Orbital Period (orbital + period)

Distribution by Scientific Domains

Selected Abstracts

Rotational velocities of the giants in symbiotic stars , III.

Evidence of fast rotation in S-type symbiotics
ABSTRACT We have measured the projected rotational velocities (v sin i) in a number of symbiotic stars and M giants using high-resolution spectroscopic observations. On the basis of our measurements and data from the literature, we compare the rotation of mass donors in symbiotics with v sin i of field giants and find that: (i) the K giants in S-type symbiotics rotate at v sin i > 4.5 km s,1, which is 2,4 times faster than the field K giants; (ii) the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. Statistical tests show that these differences are highly significant , p-value <10,3 in the spectral-type bins K2III-K5III, M0III-M6III and M2III-M5III and (iii) our new observations of D'-type symbiotics also confirm that they are fast rotators. As a result of the rapid rotation, the cool giants in symbiotics should have 3,30 times larger mass-loss rates. Our results suggest also that bipolar ejections in symbiotics seem to happen in objects where the mass donors rotate faster than the orbital period. All spectra used in our series of papers can be obtained upon request from the authors. [source]

Two-Micron All-Sky Survey J01542930+0053266: a new eclipsing M dwarf binary system

A. C. Becker
ABSTRACT We report on Two-Micron All-Sky Survey (2MASS) J01542930+0053266, a faint eclipsing system composed of two M dwarfs. The variability of this system was originally discovered during a pilot study of the 2MASS Calibration Point Source Working Data base. Additional photometry from the Sloan Digital Sky Survey yields an eight-passband light curve from which we derive an orbital period of 2.639 0157 ± 0.000 0016 d. Spectroscopic followup confirms our photometric classification of the system, which is likely composed of M0 and M1 dwarfs. Radial velocity measurements allow us to derive the masses (M1= 0.66 ± 0.03 M,; M2= 0.62 ± 0.03 M,) and radii (R1= 0.64 ± 0.08 R,; R2= 0.61 ± 0.09 R,) of the components, which are consistent with empirical mass,radius relationships for low-mass stars in binary systems. We perform Monte Carlo simulations of the light curves which allow us to uncover complicated degeneracies between the system parameters. Both stars show evidence of H, emission, something not common in early-type M dwarfs. This suggests that binarity may influence the magnetic activity properties of low-mass stars; activity in the binary may persist long after the dynamos in their isolated counterparts have decayed, yielding a new potential foreground of flaring activity for next generation variability surveys. [source]

Optical photometry and spectroscopy of the accretion-powered millisecond pulsar HETE J1900.1 , 2455

P. 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]

Detection of the irradiated donor in the LMXBs 4U 1636-536 (=V801 Ara) and 4U 1735-444 (=V926 Sco)

J. Casares
ABSTRACT Phase-resolved VLT spectroscopy of the bursting low-mass X-ray binaries 4U 1636-536/V801 Ara and 4U 1735-444/V926 Sco is presented. Doppler images of the N iii,4640 Bowen transition reveal compact spots which we attribute to fluorescent emission from the donor star and enable us to define a new set of spectroscopic ephemerides. We measure Kem= 277 ± 22 and 226 ± 22 km s,1 from the N iii spots in V801 Ara and V926 Sco, respectively, which represent strict lower limits to the radial velocity semi-amplitude of the donor stars. Our new ephemerides provide confirmation that light-curve maxima in V801 Ara and likely V926 Sco occur at superior conjunction of the donor star and hence photometric modulation is caused by the visibility of the X-ray heated donor. The velocities of He ii,4686 and the broad Bowen blend are strongly modulated with the orbital period, with phasing supporting emission dominated by the disc bulge. In addition, a reanalysis of burst oscillations in V801 Ara, using our spectroscopic T0, leads to K1= 90,113 km s,1. We also estimate the K -corrections for all possible disc flaring angles and present the first dynamical constraints on the masses of these X-ray bursters. These are K2= 360 ± 74 km s,1, f(M) = 0.76 ± 0.47 M, and q= 0.21,0.34 for V801 Ara and K2= 298 ± 83 km s,1, f(M) = 0.53 ± 0.44 M, and q= 0.05,0.41 for V926 Sco. Disc flaring angles ,, 12° and q, 0.26,0.34 are favoured for V801 Ara whereas the lack of K1 constraint for V926 Sco prevents tight constraints on this system. Although both binaries seem to have intermediate inclinations, the larger equivalent width of the narrow N iii line in V801 Ara at phase 0.5 relative to phase 0 suggests that it has the higher inclination of the two. [source]

High-eccentricity planets from the Anglo-Australian Planet Search

Hugh R. A. Jones
ABSTRACT We report Doppler measurements of the stars HD 187085 and HD 20782 which indicate two high eccentricity low-mass companions to the stars. We find HD 187085 has a Jupiter-mass companion with a ,1000-d orbit. Our formal ,best-fitting' solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on rms and ,2,) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD 187085. Our data set for HD 20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD 20782 has M sin i= 1.77 ± 0.22 MJup, an orbital period of 595.86 ± 0.03 d and an orbit with an eccentricity of 0.92 ± 0.03. The detection of such high-eccentricity (and relatively low-velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high-eccentricity systems. [source]

Physical parameters of the O6.5V+B1V eclipsing binary system LS 1135

E. Fernández Lajús
ABSTRACT The ,All Sky Automated Survey' (ASAS) photometric observations of LS 1135, an O-type single-lined binary (SB1) system with an orbital period of 2.7 d, show that the system is also eclipsing performing a numerical model of this binary based on the Wilson,Devinney method. We obtained an orbital inclination . With this value of the inclination, we deduced masses M1, 30 ± 1 M, and M2, 9 ± 1 M,, and radii R1, 12 ± 1 R, and R2, 5 ± 1 R, for primary and secondary components, respectively. Both the components are well inside their respective Roche lobes. Fixing the Teff of the primary to the value corresponding to its spectral type (O6.5V), the Teff obtained for the secondary component corresponds approximately to a spectral type of B1V. The mass ratio M2/M1, 0.3 is among the lowest known values for spectroscopic binaries with O-type components. [source]

A ZZ Ceti white dwarf in SDSS J133941.11+484727.5

B. T. Gänsicke
ABSTRACT We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J133941.11+484727.5 (SDSS 1339) which has been discovered in the Sloan Digital Sky Survey (SDSS) Data Release 4. The orbital period determined from radial velocity studies is 82.524(24) min, close to the observed period minimum. The optical spectrum of SDSS 1339 is dominated to 90 per cent by emission from the white dwarf (WD). The spectrum can be successfully reproduced by a three-component model (white dwarf, disc, secondary) with TWD=12 500 K for a fixed log g= 8.0, d= 170 pc, and a spectral type of the secondary later than M8. The mass-transfer rate corresponding to the optical luminosity of the accretion disc is very low, , 1.7 × 10,13 M, yr,1. Optical photometry reveals a coherent variability at 641 s with an amplitude of 0.025 mag, which we interpret as non-radial pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320 or 344 min and an amplitude of 0.025 mag is detected, which bears no apparent relation with the orbital period of the system. Similar long-period photometric signals have been found in the CVs SDSS J123813.73,033933.0, SDSS J204817.85,061044.8, GW Lib and FS Aur, but so far no working model for this behaviour is available. [source]

A non-main-sequence secondary in SY Cancri

Robert 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]

Orbital parameters, masses and distance to , Centauri determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy

J. Davis
ABSTRACT The bright southern binary star , Centauri (HR 5267) has been observed with the Sydney University Stellar Interferometer (SUSI) and spectroscopically with the European Southern Observatory Coude Auxiliary Telescope and Swiss Euler telescope at La Silla. The interferometric observations have confirmed the binary nature of the primary component and have enabled the determination of the orbital parameters of the system. At the observing wavelength of 442 nm the two components of the primary system have a magnitude difference of 0.15 ± 0.02. The combination of interferometric and spectroscopic data gives the following results: orbital period 357.00 ± 0.07 d, semimajor axis 25.30 ± 0.19 mas, inclination 674 ± 03, eccentricity 0.821 ± 0.003, distance 102.3 ± 1.7 pc, primary and secondary masses M1=M2= 9.1 ± 0.3 M, and absolute visual magnitudes of the primary and secondary M1V=,3.85 ± 0.05 and M2V=,3.70 ± 0.05, respectively. The high degree of accuracy of the results offers a fruitful starting point for future asteroseismic modelling of the pulsating binary components. [source]

Eclipsing binaries in open clusters , III.

Persei, 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]

Substellar companions and isolated planetary-mass objects from protostellar disc fragmentation

W. K. M. Rice
ABSTRACT Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time-scale that is short compared with the orbital period. We use a combination of hydrodynamic simulations and N -body orbit integrations to study the long-term evolution of a fragmenting disc with an initial mass ratio to the star of Mdisc/M*= 0.1. For a disc that is initially unstable across a range of radii, a combination of collapse and subsequent accretion yields substellar objects with a spectrum of masses extending (for a Solar-mass star) up to ,0.01 M,. Subsequent gravitational evolution ejects most of the lower mass objects within a few million years, leaving a small number of very massive planets or brown dwarfs in eccentric orbits at moderately small radii. Based on these results, systems such as HD 168443 , in which the companions are close to or beyond the deuterium burning limit , appear to be the best candidates to have formed via gravitational instability. If massive substellar companions originate from disc fragmentation, while lower-mass planetary companions originate from core accretion, the metallicity distribution of stars which host massive substellar companions at radii of ,1 au should differ from that of stars with lower mass planetary companions. [source]

On the evolution of the nova-like variable AE Aquarii

P. 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]

Optical spectroscopy of GX 339,4 during the high,soft and low,hard states , II.

Line ionization, emission region
We have carried out observations of the X-ray transient GX 339,4 during its high,soft and low,hard X-ray spectral states. Our high-resolution spectroscopic observation in 1999 April suggests that the H, line has a single-peaked profile in the low,hard state as speculated in our previous paper. The He ii,4686 line, however, has a double-peaked profile in both the high,soft and low,hard states. This suggests that the line-emission mechanism is different in the two states. Our interpretation is that double-peaked lines are emitted from a temperature-inversion layer on the accretion disc surface when it is irradiatively heated by soft X-rays. Single-peaked lines may be emitted from outflow/wind matter driven by hard X-ray heating. We have constructed a simple plane-parallel model and we use it to illustrate that a temperature-inversion layer can be formed at the disc surface under X-ray illumination. We also discuss the conditions required for the formation of temperature inversion and line emission. Based on the velocity separations measured for the double-peaked lines in the high,soft state, we propose that GX 339,4 is a low-inclination binary system. The orbital inclination is about 15° if the orbital period is 14.8 h. [source]

Detection of an orbital period in the supergiant high-mass X-ray binary IGR J16465-4507 with Swift,BAT

V. La Parola
ABSTRACT We analysed the IGR J16465,4507 Burst Alert Telescope (BAT) survey data collected during the first 54 months of the Swift mission. The source is in a crowded field and it is revealed through an ad hoc imaging analysis at a significance level of ,14 standard deviations. The 15,50 keV average flux is . The timing analysis reveals an orbital period of 30.243 ± 0.035 d. The folded light curve shows the presence of a wide phase interval of minimum intensity, lasting ,20 per cent of the orbital period. This could be explained with a full eclipse of the compact object in an extremely eccentric orbit or with the passage of the compact source through a lower density wind at the orbit apastron. The modest dynamical range observed during the BAT monitoring suggests that IGR J16465,4507 is a wind-fed system, continuously accreting from a rather homogeneous wind, and not a member of the supergiant fast X-ray transient class. [source]

Discovery of a short orbital period in the Supergiant Fast X-ray Transient IGR J16479,4514

Chetana Jain
ABSTRACT We report here the discovery of a 3.32 d orbital period in the Supergiant Fast X-ray Transient (SFXT) source IGR J16479,4514. Using the long-term light curve of this source obtained with Swift Burst Alert Telescope (BAT) in the energy range of 15,50 keV, we have clearly detected an orbital modulation including a full eclipse of duration ,0.6 d. In the hard X-ray band of the BAT instrument, the eclipse ingress and egress are rapid. We have also used the long-term light curve obtained with the Rossi X-ray Timing Explorer (RXTE) All Sky Monitor (ASM) in the energy range of 1.5,12 keV. Taken independently, the detection of orbital modulation in the RXTE,ASM light curve is not significant. However, considering a clear detection of orbital modulation in the BAT light curve, we have used the ASM light curve for a more precise determination of the orbital period. IGR J16479,4514 has the shortest orbital period among the three SFXTs with measured/known orbital period. We discuss the implication of a short orbital period with the various mechanisms proposed to explain the transient nature of this class of sources. [source]

WASP-5b: a dense, very hot Jupiter transiting a 12th-mag Southern-hemisphere star

D. R. Anderson
ABSTRACT We report the discovery of WASP-5b, a Jupiter-mass planet orbiting a 12th-mag G-type star in the Southern hemisphere. The 1.6-d orbital period places WASP-5b in the class of very hot Jupiters and leads to a predicted equilibrium temperature of 1750 K. WASP-5b is the densest of any known Jovian-mass planet, being a factor of 7 denser than TrES-4, which is subject to similar stellar insolation, and a factor of 3 denser than WASP-4b, which has a similar orbital period. We present transit photometry and radial velocity measurements of WASP-5 (= USNO-B1 0487,0799749), from which we derive the mass, radius and density of the planet: MP= 1.58+0.13,0.08 MJ, RP= 1.090+0.094,0.058 RJ and ,P= 1.22+0.19,0.24 ,J. The orbital period is P= 1.6284296+0.0000048,0.0000037 d and the mid-transit epoch is TC (HJD) = 245 4375.62466+0.00026,0.00025. [source]

Discovery of the strongly eccentric, short-period binary nature of the B-type system HD 313926 by the MOST satellite,

Slavek M. Rucinski
ABSTRACT The MOST photometric space mission discovered an eclipsing binary among its guide stars in 2006 June which combines a relatively large eccentricity e= 0.20 with an orbital period of only 2.27 d. HD 313926 appears to consist of two early-type stars of spectral type B3,B7. It has the largest eccentricity among known early-type binaries with periods less than 3.5 d. Despite the large components indicated by its spectral type and light curve model, and its short period, the orbit of HD 313926 has not yet circularized so it is probably very young, even compared with other young B stars. [source]

A method for the direct determination of the surface gravities of transiting extrasolar planets

John Southworth
ABSTRACT We show that the surface gravity of a transiting extrasolar planet can be calculated from only the spectroscopic orbit of its parent star and the analysis of its transit light curve. This does not require additional constraints, such as are often inferred from theoretical stellar models or model atmospheres. The surface gravity of the planet can therefore be measured precisely and from only directly observable quantities. We outline the method and apply it to the case of the first known transiting extrasolar planet, HD 209458b. We find a surface gravity of gp= 9.28 ± 0.15 m s,2, which is an order of magnitude more precise than the best available measurements of its mass, radius and density. This confirms that the planet has a much lower surface gravity than that predicted by published theoretical models of gas giant planets. We apply our method to all 14 known transiting extrasolar planets and find a significant correlation between surface gravity and orbital period, which is related to the known correlation between mass and period. This correlation may be the underlying effect as surface gravity is a fundamental parameter in the evaporation of planetary atmospheres. [source]

TYC 1031 01262 1: the first known Galactic eclipsing binary with a Type II Cepheid component

S. V. Antipin
ABSTRACT We present the discovery and CCD observations of the first eclipsing binary with a Type II Cepheid component in our Galaxy. The pulsation and orbital periods are found to be 4.1523 and 51.38 d, respectively, i.e. this variable is the system with the shortest orbital period among known Cepheid binaries. Pulsations dominate the brightness variations. The eclipses are assumed to be partial. The EB-subtype eclipsing light curve leads us to believe that the binary components are non-spherical. [source]

The ultraluminous X-ray source in M82: an intermediate-mass black hole with a giant companion

A. Patruno
ABSTRACT The starburst galaxy M82, at a distance of 12 million light years, is the host of an unusually bright 2.4,16 × 1040 erg s,1 X-ray point source, which is best explained by an accreting black hole 102 to 104 times more massive than the Sun. Though the strongest candidate for a so-called intermediate-mass black hole, the only support stems from the observed luminosity and the 0.05,0.1 Hz quasi-periodicity in its signal. Interestingly, the 7,12 Myr old star cluster MGG-11 which has been associated with the X-ray source is sufficiently dense that an intermediate mass black hole could have been produced in the cluster core via collision runaway. The recently discovered 62.0 ± 2.5 d periodicity in the X-ray source X-1 further supports the hypothesis that this source is powered by a black hole several hundred times more massive than the Sun. We perform detailed binary evolution simulations with an accreting compact object of 10,5000 M, and find that the X-ray luminosity, the age of the cluster, the observed quasi-periodic oscillations and the now observed orbital period are explained best by a black hole of 200,5000 M, that accretes material from a 22,25 M, giant companion in a state of Roche-lobe contact. Interestingly, such a companion star is consistent with the expectation based on the tidal capture in a young and dense star cluster such as MGG-11, making the picture self-consistent. [source]

Recent discoveries of supersoft X-ray sources in M 31,

M. Henze
Abstract Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central area of our neighbouring galaxy M 31. This paper presents a review of results from recent X-ray observations of M 31 with XMM-Newton and Chandra. We carried out a dedicated optical and X-ray monitoring program of CNe and SSSs in the central area ofM 31. We discovered the first SSSs in M 31 globular clusters (GCs) and their connection to the very first discovered CN in a M 31 GC. This result may have an impact on the CN rate in GCs. Furthermore, in our optical and X-ray monitoring data we discovered the CN M3 1N 2007-11a, which shows a very short SSS phase of 29,52 days. Short SSS states (durations , 100 days) of CNe indicate massive white dwarfs (WDs) that are candidate progenitors of supernovae type Ia. In the case of M31N 2007-11a, the optical and X-ray light curves suggest a binary containing a WD with MWD > 1.0 M,. Finally, we present the discovery of the SSS counterpart of the CN M31N 2006-04a. The X-ray light curve of M31N 2006-04a shows short-time variability, which might indicate an orbital period of about 2 hours (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

V5116 Sgr: A disc-ecipsed SSS post-outburst nova?,

G. Sala
Abstract Nova V5116 Sgr 2005 No. 2, discovered on 2005 July 4, was observed with XMM-Newton in March 2007, 20 months after the optical outburst. The X-ray spectrum showed that the nova had evolved to a pure supersoft X-ray source, indicative of residual H-burning on top of the white dwarf. The X-ray light-curve shows abrupt decreases and increases of the flux by a factor 8 with a periodicity of 2.97 h, consistent with the possible orbital period of the system. The EPIC spectra are well fit with an ONe white dwarf atmosphere model, with the same temperature both in the low and the high flux periods. This rules out an intrinsic variation of the X-ray source as the origin of the flux changes, and points to a possible partial eclipse as the origin of the variable light curve. The RGS high resolution spectra support this scenario showing a number of emission features in the low flux state, which either disappear or change into absorption features in the high flux state. A new XMM-Newton observation in March 2009 shows the SSS had turned off and V51 16 Sgr had evolved into a weaker and harder X-ray source (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Tidal interaction in High-Mass X-ray Binaries

K.A. Stoyanov
Abstract Our aim is to investigate tidal interaction in High-Mass X-ray Binary 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 calculate the pseudosynchronization period (Pps) and compare it with the rotational period of the mass donors (Prot). We find that (1) the Be/X-ray binaries are not synchronized, the mass donors rotate faster than the orbital period and the ratio Pps/Prot is 2,300; (2) the giant and supergiant systems are close to synchronization and for them the ratio Pps/Prot is 0.3,2 (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Planetary transit observations at the University Observatory Jena: TrES-2,

St. Raetz
Abstract We report on observations of several transit events of the transiting planet TrES-2 obtained with the Cassegrain-Teleskop-Kamera at the University Observatory Jena. Between March 2007 and November 2008 ten different transits and almost a complete orbital period were observed. Overall, in 40 nights of observation 4291 exposures (in total 71.52 h of observation) of the TrES-2 parent star were taken. With the transit timings for TrES-2 from the 34 events published by the TrES-network, the Transit Light Curve project and the Exoplanet Transit Database plus our own ten transits, we find that the orbital period is P = (2.470614 ± 0.000001) d, a slight change by ,0.6 s compared to the previously published period. We present new ephemeris for this transiting planet. Furthermore, we found a second dip after the transit which could either be due to a blended variable star or occultation of a second star or even an additional object in the system. Our observations will be useful for future investigations of timing variations caused by additional perturbing planets and/or stellar spots and/or moons (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Planetary transit observations at the University Observatory Jena: XO-1b and TrES-1,

St. Raetz
Abstract We report on observations of transit events of the transiting planets XO-1b and TrES-1 with a 25 cm telescope of the University Observatory Jena. With the transit timings for XO-1b from all 50 available XO, SuperWASP, Transit Light Curve (TLC)-Project- and Exoplanet Transit Database (ETD)-data, including our own I -band photometry obtained in March 2007, we find that the orbital period is P = (3.941501 ± 0.000001) d, a slight change by ,3 s compared to the previously published period. We present new ephemeris for this transiting planet. Furthermore, we present new R -band photometry of two transits of TrES-1. With the help of all available transit times from literature this allows us to refine the estimate of the orbital period: P = (3.0300722 ± 0.0000002) d. Our observations will be useful for future investigations of timing variations caused by additional perturbing planets and/or stellar spots and/or moons (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Photometric analysis of the eclipsing binary 2MASS 19090585+4911585,

St. Raetz
Abstract We report on observations of the eclipsing binary 2MASS 19090585+4911585 with the 25 cm auxiliary telescope of the University Observatory Jena. We show that a nearby brighter star (2MASS 19090783+4912085) was previously misclassified as the eclipsing binary and find 2MASS 19090585+4911585 to be the true source of variation. We present photometric analysis of VRI light curves. The system is an overcontact binary of W UMa type with an orbital period of (0.288374 ± 0.000010) d (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Pulsation and orbit of AU Pegasi

M. Jurkovic
Abstract AU Pegasi is a pulsating star in a spectroscopic binary system with an orbital period of 53.26 days. Between 1960 and 1990 an extremely rapid period increase was observed in the value of the pulsation period, but in the last 15 years the observation show that the period set in 2.411 days. Fourier analysis of photometric data obtained during the ASAS project and those taken at the Piszkéstet, Mountain Station of the Konkoly Observatory during 1994,2005 indicate that AU Pegasi is pulsating in two modes simultaneously, and the ratio of the frequencies of the two modes is 0.706, a value common for double-mode classical Cepheids. A careful analysis of other photometric observations obtained during the era of the strong period increase also revealed existence of a second mode. This may suggest that this star is not a Type II Cepheid, despite its galactic position. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopy

A. 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]

Magnetic braking of Ap/Bp stars: application to compact black-hole X-ray binaries

Stephen Justham
ABSTRACT We examine the proposal that the subset of neutron-star and black-hole X-ray binaries that form with Ap or Bp star companions will experience systemic angular-momentum losses due to magnetic braking, not otherwise operative with intermediate-mass companion stars. We suggest that for donor stars possessing the anomalously high magnetic fields associated with Ap and Bp stars, a magnetically coupled, irradiation-driven stellar wind can lead to substantial systemic loss of angular momentum. Hence, these systems, which would otherwise not be expected to experience ,magnetic braking', evolve to shorter orbital periods during mass transfer. In this paper, we detail how such a magnetic braking scenario operates. We apply it to a specific astrophysics problem involving the formation of compact black-hole binaries with low-mass donor stars. At present, it is not understood how these systems form, given that low-mass companion stars are not likely to provide sufficient gravitational potential to unbind the envelope of the massive progenitor of the black hole during a prior ,common-envelope' phase. On the other hand, intermediate-mass companions, such as Ap and Bp stars, could more readily eject the common envelope. However, in the absence of magnetic braking, such systems tend to evolve to long orbital periods. We show that, with the proposed magnetic braking properties afforded by Ap and Bp companions, such a scenario can lead to the formation of compact black-hole binaries with orbital periods, donor masses, lifetimes and production rates that are in accord with the observations. In spite of these successes, our models reveal a significant discrepancy between the calculated effective temperatures and the observed spectral types of the donor stars. Finally, we show that this temperature discrepancy would still exist for other scenarios invoking initially intermediate-mass donor stars, and this presents a substantial unresolved mystery. [source]

An intriguing correlation between the masses and periods of the transiting planets

Tsevi Mazeh
ABSTRACT We point out an intriguing relation between the masses of the transiting planets and their orbital periods. For the six currently known transiting planets, the data are consistent with a decreasing linear relation. The other known short-period planets, discovered through radial-velocity techniques, seem to agree with this relation. We briefly speculate about a tentative physical model to explain such a dependence. [source]