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  • Other Sources  (16)
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  • 1
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    Results of the IUE program of monitoring the ultraviolet emission line fluxes of four binary systems: HR 1099, 2 Peg, AR Lac and By Dra (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A program to obtain IUE spectra and optical photometry and spectra of three RS CVn-type binaries (HR 1099, II Peg, and AR Lac) and the prototype BY Dra system is reported. The systems were monitored for at least one orbital phase, and periodic variations in emission line flux from II Peg and HR 1099, indicative of notational modulation of an active region on these stars were detected. It is found that for II Peg the active region is in phase with photometric minimum as expected, but for HR 1099 ultraviolet emission maximum occurs at the time of photometric maximum.
    Keywords: ASTRONOMY
    Type: NASA. Goddard Space Flight Center Advan. in Ultraviolet Astron.; p 554-557
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  • 2
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    Rotational modulation and flares on RS CVn and BY Draconis stars. XIII - IUE spectroscopy and photometry of II Pegasi during September 1986 (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: UV spectroscopy obtained for the RS CVn star II Pegasi in September, 1986, indicates the presence of a rotational modulation effect for the Mg II h and k and O I 1305 A lines; the largest flux is observed when the primary spot concentration is nearly on the opposite hemisphere, and the rotational modulation is noted to be of opposite sense to that observed in 1981. Optical photometry shows the largest concentration of spots on one hemisphere ever observed on II Peg, implying a spot group covering over 50 percent of the projected area of one hemisphere.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 223; 1-2,; 219-226
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  • 3
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    Where do flares occur in RS CVn systems? Analysis of the October 3, 1981 flare on V711 Tau = HR 1099 observed by IUE (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A set of IUE observations of V711 Tau = HR 1099 (K1 IV and G2 V) in which high-resolution spectra with the SWP and LWR cameras were obtained during the luminous flare of October 3, 1981 is discussed. Multigaussian fits to the Mg II k and C IV 1548 A lines are consistent with the flare radial velocity being identical to that of the K star. Thus, the flare probably occurred on the K star. There is no evidence for flows as seen during a flare on UX Ari. The strongest emitters of UV radiation during the flare were the L alpha and Mg II lines, which emitted seven times as much energy as all the transition region lines combined. The peak luminosity of the flare in the UV emission lines is 1.5 times 10 to the 31st power ergs/sec, and the total emission in these lines during the flare was about 4 times 10 to the 35th power ergs.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of an International Symposium on New Insights in Astrophysics. Eight Years of UV Astronomy with IUE; p 161-164
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  • 4
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    Doppler imaging of active regions on AR Lacertae (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The eclipsing RS CVn system AR Lacertae was observed with IUE in October 1981 and October 1983. The phase coverage provided by the 1983 data is adequate to determine the location and size of two plage-like regions in the atmosphere of the K star using a Doppler imaging analysis of the Mg II k lines. A third epoch data set, consisting of many spectra spaced uniformly throughout a single orbital cycle was obtained in September 1985. Rotational modulation of the SWP line fluxes and an initial look at the Mg II lines reveals clear evidence of discrete chromospheric structures. These include a localized flare on the G star, a chromospherically inactive hemisphere on the G star, and plages on the K star.
    Keywords: ASTRONOMY
    Type: ESA Proceedings of an International Symposium on New Insights in Astrophysics. Eight Years of UV Astronomy with IUE; p 153-154
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  • 5
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    Models for the active and quiescent regions on the RS CVN-type system 2 Pegasi (HD 224085) (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The IUE observations of the RS CVn binary system II Pegasi obtained during the period 1981 October 1-7 were used to derive the emission measure distributions and to calculate transmission region models of the quiescent and plage (active) regions of II Peg. Active region models were calculated assuming area coverages of 10%, 6%, 3% and 1% of the visible hemisphere. These models are used to provide lower limits to the electron pressure in the quiescent and plage regions, which are compared with the available density diagnostics. The amount of mechanical energy deposition required to account for the observed radiative losses is very large.
    Keywords: ASTROPHYSICS
    Type: ESA Fourth European IUE Conf.; p 351-354
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  • 6
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    Rotational modulation and flares on RS Canum Venaticorum and BY Draconis stars. XI - Ultraviolet spectral images of AR Lacertae in September 1985 (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: High-resolution IUE SWP and LWP spectra of the bright eclipsing RS CVn system AR Lac, obtained during 40 h of continuous observations on September 18-19, 1985, are compiled and used to derive chromosphere images. The data and results are presented graphically and discussed in detail. The K 0 IV star is found to have a globally brighter trailing hemisphere and at least three distinct plage regions; the G 2 IV star has a flaring region with significant redshift and line-emission broadening and exhibits factor-of-3 variability in total emission, attributed to the presence of a large chromospherically inactive region.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 215; 1 Ma; 79-91
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  • 7
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    Rotational modulation and flares on RS CVn and BY Dra stars (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Evidence is presented for spots, plages, and flares on the noneclipsing RS CVn system II Peg and V 711 Tau. The large spot originally found on II Peg in 1981.8 could still be identified in 1983. Two spectroscopic flares of II Peg were detected. For the larger flare the fluxes in the strongest transition-region lines reached about six times their quiescent values. A comparison of the 1981 and 1983 flux variations show that active regions or plages are located on one hemisphere. On V 711 Tau at least two flares were observed. Outside of these flares, the strongest chromospheric and transition-region emission lines exhibited weak phase-dependent variations that persist over 173 orbital cycles (1981-1983) and are possibly associated with one of the proposed spots. For both stellar systems the fluxes from the higher temperature emission lines showed the greatest variations.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 204; 1-2; 177-192
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  • 8
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    Rotational modulation and flares on RS Canum Venaticorum and BY Draconis-type stars. XIV - Phase, eclipse and flare observations of YY Geminorum by Exosat and IUE (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The eclipsing spectroscopic binary YY Geminorum has been observed at optical, ultraviolet, and X-ray wavelengths for rotational modulation, eclipse variability, and flaring. The epoch T(phi = 0) = JD 2425698.3561, and the phase P = 0.81428224 d. The quiescent level of Mg II emission is remarkably steady during the three-year observing interval, with F(Mg II) roughly 3.6 x 10 to the -12th erg/sq cm/s. Both stars appear to have identical Mg II surface fluxes, with F roughly 1.8 x 10 to the 6th erg/sq cm/s. Both stars appear to be covered with evenly distributed Mg II emitting regions consistent with the proposition of Doyle (1987) that saturation of the Mg II lines occurs for stars having P less than 4 d, implying that such stars are entirely covered by plage. The transition region lines show significantly more rotational modulation and/or secular variability than Mg II. Both Mg II and the transition region lines show preflare and postflare enhancement.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 230; 2 Ap; 419-430
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  • 9
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    Rotational modulation and flares on RS CVn and BY Dra stars. VI - Physical parameters of the chromospheres/transition regions of V 711 Tau (HR 1099), II Peg and AR Lac during October 1981 (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Ground-based optical and IUE satellite-ultraviolet observations of three RS CVn stars are combined with density sensitive line ratios and differential emission measure curves to describe the physical conditions in their outer atmospheres. Solar-like densities are found to be representative of average conditions on two of the stars, V 711 Tau and AR Lac. The total radiative losses from these two stars are estimated and found to be larger than the sun by at least two orders of magnitude. Consideration of the volume emitting in two of the principal transition region lines suggests a possible relation between the disk 'filling factor' for these two lines and the dynamo-related Rossby number. Only one hemisphere of the star II Peg, the one showing least evidence of starspots, is similar. On the opposite hemisphere the presence of a discrete emitting region is deduced which is almost coincident in phase with the passage of the dominant optical spot group across the visible disk. The dimensions of this region, and an illustrative interpretation in terms of a large emitting magnetic loop, are discussed. It is compared to large active region loops on the sun.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 180; 1-2; 172-182
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  • 10
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    Rotational modulation and flares on RS CVn and BY Dra-type stars. I - Photometry and spot models for BY Dra, AU Mic, AR Lac, II Peg and V 711 Tau (= HR 1099) (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Multicolor wide-band photometry of five active stars is presented. The observations were carried out at several places before, during and after the period of IUE observations for the purpose of determining the location, sizes, and evolution of photospheric spots at the time when chromospheric, transition region, and coronal activity data were obtained from UV and radio observations. II Peg, BY Dra, and AU Mic show fairly stable quasi-sinusoidal light curves, while AR Lac and V 711 Tau show double-peaked light curves. For V 711 Tau, a remarkable evolution of the spotted area extent and/or longitude distribution is found. Small, but definite color variations that are consistent with the cool spot hypothesis have also been detected for BY Dra, II Peg and V 711 Tau.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 165; 1-2; 135-156
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