1975 through December, 1976. The instrumental photometric system used was close to the UBV. Considerable light variations and spectral changes have been recorded during the period of the observations. Yellow, blue and ultraviolet amplitudes were equal to 2.3, 3.0 and 3sub(m).3 correspondingly. The brightness of CI Cyg reached maximal value in June - July, 1975 when spectrum was F5 with Hsub(..cap alpha..) and Hsub(..beta..) in emission. A sharp and deep minimum in the light curves of CI Cyg was observed during the period of the highest brightness. It was caused by the eclipse of the hot component by the cold one in the binary system.

Possibility of star (pyramid) dune development in the area of bimodal wind regime

Science.gov (United States)

Biejat, K.

2012-04-01

Star (pyramid) dunes are the largest aeolian landforms. They can occur in three types - simple, complex and compound. Development of this type of dunes is usually connected with multidirectional or complex wind regimes. The aim of this study was to verify a hypothesis that the star dunes can also develop by a bimodal wind regime and by local modifications of nearsurface wind flow directions. Field study was performed on Erg Chebbi, in southern Morocco. Several star and transverse dunes were selected for the study of their shape. The star dunes were analysed concerning their type and position in the dune field. This erg contains all of three types of star dunes together with transverse dunes. The regional wind data show that there are two dominant wind directions - NE (Chergui) and SW (Saheli). To determine the difference in shape of star dunes, we performed topographic surveying by GPS RTK. The results allowed to create 3D models of star dunes. The models were used to determine metric characteristics of star dunes, including area of dune basis, volume, and slope angles. On the basis of 3D models, primary, secondary and, on the compound dunes, tertiary arms were determined. Primary arms on each type of star dunes, as well as crestlines of transverse dunes, have dominant orientation NW-SE, perpendicular to two dominant wind directions. This clearly confirms that star dunes of Erg Chebbi develop by a bimodal wind regime In contrast to primary arms, subsidiary (secondary and tertiary) arms are not connected to general wind regime. The secondary arms of star dunes occur to be differentially developer. There are more subsidiary arms on SW sides in comparison to the E sides of the dunes where inclination of slopes is constant. It can be therefore inferred that sand has been supplied predominantly from SW direction. This is supported by distribution of the dunes on the erg. Most compound star dunes compose a chain along the E margin of the erg. Comparison of compound star

Outbursts of symbiotic novae

International Nuclear Information System (INIS)

Kenyon, S.J.; Truran, J.W.

1983-01-01

We discuss possible conditions under which thermonuclear burning episodes in the hydrogen-rich envelopes of accreting white dwarfs give rise to outbursts similar in nature to those observed in the symbiotic stars AG Peg, RT Ser, RR Tel, AS 239, V1016 Cyg, V1329 Cyg, and HM Sge. In principle, thermonuclear runaways involving low-luminosity white dwarfs accreting matter at low rates produce configurations that evolve into A--F supergiants at maximum visual light and which resemble the outbursts of RR Tel, RT Ser, and AG peg. Very weak, nondegenerage hydrogen shell flashes on white dwarfs accreting matter at high rates (M> or approx. =10 -8 M/sub sun/ yr -1 ) do not produce cool supergiants at maximum, and may explain the outbursts in V1016 Cyg, V1329 Cyg, and HM Sge. The low accretion rates demanded for systems developing strong hydrogen shell flashes on low-luminsoity white dwarfs are not compatible with observations of ''normal'' quiescent symbiotic stars. The extremely slow outbursts of symbiotic novae appear to be typical of accreting white dwarfs in wide binaries, which suggests that the outbursts of classical novae may be accelerated by the interaction of the expanding white dwarf envelope with its close binary companion

Evolution of viscous discs. 3. Giant discs in symbiotic stars

Energy Technology Data Exchange (ETDEWEB)

Bath, G T [Oxford Univ. (UK). Dept. of Astrophysics; Pringle, J E [Cambridge Univ. (UK). Inst. of Astronomy

1982-10-01

The structure of time-dependent accretion discs in giant binaries with separation of the order of 10/sup 13/ cm is examined. Radiative ..cap alpha..-viscosity discs with ..cap alpha.. of order unity accreting on to main-sequence stars at accretion rates which generate luminosities greater than a giant companion decay on time-scales of the same order as the binary period, unlike those in dwarf nova binaries which decay on time-scales 100 times longer than the binary period. This results from the lower gravitational potential and consequent larger disc thickness (relative to the radius) of luminous 'giant' discs accreting at high accretion rates. The eruptions of the symbiotic binary C I Cygni are modelled by an ..cap alpha.. = 1 disc with outer radius 8.5 x 10/sup 12/ cm and a sequence of five mass-transfer bursts at rates between 1.5 x 10/sup 21/ and 4 x 10/sup 22/g s/sup -1/.

The Expanding Bipolar Conic Shell of the Symbiotic Star AG Peg

Science.gov (United States)

Lee, Seong-Jae; Hyung, Siek

2018-06-01

Symbiotic stars are the most interesting since some systems are believed to host the most massive white dwarf, like SN Ia progenitors. Most recently, Lee and Hyung (2018, LH18) proposed a bipolar conic shell structure for the observed high expansion Hα and Hβ line profiles and other double peak lines observed in 1998 September (phase φ = 10.24): the physical conditions for the white dwarf luminosity and the ionized HII zone, responsible for double Gaussian optical lines including Balmer and Lyman line fluxes, were taken from the P-I model with gas density, nH = 109.85 cm-3 , while the column density for the scattering neutral zone was derived from the broader line components based on the result by Monte Carlo simulations. In this investigation, we examined whether the expanding shells of the bipolar conical geometry as proposed by LH18 would be able to form the other Hα and Hβ line profiles observed in other phases, φ = 11.56 and 11.98 (in 2001 August and 2002 August). We look into the kinematical property of the bipolar conic shell structure responsible for the HII and HI zones and then we discuss the secular variation of the broad line feature and the origin of the bipolar cone, i.e., part of a common envelope formed through the mass inflows from the giant star.

Winds of Massive Magnetic Stars: Interacting Fields and Flow

Science.gov (United States)

Daley-Yates, S.; Stevens, I. R.

2018-01-01

We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

Massive stars in colliding wind systems: the GLAST perspective

International Nuclear Information System (INIS)

Reimer, Anita; Reimer, Olaf

2007-01-01

Colliding winds of massive stars in binary systems arc considered as candidate sites of high-energy non-thermal photon emission. They are already among the suggested counterparts for a few individual unidentified EGRET sources, but may constitute a detectable source population for the GLAST observatory.The present work investigates such population study of massive colliding wind systems at high-energy gamma-rays. Based on the recent detailed model (Reimer et al. 2006) for non-thermal photon production in prime candidate systems, we unveil the expected characteristics of this source class in the observables accessible at LAT energies. Combining the broadband emission model with the presently cataloged distribution of such systems and their individual parameters allows us to conclude on the expected maximum number of LAT-detections among massive stars in colliding wind binary systems

Evolution of the symbiotic binary system AG Pegasi - The slowest classical nova eruption ever recorded

Science.gov (United States)

Kenyon, Scott J.; Mikolajewska, Joanna; Mikolajewski, Maciej; Polidan, Ronald S.; Slovak, Mark H.

1993-01-01

We present an analysis of new and existing photometric and spectroscopic observations of the ongoing eruption in the symbiotic star AG Pegasi, showing that this binary has evolved considerably since the turn of the century. Recent dramatic changes in both the UV continuum and the wind from the hot component allow a more detailed analysis than in previous papers. AG Peg is composed of a normal M3 giant and a hot, compact star embedded in a dense, ionized nebula. The hot component powers the activity observed in this system, including a dense wind and a photoionized region within the outer atmosphere of the red giant. The hot component contracted in radius at roughly constant luminosity from 1850 to 1985. Its bolometric luminosity declined by a factor of about 4 during the past 5 yr. Both the mass loss rate from the hot component and the emission activity decreased in step with the hot component's total luminosity, while photospheric radiation from the red giant companion remained essentially constant.

Symbiotic Miras

International Nuclear Information System (INIS)

Whitelock, P.A.

1987-01-01

This paper concerns interacting binary systems involving Mira variables. Twenty-six objects which potentially fall into this category are identified and observations of them covering the spectral regions from X-ray to radio are reviewed. Particular emphasis is given to near-infrared observations which are pertinent to establishing the presence of a Mira variable and also to new far-infrared data from IRAS. The majority of the objects under consideration have been classified as symbiotic stars. They are closely related to the well-known binary, o Cet, which might be described as mildly symbiotic. It is shown how the knowledge of normal Miras can contribute to the understanding of the evolutionary condition and luminosities of these binary Miras. Distances are derived for those objects with measured pulsation periods. The significance of the relatively long pulsation periods shown by these objects is also discussed. 165 references

EVOLUTION OF SUPER STAR CLUSTER WINDS WITH STRONG COOLING

International Nuclear Information System (INIS)

Wuensch, Richard; Palous, Jan; Silich, Sergiy; Tenorio-Tagle, Guillermo; Munoz-Tunon, Casiana

2011-01-01

We study the evolution of super star cluster winds driven by stellar winds and supernova explosions. Time-dependent rates at which mass and energy are deposited into the cluster volume, as well as the time-dependent chemical composition of the re-inserted gas, are obtained from the population synthesis code Starburst99. These results are used as input for a semi-analytic code which determines the hydrodynamic properties of the cluster wind as a function of cluster age. Two types of winds are detected in the calculations. For the quasi-adiabatic solution, all of the inserted gas leaves the cluster in the form of a stationary wind. For the bimodal solution, some of the inserted gas becomes thermally unstable and forms dense warm clumps which accumulate inside the cluster. We calculate the evolution of the wind velocity and energy flux and integrate the amount of accumulated mass for clusters of different mass, radius, and initial metallicity. We also consider conditions with low heating efficiency of the re-inserted gas or mass loading of the hot thermalized plasma with the gas left over from star formation. We find that the bimodal regime and the related mass accumulation occur if at least one of the two conditions above is fulfilled.

Five-Phase Five-Level Open-Winding/Star-Winding Inverter Drive for Low-Voltage/High-Current Applications

DEFF Research Database (Denmark)

Padmanaban, Sanjeevi Kumar; Blaabjerg, Frede; Wheeler, Patrick

2016-01-01

This paper work proposed a five-phase five-level open-/star-winding multilevel AC converter suitable for low-voltage/high-current applications. Modular converter consists of classical two-level five-phase voltage source inverter (VSI) with slight reconfiguration to serve as a multilevel converter...... for open-/star-winding loads. Elaborately, per phase of the VSI is built with one additional bi-directional switch (MOSFET/IGBT) and all five legs links to the neutral through two capacitors. The structure allows multilevel generation to five-level output with greater potential for fault tolerability under...

Probing the extreme wind confinement of the most magnetic O star with COS spectroscopy

Science.gov (United States)

Petit, Veronique

2014-10-01

We propose to obtain phase-resolved UV spectroscopy of the recently discovered magnetic O star NGC 1624-2, which has the strongest magnetic field ever detected in a O-star, by an order of magnitude. We will use the strength and variability of the UV resonance line profiles to diagnose the density, velocity, and ionization structure of NGC 1624-2's enormous magnetosphere that results from entrapment of its stellar wind by its strong, nearly dipolar magnetic field. With this gigantic magnetosphere, NGC 1624-2 represents a new regime of extreme wind confinement that will constrain models of magnetized winds and their surface mass flux properties. A detailed understanding of such winds is necessary to study the rotational braking history of magnetic O-stars, which can shed new light on the fundamental origin of magnetism in massive, hot stars.

Discovery of a Possible Symbiotic Binary in the Large Magellanic Cloud

Science.gov (United States)

Mathew, Blesson; Reid, Warren A.; Mennickent, R. E.; Banerjee, D. P. K.

2017-12-01

We report the discovery of a possible symbiotic star, in the Large Magellanic Cloud (LMC). The object under consideration here, designated as RP 870, was detected during the course of a comprehensive H$\\alpha$ survey of the LMC by Reid & Parker (2012). The spectrum of RP 870 showed high ionization emission lines of He I, He II and [O III] and molecular absorption bands of TiO $\\lambda$$\\lambda$6180, 7100. The collective signatures of a hot component (high excitation/ionization lines) and of a cool component (TiO molecular bands) are seen in RP 870, from which we propose it as a symbiotic star. Since known symbiotic systems are rare in the LMC, possibly less than a dozen are known, we thought the present detection to be interesting enough to be reported.

Stellar winds and coronae of low-mass Population II/III stars

Science.gov (United States)

Suzuki, Takeru K.

2018-06-01

We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

Stellar winds and coronae of low-mass Population II/III stars

Science.gov (United States)

Suzuki, Takeru K.

2018-04-01

We investigated stellar winds from zero-/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfvén waves from stars with mass M = (0.6-0.8) M⊙ and metallicity Z = (0-1) Z⊙, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Alfvénic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower Z, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Population II/III stars with Z ≤ 0.01 Z⊙ is one to two orders of magnitude larger than that of a solar-metallicity star with the same mass, and as a result, the mass loss rate, \\dot{M}, is 4.5-20 times larger. This indicates that metal accretion on low-mass Pop. III stars is negligible. The soft X-ray flux of the Pop. II/III stars is also expected to be ˜1-30 times larger than that of a solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency is smaller. A larger fraction of the input Alfvénic wave energy is transmitted to the corona in low-Z stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of \\dot{M} as \\dot{M}∝ L R_{\\star }^{11/9} M_{\\star }^{-10/9} T_eff^{11/2}[\\max (Z/Z_{⊙},0.01)]^{-1/5}, where L, R⋆, and Teff are the stellar luminosity, radius, and effective temperature, respectively.

Evolution of the symbiotic binary system AG Dranconis

Science.gov (United States)

Mikolajewska, Joanna; Kenyon, Scott J; Mikolajewski, Maciej; Garcia, Michael R.; Polidan, Ronald S.

1995-01-01

We present an analysis of new and archival photometric and spectroscopic observations of the symbiotic star AG Draconis. This binary has undergone several 1 - 3 mag optical and ultraviolet eruptions during the past 15 years. Our combination of optical and ultraviolet spectroscopic data allow a more complete analysis of this system than in previous papers. AG Dra is composed of a K-type bright giant M(sub g) approximately 1.5 solar mass) and a hot, compact star M(sub h approximatelly 0.4 - 0.6 solar mass) embedded in a dense, low metallicity nebula. The hot component undergoes occasional thermonuclear runaways that produce 2 - 3 mag optical/ultraviolet eruptions. During these eruptions, the hot component develops a low velocity wind that quenches x-ray emission from the underlying hot white dwarf. The photoionized nebula changes its volume by a factor of 5 throughout an eruptin cycle. The K bright giant occults low ionization emission lines during superior conjunctions at all outburst phases but does not occult high ionization lines in outburst (and perhaps quiescence). This geometry and the component masses suggest a system inclination of i approximately 30 deg - 45 deg.

NLTE wind models of hot subdwarf stars

Czech Academy of Sciences Publication Activity Database

Krtička, J.; Kubát, Jiří

2010-01-01

Roč. 329, 1-2 (2010), s. 145-150 ISSN 0004-640X R&D Projects: GA ČR GA205/07/0031 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.437, year: 2010

CARINA OB STARS: X-RAY SIGNATURES OF WIND SHOCKS AND MAGNETIC FIELDS

International Nuclear Information System (INIS)

Gagne, Marc; Fehon, Garrett; Savoy, Michael R.; Cohen, David H.; Townsley, Leisa K.; Broos, Patrick S.; Povich, Matthew S.; Corcoran, Michael F.; Walborn, Nolan R.; Remage Evans, Nancy; Moffat, Anthony F. J.; Naze, Yael; Oskinova, Lida M.

2011-01-01

The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L X /L bol relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with a period of >30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403, and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high L X cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star.

IUE observations of variability in winds from hot stars

Science.gov (United States)

Grady, C. A.; Snow, T. P., Jr.

1981-01-01

Observations of variability in stellar winds or envelopes provide an important probe of their dynamics. For this purpose a number of O, B, Be, and Wolf-Rayet stars were repeatedly observed with the IUE satellite in high resolution mode. In the course of analysis, instrumental and data handling effects were found to introduce spurious variability in many of the spectra. software was developed to partially compensate for these effects, but limitations remain on the type of variability that can be identified from IUE spectra. With these contraints, preliminary results of multiple observations of two OB stars, one Wolf-Rayet star, and a Be star are discussed.

Nonspherical Radiation Driven Wind Models Applied to Be Stars

Science.gov (United States)

Arauxo, F. X.

1990-11-01

ABSTRACT. In this work we present a model for the structure of a radiatively driven wind in the meridional plane of a hot star. Rotation effects and simulation of viscous forces were included in the motion equations. The line radiation force is considered with the inclusion of the finite disk correction in self-consistent computations which also contain gravity darkening as well as distortion of the star by rotation. An application to a typical BlV star leads to mass-flux ratios between equator and pole of the order of 10 and mass loss rates in the range 5.l0 to Mo/yr. Our envelope models are flattened towards the equator and the wind terminal velocities in that region are rather high (1000 Km/s). However, in the region near the star the equatorial velocity field is dominated by rotation. RESUMEN. Se presenta un modelo de la estructura de un viento empujado radiativamente en el plano meridional de una estrella caliente. Se incluyeron en las ecuaciones de movimiento los efectos de rotaci6n y la simulaci6n de fuerzas viscosas. Se consider6 la fuerza de las lineas de radiaci6n incluyendo la correcci6n de disco finito en calculos autoconsistentes los cuales incluyen oscurecimiento gravitacional asi como distorsi6n de la estrella por rotaci6n. La aplicaci6n a una estrella tipica BlV lleva a cocientes de flujo de masa entre el ecuador y el polo del orden de 10 de perdida de masa en el intervalo 5.l0 a 10 Mo/ano. Nuestros modelos de envolvente estan achatados hacia el ecuador y las velocidads terminales del viento en esa regi6n son bastante altas (1000 Km/s). Sin embargo, en la regi6n cercana a la estrella el campo de velocidad ecuatorial esta dominado por la rotaci6n. Key words: STARS-BE -- STARS-WINDS

High-Resolution X-Ray Spectra of the Symbiotic Star SS73 17

Science.gov (United States)

Eze, R. N. C.; Luna, G. J. M.; Smith, R. K.

2010-01-01

SS73 17 was an innocuous Mira-type symbiotic star until the International Gamma-Ray Astrophysics Laboratory and Swift discovered its bright hard X-ray emission, adding it to the small class of "hard X-ray emitting symbiotics." Suzaku observations in 2006 then showed it emits three bright iron lines as well, with little to no emission in the 0.3-2.0 keV bandpass. We present here follow-up observations with the Chandra High Energy Transmission Grating and Suzaku that confirm the earlier detection of strong emission lines of Fe K(alpha) fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray emission. The high-resolution spectrum also shows emission lines of other highly ionized ions as Si xiv and possibly S XVI. In addition, a re-analysis of the 2006 Suzaku data using the latest calibration shows that the hard (15-50 keV) X-ray emission is brighter than previously thought and remains constant in both the 2006 and 2008 data. The G ratio calculated from the Fe xxv lines shows that these lines are thermal, not photoionized, in origin.With the exception of the hard X-ray emission, the spectra from both epochs can be fit using thermal radiation assuming a differential emission measure based on a cooling-flow model combined with a full and partial absorber. We show that acceptable fits can be obtained for all the data in the 1-10 keV band varying only the partial absorber. Based on the temperature and accretion rate, the thermal emission appears to be arising from the boundary layer between the accreting white dwarf and the accretion disk.

HIGH-RESOLUTION X-RAY SPECTRA OF THE SYMBIOTIC STAR SS73 17

International Nuclear Information System (INIS)

Eze, R. N. C.; Luna, G. J. M.; Smith, R. K.

2010-01-01

SS73 17 was an innocuous Mira-type symbiotic star until the International Gamma-Ray Astrophysics Laboratory and Swift discovered its bright hard X-ray emission, adding it to the small class of 'hard X-ray emitting symbiotics'. Suzaku observations in 2006 then showed it emits three bright iron lines as well, with little to no emission in the 0.3-2.0 keV bandpass. We present here follow-up observations with the Chandra High Energy Transmission Grating and Suzaku that confirm the earlier detection of strong emission lines of Fe Kα fluorescence, Fe XXV and Fe XXVI but also show significantly more soft X-ray emission. The high-resolution spectrum also shows emission lines of other highly ionized ions as Si XIV and possibly S XVI. In addition, a re-analysis of the 2006 Suzaku data using the latest calibration shows that the hard (15-50 keV) X-ray emission is brighter than previously thought and remains constant in both the 2006 and 2008 data. The G ratio calculated from the Fe XXV lines shows that these lines are thermal, not photoionized, in origin. With the exception of the hard X-ray emission, the spectra from both epochs can be fit using thermal radiation assuming a differential emission measure based on a cooling-flow model combined with a full and partial absorber. We show that acceptable fits can be obtained for all the data in the 1-10 keV band varying only the partial absorber. Based on the temperature and accretion rate, the thermal emission appears to be arising from the boundary layer between the accreting white dwarf and the accretion disk.

Comoving frame models of hot star winds II. Reduction of O star wind mass-loss rates in global models

Czech Academy of Sciences Publication Activity Database

Krtička, J.; Kubát, Jiří

2017-01-01

Roč. 606, October (2017), A31/1-A31/12 E-ISSN 1432-0746 R&D Projects: GA ČR GA13-10589S Institutional support: RVO:67985815 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy , Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.014, year: 2016

Possibly massive symbiotic system V 1329 Cygni

Energy Technology Data Exchange (ETDEWEB)

Iijima, T; Mammano, A; Margoni, R [Padua Univ. (Italy). Osservatorio Astrofisico

1981-04-01

A new radial velocity curve of V 1329 Cyg has been obtained from emission lines originating around an evolved star. The latter might be faced by an M-type mate, whose mass is larger than 23 +- 6 solar masses. The system seems at vertical stroke Z vertical stroke > 250 pc from the galactic plane. The lambda6830 unidentified band, found in V 1329 Cyg and among BQ ( ) stars, symbiotic stars and a few planetary nebulae, could be used as a diagnostic tool to identify very evolved stars. The close similarity of the optical spectrum of V 1329 Cyg to that of the optical counterpart of GX 1 + 4 is remarkable.

Campaign of AAVSO Monitoring of the CH Cyg Symbiotic System in Support of Chandra and HST Observations

Science.gov (United States)

Karovska, M.

2013-06-01

(Abstract only) CH Cyg is one of the most interesting interacting binaries in which a compact object, a white dwarf or a neutron star, accretes from the wind of an evolved giant or supergiant. CH Cyg is a member of the symbiotic systems group, and at about 250pc it is one of the closest systems. Symbiotic systems are accreting binaries, which are likely progenitors of a fraction of Pre-Planetary and Planetary Nebulae, and of a fraction of SN type Ia (the cosmic distance scale indicators). We carried out Chandra and HST observations of CH Cyg in March 2012 as part of a follow-up investigation of the central region of CH Cyg and its precessing jet, including the multi-structures that were discovered in 2008. I will describe here the campaign of multi-wavelength observations, including photometry and spectroscopy, that were carried out by AAVSO members in support of the space-based observations.

SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

International Nuclear Information System (INIS)

Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

2012-01-01

We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

Search for magnetic fields in the symbiotic and VV Cephei variables

International Nuclear Information System (INIS)

Slovak, M.H.

1982-01-01

The McDonald Observatory's 2.7 m photoelectric analyzer was used to examine five symbiotic and VV Cephei variables for the presence of coherent longitudinal fields. Repeated observations of magnetic Ap stars indicates an absolute sensitivity of +- 100--200 gauss. To this level, no new evidence is found supporting the reported kilogauss fields on the quiescent symbiotics AG Pegasi and EG Andromedae, nor for the VV Cephei stars VV Cephei and WY Geminorum, contrary to extant photographic determinations. Observations of CH Cygni following its 1977 eruption also yielded null results. The lack of significant line broadening correlated with effective z-values further rules out the presence of large transverse components

A 3D dynamical model of the colliding winds in binary systems

Science.gov (United States)

Parkin, E. R.; Pittard, J. M.

2008-08-01

We present a three-dimensional (3D) dynamical model of the orbital-induced curvature of the wind-wind collision region in binary star systems. Momentum balance equations are used to determine the position and shape of the contact discontinuity between the stars, while further downstream the gas is assumed to behave ballistically. An Archimedean spiral structure is formed by the motion of the stars, with clear resemblance to high-resolution images of the so-called `pinwheel nebulae'. A key advantage of this approach over grid or smoothed particle hydrodynamic models is its significantly reduced computational cost, while it also allows the study of the structure obtained in an eccentric orbit. The model is relevant to symbiotic systems and γ-ray binaries, as well as systems with O-type and Wolf-Rayet stars. As an example application, we simulate the X-ray emission from hypothetical O+O and WR+O star binaries, and describe a method of ray tracing through the 3D spiral structure to account for absorption by the circumstellar material in the system. Such calculations may be easily adapted to study observations at wavelengths ranging from the radio to γ-ray.

Detailed empirical models for the winds of early-type stars

International Nuclear Information System (INIS)

Olson, G.L.; Castor, J.I.

1981-01-01

Owing to the recent accumulation of ultraviolet data from the IUE satellite, of X-ray data from the Einstein (HEAO 2) satellite, of visible data from ground based electronic detectors, and of radio data from the Very Large Array (VLA) telescope, it is becoming possible to build much more complete models for the winds of early-type stars. The present work takes the empirical approach of assuming that there exists a coronal region at the base of a cool wind (T/sub e/roughly-equalT/sub eff/). This will be an extension of previous papers by Olson and by Cassinelli and Olson; however, refinements to the model will be presented, and the model will be applied to seven O stars and one BO star. Ionization equilibria are computed to match the line strengths found in UV spectra. The coronal fluxes that are required to produce the observed abundance of O +5 are compared to the X-ray fluxes observed by the Einstein satellite

Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Science.gov (United States)

Martínez-Núñez, Silvia; Kretschmar, Peter; Bozzo, Enrico; Oskinova, Lidia M.; Puls, Joachim; Sidoli, Lara; Sundqvist, Jon Olof; Blay, Pere; Falanga, Maurizio; Fürst, Felix; Gímenez-García, Angel; Kreykenbohm, Ingo; Kühnel, Matthias; Sander, Andreas; Torrejón, José Miguel; Wilms, Jörn

2017-10-01

Massive stars, at least ˜10 times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy. In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense "clumps". The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution. Supergiant high mass X-ray binaries (SgXBs) are among the brightest X

Infrared Spectroscopy of the Late-Type Star in the Neutron Star X-ray Symbiotic System 4U 1700+24 = V934 Herculis

Science.gov (United States)

Hinkle, Kenneth; Fekel, Francis; Joyce, Richard; Mikolajewska, Joanna; Galan, Cezary

2018-01-01

V934 Her = 4U 1700+24 is a previously known M giant - neutron star X-ray symbiotic system. Employing newly measured optical and infrared radial velocities spanning 29 years plus the extensive set of velocities in the literature, we have computed the orbit of the M III in that system. We determine an orbital period of 4391 days or 12.0 yr, far longer than the 404 day orbit commonly cited in the literature. In addition to the 12.0 yr orbital period we find a shorter period of 420 days, similar to that previously found. Instead of orbital motion, we attribute this shorter period to a long secondary pulsation (LSP) period in the SRb variable M3 III. The orbit is seen nearly pole on explaining why X-ray pulsations associated with the neutron star have not been detected. Arguments are made that this orientation supports a pulsation origin for LSP. We also measure CNO and Fe peak abundances of the M giant. Basic properties of the M giant are derived. We discuss the possible evolutionary paths this system has taken to get to its current state.

Angular Momentum in Disk Wind Revealed in the Young Star MWC 349A

Energy Technology Data Exchange (ETDEWEB)

Zhang, Qizhou; Claus, Brian; Watson, Linda; Moran, James, E-mail: qzhang@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States)

2017-03-01

Disk winds are thought to play a critical role in star birth. As winds extract excess angular momentum from accretion disks, matter in the disk can be transported inward to the star to fuel mass growth. However, observational evidence of wind carrying angular momentum has been very limited. We present Submillimeter Array (SMA) observations of the young star MWC 349A in the H26 α and H30 α recombination lines. The high signal-to-noise ratios made possible by the maser emission process allow us to constrain the relative astrometry of the maser spots to milli-arcsecond precision. Previous observations of the H30 α line with the SMA and the Plateau de Bure interferometer (PdBI) showed that masers are distributed in the disk and wind. Our new high-resolution observations of the H26 α line reveal differences in spatial distribution from that of the H30 α line. H26 α line masers in the disk are excited in a thin annulus with a radius of about 25 au, while the H30 α line masers are formed in a slightly larger annulus with a radius of 30 au. This is consistent with expectations for maser excitation in the presence of an electron density variation of approximately R {sup −4}. In addition, the H30 α and H26 α line masers arise from different parts in the wind. This difference is also expected from maser theory. The wind component of both masers exhibits line-of-sight velocities that closely follow a Keplerian law. This result provides strong evidence that the disk wind extracts significant angular momentum, thereby facilitating mass accretion in the young star.

Star Formation-Driven Winds in the Early Universe

Science.gov (United States)

Peek, Matthew; Lundgren, Britt; Brammer, Gabriel

2018-01-01

Measuring the extent of star formation-driven winds from galaxies in the early universe is crucial for understanding of how galaxies evolve over cosmic time. Using WFC3/IR grism data from the Hubble Space Telescope (HST), we have measured the star formation rates and star formation rate surface densities of several hundred galaxies at redshift (z) = 1, when the universe was roughly half its present age. The galaxies we examine are also probed by background quasars, whose spectra provide information about the extent of metal-enriched gas in their halos. We use a computational pipeline to measure the density of the star formation in each galaxy and correlate these measurements with detections of Mg II absorption in nearby quasar spectra from the Sloan Digital Sky Survey. Our preliminary results support a model in which galaxies with high SFR surface densities drive metal-enriched gas out of the disk and into these galaxies’ extended halos, where that gas is detected in the spectra of more distant quasars.

Polarized bow shocks reveal features of the winds and environments of massive stars

Science.gov (United States)

Shrestha, Manisha

2018-01-01

Massive stars strongly affect their surroundings through their energetic stellar winds and deaths as supernovae. The bow shock structures created by fast-moving massive stars contain important information about the winds and ultimate fates of these stars as well as their local interstellar medium (ISM). Since bow shocks are aspherical, the light scattered in the dense shock material becomes polarized. Analyzing this polarization reveals details of the bow shock geometry as well as the composition, velocity, density, and albedo of the scattering material. With these quantities, we can constrain the properties of the stellar wind and thus the evolutionary state of the star, as well as the dust composition of the local ISM.In my dissertation research, I use a Monte Carlo radiative transfer code that I optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (SWBS) illuminated by a central star and by shock emission. I derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (SPH) models. In the case of the analytical SWBS and electron scattering, I find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. This is due to the geometrical properties of the bow shock combined with multiple scattering effects. For dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, and viewing angle. The behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models for the local ISM. In the case of SPH density structures, I investigate how the polarization changes as a function of the evolutionary phase of the SWBS. My dissertation compares these simulations with polarization data from Betelgeuse and other massive stars with bow shocks. I discuss the

CIRCUMSTELLAR SHELL FORMATION IN SYMBIOTIC RECURRENT NOVAE

Energy Technology Data Exchange (ETDEWEB)

Moore, Kevin; Bildsten, Lars [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106 (United States)

2012-12-20

We present models of spherically symmetric recurrent nova shells interacting with circumstellar material (CSM) in a symbiotic system composed of a red giant (RG) expelling a wind and a white dwarf accreting from this material. Recurrent nova eruptions periodically eject material at high velocities ({approx}> 10{sup 3} km s{sup -1}) into the RG wind profile, creating a decelerating shock wave as CSM is swept up. High CSM densities cause the shocked wind and ejecta to have very short cooling times of days to weeks. Thus, the late-time evolution of the shell is determined by momentum conservation instead of energy conservation. We compute and show evolutionary tracks of shell deceleration, as well as post-shock structure. After sweeping up all the RG wind, the shell coasts at a velocity {approx}100 km s{sup -1}, depending on system parameters. These velocities are similar to those measured in blueshifted CSM from the symbiotic nova RS Oph, as well as a few Type Ia supernovae that show evidence of CSM, such as 2006X, 2007le, and PTF 11kx. Supernovae occurring in such systems may not show CSM interaction until the inner nova shell gets hit by the supernova ejecta, days to months after the explosion.

HIGH-RESOLUTION X-RAY SPECTROSCOPY REVEALS THE SPECIAL NATURE OF WOLF-RAYET STAR WINDS

Energy Technology Data Exchange (ETDEWEB)

Oskinova, L. M.; Hamann, W.-R. [Institute for Physics and Astronomy, University Potsdam, 14476 Potsdam (Germany); Gayley, K. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245 (United States); Huenemoerder, D. P. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 70 Vassar St., Cambridge, MA 02139 (United States); Ignace, R. [Department of Physics and Astronomy, East Tennessee State University, Johnson City, TN 37663 (United States); Pollock, A. M. T., E-mail: lida@astro.physik.uni-potsdam.de [European Space Agency XMM-Newton Science Operations Centre, European Space Astronomy Centre, Apartado 78, Villanueva de la Canada, 28691 Madrid (Spain)

2012-03-10

We present the first high-resolution X-ray spectrum of a putatively single Wolf-Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, 'cool' stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at Almost-Equal-To 6.4 keV. The presence of fluorescence is consistent with a two-component medium, where the cool wind is permeated with the hot X-ray emitting plasma. The wind must have a very porous structure to allow the observed amount of X-rays to escape. We find that neither the LDI nor any alternative binary scenario can explain the data. We suggest a scenario where X-rays are produced when the fast wind rams into slow 'sticky clumps' that resist acceleration. Our new data show that the X-rays in single WR star are generated by some special mechanism different from the one operating in the O-star winds.

Probing the clumpy winds of giant stars with high mass X-ray binaries

Science.gov (United States)

Grinberg, Victoria; Hell, Natalie; Hirsch, Maria; Garcia, Javier; Huenemoerder, David; Leutenegger, Maurice A.; Nowak, Michael; Pottschmidt, Katja; Schulz, Norbert S.; Sundqvists, Jon O.; Townsend, Richard D.; Wilms, Joern

2016-04-01

Line-driven winds from early type stars are structured, with small, overdense clumps embedded in tenuous hot gas. High mass X-ray binaries (HMXBs), systems where a neutron star or a black hole accretes from the line-driven stellar wind of an O/B-type companion, are ideal for studying such winds: the wind drives the accretion onto the compact object and thus the X-ray production. The radiation from close to the compact object is quasi-pointlike and effectively X-rays the wind.We used RXTE and Chandra-HETG observations of two of the brightest HMXBs, Cyg X-1 and Vela X-1, to decipher their wind structure. In Cyg X-1, we show that the orbital variability of absorption can be only explained by a clumpy wind model and constrain the porosity of the wind as well as the onion-like structure of the clumps. In Vela X-1 we show, using the newest reference energies for low ionization Si-lines obtained with LLNL’s EBIT-I, that the ionized phase of the circumstellar medium and the cold clumps have different velocities.

He 2-104 - A symbiotic proto-planetary nebula?

International Nuclear Information System (INIS)

Schwarz, H.E.; Aspin, C.; Lutz, J.H.

1989-01-01

CCD observations are presented for He 2-104, an object previously classified as both PN and symbiotic star, which show that this is in fact a protoplanetary nebula (PPN) with a dynamical age of about 800 yr. The presence of highly collimated jets, extending over 75 arcsec on the sky, combined with an energy distribution showing a hot as well as a cool component, indicates that He 2-104 is a binary PPN. Since the primary is probably a Mira with a 400-d period (as reported by Whitelock, 1988), it is proposed that the system is a symbiotic PPN. 16 refs

Relativistic MHD modeling of magnetized neutron stars, pulsar winds, and their nebulae

Science.gov (United States)

Del Zanna, L.; Pili, A. G.; Olmi, B.; Bucciantini, N.; Amato, E.

2018-01-01

Neutron stars are among the most fascinating astrophysical sources, being characterized by strong gravity, densities about the nuclear one or even above, and huge magnetic fields. Their observational signatures can be extremely diverse across the electromagnetic spectrum, ranging from the periodic and low-frequency signals of radio pulsars, up to the abrupt high-energy gamma-ray flares of magnetars, where energies of ∼ {10}46 {erg} are released in a few seconds. Fast-rotating and highly magnetized neutron stars are expected to launch powerful relativistic winds, whose interaction with the supernova remnants gives rise to the non-thermal emission of pulsar wind nebulae, which are known cosmic accelerators of electrons and positrons up to PeV energies. In the extreme cases of proto-magnetars (magnetic fields of ∼ {10}15 G and millisecond periods), a similar mechanism is likely to provide a viable engine for the still mysterious gamma-ray bursts. The key ingredient in all these spectacular manifestations of neutron stars is the presence of strong magnetic fields in their constituent plasma. Here we will present recent updates of a couple of state-of-the-art numerical investigations by the high-energy astrophysics group in Arcetri: a comprehensive modeling of the steady-state axisymmetric structure of rotating magnetized neutron stars in general relativity, and dynamical 3D MHD simulations of relativistic pulsar winds and their associated nebulae.

First Resolved Images of the Mira AB Symbiotic Binary at Centimeter Wavelengths

OpenAIRE

Matthews, Lynn D.; Karovska, Margarita

2005-01-01

We report the first spatially resolved radio continuum measurements of the Mira AB symbiotic binary system, based on observations obtained with the Very Large Array (VLA). This is the first time that a symbiotic binary has been resolved unambiguously at centimeter wavelengths. We describe the results of VLA monitoring of both stars over a ten month period, together with constraints on their individual spectral energy distributions, variability, and radio emission mechanisms. The emission from...

Symbiotic binaries. Part 1. Spectrophotometry of AX Persei

International Nuclear Information System (INIS)

Mikolajewska, J.; Iijima, T.

1987-01-01

Secular and eclipse variations of optical emission lines during almost three orbital cycles of the symbiotic star AX Per are presented. The permitted lines show pronounced but nontotal eclipse effects while forbidden lines (i.e. [O3], [Ne3], [Fe7]) do not show such effects. The data are discussed in terms of physical conditions and geometry of the line formation region. The possible presence of the reflection of a hot star light from a red-giant companion is considered. 37 refs., 2 figs., 1 tab. (author)

Dynamics of Mass Transfer in Wide Symbiotic Systems

Science.gov (United States)

de Val-Borro, Miguel; Karovska, M.; Sasselov, D.

2010-01-01

We investigate the formation of accretion disks around the secondary in detached systems consisting of an Asymptotic Giant Branch (AGB) star and a compact accreting companion as a function of mass loss rate and orbital parameters. In particular, we study winds from late-type stars that are gravitationally focused by a companion in a wide binary system using hydrodynamical simulations. For a typical slow and massive wind from an evolved star there is a stream flow between the stars with accretion rates of a few percent of the mass loss from the primary. Mass transfer through a focused wind is an important mechanism for a broad range of interacting binary systems and can explain the formation of Barium stars and other chemically peculiar stars.

Request for regular monitoring of the symbiotic variable RT Cru

Science.gov (United States)

Waagen, Elizabeth O.

2014-08-01

Dr. Margarita Karovska (Harvard-Smithsonian Center for Astrophysics) and colleagues have requested AAVSO observer assistance in their campaign on the symbiotic variable RT Cru (member of a new class of hard X-ray emitting symbiotic binaries). Weekly or more frequent monitoring (B, V, and visual) beginning now is requested in support of upcoming Chandra observations still to be scheduled. "We plan Chandra observations of RT Cru in the near future that will help us understand the characteristics of the accretion onto the white dwarf in this sub-class of symbiotics. This is an important step for determining the precursor conditions for formation of a fraction of asymmetric Planetary Nebulae, and the potential of symbiotic systems as progenitors of at least a fraction of Type Ia supernovae." Finder charts with sequence may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details and observations.

Discovery of radio emission from the symbiotic X-ray binary system GX 1+4

Science.gov (United States)

van den Eijnden, J.; Degenaar, N.; Russell, T. D.; Miller-Jones, J. C. A.; Wijnands, R.; Miller, J. M.; King, A. L.; Rupen, M. P.

2018-02-01

We report the discovery of radio emission from the accreting X-ray pulsar and symbiotic X-ray binary GX 1+4 with the Karl G. Jansky Very Large Array. This is the first radio detection of such a system, wherein a strongly magnetized neutron star accretes from the stellar wind of an M-type giant companion. We measure a 9 GHz radio flux density of 105.3 ± 7.3 μJy, but cannot place meaningful constraints on the spectral index due to a limited frequency range. We consider several emission mechanisms that could be responsible for the observed radio source. We conclude that the observed properties are consistent with shocks in the interaction of the accretion flow with the magnetosphere, a synchrotron-emitting jet, or a propeller-driven outflow. The stellar wind from the companion is unlikely to be the origin of the radio emission. If the detected radio emission originates from a jet, it would show that strong magnetic fields (≥1012 G) do not necessarily suppress jet formation.

The emerging planetary nebula CRL 618 and its unsettled central star(s)

Energy Technology Data Exchange (ETDEWEB)

Balick, B. [Department of Astronomy, University of Washington, Seattle, WA 98195-1580 (United States); Riera, A. [Departament de Física I Enginyeria Nuclear, EUETIB, Universitat Politècnica de Catalunya, Comte d' Urgell 187, E-08036 Barcelona (Spain); Raga, A.; Velázquez, P. F. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 D.F. (Mexico); Kwitter, K. B., E-mail: balick@uw.edu, E-mail: angels.riera@upc.edu, E-mail: raga@nucleares.unam.mx, E-mail: pablo@nucleares.unam.mx, E-mail: kkwitter@williams.edu [Department of Astronomy, Williams College, Williamstown, MA 01267 (United States)

2014-11-01

We report deep long-slit emission-line spectra, the line flux ratios, and Doppler profile shapes of various bright optical lines. The low-ionization lines (primarily [N I], [O I], [S II], and [N II]) originate in shocked knots, as reported by many previous observers. Dust-scattered lines of higher ionization are seen throughout the lobes but do not peak in the knots. Our analysis of these line profiles and the readily discernible stellar continuum shows that (1) the central star is an active symbiotic (whose spectrum resembles the central stars of highly bipolar and young planetary nebulae such as M2-9 and Hen2-437) whose compact companion shows a WC8-type spectrum, (2) extended nebular lines of [O III] and He I originate in the heavily obscured nuclear H II region, and (3) the Balmer lines observed throughout the lobes are dominated by reflected Hα emission from the symbiotic star. Comparing our line ratios with those observed historically shows that (1) the [O III]/Hβ and He I/Hβ ratios have been steadily rising by large amounts throughout the nebula, (2) the Hα/Hβ ratio is steadily decreasing while Hγ/Hβ remains nearly constant, and (3) the low-ionization line ratios formed in the shocked knots have been in decline in different ways at various locations. We show that the first two of these results might be expected if the symbiotic central star has been active and if its bright Hα line has faded significantly in the past 20 years.

VLTI-AMBER Velocity-Resolved Aperture-Synthesis Imaging of Eta Carinae with a Spectral Resolution of 12 000: Studies of the Primary Star Wind and Innermost Wind-Wind Collision Zone

Science.gov (United States)

Weigelt, G.; Hofmann, K.-H.; Schertl, D.; Clementel, N.; Corcoran, M. F.; Damineli, A.; de Wit, W.-J.; Grellmann, R.; Groh, J.; Guieu, S.;

Accretion from a clumpy massive-star wind in supergiant X-ray binaries

Science.gov (United States)

El Mellah, I.; Sundqvist, J. O.; Keppens, R.

2018-04-01

Supergiant X-ray binaries (SgXB) host a compact object, often a neutron star (NS), orbiting an evolved O/B star. Mass transfer proceeds through the intense line-driven wind of the stellar donor, a fraction of which is captured by the gravitational field of the NS. The subsequent accretion process on to the NS is responsible for the abundant X-ray emission from SgXB. They also display peak-to-peak variability of the X-ray flux by a factor of a few 10-100, along with changes in the hardness ratios possibly due to varying absorption along the line of sight. We use recent radiation-hydrodynamic simulations of inhomogeneities (a.k.a. clumps) in the non-stationary wind of massive hot stars to evaluate their impact on the time-variable accretion process. For this, we run 3D hydrodynamic simulations of the wind in the vicinity of the accretor to investigate the formation of the bow shock and follow the inhomogeneous flow over several spatial orders of magnitude, down to the NS magnetosphere. In particular, we show that the impact of the wind clumps on the time variability of the intrinsic mass accretion rate is severely tempered by the crossing of the shock, compared to the purely ballistic Bondi-Hoyle-Lyttleton estimation. We also account for the variable absorption due to clumps passing by the line of sight and estimate the final effective variability of the column density and mass accretion rate for different orbital separations. Finally, we compare our results to the most recent analysis of the X-ray flux and the hardness ratio in Vela X-1.

Spectroscopic observations of V443 Herculis - A symbiotic binary with a low mass white dwarf

Science.gov (United States)

Dobrzycka, Danuta; Kenyon, Scott J.; Mikolajewska, Joanna

1993-01-01

We present an analysis of new and existing photometric and spectroscopic observations of the symbiotic binary V443 Herculis. This binary system consists of a normal M5 giant and a hot compact star. These two objects have comparable luminosities: about 1500 solar for the M5 giant and about 1000 solar for the compact star. We identify three nebular regions in this binary: a small, highly ionized volume surrounding the hot component, a modestly ionized shell close to the red giant photosphere, and a less dense region of intermediate ionization encompassing both binary components. The system parameters for V443 Her suggest the hot component currently declines from a symbiotic nova eruption.

The Local ISM and its Interaction with the Winds of Nearby Late-type Stars

Science.gov (United States)

Wood, Brian E.; Linsky, Jeffrey L.

1998-01-01

We present new Goddard High-Resolution Spectrograph (GHRS) observations of the Ly-alpha and Mg II absorption lines seen toward the nearby stars 61 Cyg A and 40 Eri A. We use these data to measure interstellar properties along these lines of sight and to search for evidence of circumstellar hydrogen walls, which are produced by collisions between the stellar winds and the Local InterStellar Medium (LISM). We were able to model the Ly-alpha lines of both stars without hydrogen-wall absorption components, but for 61 Cyg A the fit required a stellar Ly-alpha, line profile with an improbably deep self-reversal, and for 40 Eri A the fit required a very low deuterium-to-hydrogen ratio that is inconsistent with previous GHRS measurements. Since these problems could be rectified simply by including stellar hydrogen-wall components with reasonable attributes, our preferred fits to the data include these components. We have explored several ways in which the hydrogen-wall properties measured here and in previous work can be used to study stellar winds and the LISM. We argue that the existence of a hydrogen wall around 40 Eri A and a low H I column density along that line of sight imply that either the interstellar density must decrease toward 40 Eri A or the hydrogen ionization fraction (chi) must increase. We find that hydrogen-wall temperatures are larger for stars with faster velocities through the LISM. The observed temperature-velocity relation is consistent with the predictions of hydromagnetic shock jump conditions. More precise comparison of the data and the jump conditions suggests crude upper limits for both chi and the ratio of magnetic to thermal pressure in the LISM (alpha): chi less than 0.6 and alpha less than 2. The latter upper limit corresponds to a limit on the LISM magnetic field of B less than 5 micro G. These results imply that the plasma Mach number of the interstellar wind flowing into the heliosphere is M(sub A) greater than 1.3, which indicates that

A combined HST and XMM-Newton campaign for the magnetic O9.7 V star HD 54879. Constraining the weak-wind problem of massive stars

Science.gov (United States)

Shenar, T.; Oskinova, L. M.; Järvinen, S. P.; Luckas, P.; Hainich, R.; Todt, H.; Hubrig, S.; Sander, A. A. C.; Ilyin, I.; Hamann, W.-R.

2017-10-01

Context. HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized atmospheric magnetic field has been detected. Despite their importance, little is known about the winds and evolution of magnetized massive stars. Aims: To gain insights into the interplay between atmospheres, winds, and magnetic fields of massive stars, we acquired UV and X-ray data of HD 54879 using the Hubble Space Telescope and the XMM-Newton satellite. In addition, 35 optical amateur spectra were secured to study the variability of HD 54879. Methods: A multiwavelength (X-ray to optical) spectral analysis is performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code and the xspec software. Results: The photospheric parameters (T∗ = 30.5 kK, log g = 4.0 [cm s-2], log L = 4.45 [L⊙]) are typical for an O9.7 V star. The microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (ξph,vmac,vsini ≤ 4 km s-1). An initial mass of 16 M⊙ and an age of 5 Myr are inferred from evolutionary tracks. We derive a mean X-ray emitting temperature of log TX = 6.7 [K] and an X-ray luminosity of LX = 1 × 1032 erg s-1. Short- and long-scale variability is seen in the Hα line, but only a very long period of P ≈ 5 yr could be estimated. Assessing the circumstellar density of HD 54879 using UV spectra, we can roughly estimate the mass-loss rate HD 54879 would have in the absence of a magnetic field as log ṀB = 0 ≈ -9.0 [M⊙ yr-1]. The magnetic field traps the stellar wind up to the Alfvén radius rA ≳ 12 R∗, implying that its true mass-loss rate is log Ṁ ≲ -10.2 [M⊙ yr-1]. Hence, density enhancements around magnetic stars can be exploited to estimate mass-loss rates of non-magnetic stars of similar spectral types, essential for resolving the weak wind problem. Conclusions: Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence

A Composite Light Curve Model of the Symbiotic Nova PU Vul (1979

Directory of Open Access Journals (Sweden)

Kato M.

2012-06-01

Full Text Available PU Vul (1979 is a symbiotic nova that shows a long-lasting flat optical peak followed by a slow decline. We made a quasi-evolution model for outbursts on a 0.6 M⊙ white dwarf consisting of a series of static solutions with optically-thin winds. Our theoretical models reproduce well the observed visual/UV light curves as well as the new estimates of the temperature and radius of the hot component. We also modeled the light curve of the 1980 and 1994 eclipses as the total eclipse occulted by a pulsating M-giant companion star. In the second eclipse, the visual magnitude is dominated by nebular emission which is possibly ejected from the hot component between 1990 to 2000. We have quantitatively estimated three components of emission, i.e., the white dwarf, companion and nebular, and made a composite light curve that represents well the evolution of the PU Vul outburst.

AN X-RAY AND OPTICAL LIGHT CURVE MODEL OF THE ECLIPSING SYMBIOTIC BINARY SMC3

International Nuclear Information System (INIS)

Kato, Mariko; Hachisu, Izumi; Mikołajewska, Joanna

2013-01-01

Some binary evolution scenarios for Type Ia supernovae (SNe Ia) include long-period binaries that evolve to symbiotic supersoft X-ray sources in their late stage of evolution. However, symbiotic stars with steady hydrogen burning on the white dwarf's (WD) surface are very rare, and the X-ray characteristics are not well known. SMC3 is one such rare example and a key object for understanding the evolution of symbiotic stars to SNe Ia. SMC3 is an eclipsing symbiotic binary, consisting of a massive WD and red giant (RG), with an orbital period of 4.5 years in the Small Magellanic Cloud. The long-term V light curve variations are reproduced as orbital variations in the irradiated RG, whose atmosphere fills its Roche lobe, thus supporting the idea that the RG supplies matter to the WD at rates high enough to maintain steady hydrogen burning on the WD. We also present an eclipse model in which an X-ray-emitting region around the WD is almost totally occulted by the RG swelling over the Roche lobe on the trailing side, although it is always partly obscured by a long spiral tail of neutral hydrogen surrounding the binary in the orbital plane.

Effect of rotational mixing and metallicity on the hot star wind mass-loss rates

Czech Academy of Sciences Publication Activity Database

Krtička, J.; Kubát, Jiří

2014-01-01

Roč. 567, July (2014), A63/1-A63/7 ISSN 0004-6361 R&D Projects: GA ČR GA13-10589S Grant - others:GA MŠk(CZ) LM2010005 Institutional support: RVO:67985815 Keywords : stars: winds * outflows * stars: mass-loss Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

High-entropy ejections from magnetized proto-neutron star winds: implications for heavy element nucleosynthesis

Science.gov (United States)

Thompson, Todd A.; ud-Doula, Asif

2018-06-01

Although initially thought to be promising for production of the r-process nuclei, standard models of neutrino-heated winds from proto-neutron stars (PNSs) do not reach the requisite neutron-to-seed ratio for production of the lanthanides and actinides. However, the abundance distribution created by the r-, rp-, or νp-processes in PNS winds depends sensitively on the entropy and dynamical expansion time-scale of the flow, which may be strongly affected by high magnetic fields. Here, we present results from magnetohydrodynamic simulations of non-rotating neutrino-heated PNS winds with strong dipole magnetic fields from 1014 to 1016 G, and assess their role in altering the conditions for nucleosynthesis. The strong field forms a closed zone and helmet streamer configuration at the equator, with episodic dynamical mass ejections in toroidal plasmoids. We find dramatically enhanced entropy in these regions and conditions favourable for third-peak r-process nucleosynthesis if the wind is neutron-rich. If instead the wind is proton-rich, the conditions will affect the abundances from the νp-process. We quantify the distribution of ejected matter in entropy and dynamical expansion time-scale, and the critical magnetic field strength required to affect the entropy. For B ≳1015 G, we find that ≳10-6 M⊙ and up to ˜10-5 M⊙ of high-entropy material is ejected per highly magnetized neutron star birth in the wind phase, providing a mechanism for prompt heavy element enrichment of the universe. Former binary companions identified within (magnetar-hosting) supernova remnants, the remnants themselves, and runaway stars may exhibit overabundances. We provide a comparison with a semi-analytic model of plasmoid eruption and discuss implications and extensions.

IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

Science.gov (United States)

Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

2017-04-01

We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

FIRST INVESTIGATION OF THE COMBINED IMPACT OF IONIZING RADIATION AND MOMENTUM WINDS FROM A MASSIVE STAR ON A SELF-GRAVITATING CORE

International Nuclear Information System (INIS)

Ngoumou, Judith; Hubber, David; Dale, James E.; Burkert, Andreas

2015-01-01

Massive stars shape the surrounding interstellar matter (ISM) by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum-conserving wind scheme in the smoothed particle hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self-gravitating sphere shows that on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing ultraviolet (UV) radiation, we find the momentum-driven wind to have little direct effect on the gas. We conclude that during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas

ON THE LAUNCHING AND STRUCTURE OF RADIATIVELY DRIVEN WINDS IN WOLF–RAYET STARS

Energy Technology Data Exchange (ETDEWEB)

Ro, Stephen; Matzner, Christopher D., E-mail: ro@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)

2016-04-20

Hydrostatic models of Wolf–Rayet (WR) stars typically contain low-density outer envelopes that inflate the stellar radii by a factor of several and are capped by a denser shell of gas. Inflated envelopes and density inversions are hallmarks of envelopes that become super-Eddington as they cross the iron-group opacity peak, but these features disappear when mass loss is sufficiently rapid. We re-examine the structures of steady, spherically symmetric wind solutions that cross a sonic point at high optical depth, identifying the physical mechanism through which the outflow affects the stellar structure, and provide an improved analytical estimate for the critical mass-loss rate above which extended structures are erased. Weak-flow solutions below this limit resemble hydrostatic stars even in supersonic zones; however, we infer that these fail to successfully launch optically thick winds. WR envelopes will therefore likely correspond to the strong, compact solutions. We also find that wind solutions with negligible gas pressure are stably stratified at and below the sonic point. This implies that convection is not the source of variability in WR stars, as has been suggested; however, acoustic instabilities provide an alternative explanation. Our solutions are limited to high optical depths by our neglect of Doppler enhancements to the opacity, and do not account for acoustic instabilities at high Eddington factors; yet, they do provide useful insights into WR stellar structures.

O stars and Wolf-Rayet stars

International Nuclear Information System (INIS)

Conti, P.S.; Underhill, A.B.; Jordan, S.; Thomas, R.

1988-01-01

Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented

O stars and Wolf-Rayet stars

Science.gov (United States)

Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

1988-01-01

Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

Suppressing star formation in quiescent galaxies with supermassive black hole winds.

Science.gov (United States)

Cheung, Edmond; Bundy, Kevin; Cappellari, Michele; Peirani, Sébastien; Rujopakarn, Wiphu; Westfall, Kyle; Yan, Renbin; Bershady, Matthew; Greene, Jenny E; Heckman, Timothy M; Drory, Niv; Law, David R; Masters, Karen L; Thomas, Daniel; Wake, David A; Weijmans, Anne-Marie; Rubin, Kate; Belfiore, Francesco; Vulcani, Benedetta; Chen, Yan-mei; Zhang, Kai; Gelfand, Joseph D; Bizyaev, Dmitry; Roman-Lopes, A; Schneider, Donald P

2016-05-26

Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 10(10) times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1-4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 10(10) times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy's low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

Influence of X-ray radiation on the hot star wind ionization state and on the radiative force

Czech Academy of Sciences Publication Activity Database

Krtička, J.; Kubát, Jiří

2016-01-01

Roč. 58, č. 5 (2016), s. 710-718 ISSN 0273-1177 Institutional support: RVO:67985815 Keywords : Stars * winds * early-type stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.401, year: 2016

Curtain-Lifting Winds Allow Rare Glimpse into Massive Star Factory

Science.gov (United States)

2003-06-01

Formation of Exceedingly Luminous and Hot Stars in Young Stellar Cluster Observed Directly Summary Based on a vast observational effort with different telescopes and instruments, ESO-astronomer Dieter Nürnberger has obtained a first glimpse of the very first stages in the formation of heavy stars. These critical phases of stellar evolution are normally hidden from the view, because massive protostars are deeply embedded in their native clouds of dust and gas, impenetrable barriers to observations at all but the longest wavelengths. In particular, no visual or infrared observations have yet "caught" nascent heavy stars in the act and little is therefore known so far about the related processes. Profiting from the cloud-ripping effect of strong stellar winds from adjacent, hot stars in a young stellar cluster at the center of the NGC 3603 complex, several objects located near a giant molecular cloud were found to be bona-fide massive protostars, only about 100,000 years old and still growing. Three of these objects, designated IRS 9A-C, could be studied in more detail. They are very luminous (IRS 9A is about 100,000 times intrinsically brighter than the Sun), massive (more than 10 times the mass of the Sun) and hot (about 20,000 degrees). They are surrounded by relative cold dust (about 0°C), probably partly arranged in disks around these very young objects. Two possible scenarios for the formation of massive stars are currently proposed, by accretion of large amounts of circumstellar material or by collision (coalescence) of protostars of intermediate masses. The new observations favour accretion, i.e. the same process that is active during the formation of stars of smaller masses. PR Photo 16a/03: Stellar cluster and star-forming region NGC 3603. PR Photo 16b/03: Region near very young, massive stars IRS 9A-C in NGC 3603 (8 bands from J to Q). How do massive stars form? This question is easy to pose, but so far very difficult to answer. In fact, the processes

Mining the HST "Advanced Spectral Library (ASTRAL)": The Evolution of Winds from non-coronal to hybrid giant stars

Science.gov (United States)

Nielsen, Krister E.; Carpenter, Ken G.; Kober, Gladys V.; Rau, Gioia

2018-01-01

The HST/STIS treasury program ASTRAL enables investigations of the character and dynamics of the wind and chromosphere of cool stars, using high quality spectral data. This paper shows how the wind features change with spectral class by comparing the non-coronal objects (Alpha Ori, Gamma Cru) with the hybrid stars (Gamma Dra, Beta Gem). In particular we study the intrinsic strength variation of the numerous FeII profiles observed in the near-ultraviolet HST spectrum that are sensitive to the wind opacity, turbulence and flow velocity. The FeII relative emission strength and wavelengths shifts between the absorption and emission components reflects the acceleration of the wind from the base of the chromosphere. We present the analysis of the outflowing wind characteristics when transitioning from the cool non-coronal objects toward the warmer objects with chromospheric emission from significantly hotter environments.

Details of the Classification of Symbiotic Stars: The Case of the Symbiotic Nova AG Peg

Directory of Open Access Journals (Sweden)

Tatarnikova A. A.

2016-09-01

Full Text Available We analyze archival and modern spectroscopic and photometric observations of the oldest known symbiotic nova AG Peg. Its new outburst (which began in 2015 June differs greatly from the first one (which occurred in the mid-1850s. Fast photometric evolution of the new outburst is similar to that of Z And-type outbursts. However, the SED of AG Peg during the 2015 outburst, as well as during the quiescence, can be fitted by a standard three-component model (cool component + hot component + nebula, which is not common for an Z And-type outburst.

The origin of carbon revisited: winds of carbon-stars

International Nuclear Information System (INIS)

Mattsson, L

2008-01-01

Chemical evolution models, differing in the nucleosynthesis prescriptions (yields) for carbon, nitrogen and oxygen, have been computed for the Milky Way and Andromeda (NGC 224). All models fit the observed O/H gradients well and reproduce the main characteristics of the gas distributions, but they are also designed to do so. The N/O gradient for NGC 224 cannot be reproduced without ad hoc modifications to the yields and a similar result is obtained for the Milky Way N/O gradient, although in the latter case the slopes of the gradients obtained with unmodified yields are consistent with the observed gradient. For the C/O gradients (obtained from B stars) the results are inconclusive. The C/Fe, N/Fe, O/Fe versus Fe/H, as well as C/O versus O/H trends predicted by the models for the solar neighbourhood were compared with stellar abundances from the literature. For O/Fe versus Fe/H, all models fit the data, but for C/Fe, N/Fe versus Fe/H and C/O versus O/H, only modified sets of yields provide good fits. Since in the best-fit model, the yields were modified such that carbon should be primarily produced in low-mass stars, it is quite possible that in every environment where the peak of star formation happened a few Gyr back in time, the winds of carbon stars are responsible for most of the carbon enrichment, although models with a significant contribution from high-mass stars cannot be ruled out. In the solar neighbourhood, almost two-thirds of the carbon in the interstellar medium may come from carbon stars. Finally, the challenges met by stellar evolution and nucleosynthesis modelling due to this 'carbon star hypothesis' for the origin of carbon are discussed. It is suggested that a mass-loss prescription where the mass-loss rate depends on the carbon excess may act as a self-regulating mechanism for how much carbon a carbon star can deliver to the interstellar medium.

Atomic Physics of Shocked Plasma in Winds of Massive Stars

Science.gov (United States)

Leutenegger, Maurice A.; Cohen, David H.; Owocki, Stanley P.

2012-01-01

High resolution diffraction grating spectra of X-ray emission from massive stars obtained with Chandra and XMM-Newton have revolutionized our understanding of their powerful, radiation-driven winds. Emission line shapes and line ratios provide diagnostics on a number of key wind parameters. Modeling of resolved emission line velocity profiles allows us to derive independent constraints on stellar mass-loss rates, leading to downward revisions of a factor of a few from previous measurements. Line ratios in He-like ions strongly constrain the spatial distribution of Xray emitting plasma, confirming the expectations of radiation hydrodynamic simulations that X-ray emission begins moderately close to the stellar surface and extends throughout the wind. Some outstanding questions remain, including the possibility of large optical depths in resonance lines, which is hinted at by differences in line shapes of resonance and intercombination lines from the same ion. Resonance scattering leads to nontrivial radiative transfer effects, and modeling it allows us to place constraints on shock size, density, and velocity structure

Planetary nebulae and Wolf-Rayet stars in the galactic-centre field

Energy Technology Data Exchange (ETDEWEB)

Allen, D A [Anglo-Australian Observatory, Epping (Australia)

1979-06-01

A UK Schmidt objective-prism plate of the Galactic-centre field has been examined. Of the 74 objects in the field which have been catalogued as planetary nebulae, only half appear correctly classified; the others include Be stars, symbiotic stars, and stars without emission lines. A further 19 planetary nebulae and two Wolf-Rayet stars have been discovered.

O Star Wind Mass-Loss Rates and Shock Physics from X-ray Line Profiles in Archival XMM RGS Data

Science.gov (United States)

Cohen, David

O stars are characterized by their dense, supersonic stellar winds. These winds are the site of X-ray emission from shock-heated plasma. By analyzing high-resolution X-ray spectra of these O stars, we can learn about the wind-shock heating and X-ray production mechanism. But in addition, the X-rays can also be used to measure the mass-loss rate of the stellar wind, which is a key observational quantity whose value affects stellar evolution and energy, momentum, and mass input to the Galactic interstellar medium. We make this X-ray based mass-loss measurement by analyzing the profile shapes of the X-ray emission lines observed at high resolution with the Chandra and XMM-Newton grating spectrometers. One advantage of our method is that it is insensitive to small-scale clumping that affects density-squared diagnostics. We are applying this analysis technique to O stars in the Chandra archive, and are finding mass-loss rates lower than those traditionally assumed for these O stars, and in line with more recent independent determinations that do account for clumping. By extending this analysis to the XMM RGS data archive, we will make significant contributions to the understanding of both X-ray production in O stars and to addressing the issue of the actual mass-loss rates of O stars. The XMM RGS data archive provides several extensions and advantages over the smaller Chandra HETGS archive: (1) there are roughly twice as many O and early B stars in the XMM archive; (2) the longer wavelength response of the RGS provides access to diagnostically important lines of nitrogen and carbon; (3) the very long, multiple exposures of zeta Pup provide the opportunity to study this canonical O supergiant's X-ray spectrum in unprecedented detail, including looking at the time variability of X-ray line profiles. Our research team has developed a sophisticated empirical line profile model as well as a computational infrastructure for fitting the model to high-resolution X-ray spectra

Symbiotic nature of the object M1-77

International Nuclear Information System (INIS)

Kondrt'eva, L.N.

2004-01-01

Many year spectral observations show, that the object M1-77 is the symbiotic system, which consists of a M-giant and a B-star. An emission spectra arises from an envelope, which was formed from a giant's extended atmosphere, and now is ionized by the hotter component. Some spectral changes were registered in M1-77: the forbidden lines intensities increase relatively to that of Hα. It is connected with the decrease of hydrogen emission. (author)

Simultaneous Chandra/Swift Observations of the RT Cru Symbiotic System

Science.gov (United States)

Kashyap, Vinay; Kennea, J. A.; Karovska, M.; Calibration, Chandra

2013-04-01

The symbiotic star RT Cru was observed simultaneously by the Chandra/HRC-I and Swift/XRT in Dec 2012. The observations were carried out as part of a program to calibrate the Chandra PSF. The Chandra light curve shows a number of brightenings by factors of 2, with strong indications of a softening of the spectrum at these times. Swift observations cover a brief part of the Chandra light curve, and the intensities over this duration are tightly correlated. The Swift spectral data confirm the anticorrelation between intensity and spectral hardness. However, there are differences in the correlations at different periods that are not understood. We report on our analysis of the data, with emphasis on the spectral modeling at different times and intensity levels, and discuss the implications of the results on the emission mechanisms on symbiotic stars. We also report our inferences on the structure and energy dependence of the Chandra PSF anomaly, and on the high-energy cross-calibration between the HRC-I and XRT. This work is supported by the NASA contract NAS8-03060 to the Chandra X-ray Center.

On planetary nebulae and Wolf-Rayet stars in the galactic-centre field

International Nuclear Information System (INIS)

Allen, D.A.

1979-01-01

A UK Schmidt objective-prism plate of the Galactic-centre field has been examined. Of the 74 objects in the field which have been catalogued as planetary nebulae, only half appear correctly classified; the others include Be stars, symbiotic stars, and stars without emission lines. A further 19 planetary nebulae and two Wolf-Rayet stars have been discovered. (author)

HUBBLE SPACE TELESCOPE CONSTRAINTS ON THE WINDS AND ASTROSPHERES OF RED GIANT STARS

Energy Technology Data Exchange (ETDEWEB)

Wood, Brian E. [Naval Research Laboratory, Space Science Division, Washington, DC 20375 (United States); Müller, Hans-Reinhard [Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States); Harper, Graham M., E-mail: brian.wood@nrl.navy.mil [CASA, University of Colorado, Boulder, CO 80309-0389 (United States)

2016-10-01

We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope , focusing on spectra of the Mg ii h and k lines near 2800 Å in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg ii surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities ( V {sub w} ) are generally found to decrease with spectral type, with V {sub w} decreasing from ∼40 km s{sup −1} at K2 III to ∼20 km s{sup −1} at M5 III. We find two new detections of astrospheric absorption, for σ Pup (K5 III) and γ Eri (M1 III). This absorption signature had previously only been detected for α Tau (K5 III). For the three astrospheric detections, the temperature of the wind after the termination shock (TS) correlates with V {sub w} , but is lower than predicted by the Rankine–Hugoniot shock jump conditions, consistent with the idea that red giant TSs are radiative shocks rather than simple hydrodynamic shocks. A full hydrodynamic simulation of the γ Eri astrosphere is provided to explore this further.

THE FORMATION OF SECONDARY STELLAR GENERATIONS IN MASSIVE YOUNG STAR CLUSTERS FROM RAPIDLY COOLING SHOCKED STELLAR WINDS

Energy Technology Data Exchange (ETDEWEB)

Wünsch, R.; Palouš, J.; Ehlerová, S. [Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401, 141 31 Prague (Czech Republic); Tenorio-Tagle, G. [Instituto Nacional de Astrofísica Optica y Electrónica, AP 51, 72000 Puebla, México (Mexico)

2017-01-20

We study a model of rapidly cooling shocked stellar winds in young massive clusters and estimate the circumstances under which secondary star formation, out of the reinserted winds from a first stellar generation (1G), is possible. We have used two implementations of the model: a highly idealized, computationally inexpensive, spherically symmetric semi-analytic model, and a complex, three-dimensional radiation-hydrodynamic, simulation; they are in a good mutual agreement. The results confirm our previous findings that, in a cluster with 1G mass 10{sup 7} M {sub ⊙} and half-mass–radius 2.38 pc, the shocked stellar winds become thermally unstable, collapse into dense gaseous structures that partially accumulate inside the cluster, self-shield against ionizing stellar radiation, and form the second generation (2G) of stars. We have used the semi-analytic model to explore a subset of the parameter space covering a wide range of the observationally poorly constrained parameters: the heating efficiency, η {sub he}, and the mass loading, η {sub ml}. The results show that the fraction of the 1G stellar winds accumulating inside the cluster can be larger than 50% if η {sub he} ≲ 10%, which is suggested by the observations. Furthermore, for low η {sub he}, the model provides a self-consistent mechanism predicting 2G stars forming only in the central zones of the cluster. Finally, we have calculated the accumulated warm gas emission in the H30 α recombination line, analyzed its velocity profile, and estimated its intensity for super star clusters in interacting galaxies NGC4038/9 (Antennae) showing that the warm gas should be detectable with ALMA.

Symbiotic Cognitive Computing

OpenAIRE

Farrell, Robert G.; Lenchner, Jonathan; Kephjart, Jeffrey O.; Webb, Alan M.; Muller, MIchael J.; Erikson, Thomas D.; Melville, David O.; Bellamy, Rachel K.E.; Gruen, Daniel M.; Connell, Jonathan H.; Soroker, Danny; Aaron, Andy; Trewin, Shari M.; Ashoori, Maryam; Ellis, Jason B.

2016-01-01

IBM Research is engaged in a research program in symbiotic cognitive computing to investigate how to embed cognitive computing in physical spaces. This article proposes 5 key principles of symbiotic cognitive computing.  We describe how these principles are applied in a particular symbiotic cognitive computing environment and in an illustrative application.  

2D hydrodynamic simulations of super star cluster winds in a bimodal regime

Czech Academy of Sciences Publication Activity Database

Wünsch, Richard; Palouš, Jan; Tenorio-Tagle, G.; Silich, S.

2009-01-01

Roč. 324, 2-4 (2009), s. 219-223 ISSN 0004-640X R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : stellar winds * star clusters * dynamics of ISM Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.404, year: 2009

REVEALING THE ASYMMETRY OF THE WIND OF THE VARIABLE WOLF-RAYET STAR WR1 (HD 4004) THROUGH SPECTROPOLARIZATION

Energy Technology Data Exchange (ETDEWEB)

St-Louis, N., E-mail: stlouis@astro.umontreal.ca [Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, C.P. 6128, Succ. Centre Ville, Montréal, QC H3C 3J7 (Canada)

2013-11-01

In this paper, high quality spectropolarimetric observations of the Wolf-Rayet (WR) star WR1 (HD 4004) obtained with ESPaDOnS at the Canada-France-Hawaii Telescope are presented. All major emission lines present in the spectrum show depolarization in the relative Stokes parameters Q/I and U/I. From the behavior of the amount of line depolarization as a function of line strength, the intrinsic continuum light polarization of WR1 is estimated to be P/I = 0.443% ± 0.028% with an angle of θ = –26.°2. Although such a level of polarization could in principle be caused by a wind flattened by fast rotation, the scenario in which it is a consequence of the presence of corotating interaction regions (CIRs) in the wind is preferred. This is supported by previous photometric and spectroscopic observations showing periodic variations with a period of 16.9 days. This is now the third WR star thought to exhibit CIRs in its wind that is found to have line depolarization. Previous authors have found a strong correlation between line depolarization and the presence of an ejected nebula, which they interpret as a sign that the star has relatively recently reached the WR phase since the nebula are thought to dissipate very fast. In cases where the presence of CIRs in the wind is favored to explain the depolarization across spectral lines, the above-mentioned correlation may indicate that those massive stars have only very recently transited from the previous evolutionary phase to the WR phase.

Classification spectra of Sanduleak and Stephenson emission-line stars

International Nuclear Information System (INIS)

Allen, D.A.

1978-01-01

Low dispersion slit spectra of 89 emission-line stars are described; these stars were originally located and classified by Sanduleak and Stephenson in an objective-prism survey. The new data broadly confirm the classification scheme adopted by Sanduleak and Stephenson. In particular most of the large number of symbiotic stars they classified have been confirmed and others found. Many of these contain strong, broad emission bands in their red spectra. Two new Wolf-Rayet stars, one new planetary nebula and two new bipolar reflection nebulae involving hidden emission-line stars have been found. (author)

Classification spectra of Sanduleak and Stephenson emission-line stars

Energy Technology Data Exchange (ETDEWEB)

Allen, D A [Anglo-Australian Observatory, Epping (Australia)

1978-09-01

Low dispersion slit spectra of 89 emission-line stars are described; these stars were originally located and classified by Sanduleak and Stephenson in an objective-prism survey. The new data broadly confirm the classification scheme adopted by Sanduleak and Stephenson. In particular most of the large number of symbiotic stars they classified have been confirmed and others found. Many of these contain strong, broad emission bands in their red spectra. Two new Wolf-Rayet stars, one new planetary nebula and two new bipolar reflection nebulae involving hidden emission-line stars have been found.

Dust around the Cool Component of D-Type Symbiotic Binaries

Science.gov (United States)

Jurkic, Tomislav; Kotnik-Karuza, Dubravka

2018-04-01

D type symbiotic binaries are an excellent astrophysical laboratory for investigation of the dust properties and dust formation under the influence of theMira stellar wind and nova activity and of the mass loss and mass transfer between components in such a widely separated system. We present a study of the properties of circumstellar dust in symbiotic Miras by use of long-term near-IR photometry and colour indices. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel, HM Sge and R Aqr have been collected, analyzed and corrected for short-term variations caused by Mira pulsations. Assuming spherical temperature distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case. Common dust properties of the symbiotic Miras have been found, suggesting similar conditions in the condensation region of the studied symbiotic Miras. Silicate dust with the inner dust shell radius determined by the dust condensation and with the dust temperature of 900-1200 K can fully explain the observed colour indices. R Aqr is an exception and showed lower dust temperature of 650 K. Obscuration events visible in light curves can be explained by variable dust optical depth with minimal variations of other dust properties. More active symbioticMiras that underwent recent nova outbursts showed higher dust optical depths and larger maximum grain sizes of the order of μm, which means that the post-nova activity could stimulate the dust formation and the grain growth. Optically thicker dust shells and higher dust condensation temperatures have been found in symbiotic Miras compared to their single counterparts, suggesting different conditions for dust production.

Numerical Simulations of Multiphase Winds and Fountains from Star-forming Galactic Disks. I. Solar Neighborhood TIGRESS Model

Science.gov (United States)

Kim, Chang-Goo; Ostriker, Eve C.

2018-02-01

Gas blown away from galactic disks by supernova (SN) feedback plays a key role in galaxy evolution. We investigate outflows utilizing the solar neighborhood model of our high-resolution, local galactic disk simulation suite, TIGRESS. In our numerical implementation, star formation and SN feedback are self-consistently treated and well resolved in the multiphase, turbulent, magnetized interstellar medium. Bursts of star formation produce spatially and temporally correlated SNe that drive strong outflows, consisting of hot (T> 5× {10}5 {{K}}) winds and warm (5050 {{K}} 1 {kpc} from the midplane has mass and energy fluxes nearly constant with d. The hot flow escapes our local Cartesian box barely affected by gravity, and is expected to accelerate up to terminal velocity of {v}{wind}∼ 350{--}500 {km} {{{s}}}-1. The mean mass and energy loading factors of the hot wind are 0.1 and 0.02, respectively. For warm gas, the mean outward mass flux through d=1 {kpc} is comparable to the mean star formation rate, but only a small fraction of this gas is at velocity > 50 {km} {{{s}}}-1. Thus, the warm outflows eventually fall back as inflows. The warm fountain flows are created by expanding hot superbubbles at d< 1 {kpc}; at larger d neither ram pressure acceleration nor cooling transfers significant momentum or energy flux from the hot wind to the warm outflow. The velocity distribution at launching near d∼ 1 {kpc} is a better representation of warm outflows than a single mass loading factor, potentially enabling development of subgrid models for warm galactic winds in arbitrary large-scale galactic potentials.

Wind estimation around the shipwreck of Oriental Star based on field damage surveys and radar observations.

Science.gov (United States)

Meng, Zhiyong; Yao, Dan; Bai, Lanqiang; Zheng, Yongguang; Xue, Ming; Zhang, Xiaoling; Zhao, Kun; Tian, Fuyou; Wang, Mingjun

Based on observational analyses and on-site ground and aerial damage surveys, this work aims to reveal the weather phenomena-especially the wind situation-when Oriental Star capsized in the Yangtze River on June 1, 2015. Results demonstrate that the cruise ship capsized when it encountered strong winds at speeds of at least 31 m s -1 near the apex of a bow echo embedded in a squall line. As suggested by the fallen trees within a 2-km radius around the wreck location, such strong winds were likely caused by microburst straight-line wind and/or embedded small vortices, rather than tornadoes.

Wind estimation around the shipwreck of Oriental Star based on field damage surveys and radar observations

OpenAIRE

Meng, Zhiyong; Yao, Dan; Bai, Lanqiang; Zheng, Yongguang; Xue, Ming; Zhang, Xiaoling; Zhao, Kun; Tian, Fuyou; Wang, Mingjun

2016-01-01

Based on observational analyses and on-site ground and aerial damage surveys, this work aims to reveal the weather phenomena?especially the wind situation?when Oriental Star capsized in the Yangtze River on June 1, 2015. Results demonstrate that the cruise ship capsized when it encountered strong winds at speeds of at least 31?m?s?1 near the apex of a bow echo embedded in a squall line. As suggested by the fallen trees within a 2-km radius around the wreck location, such strong winds were lik...

Possible evidence for the driving of the winds of hot stars by Alfven waves

International Nuclear Information System (INIS)

Underhill, A.B.

1983-01-01

Ultraviolet spectra of the supergiants α Cam (09.5 Ia), HD 105056 (ON9.7 Iae), and 15 Sgr (09.7 Lab) are compared, and it is shown that the terminal outflow velocity ν/sub infinity/, of HD 105056 is one-half that of the other two stars even though HD 105056 has the highest effective temperature of the three stars. This anomaly, together with the fact that the observed ν/sub infinity/ values for early-type stars scatter about an empirical correlation between ν/sub infinity/ and log T/sub eff/ by an amount which is larger than the amount which is larger than the amount expected according to the observational errors in determining ν/sub infinity/ and log T/sub eff/, leads to the conclusion that an agent in addition to radiation. Alfven waves, is driving the winds of early-type stars

Extraction of Uranium from Seawater: Design and Testing of a Symbiotic System

Energy Technology Data Exchange (ETDEWEB)

Slocum, Alex [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

2018-02-22

The U.S. Department of Energy in October 2014 awarded the Massachusetts Institute of Technology (MIT) a Nuclear Energy University Program grant (DE-NE0008268) to investigate the design and testing of a symbiotic system to harvest uranium from seawater. As defined in the proposal, the goals for the project are: 1. Address the design of machines for seawater uranium mining. 2. Develop design rules for a uranium harvesting system that would be integrated into an offshore wind power tower. 3. Fabricate a 1/50th size scale prototype for bench and pool-testing to verify initial analysis and theory. 4. Design, build, and test a second 1/10th size scale prototype in the ocean for more comprehensive testing and validation. This report describes work done as part of DE-NE0008268 from 10/01/2014 to 11/30/2017 entitled, “Extraction of Uranium from Seawater: Design and Testing of a Symbiotic System.” This effort is part of the Seawater Uranium Recovery Program. This report details the publications and presentations to date on the project, an introduction to the project’s goals and background research into previous work done to achieve these goals thus far. From there, the report describes an algorithm developed during the project used to optimize the adsorption of uranium by changing mechanical parameters such as immersion time and adsorbent reuses is described. Next, a design tool developed as part of the project to determine the global feasibility of symbiotic uranium harvesting systems. Additionally, the report details work done on shell enclosures for uranium adsorption. Moving on, the results from the design, building, and testing of a 1/50th physical scale prototype of a highly feasible symbiotic uranium harvester is described. Then, the report describes the results from flume experiment used to determine the affect of enclosure shells on the uptake of uranium by the adsorbent they enclose. From there the report details the design of a Symbiotic Machine for Ocean u

A new class of galactic discrete gamma ray sources: Chaotic winds of massive stars

Science.gov (United States)

Chen, Wan; White, Richard L.

1992-01-01

We propose a new class of galactic discrete gamma-ray sources, the chaotic, high mass-loss-rate winds from luminous early-type stars. Early-type stellar winds are highly unstable due to intrinsic line-driven instabilities, and so are permeated by numerous strong shocks. These shocks can accelerate a small fraction of thermal electrons and ions to relativistic energies via the first-order Fermi mechanism. A power-law-like photon spectrum extending from keV to above 10 MeV energies is produced by inverse Compton scattering of the extremely abundant stellar UV photons by the relativistic electrons. In addition, a typical pi(sup 0)-decay gamma-ray spectrum is generated by proton-ion interactions in the densest part of the winds.

Extragalactic gamma-ray background from AGN winds and star-forming galaxies in cosmological galaxy-formation models

Science.gov (United States)

Lamastra, A.; Menci, N.; Fiore, F.; Antonelli, L. A.; Colafrancesco, S.; Guetta, D.; Stamerra, A.

2017-10-01

We derive the contribution to the extragalactic gamma-ray background (EGB) from active galactic nuclei (AGN) winds and star-forming galaxies by including a physical model for the γ-ray emission produced by relativistic protons accelerated by AGN-driven and supernova-driven shocks into a state-of-the-art semi-analytic model of galaxy formation. This is based on galaxy interactions as triggers of AGN accretion and starburst activity and on expanding blast waves as the mechanism to communicate outwards the energy injected into the interstellar medium by the active nucleus. We compare the model predictions with the latest measurement of the EGB spectrum performed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) in the range between 100 MeV and 820 GeV. We find that AGN winds can provide 35 ± 15% of the observed EGB in the energy interval Eγ = 0.1-1 GeV, for 73 ± 15% at Eγ = 1-10 GeV, and for 60 ± 20% at Eγ ≳10 GeV. The AGN wind contribution to the EGB is predicted to be larger by a factor of 3-5 than that provided by star-forming galaxies (quiescent plus starburst) in the hierarchical clustering scenario. The cumulative γ-ray emission from AGN winds and blazars can account for the amplitude and spectral shape of the EGB, assuming the standard acceleration theory, and AGN wind parameters that agree with observations. We also compare the model prediction for the cumulative neutrino background from AGN winds with the most recent IceCube data. We find that for AGN winds with accelerated proton spectral index p = 2.2-2.3, and taking into account internal absorption of γ-rays, the Fermi-LAT and IceCube data could be reproduced simultaneously.

Introduction & Overview to Symposium 240: Binary Stars as Critical Tools and Tests in Contemporary Astrophysics

Science.gov (United States)

2006-01-01

neutron stars and black holes properties of condensed matter Post CE Binaries V471 Tau (K2 V + wd) Symbiotic Binaries (M III + wd) X-ray Binaries CH...low-mass stars the respect they deserve, since these stars may be the dominant contributor to baryonic mass in the Universe. Ben Lane discussed recent

The spectral energy distribution and nature of the symbiotic system AS 296 in outburst

International Nuclear Information System (INIS)

Munari, U.; Whitelock, P.A.

1989-01-01

Photometry covering the spectral range 0.36 to 5 μm is reported for the symbiotic star As 296 about two months after the onset of the first recorded nova-like outburst. Analysis of published pre-outburst photometry provides evidence for the presence of an accreting white dwarf of high luminosity. This information together with the new observations is used to eliminate, for the 1988 event, various mechanisms which have been suggested for the outbursts in symbiotic objects. It is shown that hydrogen burning of accreted material can produce the white dwarf luminosity during quiescence. The outburst is then the result of a thermonuclear runaway in the unburnt material. The evidence is somewhat conflicting on the question of degeneracy conditions prior to the thermonuclear runaway. (author)

EG Andromedae: A New Orbit and Additional Evidence for a Photoionized Wind

Science.gov (United States)

Kenyon, Scott J.; Garcia, Michael R.

2016-07-01

We analyze a roughly 20 yr set of spectroscopic observations for the symbiotic binary EG And. Radial velocities derived from echelle spectra are best fit with a circular orbit having an orbital period of P = 483.3 ± 1.6 days and semi-amplitude K = 7.34 ± 0.07 km s-1. Combined with previous data, these observations rule out an elliptical orbit at the 10σ level. Equivalent widths of H I Balmer emission lines and various absorption features vary in phase with the orbital period. Relative to the radius of the red giant primary, the apparent size of the H II region is consistent with a model where a hot secondary star with effective temperature T h ≈ 75,000 K ionizes the wind from the red giant.

New outburst of the symbiotic nova AG Pegasi after 165 yr

Science.gov (United States)

Skopal, A.; Shugarov, S. Yu.; Sekeráš, M.; Wolf, M.; Tarasova, T. N.; Teyssier, F.; Fujii, M.; Guarro, J.; Garde, O.; Graham, K.; Lester, T.; Bouttard, V.; Lemoult, T.; Sollecchia, U.; Montier, J.; Boyd, D.

2017-08-01

Context. AG Peg is known as the slowest symbiotic nova, which experienced its nova-like outburst around 1850. After 165 yr, during June of 2015, it erupted again showing characteristics of the Z And-type outburst. Aims: The primary objective is to determine basic characteristics, the nature and type of the 2015 outburst of AG Peg. Methods: We achieved this aim by modelling the spectral energy distribution using low-resolution spectroscopy (330-750 nm; R = 500-1000), medium-resolution spectroscopy (420-720 nm; R 11 000), and UBVRCIC photometry covering the 2015 outburst with a high cadence. Optical observations were complemented with the archival HST and FUSE spectra from the preceding quiescence. Results: During the outburst, the luminosity of the hot component was in the range of 2-11 × 1037 (d/ 0.8 kpc)2 erg s-1, being in correlation with the light curve (LC) profile. To generate the maximum luminosity by the hydrogen burning, the white dwarf (WD) had to accrete at 3 × 10-7 M⊙ yr-1, which exceeds the stable-burning limit and thus led to blowing optically thick wind from the WD. We determined its mass-loss rate to a few × 10-6 M⊙ yr-1. At the high temperature of the ionising source, 1.5-2.3 × 105 K, the wind converted a fraction of the WD's photospheric radiation into the nebular emission that dominated the optical. A one order of magnitude increase of the emission measure, from a few × 1059 (d/ 0.8 kpc)2 cm-3 during quiescence, to a few × 1060 (d/ 0.8 kpc)2 cm-3 during the outburst, caused a 2 mag brightening in the LC, which is classified as the Z And-type of the outburst. Conclusions: The very high nebular emission and the presence of a disk-like H I region encompassing the WD, as indicated by a significant broadening and high flux of the Raman-scattered O vi 6825 Å line during the outburst, is consistent with the ionisation structure of hot components in symbiotic stars during active phases. Full Table 1 and Table 6 are only available at the CDS are

The Symbiotic System SS73 17 seen with Suzaku

Science.gov (United States)

Smith, Randall K.; Mushotzky, Richard; Kallman, Tim; Tueller, Jack; Mukai, Koji; Markwardt, Craig

2007-01-01

We observed with Suzaku the symbiotic star SS73 17, motivated by the discovery by the INTEGRAL satellite and the Swift BAT survey that it emits hard X-rays. Our observations showed a highly-absorbed X-ray spectrum with NH > loz3 emp2, equivalent to Av > 26, although the source has B magnitude 11.3 and is also bright in UV. The source also shows strong, narrow iron lines including fluorescent Fe K as well as Fe xxv and Fe XXVI. The X-ray spectrum can be fit with a thermal model including an absorption component that partially covers the source. Most of the equivalent width of the iron fluorescent line in this model can be explained as a combination of reprocessing in a dense absorber plus reflection off a white dwarf surface, but it is likely that the continuum is partially seen in reflection as well. Unlike other symbiotic systems that show hard X-ray emission (CH Cyg, RT Cru, T CrB, GX1+4), SS73 17 is not known to have shown nova-like optical variability, X-ray flashes, or pulsations, and has always shown faint soft X-ray emission. As a result, although it is likely a white dwarf, the nature of the compact object in SS73 17 is still uncertain. SS73 17 is probably an extreme example of the recently discovered and relatively small class of hard X-ray emitting symbiotic systems.

Evolution of massive stars

International Nuclear Information System (INIS)

Loore, C. de

1984-01-01

The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

NEW X-RAY DETECTIONS OF WNL STARS

International Nuclear Information System (INIS)

Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner; Sokal, Kimberly R.

2012-01-01

Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L x ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v ∞ ). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L x with wind luminosity L wind = (1/2)M-dot v 2 ∞ , suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.

NEW X-RAY DETECTIONS OF WNL STARS

Energy Technology Data Exchange (ETDEWEB)

Skinner, Stephen L. [Center for Astrophysics and Space Astronomy (CASA), University of Colorado, Boulder, CO 80309-0389 (United States); Zhekov, Svetozar A. [Space and Solar-Terrestrial Research Institute, Moskovska str. 6, Sofia-1000 (Bulgaria); Guedel, Manuel [Department of Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Schmutz, Werner [Physikalisch-Meteorologisches Observatorium Davos (PMOD), Dorfstrasse 33, CH-7260 Davos Dorf (Switzerland); Sokal, Kimberly R., E-mail: Stephen.Skinner@colorado.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

2012-05-15

Previous studies have demonstrated that putatively single nitrogen-type Wolf-Rayet stars (WN stars) without known companions are X-ray sources. However, almost all WN star X-ray detections so far have been of earlier WN2-WN6 spectral subtypes. Later WN7-WN9 subtypes (also known as WNL stars) have proved more difficult to detect, an important exception being WR 79a (WN9ha). We present here new X-ray detections of the WNL stars WR 16 (WN8h) and WR 78 (WN7h). These new results, when combined with previous detections, demonstrate that X-ray emission is present in WN stars across the full range of spectral types, including later WNL stars. The two WN8 stars observed to date (WR 16 and WR 40) show unusually low X-ray luminosities (L{sub x} ) compared to other WN stars, and it is noteworthy that they also have the lowest terminal wind speeds (v{sub {infinity}}). Existing X-ray detections of about a dozen WN stars reveal a trend of increasing L{sub x} with wind luminosity L{sub wind} = (1/2)M-dot v{sup 2}{sub {infinity}}, suggesting that wind kinetic energy may play a key role in establishing X-ray luminosity levels in WN stars.

Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds. III. X-ray emission from wind-embedded shocks

Science.gov (United States)

Carneiro, L. P.; Puls, J.; Sundqvist, J. O.; Hoffmann, T. L.

2016-05-01

Context. Extreme ultraviolet (EUV) and X-ray radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres and can be the mechanism responsible for producing highly ionized atomic species detected in stellar wind UV spectra. Aims: To allow for these processes in the context of spectral analysis, we have implemented the emission from wind-embedded shocks and related physics into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. Methods: The shock structure and corresponding emission is calculated as a function of user-supplied parameters (volume filling factor, radial stratification of shock strength, and radial onset of emission). We account for a temperature and density stratification inside the postshock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included in the NLTE network. To test our implementation and to check the resulting effects, we calculated a comprehensive model grid with a variety of X-ray emission parameters. Results: We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of O iv/O v (particularly in dwarfs with Teff~ 45 000 K). Finally, we investigated the frequency dependence and radial behavior of the mass absorption coefficient, κν(r), which is important in the context of X-ray line formation in massive star winds. Conclusions: In almost all of the cases considered, direct ionization is of major influence because of the enhanced EUV radiation field, and Auger ionization only affects N vi

A PIONIER and Incisive Look at the Interacting Binary SS Lep

Science.gov (United States)

Blind, N.; Boffin, H. M. J.; Berger, J.-P.; Lebouquin, J.-B.; Mérand, A.

2011-09-01

Symbiotic stars are excellent laboratories to study a broad range of poorly understood physical processes, such as mass loss of red giants, accretion onto compact objects, and evolution of nova-like outbursts. As their evolution is strongly influenced by the mass transfer episodes, understanding the history of these systems requires foremost to determine which process is at play: Roche lobe overflow, stellar wind accretion, or some more complex mixture of both. We report here an interferometric study of the symbiotic system SS Leporis, performed with the unique PIONIER instrument. By determining the binary orbit and revisiting the parameters of the two stars, we show that the giant does not fill its Roche lobe, and that the mass transfer most likely occurs via the accretion of an important part of the giant's wind.

NuSTAR View of the Black Hole Wind in the Galaxy Merger IRAS F11119+3257

Science.gov (United States)

Tombesi, F.; Veilleux, S.; Meléndez, M.; Lohfink, A.; Reeves, J. N.; Piconcelli, E.; Fiore, F.; Feruglio, C.

2017-12-01

Galactic winds driven by active galactic nuclei (AGNs) have been invoked to play a fundamental role in the co-evolution between supermassive black holes and their host galaxies. Finding observational evidence of such feedback mechanisms is of crucial importance and it requires a multi-wavelength approach in order to compare winds at different scales and phases. In Tombesi et al., we reported the detection of a powerful ultra-fast outflow (UFO) in the Suzaku X-ray spectrum of the ultra-luminous infrared galaxy IRAS F11119+3257. The comparison with a galaxy-scale OH molecular outflow observed with Herschel in the same source supported the energy-conserving scenario for AGN feedback. The main objective of this work is to perform an independent check of the Suzaku results using the higher sensitivity and wider X-ray continuum coverage of NuSTAR. We clearly detect a highly ionized Fe K UFO in the 100 ks NuSTAR spectrum with parameters N H = (3.2 ± 1.5) × 1024 cm-2, log ξ = {4.0}-0.3+1.2 erg s-1 cm, and {v}{out}={0.253}-0.118+0.061c. The launching radius is likely at a distance of r ≥ 16r s from the black hole. The mass outflow rate is in the range of {\\dot{M}}{out} ≃ 0.5-2 M ⊙ yr-1. The UFO momentum rate and power are {\\dot{P}}{out} ≃ 0.5-2 L AGN/c and {\\dot{E}}{out} ≃ 7%-27% L AGN, respectively. The UFO parameters are consistent between the 2013 Suzaku and the 2015 NuSTAR observations. Only the column density is found to be variable, possibly suggesting a clumpy wind. The comparison with the energetics of molecular outflows estimated in infrared and millimeter wavelengths support a connection between the nuclear and galaxy-scale winds in luminous AGNs.

The solar wind in time: a change in the behaviour of older winds?

Science.gov (United States)

O'Fionnagáin, D.; Vidotto, A. A.

2018-05-01

In this paper, we model the wind of solar analogues at different ages to investigate the evolution of the solar wind. Recently, it has been suggested that winds of solar type stars might undergo a change in properties at old ages, whereby stars older than the Sun would be less efficient in carrying away angular momentum than what was traditionally believed. Adding to this, recent observations suggest that old solar-type stars show a break in coronal properties, with a steeper decay in X-ray luminosities and temperatures at older ages. We use these X-ray observations to constrain the thermal acceleration of winds of solar analogues. Our sample is based on the stars from the `Sun in Time' project with ages between 120 and 7000 Myr. The break in X-ray properties leads to a break in wind mass-loss rates (\\dot{M}) at roughly 2 Gyr, with \\dot{M} (t 2 Gyr) ∝ t-3.9. This steep decay in \\dot{M} at older ages could be the reason why older stars are less efficient at carrying away angular momentum, which would explain the anomalously rapid rotation observed in older stars. We also show that none of the stars in our sample would have winds dense enough to produce thermal emission above 1-2 GHz, explaining why their radio emissions have not yet been detected. Combining our models with dynamo evolution models for the magnetic field of the Earth, we find that, at early ages (≈100 Myr), our Earth had a magnetosphere that was three or more times smaller than its current size.

LINEAR RELATION FOR WIND-BLOWN BUBBLE SIZES OF MAIN-SEQUENCE OB STARS IN A MOLECULAR ENVIRONMENT AND IMPLICATION FOR SUPERNOVA PROGENITORS

Energy Technology Data Exchange (ETDEWEB)

Chen Yang; Zhou Ping [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Chu Youhua [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

2013-05-20

We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R{sub b} Almost-Equal-To 1.22 M/M{sub Sun} - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M{sub Sun} will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

Mass loss from Wolf-Rayet stars

International Nuclear Information System (INIS)

Willis, A.J.

1982-01-01

Recent results relating to the stellar winds and mass loss rates of the WR stars are reviewed, emphasising new data and their interpretation acquired at UV, IR and Radio wavelengths. The subject is discussed under the headings: physical and chemical properties of WR stars (effective temperatures and radiative luminosities; masses; chemical abundances); velocity, ionisation and excitation structure of WR winds; mass loss rates of WR stars; mass loss properties of WR stars in the LMC; comparisons with theoretical models of mass loss; ring nebulae around WR stars; conclusions. (author)

Kuwano's peculiar object is a novalike (symbiotic) binary with a red giant. Discussion of observational results

International Nuclear Information System (INIS)

Belyakina, T.S.; Gershberg, R.E.; Efimov, Yu.S.; Krasnobabtsev, V.I.; Pavlenko, E.P.; Petrov, P.P.; Chuvaev, K.K.; Shenavrin, V.I.

1982-01-01

Photometric, polarimetric and spectral observations carried out at the Crimea permit to conclude that the Kuwano object is a binary system that consists of an M-giant and of a low-luminosity star. During the 1979 flare, the absolute magnitude of the weak component has increased up to about -6sup(m), the M-giant had apparently small variations as well. A distance to the object is estimated to be 5-7 kpc, and it is located certainly out of the galactic plane. Similarities between the Kuwano object and slow novae and symbiotic stars are noted [ru

The extreme, possible symbiotic Mira V407 Cyg and its relevance to the OH/IR sources

International Nuclear Information System (INIS)

Munari, U.; Margoni, R.; Stagni, R.

1990-01-01

New optical and IR magnitudes are presented and we review all the available photometric data on the very interesting variable V407 Cyg. A preliminary discussion of new high- and low-resolution optical spectra is given. The nature of V407 Cyg is discussed in the light of available data and a classification as a symbiotic star is suggested. (author)

X-ray Jets in the CH Cyg Symbiotic System

Science.gov (United States)

Karovska, Margarita; Gaetz, T.; Lee, N.; Raymond, J.; Hack, W.; Carilli, C.

2009-09-01

Symbiotic binaries are interacting systems in which a compact stellar source accretes matter from the wind of the cool evolved companion. There are a few hundred symbiotic systems known today, but jet activity has been detected in only a few of them, including in CH Cyg. CH Cyg is a symbiotic system that has shown significant activity since the mid 1960s. Jets have been detected in optical and radio since 1984, and more recently in 2001 in X-rays using Chandra observations.In 2008 we carried out coordinated multi-wavelength observations of the CH Cyg system with Chandra, HST, and the VLA, in order to study the propagation and interaction with the circumbinary medium of the jet detected in 2001. We report here on the detection of the 2001 SE jet which has expanded in seven years from ˜350AU to ˜1400 AU. The apex of the loop delineating the region of interaction with the circumbinary matter is moving with a speed of ˜700 km/s. Assuming a linear expansion, the jet was launched during the 1999-2000 active phase. We also report on a detection of a powerful new jet in the SW direction, observed in X-ray, optical and radio wavelengths. The new jet has a multi-component structure including an inner jet and counter jet, and a SW component ending in several clumps extending up to a distance of about 750AU.

EG ANDROMEDAE: A NEW ORBIT AND ADDITIONAL EVIDENCE FOR A PHOTOIONIZED WIND

International Nuclear Information System (INIS)

Kenyon, Scott J.; Garcia, Michael R.

2016-01-01

We analyze a roughly 20 yr set of spectroscopic observations for the symbiotic binary EG And. Radial velocities derived from echelle spectra are best fit with a circular orbit having an orbital period of P = 483.3 ± 1.6 days and semi-amplitude K = 7.34 ± 0.07 km s −1 . Combined with previous data, these observations rule out an elliptical orbit at the 10 σ level. Equivalent widths of H i Balmer emission lines and various absorption features vary in phase with the orbital period. Relative to the radius of the red giant primary, the apparent size of the H ii region is consistent with a model where a hot secondary star with effective temperature T h ≈ 75,000 K ionizes the wind from the red giant.

EG ANDROMEDAE: A NEW ORBIT AND ADDITIONAL EVIDENCE FOR A PHOTOIONIZED WIND

Energy Technology Data Exchange (ETDEWEB)

Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Garcia, Michael R., E-mail: skenyon@cfa.harvard.edu, E-mail: michael.r.garcia@nasa.gov [NASA Headquarters, Mail Suite 3Y28, 300 E Street SW, Washington, DC 20546-0001 (United States)

2016-07-01

We analyze a roughly 20 yr set of spectroscopic observations for the symbiotic binary EG And. Radial velocities derived from echelle spectra are best fit with a circular orbit having an orbital period of P = 483.3 ± 1.6 days and semi-amplitude K = 7.34 ± 0.07 km s{sup −1}. Combined with previous data, these observations rule out an elliptical orbit at the 10 σ level. Equivalent widths of H i Balmer emission lines and various absorption features vary in phase with the orbital period. Relative to the radius of the red giant primary, the apparent size of the H ii region is consistent with a model where a hot secondary star with effective temperature T{sub h} ≈ 75,000 K ionizes the wind from the red giant.

Time-dependent mass loss from hot stars with and without radiative driving

International Nuclear Information System (INIS)

Castor, J.I.; Owocki, S.P.; Rybicki, G.B.

1988-01-01

A numerical hydrodynamics code is used to investigate two aspects of the winds of hot stars. The first is the question of the instability of the massive radiatively-driven wind of an O star that is caused by the line shape mechanism: modulation of the radiation force by velocity fluctuations. The evolution of this instability is studied in a model O star wind, and is found, /ital modulo/ some numerical uncertainty, to lead to wave structures that are compatible with observations of wind instabilities. The other area of investigation is of main-sequence B star winds. Attempts were made to simulate a radiatively-driven and a pulsation-driven wind in a B star, but in each case the wind turned out to be very weak. It is argued that the pulsation-driven wind model is not likely to apply to B stars. 28 refs., 11 figs

Spectral and Timing Nature of the Symbiotic X-Ray Binary 4U 1954+319: The Slowest Rotating Neutron Star in AN X-Ray Binary System

Science.gov (United States)

Enoto, Teruaki; Sasano, Makoto; Yamada, Shin'Ya; Tamagawa, Toru; Makishima, Kazuo; Pottschmidt, Katja; Marcu, Diana; Corbet, Robin H. D.; Fuerst, Felix; Wilms, Jorn

2014-01-01

The symbiotic X-ray binary (SyXB) 4U 1954+319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its approx. 5.4 hr NS spin period is the longest among all known accretion-powered pulsars and exhibited large (is approx. 7%) fluctuations over 8 yr. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe-K alpha line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (approx. 60%-80%), and the location in the Corbet diagram favor high B-field (approx. greater than 10(exp12) G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (10(exp33)-10(exp35) erg s(exp-1)), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a approx. 10(exp13) G NS, this scheme can explain the approx. 5.4 hr equilibrium rotation without employing the magnetar-like field (approx. 10(exp16) G) required in the disk accretion case. The timescales of multiple irregular flares (approx. 50 s) can also be attributed to the free-fall time from the Alfv´en shell for a approx. 10(exp13) G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.

Eyes in the sky. Interactions between asymptotic giant branch star winds and the interstellar magnetic field

Science.gov (United States)

van Marle, A. J.; Cox, N. L. J.; Decin, L.

2014-10-01

Context. The extended circumstellar envelopes (CSEs) of evolved low-mass stars display a large variety of morphologies. Understanding the various mechanisms that give rise to these extended structures is important to trace their mass-loss history. Aims: Here, we aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow dusty winds of asymptotic giant branch (AGB) stars in an effort to pin-point the origin of so-called eye shaped CSEs of three carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary nebula (PN) shaping can be responsible for asymmetries observed in PNe. Methods: Hydrodynamical simulations are used to study the effect of typical interstellar magnetic fields on the free-expanding spherical stellar winds as they sweep up the local interstellar medium (ISM). Results: The simulations show that typical Galactic interstellar magnetic fields of 5 to 10 μG are sufficient to alter the spherical expanding shells of AGB stars to appear as the characteristic eye shape revealed by far-infrared observations. The typical sizes of the simulated eyes are in accordance with the observed physical sizes. However, the eye shapes are transient in nature. Depending on the stellar and interstellar conditions, they develop after 20 000 to 200 000 yrs and last for about 50 000 to 500 000 yrs, assuming that the star is at rest relative to the local interstellar medium. Once formed, the eye shape develops lateral outflows parallel to the magnetic field. The explosion of a PN in the centre of the eye-shaped dust shell gives rise to an asymmetrical nebula with prominent inward pointing Rayleigh-Taylor instabilities. Conclusions: Interstellar magnetic fields can clearly affect the shaping of wind-ISM interaction shells. The occurrence of the eyes is most strongly influenced by stellar space motion and ISM density. Observability of this transient phase is favoured for lines-of-sight perpendicular to the

Epidemic Spread of Symbiotic and Non-Symbiotic Bradyrhizobium Genotypes Across California.

Science.gov (United States)

Hollowell, A C; Regus, J U; Gano, K A; Bantay, R; Centeno, D; Pham, J; Lyu, J Y; Moore, D; Bernardo, A; Lopez, G; Patil, A; Patel, S; Lii, Y; Sachs, J L

2016-04-01

The patterns and drivers of bacterial strain dominance remain poorly understood in natural populations. Here, we cultured 1292 Bradyrhizobium isolates from symbiotic root nodules and the soil root interface of the host plant Acmispon strigosus across a >840-km transect in California. To investigate epidemiology and the potential role of accessory loci as epidemic drivers, isolates were genotyped at two chromosomal loci and were assayed for presence or absence of accessory "symbiosis island" loci that encode capacity to form nodules on hosts. We found that Bradyrhizobium populations were very diverse but dominated by few haplotypes-with a single "epidemic" haplotype constituting nearly 30 % of collected isolates and spreading nearly statewide. In many Bradyrhizobium lineages, we inferred presence and absence of the symbiosis island suggesting recurrent evolutionary gain and or loss of symbiotic capacity. We did not find statistical phylogenetic evidence that the symbiosis island acquisition promotes strain dominance and both symbiotic and non-symbiotic strains exhibited population dominance and spatial spread. Our dataset reveals that a strikingly few Bradyrhizobium genotypes can rapidly spread to dominate a landscape and suggests that these epidemics are not driven by the acquisition of accessory loci as occurs in key human pathogens.

Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis

NARCIS (Netherlands)

David-Uraz, A.; Wade, G.A.; Petit, V.; ud-Doula, A.; Sundqvist, J.O.; Grunhut, J.; Schultz, M.; Neiner, C.; Alecian, E.; Henrichs, H.F.; Bouret, J.-C.

2014-01-01

OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations. In this paper, we evaluate the possible relation

INFRARED SPECTROSCOPY OF SYMBIOTIC STARS. VIII. ORBITS FOR THREE S-TYPE SYSTEMS: AE ARAE, Y CORONAE AUSTRALIS, AND SS 73-147

International Nuclear Information System (INIS)

Fekel, Francis C.; Hinkle, Kenneth H.; Joyce, Richard R.; Wood, Peter R.

2010-01-01

With new infrared radial velocities we have computed orbits of the M giants in three southern S-type symbiotic systems. AE Ara and SS 73-147 have circular orbits with periods of 803 and 820 days, respectively. The eccentric orbit of Y CrA has a period that is about twice as long, 1619 days. Except for CH Cyg it is currently the S-type symbiotic system with the longest period for which a spectroscopic orbit has been determined. The Paschen δ emission line velocities of AE Ara are nearly in antiphase with the M giant absorption feature velocities and result in a mass ratio of 2.7. Emission lines in the 1.005 μm region for the other two symbiotic systems are not good proxies for the hot components in those systems. There is no evidence that these three symbiotics are eclipsing. With spectral classes of M5.5 or M6, the three giants presumably also have velocity variations that result from pulsations, but we have been unable to identify specific pulsation periods in the absorption line velocity residuals.

Winds in cataclysmic variable stars

International Nuclear Information System (INIS)

Cordova, F.A.; Ladd, E.F.; Mason, K.O.

1984-01-01

Ultraviolet spectrophotometry of two dwarf novae, CN Ori and RX And, at various phases of their outburst cycles confirms that the far uv flux increases dramatically about 1-2 days after the optical outburst begins. At this time the uv spectral line profiles indicate the presence of a high velocity wind. The detectability of the wind depends more on the steepness of the spectrum, and thus on the flux in the extreme ultraviolet, than on the absolute value of the far uv luminosity. The uv continuum during outburst consists of (at least) two components, the most luminous of which is located behind the wind and is completely absorbed by the wind at the line frequencies. Several pieces of evidence suggest that the uv emission lines that are observed in many cataclysmic variables during quiescence have a different location in the binary than the wind, and are affected very little by the outburst

THE TRANSITION MASS-LOSS RATE: CALIBRATING THE ROLE OF LINE-DRIVEN WINDS IN MASSIVE STAR EVOLUTION

Energy Technology Data Exchange (ETDEWEB)

Vink, Jorick S.; Graefener, Goetz, E-mail: jsv@arm.ac.uk [Armagh Observatory, College Hill, BT61 9DG Armagh (United Kingdom)

2012-06-01

A debate has arisen regarding the importance of stationary versus eruptive mass loss for massive star evolution. The reason is that stellar winds have been found to be clumped, which results in the reduction of unclumped empirical mass-loss rates. Most stellar evolution models employ theoretical mass-loss rates which are already reduced by a moderate factor of {approx_equal}2-3 compared to non-corrected empirical rates. A key question is whether these reduced rates are of the correct order of magnitude, or if they should be reduced even further, which would mean that the alternative of eruptive mass loss becomes necessary. Here we introduce the transition mass-loss rate M-dot{sub trans} between O and Wolf-Rayet stars. Its novelty is that it is model independent. All that is required is postulating the spectroscopic transition point in a given data set, and determining the stellar luminosity, which is far less model dependent than the mass-loss rate. The transition mass-loss rate is subsequently used to calibrate stellar wind strength by its application to the Of/WNh stars in the Arches cluster. Good agreement is found with two alternative modeling/theoretical results, suggesting that the rates provided by current theoretical models are of the right order of magnitude in the {approx}50 M{sub Sun} mass range. Our results do not confirm the specific need for eruptive mass loss as luminous blue variables, and current stellar evolution modeling for Galactic massive stars seems sound. Mass loss through alternative mechanisms might still become necessary at lower masses, and/or metallicities, and the quantification of alternative mass loss is desirable.

THE TRANSITION MASS-LOSS RATE: CALIBRATING THE ROLE OF LINE-DRIVEN WINDS IN MASSIVE STAR EVOLUTION

International Nuclear Information System (INIS)

Vink, Jorick S.; Gräfener, Götz

2012-01-01

A debate has arisen regarding the importance of stationary versus eruptive mass loss for massive star evolution. The reason is that stellar winds have been found to be clumped, which results in the reduction of unclumped empirical mass-loss rates. Most stellar evolution models employ theoretical mass-loss rates which are already reduced by a moderate factor of ≅2-3 compared to non-corrected empirical rates. A key question is whether these reduced rates are of the correct order of magnitude, or if they should be reduced even further, which would mean that the alternative of eruptive mass loss becomes necessary. Here we introduce the transition mass-loss rate M-dot trans between O and Wolf-Rayet stars. Its novelty is that it is model independent. All that is required is postulating the spectroscopic transition point in a given data set, and determining the stellar luminosity, which is far less model dependent than the mass-loss rate. The transition mass-loss rate is subsequently used to calibrate stellar wind strength by its application to the Of/WNh stars in the Arches cluster. Good agreement is found with two alternative modeling/theoretical results, suggesting that the rates provided by current theoretical models are of the right order of magnitude in the ∼50 M ☉ mass range. Our results do not confirm the specific need for eruptive mass loss as luminous blue variables, and current stellar evolution modeling for Galactic massive stars seems sound. Mass loss through alternative mechanisms might still become necessary at lower masses, and/or metallicities, and the quantification of alternative mass loss is desirable.

Symbiotic Optimization of Behavior

Science.gov (United States)

2015-05-01

SYMBIOTIC OPTIMIZATION OF BEHAVIOR UNIVERSITY OF WASHINGTON MAY 2015 FINAL TECHNICAL REPORT APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED...2014 4. TITLE AND SUBTITLE SYMBIOTIC OPTIMIZATION OF BEHAVIOR 5a. CONTRACT NUMBER FA8750-12-1-0304 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT

New Frontiers for Massive Star Winds: Imaging and Spectroscopy with the James Webb Space Telescope

Science.gov (United States)

Sonneborn, George

2007-01-01

The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2013. JWST will find the first stars and galaxies that formed in the early universe, connecting the Big Bang to our own Milky Way galaxy. JWST will peer through dusty clouds to see stars forming planetary systems, connecting the Milky Way to our own Solar System. JWST's instruments are designed to work primarily in the infrared range of 1 - 28 microns, with some capability in the visible range. JWST will have a large mirror, 6.5 meters in diameter, and will be diffraction-limited at 2 microns (0.1 arcsec resolution). JWST will be placed in an L2 orbit about 1.5 million km from the Earth. The instruments will provide imaging, coronography, and multi-object and integral-field spectroscopy across the full 1 - 28 micron wavelength range. The breakthrough capabilities of JWST will enable new studies of massive star winds from the Milky Way to the early universe.

Emission line relative intensity variations in the symbiotic stars: CI Cygni, BF Cygni, AX Persei and V1016 Cygni

International Nuclear Information System (INIS)

Oliversen, N.A.

1982-01-01

Low resolution spectra (lambda 3800 to lambda 5900) are presented of the symbiotic stars CI Cygni, BF Cygni, AX Persei and V1016 Cygni, which were obtained with the Washburn Observatory Boller and Chivens cassegrain spectrograph and intensified Reticon. The spectra were obtained as part of a monitoring program covering 36 months since November 1978. The nebular electron temperature and density are derived from the [O III] lambda 5007 and lambda 4363 emission lines and the uv intercombination lines of lambda 1661 and lambda 1667. Relative emission line intensity variations were observed in all four stars. The relative emission line changes correlated with photometric minima for CI Cyg, AX Per and possibly BF Cyg. These changes are interpreted as due to a red giant eclipsing a nebula surrounding the exciting source. Based on the [O III] line ratio change, the nebular density of V1016 Cyg has continued to decline since 1978. The thesis also contains a discussion of the use of the emision lines of [Ne III] lambda 3869, [O III] lambda 5007, lambda 4363 and He lambda 5876 to derive nebular electron temperature and density. A decline in the intensity ratios of I(lambda 3869)/(lambda 5007) and I(lambda 5876)/I(lambda 5007) were observed during the 1980 minimum of CI Cyg. The observed I(lambda 3869)/I(lambda 5007) decline was too large to be explained by temperature or density changes. The [Ne III] and He II regions in CI Cyg are therefore closer to the hot source than the more extended (o III] emission region. Contained within the appendix is a discussion of a graphical method of solution ot the nebular temperature and density, which is based on the emission lines of [Ne III], [O III] and He I

Barium and Tc-poor S stars: Binary masqueraders among carbon stars

OpenAIRE

Jorissen, A.; Van Eck, S.

1997-01-01

The current understanding of the origin of barium and S stars is reviewed, based on new orbital elements and binary frequencies. The following questions are addressed: (i) Is binarity a necessary condition to produce a barium star? (ii) What is the mass transfer mode (wind accretion or RLOF?) responsible for their formation? (iii) Do barium stars form as dwarfs or as giants? (iv) Do barium stars evolve into Tc-poor S stars? (v) What is the relative frequency of Tc-rich and Tc-poor S stars?

A SYSTEMATIC SEARCH FOR COROTATING INTERACTION REGIONS IN APPARENTLY SINGLE GALACTIC WOLF-RAYET STARS. II. A GLOBAL VIEW OF THE WIND VARIABILITY

International Nuclear Information System (INIS)

Chene, A.-N.; St-Louis, N.

2011-01-01

This study is the second part of a survey searching for large-scale spectroscopic variability in apparently single Wolf-Rayet (WR) stars. In a previous paper (Paper I), we described and characterized the spectroscopic variability level of 25 WR stars observable from the northern hemisphere and found 3 new candidates presenting large-scale wind variability, potentially originating from large-scale structures named corotating interaction regions (CIRs). In this second paper, we discuss an additional 39 stars observable from the southern hemisphere. For each star in our sample, we obtained 4-5 high-resolution spectra with a signal-to-noise ratio of ∼100 and determined its variability level using the approach described in Paper I. In total, 10 new stars are found to show large-scale spectral variability of which 7 present CIR-type changes (WR 8, WR 44, WR55, WR 58, WR 61, WR 63, WR 100). Of the remaining stars, 20 were found to show small-amplitude changes and 9 were found to show no spectral variability as far as can be concluded from the data on hand. Also, we discuss the spectroscopic variability level of all single galactic WR stars that are brighter than v ∼ 12.5, and some WR stars with 12.5 < v ≤ 13.5, i.e., all the stars presented in our two papers and four more stars for which spectra have already been published in the literature. We find that 23/68 stars (33.8%) present large-scale variability, but only 12/54 stars (∼22.1%) are potentially of CIR type. Also, we find that 31/68 stars (45.6%) only show small-scale variability, most likely due to clumping in the wind. Finally, no spectral variability is detected based on the data on hand for 14/68 (20.6%) stars. Interestingly, the variability with the highest amplitude also has the widest mean velocity dispersion.

A STAR IN THE M31 GIANT STREAM: THE HIGHEST NEGATIVE STELLAR VELOCITY KNOWN

International Nuclear Information System (INIS)

Caldwell, Nelson; Kenyon, Scott J.; Morrison, Heather; Harding, Paul; Schiavon, Ricardo; Rose, James A.

2010-01-01

We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km s -1 . Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-main-sequence close binary, a symbiotic nova, or less likely, a post-asymptotic giant branch star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.

Stellar wind theory

International Nuclear Information System (INIS)

Summers, D.

1980-01-01

The theory of stellar winds as given by the equations of classical fluid dynamics is considered. The equations of momentum and energy describing a steady, spherically symmetric, heat-conducting, viscous stellar wind are cast in a dimensionless form which involves a thermal conduction parameter E and a viscosity parameter γ. An asymptotic analysis is carried out, for fixed γ, in the cases E→O and E→infinity (corresponding to small and large thermal conductivity, respectively), and it is found that it is possible to construct critical solutions for the wind velocity and temperature over the entire flow. The E→O solution represents a wind which emanates from the star at low, subsonic speeds, accelerates through a sonic point, and then approaches a constant asymptotic speed, with its temperature varying as r/sup -4/3/ at large distances r from the star; the E→infinity solution represents a wind which, after reaching an approximately constant speed, with temperature varying as r/sup -2/7/, decelerates through a diffuse shock and approaches a finite pressure at infinity. A categorization is made of all critical stellar wind solutions for given values of γ and E, and actual numerical examples are given. Numerical solutions are obtained by integrating upstream 'from infinity' from initial values of the flow parameters given by appropriate asymptotic expansions. The role of viscosity in stellar wind theory is discussed, viscous and inviscid stellar wind solutions are compared, and it is suggested that with certain limitations, the theory presented may be useful in analyzing winds from solar-type stars

Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. I. Solution Topology and Wind Geometry

OpenAIRE

Feldmeier, Achim; Shlosman, Isaac

1999-01-01

We analyze the dynamics of 2-D stationary, line-driven winds from accretion disks in cataclysmic variable stars. The driving force is that of line radiation pressure, in the formalism developed by Castor, Abbott & Klein for O stars. Our main assumption is that wind helical streamlines lie on straight cones. We find that the Euler equation for the disk wind has two eigenvalues, the mass loss rate and the flow tilt angle with the disk. Both are calculated self-consistently. The wind is characte...

Wind models for zeta Orionis

International Nuclear Information System (INIS)

Olson, G.L.

1979-01-01

Several models for the winds of O stars have been proposed to explain the unexpected presence of high ionization potential ions such as N +4 and O +5 . Lamers and Snow (1978) proposed that the winds of stars showing N V and O VI lines have elevated temperatures near 4 +- 2 x 10 5 K while cooler stars with anomalous Si IV lines have Tsub(e) approximately 7+-3 x 10 4 K. Alternately, Cassinelli and Olson (1978, CO) and Olson (1978) have explained the presence of these ions by showing that a thin corona at the base of a cool wind (Tsub(e) < approximately Tsub(eff)) can produce these ions by the Auger photoionization process where a single X-ray photon causes the ejection of two electrons. A third possibility is that the winds are at only slightly elevated temperatures (40 000 to 60 000K) and photoionization in an optically thick wind produces the unexpected ions. The present analysis tests the ability of these three wind models to fit the observations of zeta Orionis A 09.7 Ib. (Auth.)

The environment of the wind-wind collision region of η Carinae

Science.gov (United States)

Panagiotou, C.; Walter, R.

2018-02-01

Context. η Carinae is a colliding wind binary hosting two of the most massive stars and featuring the strongest wind collision mechanical luminosity. The wind collision region of this system is detected in X-rays and γ-rays and offers a unique laboratory for the study of particle acceleration and wind magneto-hydrodynamics. Aim. Our main goal is to use X-ray observations of η Carinae around periastron to constrain the wind collision zone geometry and understand the reasons for its variability. Methods: We analysed 10 Nuclear Spectroscopic Telescope Array (NuSTAR) observations, which were obtained around the 2014 periastron. The NuSTAR array monitored the source from 3 to 30 keV, which allowed us to grasp the continuum and absorption parameters with very good accuracy. We were able to identify several physical components and probe their variability. Results: The X-ray flux varied in a similar way as observed during previous periastrons and largely as expected if generated in the wind collision region. The flux detected within 10 days of periastron is lower than expected, suggesting a partial disruption of the central region of the wind collision zone. The Fe Kα line is likely broadened by the electrons heated along the complex shock fronts. The variability of its equivalent width indicates that the fluorescence region has a complex geometry and that the source obscuration varies quickly with the line of sight.

The evolution of massive stars

International Nuclear Information System (INIS)

Loore, C. de

1980-01-01

The evolution of stars with masses between 15 M 0 and 100 M 0 is considered. Stars in this mass range lose a considerable fraction of their matter during their evolution. The treatment of convection, semi-convection and the influence of mass loss by stellar winds at different evolutionary phases are analysed as well as the adopted opacities. Evolutionary sequences computed by various groups are examined and compared with observations, and the advanced evolution of a 15 M 0 and a 25 M 0 star from zero-age main sequence (ZAMS) through iron collapse is discussed. The effect of centrifugal forces on stellar wind mass loss and the influence of rotation on evolutionary models is examined. As a consequence of the outflow of matter deeper layers show up and when the mass loss rates are large enough layers with changed composition, due to interior nuclear reactions, appear on the surface. The evolution of massive close binaries as well during the phase of mass loss by stellar wind as during the mass exchange and mass loss phase due to Roche lobe overflow is treated in detail, and the value of the parameters governing mass and angular momentum losses are discussed. The problem of the Wolf-Rayet stars, their origin and the possibilities of their production either as single stars or as massive binaries is examined. Finally, the origin of X-ray binaries is discussed and the scenario for the formation of these objects (starting from massive ZAMS close binaries, through Wolf-Rayet binaries leading to OB-stars with a compact companion after a supernova explosion) is reviewed and completed, including stellar wind mass loss. (orig.)

Innovative Offshore Wind Plant Design Study

Energy Technology Data Exchange (ETDEWEB)

Hurley, William L. [Glosten Associates, Inc., Seattle, WA (United States); Nordstrom, Charles J. [Glosten Associates, Inc., Seattle, WA (United States); Morrison, Brent J. [Glosten Associates, Inc., Seattle, WA (United States)

2013-12-18

Technological advancements in the Glosten PelaStar floating wind turbine system have led to projected cost of energy (COE) reductions from today’s best-in-class offshore wind systems. The PelaStar system is projected to deliver a COE that is 35% lower than that delivered by the current offshore wind plants. Several technology developments have been achieved that directly target significant cost of energy reductions. These include: Application of state-of-the-art steel construction materials and methods, including fatigue-resistant welding techniques and technologies, to reduce hull steel weight; Advancements in synthetic fiber tendon design for the mooring system, which are made possible by laboratory analysis of full-scale sub-rope specimens; Investigations into selected anchor technologies to improve anchor installation methods; Refinement of the installation method, specifically through development of the PelaStar Support Barge design. Together, these technology developments drive down the capital cost and operating cost of offshore wind plants and enable access to superb wind resources in deep water locations. These technology developments also reduce the uncertainty of the PelaStar system costs, which increases confidence in the projected COE reductions.

Radio stars

International Nuclear Information System (INIS)

Hjellming, R.M.; Gibson, D.M.

1985-01-01

Studies of stellar radio emission became an important field of research in the 1970's and have now expanded to become a major area of radio astronomy with the advent of new instruments such as the Very Large Array in New Mexico and transcontinental telescope arrays. This volume contains papers from the workshop on stellar continuum radio astronomy held in Boulder, Colorado, and is the first book on the rapidly expanding field of radio emission from stars and stellar systems. Subjects covered include the observational and theoretical aspects of stellar winds from both hot and cool stars, radio flares from active double star systems and red dwarf stars, bipolar flows from star-forming regions, and the radio emission from X-ray binaries. (orig.)

The Contribution of Stellar Winds to Cosmic Ray Production

Science.gov (United States)

Seo, Jeongbhin; Kang, Hyesung; Ryu, Dongsu

2018-04-01

Massive stars blow powerful stellar winds throughout their evolutionary stages from the main sequence to Wolf-Rayet phases. The wind mechanical energy of a massive star deposited to the interstellar medium can be comparable to the explosion energy of a core-collapse supernova that detonates at the end of its life In this study, we estimate the kinetic energy deposition by massive stars in our Galaxy by considering the integrated Galactic initial mass function and modeling the stellar wind luminosity. The mass loss rate and terminal velocity of stellar winds during the main sequence, red supergiant, and Wolf-Rayet stages are estimated by adopting theoretical calculations and observational data published in the literature. We find that the total stellar wind luminosity by all massive stars in the Galaxy is about Lw ≈ 1.1×1041 ergs, which is about 1/4 of the power of supernova explosions, LSN ≈ 4.8×1041 ergs. If we assume that ˜1-1% of the wind luminosity could be converted to Galactic cosmic rays (GCRs) through collisonless shocks such as termination shocks in stellar bubbles and superbubbles, colliding-wind shocks in binaries, and bow-shocks of massive runaway stars, stellar winds are expected to make a significant contribution to GCR production, though lower than that of supernova remnants.

Revisiting Symbiotic Job Scheduling

OpenAIRE

Eyerman , Stijn; Michaud , Pierre; Rogiest , Wouter

2015-01-01

International audience; —Symbiotic job scheduling exploits the fact that in a system with shared resources, the performance of jobs is impacted by the behavior of other co-running jobs. By coscheduling combinations of jobs that have low interference, the performance of a system can be increased. In this paper, we investigate the impact of using symbiotic job scheduling for increasing throughput. We find that even for a theoretically optimal scheduler, this impact is very low, despite the subs...

Stellar winds

International Nuclear Information System (INIS)

Weymann, R.J.

1978-01-01

It is known that a steady outflow of material at comparable rates of mass loss but vastly different speeds is now known to be ubiquitous phenomenon among both the luminous hot stars and the luminous but cool red giants. The flows are probably massive enough in both cases to give rise to significant effects on stellar evolution and the mass balance between stars and the interstellar medium. The possible mechanisms for these phenomena as well as the methods of observation used are described. In particular, the mass-loss processes in stars other than the sun that also involve a steady flow of matter are considered. The evidence for their existence is described, and then the question of whether the process thought to produce the solar wind is also responsible for producing these stellar winds is explored

Comoving frame models of hot star winds I. Test of the Sobolev approximation in the case of pure line transitions

Czech Academy of Sciences Publication Activity Database

Krtička, J.; Kubát, Jiří

2010-01-01

Roč. 519, September (2010), A50/1-A50/9 ISSN 0004-6361 R&D Projects: GA ČR GA205/07/0031 Institutional research plan: CEZ:AV0Z10030501 Keywords : stars * winds * outflows Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.410, year: 2010

Modeling pulsations in hot stars with winds

Energy Technology Data Exchange (ETDEWEB)

Noels, Arlette; Godart, Melanie [Institut d' Astrophysique et de Geophysique, Liege (Belgium); Dupret, Marc-Antoine [Observatoire de Paris-Meudon, LESIA (France)], E-mail: Arlette.Noels@ulg.ac.be, E-mail: ma.dupret@obspm.fr, E-mail: Melanie.Godart@ulg.ac.be

2008-10-15

The interaction pulsation/mass loss takes different aspects. Pulsations can trigger mass loss as in LBVs and Miras; on the other hand, mass loss can modify the driving conditions within the stars. But the most spectacular aspect is the effect on stellar models which, in turn, opens a royal way to asteroseismology to test physical conditions inside massive stars, such as the extent of convective cores or the appearance of new driving mechanisms. We start with a discussion on MS stars and their strange mode instabilities. We then move on to the excitation of the LBV phenomenon. WR stars and the newly observed MOST period in WR123 are discussed in view of the power of asteroseismology. We then turn to B supergiants, in particular HD163899, and show how asteroseismology can really probe convection, semiconvection and mass loss.

Modeling pulsations in hot stars with winds

International Nuclear Information System (INIS)

Noels, Arlette; Godart, Melanie; Dupret, Marc-Antoine

2008-01-01

The interaction pulsation/mass loss takes different aspects. Pulsations can trigger mass loss as in LBVs and Miras; on the other hand, mass loss can modify the driving conditions within the stars. But the most spectacular aspect is the effect on stellar models which, in turn, opens a royal way to asteroseismology to test physical conditions inside massive stars, such as the extent of convective cores or the appearance of new driving mechanisms. We start with a discussion on MS stars and their strange mode instabilities. We then move on to the excitation of the LBV phenomenon. WR stars and the newly observed MOST period in WR123 are discussed in view of the power of asteroseismology. We then turn to B supergiants, in particular HD163899, and show how asteroseismology can really probe convection, semiconvection and mass loss.

The 5 Hour Pulse Period and Broadband Spectrum of the Symbiotic X-Ray Binary 3A 1954+319

Science.gov (United States)

Marcu, Diana M.; Fuerst, Felix; Pottschmidt, Katja; Grinberg, Victoria; Miller, Sebstian; Wilms, Joern; Postnov, Konstantin A.; Corbet, Robin H. D.; Markwardt, Craig B.; Cadolle Bel, Marion

2011-01-01

We present an analysis of the highly variable accreting X-ray pulsar 3A 1954+319 using 2005-2009 monitoring data obtained with INTEGRAL and Swift. This considerably extends the pulse period history and covers flaring episodes in 2005 and 2008. In 2006 the source was identified as one of only a few known symbiotic X-ray binaries, Le" systems composed of a neutron star accreting from the inhomogeneous medium around an M-giant star. The extremely long pulse period of approximately 5.3 h is directly visible in the 2008 INTEGRAL-ISGRI outburst light curve. The pulse profile is double peaked and not significantly energy dependent. During the outburst a strong spin-up of -1.8 x 10(exp -4) h h(exp -1) occurred. Between 2005 and 2008 a long term spin-down trend of 2.1 x 10(exp -5) h h(exp -1) was observed for the first time for this source. The 3-80 keV pulse peak spectrum of 3A 1954+319 during the 2008 flare could be well described by a thermal Comptonization model. We interpret the results within the framework of a recently developed quasi-spherical accretion model for symbiotic X-ray binaries.

Properties of hot luminous stars; Proceedings of the First Boulder-Munich Workshop, Boulder, CO, Aug. 6-11, 1988

International Nuclear Information System (INIS)

Garmany, C.D.

1990-01-01

Various papers on the properties of hot luminous stars are presented. Individual topics addressed include: problems in photometry of early-type stars; digital optical morphology of OB spectra; massive-star content of the Magellanic Clouds; observations of massive OB stars; LSS 3074, a new double-lined early O-type binary; non-LTE line blanketing with elements 1-28; non-LTE analysis of four PG1159 stars; rescaling method for model atmospheres of hot stars; stellar wind albedo effects on hot photospheres; atomic data and models for hot star abundance determinations; ring nebulae analysis as a probe for WR atmospheres; coordinated observations of P Cygni; radiation-driven winds of hot luminous stars; winds of O stars: velocities and ionization; methods of radiative transfer in expanding atmospheres; mass loss from extragalactic O stars; H-alpha observations of O- and B-type stars; applicability of steady models for hot-star winds; mass of the O6Iaf star HD 153919; stellar winds in Beta Lyrae; models of WR stars; observational abundances of WR stars, the all-variable WC7 binary HD193793

Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

Science.gov (United States)

Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

2000-08-01

We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Hα velocity field for the central region (40''×40'' rmax~30''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Hα velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (rstandard models of photoionization, shocks, and starbursts). We present four detailed emission

WR 110: A SINGLE WOLF-RAYET STAR WITH COROTATING INTERACTION REGIONS IN ITS WIND?

International Nuclear Information System (INIS)

Chene, A.-N.; Moffat, A. F. J.; Fahed, R.; St-louis, N.; Muntean, V.; Chevrotiere, A. De La; Cameron, C.; Matthews, J. M.; Gamen, R. C.; Lefevre, L.; Rowe, J. F.; Guenther, D. B.; Kuschnig, R.; Weiss, W. W.; Rucinski, S. M.; Sasselov, D.

2011-01-01

A 30 day contiguous photometric run with the Microvariability and Oscillations of STars (MOST) satellite on the WN5-6b star WR 110 (HD 165688) reveals a fundamental periodicity of P = 4.08 ± 0.55 days along with a number of harmonics at periods P/n, with n ∼ 2, 3, 4, 5, and 6, and a few other possible stray periodicities and/or stochastic variability on timescales longer than about a day. Spectroscopic radial velocity studies fail to reveal any plausible companion with a period in this range. Therefore, we conjecture that the observed light-curve cusps of amplitude ∼0.01 mag that recur at a 4.08 day timescale may arise in the inner parts, or at the base, of a corotating interaction region (CIR) seen in emission as it rotates around with the star at constant angular velocity. The hard X-ray component seen in WR 110 could then be a result of a high velocity component of the CIR shock interacting with the ambient wind at several stellar radii. Given that most hot, luminous stars showing CIRs have two CIR arms, it is possible that either the fundamental period is 8.2 days or, more likely in the case of WR 110, there is indeed a second weaker CIR arm for P = 4.08 days, that occurs ∼two-thirds of a rotation period after the main CIR. If this interpretation is correct, WR 110 therefore joins the ranks with three other single WR stars, all WN, with confirmed CIR rotation periods (WR 1, WR 6, and WR 134), albeit with WR 110 having by far the lowest amplitude photometric modulation. This illustrates the power of being able to secure intense, continuous high-precision photometry from space-based platforms such as MOST. It also opens the door to revealing low-amplitude photometric variations in other WN stars, where previous attempts have failed. If all WN stars have CIRs at some level, this could be important for revealing sources of magnetism or pulsation in addition to rotation periods.

Resonance line-profiles in galactic disk UV-bright stars

International Nuclear Information System (INIS)

Carrasco, L.; Costero, R.

1987-01-01

We have made a comparative analysis of UV resonance line-profiles in O-type stars members of young clusters and OB associations, with those of hot stars located away from sites of recent star formation (including ''runaway'' stars). The resonance line-profiles are found to be generally dominated by stellar winds that appear to depend mainly on the surface gravity and temperature of the star, and not on its mass. We also present the C IV, Si IV and N V resonance line-profiles for eleven stars not published in the previous two papers. The use of only the largest stellar wind velocity detectable in the resonance lines as a stellar population indicator, is disputed. (author)

A D'-type symbiotic binary in the planetary nebula SMP LMC 88

Science.gov (United States)

Iłkiewicz, Krystian; Mikołajewska, Joanna; Miszalski, Brent; Kozłowski, Szymon; Udalski, Andrzej

2018-05-01

SMP LMC 88 is one of the planetary nebulae (PNe) in the Large Magellanic Cloud. We identify in its spectrum Raman scattered O VI lines at 6825 and 7083 Å. This unambiguously classifies the central object of the nebula as a symbiotic star (SySt). We identified the cold component to be a K-type giant, making this the first D'-type (yellow) SySt discovered outside the Galaxy. The photometric variability in SMP LMC 88 resembles the orbital variability of Galactic D'-type SySt with its low amplitude and sinusoidal light-curve shape. The SySt classification is also supported by the He I diagnostic diagram.

News on the X-ray emission from hot subdwarf stars

Directory of Open Access Journals (Sweden)

Palombara Nicola La

2017-12-01

Full Text Available In latest years, the high sensitivity of the instruments on-board the XMM-Newton and Chandra satellites allowed us to explore the properties of the X-ray emission from hot subdwarf stars. The small but growing sample of X-ray detected hot subdwarfs includes binary systems, in which the X-ray emission is due to wind accretion onto a compact companion (white dwarf or neutron star, as well as isolated sdO stars, in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low-mass stars provide information which can be useful for our understanding of the weak winds of this type of stars and can lead to the discovery of particularly interesting binary systems. Here we report the most recent results we have recently obtained in this research area.

Bipolar Jet Growth and Decline in Hen 3-1341: A Direct Link to Fast Wind and Outburst Evolution

National Research Council Canada - National Science Library

Munari, Ulisse; Siviero, A; Henden, A

2005-01-01

We report on and investigate the evolution and disappearance in the symbiotic star Hen 3-1341 of collimated bipolar jets, which take the form of symmetrically displaced components of emission lines...

Morula-like cells in photo-symbiotic clams harboring zooxanthellae.

Science.gov (United States)

Nakayama, K; Nishijima, M; Maruyama, T

1998-06-01

Symbiosis is observed between zooxanthellae, symbiotic dinoflagellates, and giant clams and related clams which belong to the families Tridacnidae and Cardiidae. We have previously shown that a photo-symbiotic clam Tridacna crocea has three types of hemocytes, the eosinophilic granular hemocyte with phagocytic activity, the agranular cell with electron lucent granules, and the morula-like cell with large (ca. 2 mum in diameter) colorless granules. The function of the morula-like cell is not clear, but it has not been reported in any other bivalves except photo-symbiotic clams T. crocea and Tridacna maxima. In order to clarify whether it is specific to photo-symbiotic clams or not, we studied hemocytes in the photo-symbiotic clams Tridacna derasa (Tridacnidae), Hippopus hippopus (Tridacnidae) and Corculum cardissa (Cardiidae), and a closely related non-symbiotic clam Fulvia mutica (Cardiidae). The eosinophilic granular hemocytes and the agranular cells were found in all of the clams examined. However, the morula-like cells which were packed with many large electron dense granules (ca. 2 mum in diameter), were observed only in the photo-symbiotic clams. In F. mutica, a closely related non-symbiotic clam, this type of hemocyte was not found. Instead a hemocyte with vacuoles and a few large granules containing peroxidase activity was observed. The large granules of F. mutica varied in size from ca. 1-9 mum in diameter. Present data suggests that the presence of morula-like cells is restricted to photo-symbiotic clams and that the hemocytes associated with the morula-like cells may have some functional relationship to symbiosis with zooxanthellae.

X-rays from Wolf-Rayet stars observed by the Einstein observatory

International Nuclear Information System (INIS)

Sanders, W.T.; Cassinelli, J.P.; Hucht, K.A. van der

1982-01-01

Preliminary results of three X-ray surveys are presented. Out of a sample of 20 stars, X-rays were detected from four Wolf-Rayet stars and two O8f + stars. The detected stars have about the same mean value as O stars for the X-ray to total luminosity ratio, Lsub(x)/L = 10 -7 , but exhibit a much larger variation about the mean. The spectral energy distributions are also found to be like that of O stars in that they do not exhibit large attenuation of X-rays softer than 1 keV. This indicates that for both the O stars and WR stars much of the X-ray emission is coming from hot wisps or shocks in the outer regions of the winds and not from a thin source at the base of the wind. The general spectral shape and flux level place severe restrictions on models that attribute the lack of hydrogen emission lines to extremely high temperatures of the gas in the wind. (Auth.)

The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR

Science.gov (United States)

King, Ashley L.; Walton, Dominic J.; Miller, Jon M.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Fabian, Andy C.; Furst, Felix; Hailey, Charles J.;

SPARCHS: Symbiotic, Polymorphic, Automatic, Resilient, Clean-Slate, Host Security

Science.gov (United States)

2016-03-01

SPARCHS: SYMBIOTIC , POLYMORPHIC, AUTOMATIC, RESILIENT, CLEAN-SLATE, HOST SECURITY COLUMBIA UNIVERSITY MARCH 2016 FINAL... SYMBIOTIC , POLYMORPHIC, AUTOTOMIC, RESILIENT, CLEAN-SLATE, HOST SECURITY 5a. CONTRACT NUMBER N/A 5b. GRANT NUMBER FA8750-10-2-0253 5c. PROGRAM...17 4.2.3 SYMBIOTIC EMBEDDED MACHINES

Ad-hoc Symbiotic Interactive Displays through DLNA

DEFF Research Database (Denmark)

Bitsch, Jannick Elimar; Bouvin, Niels Olof

2012-01-01

The concept of symbiotic displays covers the opportunistic pairing of mobile devices with screen devices that can be discovered and controlled across a network. Mobile applications that use symbiotic displays can offer the user an improved experience, but the lack of a widely deployed infras......- tructure means that the concept has seen little use. We design and implement a solution for using DLNA playback devices as symbiotic screens. DLNA devices are not designed to support interactive content, but to share and play media content in the home. Our work includes constructing a mechanism for real...

ON THE NATURE OF THE HOT COMPONENT IN THE SYMBIOTIC, SUPERSOFT X-RAY BINARY AG DRACONIS

Energy Technology Data Exchange (ETDEWEB)

Sion, Edward M.; Moreno, Jackeline; Godon, Patrick [Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States); Sabra, Bassem [Department of Physics and Astronomy, Notre Dame University-Louaize, Zouk Mosbeh (Lebanon); Mikolajewska, Joanna, E-mail: edward.sion@villanova.edu, E-mail: jackeline.moreno@villanova.edu, E-mail: patrick.godon@villanova.edu, E-mail: bsabra@ndu.edu.lb, E-mail: mikolaj@camk.edu.pl [Copernicus Astronomical Center, Warsaw (Poland)

2012-12-01

AG Dra is a symbiotic variable consisting of a metal-poor, yellow giant mass donor underfilling its Roche lobe and a hot accreting white dwarf, possibly surrounded by an optically thick, bright accretion disk (which could be present from wind accretion). We constructed NLTE synthetic spectral models for white dwarf spectra and optically thick accretion disk spectra to model a FUSE spectrum of AG Dra, obtained when the hot component is viewed in front of the yellow giant. The spectrum has been dereddened (E(B - V) = 0.05) and the model fitting carried out, with the distance regarded as a free parameter but required to be larger than the Hipparcos lower limit of 1 kpc. We find that the best-fitting model is a bare accreting white dwarf with M{sub wd} = 0.4 M{sub Sun }, T{sub eff} = 80,000 K, and a model-derived distance of 1543 pc. Higher temperatures are ruled out due to excess flux at the shortest wavelengths while a lower temperature decreases the distance below 1 kpc. Any accretion disk that might be present is only a minor contributor to the far-UV flux. This raises the possibility that the soft X-rays originate from a very hot boundary layer between a putative accretion disk and the accreting star.

The first stars: CEMP-no stars and signatures of spinstars

Science.gov (United States)

Maeder, André; Meynet, Georges; Chiappini, Cristina

2015-04-01

Aims: The CEMP-no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s- and r-elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne-Na, and Mg-Al abundances. Methods: We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of α- and CNO-elements, as well the abundances of elements involved in the Ne-Na and Mg-Al cycles. Results: We show that CEMP-no stars exhibit products of He-burning that have gone through partial mixing and processing by the CNO cycle, producing low 12C/13C and a broad variety of [C/N] and [O/N] ratios. From a 12C/13C vs. [C/N] diagram, we conclude that neither the yields of AGB stars (in binaries or not) nor the yields of classic supernovae can fully account for the observed CNO abundances in CEMP-no stars. Better agreement is obtained once the chemical contribution by stellar winds of fast-rotating massive stars is taken into account, where partial mixing takes place, leading to various amounts of CNO being ejected. The [(C+N+O)/H] ratios of CEMP-no stars vary linearly with [Fe/H] above [Fe/H] = -4.0 indicating primary behavior by (C+N+O). Below [Fe/H] = -4.0, [(C+N+O)/H] is almost constant as a function of [Fe/H], implying very high [(C+N+O)/Fe] ratios up to 4 dex. In view of the timescales, such abundance ratios reflect more individual nucleosynthetic properties, rather than an average chemical evolution. The high [(C+N+O)/Fe] ratios (as well as the high [(C+N+O)/α-elements]) imply that stellar winds from partially mixed stars were the main source of these excesses of heavy elements now observed in CEMP-no stars. The ranges covered by the variations of [Na/Fe], [Mg/Fe], and [Al/Fe] are much broader than for the α-elements (with an atomic mass number above 24) and are comparable to the wide ranges covered

Environments of T Tauri stars

International Nuclear Information System (INIS)

Chevalier, R.A.

1983-01-01

The environments of T Tauri stars are probably determined by the interaction of a stellar wind with matter which is falling toward a newly formed star. As shown by Ulrich, the steady infall of cool gas with angular momentum toward the star leads to a density distribution with rhoproportionalr/sup -1/2/ inside a radius r/sub d/ and rhoproportionalr/sup -3/2/ outside r/sub d/. The radius r/sub d/ is determined by the angular momentum of the infalling gas. The expansion of the wind into this medium depends on the parameter α = M/sub w/v/sub w//M/sub in/v/sub in/(r/sub d/), where v/sub in/(r/sub d/) is the free-fall velocity at r/sub d/, M/sub in/ is the mass accretion rate, v/sub w/ is the wind velocity, and M/sub w/ is the mass loss rate. For α 14 cm, v/sub w/ = 150 km s -1 , M/sub in/ = 10 -7 M/sub sun/ yr -1 , and M/sub w/ = 3 x 10 -8 M/sub sun/ yr -1 . The inflow is clumpy. The shocked wind gives the radio emission and nebular emission from T Tauri, and dust within the clumps gives the infrared emission. T Tauri is in a transitory phase in which most of the wind has only recently propagated beyond r/sub d/. The model naturally predicts variable obscuration of T Tauri stars because the infalling clumps move on nonradial trajectories. The infrared emission can vary either because of structural changes in the circumstellar gas or because of variations in the stellar luminosity. Infrared variability should be small at short time scales because of light-travel time effects

Non-symbiotic haemoglobins-What's happening beyond nitric oxide scavenging?

Science.gov (United States)

Hill, Robert D

2012-01-01

Non-symbiotic haemoglobins have been an active research topic for over 30 years, during which time a considerable portfolio of knowledge has accumulated relative to their chemical and molecular properties, and their presence and mode of induction in plants. While progress has been made towards understanding their physiological role, there remain a number of unanswered questions with respect to their biological function. This review attempts to update recent progress in this area and to introduce a hypothesis as to how non-symbiotic haemoglobins might participate in regulating hormone signal transduction. Advances have been made towards understanding the structural nuances that explain some of the differences in ligand association characteristics of class 1 and class 2 non-symbiotic haemoglobins. Non-symbiotic haemoglobins have been found to function in seed development and germination, flowering, root development and differentiation, abiotic stress responses, pathogen invasion and symbiotic bacterial associations. Microarray analyses under various stress conditions yield uneven results relative to non-symbiotic haemoglobin expression. Increasing evidence of the role of nitric oxide (NO) in hormone responses and the known involvement of non-symbiotic haemoglobins in scavenging NO provide opportunities for fruitful research, particularly at the cellular level. Circumstantial evidence suggests that non-symbiotic haemoglobins may have a critical function in the signal transduction pathways of auxin, ethylene, jasmonic acid, salicylic acid, cytokinin and abscisic acid. There is a strong need for research on haemoglobin gene expression at the cellular level relative to hormone signal transduction.

INFRARED SPECTROSCOPY OF SYMBIOTIC STARS. XI. ORBITS FOR SOUTHERN S-TYPE SYSTEMS: HEN 3-461, SY MUS, HEN 3-828, AND AR PAV

International Nuclear Information System (INIS)

Fekel, Francis C.; Hinkle, Kenneth H.; Joyce, Richard R.; Wood, Peter R.

2017-01-01

Employing new infrared radial velocities, we have computed spectroscopic orbits of the cool giants in four southern S-type symbiotic systems. The orbits for two of the systems, Hen 3-461 and Hen 3-828, have been determined for the first time, while orbits of the other two, SY Mus and AR Pav, have previously been determined. For the latter two systems, we compare our results with those in the literature. The low mass of the secondary of SY Mus suggests that it has gone through a common envelope phase. Hen 3-461 has an orbital period of 2271 days, one of the longest currently known for S-type symbiotic systems. That period is very different from the orbital period proposed previously from its photometric variations. The other three binaries have periods between 600 and 700 day, values that are typical for S-type symbiotic orbits. Basic properties of the M giant components and the distance to each system are determined.

Investigating the Magnetospheres of Rapidly Rotating B-type Stars

Science.gov (United States)

Fletcher, C. L.; Petit, V.; Nazé, Y.; Wade, G. A.; Townsend, R. H.; Owocki, S. P.; Cohen, D. H.; David-Uraz, A.; Shultz, M.

2017-11-01

Recent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

Alternative model for the atmospheres of Wolf-Rayet and O stars

International Nuclear Information System (INIS)

Underhill, A.B.

1983-01-01

It is noted that postulating dense spherically symmetric outflow in order to account for the observed radio fluxes from Wolf-Rayet stars requires that much more momentum must be deposited in the wind of a Wolf-Rayet star than is available from the radiation field of the star, and it is shown that the deduced massive winds become opaque in visible wavelengths at stellar radii where the velocity of outflow is several hundred km s - 1 . To attain such a state of motion in the wind requires the action of a strong, unknown source of outward directed momentum in optically thick layers of the star. This is an unreasonable demand. An alternative model for the mantle of a Wolf-Rayet star (the part of the atmosphere in which nonradiative energy and momentum are deposited) is proposed and shown to be feasible

How supernovae launch galactic winds?

Science.gov (United States)

Fielding, Drummond; Quataert, Eliot; Martizzi, Davide; Faucher-Giguère, Claude-André

2017-09-01

We use idealized three-dimensional hydrodynamic simulations of global galactic discs to study the launching of galactic winds by supernovae (SNe). The simulations resolve the cooling radii of the majority of supernova remnants (SNRs) and thus self-consistently capture how SNe drive galactic winds. We find that SNe launch highly supersonic winds with properties that agree reasonably well with expectations from analytic models. The energy loading (η _E= \\dot{E}_wind/ \\dot{E}_SN) of the winds in our simulations are well converged with spatial resolution while the wind mass loading (η _M= \\dot{M}_wind/\\dot{M}_\\star) decreases with resolution at the resolutions we achieve. We present a simple analytic model based on the concept that SNRs with cooling radii greater than the local scaleheight break out of the disc and power the wind. This model successfully explains the dependence (or lack thereof) of ηE (and by extension ηM) on the gas surface density, star formation efficiency, disc radius and the clustering of SNe. The winds our simulations are weaker than expected in reality, likely due to the fact that we seed SNe preferentially at density peaks. Clustering SNe in time and space substantially increases the wind power.

The low-metallicity starburst NGC346: massive-star population and feedback

Science.gov (United States)

Oskinova, Lida

2017-08-01

The Small Magellanic Cloud (SMC) is ideal to study young, massive stars at low metallicity. The compact cluster NGC346 contains about half of all O-type stars in the entire SMC. The massive-star population of this cluster powers N66, the brightest and largest HII region in the SMC. We propose to use HST-STIS to slice NGC346 with 20 long-slit exposures, in order to obtain the UV spectra of most of the massive early-type stars of this cluster. Archival data of 13 exposures that cover already a minor part of this cluster will be included in our analyses. Our aim is to quantitatively analyze virtually the whole massive-star population of NGC346. We have already secured the optical spectra of all massive stars in the field with the integral-field spectrograph MUSE at the ESO-VLT. However, for the determination of the stellar-wind parameters, i.e. the mass-loss rates and the wind velocities, ultraviolet spectra are indispensable. Our advanced Potsdam Wolf-Rayet (PoWR) code will be used for modeling the stellar and wind spectra in the course of the analysis. Finally, we will obtain:(a) the fundamental stellar and wind parameters of all stars brighter than spectral type B2V in the field, which, e,g,, will constrain the initial mass function in this young low-metallicity starburst;(b) mass-loss rates of many more OB-type stars at SMC metallicity than hitherto known, allowing to better constrain their metallicity dependence;(c) the integrated feedback by ionizing radiation and stellar winds of the whole massive-star population of NGC346, which will be used as input to model the ecology of the giant HII region N66.These HST UV data will be of high legacy value.

Probing the properties of the pulsar wind via studying the dispersive effects in the pulses from the pulsar companion in a double neutron-star binary system

Science.gov (United States)

Yi, Shu-Xu; Cheng, K.-S.

2017-12-01

The velocity and density distribution of e± in the pulsar wind are crucial distinction among magnetosphere models, and contain key parameters determining the high-energy emission of pulsar binaries. In this work, a direct method is proposed, which might probe the properties of the wind from one pulsar in a double-pulsar binary. When the radio signals from the first-formed pulsar travel through the relativistic e± flow in the pulsar wind from the younger companion, the components of different radio frequencies will be dispersed. It will introduce an additional frequency-dependent time-of-arrival delay of pulses, which is function of the orbital phase. In this paper, we formulate the above-mentioned dispersive delay with the properties of the pulsar wind. As examples, we apply the formula to the double-pulsar system PSR J0737-3039A/B and the pulsar-neutron star binary PSR B1913+16. For PSR J0737-3039A/B, the time delay in 300 MHz is ≲ 10 μ s-1 near the superior conjunction, under the optimal pulsar wind parameters, which is approximately half of the current timing accuracy. For PSR B1913+16, with the assumption that the neutron-star companion has a typical spin-down luminosity of 1033 erg s-1, the time delay is as large as 10 - 20 μ s-1 in 300 MHz. The best timing precision of this pulsar is ∼ 5 μ s-1 in 1400 MHz. Therefore, it is possible that we can find this signal in archival data. Otherwise, we can set an upper limit on the spin-down luminosity. Similar analysis can be applied to other 11 known pulsar-neutron star binaries.

Non-symbiotic haemoglobins—What's happening beyond nitric oxide scavenging?

Science.gov (United States)

Hill, Robert D.

2012-01-01

Background and aims Non-symbiotic haemoglobins have been an active research topic for over 30 years, during which time a considerable portfolio of knowledge has accumulated relative to their chemical and molecular properties, and their presence and mode of induction in plants. While progress has been made towards understanding their physiological role, there remain a number of unanswered questions with respect to their biological function. This review attempts to update recent progress in this area and to introduce a hypothesis as to how non-symbiotic haemoglobins might participate in regulating hormone signal transduction. Principal results Advances have been made towards understanding the structural nuances that explain some of the differences in ligand association characteristics of class 1 and class 2 non-symbiotic haemoglobins. Non-symbiotic haemoglobins have been found to function in seed development and germination, flowering, root development and differentiation, abiotic stress responses, pathogen invasion and symbiotic bacterial associations. Microarray analyses under various stress conditions yield uneven results relative to non-symbiotic haemoglobin expression. Increasing evidence of the role of nitric oxide (NO) in hormone responses and the known involvement of non-symbiotic haemoglobins in scavenging NO provide opportunities for fruitful research, particularly at the cellular level. Conclusions Circumstantial evidence suggests that non-symbiotic haemoglobins may have a critical function in the signal transduction pathways of auxin, ethylene, jasmonic acid, salicylic acid, cytokinin and abscisic acid. There is a strong need for research on haemoglobin gene expression at the cellular level relative to hormone signal transduction. PMID:22479675

Symbiotic and nonsymbiotic hemoglobin genes of Casuarina glauca

DEFF Research Database (Denmark)

Jacobsen-Lyon, K; Jensen, Erik Østergaard; Jørgensen, Jan-Elo

1995-01-01

Frankia. Both the nonsymbiotic and symbiotic genes retained their specific patterns of expression when introduced into the legume Lotus corniculatus. We interpret this finding to mean that the controls of expression of the symbiotic gene in Casuarina must be similar to the controls of expression...... of the leghemoglobin genes that operate in nodules formed during the interaction between rhizobia and legumes. Deletion analyses of the promoters of the Casuarina symbiotic genes delineated a region that contains nodulin motifs identified in legumes; this region is critical for the controlled expression...... of the Casuarina gene. The finding that the nonsymbiotic Casuarina gene is also correctly expressed in L. corniculatus suggests to us that a comparable non-symbiotic hemoglobin gene will be found in legume species. Udgivelsesdato: 1995-Feb...

Problems with interpreting the radio emission from hot stars

International Nuclear Information System (INIS)

Underhill, A.B.

1985-01-01

The hypothesis that the radio emission from a hot star is due solely to bremsstrahlung in a spherically symmetric wind flowing at a constant velocity and the constraint that the wind be transparent enough to allow the stationary photosphere to be seen, place a limit on mass loss/v (M/V). The constraint that the momentum in the wind be provided by the radiation field places a limit on Mv. It is noted that both constraints are satisfied by the usually deduced values of M and v(infinity) for OB supergiants. The case for early O stars is marginal, while for Wolf-Rayet stars M/v and Mv are too large to satisfy the several hypotheses usually made. The trouble is due to M being too large by at least a factor 10. It is noted that postulating that part of the radio flux from Wolf-Rayet stars is caused by processes in a low-density magnetized plasma provides a solution to the dilemma. This solution offers advantages when accounting for the emission lines of Wolf-Rayet stars. (orig.)

Impact of red giant/AGB winds on active galactic nucleus jet propagation

Science.gov (United States)

Perucho, M.; Bosch-Ramon, V.; Barkov, M. V.

2017-10-01

Context. Dense stellar winds may mass-load the jets of active galactic nuclei, although it is unclear on what time and spatial scales the mixing takes place. Aims: Our aim is to study the first steps of the interaction between jets and stellar winds, and also the scales on which the stellar wind mixes with the jet and mass-loads it. Methods: We present a detailed 2D simulation - including thermal cooling - of a bubble formed by the wind of a star designed to study the initial stages of jet-star interaction. We also study the first interaction of the wind bubble with the jet using a 3D simulation in which the star enters the jet. Stability analysis is carried out for the shocked wind structure to evaluate the distances over which the jet-dragged wind, which forms a tail, can propagate without mixing with the jet flow. Results.The 2D simulations point to quick wind bubble expansion and fragmentation after about one bubble shock crossing time. Three-dimensional simulations and stability analysis point to local mixing in the case of strong perturbations and relatively low density ratios between the jet and the jet dragged-wind, and to a possibly more stable shocked wind structure at the phase of maximum tail mass flux. Analytical estimates also indicate that very early stages of the star jet-penetration time may be also relevant for mass-loading. The combination of these and previous results from the literature suggests highly unstable interaction structures and efficient wind-jet flow mixing on the scale of the jet interaction height. Conclusions: The winds of stars with strong mass loss can efficiently mix with jets from active galactic nuclei. In addition, the initial wind bubble shocked by the jet leads to a transient, large interaction surface. The interaction between jets and stars can produce strong inhomogeneities within the jet. As mixing is expected to be effective on large scales, even individual asymptotic giant branch stars can significantly contribute to

Experimental Study on New Multi-Column Tension-Leg-Type Floating Wind Turbine

Science.gov (United States)

Zhao, Yong-sheng; She, Xiao-he; He, Yan-ping; Yang, Jian-min; Peng, Tao; Kou, Yu-feng

2018-04-01

Deep-water regions often have winds favorable for offshore wind turbines, and floating turbines currently show the greatest potential to exploit such winds. This work established proper scaling laws for model tests, which were then implemented in the construction of a model wind turbine with optimally designed blades. The aerodynamic, hydrodynamic, and elastic characteristics of the proposed new multi-column tension-leg-type floating wind turbine (WindStar TLP system) were explored in the wave tank testing of a 1:50 scale model at the State Key Laboratory of Ocean Engineering at Shanghai Jiao Tong University. Tests were conducted under conditions of still water, white noise waves, irregular waves, and combined wind, wave, and current loads. The results established the natural periods of the motion, damping, motion response amplitude operators, and tendon tensions of the WindStar TLP system under different environmental conditions, and thus could serve as a reference for further research. Key words: floating wind turbine, model test, WindStar TLP, dynamic response

Effect of diseases on symbiotic systems.

Science.gov (United States)

Tiwari, Pankaj Kumar; Sasmal, Sourav Kumar; Sha, Amar; Venturino, Ezio; Chattopadhyay, Joydev

2017-09-01

There are many species living in symbiotic communities. In this study, we analyzed models in which populations are in the mutualism symbiotic relations subject to a disease spreading among one of the species. The main goal is the characterization of symbiotic relations of coexisting species through their mutual influences on their respective carrying capacities, taking into account that this influence can be quite strong. The functional dependence of the carrying capacities reflects the fact that the correlations between populations cannot be realized merely through direct interactions, as in the usual predator-prey Lotka-Volterra model, but also through the influence of each species on the carrying capacities of the other one. Equilibria are analyzed for feasibility and stability, substantiated via numerical simulations, and global sensitivity analysis identifies the important parameters having a significant impact on the model dynamics. The infective growth rate and the disease-related mortality rate may alter the stability behavior of the system. Our results show that introducing a symbiotic species is a plausible way to control the disease in the population. Copyright © 2017 Elsevier B.V. All rights reserved.

77 FR 48138 - Topaz Solar Farms LLC; High Plains Ranch II, LLC; Bethel Wind Energy LLC; Rippey Wind Energy LLC...

Science.gov (United States)

2012-08-13

... Ranch II, LLC; Bethel Wind Energy LLC; Rippey Wind Energy LLC; Pacific Wind, LLC; Colorado Highlands Wind, LLC; Shooting Star Wind Project, LLC; Notice of Effectiveness of Exempt Wholesale Generator or... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Docket Nos. EG12-63-000; EG12-64-000...

X-RAY EMISSION FROM MAGNETIC MASSIVE STARS

International Nuclear Information System (INIS)

Nazé, Yaël; Petit, Véronique; Rinbrand, Melanie; Owocki, Stan; Cohen, David; Ud-Doula, Asif; Wade, Gregg A.

2014-01-01

Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. To clarify the systematics of the observed X-ray properties, we have analyzed a large series of Chandra and XMM-Newton observations, corresponding to all available exposures of known massive magnetic stars (over 100 exposures covering ∼60% of stars compiled in the catalog of Petit et al.). We show that the X-ray luminosity is strongly correlated with the stellar wind mass-loss rate, with a power-law form that is slightly steeper than linear for the majority of the less luminous, lower- M-dot B stars and flattens for the more luminous, higher- M-dot O stars. As the winds are radiatively driven, these scalings can be equivalently written as relations with the bolometric luminosity. The observed X-ray luminosities, and their trend with mass-loss rates, are well reproduced by new MHD models, although a few overluminous stars (mostly rapidly rotating objects) exist. No relation is found between other X-ray properties (plasma temperature, absorption) and stellar or magnetic parameters, contrary to expectations (e.g., higher temperature for stronger mass-loss rate). This suggests that the main driver for the plasma properties is different from the main determinant of the X-ray luminosity. Finally, variations of the X-ray hardnesses and luminosities, in phase with the stellar rotation period, are detected for some objects and they suggest that some temperature stratification exists in massive stars' magnetospheres

THE DUSTIEST POST-MAIN SEQUENCE STARS IN THE MAGELLANIC CLOUDS

Energy Technology Data Exchange (ETDEWEB)

Jones, Olivia C.; Meixner, Margaret; Roman-Duval, Julia [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sargent, Benjamin A. [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States); Boyer, Martha L. [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Sewiło, Marta [The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Hony, Sacha [Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universitt Heidelberg, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

2015-10-01

Using observations from the Herschel Inventory of The Agents of Galaxy Evolution (HERITAGE) survey of the Magellanic Clouds (MC), we have found 35 evolved stars and stellar end products that are bright in the far-infrared. These 28 (LMC) and 7 (SMC) sources were selected from the 529 evolved star candidates in the HERITAGE far-infrared point source catalogs. Our source identification method is based on spectral confirmation, spectral energy distribution characteristics, careful examination of the multiwavelength images and includes constraints on the luminosity, resulting in a thoroughly vetted list of evolved stars. These sources span a wide range in luminosity and hence initial mass. We found 13 low- to intermediate-mass evolved stars, including asymptotic giant branch (AGB) stars, post-AGB stars, planetary nebulae, and a symbiotic star. We also identify 10 high mass stars, including 4 of the 15 known B[e] stars in the MC, 3 extreme red supergiants that are highly enshrouded by dust, a Luminous Blue Variable, a Wolf–Rayet star, and two supernova remnants. Further, we report the detection of 9 probable evolved objects which were previously undescribed in the literature. These sources are likely to be among the dustiest evolved objects in the MC. The Herschel emission may either be due to dust produced by the evolved star or it may arise from swept-up interstellar medium material.

Dust in the Quasar Wind (Artist Concept)

Science.gov (United States)

2007-01-01

Dusty grains -- including tiny specks of the minerals found in the gemstones peridot, sapphires and rubies -- can be seen blowing in the winds of a quasar, or active black hole, in this artist's concept. The quasar is at the center of a distant galaxy. Astronomers using NASA's Spitzer Space Telescope found evidence that such quasar winds might have forged these dusty particles in the very early universe. The findings are another clue in an ongoing cosmic mystery: where did all the dust in our young universe come from? Dust is crucial for efficient star formation as it allows the giant clouds where stars are born to cool quickly and collapse into new stars. Once a star has formed, dust is also needed to make planets and living creatures. Dust has been seen as far back as when the universe was less than a tenth of its current age, but how did it get there? Most dust in our current epoch forms in the winds of evolved stars that did not exist when the universe was young. Theorists had predicted that winds from quasars growing in the centers of distant galaxies might be a source of this dust. While the environment close to a quasar is too hot for large molecules like dust grains to survive, dust has been found in the cooler, outer regions. Astronomers now have evidence that dust is created in these outer winds. Using Spitzer's infrared spectrograph instrument, scientists found a wealth of dust grains in a quasar called PG2112+059 located at the center of a galaxy 8 billion light-years away. The grains - including corundum (sapphires and rubies); forsterite (peridot); and periclase (naturally occurring in marble) - are not typically found in galaxies without quasars, suggesting they might have been freshly formed in the quasar's winds.

Observations of mass loss from OB and Wolf-Rayet stars

International Nuclear Information System (INIS)

Barlow, M.J.

1982-01-01

In this review, three observationally accessible parameters of the winds of OB and Wolf-Rayet stars are discussed: (1) Terminal velocities, (2) Velocity laws, (3) Mass loss rates. In addition, some discussion of the ionisation structure of the winds is included. In general, only the most recent results for OB stars are mentioned. (Auth.)

Cytokinins in Symbiotic Nodulation: When, Where, What For?

Science.gov (United States)

Gamas, Pascal; Brault, Mathias; Jardinaud, Marie-Françoise; Frugier, Florian

2017-09-01

Substantial progress has been made in the understanding of early stages of the symbiotic interaction between legume plants and rhizobium bacteria. Those include the specific recognition of symbiotic partners, the initiation of bacterial infection in root hair cells, and the inception of a specific organ in the root cortex, the nodule. Increasingly complex regulatory networks have been uncovered in which cytokinin (CK) phytohormones play essential roles in different aspects of early symbiotic stages. Intriguingly, these roles can be either positive or negative, cell autonomous or non-cell autonomous, and vary, depending on time, root tissues, and possibly legume species. Recent developments on CK symbiotic functions and interconnections with other signaling pathways during nodule initiation are the focus of this review. Copyright © 2017 Elsevier Ltd. All rights reserved.

Effects of symbiotic bacteria on chemical sensitivity of Daphnia magna.

Science.gov (United States)

Manakul, Patcharaporn; Peerakietkhajorn, Saranya; Matsuura, Tomoaki; Kato, Yasuhiko; Watanabe, Hajime

2017-07-01

The crustacean zooplankton Daphnia magna has been widely used for chemical toxicity tests. Although abiotic factors have been well documented in ecotoxicological test protocols, biotic factors that may affect the sensitivity to chemical compounds remain limited. Recently, we identified symbiotic bacteria that are critical for the growth and reproduction of D. magna. The presence of symbiotic bacteria on Daphnia raised the question as to whether these bacteria have a positive or negative effect on toxicity tests. In order to evaluate the effects of symbiotic bacteria on toxicity tests, bacteria-free Daphnia were prepared, and their chemical sensitivities were compared with that of Daphnia with symbiotic bacteria based on an acute immobilization test. The Daphnia with symbiotic bacteria showed higher chemical resistance to nonylphenol, fenoxycarb, and pentachlorophenol than bacteria-free Daphnia. These results suggested potential roles of symbiotic bacteria in the chemical resistance of its host Daphnia. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mass-loss rates of cool stars

Science.gov (United States)

Katrien Els Decin, Leen

2015-08-01

Over much of the initial mass function, stars lose a significant fraction of their mass through a stellar wind during the late stages of their evolution when being a (super)giant star. As of today, we can not yet predict the mass-loss rate during the (super)giant phase for a given star with specific stellar parameters from first principles. This uncertainty directly impacts the accuracy of current stellar evolution and population synthesis models that predict the enrichment of the interstellar medium by these stellar winds. Efforts to establish the link between the initial physical and chemical conditions at stellar birth and the mass-loss rate during the (super)giant phase have proceeded on two separate tracks: (1) more detailed studies of the chemical and morpho-kinematical structure of the stellar winds of (super)giant stars in our own Milky Way by virtue of the proximity, and (2) large scale and statistical studies of a (large) sample of stars in other galaxies (such as the LMC and SMC) and globular clusters eliminating the uncertainty on the distance estimate and providing insight into the dependence of the mass-loss rate on the metallicity. In this review, I will present recent results of both tracks, will show how recent measurements confirm (some) theoretical predictions, but also how results from the first track admonish of common misconceptions inherent in the often more simplified analysis used to analyse the large samples from track 2.

He II lambda-4686 in Eta Carinae: Collapse of the Wind-Wind Collision Region During Periastron Passage

Science.gov (United States)

Teodoro, M.; Damineli, A.; Arias, J. I.; DeAraujo, F. X.; Barba, R. H.; Corcoran, M. F.; Fernandes, M. Borges; Fernandez-Lajus, E.; Fraga, L.; Gamen, R. C.;

Gamma rays from active regions in the galaxy: the possible contribution of stellar winds

International Nuclear Information System (INIS)

Cesarsky, C.J.; Montmerle, Thierry.

1982-08-01

Massive stars release a considerable amount of mechanical energy in the form of strong stellar winds. A fraction of this energy may be transferred to relativistic cosmic rays by diffusive shock acceleration at the wind boundary, and/or in the expanding, turbulent wind itself. Massive stars are most frequently found in OB associations, surrounded by H II regions lying at the edge of dense molecular clouds. The interaction of the freshly accelerated particles with matter gives rise to #betta#-ray emission. In this paper, we first briefly review the current knowledge on the energetics of strong stellar winds from O and Wolf-Rayet stars, as well as from T Tauri stars. Taking into account the finite lifetime of these stars, we then proceed to show that stellar winds dominate the energetics of OB associations during the first 4 to 6 million years, after which supernovae take over. In the solar neighborhood, the star formation rate is constant, and a steady-state situation prevails, in which the supernova contribution is found to be dominant. A small, but meaningful fraction of the CO S-B #betta#-ray sources may be fueled by WR and O stellar winds in OB associations, while the power released by T Tauri stars alone is perhaps insufficient to account for the #betta#-ray emission of nearby dark clouds. Finally, we discuss some controversial aspects of the physics of particle acceleration by stellar winds

Symbiotic Origin of Aging.

Science.gov (United States)

Greenberg, Edward F; Vatolin, Sergei

2018-06-01

Normally aging cells are characterized by an unbalanced mitochondrial dynamic skewed toward punctate mitochondria. Genetic and pharmacological manipulation of mitochondrial fission/fusion cycles can contribute to both accelerated and decelerated cellular or organismal aging. In this work, we connect these experimental data with the symbiotic theory of mitochondrial origin to generate new insight into the evolutionary origin of aging. Mitochondria originated from autotrophic α-proteobacteria during an ancient endosymbiotic event early in eukaryote evolution. To expand beyond individual host cells, dividing α-proteobacteria initiated host cell lysis; apoptosis is a product of this original symbiont cell lytic exit program. Over the course of evolution, the host eukaryotic cell attenuated the harmful effect of symbiotic proto-mitochondria, and modern mitochondria are now functionally interdependent with eukaryotic cells; they retain their own circular genomes and independent replication timing. In nondividing differentiated or multipotent eukaryotic cells, intracellular mitochondria undergo repeated fission/fusion cycles, favoring fission as organisms age. The discordance between cellular quiescence and mitochondrial proliferation generates intracellular stress, eventually leading to a gradual decline in host cell performance and age-related pathology. Hence, aging evolved from a conflict between maintenance of a quiescent, nonproliferative state and the evolutionarily conserved propagation program driving the life cycle of former symbiotic organisms: mitochondria.

PULSATION-TRIGGERED MASS LOSS FROM AGB STARS: THE 60 DAY CRITICAL PERIOD

International Nuclear Information System (INIS)

McDonald, I.; Zijlstra, A. A.

2016-01-01

Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here, we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalog. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately coincides with the point where the star transitions to the first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increasing at this point, by a factor of ∼10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode at a period of ∼300 days.

Isolated/Non-Isolated Quad-Inverter Configuration for Multilevel Symmetrical/Asymmetrical Dual Six-Phase Star-Winding Converter

DEFF Research Database (Denmark)

Padmanaban, Sanjeevi Kumar; Hontz, Michael R.; Khanna, Raghav

2016-01-01

This article presents the developments of a novel isolated/non-isolated quad inverter configuration for multilevel dual six-phase (twelve-phase) star-winding converter. The modular circuit consists of four standard voltage source inverters (VSIs). Each VSI is incorporated with one bi-directional ...... systems, electrical vehicles, AC tractions, and `More-Electric Aircraft' propulsion systems....... converter is numerically modeled using Matlab/PLECS simulation software and the predicted behavior of the system is analyzed and presented. Good agreement is obtained between these results and the theoretical analysis. Suitable applications for the converter include (low-voltage/high-current) medium power...

Plant Genes Involved in Symbiotic Sinal Perception/Signal Transduction

DEFF Research Database (Denmark)

Binder, A; Soyano, T; Hayashi, H

2014-01-01

to nodule primordia formation, and the infection thread initiation in the root hairs guiding bacteria towards dividing cortical cells. This chapter focuses on the plant genes involved in the recognition of the symbiotic signal produced by rhizobia, and the downstream genes, which are part of a complex...... symbiotic signalling pathway that leads to the generation of calcium spiking in the nuclear regions and activation of transcription factors controlling symbiotic genes induction...

Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

NARCIS (Netherlands)

Schneider, F.R.N.; Izzard, R.G.; de Mink, S.E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V.V.; Huβman, B.; Liermann, A.; Sana, H.

2014-01-01

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass

Intracellular pH and its response to CO2-driven seawater acidification in symbiotic versus non-symbiotic coral cells.

Science.gov (United States)

Gibbin, Emma M; Putnam, Hollie M; Davy, Simon K; Gates, Ruth D

2014-06-01

Regulating intracellular pH (pHi) is critical for optimising the metabolic activity of corals, yet the mechanisms involved in pH regulation and the buffering capacity within coral cells are not well understood. Our study investigated how the presence of symbiotic dinoflagellates affects the response of pHi to PCO2-driven seawater acidification in cells isolated from Pocillopora damicornis. Using the fluorescent dye BCECF-AM, in conjunction with confocal microscopy, we simultaneously characterised the pHi response in host coral cells and their dinoflagellate symbionts, in symbiotic and non-symbiotic states under saturating light, with and without the photosynthetic inhibitor DCMU. Each treatment was run under control (pH 7.8) and CO2-acidified seawater conditions (decreasing pH from 7.8 to 6.8). After 105 min of CO2 addition, by which time the external pH (pHe) had declined to 6.8, the dinoflagellate symbionts had increased their pHi by 0.5 pH units above control levels when in the absence of DCMU. In contrast, in both symbiotic and non-symbiotic host coral cells, 15 min of CO2 addition (0.2 pH unit drop in pHe) led to cytoplasmic acidosis equivalent to 0.3-0.4 pH units irrespective of whether DCMU was present. Despite further seawater acidification over the duration of the experiment, the pHi of non-symbiotic coral cells did not change, though in host cells containing a symbiont cell the pHi recovered to control levels when photsynthesis was not inhibited. This recovery was negated when cells were incubated with DCMU. Our results reveal that photosynthetic activity of the endosymbiont is tightly coupled with the ability of the host cell to recover from cellular acidosis after exposure to high CO2/low pH. © 2014. Published by The Company of Biologists Ltd.

High Energy Emission of Symbiotic Recurrent Novae: RS Oph and V407 Cyg

Directory of Open Access Journals (Sweden)

Hernanz M.

2012-06-01

Full Text Available Recurrent novae occurring in symbiotic binaries are candidate sources of high energy photons, reaching GeV energies. Such emission is a consequence of particle acceleration leading to pion production. the shock between matter ejected by the white dwarf, undergoing a nova explosion, and the wind from the red giant companion are responsible for such a process, which mimics a supernova remnant but with much smaller energetic output and much shorter time scales. Inverse Compton can also be responsible for high energy emission. Recent examples are V407 Cyg, detected by Fermi, and RS Oph, which unfortunately exploded in 2006, before Fermi was launched.

Interacting Winds in Eclipsing Symbiotic Systems – The Case Study ...

Indian Academy of Sciences (India)

produced by the collision of two stellar winds (Vogel 1991, 1993; Girard & Willson ... Therefore, in the nebular environment an energetic zone .... 1b and 1d). .... By applying Kepler's second law, we obtain the time required to cover the corre-.

Effect of neem cake/fertilizers on symbiotic and non-symbiotic N2 fixing bacteria

International Nuclear Information System (INIS)

Akhtar, S.; Solangi, A.H.; Gilani, G.; Pirzada, M.H.

2002-01-01

Neem cake amendment in soil at 1.3% no adverse effect on the population of four symbiotic Rhizobium species viz., japonicum, R. leguminosarum, R. Phaseoli and R. Fredii and three non-symbiotic free living nitrogen fixers bacteria viz., Pseudomonas diazotrophicus, Klebsiella planticola and Enterobacter cloacae. Neem cake extracted with n-hexane stimulated the growth of Rhizobium species in vitro, whereas Neem cake expeller extracted neither inhibited nor stimulated the growth of Rhizobium species except for R. Fredii, whose was slightly retarded. The fertilizers (urea, NPK and DAP) had no adverse effect on these bacteria even at the dosage ten times higher the recommended dose. (author)

THE DISK WIND IN THE RAPIDLY SPINNING STELLAR-MASS BLACK HOLE 4U 1630–472 OBSERVED WITH NuSTAR

Energy Technology Data Exchange (ETDEWEB)

King, Ashley L.; Miller, Jon M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Walton, Dominic J.; Fürst, Felix; Harrison, Fiona A. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Barret, Didier [Université de Toulouse, UPS-OMP, IRAP, Toulouse (France); Boggs, Steven E.; Craig, William W.; Krivonos, Roman; Tomsick, John A. [Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States); Christensen, Finn E. [DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Fabian, Andy C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Hailey, Charles J.; Mori, Kaya [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Natalucci, Lorenzo [Istituto Nazionale di Astrofisica, INAF-IAPS, via del Fosso del Cavaliere, I-00133 Roma (Italy); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States); Zhang, William W., E-mail: ashking@umich.edu [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2014-03-20

We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630–472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, a{sub ∗}=0.985{sub −0.014}{sup +0.005} (1σ statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at 7.03 ± 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log ξ=3.6{sub −0.3}{sup +0.2}) and is dominated by He-like Fe XXV, the wind has a velocity of v/c=0.043{sub −0.007}{sup +0.002} (12900{sub −2100}{sup +600} km s{sup –1}). If the line is instead associated with a more highly ionized gas (log ξ=6.1{sub −0.6}{sup +0.7}), and is dominated by Fe XXVI, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.

Spiraling Out of Control: Three-dimensional Hydrodynamical Modeling of the Colliding Winds in η Carinae

Science.gov (United States)

Parkin, E. R.; Pittard, J. M.; Corcoran, M. F.; Hamaguchi, K.

2011-01-01

Three-dimensional adaptive mesh refinement hydrodynamical simulations of the wind-wind collision between the enigmatic supermassive star η Car and its mysterious companion star are presented which include radiative driving of the stellar winds, gravity, optically thin radiative cooling, and orbital motion. Simulations with static stars with a periastron passage separation reveal that the preshock companion star's wind speed is sufficiently reduced so that radiative cooling in the postshock gas becomes important, permitting the runaway growth of nonlinear thin-shell instabilities (NTSIs) which massively distort the wind-wind collision region (WCR). However, large-scale simulations, which include the orbital motion of the stars, show that orbital motion reduces the impact of radiative inhibition and thus increases the acquired preshock velocities. As such, the postshock gas temperature and cooling time see a commensurate increase, and sufficient gas pressure is preserved to stabilize the WCR against catastrophic instability growth. We then compute synthetic X-ray spectra and light curves and find that, compared to previous models, the X-ray spectra agree much better with XMM-Newton observations just prior to periastron. The narrow width of the 2009 X-ray minimum can also be reproduced. However, the models fail to reproduce the extended X-ray minimum from previous cycles. We conclude that the key to explaining the extended X-ray minimum is the rate of cooling of the companion star's postshock wind. If cooling is rapid then powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the companion star's preshock wind, albeit with a stronger radiation-wind coupling than explored in this work, could be an effective trigger.

SPIRALING OUT OF CONTROL: THREE-DIMENSIONAL HYDRODYNAMICAL MODELING OF THE COLLIDING WINDS IN η CARINAE

International Nuclear Information System (INIS)

Parkin, E. R.; Pittard, J. M.; Corcoran, M. F.; Hamaguchi, K.

2011-01-01

Three-dimensional adaptive mesh refinement hydrodynamical simulations of the wind-wind collision between the enigmatic supermassive star η Car and its mysterious companion star are presented which include radiative driving of the stellar winds, gravity, optically thin radiative cooling, and orbital motion. Simulations with static stars with a periastron passage separation reveal that the preshock companion star's wind speed is sufficiently reduced so that radiative cooling in the postshock gas becomes important, permitting the runaway growth of nonlinear thin-shell instabilities (NTSIs) which massively distort the wind-wind collision region (WCR). However, large-scale simulations, which include the orbital motion of the stars, show that orbital motion reduces the impact of radiative inhibition and thus increases the acquired preshock velocities. As such, the postshock gas temperature and cooling time see a commensurate increase, and sufficient gas pressure is preserved to stabilize the WCR against catastrophic instability growth. We then compute synthetic X-ray spectra and light curves and find that, compared to previous models, the X-ray spectra agree much better with XMM-Newton observations just prior to periastron. The narrow width of the 2009 X-ray minimum can also be reproduced. However, the models fail to reproduce the extended X-ray minimum from previous cycles. We conclude that the key to explaining the extended X-ray minimum is the rate of cooling of the companion star's postshock wind. If cooling is rapid then powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the companion star's preshock wind, albeit with a stronger radiation-wind coupling than explored in this work, could be an effective trigger.

WIND BRAKING OF MAGNETARS

International Nuclear Information System (INIS)

Tong, H.; Xu, R. X.; Qiao, G. J.; Song, L. M.

2013-01-01

We explore the wind braking of magnetars considering recent observations challenging the traditional magnetar model. There is evidence for strong multipole magnetic fields in active magnetars, but the dipole field inferred from spin-down measurements may be strongly biased by particle wind. Recent observations challenging the traditional model of magnetars may be explained naturally by the wind braking scenario: (1) the supernova energies of magnetars are of normal value; (2) the non-detection in Fermi observations of magnetars; (3) the problem posed by low magnetic field soft gamma-ray repeaters; (4) the relation between magnetars and high magnetic field pulsars; and (5) a decreasing period derivative during magnetar outbursts. Transient magnetars with L x rot may still be magnetic dipole braking. This may explain why low luminosity magnetars are more likely to have radio emissions. A strong reduction of the dipole magnetic field is possible only when the particle wind is very collimated at the star surface. A small reduction of the dipole magnetic field may result from detailed considerations of magnetar wind luminosity. In the wind braking scenario, magnetars are neutron stars with a strong multipole field. For some sources, a strong dipole field may no longer be needed. A magnetism-powered pulsar wind nebula will be one of the consequences of wind braking. For a magnetism-powered pulsar wind nebula, we should see a correlation between the nebula luminosity and the magnetar luminosity. Under the wind braking scenario, a braking index smaller than three is expected. Future braking index measurement of a magnetar may tell us whether magnetars are wind braking or magnetic dipole braking.

Phylogeny of Symbiotic Genes and the Symbiotic Properties of Rhizobia Specific to Astragalus glycyphyllos L.

Science.gov (United States)

Gnat, Sebastian; Małek, Wanda; Oleńska, Ewa; Wdowiak-Wróbel, Sylwia; Kalita, Michał; Łotocka, Barbara; Wójcik, Magdalena

2015-01-01

The phylogeny of symbiotic genes of Astragalus glycyphyllos L. (liquorice milkvetch) nodule isolates was studied by comparative sequence analysis of nodA, nodC, nodH and nifH loci. In all these genes phylograms, liquorice milkvetch rhizobia (closely related to bacteria of three species, i.e. Mesorhizobium amorphae, Mesorhizobium septentrionale and Mesorhizobium ciceri) formed one clearly separate cluster suggesting the horizontal transfer of symbiotic genes from a single ancestor to the bacteria being studied. The high sequence similarity of the symbiotic genes of A. glycyphyllos rhizobia (99-100% in the case of nodAC and nifH genes, and 98-99% in the case of nodH one) points to the relatively recent (in evolutionary scale) lateral transfer of these genes. In the nodACH and nifH phylograms, A. glycyphyllos nodule isolates were grouped together with the genus Mesorhizobium species in one monophyletic clade, close to M. ciceri, Mesorhizobium opportunistum and Mesorhizobium australicum symbiovar biserrulae bacteria, which correlates with the close relationship of these rhizobia host plants. Plant tests revealed the narrow host range of A. glycyphyllos rhizobia. They formed effective symbiotic interactions with their native host (A. glycyphyllos) and Amorpha fruticosa but not with 11 other fabacean species. The nodules induced on A. glycyphyllos roots were indeterminate with apical, persistent meristem, an age gradient of nodule tissues and cortical vascular bundles. To reflect the symbiosis-adaptive phenotype of rhizobia, specific for A. glycyphyllos, we propose for these bacteria the new symbiovar "glycyphyllae", based on nodA and nodC genes sequences.

Evolutionary Instability of Symbiotic Function in Bradyrhizobium japonicum

Science.gov (United States)

Sachs, Joel L.; Russell, James E.; Hollowell, Amanda C.

2011-01-01

Bacterial mutualists are often acquired from the environment by eukaryotic hosts. However, both theory and empirical work suggest that this bacterial lifestyle is evolutionarily unstable. Bacterial evolution outside of the host is predicted to favor traits that promote an independent lifestyle in the environment at a cost to symbiotic function. Consistent with these predictions, environmentally-acquired bacterial mutualists often lose symbiotic function over evolutionary time. Here, we investigate the evolutionary erosion of symbiotic traits in Bradyrhizobium japonicum, a nodulating root symbiont of legumes. Building on a previous published phylogeny we infer loss events of nodulation capability in a natural population of Bradyrhizobium, potentially driven by mutation or deletion of symbiosis loci. Subsequently, we experimentally evolved representative strains from the symbiont population under host-free in vitro conditions to examine potential drivers of these loss events. Among Bradyrhizobium genotypes that evolved significant increases in fitness in vitro, two exhibited reduced symbiotic quality, but no experimentally evolved strain lost nodulation capability or evolved any fixed changes at six sequenced loci. Our results are consistent with trade-offs between symbiotic quality and fitness in a host free environment. However, the drivers of loss-of-nodulation events in natural Bradyrhizobium populations remain unknown. PMID:22073160

[Progress of heterotrophic studies on symbiotic corals].

Science.gov (United States)

Yang, Yang-Chu-Qiao; Hong, Wen Ting; Wang, Shu Hong

2017-12-01

Heterotrophy of zooxanthellae symbiotic corals refers to the nutrition directly coming from food absorption, not the nutrition obtained from photosynthesis. Most ex situ propagation of symbiotic corals focused on the effects of irradiation, flow rate and water quality on corals, few of them involved in the demand and supply of coral heterotrophic nutrition. This paper reviewed the significance of heterotrophic nutrient supply to symbiotic corals from the sources of coral heterotrophic nutrition, the factors affecting the supply of coral heterotrophic nutrient, and the methods of how to study the coral heterotrophy. In general, the research of coral heterotrophy is just at the beginning stage, and future studies should focus on the inherent mechanism of coral feeding selection and developing more effective research methods.

The Evolution of Low-Metallicity Massive Stars

Science.gov (United States)

Szécsi, Dorottya

2016-07-01

Massive star evolution taking place in astrophysical environments consisting almost entirely of hydrogen and helium - in other words, low-metallicity environments - is responsible for some of the most intriguing and energetic cosmic phenomena, including supernovae, gamma-ray bursts and gravitational waves. This thesis aims to investigate the life and death of metal-poor massive stars, using theoretical simulations of the stellar structure and evolution. Evolutionary models of rotating, massive stars (9-600 Msun) with an initial metal composition appropriate for the low-metallicity dwarf galaxy I Zwicky 18 are presented and analyzed. We find that the fast rotating models (300 km/s) become a particular type of objects predicted only at low-metallicity: the so-called Transparent Wind Ultraviolet INtense (TWUIN) stars. TWUIN stars are fast rotating massive stars that are extremely hot (90 kK), very bright and as compact as Wolf-Rayet stars. However, as opposed to Wolf-Rayet stars, their stellar winds are optically thin. As these hot objects emit intense UV radiation, we show that they can explain the unusually high number of ionizing photons of the dwarf galaxy I Zwicky 18, an observational quantity that cannot be understood solely based on the normal stellar population of this galaxy. On the other hand, we find that the most massive, slowly rotating models become another special type of object predicted only at low-metallicity: core-hydrogen-burning cool supergiant stars. Having a slow but strong stellar wind, these supergiants may be important contributors in the chemical evolution of young galactic globular clusters. In particular, we suggest that the low mass stars observed today could form in a dense, massive and cool shell around these, now dead, supergiants. This scenario is shown to explain the anomalous surface abundances observed in these low mass stars, since the shell itself, having been made of the mass ejected by the supergiant’s wind, contains nuclear

[Response of arbuscular mycorrhizal fungal lipid metabolism to symbiotic signals in mycorrhiza].

Science.gov (United States)

Tian, Lei; Li, Yuanjing; Tian, Chunjie

2016-01-04

Arbuscular mycorrhizal (AM) fungi play an important role in energy flow and nutrient cycling, besides their wide distribution in the cosystem. With a long co-evolution, AM fungi and host plant have formed a symbiotic relationship, and fungal lipid metabolism may be the key point to find the symbiotic mechanism in arbusculart mycorrhiza. Here, we reviewed the most recent progress on the interaction between AM fungal lipid metabolism and symbiotic signaling networks, especially the response of AM fungal lipid metabolism to symbiotic signals. Furthermore, we discussed the response of AM fungal lipid storage and release to symbiotic or non-symbiotic status, and the correlation between fungal lipid metabolism and nutrient transfer in mycorrhiza. In addition, we explored the feedback of the lipolysis process to molecular signals during the establishment of symbiosis, and the corresponding material conversion and energy metabolism besides the crosstalk of fungal lipid metabolism and signaling networks. This review will help understand symbiotic mechanism of arbuscular mycorrhiza fungi and further application in ecosystem.

Microscopic observation of symbiotic and aposymbiotic juvenile corals in nutrient-enriched seawater.

Science.gov (United States)

Tanaka, Yasuaki; Iguchi, Akira; Inoue, Mayuri; Mori, Chiharu; Sakai, Kazuhiko; Suzuki, Atsushi; Kawahata, Hodaka; Nakamura, Takashi

2013-03-15

Symbiotic and aposymbiotic juvenile corals, which were grown in the laboratory from the gametes of the scleractinian coral Acropora digitifera and had settled down onto plastic culture plates, were observed with a microscope under different nutrient conditions. The symbiotic corals successfully removed the surrounding benthic microalgae (BMA), whereas the aposymbiotic corals were in close physical contact with BMA. The areal growth rate of the symbiotic corals was significantly higher than that of the aposymbiotic corals. The addition of nutrients to the culture seawater increased the chlorophyll a content in the symbiotic coral polyps and enhanced the growth of some of the symbiotic corals, however the average growth rate was not significantly affected, most likely because of the competition with BMA. The comparison between the symbiotic and aposymbiotic juvenile corals showed that the establishment of a symbiotic association could be imperative for post-settlement juvenile corals to survive in high-nutrient seawater. Copyright © 2012 Elsevier Ltd. All rights reserved.

Symbiotic regulation of plant growth, development and reproduction

Science.gov (United States)

Russell J. Rodriguez; D. Carl Freeman; E. Durant McArthur; Yong Ok Kim; Regina S. Redman

2009-01-01

The growth and development of rice (Oryzae sativa) seedlings was shown to be regulated epigenetically by a fungal endophyte. In contrast to un-inoculated (nonsymbiotic) plants, endophyte colonized (symbiotic) plants preferentially allocated resources into root growth until root hairs were well established. During that time symbiotic roots expanded at...

The theory of radiation driven stellar winds and the Wolf-Rayet phenomenon

International Nuclear Information System (INIS)

Abbott, D.C.

1982-01-01

The author considers the question of whether the mass loss observed from Wolf-Rayet stars can be explained by a version of wind theory which is scaled to the conditions found in the envelopes of Wolf-Rayet stars. He discusses the following topics: - The calculated radiation pressure in OB stars, and its dependence on temperature, density, and chemical composition. - A comparison between predicted and observed mass loss rates and terminal velocities for OB stars. - The applicability of the standard radiation driven wind models to Wolf-Rayet stars. - Speculations on how Wolf-Rayet stars achieve their enormous mass loss rates within the context of the radiation pressure mechanism. (Auth.)

Changes in the Silicate Dust Features of the Symbiotic Star R Aquarii Prior to the Upcoming 2022 Eclipse and Periastron Events

Science.gov (United States)

Omelian, Eric; Sankrit, Ravi; Helton, Andrew; Gorti, Uma; Wagner, R. Mark

2018-01-01

The symbiotic star, R Aquarii (R Aqr) consists of a dusty, pulsating Mira (period 387 days) and a hot white dwarf (WD) that orbit each other with a period of about 44 years. Based on the light curve from ca. 1890 CE onwards, and associated nebular and jet activity, it has been established (with a high degree of confidence) that the WD eclipses the Mira around the time of the periastron passage. One of the phenomena associated with this phase in the orbit is enhanced accretion onto the WD, which in turn energizes the jet outflow. The next eclipse is imminent, and it is estimated that periastron will occur in 2022. Infrared observations of R Aqr have established that the emission consists of a thermal spectrum with an effective temperature of about 2500 K with superposed silicate dust features. These silicate features are known to vary with time, and UKIRT spectra taken within a single Mira phase have shown that some of the variation is correlated with the pulsation of the dust envelope of the AGB star.We have used the FORCAST instrument on SOFIA to observe R Aqr during Cycles 4 and 5 as part of an ongoing monitoring of the system as it goes through eclipse and periastron. Photometry between 6 and 37 μm, and spectra covering the 10 and 18 μm silicate features have shown significant changes in the spectrum compared with earlier data in the same wavelength range obtained by ISO at an epoch closer to apastron. We present our data along with archival data from other IR observatories and use them to characterize the changes in the silicate emission. These data are presented along with model calculations using DUSTY and RADMC-3D that we have used to explore the changes in dust properties that are necessary to explain the differences in the emission profiles. We also present our plans for continued monitoring of R Aqr through the upcoming eclipse, which is required in order to separate the effects of pulsation from the longer-term orbital effects on the dust profiles.

Comprehensive EST analysis of the symbiotic sea anemone, Anemonia viridis.

Science.gov (United States)

Sabourault, Cécile; Ganot, Philippe; Deleury, Emeline; Allemand, Denis; Furla, Paola

2009-07-23

Coral reef ecosystems are renowned for their diversity and beauty. Their immense ecological success is due to a symbiotic association between cnidarian hosts and unicellular dinoflagellate algae, known as zooxanthellae. These algae are photosynthetic and the cnidarian-zooxanthellae association is based on nutritional exchanges. Maintenance of such an intimate cellular partnership involves many crosstalks between the partners. To better characterize symbiotic relationships between a cnidarian host and its dinoflagellate symbionts, we conducted a large-scale EST study on a symbiotic sea anemone, Anemonia viridis, in which the two tissue layers (epiderm and gastroderm) can be easily separated. A single cDNA library was constructed from symbiotic tissue of sea anemones A. viridis in various environmental conditions (both normal and stressed). We generated 39,939 high quality ESTs, which were assembled into 14,504 unique sequences (UniSeqs). Sequences were analysed and sorted according to their putative origin (animal, algal or bacterial). We identified many new repeated elements in the 3'UTR of most animal genes, suggesting that these elements potentially have a biological role, especially with respect to gene expression regulation. We identified genes of animal origin that have no homolog in the non-symbiotic starlet sea anemone Nematostella vectensis genome, but in other symbiotic cnidarians, and may therefore be involved in the symbiosis relationship in A. viridis. Comparison of protein domain occurrence in A. viridis with that in N. vectensis demonstrated an increase in abundance of some molecular functions, such as protein binding or antioxidant activity, suggesting that these functions are essential for the symbiotic state and may be specific adaptations. This large dataset of sequences provides a valuable resource for future studies on symbiotic interactions in Cnidaria. The comparison with the closest available genome, the sea anemone N. vectensis, as well as

Comprehensive EST analysis of the symbiotic sea anemone, Anemonia viridis

Directory of Open Access Journals (Sweden)

Deleury Emeline

2009-07-01

Full Text Available Abstract Background Coral reef ecosystems are renowned for their diversity and beauty. Their immense ecological success is due to a symbiotic association between cnidarian hosts and unicellular dinoflagellate algae, known as zooxanthellae. These algae are photosynthetic and the cnidarian-zooxanthellae association is based on nutritional exchanges. Maintenance of such an intimate cellular partnership involves many crosstalks between the partners. To better characterize symbiotic relationships between a cnidarian host and its dinoflagellate symbionts, we conducted a large-scale EST study on a symbiotic sea anemone, Anemonia viridis, in which the two tissue layers (epiderm and gastroderm can be easily separated. Results A single cDNA library was constructed from symbiotic tissue of sea anemones A. viridis in various environmental conditions (both normal and stressed. We generated 39,939 high quality ESTs, which were assembled into 14,504 unique sequences (UniSeqs. Sequences were analysed and sorted according to their putative origin (animal, algal or bacterial. We identified many new repeated elements in the 3'UTR of most animal genes, suggesting that these elements potentially have a biological role, especially with respect to gene expression regulation. We identified genes of animal origin that have no homolog in the non-symbiotic starlet sea anemone Nematostella vectensis genome, but in other symbiotic cnidarians, and may therefore be involved in the symbiosis relationship in A. viridis. Comparison of protein domain occurrence in A. viridis with that in N. vectensis demonstrated an increase in abundance of some molecular functions, such as protein binding or antioxidant activity, suggesting that these functions are essential for the symbiotic state and may be specific adaptations. Conclusion This large dataset of sequences provides a valuable resource for future studies on symbiotic interactions in Cnidaria. The comparison with the closest

Infrared properties of Mira-type variables and other cool stars as determined from JHKL photometry

Energy Technology Data Exchange (ETDEWEB)

Feast, M W; Robertson, B S.C.; Catchpole, R M; Evans, T L; Glass, I S; Carter, B S [South African Astronomical Observatory, Cape

1982-11-01

Extensive infrared photometry of Me(Mira) variables and of C, S, SC and related stars is used to establish two-colour diagrams and period-colour relations. The characteristic areas in these plots occupied by the different classes of objects are delineated. The main aim is to provide a norm with which other stars (e.g. red variables in the Galactic Center and in the Magellanic Clouds and peculiar stars) can be compared. The (J-H) versus period relation offers a method for determining the interstellar reddenings of Me variables. The strong concentration to the longer periods of Miras which are OH masers is probably due primarily to the fact that in the sample surveyed, these stars also have the brightest apparent bolometric magnitudes. Period-amplitude plots are shown for Me variables. The Mira components in symbiotic stars are found to have exceptionally large amplitudes.

Evolutionary signals of symbiotic persistence in the legume-rhizobia mutualism.

Science.gov (United States)

Werner, Gijsbert D A; Cornwell, William K; Cornelissen, Johannes H C; Kiers, E Toby

2015-08-18

Understanding the origins and evolutionary trajectories of symbiotic partnerships remains a major challenge. Why are some symbioses lost over evolutionary time whereas others become crucial for survival? Here, we use a quantitative trait reconstruction method to characterize different evolutionary stages in the ancient symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria, asking how labile is symbiosis across different host clades. We find that more than half of the 1,195 extant nodulating legumes analyzed have a high likelihood (>95%) of being in a state of high symbiotic persistence, meaning that they show a continued capacity to form the symbiosis over evolutionary time, even though the partnership has remained facultative and is not obligate. To explore patterns associated with the likelihood of loss and retention of the N2-fixing symbiosis, we tested for correlations between symbiotic persistence and legume distribution, climate, soil and trait data. We found a strong latitudinal effect and demonstrated that low mean annual temperatures are associated with high symbiotic persistence in legumes. Although no significant correlations between soil variables and symbiotic persistence were found, nitrogen and phosphorus leaf contents were positively correlated with legumes in a state of high symbiotic persistence. This pattern suggests that highly demanding nutrient lifestyles are associated with more stable partnerships, potentially because they "lock" the hosts into symbiotic dependency. Quantitative reconstruction methods are emerging as a powerful comparative tool to study broad patterns of symbiont loss and retention across diverse partnerships.

Evolutionary signals of symbiotic persistence in the legume–rhizobia mutualism

Science.gov (United States)

Werner, Gijsbert D. A.; Cornwell, William K.; Cornelissen, Johannes H. C.; Kiers, E. Toby

2015-01-01

Understanding the origins and evolutionary trajectories of symbiotic partnerships remains a major challenge. Why are some symbioses lost over evolutionary time whereas others become crucial for survival? Here, we use a quantitative trait reconstruction method to characterize different evolutionary stages in the ancient symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria, asking how labile is symbiosis across different host clades. We find that more than half of the 1,195 extant nodulating legumes analyzed have a high likelihood (>95%) of being in a state of high symbiotic persistence, meaning that they show a continued capacity to form the symbiosis over evolutionary time, even though the partnership has remained facultative and is not obligate. To explore patterns associated with the likelihood of loss and retention of the N2-fixing symbiosis, we tested for correlations between symbiotic persistence and legume distribution, climate, soil and trait data. We found a strong latitudinal effect and demonstrated that low mean annual temperatures are associated with high symbiotic persistence in legumes. Although no significant correlations between soil variables and symbiotic persistence were found, nitrogen and phosphorus leaf contents were positively correlated with legumes in a state of high symbiotic persistence. This pattern suggests that highly demanding nutrient lifestyles are associated with more stable partnerships, potentially because they “lock” the hosts into symbiotic dependency. Quantitative reconstruction methods are emerging as a powerful comparative tool to study broad patterns of symbiont loss and retention across diverse partnerships. PMID:26041807

Peculiar variable star R Aquarii and its jet

Energy Technology Data Exchange (ETDEWEB)

Kafatos, M; Michalitsianos, A G [National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center

1982-08-05

The formation of a jet from the central star in the symbiotic variable R Aquarii is discussed and it is suggested that it is the result of supercritical accretion of mass transferred from the cool 387-day period Mira to the hot companion in a highly elliptical orbit. Ancient Japanese astronomical records suggest a nova outburst in AD930 may be associated with R Aquarii which formed the outer extended nebulosity. It is considered that the jet may help explain the outbursts of this object as well as the excitation of the R Aquarii nebula.

What Powers the 2006 Outburst of the Symbiotic Star BF Cygni?

Directory of Open Access Journals (Sweden)

A. Skopal

2015-02-01

Full Text Available BF Cygni is a classical symbiotic binary. Its optical light curve occasionally shows outbursts of the Z And-type, whose nature is not well understood. During the 2006 August, BF Cyg underwent the recent outburst, and continues its active phase to the present. The aim of this contribution is to determine the fundamental parameters of the hot component in the binary during the active phase. For this purpose we used a high- and low-resolution optical spectroscopy and the multicolour UBV RCIC photometry. Our photometric monitoring revealed that a high level of the star’s brightness lasts for unusually long time of > 7 years. A sharp violet-shifted absorption component and broad emission wings in the Hα profile developed during the whole active phase. From 2009, our spectra revealed a bipolar ejection from the white dwarf (WD. Modelling the spectral energy distribution (SED of the low-resolution spectra showed simultaneous presence of a warm (< 10 000 K disk-like pseudophotosphere and a strong nebular component of radiation (emission measure of ~1061 cm−3. The luminosity of the hot active object was estimated to > 5−8×103 Lʘ. Such high luminosity, sustained for the time of years, can be understood as a result of an enhanced transient accretion rate throughout a large disk, leading also to formation of collimated ejection from the WD.

Gamma-ray bursts from tidally spun-up Wolf-Rayet stars?

NARCIS (Netherlands)

Detmers, R.G.; Langer, N.; Podsiadlowski, Ph.; Izzard, R.G.

2008-01-01

Context. The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds. Aims. We investigate whether the tidal interaction of a Wolf-Rayet star with a compact

Dynamics of H II regions around exiled O stars

Science.gov (United States)

Mackey, Jonathan; Langer, Norbert; Gvaramadze, Vasilii V.

2013-11-01

At least 25 per cent of massive stars are ejected from their parent cluster, becoming runaways or exiles, travelling with often-supersonic space velocities through the interstellar medium (ISM). Their overpressurized H II regions impart kinetic energy and momentum to the ISM, compress and/or evaporate dense clouds, and can constrain properties of both the star and the ISM. Here, we present one-, two- and (the first) three-dimensional simulations of the H II region around a massive star moving supersonically through a uniform, magnetized ISM, with properties appropriate for the nearby O star ζ Oph. The H II region leaves an expanding overdense shell behind the star and, inside this, an underdense wake that should be filled with hot gas from the shocked stellar wind. The gas column density in the shell is strongly influenced by the ISM magnetic field strength and orientation. Hα emission maps show that H II region remains roughly circular, although the star is displaced somewhat from the centre of emission. For our model parameters, the kinetic energy feedback from the H II region is comparable to the mechanical luminosity of the stellar wind, and the momentum feedback rate is >100 times larger than that from the wind and ≈10 times larger than the total momentum input rate available from radiation pressure. Compared to the star's eventual supernova explosion, the kinetic energy feedback from the H II region over the star's main-sequence lifetime is >100 times less, but the momentum feedback is up to 4 times larger. H II region dynamics are found to have only a small effect on the ISM conditions that a bow shock close to the star would encounter.

He II {lambda}4686 IN {eta} CARINAE: COLLAPSE OF THE WIND-WIND COLLISION REGION DURING PERIASTRON PASSAGE

Energy Technology Data Exchange (ETDEWEB)

Teodoro, M.; Damineli, A. [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo 05508-900 (Brazil); Arias, J. I. [Departamento de Fisica, Universidad de La Serena, Av. Cisternas 1200 Norte, La Serena (Chile); De Araujo, F. X.; Borges Fernandes, M.; Pereira, C. B. [Observatorio Nacional, Rua General Jose Cristino 77, Sao Cristovao, Rio de Janeiro 20921-400 (Brazil); Barba, R. H.; Gonzalez, J. F. [Instituto de Ciencias Astronomicas, de la Tierra, y del Espacio (ICATE-CONICET), Avenida Espana Sur 1512, J5402DSP San Juan (Argentina); Corcoran, M. F. [CRESST and X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Fernandez-Lajus, E.; Gamen, R. C.; Solivella, G. R. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, BA, B1900FWA (Argentina); Fraga, L. [Southern Observatory for Astrophysical Research, Colina El Pino s/n, Casilla 603, La Serena (Chile); Groh, J. H. [Max-Planck-Institute fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Marshall, J. L. [Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843-4242 (United States); McGregor, P. J.; Nicholls, D. C.; Parkin, E. R. [Research School of Astronomy and Astrophysics (RSAA), Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia); Morrell, N.; Phillips, M. M., E-mail: mairan@astro.iag.usp.br [Las Campanas Observatory, Observatories of the Carnegie Institution of Washington, Casilla 601, La Serena (Chile); and others

2012-02-10

The periodic spectroscopic events in {eta} Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of {eta} Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II {lambda}4686 emission line (L {approx} 310 L{sub Sun }) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II {lambda}4686 light curves. After a short-lived minimum, He II {lambda}4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the 'surface' of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.

He II λ4686 IN η CARINAE: COLLAPSE OF THE WIND-WIND COLLISION REGION DURING PERIASTRON PASSAGE

International Nuclear Information System (INIS)

Teodoro, M.; Damineli, A.; Arias, J. I.; De Araújo, F. X.; Borges Fernandes, M.; Pereira, C. B.; Barbá, R. H.; González, J. F.; Corcoran, M. F.; Fernández-Lajús, E.; Gamen, R. C.; Solivella, G. R.; Fraga, L.; Groh, J. H.; Marshall, J. L.; McGregor, P. J.; Nicholls, D. C.; Parkin, E. R.; Morrell, N.; Phillips, M. M.

2012-01-01

The periodic spectroscopic events in η Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of η Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II λ4686 emission line (L ∼ 310 L ☉ ) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II λ4686 light curves. After a short-lived minimum, He II λ4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the 'surface' of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.

Observation of solar wind with radio-star scintillation

International Nuclear Information System (INIS)

Watanabe, Takashi

1974-01-01

Large solar flares occurred in groups in early August 1972, and many interesting phenomena were observed. The solar wind condition during this period, obtained by scintillation observation, is reviewed. The velocity of solar wind has been determined from the observation of interplanetary space scintillation at Toyokawa, Fujigamine and Sugadaira. Four to ten radio wave sources were observed for ten minutes at each southing every day. Strong earth magnetic storm and the Forbush decrease of cosmic ray were observed during the period from August 3rd to 7th. Pioneer 9 observed a solar wind having the maximum velocity as high as 1,100 km/sec, and HEOS-II observed a solar wind having the velocity close to 2,000 km/sec. On the other hand, according to the scintillation of 3C-48 and 3C-144, the velocity of solar wind passing in the interplanetary space on the westside of the earth was only 300 to 400 km/sec. Therefore it is considered that the condition of solar wind on the east side of the earth differs from that on the west side of the earth. Pioneer 9 observed the pass of a shock wave on August 9th. With all radio wave sources, high velocity solar wind was observed and Pioneer 6 positioned on the west side of the earth also observed it. The thickness of this shock wave is at least 0.3 AU. Discussion is made on the cause for the difference between the asymmetric shock wave in the direction of south-west and symmetrical shock wave. The former may be blast wave, and the latter may be piston driven shock wave and the like. (Iwakiri, K.)

THE STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF STAR-FORMING GALAXIES IN THE NEARBY UNIVERSE

International Nuclear Information System (INIS)

Torres-Papaqui, J. P.; Coziol, R.; Ortega-Minakata, R. A.; Neri-Larios, D. M.

2012-01-01

We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z ≤ 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more

Orbital evolution of colliding star and pulsar winds in 2D and 3D: effects of dimensionality, EoS, resolution, and grid size

Science.gov (United States)

Bosch-Ramon, V.; Barkov, M. V.; Perucho, M.

2015-05-01

Context. The structure formed by the shocked winds of a massive star and a non-accreting pulsar in a binary system suffers periodic and random variations of orbital and non-linear dynamical origins. The characterization of the evolution of the wind interaction region is necessary for understanding the rich phenomenology of these sources. Aims: For the first time, we simulate in 3 dimensions the interaction of isotropic stellar and relativistic pulsar winds along one full orbit, on scales well beyond the binary size. We also investigate the impact of grid resolution and size, and of different state equations: a γ̂-constant ideal gas, and an ideal gas with γ̂ dependent on temperature. Methods: We used the code PLUTO to carry out relativistic hydrodynamical simulations in 2 and 3 dimensions of the interaction between a slow dense wind and a mildly relativistic wind with Lorentz factor 2, along one full orbit in a region up to ~100 times the binary size. The different 2-dimensional simulations were carried out with equal and larger grid resolution and size, and one was done with a more realistic equation of state than in 3 dimensions. Results: The simulations in 3 dimensions confirm previous results in 2 dimensions, showing: a strong shock induced by Coriolis forces that terminates the pulsar wind also in the opposite direction to the star; strong bending of the shocked-wind structure against the pulsar motion; and the generation of turbulence. The shocked flows are also subject to a faster development of instabilities in 3 dimensions, which enhances shocks, two-wind mixing, and large-scale disruption of the shocked structure. In 2 dimensions, higher resolution simulations confirm lower resolution results, simulations with larger grid sizes strengthen the case for the loss of the general coherence of the shocked structure, and simulations with two different equations of state yield very similar results. In addition to the Kelvin-Helmholtz instability, discussed in

Coevolution of Symbiotic Species

OpenAIRE

Leok, Boon Tiong Melvin

1996-01-01

This paper will consider the coevolution of species which are symbiotic in their interaction. In particular, we shall analyse the interaction of squirrels and oak trees, and develop a mathematical framework for determining the coevolutionary equilibrium for consumption and production patterns.

Searching for magnetic fields in 11 Wolf-Rayet stars: Analysis of circular polarization measurements from ESPaDOnS

Energy Technology Data Exchange (ETDEWEB)

De la Chevrotière, A.; St-Louis, N.; Moffat, A. F. J. [Centre de Recherche en Astrophysique du Québec (CRAQ), Département de physique, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, Québec H3C 3J7 (Canada); Collaboration: MiMeS Collaboration

2014-02-01

With recent detections of magnetic fields in some of their progenitor O stars, combined with known strong fields in their possible descendant neutron stars, it is natural to search for magnetic fields in Wolf-Rayet (WR) stars, despite the problems associated with the presence of winds enhanced by an order of magnitude over those of O stars. We continue our search among a sample of 11 bright WR stars following our introductory study in a previous paper of WR6 = EZ CMa using the spectropolarimeter ESPaDOnS at Canada-France-Hawaii Telescope, most of them in all four Stokes parameters. This sample includes six WN stars and five WC stars encompassing a range of spectral subclasses. Six are medium/long-period binaries and three show corotating interaction regions. We report no definite detections of a magnetic field in the winds in which the lines form (which is about the same distance from the center of the star as it is from the surface of the progenitor O star) for any of the eleven stars. Possible reasons and their implications are discussed. Nonetheless, the data show evidence supporting marginal detections for WR134, WR137, and WR138. According to the Bayesian analysis, the most probable field intensities are B {sub wind} ∼ 200, 130, and 80 G, respectively, with a 95.4% probability that the magnetic fields present in the observable parts of their stellar wind, if stronger, does not exceed B{sub wind}{sup max}∼1900 G, ∼1500 G, and ∼1500 G, respectively. In the case of non-detections, we report an average field strength upper limit of B{sub wind}{sup max}∼500 G.

Low-mass stars with mass loss and low-luminosity carbon star formation

International Nuclear Information System (INIS)

Boothroyd, A.I.

1987-01-01

The effects of large carbon enrichments in static stellar envelopes were investigated, using new Los Alamos opacities (including low-temperature carbon and molecular opacities) and including carbon ionizations. To search for the production of low-mass,low-luminosity carbon stars, detailed stellar evolutionary computations were carried out for a grid of low-mass stars of two different metallicities. The stars were evolved from the main sequence through all intermediate stages and through helium-shell flashes on the asymptotic giant branch. The effects of the latest nuclear reaction rates, the new Los Alamos opacities, Reimers-type wind mass loss, and detailed treatment of convection and semi-convection were investigated. Two low-luminosity carbon stars were achieved, in excellent agreement with observations. Conditions favoring dredge-up (and thus carbon-star production) include a reasonably large convective mixing length, low metallicity, relatively large envelope mass, and high flash strength. Mass loss was of major importance, tending to oppose dredge-up; the total mass-loss amounts inferred from observations suffice to prevent formation of high-mass, high-luminosity carbon stars

The relative impact of photoionizing radiation and stellar winds on different environments

Science.gov (United States)

Haid, S.; Walch, S.; Seifried, D.; Wünsch, R.; Dinnbier, F.; Naab, T.

2018-05-01

Photoionizing radiation and stellar winds from massive stars deposit energy and momentum into the interstellar medium (ISM). They might disperse the local ISM, change its turbulent multi-phase structure, and even regulate star formation. Ionizing radiation dominates the massive stars' energy output, but the relative effect of winds might change with stellar mass and the properties of the ambient ISM. We present simulations of the interaction of stellar winds and ionizing radiation of 12, 23, and 60 M⊙ stars within a cold neutral (CNM, n0 = 100 cm-3), warm neutral (WNM, n0 = 1, 10 cm-3) or warm ionized (WIM, n0 = 0.1 cm-3) medium. The FLASH simulations adopt the novel tree-based radiation transfer algorithm TREERAY. With the On-the-Spot approximation and a temperature-dependent recombination coefficient, it is coupled to a chemical network with radiative heating and cooling. In the homogeneous CNM, the total momentum injection ranges from 1.6× 104 to 4× 105 M⊙ km s-1 and is always dominated by the expansion of the ionized HII region. In the WIM, stellar winds dominate (2× 102 to 5× 103 M⊙ km s-1), while the input from radiation is small (˜ 102 M⊙ km s-1). The WNM (n0 = 1 cm-3) is a transition regime. Energetically, stellar winds couple more efficiently to the ISM (˜ 0.1 percent of wind luminosity) than radiation (< 0.001 percent of ionizing luminosity). For estimating the impact of massive stars, the strongly mass-dependent ratios of wind to ionizing luminosity and the properties of the ambient medium have to be considered.

Wind-driven angular momentum loss in binary systems. I - Ballistic case

Science.gov (United States)

Brookshaw, Leigh; Tavani, Marco

1993-01-01

We study numerically the average loss of specific angular momentum from binary systems due to mass outflow from one of the two stars for a variety of initial injection geometries and wind velocities. We present results of ballistic calculations in three dimensions for initial mass ratios q of the mass-losing star to primary star in the range q between 10 exp -5 and 10. We consider injection surfaces close to the Roche lobe equipotential surface of the mass-losing star, and also cases with the mass-losing star underfilling its Roche lobe. We obtain that the orbital period is expected to have a negative time derivative for wind-driven secular evolution of binaries with q greater than about 3 and with the mass-losing star near filling its Roche lobe. We also study the effect of the presence of an absorbing surface approximating an accretion disk on the average final value of the specific angular momentum loss. We find that the effect of an accretion disk is to increase the wind-driven angular momentum loss. Our results are relevant for evolutionary models of high-mass binaries and low-mass X-ray binaries.

MASSIVE INFANT STARS ROCK THEIR CRADLE

Science.gov (United States)

2002-01-01

Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B, also known as NGC 1748. A new NASA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation of a star-forming region in a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our Milky Way in regions like the Orion Nebula. The Hubble telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighboring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our Milky Way and can easily be seen with the naked eye from the Southern Hemisphere. Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then only with very high-resolution telescopes. Astronomers from France, the U.S., and Germany have used Hubble to study the fascinating interplay between gas, dust, and radiation from the newly born stars in this nebula. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars

Identification of new fluorescence processes in the UV spectra of cool stars from new energy levels of Fe II and Cr II

Science.gov (United States)

Johansson, Sveneric; Carpenter, Kenneth G.

1988-01-01

Two fluorescence processes operating in atmospheres of cool stars, symbiotic stars, and the Sun are presented. Two emission lines, at 1347.03 and 1360.17 A, are identified as fluorescence lines of Cr II and Fe II. The lines are due to transitions from highly excited levels, which are populated radiatively by the hydrogen Lyman alpha line due to accidental wavelength coincidences. Three energy levels, one in Cr II and two in Fe II, are reported.

Interacting supernovae from photoionization-confined shells around red supergiant stars

Science.gov (United States)

Mackey, Jonathan; Mohamed, Shazrene; Gvaramadze, Vasilii V.; Kotak, Rubina; Langer, Norbert; Meyer, Dominique M.-A.; Moriya, Takashi J.; Neilson, Hilding R.

2014-08-01

Betelgeuse, a nearby red supergiant, is a fast-moving star with a powerful stellar wind that drives a bow shock into its surroundings. This picture has been challenged by the discovery of a dense and almost static shell that is three times closer to the star than the bow shock and has been decelerated by some external force. The two physically distinct structures cannot both be formed by the hydrodynamic interaction of the wind with the interstellar medium. Here we report that a model in which Betelgeuse's wind is photoionized by radiation from external sources can explain the static shell without requiring a new understanding of the bow shock. Pressure from the photoionized wind generates a standing shock in the neutral part of the wind and forms an almost static, photoionization-confined shell. Other red supergiants should have much more massive shells than Betelgeuse, because the photoionization-confined shell traps up to 35 per cent of all mass lost during the red supergiant phase, confining this gas close to the star until it explodes. After the supernova explosion, massive shells dramatically affect the supernova light curve, providing a natural explanation for the many supernovae that have signatures of circumstellar interaction.

Nodulation outer proteins: double-edged swords of symbiotic rhizobia.

Science.gov (United States)

Staehelin, Christian; Krishnan, Hari B

2015-09-15

Rhizobia are nitrogen-fixing bacteria that establish a nodule symbiosis with legumes. Nodule formation depends on signals and surface determinants produced by both symbiotic partners. Among them, rhizobial Nops (nodulation outer proteins) play a crucial symbiotic role in many strain-host combinations. Nops are defined as proteins secreted via a rhizobial T3SS (type III secretion system). Functional T3SSs have been characterized in many rhizobial strains. Nops have been identified using various genetic, biochemical, proteomic, genomic and experimental approaches. Certain Nops represent extracellular components of the T3SS, which are visible in electron micrographs as bacterial surface appendages called T3 (type III) pili. Other Nops are T3 effector proteins that can be translocated into plant cells. Rhizobial T3 effectors manipulate cellular processes in host cells to suppress plant defence responses against rhizobia and to promote symbiosis-related processes. Accordingly, mutant strains deficient in synthesis or secretion of T3 effectors show reduced symbiotic properties on certain host plants. On the other hand, direct or indirect recognition of T3 effectors by plant cells expressing specific R (resistance) proteins can result in effector triggered defence responses that negatively affect rhizobial infection. Hence Nops are double-edged swords that may promote establishment of symbiosis with one legume (symbiotic factors) and impair symbiotic processes when bacteria are inoculated on another legume species (asymbiotic factors). In the present review, we provide an overview of our current understanding of Nops. We summarize their symbiotic effects, their biochemical properties and their possible modes of action. Finally, we discuss future perspectives in the field of T3 effector research. © 2015 Authors; published by Portland Press Limited.

Neutron Stars and Pulsars

CERN Document Server

Becker, Werner

2009-01-01

Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

Mass Transfer in Mira-Type Binaries

Directory of Open Access Journals (Sweden)

Mohamed S.

2012-06-01

Full Text Available Detached, symbiotic binaries are generally assumed to interact via Bondi-Hoyle-Littleton (BHL wind accretion. However, the accretion rates and outflow geometries that result from this mass-transfer mechanism cannot adequately explain the observations of the nearest and best studied symbiotic binary, Mira, or the formation of some post-AGB binaries, e.g. barium stars. We propose a new mass-transfer mode for Mira-type binaries, which we call ‘wind Roche-lobe overflow’ (WRLOF, and which we demonstrate with 3D hydrodynamic simulations. Importantly, we show that the circumstellar outflows which result from WRLOF tend to be highly aspherical and strongly focused towards the binary orbital plane. Furthermore, the subsequent mass-transfer rates are at least an order of magnitude greater than the analogous BHL values. We discuss the implications of these results for the shaping of bipolar (proto-planetary nebulae and other related systems.

Gene expression in gut symbiotic organ of stinkbug affected by extracellular bacterial symbiont.

Science.gov (United States)

Futahashi, Ryo; Tanaka, Kohjiro; Tanahashi, Masahiko; Nikoh, Naruo; Kikuchi, Yoshitomo; Lee, Bok Luel; Fukatsu, Takema

2013-01-01

The bean bug Riptortus pedestris possesses a specialized symbiotic organ in a posterior region of the midgut, where numerous crypts harbor extracellular betaproteobacterial symbionts of the genus Burkholderia. Second instar nymphs orally acquire the symbiont from the environment, and the symbiont infection benefits the host by facilitating growth and by occasionally conferring insecticide resistance. Here we performed comparative transcriptomic analyses of insect genes expressed in symbiotic and non-symbiotic regions of the midgut dissected from Burkholderia-infected and uninfected R. pedestris. Expression sequence tag analysis of cDNA libraries and quantitative reverse transcription PCR identified a number of insect genes expressed in symbiosis- or aposymbiosis-associated patterns. For example, genes up-regulated in symbiotic relative to aposymbiotic individuals, including many cysteine-rich secreted protein genes and many cathepsin protease genes, are likely to play a role in regulating the symbiosis. Conversely, genes up-regulated in aposymbiotic relative to symbiotic individuals, including a chicken-type lysozyme gene and a defensin-like protein gene, are possibly involved in regulation of non-symbiotic bacterial infections. Our study presents the first transcriptomic data on gut symbiotic organ of a stinkbug, which provides initial clues to understanding of molecular mechanisms underlying the insect-bacterium gut symbiosis and sheds light on several intriguing commonalities between endocellular and extracellular symbiotic associations.

Novel, non-symbiotic isolates of Neorhizobium from a dryland agricultural soil.

Science.gov (United States)

Soenens, Amalia; Imperial, Juan

2018-01-01

Semi-selective enrichment, followed by PCR screening, resulted in the successful direct isolation of fast-growing Rhizobia from a dryland agricultural soil. Over 50% of these isolates belong to the genus Neorhizobium , as concluded from partial rpoB and near-complete 16S rDNA sequence analysis. Further genotypic and genomic analysis of five representative isolates confirmed that they form a coherent group within Neorhizobium , closer to N. galegae than to the remaining Neorhizobium species, but clearly differentiated from the former, and constituting at least one new genomospecies within Neorhizobium. All the isolates lacked nod and nif symbiotic genes but contained a repABC replication/maintenance region, characteristic of rhizobial plasmids, within large contigs from their draft genome sequences. These repABC sequences were related, but not identical, to repABC sequences found in symbiotic plasmids from N. galegae , suggesting that the non-symbiotic isolates have the potential to harbor symbiotic plasmids. This is the first report of non-symbiotic members of Neorhizobium from soil.

The iron curtain of WC9 stars

International Nuclear Information System (INIS)

Hucht, K.A. van der; Willis, A.J.

1982-01-01

High resolution (Δlambda approximately equal to 0.1 A) IUE spectra have been obtained of the two WC9 stars HD 164270 and HD 136488, covering the wavelength range lambdalambda1150-2050. The former star shows P Cygni profiles indicating a stellar wind terminal velocity of Vsub(infinity) approximately equal to 1400 km s -1 , and the latter Vsub(infinity) approximately equal to -1800 km s -1 . A common feature in the spectra of both stars is narrow displaced absorptions due to Fe III (UV34) transitions arising from a metastable lower level. These features are displaced at sub-terminal velocities (-830 km s -1 for HD 164270 and -1030 km s -1 for Hd 136488) and are believed to be formed in the deceleration region of their stellar winds. The properties of these inferred Fe III circumstellar shells derived from these data are discussed. (Auth.)

International conference entitled Zdeněk Kopal’s Binary Star Legacy

CERN Document Server

Drechsel, Horst; ZDENEK KOPAL’S BINARY STAR LEGACY

2005-01-01

An international conference entitled "Zdenek Kopal's Binary Star Legacy" was held on the occasion of the late Professor Kopal's 90th birthday in his home town of Litomyšl/Czech Republic and dedicated to the memory of one of the leading astronomers of the 20th century. Professor Kopal, who devoted 60 years of his scientific life to the exploration of close binary systems, initiated a breakthrough in this field with his description of binary components as non-spherical stars deformed by gravity, with surfaces following Roche equipotentials. Such knowledge triggered the development of new branches of astrophysics dealing with the structure and evolution of close binaries and the interaction effects displayed by exciting objects such as cataclysmic variables, symbiotic stars or X-ray binaries. Contributions to this conference included praise of the achievements of a great astronomer and personal reminiscences brought forward by Kopal's former students and colleagues, and reflected the state of the art of the dyn...

Science.gov (United States)

Morisset, C.; Delgado-Inglada, G.; Torres-Peimbert, S.

2014-04-01

Most - if not all - planetary nebulae exhibit a complex structure, far from the spherical shape. The reasons for this dramatic change in symmetry, that occurs in early stage of the development of the nebula, remain controversial. The same physics operates in a variety of stars, from young (winds from young stars and/or high mass stars) to old (novae, symbiotic stars). The aim of the APN series of conferences has been to offer the opportunity to anyone involved in the study of asymmetric planetary nebulae (and related objects) to discuss the latest results obtained in this field. The APN VI conference was organized by the Instituto de Astronomia (UNAM) and took place on Riviera Maya, Quintana Roo, México, 4-8 Nov. 2013

The Physics of Wind-Fed Accretion

International Nuclear Information System (INIS)

Mauche, Christopher W.; Liedahl, Duane A.; Akiyama, Shizuka; Plewa, Tomasz

2008-01-01

We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a program to develop global models of the radiatively-driven photoionized winds and accretion flows of HMXBs, with particular attention to the prototypical system Vela X-l. The models combine XSTAR photoionization calculations, HULLAC emission models appropriate to X-ray photoionized plasmas, improved models of the radiative driving of photoionized winds, FLASH time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo radiation transport. We present two- and three-dimensional maps of the density, temperature, velocity, ionization parameter, and emissivity distributions of representative X-ray emission lines, as well as synthetic global Monte Carlo X-ray spectra. Such models help to better constrain the properties of the winds of HMXBs, which bear on such fundamental questions as the long-term evolution of these binaries and the chemical enrichment of the interstellar medium.

Effects of stellar evolution and ionizing radiation on the environments of massive stars

Science.gov (United States)

Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

2014-09-01

We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae.

Science.gov (United States)

Blackman, E G; Frank, A; Markiel, J A; Thomas, J H; Van Horn, H M

2001-01-25

Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage. A shock forms near the boundary between the winds, creating the relatively dense shell characteristic of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape. A magnetic field could launch and collimate a bipolar outflow, but the origin of such a field has hitherto been unclear, and some previous work has even suggested that a field could not be generated. Here we show that an asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field, having as its origin a dynamo at the interface between the rapidly rotating core and the more slowly rotating envelope of the star. The fields are strong enough to shape the bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic braking of the stellar core during this process may also explain the puzzlingly slow rotation of most white dwarf stars.

THE MASS-DEPENDENCE OF ANGULAR MOMENTUM EVOLUTION IN SUN-LIKE STARS

International Nuclear Information System (INIS)

Matt, Sean P.; Baraffe, Isabelle; Chabrier, Gilles; Brun, A. Sacha; Bouvier, Jérôme

2015-01-01

To better understand the observed distributions of the rotation rate and magnetic activity of Sun-like and low-mass stars, we derive a physically motivated scaling for the dependence of the stellar wind torque on the Rossby number. The torque also contains an empirically derived scaling with stellar mass (and radius), which provides new insight into the mass-dependence of stellar magnetic and wind properties. We demonstrate that this new formulation explains why the lowest mass stars are observed to maintain rapid rotation for much longer than solar-mass stars, and simultaneously why older populations exhibit a sequence of slowly rotating stars, in which the low-mass stars rotate more slowly than solar-mass stars. The model also reproduces some previously unexplained features in the period-mass diagram for the Kepler field, notably: the particular shape of the ''upper envelope'' of the distribution, suggesting that ∼95% of Kepler field stars with measured rotation periods are younger than ∼4 Gyr; and the shape of the ''lower envelope'', corresponding to the location where stars transition between magnetically saturated and unsaturated regimes

Spectra of Wolf-Rayet stars. I. Optical line strengths and the hydrogen-to-helium ratios in WN type stars

International Nuclear Information System (INIS)

Conti, P.S.; Leep, E.M.; Perry, D.N.

1983-01-01

We begin a series of systematic studies of spectra of Wolf-Rayet stars by examining the optical line strengths of WN stars in the Galaxy and the Large Magellanic Cloud to see what similarities and differences exist among them. Tables of equivalent widths extracted from spectra are presented and some conclusions are drawn. We have found that there is a wide dispersion, up to a factor of 10 or more, in line strengths for all ions even among stars of the same subtype, with WN 7 stars weaker overall than surrounding types. Type-to-type trends are consistent with changing ionization balance in the stellar wind. Nitrogen line ratios indicate that the WN subtypes represent an ionization sequence, but one with considerable overlap: the classification scheme is not single valued; other physical parameters must play a role. The line strength dispersion does not appear to be primarily due to ionization, or luminosity. The Balmer-Pickering decrement has been used to estimate the H/He ratio for most of the WN stars with available spectra; semiquantitative results are presented. Significant differences in H/He are observed (10 stars may have H/He>2). At a given subclass, the strongest line stars have no detectable H. The abundance of H probably relates to structural differences in the winds that, in part, give rise to a dispersion in observed line strengths. Finally, we have estimated the C/N ratio from the C IV lambda5805/N IV lambda4057 line ratio. In most cases our observations suggest that the C/N ratio is consistent with ''evolved'' models for WN stars. A few stars show strong C IV implying much larger values for C/N, but hydrogen was not detected in them. These stars may be in transition from the WN to WC classes

Role of antimicrobial peptides in controlling symbiotic bacterial populations.

Science.gov (United States)

Mergaert, P

2018-04-25

Covering: up to 2018 Antimicrobial peptides (AMPs) have been known for well over three decades as crucial mediators of the innate immune response in animals and plants, where they are involved in the killing of infecting microbes. However, AMPs have now also been found to be produced by eukaryotic hosts during symbiotic interactions with bacteria. These symbiotic AMPs target the symbionts and therefore have a more subtle biological role: not eliminating the microbial symbiont population but rather keeping it in check. The arsenal of AMPs and the symbionts' adaptations to resist them are in a careful balance, which contributes to the establishment of the host-microbe homeostasis. Although in many cases the biological roles of symbiotic AMPs remain elusive, for a number of symbiotic interactions, precise functions have been assigned or proposed to the AMPs, which are discussed here. The microbiota living on epithelia in animals, from the most primitive ones to the mammals, are challenged by a cocktail of AMPs that determine the specific composition of the bacterial community as well as its spatial organization. In the symbiosis of legume plants with nitrogen-fixing rhizobium bacteria, the host deploys an extremely large panel of AMPs - called nodule-specific cysteine-rich (NCR) peptides - that drive the bacteria into a terminally differentiated state and manipulate the symbiont physiology to maximize the benefit for the host. The NCR peptides are used as tools to enslave the bacterial symbionts, limiting their reproduction but keeping them metabolically active for nitrogen fixation. In the nutritional symbiotic interactions of insects and protists that have vertically transmitted bacterial symbionts with reduced genomes, symbiotic AMPs could facilitate the integration of the endosymbiont and host metabolism by favouring the flow of metabolites across the symbiont membrane through membrane permeabilization.

Effect of Subliminal Stimulation of Symbiotic Fantasies on Behavior Modification Treatment of Obesity.

Science.gov (United States)

And Others; Silverman, Lloyd H.

1978-01-01

Obese women were treated in behavior modification programs for overeating. Behavior programs were accompanied by subliminal stimulation and by symbiotic and control messages. The symbiotic condition gave evidence of enhancing weight loss. This finding supports the proposition that subliminal stimulation of symbiotic fantasies can enhance the…

The Impact of Transformer Winding Connections of A Grid-Connected PV on Voltage Quality Improvement

Energy Technology Data Exchange (ETDEWEB)

Muljadi, Eduard [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Tumbelaka, Hanny H. [Petra Christian University; Gao, Wenzhong [University of Denver

2018-03-01

In this paper, the high-power PV plant is connected to the weak grid by means of a three-phase power transformer. The selection of transformer winding connection is critical especially when the PV inverter has a reactive power controller. In general, transformer winding connection can be arranged in star-star (with neutral earthed) or star-delta. The reactive power controller supports voltage regulation of the power system particularly under transient faults. Its control strategy is based on utilizing the grid currents to make a three-phase reactive unbalanced current with a small gain. The gain is determined by the system impedance. Simulation results exhibit that the control strategy works very well particularly under disturbance conditions when the transformer winding connection is star-star with both neutrals grounded. The power quality in terms of the voltage quality is improved.

Detecting stellar-wind bubbles through infrared arcs in H II regions

Science.gov (United States)

Mackey, Jonathan; Haworth, Thomas J.; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert; Harries, Tim J.

2016-02-01

Mid-infrared arcs of dust emission are often seen near ionizing stars within H II regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional, radiation-hydrodynamics simulations of wind bubbles within H II regions around individual stars to predict the infrared emission properties of the dust within the H II region. We assume that dust and gas are dynamically well-coupled and that dust properties (composition, size distribution) are the same in the H II region as outside it, and that the wind bubble contains no dust. We post-process the simulations to make synthetic intensity maps at infrared wavebands using the torus code. We find that the outer edge of a wind bubble emits brightly at 24 μm through starlight absorbed by dust grains and re-radiated thermally in the infrared. This produces a bright arc of emission for slowly moving stars that have asymmetric wind bubbles, even for cases where there is no bow shock or any corresponding feature in tracers of gas emission. The 24 μm intensity decreases exponentially from the arc with increasing distance from the star because the dust temperature decreases with distance. The size distribution and composition of the dust grains has quantitative but not qualitative effects on our results. Despite the simplifications of our model, we find good qualitative agreement with observations of the H II region RCW 120, and can provide physical explanations for any quantitative differences. Our model produces an infrared arc with the same shape and size as the arc around CD -38°11636 in RCW 120, and with comparable brightness. This suggests that infrared arcs around O stars in H II regions may be revealing the extent of stellar wind bubbles, although we have not excluded other explanations.

Novel, non-symbiotic isolates of Neorhizobium from a dryland agricultural soil

Directory of Open Access Journals (Sweden)

Amalia Soenens

2018-05-01

Full Text Available Semi-selective enrichment, followed by PCR screening, resulted in the successful direct isolation of fast-growing Rhizobia from a dryland agricultural soil. Over 50% of these isolates belong to the genus Neorhizobium, as concluded from partial rpoB and near-complete 16S rDNA sequence analysis. Further genotypic and genomic analysis of five representative isolates confirmed that they form a coherent group within Neorhizobium, closer to N. galegae than to the remaining Neorhizobium species, but clearly differentiated from the former, and constituting at least one new genomospecies within Neorhizobium. All the isolates lacked nod and nif symbiotic genes but contained a repABC replication/maintenance region, characteristic of rhizobial plasmids, within large contigs from their draft genome sequences. These repABC sequences were related, but not identical, to repABC sequences found in symbiotic plasmids from N. galegae, suggesting that the non-symbiotic isolates have the potential to harbor symbiotic plasmids. This is the first report of non-symbiotic members of Neorhizobium from soil.

Feedback by AGN Jets and Wide-angle Winds on a Galactic Scale

Energy Technology Data Exchange (ETDEWEB)

Dugan, Zachary; Silk, Joseph [The Johns Hopkins University Department of Physics and Astronomy, Bloomberg Center for Physics and Astronomy, Room 366, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Gaibler, Volker [Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

2017-07-20

To investigate the differences in mechanical feedback from radio-loud and radio-quiet active galactic nuclei on the host galaxy, we perform 3D AMR hydrodynamic simulations of wide-angle, radio-quiet winds with different inclinations on a single, massive, gas-rich disk galaxy at a redshift of 2–3. We compare our results to hydrodynamic simulations of the same galaxy but with a jet. The jet has an inclination of 0° (perpendicular to the galactic plane), and the winds have inclinations of 0°, 45°, and 90°. We analyze the impact on the host’s gas, star formation, and circumgalactic medium. We find that jet feedback is energy-driven and wind feedback is momentum-driven. In all the simulations, the jet or wind creates a cavity mostly devoid of dense gas in the nuclear region where star formation is then quenched, but we find strong positive feedback in all the simulations at radii greater than 3 kpc. All four simulations have similar SFRs and stellar velocities with large radial and vertical components. However, the wind at an inclination of 90° creates the highest density regions through ram pressure and generates the highest rates of star formation due to its ongoing strong interaction with the dense gas of the galactic plane. With increased wind inclination, we find greater asymmetry in gas distribution and resulting star formation. Our model generates an expanding ring of triggered star formation with typical velocities of the order of 1/3 of the circular velocity, superimposed on the older stellar population. This should result in a potentially detectable blue asymmetry in stellar absorption features at kiloparsec scales.

RECONSTRUCTING THE SOLAR WIND FROM ITS EARLY HISTORY TO CURRENT EPOCH

Energy Technology Data Exchange (ETDEWEB)

Airapetian, Vladimir S.; Usmanov, Arcadi V., E-mail: vladimir.airapetian@nasa.gov, E-mail: avusmanov@gmail.com [NASA Goddard Space Flight Center, Greenbelt, MD (United States)

2016-02-01

Stellar winds from active solar-type stars can play a crucial role in removal of stellar angular momentum and erosion of planetary atmospheres. However, major wind properties except for mass-loss rates cannot be directly derived from observations. We employed a three-dimensional magnetohydrodynamic Alfvén wave driven solar wind model, ALF3D, to reconstruct the solar wind parameters including the mass-loss rate, terminal velocity, and wind temperature at 0.7, 2, and 4.65 Gyr. Our model treats the wind thermal electrons, protons, and pickup protons as separate fluids and incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating to properly describe proton and electron temperatures of the solar wind. To study the evolution of the solar wind, we specified three input model parameters, the plasma density, Alfvén wave amplitude, and the strength of the dipole magnetic field at the wind base for each of three solar wind evolution models that are consistent with observational constrains. Our model results show that the velocity of the paleo solar wind was twice as fast, ∼50 times denser and 2 times hotter at 1 AU in the Sun's early history at 0.7 Gyr. The theoretical calculations of mass-loss rate appear to be in agreement with the empirically derived values for stars of various ages. These results can provide realistic constraints for wind dynamic pressures on magnetospheres of (exo)planets around the young Sun and other active stars, which is crucial in realistic assessment of the Joule heating of their ionospheres and corresponding effects of atmospheric erosion.

RECONSTRUCTING THE SOLAR WIND FROM ITS EARLY HISTORY TO CURRENT EPOCH

International Nuclear Information System (INIS)

Airapetian, Vladimir S.; Usmanov, Arcadi V.

2016-01-01

Stellar winds from active solar-type stars can play a crucial role in removal of stellar angular momentum and erosion of planetary atmospheres. However, major wind properties except for mass-loss rates cannot be directly derived from observations. We employed a three-dimensional magnetohydrodynamic Alfvén wave driven solar wind model, ALF3D, to reconstruct the solar wind parameters including the mass-loss rate, terminal velocity, and wind temperature at 0.7, 2, and 4.65 Gyr. Our model treats the wind thermal electrons, protons, and pickup protons as separate fluids and incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating to properly describe proton and electron temperatures of the solar wind. To study the evolution of the solar wind, we specified three input model parameters, the plasma density, Alfvén wave amplitude, and the strength of the dipole magnetic field at the wind base for each of three solar wind evolution models that are consistent with observational constrains. Our model results show that the velocity of the paleo solar wind was twice as fast, ∼50 times denser and 2 times hotter at 1 AU in the Sun's early history at 0.7 Gyr. The theoretical calculations of mass-loss rate appear to be in agreement with the empirically derived values for stars of various ages. These results can provide realistic constraints for wind dynamic pressures on magnetospheres of (exo)planets around the young Sun and other active stars, which is crucial in realistic assessment of the Joule heating of their ionospheres and corresponding effects of atmospheric erosion

The coupling between pulsation and mass loss in massive stars

OpenAIRE

Townsend, Rich

2007-01-01

To what extent can pulsational instabilities resolve the mass-loss problem of massive stars? How important is pulsation in structuring and modulating the winds of these stars? What role does pulsation play in redistributing angular momentum in massive stars? Although I cannot offer answers to these questions, I hope at the very least to explain how they come to be asked.

Symbiotic polydnavirus and venom reveal parasitoid to its hyperparasitoids.

Science.gov (United States)

Zhu, Feng; Cusumano, Antonino; Bloem, Janneke; Weldegergis, Berhane T; Villela, Alexandre; Fatouros, Nina E; van Loon, Joop J A; Dicke, Marcel; Harvey, Jeffrey A; Vogel, Heiko; Poelman, Erik H

2018-05-15

Symbiotic relationships may provide organisms with key innovations that aid in the establishment of new niches. For example, during oviposition, some species of parasitoid wasps, whose larvae develop inside the bodies of other insects, inject polydnaviruses into their hosts. These symbiotic viruses disrupt host immune responses, allowing the parasitoid's progeny to survive. Here we show that symbiotic polydnaviruses also have a downside to the parasitoid's progeny by initiating a multitrophic chain of interactions that reveals the parasitoid larvae to their enemies. These enemies are hyperparasitoids that use the parasitoid progeny as host for their own offspring. We found that the virus and venom injected by the parasitoid during oviposition, but not the parasitoid progeny itself, affected hyperparasitoid attraction toward plant volatiles induced by feeding of parasitized caterpillars. We identified activity of virus-related genes in the caterpillar salivary gland. Moreover, the virus affected the activity of elicitors of salivary origin that induce plant responses to caterpillar feeding. The changes in caterpillar saliva were critical in inducing plant volatiles that are used by hyperparasitoids to locate parasitized caterpillars. Our results show that symbiotic organisms may be key drivers of multitrophic ecological interactions. We anticipate that this phenomenon is widespread in nature, because of the abundance of symbiotic microorganisms across trophic levels in ecological communities. Their role should be more prominently integrated in community ecology to understand organization of natural and managed ecosystems, as well as adaptations of individual organisms that are part of these communities.

Properties of O dwarf stars in 30 Doradus

Science.gov (United States)

Sabín-Sanjulián, Carolina; VFTS Collaboration

2017-11-01

We perform a quantitative spectroscopic analysis of 105 presumably single O dwarf stars in 30 Doradus, located within the Large Magellanic Cloud. We use mid-to-high resolution multi-epoch optical spectroscopic data obtained within the VLT-FLAMES Tarantula Survey. Stellar and wind parameters are derived by means of the automatic tool iacob-gbat, which is based on a large grid of fastwind models. We also benefit from the Bayesian tool bonnsai to estimate evolutionary masses. We provide a spectral calibration for the effective temperature of O dwarf stars in the LMC, deal with the mass discrepancy problem and investigate the wind properties of the sample.

The s-Process Nucleosynthesis in Extremely Metal-Poor Stars as the Generating Mechanism of Carbon Enhanced Metal-Poor Stars

Science.gov (United States)

Suda, Takuma; Yamada, Shimako; Fujimoto, Masayuki Y.

The origin of carbon-enhanced metal-poor (CEMP) stars plays a key role in characterising the formation and evolution of the first stars and the Galaxy since the extremely-metal-poor (EMP) stars with [Fe/H] ≤ -2.5 share the common features of carbon enhancement in their surface chemical compositions. The origin of these stars is not yet established due to the controversy of the origin of CEMP stars without the enhancement of s-process element abundances, i.e., so called CEMP-no stars. In this paper, we elaborate the s-process nucleosynthesis in the EMP AGB stars and explore the origin of CEMP stars. We find that the efficiency of the s-process is controlled by O rather than Fe at [Fe/H] ≲ -2. We demonstrate that the relative abundances of Sr, Ba, Pb to C are explained in terms of the wind accretion from AGB stars in binary systems.

Radio emission from symbiotic variables: CI Cygni, Z Andromedae, and EG Andromedae - Temporal variability as clues to the nature of symbiotics

International Nuclear Information System (INIS)

Torbett, M.V.; Campbell, B.

1989-01-01

A continuing survey of interacting binary systems has yielded first detections of the symbiotic variables CI Cyg and EG And and reproduced previous flux measurements for Z And. The CI Cyg observation implies considerable radio variability for some symbiotics, while the radio flux from Z And indicates this object has been reasonably stable in the radio for years. Rapid radio variability may indicate the presence of mass transfer through an accretion disk. 27 refs

Comparative energetics of three fusion-fission symbiotic nuclear reactor systems

International Nuclear Information System (INIS)

Gordon, C.W.; Harms, A.A.

1975-01-01

The energetics of three symbiotic fusion-fission nuclear reactor concepts are investigated. The fuel and power balances are considered for various values of systems parameters. The results from this analysis suggest that symbiotic fusion-fission systems are advantageous from the standpoint of economy and resource utilization. (Auth.)

Comparative symbiotic plasmid analysis indicates that symbiosis gene ancestor type affects plasmid genetic evolution.

Science.gov (United States)

Wang, X; Zhao, L; Zhang, L; Wu, Y; Chou, M; Wei, G

2018-07-01

Rhizobial symbiotic plasmids play vital roles in mutualistic symbiosis with legume plants by executing the functions of nodulation and nitrogen fixation. To explore the gene composition and genetic constitution of rhizobial symbiotic plasmids, comparison analyses of 24 rhizobial symbiotic plasmids derived from four rhizobial genera was carried out. Results illustrated that rhizobial symbiotic plasmids had higher proportion of functional genes participating in amino acid transport and metabolism, replication; recombination and repair; carbohydrate transport and metabolism; energy production and conversion and transcription. Mesorhizobium amorphae CCNWGS0123 symbiotic plasmid - pM0123d had similar gene composition with pR899b and pSNGR234a. All symbiotic plasmids shared 13 orthologous genes, including five nod and eight nif/fix genes which participate in the rhizobia-legume symbiosis process. These plasmids contained nod genes from four ancestors and fix genes from six ancestors. The ancestral type of pM0123d nod genes was similar with that of Rhizobium etli plasmids, while the ancestral type of pM0123d fix genes was same as that of pM7653Rb. The phylogenetic trees constructed based on nodCIJ and fixABC displayed different topological structures mainly due to nodCIJ and fixABC ancestral type discordance. The study presents valuable insights into mosaic structures and the evolution of rhizobial symbiotic plasmids. This study compared 24 rhizobial symbiotic plasmids that included four genera and 11 species, illuminating the functional gene composition and symbiosis gene ancestor types of symbiotic plasmids from higher taxonomy. It provides valuable insights into mosaic structures and the evolution of symbiotic plasmids. © 2018 The Society for Applied Microbiology.

Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?

OpenAIRE

Detmers, R. G.; Langer, N.; Podsiadlowski, Ph.; Izzard, R. G.

2008-01-01

Context. The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds. Aims. We investigate whether the tidal interaction of a Wolf-Rayet star with a compact object in a binary system can spin up the Wolf-Rayet star enough to produce a collapsar. Methods. We compute the evolution of close Wolf-Rayet binaries, including tidal angular momentum exchange, ...

Instabilities in Interacting Binary Stars

Science.gov (United States)

Andronov, I. L.; Andrych, K. D.; Antoniuk, K. A.; Baklanov, A. V.; Beringer, P.; Breus, V. V.; Burwitz, V.; Chinarova, L. L.; Chochol, D.; Cook, L. M.; Cook, M.; Dubovský, P.; Godlowski, W.; Hegedüs, T.; Hoňková, K.; Hric, L.; Jeon, Y.-B.; Juryšek, J.; Kim, C.-H.; Kim, Y.; Kim, Y.-H.; Kolesnikov, S. V.; Kudashkina, L. S.; Kusakin, A. V.; Marsakova, V. I.; Mason, P. A.; Mašek, M.; Mishevskiy, N.; Nelson, R. H.; Oksanen, A.; Parimucha, S.; Park, J.-W.; Petrík, K.; Quiñones, C.; Reinsch, K.; Robertson, J. W.; Sergey, I. M.; Szpanko, M.; Tkachenko, M. G.; Tkachuk, L. G.; Traulsen, I.; Tremko, J.; Tsehmeystrenko, V. S.; Yoon, J.-N.; Zola, S.; Shakhovskoy, N. M.

2017-07-01

The types of instability in the interacting binary stars are briefly reviewed. The project “Inter-Longitude Astronomy” is a series of smaller projects on concrete stars or groups of stars. It has no special funds, and is supported from resources and grants of participating organizations, when informal working groups are created. This “ILA” project is in some kind similar and complementary to other projects like WET, CBA, UkrVO, VSOLJ, BRNO, MEDUZA, AstroStatistics, where many of us collaborate. Totally we studied 1900+ variable stars of different types, including newly discovered variables. The characteristic timescale is from seconds to decades and (extrapolating) even more. The monitoring of the first star of our sample AM Her was initiated by Prof. V.P. Tsesevich (1907-1983). Since more than 358 ADS papers were published. In this short review, we present some highlights of our photometric and photo-polarimetric monitoring and mathematical modeling of interacting binary stars of different types: classical (AM Her, QQ Vul, V808 Aur = CSS 081231:071126+440405, FL Cet), asynchronous (BY Cam, V1432 Aql), intermediate (V405 Aql, BG CMi, MU Cam, V1343 Her, FO Aqr, AO Psc, RXJ 2123, 2133, 0636, 0704) polars and magnetic dwarf novae (DO Dra) with 25 timescales corresponding to different physical mechanisms and their combinations (part “Polar”); negative and positive superhumpers in nova-like (TT Ari, MV Lyr, V603 Aql, V795 Her) and many dwarf novae stars (“Superhumper”); eclipsing “non-magnetic” cataclysmic variables(BH Lyn, DW UMa, EM Cyg; PX And); symbiotic systems (“Symbiosis”); super-soft sources (SSS, QR And); spotted (and not spotted) eclipsing variables with (and without) evidence for a current mass transfer (“Eclipser”) with a special emphasis on systems with a direct impact of the stream into the gainer star's atmosphere, which we propose to call “Impactor” (short from “Extreme Direct Impactor”), or V361 Lyr-type stars. Other

ζ Oph and the weak-wind problem

Science.gov (United States)

Gvaramadze, V. V.; Langer, N.; Mackey, J.

2012-11-01

Mass-loss rate, ?, is one of the key parameters affecting evolution and observational manifestations of massive stars and their impact on the ambient medium. Despite its importance, there is a factor of ˜100 discrepancy between empirical and theoretical ? of late-type O dwarfs, the so-called weak-wind problem. In this Letter, we propose a simple novel method to constrain ? of runaway massive stars through observation of their bow shocks and Strömgren spheres, which might be of decisive importance for resolving the weak-wind problem. Using this method, we found that ? of the well-known runaway O9.5 V star ζ Oph is more than an order of magnitude higher than that derived from ultraviolet (UV) line fitting and is by a factor of 6-7 lower than those based on the theoretical recipe by Vink et al. and the Hα line. The discrepancy between ? derived by our method and that based on UV lines would be even more severe if the stellar wind is clumpy. At the same time, our estimate of ? agrees with that predicted by the moving reversing layer theory by Lucy.

Galactic Winds Driven by Supernovae and Radiation Pressure: Theory and Simulations

Science.gov (United States)

Zhang, Dong; Davis, Shane

2018-01-01

Galactic winds are ubiquitous in most rapidly star-forming galaxies. They are crucial to the process of galaxy formation and evolution, regulating star formation, shaping the stellar mass function and the mass-metallicity relation, and enriching the intergalactic medium with metals. Although important, the physics of galactic winds is still unclear. Winds may be driven by many mechanisms including overlapping supernovae explosions, radiation pressure of starlight on dust grains, and cosmic rays. However, the growing observations of multiphase structure in galactic winds in a large number of galaxies have not been well explained by any models. In this talk I will focus on the models of supernova- and radiation-pressure-driven winds. Using the state-of-the-art numerical simulations, I will assess the relative merits of these driving mechanisms for accelerating cold and warm clouds to observed velocities, and momentum flux boost during wind propagation.

Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18

NARCIS (Netherlands)

Szécsi, D.; Langer, N.; Yoon, S.C.; Sanyal, D.; de Mink, S.; Evans, C.J.; Dermine, T.

2015-01-01

Context. Low-metallicity environments such as the early Universe and compact star-forming dwarf galaxies contain many massive stars. These stars influence their surroundings through intense UV radiation, strong winds and explosive deaths. A good understanding of low-metallicity environments requires

Diversity, Roles, and Biotechnological Applications of Symbiotic Microorganisms in the Gut of Termite.

Science.gov (United States)

Zhou, Jing; Duan, Jiwei; Gao, Mingkun; Wang, Ying; Wang, Xiaohua; Zhao, Kai

2018-05-12

Termites are global pests and can cause serious damage to buildings, crops, and plantation forests. The symbiotic intestinal flora plays an important role in the digestion of cellulose and nitrogen in the life of termites. Termites and their symbiotic microbes in the gut form a synergistic system. These organism work together to digest lignocellulose to make the termites grow on nitrogen deficient food. In this paper, the diversity of symbiotic microorganisms in the gut of termites, including protozoan, spirochetes, actinomycetes, fungus and bacteria, and their role in the digestion of lignocellulose and also the biotechnological applications of these symbiotic microorganisms are discussed. The high efficiency lignocellulose degradation systems of symbiotic microbes in termite gut not only provided a new way of biological energy development, but also has immense prospect in the application of cellulase enzymes. In addition, the study on the symbiotic microorganisms in the gut of termites will also provide a new method for the biological control of termites by the endophytic bacteria in the gut of termites.

"Wonderful" Star Reveals its Hot Nature

Science.gov (United States)

2005-04-01

to become a white dwarf. The internal turmoil in Mira A could create magnetic disturbances in the upper atmosphere of the star and lead to the observed X-ray outbursts, as well as the rapid loss of material from the star in a blustery, strong, stellar wind. Some of the gas and dust escaping from Mira A is captured by its companion Mira B. In stark contrast to Mira A, Mira B is thought to be a white dwarf star about the size of the Earth. Some of the material in the wind from Mira A is captured in an accretion disk around Mira B, where collisions between rapidly moving particles produce X-rays. Animation of Interacting Stars Animation of Interacting Stars One of the more intriguing aspects of the observations of Mira AB at both X-ray and ultraviolet wavelengths is the evidence for a faint bridge of material joining the two stars. The existence of a bridge would indicate that, in addition to capturing material from the stellar wind, Mira B is also pulling material directly off Mira A into the accretion disk. Chandra observed Mira with its Advanced CCD Imaging Spectrometer on December 6, 2003 for about 19 hours. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Old and new neutron stars

International Nuclear Information System (INIS)

Ruderman, M.

1984-09-01

The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10 38 s -1 of 10 12 eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10 8 old dead pulsars in the Galaxy are the most probable source for the isotropically distributed γ-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables

"SYMBIOTIC" HEMOFILTRATION FOR CHRONIC RENAL F AILURE COMPENSATION

Directory of Open Access Journals (Sweden)

E. A. Yumatov

2015-01-01

Full Text Available AbstractWidely used nowadays hemodialysis and hemofiltration cannot replace completely the excretory function of human kidneys in the natural conditions of physiological regulation. The aim of our study is to develop and create a new method and apparatus for CRF patients «symbiotic» compensation, based on hemofiltration and healthy humans kidneys natural physiological functions, excluding mixing of partners blood.Method of «symbiotic» hemofiltration is based on mutual exchange of equivalent blood ultrafiltrate volumes between healthy person and CRF patient, needed to be cleansed from metabolites. During exchange procedure patient’s and a healthy person’s circulations are separated by hemofilters excluding blood mixing.During CRF patient’s blood cleansing from metabolic products separate hemofiltration of healthy donor and CRF patient in equal volumes is processed. Patient’s blood ultrafiltrate enters the bloodstream of a healthy person, as a healthy person ultrafiltrate in the same extent enters the bloodstream of CRF patient. At the same time remaining after filtration blood components of donor and patient are returned in their bloodstream respectively.Fundamentally important advantage of «symbiotic» hemofiltration is that CRF patient’s blood is cleansed from uremic metabolites due to healthy human kidneys natural physiological functions. «Symbiotic» hemofiltration is a highly effective physiological method of CRP patient’s blood purification from the uremic substances.

Early X- and HE γ-ray emission from the symbiotic recurrent novae V745 Sco & RS Oph.

Science.gov (United States)

Delgado, L.; Hernanz, M.

2017-10-01

RS Oph was the first nova for which evidence of particle acceleration during its 2006 outburst was found. In recent years, several nova explosions - eight classical and two symbiotic recurrent novae - have been detected by Fermi/LAT at E>100 MeV. In most cases, this emission has been observed early after the explosion, around the optical maximum, and for a short period of time. The high-energy γ-ray emission is a consequence of π^{0} decay and/or Inverse Compton, which are related to particle (p and e^{-}) acceleration in the strong shock between the nova ejecta and the circumstellar matter. Our aim is to understand the acceleration process through the analysis of contemporaneous X-ray emission, and in particular, through the evolution of the shock wave. A deep analysis of early X-ray observations of the symbiotic recurrent novae V745 Sco (2014) by Swift/XRT, Chandra/HETG and NuStar, and RS Oph (2006) by XMM-Newton/EPIC and RGS, Swift/XRT and BAT and RXTE/PCA is presented taking into account the contemporaneous information from the IR and radio observations. This provides for the first time a global view of the early evolution of a nova remnant and its relationship with particle acceleration.

Spectrophotometry of ring nebulae around Wolf-Rayet stars

International Nuclear Information System (INIS)

Kwitter, K.B.

1979-01-01

Spectrophotometric observations of four ring nebulae surrounding population I Wolf-Rayet (WN) stars have been obtained, and four additional filamentary nebulae in order to determine the physical conditions and chemical abundances in these objects. It was concluded that the ring nebulae are enriched in nitrogen and helium as a result of contamination of the ambient interstellar medium by the helium- and nitrogen-rich wind from the central Wolf-Rayet star. Of the additional nebulae studied, two were found to be Peimbert Type I planetary nebulae, overabundant in nitrogen and helium due to mixing of CNO processed material into the parent envelope prior to ejection. One of the remaining objects, a shell around an Oef star, is found to have normal abundances; the other, a small H II region around an early Be star, also exhibits normal abundances. It was attempted to interpret the ring nebulae and the Oef shell as interstellar bubbles, according to recent theory; it met with varying degrees of success. For two of the ring nebulae, the fraction of nebular mass contributed by the central star can be estimated from published stellar abundances. It was found that in these two cases, the stellar wind has provided less than 10% of the observed nebular mass

Are luminous and metal-rich Wolf Rayet stars inflated?

NARCIS (Netherlands)

Petrovic, J.; Pols, O.; Langer, N.

2006-01-01

Aims. We investigate the influence of metallicity and stellar wind mass loss on the radius of Wolf-Rayet stars. Methods. We have calculated chemically homogeneous models of Wolf-Rayet stars of 10 to 200 M for two metallicities (Z = 0.02 and Z = 0.001), without mass loss, using OPAL opacities. We

How Massive Single Stars End Their Life

Science.gov (United States)

Heger, A.; Fryer, C. L.; Woosley, S. E.; Langer, N.; Hartmann, D. H.

2003-01-01

How massive stars die-what sort of explosion and remnant each produces-depends chiefly on the masses of their helium cores and hydrogen envelopes at death. For single stars, stellar winds are the only means of mass loss, and these are a function of the metallicity of the star. We discuss how metallicity, and a simplified prescription for its effect on mass loss, affects the evolution and final fate of massive stars. We map, as a function of mass and metallicity, where black holes and neutron stars are likely to form and where different types of supernovae are produced. Integrating over an initial mass function, we derive the relative populations as a function of metallicity. Provided that single stars rotate rapidly enough at death, we speculate on stellar populations that might produce gamma-ray bursts and jet-driven supernovae.

Theory of neutron star magnetospheres

CERN Document Server

Curtis Michel, F

1990-01-01

An incomparable reference for astrophysicists studying pulsars and other kinds of neutron stars, "Theory of Neutron Star Magnetospheres" sums up two decades of astrophysical research. It provides in one volume the most important findings to date on this topic, essential to astrophysicists faced with a huge and widely scattered literature. F. Curtis Michel, who was among the first theorists to propose a neutron star model for radio pulsars, analyzes competing models of pulsars, radio emission models, winds and jets from pulsars, pulsating X-ray sources, gamma-ray burst sources, and other neutron-star driven phenomena. Although the book places primary emphasis on theoretical essentials, it also provides a considerable introduction to the observational data and its organization. Michel emphasizes the problems and uncertainties that have arisen in the research as well as the considerable progress that has been made to date.

The circumstellar environment of evolved stars as traced by molecules and dust. The diagnostic power of Herschel

Science.gov (United States)

Lombaert, Robin

2013-12-01

Low-to-intermediate mass stars end their life on the asymptotic giant branch (AGB), an evolutionary phase in which the star sheds most of its mantle into the circumstellar environment through a stellar wind. This stellar wind expands at relatively low velocities and enriches the interstellar medium with elements newly made in the stellar interior. The physical processes controlling the gas and dust chemistry in the outflow, as well as the driving mechanism of the wind itself, are poorly understood and constitute the broader context of this thesis work. In a first chapter, we consider the thermodynamics of the high-density wind of the oxygen-rich star oh, using observations obtained with the PACS instrument onboard the Herschel Space Telescope. Being one of the most abundant molecules, water vapor can be dominant in the energy balance of the inner wind of these types of stars, but to date, its cooling contribution is poorly understood. We aim to improve the constraints on water properties by careful combination of both dust and gas radiative-transfer models. This unified treatment is needed due to the high sensitivity of water excitation to dust properties. A combination of three types of diagnostics reveals a positive radial gradient of the dust-to-gas ratio in oh. The second chapter deals with the dust chemistry of carbon-rich winds. The 30-mic dust emission feature is commonly identified as due to magnesium sulfide (MgS). However, the lack of short-wavelength measurements of the optical properties of this dust species prohibits the determination of the temperature profile of MgS, and hence its feature strength and shape, questioning whether this species is responsible for the 30-mic feature. By considering the very optically thick wind of the extreme carbon star LL Peg, this problem can be circumvented because in this case the short-wavelength optical properties are not important for the radial temperature distribution. We attribute the 30-mic feature to MgS, but

Exploring the potential of symbiotic fungal endophytes in cereal disease suppression

DEFF Research Database (Denmark)

O'Hanlon, Karen; Knorr, Kamilla; Jørgensen, Lise Nistrup

2012-01-01

, and environmental and health concerns surrounding the use of chemical treatments. There is currently a demand for new disease control strategies, and one such strategy involves the use of symbiotic fungal endophytes as biological control agents against fungal pathogens in cereals. Despite the fact that biological...... control by symbiotic fungal endophytes has been documented, particularly with respect to clavicipitaceous endophytes in C3 cool-season grasses, this area remains relatively underexplored in cereals. We highlight for the first time the potential in using symbiotic fungal endophytes to control foliar cereal...

Three-dimensional Hydrodynamical Simulations of Mass Transfer in Binary Systems by a Free Wind

Energy Technology Data Exchange (ETDEWEB)

Liu, Zheng-Wei; Stancliffe, Richard J.; Abate, Carlo; Matrozis, Elvijs, E-mail: zwliu@ynao.ac.cn [Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121, Bonn (Germany)

2017-09-10

A large fraction of stars in binary systems are expected to undergo mass and angular momentum exchange at some point in their evolution, which can drastically alter the chemical and dynamical properties and fates of the systems. Interaction by stellar wind is an important process in wide binaries. However, the details of wind mass transfer are still not well understood. We perform three-dimensional hydrodynamical simulations of wind mass transfer in binary systems to explore mass-accretion efficiencies and geometries of mass outflows, for a range of mass ratios from 0.05 to 1.0. In particular, we focus on the case of a free wind, in which some physical mechanism accelerates the expelled wind material balancing the gravity of the mass-losing star with the wind velocity comparable to the orbital velocity of the system. We find that the mass-accretion efficiency and accreted specific angular momentum increase with the mass ratio of the system. For an adiabatic wind, we obtain that the accretion efficiency onto the secondary star varies from about 0.1% to 8% for mass ratios between 0.05 and 1.0.

Body size and symbiotic status influence gonad development in Aiptasia pallida anemones.

Science.gov (United States)

Carlisle, Judith F; Murphy, Grant K; Roark, Alison M

2017-01-01

Pale anemones ( Aiptasia pallida ) coexist with dinoflagellates (primarily Symbiodinium minutum ) in a mutualistic relationship. The purpose of this study was to investigate the role of these symbionts in gonad development of anemone hosts. Symbiotic and aposymbiotic anemones were subjected to light cycles that induced gametogenesis. These anemones were then sampled weekly for nine weeks, and gonad development was analyzed histologically. Anemone size was measured as mean body column diameter, and oocytes or sperm follicles were counted for each anemone. Generalized linear models were used to evaluate the influence of body size and symbiotic status on whether gonads were present and on the number of oocytes or sperm follicles produced. Body size predicted whether gonads were present, with larger anemones being more likely than smaller anemones to develop gonads. Both body size and symbiotic status predicted gonad size, such that larger and symbiotic anemones produced more oocytes and sperm follicles than smaller and aposymbiotic anemones. Overall, only 22 % of aposymbiotic females produced oocytes, whereas 63 % of symbiotic females produced oocytes. Similarly, 6 % of aposymbiotic males produced sperm follicles, whereas 60 % of symbiotic males produced sperm follicles. Thus, while gonads were present in 62 % of symbiotic anemones, they were present in only 11 % of aposymbiotic anemones. These results indicate that dinoflagellate symbionts influence gonad development and thus sexual maturation in both female and male Aiptasia pallida anemones. This finding substantiates and expands our current understanding of the importance of symbionts in the development and physiology of cnidarian hosts.

Stellar feedback in galaxies and the origin of galaxy-scale winds

Science.gov (United States)

Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

2012-04-01

Feedback from massive stars is believed to play a critical role in driving galactic super-winds that enrich the intergalactic medium and shape the galaxy mass function, mass-metallicity relation and other global galaxy properties. In previous papers, we have introduced new numerical methods for implementing stellar feedback on sub-giant molecular cloud (sub-GMC) through galactic scales in numerical simulations of galaxies; the key physical processes include radiation pressure in the ultraviolet through infrared, supernovae (Type I and Type II), stellar winds ('fast' O star through 'slow' asymptotic giant branch winds), and H II photoionization. Here, we show that these feedback mechanisms drive galactic winds with outflow rates as high as ˜10-20 times the galaxy star formation rate. The mass-loading efficiency (wind mass-loss rate divided by the star formation rate) scales roughly as ? (where Vc is the galaxy circular velocity), consistent with simple momentum-conservation expectations. We use our suite of simulations to study the relative contribution of each feedback mechanism to the generation of galactic winds in a range of galaxy models, from Small Magellanic Cloud like dwarfs and Milky Way (MW) analogues to z˜ 2 clumpy discs. In massive, gas-rich systems (local starbursts and high-z galaxies), radiation pressure dominates the wind generation. By contrast, for MW-like spirals and dwarf galaxies the gas densities are much lower and sources of shock-heated gas such as supernovae and stellar winds dominate the production of large-scale outflows. In all of our models, however, the winds have a complex multiphase structure that depends on the interaction between multiple feedback mechanisms operating on different spatial scales and time-scales: any single feedback mechanism fails to reproduce the winds observed. We use our simulations to provide fitting functions to the wind mass loading and velocities as a function of galaxy properties, for use in cosmological

Weaving the history of the solar wind with magnetic field lines

Science.gov (United States)

Alvarado Gomez, Julian

2017-08-01

Despite its fundamental role for the evolution of the solar system, our observational knowledge of the wind properties of the young Sun comes from a single stellar observation. This unexpected fact for a field such as astrophysics arises from the difficulty of detecting Sun-like stellar winds. Their detection relies on the appearance of an astrospheric signature (from the stellar wind-ISM interaction region), visible only with the aid of high-resolution HST Lyman-alpha spectra. However, observations and modelling of the present day Sun have revealed that magnetic fields constitute the main driver of the solar wind, providing guidance on how such winds would look like back in time. In this context we propose observations of four young Sun-like stars in order to detect their astrospheres and characterise their stellar winds. For all these objects we have recovered surface magnetic field maps using the technique of Zeeman Doppler Imaging, and developed detailed wind models based on these observed field distributions. Even a single detection would represent a major step forward for our understanding of the history of the solar wind, and the outflows in more active stars. Mass loss rate estimates from HST will be confronted with predictions from realistic models of the corona/stellar wind. In one of our objects the comparison would allow us to quantify the wind variability induced by the magnetic cycle of a star, other than the Sun, for the first time. Three of our targets are planet hosts, thus the HST spectra would also provide key information on the high-energy environment of these systems, guaranteeing their legacy value for the growing field of exoplanet characterisation.

Mottled Protoplanetary Disk Ionization by Magnetically Channeled T Tauri Star Energetic Particles

Science.gov (United States)

Fraschetti, F.; Drake, J. J.; Cohen, O.; Garraffo, C.

2018-02-01

The evolution of protoplanetary disks is believed to be driven largely by angular momentum transport resulting from magnetized disk winds and turbulent viscosity. The ionization of the disk that is essential for these processes has been thought to be due to host star coronal X-rays but could also arise from energetic particles produced by coronal flares, or traveling shock waves, and advected by the stellar wind. We have performed test-particle numerical simulations of energetic protons propagating into a realistic T Tauri stellar wind, including a superposed small-scale magnetostatic turbulence. The isotropic (Kolmogorov power spectrum) turbulent component is synthesized along the individual particle trajectories. We have investigated the energy range [0.1–10] GeV, consistent with expectations from Chandra X-ray observations of large flares on T Tauri stars and recent indications by the Herschel Space Observatory of a significant contribution of energetic particles to the disk ionization of young stars. In contrast with a previous theoretical study finding a dominance of energetic particles over X-rays in the ionization throughout the disk, we find that the disk ionization is likely dominated by X-rays over much of its area, except within narrow regions where particles are channeled onto the disk by the strongly tangled and turbulent magnetic field. The radial thickness of such regions is 5 stellar radii close to the star and broadens with increasing radial distance. This likely continues out to large distances from the star (10 au or greater), where particles can be copiously advected and diffused by the turbulent wind.

Are luminous and metal-rich Wolf-Rayet stars inflated?

NARCIS (Netherlands)

Petrovic, J.; Pols, O.; Langer, N.

2006-01-01

Aims.We investigate the influence of metallicity and stellar wind mass loss on the radius of Wolf-Rayet stars.
Methods: .We have calculated chemically homogeneous models of Wolf-Rayet stars of 10 to 200 M_o for two metallicities (Z=0.02 and Z=0.001), without mass loss, using OPAL

Self-regulating star formation and disk structure

International Nuclear Information System (INIS)

Dopita, M.A.

1987-01-01

Star formation processes determine the disk structure of galaxies. Stars heavier than about 1 solar mass determine the chemical evolution of the system and are produced at a rate which maintains (by the momentum input of the stars) the phase structure, pressure, and vertical velocity dispersion of the gas. Low mass stars are produced quiescently within molecular clouds, and their associated T-Tauri winds maintain the support of molecular clouds and regulate the star formation rate. Inefficient cooling suppresses this mode of star formation at low metallicity. Applied to the solar neighborhood, such a model can account for age/metallicity relationships, the increase in the O/Fe ratio at low metallicity, the paucity of metal-poor G and K dwarf stars, the missing mass in the disk and, possibly, the existence of a metal-poor thick disk. For other galaxies, it accounts for constant w-velocity dispersion of the gas, the relationship between gas content and specific rates of star formation, the surface brightness/metallicity relationship and for the shallow radial gradients in both star formation rates and HI content. 71 references

Evolutionary effects of mass loss in low-mass stars

International Nuclear Information System (INIS)

Renzini, A.

1981-01-01

The effects of mass loss on the evolution of low-mass stars (actual mass smaller than 1.4 solar masses) are reviewed. The case of globular cluster stars is discussed in some detail, and it is shown that evolutionary theory sets quite precise limits to the mass-loss rate in population II red giants. The effects of mass loss on the final evolutionary stages of stars producing white dwarfs is also discussed. In particular, the interaction of the wind from the hot central star with the surrounding planetary nebula is considered. Finally, the problem of the origin of hydrogen-deficient stars is briefly discussed. (Auth.)

HUBBLE'S PANORAMIC PORTRAIT OF A VAST STAR-FORMING REGION

Science.gov (United States)

2002-01-01

NASA's Hubble Space Telescope has snapped a panoramic portrait of a vast, sculpted landscape of gas and dust where thousands of stars are being born. This fertile star-forming region, called the 30 Doradus Nebula, has a sparkling stellar centerpiece: the most spectacular cluster of massive stars in our cosmic neighborhood of about 25 galaxies. The mosaic picture shows that ultraviolet radiation and high-speed material unleashed by the stars in the cluster, called R136 [the large blue blob left of center], are weaving a tapestry of creation and destruction, triggering the collapse of looming gas and dust clouds and forming pillar-like structures that are incubators for nascent stars. The photo offers an unprecedented, detailed view of the entire inner region of 30 Doradus, measuring 200 light-years wide by 150 light-years high. The nebula resides in the Large Magellanic Cloud (a satellite galaxy of the Milky Way), 170,000 light-years from Earth. Nebulas like 30 Doradus are the 'signposts' of recent star birth. High-energy ultraviolet radiation from the young, hot, massive stars in R136 causes the surrounding gaseous material to glow. Previous Hubble telescope observations showed that R136 contains several dozen of the most massive stars known, each about 100 times the mass of the Sun and about 10 times as hot. These stellar behemoths all formed at the same time about 2 million years ago. The stars in R136 are producing intense 'stellar winds' (streams of material traveling at several million miles an hour), which are wreaking havoc on the gas and dust in the surrounding neighborhood. The winds are pushing the gas away from the cluster and compressing the inner regions of the surrounding gas and dust clouds [the pinkish material]. The intense pressure is triggering the collapse of parts of the clouds, producing a new generation of star formation around the central cluster. The new stellar nursery is about 30 to 50 light-years from R136. Most of the stars in the

Genetic and Molecular Mechanisms Underlying Symbiotic Specificity in Legume-Rhizobium Interactions.

Science.gov (United States)

Wang, Qi; Liu, Jinge; Zhu, Hongyan

2018-01-01

Legumes are able to form a symbiotic relationship with nitrogen-fixing soil bacteria called rhizobia. The result of this symbiosis is to form nodules on the plant root, within which the bacteria can convert atmospheric nitrogen into ammonia that can be used by the plant. Establishment of a successful symbiosis requires the two symbiotic partners to be compatible with each other throughout the process of symbiotic development. However, incompatibility frequently occurs, such that a bacterial strain is unable to nodulate a particular host plant or forms nodules that are incapable of fixing nitrogen. Genetic and molecular mechanisms that regulate symbiotic specificity are diverse, involving a wide range of host and bacterial genes/signals with various modes of action. In this review, we will provide an update on our current knowledge of how the recognition specificity has evolved in the context of symbiosis signaling and plant immunity.