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Secondary Star (secondary + star)
Selected AbstractsSpectroscopic and photometric observations of the selected Algol-type binaries , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008V2080 Cygni, V2365 Ophiuchi ABSTRACT This paper is the second in the planned series of investigations. We present new radial velocities and photometric observations of V2080 Cyg and V2365 Oph. New UBV photometric data and radial velocities were analysed for the systems' parameters. While V2080 Cyg consists of two nearly equal F-type main-sequence stars, V2365 Oph has two different components, namely an early A-type primary and a G-type secondary star. New ephemerides are calculated for both systems. The masses of the component stars have been derived as 1.19 ± 0.02 and 1.16 ± 0.02 M, for V2080 Cyg and 1.97 ± 0.02 and 1.06 ± 0.01 M, for V2365 Oph. The effective temperatures and reddening of the systems have been estimated from Johnson wide-band UBV photometric calibrations. The radii have been measured by simultaneous fitting the UBV light curves using Wilson,Devinney code and are 1.60 ± 0.01 R, for both components of V2080 Cyg and 2.19 ± 0.01 and 0.934 ± 0.004 R, for V2365 Oph. The absolute parameters of the stars in both systems lie within the same ranges in the mass,radius, mass,effective temperature, mass,luminosity and luminosity,effective temperature planes as in detached Algol systems. A comparison between the properties of the systems of interest and the predictions of theoretical evolutionary models is undertaken in the log g,logTeff, log R, log M and radius,log age diagrams. The model predictions match the measured properties of V2080 Cyg for an age of about 5.6 Gyr and a ,solar' metal abundance (Z= 0.019), indicating the components near the end of their core hydrogen-burning phases. However, the position of the components of V2365 Oph on the Hertzsprung,Russell (HR) diagram is best reproduced with evolutionary models for somewhat metal-deficient (Z= 0.004) stars. We found an age of about 700 Myr, with the primary component slightly evolved off the zero-age main-sequence and the secondary one still very close to it. From the basic stellar parameters we have also redetermined the distances to V2080 Cyg and V2365 Oph as 78 ± 1 and 251 ± 8 pc, which are in agreement with, and more accurate than, Hipparcos values. The observations show that at least one of the components of V2365 Oph is an intrinsic variable with a period and peak-to-peak amplitude of 0.07 d and 0.05 mag, respectively. In accordance with its position in the HR diagram, the primary component should be considered as a , Scuti star and it is believed to be the variable star in the system. [source] Optical photometry and spectroscopy of the accretion-powered millisecond pulsar HETE J1900.1 , 2455MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008P. Elebert ABSTRACT We present phase resolved optical photometry and spectroscopy of the accreting millisecond pulsar HETE J1900.1,2455. Our R -band light curves exhibit a sinusoidal modulation, at close to the orbital period, which we initially attributed to X-ray heating of the irradiated face of the secondary star. However, further analysis reveals that the source of the modulation is more likely due to superhumps caused by a precessing accretion disc. Doppler tomography of a broad H, emission line reveals an emission ring, consistent with that expected from an accretion disc. Using the velocity of the emission ring as an estimate for the projected outer disc velocity, we constrain the maximum projected velocity of the secondary to be 200 km s,1, placing a lower limit of 0.05 M, on the secondary mass. For a 1.4 M, primary, this implies that the orbital inclination is low, ,20°. Utilizing the observed relationship between the secondary mass and the orbital period in short-period cataclysmic variables, we estimate the secondary mass to be ,0.085 M,, which implies an upper limit of ,2.4 M, for the primary mass. [source] The remarkable properties of the symbiotic star AE CircinusMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008R. Mennickent ABSTRACT We present new optical spectroscopy and photometry, Two-Micron All-Sky Survey (2MASS) infrared observations and 24 yr of combined American Association of Variable Star Observers (AAVSO) and Association Francaise des Observateurs d'Etoiles Variables (AFOEV) photometry of the symbiotic star candidate AE Cir. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of ,2 × 10,4 mag d,1. The whole range of variability of the star in the V band is about 4 mag. The periodogram of the photometric data reveals strong signals at ,342 and 171 d. The presence of the emission feature at ,6830 Å at minimum and the detection of absorption lines of a ,K5 type star confirm the symbiotic classification and suggest that AE Cir is a new member of the small group of s-type yellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrum taken at the high state shows a much flatter spectral energy distribution, the disappearance of the ,6830 Å emission feature and the weakness of the He ii 4686 emission relative to the Balmer emission lines. Our observations indicate the presence of emission-line flickering in time-scales of minutes in 2001. The peculiar character of AE Cir is revealed in the visibility of the secondary star at the high and low state, the light curve resembling a dwarf nova superoutburst and the relatively short low states. The data are hard to reconciliate with standard models for symbiotic star outbursts. [source] Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007A. Rebassa-Mansergas ABSTRACT We present a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available. We detect significant radial velocity variations in 18 WDMS, identifying them as post-common-envelope binaries (PCEBs) or strong PCEB candidates. Strict upper limits to the orbital periods are calculated, ranging from 0.43 to 7880 d. Given the sparse temporal sampling and relatively low spectral resolution of the SDSS spectra, our results imply a PCEB fraction of ,15 per cent among the WDMS in the SDSS data base. Using a spectral decomposition/fitting technique we determined the white dwarf effective temperatures and surface gravities, masses and secondary star spectral types for all WDMS in our sample. Two independent distance estimates are obtained from the flux-scaling factors between the WDMS spectra, and the white dwarf models and main-sequence star templates, respectively. Approximately one-third of the systems in our sample show a significant discrepancy between the two distance estimates. In the majority of discrepant cases, the distance estimate based on the secondary star is too large. A possible explanation for this behaviour is that the secondary star spectral types that we determined from the SDSS spectra are systematically too early by one to two spectral classes. This behaviour could be explained by stellar activity, if covering a significant fraction of the star by cool dark spots will raise the temperature of the interspot regions. Finally, we discuss the selection effects of the WDMS sample provided by the SDSS project. [source] A non-main-sequence secondary in SY CancriMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005Robert Connon Smith ABSTRACT Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Na i doublet, yielded a semi-amplitude of K2= 127 ± 23 km s,1. Taking the published value of 86 ± 9 km s,1 for K1 gives a mass ratio of q=M2/M1= 0.68 ± 0.14; this is very different from the value of 1.13 ± 0.35 quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass,radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star. [source] Eclipsing binaries in open clusters , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004Persei, V621 Per in ABSTRACT V621 Persei is a detached eclipsing binary in the open cluster , Persei, which is composed of an early B-type giant star and a main-sequence secondary component. From high-resolution spectroscopic observations and radial velocities from the literature, we determine the orbital period to be 25.5 d and the primary velocity semi-amplitude to be K= 64.5 ± 0.4 km s,1. No trace of the secondary star has been found in the spectrum. We solve the discovery light curves of this totally eclipsing binary and find that the surface gravity of the secondary star is log gB= 4.244 ± 0.054. We compare the absolute masses and radii of the two stars in the mass,radius diagram, for different possible values of the primary surface gravity, with the predictions of stellar models. We find that log gA, 3.55, in agreement with values found from fitting Balmer lines with synthetic profiles. The expected masses of the two stars are 12 and 6 M, and the expected radii are 10 and 3 R,. The primary component is near the blue loop stage in its evolution. [source] PSR J0609+2130: a disrupted binary pulsar?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004D. R. Lorimer ABSTRACT We report the discovery and initial timing observations of a 55.7-ms pulsar, J0609+2130, found during a 430-MHz drift-scan survey with the Arecibo radio telescope. With a spin-down rate of 3.1 × 10,19 s s,1 and an inferred surface dipole magnetic field of only 4.2 × 109 G, J0609+2130 has very similar spin parameters to the isolated pulsar J2235+1506 found by Camilo, Nice & Taylor. While the origin of these weakly magnetized isolated neutron stars is not fully understood, one intriguing possibility is that they are the remains of high-mass X-ray binary systems which were disrupted by the supernova explosion of the secondary star. [source] Superhumps, magnetic fields and the mass ratio in AM Canum VenaticorumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003K. J. Pearson ABSTRACT We show that the observed K velocities and periodicities of AM CVn can be reconciled given a mass ratio q, 0.22 and a secondary star with a modest magnetic field of surface strength B, 1 T. We see that the new mass ratio implies that the secondary is most likely semidegenerate. The effect of the field on the accretion disc structure is examined. The theory of precessing discs and resonant orbits is generalized to encompass higher order resonances than 3 : 2 and shown to retain consistency with the new mass ratio. [source] On the evolution of the nova-like variable AE AquariiMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002P. J. Meintjes Abstract A possible evolution for the enigmatic cataclysmic variable AE Aquarii is considered that may put into context the long orbital period and short white dwarf rotation period compared with other DQ Her systems. It has been shown that mass transfer could have been initiated when the secondary KIV,V star was already somewhat evolved when it established Roche lobe contact. In this initial phase the orbital period of the system was probably Porb,i, 8.5 h, and the white dwarf rotation period P*,i > 1 h. Mass transfer in the form of diamagnetic gas blobs will result in an initial discless accretion process, resulting in an efficient drain of the binary orbital angular momentum. Since the initial mass ratio of the binary was probably qi, 0.8, a high mass transfer rate and a slow expansion of the Roche lobe of the secondary star followed, accompanied by a fast expanding secondary following the mass loss. This could have resulted in the KIV,V secondary flooding its Roche surface, causing a run-away mass transfer of that lasted for approximately , during which time the binary expanded to an orbital period of approximately Porb, 11 h. During this phase the mass accretion rate on to the surface of the white dwarf most probably exceeded the critical value for stable nuclear burning , which could have resulted in AE Aqr turning into an ultrasoft X-ray source. The high mass transfer terminated when a critical mass ratio of qcrit= 0.73 was reached. Disc torques spun-up the white dwarf to a period close to 33 s within the time-scale before the high mass transfer shut down when qcrit was reached. The decrease in the mass loss of the secondary allowed it to re-establish hydrostatic equilibrium on the dynamical time-scale (fraction of a day). From this point when qcrit is reached the mass transfer and binary evolution proceed at a slower rate since mass transfer from the secondary star is driven by magnetic braking of the secondary on a time-scale , which is the same as the thermal time-scale tth, 6.3 × 107 yr, i.e. the time-scale on which the secondary shrinks to restore its perturbed thermal equilibrium after the high mass loss. The significantly lower mass transfer in this phase will result in mass ejection from the system. This propeller,ejector action erodes the rotational kinetic energy of the white dwarf, channelling it into mass ejection and non-thermal activity, which explains the non-thermal outbursts that are observed at radio wavelengths and occasionally also at TeV energies. [source] The stellar mass ratio of GK PerseiMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2002L. Morales-Rueda We study the absorption lines present in the spectra of the long-period cataclysmic variable GK Per during its quiescent state, which are associated with the secondary star. By comparing quiescent data with outburst spectra we infer that the donor star appears identical during the two states and the inner face of the secondary star is not noticeably irradiated by flux from the accreting regions. We obtain new values for the radial velocity semi-amplitude of the secondary star, , a projected rotational velocity, and consequently a measurement of the stellar mass ratio of GK Per, . The inferred white dwarf radial velocities are greater than those measured traditionally using the wings of Doppler-broadened emission lines suspected to originate in an accretion disc, highlighting the unsuitability of emission lines for mass determinations in cataclysmic variables. We determine mass limits for both components in the binary, and . [source] The mass of the white dwarf in the recurrent nova U ScorpiiMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001T.D. Thoroughgood We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be from the motion of the wings of the He ii,4686-Å emission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be . From these parameters, we obtain a mass of for the white dwarf primary star and a mass of for the secondary star. The radius of the secondary is calculated to be , confirming that it is evolved. The inclination of the system is calculated to be , consistent with the deep eclipse seen in the light-curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ,700 000 yr. [source] Mirror eclipses in the cataclysmic variable IP PegMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001S.P. Littlefair We present time resolved K -band infrared spectra of the dwarf nova (DN) IP Peg in early quiescence. The Brackett , and He i (,2.0581) lines in our data show hitherto unseen behaviour, which we term a mirror eclipse, and interpret as an eclipse of the secondary star by an optically thin accretion disc. Mirror eclipses are a direct probe of the structure and physical conditions of accretion discs. For example, on assuming the relevant level populations to be in local thermal equilibrium, we constrain the temperature and density of the optically thin material, causing the mirror eclipse in IP Peg to be and respectively. In order to match our data, we find that at least the outermost 20 per cent of the disc (in radius) must be entirely optically thin. Implications for time-dependent disc models are examined. [source] Effects of local thermodynamics and of stellar mass ratio on accretion disc stability in close binariesASTRONOMISCHE NACHRICHTEN, Issue 8 2009G. Lanzafame Abstract Inflow kinematics at the inner Lagrangian point L1, gas compressibility, and physical turbulent viscosity play a fundamental role on accretion disc dynamics and structure in a close binary (CB). Physical viscosity supports the accretion disc development inside the primary gravitational potential well, developing the gas radial transport, converting mechanical energy into heat. The Stellar-Mass-Ratio (SMR) between the compact primary and the secondary star (M1/M2) is also effective, not only in the location of the inner Lagrangian point, but also in the angular kinematics of the mass transfer and in the geometry ofthe gravitational potential wells. In this work we pay attention in particular to the role ofthe SMR, evaluating boundaries, separating theoretical domains in compressibility-viscosity graphs where physical conditions allow a well-bound disc development, as a function ofmass transfer kinematic conditions. In such domains, the lower is the gas compressibility (the higher the polytropic index ,), the higher is the physical viscosity (,) requested. In this work, we show how the boundaries of such domains vary as a function of M1/M2. Conclusions as far as dwarf novae outbursts are concerned, induced by mass transfer rate variations, are also reported. The smaller M1/M2, the shorter the duration of the active-to-quiet and vice-versa transitional phases. Time-scales are of the order of outburst duration of SU Uma, OY Car, Z Cha and SS Cyg-like objects. Moreover, conclusions as far as active-quiet-active phenomena in a CB, according to viscous-thermal instabilities, in accordance to such domains, are also reported (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Roche tomography of the secondary stars in CVsASTRONOMISCHE NACHRICHTEN, Issue 3 2004C. A. Watson Abstract The secondary stars in cataclysmic variables (CVs) are key to our understanding of the origin, evolution and behaviour of this class of interacting binary. In seeking a fuller understanding of these objects, the challenge for observers is to obtain images of the secondary star. This goal can be achieved through Roche tomography, an indirect imaging technique that can be used to map the Roche-lobe-filling secondary. The review begins with a description of the basic principles that underpin Roche tomography, including methods for determining the system parameters. Finally, we conclude with a look at the main scientific highlights to date, including the first unambiguous detection of starspots on AE Aqr B, and consider the future prospects of this technique. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||