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  • ASTROPHYSICS  (5)
  • ASTRONOMY  (2)
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  • 1
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    Spectral images of HD 199178 (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: High-resolution IUE spectra of the Mg II k line of HD 199178 were analyzed, applying spectral imaging techniques to derive an image of the chromospheric structure and to study the transient behavior of the chromosphere. All spectra in the IUE archives were uniformly reduced and analyzed. Results are compared with ground-based observations of the photosphere. Four ultraviolet flares on HD 199178 are observed; 3 of these occurred at roughly the same rotational phase. There is no clear phase-dependence of the SWP line fluxes, but there is for the Mg II k flux. The emission centroid of the Mg II k line varies in a quasi-sinusoidal fashion, presumably due to the rotation of a nonuniform chromosphere.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 291-293
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  • 2
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    Rotational modulation of hydrogen Lyman alpha flux from 44ii Bootis (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observations with IUE that cover the entire 6.4 hr orbital cycle of the late-type contact binary 44i Bootis are presented. Intrinsic stellar hydrogen Lyman alpha emission flux was determined from low-resolution IUE spectra, compensating for geocoronal emission and for interstellar absorption. The variation of the stellar Lyman alpha emission flux correlates well with the variation of the C II and C IV emission fluxes, and shows orbital modulation in phase with the visual light curve. The ratio of Lyman alpha to CII flux (15 to 20) is similar to that observed in solar active regions. Hydrogen Lyman alpha emission is thus one of the most important cooling channels in the outer atmosphere of 44i Boo. A high-resolution spectrum of the Lyman alpha line was obtained between orbital phases 0.0 and 0.6. The integrated flux in the observed high-resolution Lyman alpha profile is consistent with the fluxes determined using low-resolution spectra, and the composite profile indicates that both components of this binary have equally active chromospheres and transition regions. The uncertainty in the interstellar hydrogen column density cannot mimic the observed variation in the integrated Lyman alpha flux, because the stellar line is very much broader than the interstellar absorption.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 299-302
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  • 3
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    Coordinated Ginga, IUE, and VLA observations of stellar activity in Sigma(2) Coronae Borealis (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Observations of the active cool star binary system Sigma(2) Corona Borealis with the Large Area Counters on the Ginga X-ray satellite over 2.5 d, or about two orbital periods, are reported. Throughout the observations, Sigma(2) CrB exhibited X-ray variability on time scales ranging from tens of minutes to hours. The X-ray light curve shows evidence of flaring during the course of the observations. The summed X-ray pulse height spectrum from flaring events compared with similar spectra from quiescent periods indicates an increase in coronal temperature. Periodogram analysis of the entire X-ray light curve shows a possible periodicity at about 0.40-0.44 d, with no strong signal at the orbital period or 1/2 of the orbital period. Coordinated multiwavelength observations of IUE and the VLA indicate both UV and microwave flaring during one X-ray outburst. The quiescent microwave spectrum is not consistent with a thermal gyrosynchrotron process; nonthermal gyrosynchrotron radiation is argued to be the most likely emission process.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 2 Ju; 760-772
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  • 4
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    Rotational modulation of hydrogen Lyman alpha flux from 44i Bootis (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Observations with IUE that cover the entire 6.4 hr orbital cycle of the late-type contact binary 44i Bootis are presented. Intrinsic stellar hydrogen Lyman alpha emission flux was determined from low-resolution IUE spectra, compensating for geocoronal emission and for interstellar absorption. The variation of the stellar Lyman alpha emission flux correlates well with the variation of the CII and CIV emission fluxes, and shows orbital modulation in phase with the visual light curve. The ratio of Lyman alpha to CII flux (15 to 20) is similar to that observed in solar active regions. Hydrogen Lyman alpha emission is thus one of the most important cooling channels in the outer atmosphere of 44i Boo. A high-resolution spectrum of the Lyman alpha line was obtained between orbital phases 0.0 and 0.6. The integrated flux in the observed high-resolution Lyman alpha profile is consistent with the fluxes determined using low-resolution spectra, and the composite profile indicates that both components of this binary have equally active chromospheres and transition regions. The uncertainty in the interstellar hydrogen column density cannot mimic the observed variation in the integrated Lyman alpha flux, because the stellar line is very much broader than the interstellar absorption.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 208; 1-2; 201-207
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  • 5
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    IUE observations of the M dwarfs CM Draconis and Rossiter 137 B - Magnetic activity at saturated levels (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: IUE observations of two active M dwarfs with known rotation rate or age and presumed to be almost totally convective are presented. The first of these stars, CM Draconis (Gl 630.1), is an old Population II binary with its components in tidally induced rapid rotation (P = 1.27 d, dM 4 + dM 4). The other one, Rossiter 137 B, forms with HD 36705 (AB Dor) a visual pair of young active stars. The activity of CM Dra is due to the forced rotation in a close binary, while Rst 137 B is assumed to rotate fast enough to generate its magnetica activity. These results are compared with those for M dwarfs, particularly AU Mic and YZ CMi, that have known rotational periods and measured ultraviolet emission line fluxes. The chromospheric-coronal saturation levels of cool dwarfs between 0.3 less than B-V less than 1.6 is determined. It is found that saturated F stars have stronger chromospheres than saturated M stars, but the opposite is true for the corona. Results of these observations seem to favor a rotation-dependent distributed dynamo generating magnetic flux in totally convective stars.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 222; 2-Jan
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  • 6
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    First ultraviolet observations of the transition regions of X-ray bright solar-type stars in the Pleiades (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are reported from A UV study of the transition regions of two X-ray-bright solar-type stars from the Pleiades, in an attempt to extend the main sequence age baseline for the transition-region activity-age relation over more than two orders of magnitude. However, no emission lines were detected from either star; the upper limits to the fluxes are consistent with previously determined saturation levels, but do not help to further constrain evolutionary models.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 10; 2 19
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  • 7
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    Detection of X-ray emission from the young low-mass star Rossiter 137B (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Rst 137B, a close M-dwarf companion to the active K-star HD 36705, has been detected in a High Resolution Image in the Einstein Observatory Archive. The X-ray surface fluxes (0.2-4 keV) from both stars are close to the empirical saturation level, F(x)/F(bol) of about 0.001, defined by rapid rotators and very young stars. This supports the earlier results of the youthfulness of the system. This young couple is an excellent subject for studies of dependence of early evolution on stellar mass. Rst 137B is one of the latest spectral types and thus lowest-mass premain-sequence stars yet detected as an X-ray source.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 1071-107
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