121 research outputs found
The Sun as a Star: 13 years of SoHO
The best known Solar oscillation-like star is the Sun. During the last 14
years, the ESA/NASA Solar and Heliospheric Observatory (SoHO) has been
continuously observing this star from the Lagrange point L1 with an enormous
success. Among the 11 instruments placed onboard, 3 of them are dedicated to
helioseismology: GOLF, VIRGO and MDI. The first two observe the Sun as a star
by integrating the velocity or intensity signal of the visible solar disk into
a single point. They are thus similar to any other observation done in
asteroseismology. During this review I will present the most important results
obtained during the mission concerning the Sun seen as a star and how this
results have evolved our thoughts of the inside of our star.Comment: Proceedings of the Stellar Pulsation Conference. Santa Fe. 6 pages, 4
figure
Changes in Mean Global Physical Parameters of Blazhko RR Lyrae stars -- Derived from Multicolor Photometry
We developed an Inverse Photometric method (IPM) to determine global physical
parameters of RR Lyrae stars exclusively from multicolor light curves (S\'odor,
Jurcsik & Szeidl, 2009, MNRAS, 394, 261). We showed that for good quality
photometric observations of unmodulated RRab stars, the IPM gives similarly
good results as direct Baade-Wesselink analyses do, but without the need for
spectroscopic measurements. In the course of the development, we payed special
attention to the applicability of the IPM for modulated RR Lyrae stars. Since
there is no simultaneous spectroscopic radial velocity and photometric
observations of any Blazhko star with good phase coverage both in pulsation and
modulation, which would allow spectroscopic Baade-Wesselink analysis, the IPM
is the only possibility today to study changes in the global physical
parameters of Blazhko RR Lyrae stars during the modulation cycle. With the IPM,
we have studied the extensive multicolor light curves of 4 Blazhko RRab stars
we observed with the 24-inch telescope of the Konkoly Observatory during the
past 5 years in the frame of the Konkoly Blazhko Survey. Small but unambiguous
changes in the pulsation-averaged mean temperature, mean radius and mean
luminosity have been detected in each star. Results on these Blazhko stars (SS
Cnc, DM Cyg, RR Gem, and MW Lyr) are shown in this paper.Comment: 5 pages, 1 figure. Appeared in STELLAR PULSATION: CHALLENGES FOR
THEORY AND OBSERVATION: Proceedings of the International Conference. AIP
Conference Proceedings, Volume 1170, pp. 294-298 (2009
New Results of the Konkoly Blazhko Group
During the recent years the Konkoly Blazhko Group (PIs Johanna Jurcsik and
B\'ela Szeidl, co-workers \'Ad\'am S\'odor, Zsombor Hurta and several
undergraduate, graduate students) published new important results of Blazhko
variables in 15 reviewed Journal articles. These results utilize multicolor CCD
observations obtained with an automatic 60 cm telescope, and also previously
unpublished Konkoly archive photometric data. Our light curves are the most
extended multicolor data-sets ever obtained for a Blazhko variable, the
observations cover each phase of the pulsation and the modulation as well. We
have detected many previously unknown features of the light curve modulation,
and based on the different band's observations we also revealed the underlying
variations of the mean physical parameters during the Blazhko cycle. In my
contribution the main achievements of the Konkoly Blazhko Group are summarised.Comment: in "Stellar Pulsation: Challenges for Theory and Observation", Eds.
J. Guzik and P. Bradley. (5 pages, 5 figures
The Cepheid Distance Scale: recent progress in fundamental techniques
This review examines progress on the Pop I, fundamental-mode Cepheid distance
scale with emphasis on recent developments in geometric and quasi-geometric
techniques for Cepheid distance determination. Specifically I examine the
surface brightness method, interferometric pulsation method, and trigonometric
measurements. The three techniques are found to be in excellent agreement for
distance measures in the Galaxy. The velocity p-factor is of crucial importance
in the first two of these methods. A comparison of recent determinations of the
p-factor for Cepheids demonstrates that observational measures of p and
theoretical predictions agree within their uncertainties for Galactic Cepheids.Comment: An invited review at the Santa Fe, NM, conference -- Stellar
Pulsation: Challenges for Theory and Observation; May 31-June 5, 2009 10
pages, 8 figure
Fundamental Parameters of Cepheids: Masses and Multiplicity
Masses determined from classical Cepheids in binary systems are a primary
test of both pulsation and evolutionary calculations. The first step is to
determine the orbit from ground-based radial velocities. Complementary
satellite data from Hubble, FUSE, IUE, and Chandra provide full information
about the system. A summary of recent results on masses is given. Cepheids have
also provided copious information about the multiplicity of massive stars, as
well as the distribution of mass ratios and separations. This provides some
important constraints for star formation scenarios including differences
between high and low mass results and differences between close and wide
binaries
Pulsation-Initiated Mass Loss in Luminous Blue Variables: A Parameter Study
Luminous blue variables (LBVs) are characterized by semi-periodic episodes of
enhanced mass-loss, or outburst. The cause of these outbursts has thus far been
a mystery. One explanation is that they are initiated by kappa-effect
pulsations in the atmosphere caused by an increase in luminosity at
temperatures near the so-called ``iron bump'' (T ~ 200,000 K), where the Fe
opacity suddenly increases. Due to a lag in the onset of convection, this
luminosity can build until it exceeds the Eddington limit locally, seeding
pulsations and possibly driving some mass from the star. We present some
preliminary results from a parameter study focusing on the conditions necessary
to trigger normal S-Dor type (as opposed to extreme eta-Car type) outbursts. We
find that as Y increases or Z decreases, the pulsational amplitude decreases
and outburst-like behavior, indicated by a large, sudden increase in
photospheric velocity, becomes likes likely.Comment: 6 pages, 4 figures, to be published in the Proceedings of Massive
Stars as Cosmic Engines, IAU Symp 250, ed. F. Bresolin, P. A. Crowther, & J.
Puls (Cambridge Univ. Press
IRSF/SIRIUS JHKs near-infrared variable star survey in the Magellanic Clouds
We carried out a NIR variable star survey toward the Large and Small
Magellanic Clouds using the InfraRed Survey Facility (IRSF) at Sutherland,
South African Astronomical Observatory. This survey project was initiated in
Dember 2000, and since then, we kept monitoring a total area of 3 square
degrees along the LMC bar and also an area of 1 square degree around the center
of the SMC, sufficiently large to do statistical analysis and to make complete
catalog of variable red giants in the Magellanic Clouds. The detection limits
(S/N=10) of the survey are 17.0, 16.5 and 15.5 at J, H and Ks, respectively. In
this article, we present some results on infrared variables that are not
detected by the previous optical surveys. We show that they do not fall on the
standard period-Ks magnitude relation for Mira-type variables pulsating in the
fundamental mode.Comment: 3 pages, 2 figures. To appear in "Stellar Pulsation: Challenges for
Theory and Observation", Eds. J. Guzik and P. Bradle
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