Similar Orbital Periods Research Articles

Global Disk Oscillations in Binary Be Stars

Abstract We consider the effects of the tidal interaction with the companion, via orbital separation and the binary mass ratio, on the global one-armed oscillation modes in disks around binary Be stars. Our model takes into account a three-dimensional effect that contributes to mode confinement, which was recently found by Ogilvie (2008). We find that the one-armed oscillations are well confined in systems with disks larger than a few tens of stellar radii. In such systems, the oscillation period depends little on the binary parameters. On the other hand, in systems with smaller disks, where mode confinement is incomplete, the oscillation period increases with increasing orbital separation and/or decreasing binary mass ratio. The eigenmode is insensitive to the spectral type of the central star. Our results suggest that the dependence of the V$/$R oscillation period on the orbital separation and binary mass ratio should be observed only in short-period binary systems, and that, for systems with a similar orbital period, those with higher mass ratios will show shorter V$/$R variations.

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

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+0.13−0.08MJ, RP= 1.090+0.094−0.058RJ and ρP= 1.22+0.19−0.24 ρJ. 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.

On the masses and evolutionary status of the black hole binary GX 339-4: a twin system of XTE J1550-564?

We apply the K-correction to the black hole LMXB GX 339-4 which implies Mx > 6 Msun by only assuming that the companion is more massive than ~0.17 Msun, the lower limit allowed by applying a 'stripped-giant' model. This evolutionary model successfully reproduces the observed properties of the system. We obtain a maximum mass for the companion of M2 0.3 Msun and Mx > 7 Msun. We have also applied this scenario to the black hole binary XTE J1550-564, which has a similar orbital period but the donor is detected spectroscopically. The model successfully reproduces the observed stellar parameters.

An XMM–Newton observation of the neutron star X-ray transient 2S 1803−245 in quiescence

We observed the neutron star X-ray transient 2S 1803-245 in quiescence with the X-ray satellite XMM-Newton, but did not detect it. An analysis of the X-ray bursts observed during the 1998 outburst of 2S 1803-245 gives an upper limit to the distance of <=7.3 kpc, leading to an upper limit on the quiescent 0.5-10 keV X-ray luminosity of <=2.8 × 1032 erg s-1 (3sigma). Since the expected orbital period of 2S 1803-245 is several hours, this limit is not much higher than those observed for the quiescent black hole transients with similar orbital periods.

XMM-Newton observations of the black hole X-ray transient XTE J1650-500 in quiescence

We report the result of an XMM-Newton observation of the black-hole X-ray transient XTE J1650-500 in quiescence. The source was not detected and we set upper limits on the 0.5-10 keV luminosity of 0.9e31-1.0e31 erg/s (for a newly derived distance of 2.6 kpc). These limits are in line with the quiescent luminosities of black-hole X-ray binaries with similar orbital periods (~7-8 hr)

V4140 Sgr: A short period dwarf nova with a peculiar behavior

We report on time series of CCD photometry of V4140 Sgr between 1991 and 2001. The analysis reveals that the object was in the decline from an outburst in 1992 and again in outburst in 2001. The historical light curve collected by amateur astronomers shows low amplitude (1-2 mag) outbursts 5-10 days long, recurrent every 80-90 days, confirming its dwarf nova nature. We derive an outburst decline time scale of 1.2 days mag$^{-1}$. Eclipse mapping techniques were applied to data both in quiescence and in outburst to derive accretion disc surface brightness maps. A distance of $d = 170 \pm 30$ pc is obtained from a method similar to that used to constrain the distance to open clusters. From this distance, disc radial brightness temperature distributions are determined. The temperatures in the quiescent disc vary from $6 000$ K in the inner regions to $3 000$ K near the outer disc and are flatter than the $T \propto r^{-{3/4}}$ law for optically thick steady-state disc. The outburst occurs mainly with a significant increase in brightness of the intermediate and outer disc regions. The disc temperatures remain below the critical effective temperature $T_{\rm crit}$ at all disc radii during outburst. The radial temperature distributions in quiescence and in outburst are significantly different from those of other dwarf novae of similar orbital period. These results cannot be explained within the framework of the disc instability model. We suggest that the small amplitude outbursts of V4140 Sgr are caused by bursts of enhanced mass transfer rate from the secondary star.

Paleocurrent reconstruction of the deep Pacific inflow during the middle Miocene: Reflections of East Antarctic Ice Sheet growth

Today the deep western boundary current (DWBC) east of New Zealand is the most important route for deep water entering the Pacific Ocean. Large‐scale changes in deep water circulation patterns are thought to have been associated with the development of the East Antarctic Ice Sheet (EAIS) close to the main source of bottom water for the DWBC. Here we reconstruct the changing speed of the southwest Pacific DWBC during the middle Miocene from ∼15.5–12.5 Ma, a period of significant global ice accumulation associated with EAIS growth. Sortable silt mean grain sizes from Ocean Drilling Program Site 1123 reveal variability in the speed of the Pacific inflow on the timescale of the 41 kyr orbital obliquity cycle. Similar orbital period flow changes have recently been demonstrated for the Pleistocene epoch. Collectively, these observations suggest that a strong coupling between changes in the speed of the deep Pacific inflow and high‐latitude climate forcing may have been a persistent feature of the global thermohaline circulation system for at least the past 15 Myr. Furthermore, long‐term changes in flow speed suggest an intensification of the DWBC under an inferred increase in Southern Component Water production. This occurred at the same time as decreasing Tethyan outflow and major EAIS growth between ∼15.5 and 13.5 Ma. These results provide evidence that a major component of the deep thermohaline circulation was associated with the middle Miocene growth of the EAIS and support the view that this time interval represents an important step in the development of the Neogene icehouse climate.

Outburst Photometry of the Eclipsing Dwarf Nova GY Cancri

Abstract We observed the ROSAT-selected eclipsing dwarf nova GY Cnc ($= \mathrm{RX}\,\mathrm{J}0909.8{+}1849$) during the 2001 November outburst. We refined the orbital period to be 0.17544251(5)d. The fading portion of the outburst was indistinguishable from those of typical dwarf novae with similar orbital periods. However, the signature of the orbital humps (or a hot spot) was far less prominently observed in the orbital light curves and eclipse profiles than in usual dwarf novae with similar orbital periods. The combination of a low frequency of outbursts and an apparent lack of slowly rising, long outbursts in GY Cnc is difficult to reconcile within the standard framework of dwarf novae. We suspect that GY Cnc may be the first above-the-gap counterpart of the unusual eclipsing dwarf novae HT Cas and IR Com.

Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402

ABSTRACTWe report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high‐excitation spectra, complex line profiles signifying mass loss at particular orbital phases, and similar orbital periods (respectively, 0.12433 and 0.12056 days). They are well‐credentialed members of the SW Sex class of cataclysmic variables. Their light curves are also quite complex. V442 Oph shows periodic signals with periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar signals at 0.11696(8) and 4.05(12) days. We interpret these short and long periods, respectively, as a “negative superhump” and the wobble period of the accretion disk. The superhump could then possibly arise from the heating of the secondary (and structures fixed in the orbital frame) by inner‐disk radiation, which reaches the secondary relatively unimpeded since the disk is not coplanar. At higher frequencies, both stars show another type of variability: quasi‐periodic oscillations with a period near 1000 s. Underlying these strong signals of low stability may be weak signals of higher stability. Similar quasi‐periodic oscillations, and negative superhumps, are quite common features in SW Sex stars. Both can in principle be explained by ascribing strong magnetism to the white dwarf member of the binary; and we suggest that SW Sex stars are borderline AM Herculis binaries, usually drowned by a high accretion rate. This would provide an ancestor channel for AM Hers, whose origin is still mysterious.

The origin of subdwarf B stars – I. The formation channels

Subdwarf B (sdB) stars (and related sdO/sdOB stars) are believed to be helium-core-burning objects with very thin hydrogen-rich envelopes. In recent years it has become increasingly clear from observational surveys that a large fraction of these objects are members of binary systems. To understand their formation better, we present the results of a detailed investigation of the three main binary evolution channels that can lead to the formation of sdB stars: the common-envelope (CE) ejection channel, the stable Roche lobe overflow (RLOF) channel, and the double helium white dwarfs (WDs) merger channel. The CE ejection channel leads to the formation of sdB stars in short-period binaries with typical orbital periods between 0.1 and 10 d, very thin hydrogen-rich envelopes and a mass distribution sharply peaked around ∼0.46 M⊙. On the other hand, under the assumption that all mass transferred is soon lost, the stable RLOF channel produces sdB stars with similar masses but long orbital periods (400–1500 d) and with rather thick hydrogen-rich envelopes. The merger channel gives rise to single sdB stars whose hydrogen-rich envelopes are extremely thin but which have a fairly wide distribution of masses (0.4−0.65 M⊙). We obtained the conditions for the formation of sdB stars from each of these channels using detailed stellar and binary evolution calculations where we modelled the detailed evolution of sdB stars and carried out simplified binary population synthesis simulations. The observed period distribution of sdB stars in compact binaries strongly constrains the CE ejection parameters. The best fits to the observations are obtained for very efficient CE ejection where the envelope ionization energy is included, consistent with previous results. We also present the distribution of sdB stars in the Teff−log g diagram, the Hertzsprung–Russell diagram and the distribution of mass functions.

The measurement of rotational broadening in post-common-envelope binaries

We employ high-resolution echelle spectroscopy to measure the projected rotational velocity, V r o t sin i, in the post-common-envelope binaries EG UMa, HZ 9 and RE J1629 + 780. For EG UMa we obtain consistent V r o t σin ι measurements from the Na I doublet at 8183, 8195 A (31.2 ′ 3.7 km s - 1 ), the Fe and Ti intrinsically narrow metal (INM) lines in the region 8374-8430 A (26.6 ′ 2.7 and 27.8 ′ 3.0 km s - 1 ) and the K I line at 7698.9 A (26.2 ′ 3.5 km s - 1 ). This is in contrast to previous measurements of V r o t sin i from the Na I doublet and INM features derived using lower-resolution spectra, which were not consistent. Possible origins for the disagreement observed previously are discussed, including the inaccurate removal of telluric absorption. The values of V r o t sin i measured from the high-resolution EG UMa spectra are also consistent with that expected from system parameters derived from previous observational data. We also update the ephemeris and orbital period of EG UMa. We obtained rotation rate measurements of 34.3 ′ 3.8 km s - 1 for HZ 9 and 25.1 ′ 2.3 km s - 1 for RE J1629 + 780, as measured from the Na I doublet at 8183, 8195 A and the INM lines. In both systems there is agreement between the V r o t sin i values measured from the two regions. The value of V r o t sin i measured in HZ 9 is similar to that measured for EG UMa. This is expected, as these systems share a similar orbital period and secondary star spectral type. The measurement of V r o t sin i in RE J1629 + 780 indicates that this system, which lacks radial velocity shifts due to orbital motion, is a wide binary as opposed to a low-inclination system.

Cool White Dwarfs in Cataclysmic Variables:Hubble Space TelescopeResults on EG Cancri and HV Virginis

Our Hubble Space Telescope (HST) ultraviolet spectra of the low mass transfer rate cataclysmic variables EG Cnc and HV Vir at 4 yr and 8 yr past their last superoutburst have shown that the white dwarfs in these systems are among the coolest yet observed in disk-accreting close binaries. The UV-optical fluxes of EG Cnc are consistent with a 11,700-13,000 K white dwarf at a distance of 350-475 pc, while those of HV Vir fit with a 12,500-14,000 K white dwarf at 400-550 pc, with log g = 8.0 ± 0.5 for both stars. In each case, the metal abundance is near 0.3 solar, while the rotation rates are considerably less than breakup. If these systems formed above the period gap and evolved to their short periods in an evolution time of several Gyr, then their white dwarfs are hotter than field white dwarfs of comparable age and hotter than those in close binary systems of similar orbital period that contain magnetic white dwarfs. If these systems have indeed passed the period minimum in their evolution, the implication is that they are significantly heated by the long-term effects of mass transfer from their close companions.

Apsidal motion and light-time effect in eclipsing binaries HS Herculis and U Ophiuchi

Several new times of minima, based on photoelectric observations, have been secured for two bright and well-known eclipsing binaries with eccentric orbits and with very similar orbital periods: HS Her ($P = 1\fd637, e = 0.02$) and U Oph ($P = 1\fd677, e = 0.003$). For HS Her, an apsidal motion with a period of 78 years is confirmed and a third body in an eccentric orbit with a period of 85 years is found. An analysis of all available eclipse timings of U Oph has confirmed the presence of an apsidal motion with one of the shortest known periods (20.1 yr) and a light-time effect with the improved period of 37.6 yr. The corresponding internal structure constants log k 2 were also derived. It is estimated that the tertiaries of both systems are detectable via speckle interferometry.

Nova‐induced Mass Transfer Variations

We investigate variations of the mass transfer rate in cataclysmic variables (CVs) that are induced by nova outbursts. The ejection of nova shells leads to a spread of transfer rates in systems with similar orbital period. The effect is maximal if the specific angular momentum in the shell is the same as the specific orbital angular momentum of the white dwarf. We show analytically that in this case the nova-induced widening of the mass transfer rate distribution can be significant if the system, in the absence of nova outbursts, is close to mass transfer instability (i.e., within a factor of ~1.5 of the critical mass ratio). Hence, the effect is negligible below the period gap and for systems with high-mass white dwarfs. At orbital periods between about 3 and 6 hr the width of the mass transfer rate distribution exceeds an order of magnitude if the mass accreted on the white dwarf prior to the runaway is larger than a few 10-4 M☉. At a given orbital period in this range, systems with the highest transfer rate should on average have the largest ratio of donor to white dwarf mass. We show results of population synthesis models that confirm and augment the analytic results.

The Accretion Disk and White Dwarf in the Short‐Period Dwarf Novae TY Piscium and V436 Centauri during Quiescence

ABSTRACTThe short‐period dwarf novae TY Psc and V436 Cen are SU UMa systems with very similar orbital periods, similar recurrence times for normal outbursts (∼23 days) and superoutbursts (∼340 days), and nearly identical outburst amplitudes. We have carried out high‐gravity model atmosphere and accretion disk synthetic spectra from the grid of Wade & Hubeny. The best‐fit stellar model spectrum, from spectral slope and line fitting, is a white dwarf photosphere having Teff = 25,000 K, log g = 8, and essentially solar chemical abundances, while the best‐fit optically thick accretion disk model, from spectral slope fitting, has Mwd = 0.55 M⊙, M˙ = 10-9.5 M⊙ yr−1, and an inclination i = 18°. The implied accretion rate is almost certainly too large for dwarf nova quiescence. The predicted fluxes using parameters from the photosphere and disk spectral slope fitting models reveal enormous differences compared with the observed luminosity using a reasonable distance estimate. For TY Psc, the predicted accretion disk luminosity is ∼100 times too luminous, while the stellar luminosity is too luminous by a factor of ∼10. For V436 Cen, the best‐fit high‐gravity model photosphere, from spectral slope fitting, yields Teff = 24,000 K, log g = 8, and essentially solar abundance, while the best‐fit accretion disk models, from spectral slope fitting, yield Mwd = 0.8 M⊙, M˙ = 10-10 M⊙ yr−1, and i = 75°. The presence of broad absorption troughs at unusual wavelength positions suggests the presence of an absorption curtain (upper disk atmosphere) in V436 Cen. The temperatures we have for TY Psc and V436 Cen are higher than normal for the accreting white dwarfs in dwarf novae below the period gap. This could indicate that the systems were not in the deepest level of quiescence when they were observed.

Parent Stars of Extrasolar Planets. IV. 14 Herculis, HD 187123, and HD 210277

Spectroscopic analyses of 14 Her, HD 187123, and HD 210277, recently reported to harbor planets, reveal that these stars are metal rich. We find [Fe/H]=0.50 ± 0.05, 0.16 ± 0.05, and 0.24 ± 0.05 for 14 Her, HD 187123, and HD 210277, respectively. This is the first spectroscopic analysis of HD 187123; our results for 14 Her and HD 210277 are in agreement with published studies. It is shown that 14 Her and ρ1 Cnc are nearly identical in their bulk physical characteristics. This result, combined with their extreme metallicities, suggests that their physical parameters have been affected by the process that formed their planets. These two stars join a group of about half a dozen stars in the solar neighborhood with [Fe/H] ≥ 0.4. It is also shown that 51 Peg and HD 187123, which have companions with similar orbital periods and masses, are nearly identical. We find v sin i ≈ 2.0 km s-1 for HD 210277 from a high-resolution spectrum.

An abundance analysis of the single-lined spectroscopic binaries with barium stars-like orbital elements

Detailed abundance analyses have been car- ried out for 17 single-lined binaries (giants and dwarfs) with orbital elements and mass functions similar to those of barium stars, using high-dispersion CCD spectra and model atmospheres. All these binary systems contain an unseen low-mass component, presumably, a white dwarf. A mild enhancement (+0:1 0:25 dex) of the averaged s- process elements abundances has been found only for two stars. The heavy-element overabundances in these stars are much less marked than those of the classical barium stars having similar orbital periods. We have concluded that the existence of a white dwarf (WD) companion in binary systems with barium star like characteristics is not sucient to produce a strong barium star. However, ve of the analyzed giants show a signicant enhancement (0:2 0:3 dex) of barium. The analysis indicates that a main sequence companion has not a signicant influ- ence (due to tidal mixing, as has been sometimes sug- gested) on the internal structure (chemical composition) of the primary star. Since barium enhanced giants occupy a place on the (eccentricity-orbital period) plane similar to BaII stars we have concluded that a mild barium enhance- ment in these stars is due to mass transfer from the com- panion during its late phases of evolution. Thus it seems likely that all giants (primaries) in barium star like binary systems with WD component have chemical peculiarities (very slight in some cases) depending, apparently, on the eciency of mass transfer in a specic binary system. The signicant enhancement of heavy elements in the atmo- spheres of two radial velocity non-variable barium stars

The X-ray evidence that the 51 Peg companion is a planet

51 Pegasi is a nearby G2-3 V star which is similar to the Sun. Mayor & Queloz (1995) [Natur, 378, 355] have recently found that 51 Peg has sinusoidal radial velocity variations with a period of 4.2 days and amplitude of 59 m/s. The radial velocity, if due to orbital motion around the system center-of-mass, implies a minimum companion mass of 0.47 Jupiter masses, which results from the assumption that the inclination angle of the system is 90° from the line of sight. However, because the inclination angle is not directly measured there remains an uncertainty in the companion mass. In the limit of a near-zero inclination angle the companion could even be a late-type dwarf star. We argue that the low measured X-ray luminosity of the 51 Peg system supports the conclusion that the companion is a planet, independent of any assumption about the inclination angle. If 51 Peg were a binary stellar system with a 4-day orbital period its X-ray emission would be in marked contrast with ALL known binary stellar systems with similar orbital periods. When compared to the distribution of binary star X-ray luminosities, a system with the 51 Peg X-ray luminosity have an occurrence probability of only 1.7 × 10 −6. The low X-ray luminosity also confirms that 51 Peg is a slow rotator based upon the correlation between X-ray emission and rotational velocity. We discuss the lack of synchronization between the 51 Peg orbital and rotational periods and calculate model-dependent upper limits on the companion mass which also indicate that it is a planet. Steven Beckwith

Ultraviolet Observations of SW Ursae Majoris, BC Ursae Majoris, and TV Corvi (1217--18): IUE Spectroscopy and Outburst Light Curves

We present lUE superoutburst observations of three tremendous outburst amplitude dwarf novae. Limited ground-based optical photometry was also obtained contemporaneously. This is the first such ultraviolet spectroscopy of these systems, and we compare our results with other well-studied dwarf novae of similar orbital periods. We find that the slope of the ultraviolet spectra are similar to that for typical dwarf novae during normal outburst but are slightly bluer than other short-period systems at superoutburst. Complex line profiles exist and show large wind velocities which exceed the white dwarf escape velocity and are at or above the largest velocities seen in normal dwarf novae. We also present an observational summary of the outburst lightcurves of SW UMa and how these may be related to other large outburst dwarf novae.

Spectroscopy of faint, high latitude cataclysmic variable candidates

Summary The fields of several variable stars believed to be cataclysmic binaries at large distances above the Galactic plane have been examined using low resolution spectroscopy in the 3600-10000 Å wavelength range. The spectral characteristics of the stars observed are presented. We find that AL Com may be an intermediate polar on the basis of its modulation period, and the observation of hydrogen lines in its spectrum. In four systems, ARCnc, DVUMa, DODra and BCUMa, there is evidence for the spectral signature of the mass-donating secondary, and we use the spectral type of the secondary to estimate the system parameters. At least two of these binaries, ARCnc and DVUMa, are eclipsing. The inferred absolute magnitude of BC UMa is faint, in the range 11.0-13.5. The blue spectrum of this star is remarkably similar to that of the unusual cataclysmic variable WZ Sge. We note that BC UMa and WZ Sge also exhibit similar, and extreme, outburst amplitudes, and have very similar orbital periods.