604 research outputs found
Orbital phase dependent IUE spectra of the nova like binary II Arietis
Nine low dispersion IUE spectra of the nova like binary TT Ari over its 3h17m orbital period were obtained. Four short wave spectra and five long wave spectra exhibit marked changes in line strength and continuum shape with orbital phase. The short wave spectra show the presence in absorption of C III, Lyman alpha, SiIII, NV, SiIV, CIV, HeII, AlIII, and NIV. The CIV shows a P Cygni profile on two of the spectra. Implications of these spectra for the nature of nova like variables are discussed
Visible-band and IUE observations of mu Sagittarii
H alpha and U band photometry and IUE spectra of the binary system mu Sagittarii are discussed. An estimate of mass-loss is made from the observed P Cygni profiles. There are indications of pulsation in the supergiant B8 component
The Best Brown Dwarf Yet?: A Companion to the Hyades Eclipsing Binary V471 Tau
We have carried out an analysis of about 160 eclipse timings spanning over 30
years of the Hyades eclipsing binary V471 Tauri that shows a long-term
quasi-sinusoidal modulation of its observed eclipse arrival times. The O-Cs
have been analyzed for the ``light-time'' effect that arises from the
gravitational influence of a tertiary companion. The presence of a third body
causes the relative distance of the eclipsing pair to the Earth to change as it
orbits the barycenter of the triple system. The result of the analysis of the
eclipse times yields a light-time semi-amplitude of 137.2+/-12.0 s, an orbital
period of P_3 = 30.5+/-1.6 yr and an eccentricity of e_3 = 0.31+/-0.04. The
mass of the tertiary component is M_3 sin i_3 = 0.0393+/-0.0038 Mo when a total
mass of 1.61+/-0.06 Mo for V471 Tau is adopted. For orbital inclinations i_3 >
35 deg, the mass of the third body would be below the stable hydrogen burning
limit of M = 0.07 Mo and it thus would be a brown dwarf. In the next several
years (near maximum elongation), it should be feasible to obtain IR images and
spectra of V471 Tau C that, when combined with the known mass, age, distance,
and [Fe/H], will serve as a benchmark for understanding the physical properties
and evolution of brown dwarfs.Comment: 9 pages, 3 figures, accepted for publication in ApJ Letter
Astrobiological Effects of F, G, K and M Main-Sequence Stars
We focus on the astrobiological effects of photospheric radiation produced by
main-sequence stars of spectral types F, G, K, and M. The photospheric
radiation is represented by using realistic spectra, taking into account
millions or hundred of millions of lines for atoms and molecules. DNA is taken
as a proxy for carbon-based macromolecules, assumed to be the chemical
centerpiece of extraterrestrial life forms. Emphasis is placed on the
investigation of the radiative environment in conservative as well as
generalized habitable zones.Comment: 3 pages, 3 figures; submitted to: Exoplanets: Detection, Formation
and Dynamics, IAU Symposium 249, eds. Y.S. Sun and S. Ferraz-Mello (San
Francisco: Astr. Soc. Pac.
X-Ray Emission from the Sun in Its Youth and Old Age
We have obtained ROSAT PSPC (Roentgen Satellite Position Sensitive Proportional Counter) pointed observations of two nearby G stars of ages 70 Myr and 9.5 Gyr that are of unique importance as proxies for the Sun at the two extremes of its main-sequence evolutionary lifetime. The younger star, HD 129333 (EK Dra; G0 V), a rapid rotator with a 2.7 day period, is a strong source with an X-ray luminosity L(x)(0.2-2.4 keV) = (7.5-11.5) x 10(exp 29) erg/s. Modeling suggests a two-temperature corona with T(1) = (2.0 +/- 0.3) x 10(exp 6) K and T(2) = (9.7 +/- 0.3) x 10(exp 6) K (formal uncertainties). A continuous emission measure distribution, increasing to higher temperatures and with a cutoff at (20-30) x 10(exp 6) K, yields even better fits to the data. The old star, beta Hyi (HR 98; G2 IV), represents the Sun in the future, near the end of its hydrogen-core burning stage, when it should be rotating more slowly (present P(rot) = 25.4 day) and should have lower levels of activity. The ROSAT measurements yield L(x) = (0.9-3.0) x 10(exp 27) ergs/s and a rather cool, single coronal temperature of T = (1.7 +/- 0.4) x 10(exp 6) K. For comparison, the Sun has L(x) approx. equal to 2 x 10(exp 27) ergs/s and a coronal temperature of about T = 2 x 10(exp 6) K. These stars provide information on the decline of the stellar (and specifically solar) magnetic activity from extreme youth to old age. HD 129333 is also important in that it yields an estimate of the solar soft X-ray flux in the early solar system at the epoch of the terminal stages of planetary accretion
Searching for Weak or Complex Magnetic Fields in Polarized Spectra of Rigel
Seventy-eight high-resolution Stokes V, Q and U spectra of the B8Iae
supergiant Rigel were obtained with the ESPaDOnS spectropolarimeter at CFHT and
its clone NARVAL at TBL in the context of the Magnetism in Massive Stars
(MiMeS) Large Program, in order to scrutinize this core-collapse supernova
progenitor for evidence of weak and/or complex magnetic fields. In this paper
we describe the reduction and analysis of the data, the constraints obtained on
any photospheric magnetic field, and the variability of photospheric and wind
lines.Comment: IAUS272 - Active OB Stars: Structure, Evolution, Mass Loss and
Critical Limit
X-Ray, FUV, and UV Observations of alpha Centauri B: Determination of Long-term Magnetic Activity Cycle and Rotation Period
We have been carrying out a study of stellar magnetic activity, dynamos,
atmospheric physics, and spectral irradiances from a sample of solar-type G0-5
V stars with different ages. One of the major goals of this program is to study
the evolution of the Sun's X-ray through NUV spectral irradiances with age. Of
particular interest is the determination of the young Sun's elevated levels of
high-energy fluxes because of the critical roles that X-ray through FUV
emissions play on the photochemical and photoionization evolution of early,
young planetary atmospheres and ionospheres. Motivated by the current
exoplanetary search missions that are hunting for earth-size planets in the
habitable zones of nearby main-sequence G-M stars, we are expanding our program
to cooler, less luminous, but much more numerous main-sequence K-type stars,
such as alpha Centauri B. The long life (2-3x longer than our Sun) and slow
evolution of K stars provide nearly constant energy sources for possible hosted
planets. Presented here are X-ray, UV, and recently acquired FUV observations
of the K1 V star alpha Cen B. These combined high-energy measures provide a
more complete look into the nature of alpha Cen B's magnetic activity and X-UV
radiances. We find that alpha Cen B has exhibited significant long-term
variability in X-ray through NUV emission fluxes, indicating a solar-like
long-term activity cycle of P_cycle = 8.84 years. In addition, analysis of the
short-term rotational modulation of mean light due to the effects of
magnetically active regions has yielded a well-determined rotation period of
P_rotation = 36.2 days. alpha Cen B is the only old main-sequence K star with a
reliably determined age and rotation period, and for early K-stars, is an
important calibrator for stellar age/rotation/activity relations
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