UX Ari Research Articles

The position of the radio/optical emission from the stars HR 1099 and UX Ari

view Abstract Citations (25) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The position of the radio/optical emission from the stars HR 1099 and UX Ari. Johnston, K. J. ; Wade, C. M. ; Florkowski, D. R. ; de Vegt, C. Abstract The radio and optical positions of the stars HR 1099 and UX Ari have been measured at nearby epochs. The radio positions are referred to background quasars, and the optical positions are on the FK4 system. The radio and optical coordinates agree within the 0arcsec.05 accuracy of the optical measurements, except for a discrepancy of 0arcsec.27±0arcsec.06 in the right ascension of HR 1099. The latter may result from the combined effects of local deviations in the two reference frames, atmospheric effects, or differences in source structure at radio and optical wavelengths. The radio and optical measurements of the proper motions agree well. Publication: The Astronomical Journal Pub Date: July 1985 DOI: 10.1086/113840 Bibcode: 1985AJ.....90.1343J Keywords: Astrometry; Binary Stars; Radio Stars; Star Distribution; Optical Emission Spectroscopy; Position (Location); Quasars; Astronomy full text sources ADS | data products SIMBAD (2)

Dual polarization VLBI observations of stellar binary systems at 5 GHz

The binary systems Sigma CrB, SZ Psc, HR 1099, UX Ari, HR 5110, Algol, and Cyg X-1 are characterized in terms of marcsec-scale radio structure on the basis of dual-polarization observations at 4.969-4.997 GHz, obtained with an international VLBI array comprising the 100-m Effelsberg, 36-m Haystack, 42-m Green Bank, 26-m Fort Davis, 130-m-equivalent VLA, and 40-m Owens Valley telescopes (system temperatures 40-70 K) at 22-14 h UT on July 26-27, 1983. The data are presented in graphs and tables and discussed in detail. Single Gaussian brightness distributions with theta(FWHM) = 0.5-2.0 marcsec and brightness temperatures (2-200) x 10 to the 8th K are determined for four sources; core-halo structures are found for UX Ari and Algol; and an upper limit of 50 microarcsec is established for the angular separation of the regions of left and right circular polarization. The gross features seen in RS CVn systems are explained in terms of a simple expanding-coronal-loop model of flare events.

Starspot areas and temperatures in nine binary systems with late-type components

view Abstract Citations (151) References (69) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Starspot areas and temperatures in nine binary systems with late-type components Poe, C. H. ; Eaton, J. A. Abstract A computer program that generates light curves for rotating spotted stars has been used to solve multicolor light curves of BY Dra, II Peg, HK Lac, HR 7275, IM Peg, λ And, UX Ari, σ Gem, and LX Per. The flux ratio of spot to photosphere in the photometric bands was determined from a revision of the Barnes-Evans relations. One or two circular spots could accurately reproduce the photometric behavior for most of these systems. The wavelength dependence of limb darkening was found to contribute a surprisingly large amount of the variation in the visible colors. The changes in the spot activity on II Peg were followed from 1976 through 1982. Definite spot temperatures were derived for most of the systems. The temperature of the spots ranges from 4050 to 3330K, while the temperature of the unspotted photospheres of the stars varied by only about 400K. The data suggest that the spots consist primarily of material at a single temperature, and that they are not divided into roughly equal amounts of umbral and penumbral material. Publication: The Astrophysical Journal Pub Date: February 1985 DOI: 10.1086/162928 Bibcode: 1985ApJ...289..644P Keywords: Binary Stars; Late Stars; Starspots; Variable Stars; Computational Astrophysics; Light Curve; Spectrum Analysis; Stellar Models; Astrophysics full text sources ADS |

A solar spectral line list between 10 and 200 A modified for application to high spectral resolution X-ray astronomy

A spectral line list for the 10-200 A range is developed from existing solar spectra for application to high spectral resolution measurements of astrophysical plasmas. The solar spectral line lists are merged into a single comprehensive list. The effect of the solar emission measure distribution is removed from the line intensities, which results in a set of emission rates for the lines that can be applied to many optically thin, low density high temperature plasmas in ionization equilibrium. In addition to the measured solar lines, 250 theoretical lines are added to this list. These lines fall in wavelength regions where the existing solar lists have few lines because of limitations in instrumental sensitivity. Also, some lines have been added because the sun has very little plasma at temperatures of about one million K, and consequently these lines are weak or absent in solar spectra. The entire list contains about 600 lines. Finally, predicted spectra of the two RS CVn stars, alpha Aur (Capella) and UX Ari, are presented at 1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at 1 A resolution, and the emission rate spectrum (spectrum not modified by an emission measure distribution) is shown at very high spectral resolution. The predicted spectra for Capella and UX Ari are based on results obtained from the Einstein and International Ultraviolet Explorer (IUE) spacecraft.

The magnetic fields of the late-type stars

view Abstract Citations (79) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The magnetic fields of the late-type stars. Borra, E. F. ; Edwards, G. ; Mayor, M. Abstract A powerful stellar magnetometer capable of measuring longitudinal magnetic fields as small as a few gauss has been assembled. Observations of known magnetic stars show that the instrument yields the expected values. A detailed study of the formal errors shows that they are realistic, although it cannot be excluded that the most precise measurements may have errors that are twice as large as those claimed. A large number of late-type stars have been observed, and mostly nulls or detections that are suspect have been obtained. However, definite detections for the Ca II emission dwarf Xi Boo A and probable detections in the RS CVn star UX Ari have been found. Observations of the transverse Zeeman effect do not show evidence of strong transverse fields, but the uncertainties are large (a few hundred gauss). An approximate estimate of the magnetic geometries of active dwarfs is made concluding that the most likely geometry is complex and composed of several hundred patches of opposite polarities. Publication: The Astrophysical Journal Pub Date: September 1984 DOI: 10.1086/162400 Bibcode: 1984ApJ...284..211B Keywords: Dwarf Stars; Late Stars; Magnetic Stars; Stellar Magnetic Fields; Error Analysis; Instrument Errors; Magnetic Field Configurations; Magnetometers; Polarimetry; Stellar Activity; Zeeman Effect; Astrophysics full text sources ADS | data products SIMBAD (3)

Spot activity in the RS CVn binary UX arietis

Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation.

IUE observation of RS CVn-like binary Corona Borealis

High and low resolution IUE observations of the triple system σ CrB are presented. The spectra show the presence of chromospheric (O I, Si II, Mg II) and transition region lines (He II, C II, C IV) in emission. The surface fluxes of these lines are orders of magnitude higher than those observed in the Sun but are comparable to their values in RS CVn binaries like UX Ari. A comparison of continuum and emission line fluxes through the small and large apertures suggests that the observed continuum and chromospheric and transition region lines are from the primary star HD 146361 which is a spectroscopic binary; the secondary, HD 146362 which is 5.3 arcsec away from the primary may be contributing a small fraction to the O I emission only. This confirms that HD 146361 is indeed an RS CVn binary and the source of X-rays from the triple system. The profiles of the h and k lines of Mg II suggest almost equal contribution from the two components of the spectroscopic binary HD 146361. This hypothesis is supported by the profiles of absorption lines. Interstellar Fe II absorptions give a value of 0.05 cm−3 for the mean interstellar hydrogen density towards σ CrB. A hydrostatic model for the chromosphere, transition region and corona of HD 146361 has been developed and its implications have been discussed.

VLBI observations of the RS Canum Venaticorum binary systems UX ARIETIS and HR 1099 at 1.65 GHz

VLBI observations of the RS CVn binaries UX Arietis and HR 1099 have been made at 1.65 GHz using a three-element array with a minimum fringe spacing of 11.5 milli-arcsec. Both sources were found to be unresolved within measurement uncertainties. In both cases, the derived upper limit to the source size was comparable to the overall size of each binary system. The lower limits to the brightness temperature were 1.4 x 10 to the 10th K for UX Arietis and 2.9 x 10 to the 10th K for HR 1099. Simultaneous polarization measurements at the VLA showed 4-8 percent circular polarization and less than 2 percent linear polarization. It is found that the data are consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field B less than or approximately equal to 6 gauss.

VLBI Observations of Stellar Binary Systems

Since 1982 July we have been engaged in a systematic investigation of the milliarcsecond structure of the radio emission from several binary star systems, mainly in the RS CVn class (Hall, 1976). The first few observations utilized the MkII VLBI recording scheme, but no useful data were obtainable because of the relatively low flux levels involved Beginning in 1982 December, we have been using the MkIII system with large telescopes and have successfully detected seven binary systems (UX Arietis, HR 1099, Algol, II Peg, σ Crb, and the distant system LSI 61°303). A summary of the three experiments already completed is given in Table 1.

Infrared observations of RS CVn stars

The paper presents infrared photometry of the RS CVn binary stars AR Lac (1.2-10 microns) and MM Her (1.2-3.5 microns) as they egressed from their primary and secondary eclipses; of the eclipsing systems RS CVn and Z Her at maximum light (1.2-10 microns) and of the non-eclipsing systems UX Ari and HR 1099 (1.2-10 microns). An analysis of these and published V data based on flux ratio diagrams (linear analogues of color-color diagrams) shows that G and K stars supply the infrared light of these systems. In AR Lac, the combined light of a G5-K0 subgiant and either a late F dwarf or an early F subgiant can account for the observed visual and infrared light curves. None of these systems shows infrared emission from circumstellar matter. This result is simply understood: dust grains would not be expected to form in the physical conditions surrounding the subgiant, and the corona and chromosphere (whose properties have been deduced from spectroscopic X-ray observations) should not produce appreciable infrared emission.

Near infrared photometry of some RS CVn systems and candidates

Infrared observations in the J, H, and K bands were made on eleven RS CVn systems. Infrared (IR) excess ≳0.3 mag in the J, H, and K bands was observed from the three systems UX Ari, HR 1099 and σ CrB. Similar observations were also made on the RS CVn candidates HD 26354, 39937, 42449, 51268, and 86005.

H ALF PHOTOMETRY OF UX ARI DURING 1979-80.

ABSTRACT The 6.438 d RS CVn-type binary UX Ari was photoelectrically observed on 17 nights from October 1979 to February 1980. Using narrow- and intermediate-band interference filters centered near tne Balmer H-alpha line, the alpha index was formed from data yielding the net H-alpha line strength. The light curve formed from 6585 wavelength intermediate-band data was observed with an amplitude of 0.04 m, and minimum light occurring near the 0.87 phase. The value of the alpha index indicates H-alpha emission at all orbital phases and a study of all available photometry of the system reveals significant changes in the light amplitude, mean light level, and the phase at which minimum light occurs. It is concluded that small light amplitudes are due to star spots located at high stellar latitudes or spread evenly over the stellar surface, and large amplitudes are the result of spots located closer to the equator.

IUE ultraviolet spectra and chromospheric models of HR 1099 and UX ARIETIS

IUE spectra in the region 1150-3200 A of the RS CVn-type variables HR 1099 and UX Arietis are presented and analyzed in terms of chromospheric models. Measurements of Mg h and k lines and Ca II H-K and H alpha spectra are indicated which are found not to be correlated with orbital phase or radio flares and which suggest that the strong emission arises in the K star rather than the G star in these systems. Under the assumption that the UV emission lines are associated with the K star, surface gravities of log g = 3.6 and 3.4 and effective temperatures of 4850 and 5000 K are adopted for HR 1099 and UX Ari, respectively, along with solar metal abundances for each. Model calculations of the chromospheric structure necessary to account for observed C(+), Mg(+), Si(+) and Si(+2) line fluxes are presented which indicate that the transition region pressure lies in the range 0.18-1.0 dynes/sq cm, implying transition regions that are more extended than that of the sun and are not conductively heated. It is noted that pressure scaling laws and the use of Mg II and C II lines as pressure diagnostics may be invalid, possibly due to atmospheric inhomogeneities or gas flows.

IUE spectra of a flare in the RS Canum Venaticorum-type system UX ARIETIS

IUE spectra of UX Ari obtained during the large flare of 1979 January 1 exhibit chromospheric and transition-region emission-line fluxes about 2.5 and 5.5 times brighter than quiescent fluxes, respectively, and up to 1400 times brighter than the quiet sun. A high-dispersion spectrum of the 2000-3000 A region exhibits enhanced Fe II emission, which is probably associated mainly with the K0 IV star, and enhanced Mg II emission with asymmetric wings extending to +475 km/s. These line wings are interpreted as evidence for mass flow from the K0 IV star to the G5 V star. A speculative scenario of major long-lived RS CVn flares is proposed in which the component stars have very large corotating flux tubes, which occasionally interact. Magnetic reconnection results in flux tubes that temporarily connect the two stars.

Radio Flare Activity of RS CVn Stars

For several years, a systematic program to observe RS CVn and similar binaries has been undertaken with the 46-m telescope of the Algonquin Radio Observatory. A number of large radio outbursts at 2.8 cm wavelength has been found from HR 1099, AR Lac, SZ Psc, UX Ari, and HR 5110. In several cases, simultaneous, or nearly simultaneous, observations of these stars were made by cooperating observers at (other) radio, optical, UV, and X-ray wavelengths. It is now clearly established that the mechanism responsible for the cm-wavelength radio emission is nonthermal gyrosynchrotron radiation in a volume whose characteristic dimension is comparable with the binary star separation. More generally, a semi-quantitative model for the radio flare activity of these stars seems to be possible using greatly scaled-up analogues of solar magnetic activity.

Radio Aspects of Stellar Activity in Close Binaries

Excluding single stars, star systems with very strong X-ray sources, thermally radiating winds and circumstellar envelopes, marginal detections, and binary systems that are far from “normal”, there are about 21 close binary systems that show clear signs of stellar activity in the form of variable radio emission. Sixteen of these are RS CVn binaries. Typical events are smoothly varying with time scales of from a few hours to a few days. In the RS CVn binaries UX Ari and V711 Tau variable circular polarization is sometimes observed, with occasional appearence of components with only one frequency and one circular polarization, part of which shows “oscillations” with “periods” of about 4 minutes. Different stars and different events typically have inferred electron energies of about 5 MeV and inferred magnetic fields of 1 - 30 Gauss. The radiation mechanisms are usually assumed to be synchrotron or gyro-synchrotron; however, radiation from plasma processes cannot be ruled out in some cases, and it will be very important to establish or rule out this possibility. Most radio binary events show clear signs of self-absorption, so the variations appear most strongly at the higher frequencies. Typical rise times of events are about 30% of decay times. Maximum radio luminosities range from 1013 to a few times 1017 ergs s-1 Hz-1. Most radio flares are mainly at cm-wavelenghts and have observable and inferred energies 104 - 106 times those for the largest solar events, a scaling which is similar to that for X-ray emission measures of these stars when compared to solar coronal loop emission measures. Most importantly, VLBI measurements of Algol indicate that the sizes of the radio emitting regions for very strong events are of the order of 2 - 3 stellar radii. Single stars appear to be active at radio wavelengths much less commonly than close binary systems. In many cases this may be due to the way dynamo action and convection near the surface are affected by increased rotation forced by the synchronization induced by the binary system.

Hydrogen and CA II emission during the February 1978 radio outburst of HR 1099

view Abstract Citations (22) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hydrogen and Ca II emission during the February 1978 radio outburst of HR 1099. Popper, D. M. Abstract The intensities of emission lines Ha, He, and H and K of Ca II in the spectrum of HR 1099 are evaluated at one time during the radio outburst of February 1978. The energy in Ha at this time was roughly a factor of 2 greater than at times before the outburst, while the ratio for He was a very uncertain factor of 10 greater than at a single epoch a year earlier. The increase in Ca ii emission was 40%. On the basis of limited data for HR 1099 and UX Ari, the Ca ii emission (at least) does not appear confined to a heavily spotted hemisphere, called upon to explain some phenomena in these and other systems. Publication: The Astronomical Journal Pub Date: December 1978 DOI: 10.1086/112356 Bibcode: 1978AJ.....83.1522P Keywords: Binary Stars; Calcium; H Lines; K Lines; Radio Bursts; Radio Stars; Stellar Spectra; H Alpha Line; Radiant Flux Density; Astrophysics; Emission Lines:RS CVn Binaries; H Alpha:RS CVn Binaries full text sources ADS | data products SIMBAD (2)

Survey of H-alpha emission in V711 Tau /HR 1099/ and related CA II emission binaries

view Abstract Citations (88) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Survey of Halpha emission in V711 Tau (HR 1099) and related Ca II emission binaries. Bopp, B. W. ; Talcott, J. C. Abstract We report the results of a survey of V7 11 Tau (HR 1099), UX Ari, and 26 other RS CVn and Ca II emission binaries for Ha emission. A total of six stars show Ha continuously or sporadically in emission while the remainder show pure absorption profiles at 1-A resolution. Observations of UX Ari during 19761977 indicate that the equivalent width (EW) of the emission is correlated with the orbital phase with maximum strength occurring near = O .6. At this same epoch, Hall found the phase of photometric minimum to be O .8 in late 1976 moving to 0 .7 in early 1977. Another RS CVn binary, V71 1 Tau, has been observed for three years and intensively during two major radio flares. Though Ha is enhanced by a factor of two to three during radio outbursts, the EW in HR 1099 is not correlated with orbital phase and no long-term variations are apparent. Four stars show sporadic emission: HD 86590, HK Lac, AR Lac, and SZ Psc. Publication: The Astronomical Journal Pub Date: December 1978 DOI: 10.1086/112355 Bibcode: 1978AJ.....83.1517B Keywords: Binary Stars; Calcium; Emission Spectra; H Alpha Line; K Lines; Radio Stars; Stellar Spectra; Line Spectra; Stellar Spectrophotometry; Astrophysics; Emission Lines:RS CVn Binaries; H Alpha:RS CVn Binaries full text sources ADS | data products SIMBAD (29)

Two-frequency radio polarimetry of UX ARIETIS and HR 1099

Two-frequency radio polarimetry of UX ARIETIS and HR 1099

Coordinated ultraviolet, optical, and radio observations of HR 1099 and UX ARIETIS

view Abstract Citations (62) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Coordinated ultraviolet, optical, and radio observations of HR 1099 and UX Arietis. Weiler, E. J. ; Owen, F. N. ; Bopp, B. W. ; Schmitz, M. ; Hall, D. S. ; Fraquelli, D. A. ; Piirola, V. ; Ryle, M. ; Gibson, D. M. Abstract Simultaneous radio, visual, and ultraviolet observations of the RS Canum Venaticorum binaries UX Arietis and HR 1099 are reported. The joint program covered the interval 1976 September 22 through October 3. The observations consisted of (1) radio flux density measurements at 1660, 2695, and 8085 MHz; (2) UV spectrophotometry of La and Mg ii h and k; (3) Ha and Ca ii H and K spectroscopy; (4) V-band photometry; and (5) UB V polarimetry. As in many of the RS Canum Venaticorum binaries, a quasi-sinusoidal variation in V was observed in both systems. The period of this variation was approximately equal to the orbital period. No significant optical polarization was observed from either system. Variable radio emission was detected from both binaries throughout the program. Variable Ha and La emission were observed from HR 1099. UX Ari also exhibited La emission. Multiple Mg ii emission components with peculiar velocities of up to 250 km s -` were often seen from both systems. Each Mg ii observation also exhibited a strong and variable central velocity component which always seemed to match the orbital velocity of the more massive star in each system. HR 1099 exhibited strong Ca ii H and K emission which was not significantly variable. The joint observations provide strong evidence for chromospheric activity associated with the more massive star in each binary. Although the radio emission is produced in a larger volume than the optical and UV activity, temporal correlations suggest that a physical connection may exist between the two phenomena. Subject headings: stars: eclipsing binaries - stars: individual - stars: radio radiation - ultraviolet: spectra Publication: The Astrophysical Journal Pub Date: November 1978 DOI: 10.1086/156558 Bibcode: 1978ApJ...225..919W Keywords: Eclipsing Binary Stars; Lyman Alpha Radiation; Optical Emission Spectroscopy; Radio Astronomy; Stellar Spectrophotometry; Ultraviolet Astronomy; Visual Observation; H Alpha Line; Light Curve; Line Spectra; Oao 3; Polarimetry; Ubv Spectra; Ultraviolet Spectra; Astrophysics; Photometry:RS CVn Binaries; Polarization:Rs Cvn Binaries; Radio Radiation:RS CVn Binaries; RS CVn Binaries:UV full text sources ADS | data products SIMBAD (2) Related Materials (1) Erratum: 1979ApJ...228..367W