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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

OPTICAL AND X-RAY STUDIES OF 10 X-RAY-SELECTED CATACLYSMIC BINARIES

We report on ground-based optical observations of 10 cataclysmic binaries that were discovered through their X-ray emission. Time-resolved radial velocity spectroscopy yields unambiguous orbital periods for eight objects and ambiguous results for the remaining two. The orbital periods range from 87 minutes to 9.38 hr. We also obtained time-series optical photometry for six targets, four of which have coherent pulsations. These periods are 1218 s for 1RXS J045707.4+452751, 628 s for AX J1740.2–2903, 477 s for AX J1853.3–0128, and 935 s for IGR J19267+1325. A total of seven of the sources have coherent oscillations in X-rays or optical, indicating that they are intermediate polars (DQ Herculis stars). Time-resolved spectroscopy of one object, Swift J2218.4+1925, shows that it is an AM Herculis star, or polar, and IGR J19552+0044 may also be in that class. For another object, Swift J0746.2–1611, we find an orbital period of 9.384 hr and detect the spectrum of the secondary star. The secondary's spectral contribution implies a distance of 900 (+190, –150) pc, where the error bars are estimated using a Monte Carlo technique to account for correlated uncertainties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Multi-wavelength photometry of the T Tauri binary V582 Mon (KH 15D): A new epoch of occultations

We present multi-wavelength (VRIJHK) observations of KH 15D obtained in 2012/2013, as well as a master table of standard photometry spanning the years 1967 to 2013. The system is a close, eccentric T Tauri binary embedded in an inclined precessing circumbinary (CB) ring. The most recent data show the continued rise of star B with respect to the trailing edge of the occulting horizon as the system's maximum brightness steadily increases. The wealth of data in time and wavelength domains allows us to track the long-term CCD color evolution of KH 15D. We find that the V – I behavior is consistent with direct and scattered light from the composite color of two stars with slightly different temperatures. There is no evidence for any reddening or bluing associated with extinction or scattering by interstellar-medium-size dust grains. Furthermore, we probe the system's faint phase behavior at near-infrared wavelengths in order to investigate extinction properties of the ring and signatures of a possible shepherding planet sometimes invoked to confine the CB ring at ∼5 AU. The wavelength independence of eclipse depth at second contact is consistent with the ring material being fully opaque to 2.2 μm. The color-magnitude diagrams demonstrate excess flux in J and H at low light levels, which may be due to the presence of a hot, young Jupiter-mass planet.

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DOE OSTI2014

The triple binary star EQ Tau with an active component

New photometric data of EQ Tau observed in 2010 and 2013 are presented. Light curves obtained in 2000 and 2004 by Yuan and Qian and 2001 by Yang and Liu, together with our two newly determined sets of light curves, were analyzed using the Wilson-Devinney code. The five sets of light curves exhibit very obvious variations, implying that the light curves of EQ Tau show a strong O'Connell effect. We found that EQ Tau is an A-type shallow contact binary with a contact degree of f = 11.8%; variable dark spots on the primary component of EQ Tau were also observed. Using 10 new times of minimum light, together with those collected from the literature, the orbital period change of EQ Tau was analyzed. We found that its orbital period includes a secular decrease (dP/dt = –3.63 × 10{sup –8} days yr{sup –1}) and a cyclic oscillation (A {sub 3} = 0.0058 days and P {sub 3} = 22.7 yr). The secular increase of the period can be explained by mass transfer from the more massive component to the less massive one or/and angular momentum loss due to a magnetic stellar wind. The Applegate mechanism cannot explain the cyclic orbital period change. A probable transit-like event was observed in 2010. Therefore, the cyclic orbital period change of EQ Tau may be due to the light time effect of a third body.

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DOE OSTI2014

Absolute properties of the eclipsing binary star AP Andromedae

AP And is a well-detached F5 eclipsing binary star for which only a very limited amount of information was available before this publication. We have obtained very extensive measurements of the light curve (19,097 differential V magnitude observations) and a radial velocity curve (83 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.277 ± 0.004 and 1.251 ± 0.004 M {sub ☉}, radii of 1.233 ± 0.006 and 1.1953 ± 0.005 R {sub ☉}, and temperatures of 6565 ± 150 K and 6495 ± 150 K. The distance to the system is about 400 ± 30 pc. Comparison with the theoretical properties of the stellar evolutionary models of the Yonsei-Yale series of Yi et al. shows good agreement between the observations and the theory at an age of about 500 Myr and a slightly sub-solar metallicity.

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DOE OSTI2014

Study of eclipsing binary and multiple systems in ob associations. II. The cygnus ob region: V443 Cyg, V456 Cyg, and V2107 Cyg

Three presumably young eclipsing binary systems in the direction of the Cygnus OB1, OB3, and OB9 associations are studied. Component spectra are reconstructed and their orbits are determined using light curves and spectra disentangling techniques. V443 Cyg and V456 Cyg have circular orbits while the light curve of V2107 Cyg imposes a slightly eccentric orbit (e = 0.045 ± 0.03). V443 Cyg harbors F-type stars, not young early-A stars as previously suggested in the literature based solely on photometry. It appears to be situated in the foreground (distance 0.6 ± 0.2 kpc) of the young stellar populations in Cygnus. V456 Cyg, at a distance of 0.50 ± 0.03 kpc, consists of a slightly metal-weak A-type star and an early-F star. The age of both systems, on or very near to the main sequence, remains uncertain by an order of magnitude. V2107 Cyg is a more massive system (8.9 ± 2 and 4.5 ± 1.2 M {sub ☉}) at 1.5 ± 0.5 kpc and, also kinematically, a strong candidate-member of Cyg OB1. The more massive component is slightly evolved and appears to undergo non-radial βCep-type pulsations. The Doppler signal of the secondary is barely detectable. A more extensive, asteroseismological study is necessary to fix masses more precisely. Nevertheless, the position of the primary in the H-R diagram confines the age reasonably well to 20 ± 5 Myr, indicating that for Cyg OB1 has a similar extent of star formation history as that established for Cyg OB2.

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DOE OSTI2014

Short apsidal period of three eccentric eclipsing binaries discovered in the Large Magellanic Cloud

We present new elements of apsidal motion in three eccentric eclipsing binaries located in the Large Magellanic Cloud. The apsidal motions of the systems were analyzed using both light curves and eclipse timings. The OGLE-III data obtained during the long period of 8 yr (2002-2009) allowed us to determine the apsidal motion period from their analyses. The existence of third light in all selected systems was investigated by light curve analysis. The O – C diagrams of EROS 1018, EROS 1041, and EROS 1054 were analyzed using the 30, 44, and 26 new times of minimum light, respectively, determined from full light curves constructed from EROS, MACHO, OGLE-II, OGLE-III, and our own observations. This enabled a detailed study of the apsidal motion in these systems for the first time. All of the systems have a significant apsidal motion below 100 yr. In particular, EROS 1018 shows a very fast apsidal period of 19.9 ± 2.2 yr in a detached system.

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DOE OSTI2014

Optical BVRI photometry of common proper motion F/G/K+M wide separation binaries

We present optical (BVRI) photometric measurements of a sample of 76 common proper motion wide separation main-sequence binary pairs. The pairs are composed of a F-, G-, or K-type primary star and an M-type secondary. The sample is selected from the revised NLTT catalog and the LSPM catalog. The photometry is generally precise to 0.03 mag in all bands. We separate our sample into two groups, dwarf candidates and subdwarf candidates, using the reduced proper motion diagram constructed with our improved photometry. The M subdwarf candidates in general have larger V – R colors than the M dwarf candidates at a given V – I color. This is consistent with an average metallicity difference between the two groups, as predicted by the PHOENIX/BT-Settl models. The improved photometry will be used as input into a technique to determine the metallicities of the M-type stars.

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DOE OSTI2014

Absolute properties of the eclipsing binary star V501 Herculis

V501 Her is a well detached G3 eclipsing binary star with a period of 8.597687 days for which we have determined very accurate light and radial-velocity curves using robotic telescopes. Results of these data indicate that the component stars have masses of 1.269 ± 0.004 and 1.211 ± 0.003 solar masses, radii of 2.001 ± 0.003 and 1.511 ± 0.003 solar radii, and temperatures of 5683 ± 100 K and 5720 ± 100 K, respectively. Comparison with the Yonsei-Yale series of evolutionary models results in good agreement at an age of about 5.1 Gyr for a somewhat metal-rich composition. Those models indicate that the more massive, larger, slightly cooler star is just beyond core hydrogen exhaustion while the less massive, smaller, slightly hotter star has not quite reached core hydrogen exhaustion. The orbit is not yet circularized, and the components are rotating at or near their pseudosynchronous velocities. The distance to the system is 420 ± 30 pc.

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DOE OSTI2014

The first photometric analysis of the near contact binary IR Cas

The first photometric analysis of IR Cas was carried out based on the new observed BVRI light curves. The symmetric light curves and nearly flat secondary minimum indicate that very precise photometric results can be determined. We found that IR Cas is a near contact binary with the primary component filling its Roche lobe. An analysis of the O – C diagram based on all available times of minimum light reveals evidence for a periodic change with a semi-amplitude of 0.0153 days and a period of 39.7 yr superimposed on a secular decrease at a rate of dp/dt = –1.28(± 0.09) × 10{sup –7} days yr{sup –1}. The most reasonable explanation for the periodic change is the light time-travel effect due to a third body. The period decrease may be caused by mass transfer from the primary component to the secondary. With the decreasing period, IR Cas would eventually evolve into a contact system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Absolute properties of the eclipsing binary star IM Persei

IM Per is a detached A7 eccentric eclipsing binary star. We have obtained extensive measurements of the light curve (28,225 differential magnitude observations) and radial velocity curve (81 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.7831 ± 0.0094 and 1.7741 ± 0.0097 solar masses, and radii of 2.409 ± 0.018 and 2.366 ± 0.017 solar radii. The orbital period is 2.25422694(15) days and the eccentricity is 0.0473(26). A faint third component was detected in the analysis of the light curves, and also directly observed in the spectra. The observed rate of apsidal motion is consistent with theory (U = 151.4 ± 8.4 year). We determine a distance to the system of 566 ± 46 pc.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

SELF-CONSISTENT ORBITS AND PHYSICAL PROPERTIES FOR EIGHT SINGLE-LINED SPECTROSCOPIC BINARIES

For single-lined spectroscopic binaries (SB1s), self-consistent orbits can be determined via a simultaneous fit including both radial velocity data and the Hipparcos Intermediate Astrometric Data. Using the ratio λ of the semimajor axes of the photocenter to the primary orbits, the present paper develops an iterative fitting method. First, an initial orbit of an SB1 is determined with the assumption that λ equals 1. On the basis of this orbit, we use a stellar evolutionary model to distribute the total mass and luminosity to the primary and the secondary and update λ from the component mass and luminosity ratios. Then the orbit is updated using the updated value of λ, which completes a step of the iterative process. If this process is convergent, the resulting orbit is compatible with the physical properties of component stars. By using this method, the orbital solutions of eight SB1s as well as the physical properties are determined. We find that the component magnitude differences of these systems are very large, except for HIP 7143 and 45333. This suggests that only the secondaries of the two systems can be resolved with the present-day observational techniques, which is in agreement with recent observations.

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DOE OSTI2015

THE CLUSTER AGES EXPERIMENT (CASE). VII. ANALYSIS OF TWO ECLIPSING BINARIES IN THE GLOBULAR CLUSTER NGC 6362

We use photometric and spectroscopic observations of the detached eclipsing binaries V40 and V41 in the globular cluster NGC 6362 to derive masses, radii, and luminosities of the component stars. The orbital periods of these systems are 5.30 and 17.89 days, respectively. The measured masses of the primary and secondary components (M{sub p}, M{sub s}) are (0.8337 ± 0.0063, 0.7947 ± 0.0048) M{sub ⊙} for V40 and (0.8215 ± 0.0058, 0.7280 ± 0.0047) M{sub ⊙} for V41. The measured radii (R{sub p}, R{sub s}) are (1.3253 ± 0.0075, 0.997 ± 0.013) R{sub ⊙} for V40 and (1.0739 ± 0.0048, 0.7307 ± 0.0046) R{sub ⊙} for V41. Based on the derived luminosities, we find that the distance modulus of the cluster is 14.74 ± 0.04 mag—in good agreement with 14.72 mag obtained from color–magnitude diagram (CMD) fitting. We compare the absolute parameters of component stars with theoretical isochrones in mass–radius and mass–luminosity diagrams. For assumed abundances [Fe/H] = −1.07, [α/Fe] = 0.4, and Y = 0.25 we find the most probable age of V40 to be 11.7 ± 0.2 Gyr, compatible with the age of the cluster derived from CMD fitting (12.5 ± 0.5 Gyr). V41 seems to be markedly younger than V40. If independently confirmed, this result will suggest that V41 belongs to the younger of the two stellar populations recently discovered in NGC 6362. The orbits of both systems are eccentric. Given the orbital period and age of V40, its orbit should have been tidally circularized some ∼7 Gyr ago. The observed eccentricity is most likely the result of a relatively recent close stellar encounter.

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DOE OSTI2015

OPTICAL STUDIES OF 13 HARD X-RAY SELECTED CATACLYSMIC BINARIES FROM THE SWIFT-BAT SURVEY

From a set of 13 cataclysmic binaries that were discovered in the Swift Burst Alert Telescope (BAT) survey, we conducted time-resolved optical spectroscopy and/or time-series photometry of 11, with the goal of measuring their orbital periods and searching for spin periods. Seven of the objects in this study are new optical identifications. Orbital periods are found for seven targets, ranging from 81 minutes to 20.4 hr. PBC J0706.7+0327 is an AM Herculis star (polar) based on its emission-line variations and large amplitude photometric modulation on the same period. Swift J2341.0+7645 may be a polar, although the evidence here is less secure. Coherent pulsations are detected from two objects, Swift J0503.7−2819 (975 s) and Swift J0614.0+1709 (1412 s and 1530 s, spin and beat periods, respectively), indicating that they are probable intermediate polars (DQ Herculis stars). For two other stars, longer spin periods are tentatively suggested. We also present the discovery of a 2.00 hr X-ray modulation from RX J2015.6+3711, possibly a contributor to Swift J2015.9+3715, and likely a polar.

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DOE OSTI2012

AN Fe XXIV ABSORPTION LINE IN THE PERSISTENT SPECTRUM OF THE DIPPING LOW-MASS X-RAY BINARY 1A 1744-361

We report on Chandra X-ray Observatory (Chandra) High Energy Transmission Grating spectra of the dipping low-mass X-ray binary 1A 1744-361 during its 2008 July outburst. We find that its persistent emission is well modeled by a blackbody (kT {approx} 1.0 keV) plus power law ({Gamma} {approx} 1.7) with an absorption edge. In the residuals of the combined spectrum, we find a significant absorption line at 6.961 {+-} 0.002 keV, consistent with the Fe XXVI (hydrogen-like Fe) 2-1 transition. We place an upper limit on the velocity of a redshifted flow of v < 221 km s{sup -1}. We find an equivalent width for the line of 27{sup +2}{sub -3} eV, from which we determine a column density of (7 {+-} 1) Multiplication-Sign 10{sup 17} cm{sup -2} via a curve-of-growth analysis. Using XSTAR simulations, we place a lower limit on the ionization parameter of >10{sup 3.6} erg cm s{sup -1}. We discuss what implications the feature has on the system and its geometry. We also present Rossi X-ray Timing Explorer data accumulated during this latest outburst and, via an updated color-color diagram, clearly show that 1A 1744-361 is an 'atoll' source.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

MULTI-WAVELENGTH STUDY OF THE Be/X-RAY BINARY MXB 0656-072

We present and analyze the optical photometric and spectroscopic data of the Be/X-ray binary MXB 0656-072 from 2006 to 2009. A 101.2 day orbital period is found, for the first time, from the present public X-ray data (Swift/BAT and RXTE/ASM). The anti-correlation between the H{alpha} emission and the UBV brightness of MXB 0656-072 during our 2007 observations indicates that a mass ejection event took place in the system. After the mass ejection, a low-density region might develop around the Oe star. With the outward motion of the circumstellar disk, the outer part of the disk interacted with the neutron star around its periastron passage and a series of X-ray outbursts were triggered between MJD 54350 and MJD 54850. The Proportional Counter Array-HEXTE spectra during the 2007-2008 X-ray outbursts could be well fitted by a cutoff power law with low-energy absorption, together with an iron line around 6.4 keV, and a broad cyclotron resonance feature around 30 keV. The same variability of the soft and hard X-ray colors in 2.3-21 keV indicated that there were no overall changes in the spectral shape during the X-ray outbursts, which might only be connected with the changes of the mass accretion rate onto the neutron star.

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DOE OSTI2012

THE ROMER DELAY AND MASS RATIO OF THE sdB+dM BINARY 2M 1938+4603 FROM KEPLER ECLIPSE TIMINGS

The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf B star and a cool M dwarf companion in an effectively circular three-hour orbit. The light curve shows both primary and secondary eclipses, along with a strong reflection effect from the cool companion. Here, we present constraints on the component masses and eccentricity derived from the Romer delay of the secondary eclipse. Using six months of publicly available Kepler photometry obtained in short-cadence mode, we fit model profiles to the primary and secondary eclipses to measure their centroid values. We find that the secondary eclipse arrives on average 2.06 {+-} 0.12 s after the midpoint between primary eclipses. Under the assumption of a circular orbit, we calculate from this time delay a mass ratio of q = 0.2691 {+-} 0.0018 and individual masses of M{sub sd} = 0.372 {+-} 0.024 M{sub Sun} and M{sub c} = 0.1002 {+-} 0.0065 M{sub Sun} for the sdB and M dwarf, respectively. These results differ slightly from those of a previously published light-curve modeling solution; this difference, however, may be reconciled with a very small eccentricity, ecos {omega} Almost-Equal-To 0.00004. We also report a decrease in the orbital period of P-dot = (-1.23 {+-} 0.07) Multiplication-Sign 10{sup -10}.

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DOE OSTI2012

X-RAY EMISSION FROM TRANSIENT JET MODEL IN BLACK HOLE BINARIES

While the non-thermal radio through at least near-infrared emission in the hard state in X-ray binaries (XRBs) is known to originate in jets, the source of the non-thermal X-ray component is still uncertain. We introduce a new model for this emission, which takes into account the transient nature of outflows, and show that it can explain the observed properties of the X-ray spectrum. Rapid radiative cooling of the electrons naturally accounts for the break often seen below around 10 keV, and for the canonical spectral slope F{sub {nu}}{proportional_to}{nu}{sup -1/2} observed below the break. We derive the constraints set by the data for both synchrotron- and Compton-dominated models. We show that for the synchrotron-dominated case, the jet should be launched at radii comparable to the inner radius of the disk ({approx}few 100 r{sub s} for the 2000 outburst of XTE J1118+480), with typical magnetic field B {approx}> 10{sup 6} G. We discuss the consequences of our results for the possible connection between the inflow and outflow in the hard state of XRBs.

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DOE OSTI2012

TESTS OF GENERAL RELATIVITY IN THE STRONG-GRAVITY REGIME BASED ON X-RAY SPECTROPOLARIMETRIC OBSERVATIONS OF BLACK HOLES IN X-RAY BINARIES

Although general relativity (GR) has been tested extensively in the weak-gravity regime, similar tests in the strong-gravity regime are still missing. In this paper, we explore the possibility to use X-ray spectropolarimetric observations of black holes in X-ray binaries to distinguish between the Kerr metric and the phenomenological metrics introduced by Johannsen and Psaltis (which are not vacuum solutions of Einstein's equation) and thus to test the no-hair theorem of GR. To this end, we have developed a numerical code that calculates the radial brightness profiles of accretion disks and parallel transports the wave vector and polarization vector of photons through the Kerr and non-GR spacetimes. We used the code to predict the observational appearance of GR and non-GR accreting black hole systems. We find that the predicted energy spectra and energy-dependent polarization degree and polarization direction do depend strongly on the underlying spacetime. However, for large regions of the parameter space, the GR and non-GR metrics lead to very similar observational signatures, making it difficult to observationally distinguish between the two types of models.

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