Ursa Major Research Articles

The 1993 August Minioutburst of GRO J0422+32

We report on observations of the soft X-ray transient (SXT) GRO J0422+32 made with the ROSAT Position Sensitive Proportional Counter (PSPC) and the ASCA GIS and SIS X-ray imaging spectrometers during its 1993 August outburst. This event occurred approximately one year after the primary outburst of the source and was characterized by an X-ray-to-optical luminosity ratio much smaller than that typically seen in SXT outbursts or in steady, low-mass X-ray binaries. Our X-ray observations with the ROSAT PSPC, spread over 6.2 days and totalling 28.8 ks, combined with our archival analysis of 17 ks of ASCA observations, indicate an approximately 1 mcrab source that turned and subsequently back on over a 10 day period, with distinct spectral characteristics in each case. In addition to our analysis of the X-ray spectra, we report on optical photometry and spectroscopy bracketing the X-ray observations. It is noteworthy that the optical light curves remain approximately constant, at least in our data's almost daily sampling, during the turning and turning on sequence seen in the X-rays. Optical spectroscopy reveals large, asymmetric redshifted and blueshifted components in the double-peaked emission lines He II λ4686 and Hβ λ4861, which can be interpreted as evidence for a wind emanating from the secondary. The phasing of these shifts ruled out a wind originating from the disk. On the other hand, the X-ray power illuminating the star seems insufficient for driving such a wind. Comparisons are made with the primary (1992) outburst and decay phase of GRO J0422+32. Implications for X-ray reprocessing scenarios of the production of optical and UV emission and for other possible scenarios, such as advection-dominated accretion, are briefly considered. An upper limit to the quiescent X-ray luminosity is estimated using data acquired during the X-ray off state. A similarity between the X-ray-to-optical behavior of GRO J0422+32 during this minioutburst and previously documented optical-to-EUV behavior of certain SU Ursae Majoris system outbursts is noted. A physical interpretation of this analogous behavior, suggesting that the hot and cold branches of the S-shaped stability curve may be relatively closely spaced in GRO J0422+32, is offered.

TIME-SERIES ENSEMBLE PHOTOMETRY OF SX PHOENICIS STARS. II. AE URSAE MAJORIS

ABSTRACT We have examined the short period, double-mode variable star AE Ursae Majoris. Using time series ensemble photometry we have determined six new times of maximum light. We also applied a Fourier decomposition to the data to determine the component frequencies of the light curve. Using our data, along with archival data, we find that the period of AE UMa is continually decreasing at a rate of -1.14x 10-10 d d-1 . However, from the Fourier decomposition we find that the period ratio P1/P0 has remained constant at 0.773. We also find that AE UMa is incorrectly classified as a SX Phoenicis star.

Multichannel optical aperture synthesis imaging of lambda1 URSAE majoris with the Navy prototype optical interferometer.

We have used the Navy Prototype Optical Interferometer (NPOI) to obtain the first multichannel optical aperture synthesis images of a star. We observed the spectroscopic binary ~ 1 Ursae Majoris at 6 to 10 milliarcseconds separation during seven nights, using three interferometric baselines and 19 spectral channels (A.A. 520-850 nm) of the NPOI. After editing, a typical90 sec scan yielded fringe visibilities at 50 spatial frequencies and closure phases at 15 wavelengths. Three to five scans were obtained each night. The separations and position angles are in good agreement with the visual orbit obtained with the Mark III interferometer (Hummel et al. 1995, AJ, 110, 376) but show small systematic difference that can be used to improve the orbit. The closure phase data provide a sensitive measure of the magnitude difference between the components. These results demonstrate the power of broad-band interferometric observations for fast imaging and the utility of vacuum delay lines for simultaneous observations over a wide band. These observations are the first to produce simultaneous visibilities and closure phases with a separate-aperture optical interferometer, and the second to produce closure phase images, following the results from COAST reported by Baldwin et al. (1996, A&A, 306, L13). The angular resolution here is the highest ever achieved at visual wavelengths, exceeding by an order of magnitude the best thus far achieved by any single-aperture optical telescope. We generated complex visibilities and closure phases (the data types commonly used in radio interferometry) from the optical data and used standard radio interferometry techniques to produce these images. However, the fundamental observables of optical interferometry, the squared visibility amplitude and the closure phase, require the development of new analysis techniques. © 1997 American Astronomical Society. [S0004-6256(97)01709-3]

Eclipse Mapping of the Accretion Disk Wind in the Cataclysmic Variable UX Ursae Majoris

We present the results of an effort to model recent HST eclipse observations of the C IV 1550 A resonance line in the high-inclination nova-like cataclysmic variable UX UMa. Assuming this line to be predominantly wind-formed, we are able to roughly reproduce the shapes and strengths of the observed line profiles (both away from and during eclipse) within the framework of a simple kinematic model in which the outflow is described as a rotating, biconical accretion disk wind. Our preferred model also matches most of the detailed behavior of different parts of the C IV line profile (blue wing, line center, and red wing) as a function of orbital phase. The most important result of our modeling is that it strongly suggests the presence of a high column (NH ~ 1023 cm-2), relatively dense (ne 4 × 1012 cm-3), and only slowly outflowing (vpoloidal vescape) transition region between the disk photosphere and the fast-moving wind. We also find that the outflow from UX UMa is probably only moderately collimated (the outer opening angle of our preferred model is θmax 65°). Finally, the rotational disturbance seen in the data is fitted reasonably well by our model, in which the rotational component of motion in the wind is fixed by conserving the specific angular momentum of the outflowing material. The implications of these results for dynamical models of disk-driven winds are discussed.

Habitable moons around extrasolar giant planets.

Possible planetary objects have now been discovered orbiting nine different main-sequence stars. These companion objects (some of which might actually be brown dwarfs) all have a mass at least half that of Jupiter, and are therefore unlikely to be hospitable to Earth-like life: jovian planets and brown dwarfs support neither a solid nor a liquid surface near which organisms might dwell. Here we argue that rocky moons orbiting these companions could be habitable if the planet-moon system orbits the parent star within the so-called 'habitable zone', where life-supporting liquid water could be present. The companions to the stars 16 Cygni B and 47 Ursae Majoris might satisfy this criterion. Such a moon would, however, need to be large enough (>0.12 Earth masses) to retain a substantial and long-lived atmosphere, and would also need to possess a strong magnetic field in order to prevent its atmosphere from being sputtered away by the constant bombardment of energetic ions from the planet's magnetosphere.

A Search for Artificial Signals from the Newly Discovered Planetarty Systems

AbstractWe conducted a search for narrowband artificial signals from the regions of stars around which planetary companions have been recently found: 51 Pegasi, Gliese 229, 70 Virginis and 47 Ursae Majoris. We used the large Nançay decimetric telescope, with a frequency resolution of 50 Hz, and we scanned over 0.64 MHz and 2.24 MHz respectively around the hydrogen and hydroxyl lines.

Uncovering Flickering in Time-Resolved Spectroscopy for the Nova-like Variable UX Ursa Majoris

AbstractThe flickering phenomenon in cataclysmic variables (CVs) is manifest photometrically as variations in system brightness with amplitudes up to about 1 mag and on timescales from seconds to tens of minutes. Although a pronounced characteristic of CVs, flickering has been studied, in general, only tangentially and in the context of overall CV photometric properties. It is usually uncovered in CV photometry, yet my Doppler tomographic analysis of data collected on the KPNO 2.1-meter telescope in 1982 by Schlegel, Honeycutt, and Kaitchuck (1983) for the nova-like variable UX Ursa Majoris suggests that flickering also exists in this system’s spectroscopy.Using the integrated continuum flux from the UX UMa observations and Bruch’s (1992) methodology for classifying high- and low-flicker data, I constructed two data subsets corresponding to high- and low-flicker states. I generated Doppler tomograms of these high- and low-flicker states and interpret differences between the tomograms as spectroscopic signatures of flickering in the system.In UX UMa’s Hβ Doppler tomograms, a small, faint, incomplete ring of emission is visible for both flickering states. Dominating ring emission is strong emission in the (+Vx,+Vy) quadrant. The usual location for Swave emission, in the (−Vx,+Vy) quadrant, is here the region of faintest emission. Differenced Doppler tomograms, produced by subtracting from the tomograms the symmetric ring-emission component, show clear differences between the high- and low-flicker states. Further, these early results suggest Doppler tomography may be a useful technique for studying the secondary stars in CVs imaged in this manner. Enhanced chromospheric activity of the red dwarf companion is clearly visible in the high-flickering state tomogram at (0, Krd) and may, therefore, afford investigators the opportunity to estimate the chromospheric flux and radial velocity of the secondary star.

Stars resembling the Sun

This review is primarily directed to the question whether photometric solar analogues remain such when subjected to detailed spectroscopic analyses and interpreted with the help of internal stucture models. In other words, whether the physical parameters: mass, chemical composition, age (determining effective temperature and luminosity), chromospheric activity, equatorial rotation, lithium abundance, velocity fields etc., we derive from the spectral analysis of a photometric solar analogue, are really close to those of the Sun. We start from 109 photometric solar analogues extracted from different authors. The stars selected had to satisfy three conditions: i) their colour index $(B-V)$ must be contained in the interval: $\Delta (B-V) = 0.59$ –0.69, ii) they must possess a trigonometric parallax, iii) they must have undergone a high resolution detailed spectroscopic analysis. First, this review presents photometric and spectrophotometric researches on solar analogues and recalls the pionneering work on these stars by the late Johannes Hardorp. After a brief discussion on low and high resolution spectroscopic researches, a comparison is made between effective temperatures as obtained, directly, from detailed spectral analyses and those obtained, indirectly, from different photometric relations. An interesting point in this review is the discussion on the tantalilizing value of the $(B-V)_\odot$ of the Sun, and the presentation of a new reliable value of this index. A short restatement of the kinematic properties of the sample of solar analogues is also made. And, finally, the observational $(\log T_{\rm eff}, M_{\rm bol})$ diagram, obtained with 99 of the initially presented 109 analogues, is compared to a theoretical $(\log T_{\rm eff}, M_{\rm bol})$ diagram. This latter has been constructed with a grid of internal structure models for which, (very important for this investigation), the Sun was used as gauge. In analysing the position, with respect to the Sun, of each star we hoped to find a certain number of stars tightly neighbouring the Sun in mass, chemical composition and state of evolution. The surprising result is that the stars occupy in this HR Diagram a rather extended region around the Sun, many of them seem more evolved and older than the Sun, and only 4 of the evolved stars seem younger. The age of some stars in the sample is also discussed in terms of chromospheric activity and Li-content. Our conclusion is much the same as that contained in previous papers we have written on the subject: in spite of a much larger number of stars, we have not been able to nominate a single star of the sample for a “perfect good solar twin”. Another aim in beginning, 25 years ago, this search for solar analogues, was to have ready a bunch of stars resembling the Sun and analysed spectroscopically in detail, in order that, when planets hunters of solar type stars, finally would have found such a specimen, we would have been able to immediately compare the physical parameters of this star to those of the Sun. We have been lucky enough: one of the good solar analogues we present herewith, is 51 Pegasi (HD 217014) which, according to the very recent observations by Mayor and Queloz (1995), has a planet orbiting around it. And what is more: two other stars possessing planets: 47 Ursae Majoris (HD 95128) and 70 Virginis (HD 117176), have just been discovered by Marcy and Butler (187 $^{\rm th}$ Meeting of the AAS, January 1996). One of them, 47 Ursae Majoris, is also included in the list of photometric solar analogues. The other star, 70 Virginis, has only been included after the “Planets News”, because the colour index $(B-V)$ of this star is slightly higher than the prescribted limit of the selection, ( $B-V = 0.71$ , instead, 0.69). It would have been a pity to leave the third ” planet star out of the competition.

BL Eridani: An unstable W Ursae Majoris system with spotted components

New complete BV light curves of BL Eri are presented. Light-curve variability and asymmetry are seen in both B and V bands, and the observed times of light minimum indicate period changes. The light curves have been analyzed by using the light-curve-synthesis method. Our photometric solution reveals that BL Eri is a contact binary with a common convective envelope. An examination of the available photometric and spectroscopic data indicates that the light-curve variability may be due to changes of the component radii and the light-curve asymmetry may be consistent with starspot activity on one or both components.

More neighbors

Just 3 months after the discovery of a planet around the star 51 Pegasus, Geoffrey Marcy and Paul Butler of San Francisco State University and UC Berkeley announced that they have found two Jupiter‐sized planets orbiting stars just 35 light years from Earth. Studying the stars 70 Virginis (in the constellation Virgo) and 47 Ursae Majoris (in the Big Dipper and Ursa Major), Marcy and Butler detected a tell‐tale wobble in the motion of each star. Essentially, the researchers observed slight modulations in the light coming from the star, which are attributed to the gravitational tugs between planets and stars.The planet around 70 Virginis is believed to have a mass nine times that of Jupiter, an orbital period of 116 days at 0.43 AU from the star, and a temperature of roughly 85°C.

SUPERHUMPS IN CATACLYSMIC BINARIES. VII. CY URSAE MAJORIS

ABSTRACT We report photometry of the dwarf nova CY Ursae Majoris during its 1995 superoutburst. A large-amplitude "superhump" at P = 0.07210 ± 0.00003 d was observed; the period decreased with P = -6 x 10-5 over the 12 days of observation. The properties of the superhump appeared normal for SU UMa stars. But the frequencies of high harmonics were slightly blue-shifted from exact integer multiples of the fundamental, an effect which is unexplained but may require invoking differential precession of the accretion disk.

The Stroboscopic Method Applied to the Stellar Three-Body Problem: The Keplerian Outer Orbit Approximation

view Abstract Citations (4) References (3) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Stroboscopic Method Applied to the Stellar Three-Body Problem: The Keplerian Outer Orbit Approximation Ling, J. F. ; Docobo, J. A. ; Abad, A. J. Abstract This article discusses the stellar three-body problem using an approximation in which the outer orbit is assumed to be Keplerian. The equations of motion are integrated by the stroboscopic method, i.e., basically at successive periods of a rapidly changing variable (the eccentric anomaly of the inner orbit). The theory is applied to the triple-star system ξ Ursae Majoris. Publication: The Astronomical Journal Pub Date: August 1995 DOI: 10.1086/117570 Bibcode: 1995AJ....110..875L Keywords: CELESTIAL MECHANICS full text sources ADS |

Orbits of Small Angular Scale Binaries Resolved with the Mark III Interferometer

view Abstract Citations (78) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Orbits of Small Angular Scale Binaries Resolved with the Mark III Interferometer Hummel, C. A. ; Armstrong, J. T. ; Buscher, D. F. ; Mozurkewich, D. ; Quirrenbach, A. ; Vivekanand, M. Abstract We present relative orbits of eight spectroscopic binaries with semimajor axes ranging from 3 milliarcsec (mas) to 10 mas. The stars, π Andromedae, θ Aquilae, β Aurigae, ζ1 Ursae Majoris, 93 Leonis, 113 Herculis, β Trianguli, and δ Trianguli, represent some of the smallest angular scale binaries resolved with the Mark III optical interferometer on Mount Wilson, California. In addition to the orbital elements, we measured the magnitude difference between the components at λλ8OO, 550, 500, and 450 nm. Spectroscopic orbital elements for both primary and secondary components are available for all stars except 113 Herculis. The available data allow the determination of the distance to four of the binaries, as well as of their component masses and luminosities. The results are compared with stellar evolution models. Publication: The Astronomical Journal Pub Date: July 1995 DOI: 10.1086/117528 Bibcode: 1995AJ....110..376H Keywords: BINARIES: SPECTROSCOPIC; INSTRUMENTATION: INTERFEROMETERS full text sources ADS | data products SIMBAD (9)

Hubble Space Telescope and R-Band Eclipse Maps of the UX Ursae Majoris Accretion Disk

view Abstract Citations (66) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hubble Space Telescope and R-Band Eclipse Maps of the UX Ursae Majoris Accretion Disk Baptista, R. ; Horne, Keith ; Hilditch, R. W. ; Mason, K. O. ; Drew, J. E. Abstract Hubble Space Telescope time-resolved spectroscopic and ground-based R-band photometric data of UX UMa during eclipse are presented and discussed. The spectroscopy covers the C IV λ1550 and He II λ1640 spectral regions. The eclipses in the UV continuum are deep, nearly reaching the zero level at mid-eclipse phases. Sharp ingress and egress features reveal the occultation of the white dwarf at disk center but there is no evidence of the orbital hump or of the bright spot. The steep ultraviolet eclipse light curves are used to estimate the radius of the white dwarf and to constrain the binary parameters. We find M1 = M2 = 0.47 Msun and i = 71°.0±0°.6. The white dwarf contributes with ≃25% of the light at λ1600 Å. If the inner disk is optically thick it has a temperature of Twd ≳ 65,000 K. Velocity-resolved light curves in the C IV λ1550 line show evidence of rotational disturbance and a strong orbital modulation is seen in the line center light curve. Maximum-entropy eclipse mapping techniques are used to solve for a map of the disk brightness distribution and for fluxes of an additional uneclipsed component in 18 narrow UV bands and in the R band. The angular scale of the disk and the distance to UX UMa are estimated from a color-magnitude diagram by a method similar to cluster main-sequence fitting. We find D = 345±34 pc. The radial temperature profiles derived from the UV continuum maps range from 8000 K in the outer disk regions to 30,000 K in the inner disk and reasonably follow the T ∝ R-¾ law for steady mass accretion at a rate of M = 10-8.0±0.2 Msun yr-1. The comparison of R-band eclipse maps from observations 2 months apart indicates changes in the structure of the outer disk which are probably due to small changes (≲20%) in the mass transfer rate from the secondary star. The maps in the C IV and He II line profiles are affected by emission from the disk wind. The radial temperature profiles of both line center maps show a flat slope. It is suggested that at low velocities the eclipsed part of the line emission arises from an opaque and extended region with a rather uniform spatial intensity distribution as projected in the plane of the sky. When plotted as a sequence of spatially resolved spectra these lines appear in absorption at disk center and change to emission in the outer disk regions besides showing large uneclipsed components. This behavior is similar to that found by Rutten et al. for the Balmer lines and suggests that these optical lines may also have a wind component. We obtain a revised ephemeris for the times of minimum and an upper limit for secular period changes of |Pdot| < 1.3 × 10-12 s s-1. The mass transfer rate inferred from this limit is an order of magnitude smaller than the value derived from the eclipse mapping, suggesting that the high mass transfer rate of UX UMa is not the consequence of its secular period decrease. Publication: The Astrophysical Journal Pub Date: July 1995 DOI: 10.1086/175970 Bibcode: 1995ApJ...448..395B Keywords: STARS: BINARIES: ECLIPSING; STARS: INDIVIDUAL CONSTELLATION NAME: UX URSAE MAJORIS; STARS: NOVAE; CATACLYSMIC VARIABLES; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (3) MAST (1) ESA (1)

The minimum mass ratio of W Ursae Majoris binaries

The minimum mass ratio for tidal stability of a contact binary containing two unevolved main-sequence stars is calculated to be $\qmin\simeq0.09$ in the case of a mostly radiative primary, and is higher if an appreciable fraction of the mass lies in a convective envelope. At least one observed system, AW UMa, has a mass ratio just below this value ($q=0.075$), implying, if the system is stable, that the primary must be slightly evolved and must have a very shallow convective envelope. Contact binaries with mass ratios significantly below that of AW UMa should not be observed, since they are tidally unstable and quickly merge into a single, rapidly rotating object, on a timescale $\sim10^3$--$10^4\,$yr.

Be Ursae Majoris: Precataclysmic binary system and planetary nucleus

view Abstract Citations (33) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS BE Ursae Majoris: Precataclysmic Binary System and Planetary Nucleus Liebert, James ; Tweedy, R. W. ; Napiwotzki, R. ; Fulbright, M. S. Abstract This paper presents new spectrophotometric observations and a new analysis of the hot and cool components of the evolved binary system BE Ursae Majoris, and we report the discovery of a planetary nebula around it. The primary star can be classified as a subdwarf O or borderline DAO white dwarf with Teff = 105,000 K +/- 11,000 K, log g = 6.5 +/- 0.25, based on Non Local Thermodynamic Equilibrium (NLTE) model atmosphere profile fits to the H and He II lines. Observations of the secondary during eclipse indicate a spectral type of K5. Its estimated brightness during eclipse is consistent with a main-sequence star of K5 at the distance of 1.9 kpc derived from analysis of the primary star. The nebula is roughly circular with a diameter of 3 min. This corresponds to a physical diameter of 1.5 pc at the estimated distance. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175366 Bibcode: 1995ApJ...441..424L Keywords: Cataclysmic Variables; Eclipsing Binary Stars; K Stars; Planetary Nebulae; White Dwarf Stars; Atmospheric Models; Local Thermodynamic Equilibrium; Stellar Models; Stellar Spectrophotometry; Astronomy full text sources ADS | data products SIMBAD (1)

ANALYSIS OF CCD PHOTOMETRY FOR THE VERY SHORT PERIOD ECLIPSING BINARY BM URSAE MAJORIS

ABSTRACT CCD images of the fourteenth magnitude variable BM Ursae Majoris were taken in the spring of 1991. The observations were taken at Lowell Observatory. An RCA CCD camera system and a standard PMT were used. Four times of minimum light were determined and improved linear and quadratic ephemerides were calculated. A period study, spanning over a thirty year interval, shows that the system is undergoing a small but continuous period decrease of ~5 X 10-8 d/yr. This may be due to angular momentum loss (AML) caused by stellar winds. The V, R, I light curves formed from the present precision observations, show that BM UMa is a W-type W UMa system. The first synthetic light curve solution of BM UMa is also presented. This solution reveals that BM UMa is a contact binary consisting of two early K spectral type components with a fill out of ~20% and a mass ratio of ~0.5. A subtantial temperature difference of ~400 K was determined. Both unspotted and spotted models were calculated. The spotted model indicates the presence of a region of enhanced birghtness in the neck of the secondary component. This may be attributed to fluid dynamics of mass in transit rather than to magnetic activity.

Binary star orbits from speckle interferometry. 7: The multiple system XI Ursae Majoris

view Abstract Citations (58) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Binary Star Orbits From Speckle Interferometry. VII. The Multiple System XI Ursae Majoris Mason, Brian D. ; McAlister, Harold A. ; Hartkopf, William I. ; Shara, M. M. Abstract Xi Ursae Majoris (HR 4374/5) consists of a visual binary having a period of nearly 60 yr, the primary component of which is a 669 day astrometric and spectroscopic subsystem, and the secondary is a 4 day spectroscopic binary. We report here improved elements for the long-period visual system (AB) and the short-period astrometric system (Aa). We also report the first direct detection of a fifth component to the multiple system (Bc) from speckle observations obtained in 1988 at the Canada-France-Hawaii Telescope. Publication: The Astronomical Journal Pub Date: January 1995 DOI: 10.1086/117277 Bibcode: 1995AJ....109..332M Keywords: Binary Stars; Orbital Elements; Speckle Interferometry; Astronomical Spectroscopy; Stellar Systems; Astronomy; STARS: INDIVIDUAL: XI URSAE MAJORIS; BINARIES: VISUAL full text sources ADS | data products SIMBAD (3) Related Materials (11) Part 1: 1988AJ.....96.1431M Part 2: 1992AJ....104.1961M Part 3: 1993AJ....106.2072G Part 4: 1995AJ....110..366M Part 6: 1996AJ....111..370H Part 7: 1996AJ....112..276M Part 8: 1997AJ....114.1607M Part 9: 1997AJ....114..808M Part 10: 1999ASPC..174...41M Part 11: 1999AJ....117.1023M Part 12: 2002AJ....123.1023S

SPOT and chromospheric activity on the RS CVN star DM Ursae Majoris

SPOT and chromospheric activity on the RS CVN star DM Ursae Majoris

Nightly variations of nonradial oscillations in the Delta Scuti star upsilon Ursae Majoris

Nightly variations of nonradial oscillations in the Delta Scuti star upsilon Ursae Majoris