Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe extreme O-type spectroscopic binary HD 93129A
68
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
HD 93129A was classified as the earliest O-type star in the Galaxy (O2~If*) and is considered as the prototype of its spectral class. However, interferometry shows that this object is a binary system, while recent observations even suggest a triple configuration. None of the previous spectral analyses of this object accounted for its multiplicity. With new high-resolution UV and optical spectra, we have the possibility to reanalyze this key object, taking its binary nature into account for the first time. We aim to derive the fundamental parameters and the evolutionary status of HD 93129A, identifying the contributions of both components to the composite spectrum. We analyzed UV and optical observations acquired with the Hubble Space Telescope and ESOs Very Large Telescope. A multiwavelength analysis of the system was performed using the latest version of the Potsdam Wolf-Rayet model atmosphere code. Despite the similar spectral types of the two components, we are able to find signatures from each of the components in the combined spectrum, which allows us to estimate the parameters of both stars. We derive $log (L/L_odot) = 6.15$, $T_{textrm{eff}}=52$ kK, and $log dot{M}=-4.7 [M_odottext{yr}^{-1}]$ for the primary Aa, and $log (L/L_odot)=5.58$, $T_{textrm{eff}}=45$ kK, and $logdot{M}=-5.8 [M_odottext{yr}^{-1}]$ for the secondary Ab. Even when accounting for the binary nature, the primary of HD 93129A is found to be one of the hottest and most luminous O stars in our Galaxy. Based on the theoretical decomposition of the spectra, we assign spectral types O2~If* and O3~III(f*) to components Aa and Ab, respectively. While we achieve a good fit for a wide spectral range, specific spectral features are not fully reproduced. The data are not sufficient to identify contributions from a hypothetical third component in the system.
rate research
Read More
Radio observations are an effective tool to discover particle acceleration regions in colliding-wind binaries, through detection of synchrotron radiation; these regions are natural laboratories for the study of relativistic particles. Wind-collision region (WCR) models can reproduce the radio continuum spectra of massive binaries that contain both thermal and non-thermal radio emission; however, key constraints for models come from high-resolution imaging. Only five WCRs have been resolved to date at radio frequencies at milliarcsec (mas) angular scales. The source HD 93129A, prototype of the very few known O2 I stars, is a promising target for study: recently, a second massive, early-type star about 50 mas away was discovered, and a non-thermal radio source detected in the region. Preliminary long-baseline array data suggest that a significant fraction of the radio emission from the system comes from a putative WCR. We sought evidence that HD 93129A is a massive binary system with colliding stellar winds that produce non-thermal radiation, through spatially resolved images of the radio emitting regions. We completed observations with the Australian Long Baseline Array (LBA) to resolve the system at mas angular resolutions and reduced archival Australia Telescope Compact Array (ATCA) data to derive the total radio emission. We also compiled optical astrometric data of the system in a homogeneous way. We reduced historical Hubble Space Telescope data and obtained absolute and relative astrometry with milliarcsec accuracy. The astrometric analysis leads us to conclude that the two stars in HD 93129A form a gravitationally bound system. The LBA data reveal an extended arc-shaped non-thermal source between the two stars, indicative of a WCR. The wind momentum-rate ratio of the two stellar winds is estimated. The ATCA data show a point source with a change in flux level ...
We study the O-type star HD 161853, which has been noted as a probable double-lined spectroscopic binary system. We secured high-resolution spectra of HD 161853 during the past nine years. We separated the two components in the system and measured their respective radial velocities for the first time. We confirm that HD 161853 is an $sim$1 Ma old binary system consisting of an O8 V star ($M_{rm A,RV} geq 22$ M$_odot$) and a B1--3 V star ($M_{rm B,RV} geq 7.2$ M$_odot$) at about 1.3 kpc. From the radial velocity curve, we measure an orbital period $P$ = 2.66765$pm$0.00001 d and an eccentricity $e$ = 0.121$pm$0.007. Its $V$-band light curve is constant within 0.014 mag and does not display eclipses, from which we impose a maximum orbital inclination $i=54$ deg. HD 161853 is probably associated with an H II region and a poorly investigated very young open cluster. In addition, we detect a compact emission region at 50 arcsec to HD 161853 in 22$mu$m-WISE and 24$mu$m-Spitzer images, which may be identified as a dust wave piled up by the radiation pressure of the massive binary system.
We present analysis of both the resolved X-ray emission line profiles and the broadband X-ray spectrum of the O2 If* star HD 93129A, measured with the Chandra HETGS. This star is among the earliest and most massive stars in the Galaxy, and provides a test of the embedded wind shock scenario in a very dense and powerful wind. A major new result is that continuum absorption by the dense wind is the primary cause of the hardness of the observed X-ray spectrum, while intrinsically hard emission from colliding wind shocks contributes less than 10% of the X-ray flux. We find results consistent with the predictions of numerical simulations of the line-driving instability, including line broadening indicating an onset radius of X-ray emission of several tenths Rstar. Helium-like forbidden-to-intercombination line ratios are consistent with this onset radius, and inconsistent with being formed in a wind-collision interface with the stars closest visual companion at a distance of ~100 AU. The broadband X-ray spectrum is fit with a dominant emission temperature of just kT = 0.6 keV along with significant wind absorption. The broadband wind absorption and the line profiles provide two independent measurements of the wind mass-loss rate: Mdot = 5.2_{-1.5}^{+1.8} times 10^{-6} Msun/yr and Mdot = 6.8_{-2.2}^{+2.8} times 10^{-6} Msun/yr, respectively. This is the first consistent modeling of the X-ray line profile shapes and broadband X-ray spectral energy distribution in a massive star, and represents a reduction of a factor of 3 to 4 compared to the standard H-alpha mass-loss rate that assumes a smooth wind.
We present a study of the extreme O-type supergiant He 3-759 using new high-resolution FEROS data, revealing that it is a near spectroscopic twin of HD 151804 (O8 Iaf). We investigate the extinction towards He 3-759 using a variety of methods, revealing A_V ~ 4.7 mag. If we assume He 3-759 has an identical absolute K-band magnitude to HD 151804 we find that it lies in the Sagittarius-Carina spiral arm at a distance of ~6.5 kpc. We derive the physical and wind properties for He 3-759, revealing T* = 30.5 kK, log L/L(sun) = 5.9 and dM/dt = 10^-5.17 M(sun)/yr for a clumped wind whose terminal velocity is estimated at 1000 km/s. The atmosphere of He 3-759 is enriched in helium (X_He = 49%) and nitrogen (X_N = 0.3%). A reanalysis of HD 151804 and HD 152408 (WN9ha) reveals similar parameters except that the WN9ha star possesses a stronger wind and reduced surface hydrogen content. HD 151804 and HD 152408 lie within the Sco OB1 association, with initial masses of ~60 M(sun) and ages ~2.7 Myr, consistent with NGC 6231 cluster members using standard Geneva isochrones. Improved agreement with observed surface abundances are obtained for similar initial masses with more recent Geneva group predictions from which higher ages of ~3.75 Myr are obtained. No young, massive star cluster is known to be associated with He 3-759.
The binary stellar system HD 93129A is one of the most massive known binaries in our Galaxy. This system presents non-thermal emission in the radio band, which can be used to infer its physical conditions and predict its emission in the high-energy band. We intend to constrain some of the unknown parameters of HD 93129A through modelling the non-thermal emitter, and also to analyse the detectability of this source in hard X-rays and $gamma$-rays. We develop a broadband radiative model for the wind-collision region taking into account the evolution of the accelerated particles streaming along the shocked region, the emission by different radiative processes, and the attenuation of the emission propagating through the local matter and radiation fields. From the analysis of the radio emission, we find that the binary HD~93129A is more likely to have a low inclination and a high eccentricity. The minimum energy of the non-thermal electrons seems to be between $sim 20 - 100$MeV, depending on the intensity of the magnetic field in the wind-collision region. The latter can be in the range $sim 20 - 1500$ mG. Our model is able to reproduce the observed radio emission, and predicts that the non-thermal radiation from HD~93129A will increase in the near future. With instruments such as textit{NuSTAR}, textit{Fermi}, and CTA, it will be possible to constrain the relativistic particle content of the source, and other parameters such as the magnetic field strength in the wind collision zone, which in turn can be used to obtain upper-limits of the magnetic field on the surface of the very massive stars, thereby inferring whether magnetic field amplification is taking place in the particle acceleration region.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
