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Irish Astronomical Journal. 08/1993; 21:83.
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ABSTRACT: 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.
11/1988;
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A. D. Andrews,
M. Rodono,
J. L. Linsky,
A. Brown,
C. J. Butler,
S. Catalano,
F. Scaltriti,
M. Busso,
Il-Seong Nha,
J. Y. Oh,
M. C. D. Henry,
J. L. Hopkins,
H. J. Landis,
S. Engelbrektson
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ABSTRACT: 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.
Astronomy and Astrophysics 09/1988; 204:177-192. · 4.59 Impact Factor
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ABSTRACT: The modulation of the strong chromospheric and transition region lines over one cycle of the optical light curves of BY Dra and AU Mic is studied using IUE observations. The IUE observations were made from October 2-5, 1981 and include 7 short wavelength (SW) spectra and 13 long wavelength (LW) spectra. The integrated line flux data reveal that for BY Dra in the SW spectra there is modulation in the C IV, C II, O I, and He II lines and nonflare surface fluxes; and in the LW spectra, flares are detected in the Mg II and Fe II bands. It is observed that there is no modulation in AU Mic, and the optical photometry data reveal a poor correlation between optical flare strength and UV emission line enhancements. The differential emission measure curves for BY Dra and AU Mic are compared with solar curves. It is noted that both stars show the presence of hot material throughout their rotation period.
04/1987;
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ABSTRACT: 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.
10/1986;
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M. Rodono,
G. Cutispoto,
V. Pazzani,
S. Catalano,
P. B. Byrne,
J. G. Doyle,
C. J. Butler, A. D. Andrews,
C. Blanco,
E. Marilli, [......],
M. Busso,
A. Cellino,
J. L. Hopkins,
A. Okazaki,
S. S. Hayashi,
M. Zeilik,
R. Helston,
G. Henson,
P. Smith,
T. Simon
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ABSTRACT: 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.
Astronomy and Astrophysics 08/1986; 165:135-156. · 4.59 Impact Factor
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B. H. Foing,
M. Rodono,
G. Cutispoto,
S. Catalano,
J. L. Linsky,
D. M. Gibson,
A. Brown,
B. M. Haisch,
C. J. Butler,
P. B. Byrne, A. D. Andrews,
J. G. Doyle,
D. E. Gary,
G. W. Henry,
G. Russo,
A. Vittone,
F. Scaltriti
Revista mexicana de astronomía y astrofísica 01/1986; 12:213. · 1.00 Impact Factor
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ABSTRACT: The authors present optical photometry of flares and possible spot
variations on the star Gl 735. Consideration of the energetics of the
optical flares suggests that the star may be underactive when compared
to other flare stars of the same spectral type. This conclusion is not
supported however by an estimate of the radiative loss rate from the
lower chromosphere due to Mg II h and k. Radiative losses from the upper
chromosphere, transition zone and corona are also normal for a flare
star of its spectral type.
Monthly Notices of the Royal Astronomical Society 11/1984; 211:607-616. · 4.90 Impact Factor
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ABSTRACT: 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.
08/1984;
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02/1984; 16:473.
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02/1983; 15:650.
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Information Bulletin on Variable Stars. 12/1982; 2258:1.
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ABSTRACT: Ground based optical, and IUE observations of AU Mic are described. One
definite flaring event, remarkable changes of the BY Dra-type optical
light curve and evidence of slow variability in the chromospheric and
transition region line fluxes (probably due to the rotational modulation
of photospheric starspots and plages, respectively), was found. The
fractional surface area covered by active regions (filling factor) shows
a definite variability with the temperature of line formation, i.e.,
with atmospheric height. This suggests significant surface and vertical
structuring of active regions in the outer atmosphere of AU Mic.
05/1982; 176:165-167.
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ABSTRACT: 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.
02/1982;
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ABSTRACT: Short-wavelength IUE spectra of three nearby M-type dwarfs are
presented. Two of these stars, Gliese 867 A and AU Mic, are active UV
Ceti flare stars and their UV spectra exhibit strong emission lines,
characteristic of active chromospheres. The third star, Gliese 825, is a
low-activity flare star and its spectrum reveals no chromospheric lines.
A strong UV continuum exists in one of the spectra of Gliese 867 A and
it is deduced that a flare took place during the exposure. A spectrum of
the flare light is extracted and compared with the predictions of
various flare models.
Monthly Notices of the Royal Astronomical Society 11/1981; 197:815-827. · 4.90 Impact Factor
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02/1981; 13:872.
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ABSTRACT: Results of an IUE satellite investigation of a selection of nearby dwarf
stars of spectral type M are given. Spectra were obtained for seven
stars in IUE's long wavelength range and for three stars in the short
wavelength range, including both known flare stars and stars as yet not
known to flare. The most prominent feature of the long wavelength
spectra is the ionized magnesium h and k resonance doublet at 2795/7A
wavelength. Radii are estimated from the mean of results obtained from
mean relationships between radius and absolute magnitude, radius and
spectral type, and from empirical relationships between radius and the
star's colors. The most active flare stars show higher emission,
suggesting a greater rate of energy deposition in their lower
chromospheres. The short wavelength data included the first-ever UV
spectrum of a flaring star. Most sample stars showed strong lines in the
short wavelength region, and their surface fluxes were calculated and
compared to the quiet sun.
Irish Astronomical Journal. 08/1980; 14:219-226.
