Close Stars Research Articles

Detection of a tertiary companion in the eclipsing binary AD Andromeda

New orbital period variation of the eclipsing binary, AD Andromeda, was analyzed based on one CCD photometric times of minimum we have obtained and all available photoelectric and CCD values collected from the literatures. It is discovered that the orbital period of the binary shows a periodic oscillation with a period of 14.38 years and an amplitude of 0.0186 days. The periodic oscillation can be explained by the light-time effect via the presence of a tertiary component in a nearly circular orbit with a small eccentricity of e = 0.30 in the system. Based on the present analysis, it is estimated that the mass of the third body is no less than 1.76 ( ± 0.08 ) M ⊙ , and it should contribute light to the total system. Meanwhile, the photoelectric light curve obtained in yellow light by Ruciński [Ruciński, S.M., 1966. AcA 16, 307] was reanalyzed with the 2003 version of the W–D code. The results show that AD Andromeda is a detached eclipsing binary, and photometric solutions were computed. Based on the analysis, we obtained a small amount of third light in the system ( L 3 V ∼ 0.001 ) , which is too small for the contribution of the tertiary companion star. The low luminosity of the third companion may be explained in two possible ways, either: (1) the third companion might itself be a close double star consisting of two stars of 0.88 solar masses, or (2) it is a dark star such as a neutron star. We think the first possibility is a more likely one than a neutron star companion. New photometric and spectroscopic observations and a detailed investigation of those data are urgently required in the future.

Future Observations of Transits and Light Curves from Space

AbstractA variety of new observational opportunities have made transit and more generally light curve analysis central to the study of exoplanets. Talks at this IAU 253 Symposium have dramatically highlighted the measurement of the radius, density, atmospheric composition and atmospheric thermal structure, presently for relatively large, hot planets, but soon for smaller planets orbiting further from their host stars. On-going and future space observations will play a key role in the detection and characterization of these planetary systems. After a brief review, I focus on two topics: the need for a sensitive all-sky survey for planets transiting the brightest, closest stars and the follow-up opportunities afforded by the James Webb Space Telescope (JWST).

Investigating the correlation between the motions of the images of close stars for laser communications experiments with the artemis satellite

We investigated the correlation between the motions of the images of the components of the double star Gem. The angular distance between the components (4.8) corresponds approximately to the laser communications experiments with the geostationary Artemis satellite. The images were ac- quired with CCD cameras at the ESA's Optical Ground Station (the Canary Islands) and at the AZT-2 telescope of the Main Astronomical Observatory (Kyiv, Ukraine). Short exposures were made every second with narrow filters at a wavelength of about 850 m. Mean photometric positions of the Gem component images and their deviations were determined, and the correlation coefficients for the dis- placements of two images in the X and Y coordinates were calculated: K X = 0.96 and K Y = 0.95. The defocusing of the images was examined with the use of their full widths at half-maximum. We demon- strate that the atmospheric turbulence in the laser communications experiments with the geostationary satellite Artemis can be compensated for with the use of the data on the image motion observed in the di- rection toward the visible position of the satellite.

The occurence of interstellar meteoroids in the vicinity of the Earth

AbstractIf interstellar meteors are present among the registered meteor orbits, the distribution of the excesses of their heliocentric velocities should correspond to the distribution of radial velocities of close stars. Hence, for the velocity vi = 20 kms−1 of an interstellar meteor (with respect to the Sun) we obtain a heliocentric velocity vH = 46.6 kms−1 of an interstellar meteor arriving at the Earth. Moreover, a concentration of radiants to the Sun's apex should be observed. An analysis of the hyperbolic meteors among the 4581 photographic orbits of the IAU Meteor Data Center showed that the identification of the vast majority of the hyperbolic orbits in these catalogues has been caused by an erroneous determination of their heliocentric velocity and/or other parameters. Any error in the determination of vH, especially near the parabolic limit, can create an artificial hyperbolic orbit that does not really exist. On the basis of photographic meteors from the IAU MDC, the proportion of possible interstellar meteors decreased significantly (greater than 1 order of magnitude) after error analysis and does not exceed the value 2.5 × 10−4. Neither any concentration of radiants to the Sun's apex, nor any distribution following the motion of interstellar material has been found.

Interactions, star formation and AGN activity

It has long been known that galaxy interactions are associated with enhanced star formation. In a companion paper, we explored this connection by applying a variety of statistics to Sloan Digital Sky Survey (SDSS) data. In particular, we showed that specific star formation rates of galaxies are higher if they have close neighbours. Here, we apply exactly the same techniques to active galactic nuclei (AGN) in the survey, showing that close neighbours are not associated with any similar enhancement of nuclear activity. Star formation is enhanced in AGN with close neighbours in exactly the same way as in inactive galaxies, but the accretion rate on to the black hole, as estimated from the extinction-corrected [O iii] luminosity, is not influenced by the presence or absence of companions. Previous work has shown that galaxies with more strongly accreting black holes contain more young stars in their inner regions. This leads us to conclude that star formation induced by a close companion and star formation associated with black hole accretion are distinct events. These events may be part of the same physical process, for example a merger, provided they are separated in time. In this case, accretion on to the black hole and its associated star formation would occur only after the two interacting galaxies have merged. The major caveat in this work is our assumption that the extinction-corrected [O iii] luminosity is a robust indicator of the bolometric luminosity of the central black hole. It is thus important to check our results using indicators of AGN activity at other wavelengths.

Inspiration from relativistic solar cosmic ray events

High energy cosmic rays provide significant information about distance celestial bodies. The solar cosmic rays produced at the closest star, the Sun, not only bring us the particle acceleration in interplanetary and at the Sun, but also help us to well understand the high energy processes of galactic cosmic rays. Solar cosmic rays also directly affect the terrestrial environment and human life. During solar cycle 23 two extreme solar cosmic ray events were recorded on 14 July 2000 and 20 January 2005. The former event occurred in the peak years of solar activity had a soft energy spectrum. However, the spectrum of the later event was the hardest in current solar cycle although it happened close the end of solar cycle. We compare their features in the aspects of flares, radio bursts, coronal mass ejections, and solar proton spectra. The reasons of differences in energy release and particle acceleration was discussed, which may be useful for us to study very high energy cosmic rays.

Occultation by (22) Kalliope and its satellite Linus

AbstractThe occultation of a 9.1 magnitude star by asteroid (22) Kalliope and its satellite Linus was successfully observed in Japan in 2006 November 7.826 UT. This was the first definite observation of an occultation of a satellite of an asteroid that was discovered previously by other means. As a result the position of the satellite relative to Kalliope was obtained to be d = 0.246 ± 0.011 (arcsec), and P = 313.8 ± 2.7 (deg), where d is the angular distance and P is the position angle. The derived size for Kalliope is (209 ± 40)km × (136 ± 26)km (with the major axis in position angle of (8 ± 17) deg), and that for Linus is (33 ± 3) km. From the observations, the occulted star is also found to be a close double star whose separation is about 0.7 mas in position angle of about 300 deg, and the magnitudes of the components are found to be almost the same (~9.9 mag).

Tidal and rotational effects in the perturbations of hierarchical triple stellar systems

Aims.We study the perturbations of a relatively close third star on a tidally distorted eccentric eclipsing binary. We consider both the observational consequences of the variations of the orbital elements and the interactions of the stellar rotation with the orbital revolution in the presence of dissipation. We concentrate mainly on the effect of a hypothetical third companion on both the real, and the observed apsidal motion period. We investigate how the observed period derived mainly from some variants of the O–C relates to the real apsidal motion period.

Three-dimensional explosion dynamics of a critical-mass neutron star (in a binary)

In a close neutron star binary resulting from the collapse of the rotating iron core of a collapsing supernova, the low-mass component of mass m undergoes explosive disruption at the final evolutionary stage of this binary. We have obtained a numerical solution for the three-dimensional dynamics of 0.1 M ⊙ iron ejecta with energy release 4.7 MeV per nucleon in the gravitational field of a massive neutron star with mass M. The numerical solution has been obtained by the method of particles, which is adequate for a collisionless description of the ejecta dynamics in the absence of an interstellar medium. As a test problem, the suggested model is compared with the well-known asymptotic solution (for m/M → 0), which we have also been able to slightly improve and extend. We analyze in detail the separation of the ejecta into two categories of particles with hyperbolic and elliptical orbits. We have been able to obtain a number of corollaries from the analytical solution. These have allowed us to estimate the kinetic energy of the ejecta as a function of the binary component mass ratio and the final pulsar velocity by applying the momentum conservation law in the pulsar—ejecta system. Further use of our calculations is promising for the formulation of initial conditions for the three-dimensional hydrodynamic problem of the collision of ejecta with presupernova shells, in particular, with the toroidal iron atmosphere obtained previously in our two-dimensional calculations of the collapse of a rotating stellar core.

A pseudo-photon in non-trivial background fields

We show that in the presence of external fields for which either B ˙ ext ≠ 0 or ∇ × E ext ≠ 0 it is not possible to derive the classical Maxwell equations from an action with only one gauge field. We suggest that one possible solution is to consider a second physical pseudo-vector gauge field C. The action for this theory is originally motivated by the inclusion of magnetic monopoles. These particles play no role in this work and our argument is only based in, that the violation of the Bianchi identities, cannot be accounted at the action level with only the standard gauge field. We give a particular example for a periodic rotating external magnetic field. Our construction holds that at classical level both the vector and pseudo-vector gauge fields A and C are regular. We compare pseudo-photon with paraphoton (graviphoton) theories concluding that, besides the mechanisms of gauge symmetry breaking already studied, the Bianchi identities violation is a crucial difference between both theories. We also show that, due to Dirac's quantization condition, at quantum field theory level the effects due to pseudo-photons and photons can be distinguished by the respective contributions to the magnetic moment of fermions and vacuum polarization. These effects may be relevant in astrophysical environments, namely close and inside neutron stars and magnetars.

Production of high-energy μ neutrinos from young neutron stars

Young, rapidly rotating neutron stars could accelerate protons to energies of ∼ 1 PeV close to the stellar surface, which scatter with x-rays from the stellar surface through the Δ resonance and produce pions. The pions subsequently decay to produce muon neutrinos. We find that the energy spectrum of muon neutrinos consists of a sharp rise at ∼ 50 TeV, corresponding to the onset of the resonance, above which the flux drops as ϵ ν −2 an upper-energy cut-off that is determined by either kinematics or by the maximum energy to which protons are accelerated. We predict event rates as high as 10-50 km−2 yr−1 from relatively young, close neutron stars. Such fluxes would be detectable by IceCube.

Young Close-By Neutron Stars: The Gould Belt Vs. The Galactic Disc

We present new population synthesis calculations of close young neutron stars. In comparison with our previous investigation we use a different neutron star mass spectrum and different initial spatial and velocity distributions. The results confirm that most of ROSAT dim radioquiet isolated neutron stars had their origin in the Gould Belt. We predict that about several tens of young neutron stars can be identified in ROSAT All Sky Survey data at low galactic latitudes. Some of these sources also can have counterparts among EGRET unidentified sources.

The primordial binary population

We present the results of a near-infrared adaptive optics survey with the aim to detect close companions to Hipparcos members in the three subgroups of the nearby OB association Sco OB2: Upper Scorpius (US), Upper Centaurus Lupus (UCL) and Lower Centaurus Crux (LCC). We have targeted 199 A-type and late B-type stars in the KS band, and a subset also in the J and H band. We find 151 stellar components other than the target stars. A brightness criterion is used to separate these components into 77 background stars and 74 candidate physical companion stars. Out of these 74 candidate companions, 41 have not been reported before (14 in US; 13 in UCL; 14 in LCC). The angular separation between primaries and observed companion stars ranges from to . At the mean distance of Sco OB2 (130 pc) this corresponds to a projected separation of 28.6 AU to 1612 AU. Absolute magnitudes are derived for all primaries and observed companions using the parallax and interstellar extinction for each star individually. For each object we derive the mass from KS, assuming an age of 5 Myr for the US subgroup, and 20 Myr for the UCL and LCC subgroups. Companion star masses range from to . The mass ratio distribution follows with , which excludes random pairing. No close () companion stars or background stars are found in the magnitude range . The lack of stars with these properties cannot be explained by low-number statistics, and may imply a lower limit on the companion mass of ~. Close stellar components with are observed. If these components are very low-mass companion stars, a gap in the companion mass distribution might be present. The small number of close low-mass companion stars could support the embryo-ejection formation scenario for brown dwarfs. Our findings are compared with and complementary to visual, spectroscopic, and astrometric data on binarity in Sco OB2. We find an overall companion star fraction of 0.52 in this association. This is a lower limit since the data from the observations and from literature are hampered by observational biases and selection effects. This paper is the first step toward our goal to derive the primordial binary population in Sco OB2.

Using close stars as probes of hot accretion flow in Sgr A*

The extremely hot and tenuous accretion flow in the immediate vicinity of Sgr A ∗ is believed to be invisible (too dim) in the X-ray band, except for short X-ray flares. Here we point out that during pericenter passages, close brightest stars irradiate the inner region of the accretion flow, providing a plenty of optical/UV photons. These seed photons are Compton up-scattered by the hot electrons of the accretion flow to higher frequencies, some into the X-ray band, potentially making the innermost accretion flow much brighter in X-rays than usual. We propose to use coordinated near infra-red and X-ray observations of close star passages to put constraints onto Sgr A ∗ accretion theories. The absence of a noticeable change in the steady emission of Sgr A ∗ as observed by Chandra in the year 2002, when the star named S2 passed through a pericenter of its orbit, already rules out the hotter of the standard Advection-Dominated Accretion Flows. The less dense accretion flows, in particular the model of Yuan et al. (2003), passes the test and is constrained to accretion rates no larger than ∼ few × 10 −7 Myear −1 .

Close stars and accretion in low-luminosity active galactic nuclei

Quasar accretion discs are believed to form stars by self-gravity. Low-luminosity active galactic nuclei (LLAGNs) are much dimmer galactic centres, and are often believed to be quasars that ran out of gaseous fuel. LLAGN accretion discs should thus coexist with thousands to millions of stars or protostars left from the previous stronger accretion activity. In principle, these stars may produce several important effects: (i) contribute to the optical/ultraviolet spectra of some LLAGNs; (ii) the dusty discs could reprocess stellar radiation in the infrared frequencies and then dominate the LLAGN spectra in that region; (iii) deplete the (accretion) gas disc much faster than it can accrete on to the supermassive black hole; (iv) stars, individually or in groups, may slow down and modulate the accretion flow significantly due to their inertia. In this way they may produce the LLAGN cut-off discs; (v) alternatively, frequent enough stellar collisions and resulting stellar disruptions could keep the inner disc empty. Here we explore these ideas. We find that, despite 'low' luminosities of LLAGNs, unrealistically high stellar densities are required to make a sizable radiative contribution to the Hubble Space Telescope optical/ultraviolet spectra of these galactic nuclei. Stellar contribution to the infrared spectrum is more likely. Further, if LLAGNs are in a quasi-steady state for as long as 10 7 yr or more, too high stellar densities would again be required to significantly affect the dynamics of accretion flow. However, if LLAGNs are 'short-lived' phenomena, e.g. t ≤ 10 5 yr, the low-activity states of quiescence-outburst cycles, then embedded stars may be much more important through the mass effects (iii)-(v). With observations of LLAGNs becoming progressively better, it will be more and more difficult to neglect the presence of close stars in and around nuclear accretion discs.

The formation of the double neutron star pulsar J0737 − 3039

We find that the orbital period (2.4 h), eccentricity (0.09), dipole magnetic field strength (6.9 x 10 9 G) and spin period (22 ms) of the new highly relativistic double neutron star system PSR J0737 - 3039 can all be consistently explained if this system originated from a close helium star plus neutron star (HeS-NS) binary in which at the onset of the evolution the helium star had a mass in the range 4.0-6.5 M ○. and an orbital period in the range 0.1-0.2 d. Such systems are the post-common-envelope remnants of wide Be/X-ray binaries (orbital period ∼100 to 1000 d) which consist of a normal hydrogen-rich star with a mass in the range 10-20 M ○. and a neutron star. The close HeS-NS progenitor system went through a phase of mass transfer by Roche-lobe overflow at a high rate lasting a few times 10 4 yr; assuming Eddington-limited disc accretion on to the neutron star, this star was spun up to its present rapid spin rate. At the moment of the second supernova explosion the He star had a mass in the range 2.3-3.3 M ○. , and in order to obtain the present orbital parameters of PSR J0737 - 3039 a kick velocity in the range 70-230 km s -1 must have been imparted to the second neutron star at its birth.

The infrared L'-band view of the Galactic Center with NAOS-CONICA at VLT

We report on Galactic Center L'-band observations made during NAOS/CONICA Science Verification. Colors of the inner 2 stars reveal an infrared excess of S2, the closest star to the black hole, that could sign the first thermal infrared detection of Sgr A*. A multi-wavelength maximum likelihood analysis has allowed us to eliminate all but two of the candidates for gravitational lensing proposed by Alexander (2001). Our observations of the thin and intersecting structures ofthe Northern Arm could trace several shocks heating the neighbooring dust rather than a stream of matter in orbit around the central mass as previously thought.

Dual-Star Photometer at the Tallinn Observatory

Abstract We briefly describe the dual-star photometer designed by P. Kalv, a former director of Tallinn Observatory (1934-2002) for multicolor photometry of close binaries and intrinsic variable stars.

Bright stars and an optically thick inactive disk in Sgr A*and other dormant galaxy centers

Cold inactive disks are believed to exist in Low Luminosity AGN (LLAGN). They may also exist in the nuclei of inactive galaxies and in the center of our own Galaxy. These disks would then be embedded in the observed dense nuclear stellar clusters. Making the simplest assumption of an optically thick disk, we explore several ways to detect the disk presence through its interaction with the cluster. The first of these is the eclipse of close bright stars by the disk. The second is the increase in the infrared flux of the disk due to illumination of its surface by such stars during close passages. Finally the surface brightness of the star cluster should show an anisotropy that depends on the inclination angle of the disk. We apply the first two of the methods to Sgr A*, the super-massive black hole in our Galactic Center. Using the orbital parameters of the close star S2, we strongly rule out a disk optically thick in the near infrared unless it has a relatively large inner hole. For disks with no inner holes, we estimate that the data permit a disk with infrared optical depth no larger than about 0.01. Such a disk could also be responsible for the detected 3.8 μm excess in the spectrum of S2. The constraints on the disk that we obtain here can be reconciled with the disk parameters needed to explain the observed X-ray flares if dust particles in the disk have sizes greater than m. The destruction of small dust particles by strong UV heating and shocks from star passages through the disk, and grain growth during “quiescent” times, are mentioned as possible mechanisms of creating the unusual grain size distribution. We estimate the emissivity of the thin layer photo-ionized by the star in Hydrogen Brγ line and in the continuum recombination in the 2.2 μm band, and find that it may be detectable in the future if the disk exists.

Spectroscopy of the optical counterpart to Ser X-1

We present William Herschel Telescope (WHT) and Very Large Telescope (VLT) spectroscopy of MM Ser, the optical counterpart to Ser X-1. We deblend the red spectra of the two close stars identified by Wachter and show that the brighter of the two is responsible for the Ha and He I emission, hence confirming that this is the true counterpart of the X-ray source. We also identify several He II and N III lines in the blue spectrum. The isolated emission lines are all remarkably narrow, with FWHM 200-300 km s -1 . The Bowen blend has structure suggesting that the individual components are also narrow. These narrow lines could be from the disc if the binary inclination is quite low, or they could come from a more localized region such as the heated face of the companion star. Several interstellar lines are detected and indicate that the reddening is moderate, and consistent with the neutral hydrogen column density inferred in X-rays.