Laurits pedersen astrologi
Storytelling and Science Under the Stars. This summer the Aspen Center for Physics and the Aspen Science Center collaborated with a small team of astrophysicists to host a joint stargazing, storytelling, ask an astronomer, and ice cream social event. The team consisted of staff members from the ACP and the ASC, four visting professional astrophysicists, and professional storytellers from the international organization "Spellbinders" including the two founders.
The event kicked off with liquid nitrogen ice cream making, which was a big hit with the more than people in attendance. At dusk we divided into 4 groups and teams of two a Spellbinder and an astrophysicist circulated from group to group telling stories about the sky from all over the world, and answering questions about planets, stars , galaxies, and black holes. Three small telescopes focused on Saturn and lines formed after it finally got dark.
I'll discuss how we put this event together, why it is important to join science and culture in order to engage the public, and how fantastic the stars are for creating this union. Observing variable stars at the University of Athens Observatory. In the University of Athens installed a 0. Although the telescope was built for educational purposes, we found it can be a perfect research instrument, as we can obtain fine quality light curves of bright variable stars , even from a place close to the city center. To date, we succeed in making photometry of stars down to 15th magnitude with satisfactory results.
We expect to achieve even better results in the future, as our methods still improve, and as the large number of relatively bright stars gives us the chance to study various fields of CCD photometry of variables. The Catalina Surveys Southern periodic variable star catalogue. Drake, A. This completes a search for periodic variable stars within the 30 deg2 of the sky covered by the Catalina Surveys. For the known sources, we find excellent agreement between our catalogue and prior values of luminosity, period, and amplitude.
However, we find many variable stars that had previously been misclassified. A new survey of the variable stars in the Draco dwarf spheroidal galaxy updates the pioneering study of this galaxy by Baade and Swope Our improved data, taken in BVI filters with CCD cameras on three telescopes at more than 80 epochs, allow us to investigate the known variables and to discover new, mostly low-amplitude variables. Approximately variables are found and classified, more than double the number of variables analyzed previously. This large sample of variables provides a unique opportunity to study the properties of these stars in a single system.
This long neglected data set, taken with a 0. During the course of the survey, each field was visited from 10 to several thousand times, so our initial pass is just to identify potential variable stars. Our initial "quick-look" effort shows several thousand potential candidates and includes at least one nearby supernova.
We present our plans for a follow-up observational program for further identification of variable types and period determinations. Variable Stars. The images were obtained during two observing runs in — We identified variables , eight of which are new discoveries. We provide Fourier decomposition parameters for the RR Lyrae, and discuss the physical parameters and photometric metallicity derived therefrom.
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The M14 distance modulus is also discussed, based on different approaches for the calibration of the absolute magnitudes of RR Lyrae stars. The possible presence of second-overtone RR Lyrae in M14 is critically addressed, with our results arguing against this possibility. This, together with the position of the RR Lyrae stars of both Bailey types in the period—amplitude diagram, suggests an Oosterhoff-intermediate classification for the cluster.
Such an intermediate Oosterhoff type is much more commonly found in nearby extragalactic systems, and we critically discuss several other possible indications that may point to an extragalactic origin for this cluster. Based on observations obtained with the 0. The detection of X-ray variability in O stars.
Seven O stars known to have strong, and sometimes variable , stellar winds have been observed repeatedly with the Imaging Proportional Counter on the Einstein Observatory, in a program designed to determine whether the X-ray fluxes from these stars are variable. In three cases, definite changes were seen, either on a time scale of a year Iota Ori and Delta Ori or five days 15 Mon.
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In two of these cases, the X-ray spectrum was harder when the overall flux was higher, indicating that some of the fluctuations may take place in a hot approximately 10 to the 7th K emitting region at the bottom of the winds. Observations of the Leo A dwarf galaxy, obtained over the period from to are reported. A total of 14 suspected variables were found, 9 had sufficient coverage for period determination, and 5 had Cepheid light curves. The main purpose is to search for new variable stars and to study the light curves of binary systems as well as the oscillation spectra of pulsating stars.
Several variable stars are reported including three eclipsing binary stars , one of which is an eclipsing binary star with a pulsating component V Aur. A frequency analysis of the eclipse-subtracted light curve was also performed. Therefore, high-resolution, high-quality spectra will be needed to derive accurate component radial velocities of the faint eclipsing binaries which are located in the field of NGC The new Devasthal Optical Telescope, suitably equipped, could in principle do this.
Circumstellar disks are common among many stars , all spectral types, and at different stages of their lifetimes. We present data for a subset of cases where observations have been obtained throughout the different phases of the disk cycle.
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The second stage of our project is to examine a sample of star clusters known to contain Be stars , with the goal to develop a more statistically significant sample of variable circumstellar disk systems. With a robust multi-epoch study we can determine whether these Be stars exhibit disk-loss or disk-renewal phases. The larger sample will enable a better understanding of the prevalence of these disk events.
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Kuehn, Charles A. This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We present photometric parameters and light curves for these stars.
We also present physical properties, derived from Fourier analysis of light curves, for some of the RR Lyrae stars. We discuss the Oosterhoff classification of Reticulum and use our results to re-derive the distance modulus and age of the cluster. This book, which is a reworked and updated version of Steven Bloemen's original PhD thesis, reports on several high-precision studies of compact variable stars.
Its strength lies in the large variety of observational, theoretical and instrumentation techniques that are presented and used and paves the way towards new and detailed asteroseismic applications of single and binary subdwarf stars. Close binary stars are studied using high cadence spectroscopic datasets collected with state of the art electron multiplying CCDs and analysed using Doppler tomography visualization techniques.
The work touches upon instrumentation, presenting the calibration of a new fast, multi-colour camera installed at the Mercator Telescope on La Palma. The thesis also includes theoretical work on the computation of the temperature range in which stellar oscillations can be driven in subdwarf B- stars.
Finally, the highlight of the thesis is the measurement of velocities of stars using only photometric data from NASA's Kepler satellite. Doppler beaming causes stars to appear slightly brighter when they move towards us in their orbits, and this subtle effect can be seen in Kepler's brightness measurements. The thesis presents the first validation of such velocity measurements using independent spectroscopic measurements. Since the detection and validation of this Doppler beaming effect, it has been used in tens of studies to detect and characterize binary star systems, which are key calibrators in stellar astronomy.
Their star formation histories. Close together in the sky, of similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? Here, we present the first reconstruction of the star formation histories of NGC and NGC using long-period variable stars. These represent the final phase of evolution of low- and intermediate-mass stars at the asymptotic giant branch, when their luminosity is related to their birth mass.
Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC , we found that the main epoch of star formation occurred 8. Despite their similar masses, NGC has evolved more slowly than NGC initially, but more dramatically in more recent times. Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night.
We present high-cadence time-series aperture photometry of 10, stars with i variable stars.
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One variable may be a transiting exoplanet. We present a reference study of the long-term optical variability of young stars using data from the WASP project. WASP light curves cover time-scales of up to 7 yr and typically contain 10 data points. We quantify the variability as a function of time-scale using the time-dependent standard deviation 'pooled sigma'.
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An even smaller fraction 13 per cent in our sample, 6 per cent in the control show evidence for an increase in variability amplitude as a function of time-scale from weeks to months or years. This shows that the long-term variations in CTTSs are predominantly driven by processes in the inner disc and in the accretion zone. Four of the stars with long-term variations show periods of d, significantly longer than the rotation periods and stable over months to years.
One possible explanation is cyclic changes in the interaction between the disc and the stellar magnetic field.
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X-Ray Variability and the Secondary Star. We discuss the history of X-ray observations of the 11 Car system, concentrating on the periodic variability discovered in the s. We discuss the interpretation of these variations, concentrating on a model of the system as a "collidingwind" binary.
This interpretation allows the physical and orbital parameters of eta Car and its companion star to be constrained. We find Draco RV member Armandroff et al. Draco RV member Olszewski et al. We describe and evaluate a summer undergraduate research project and experience by one of us AA , under the supervision of the other JP. The aim of the project was to sample current approaches to analyzing variable star data, and topics related to the study of Mira variable stars and their astrophysical importance.
SURP allowed undergraduate students to explore and learn about many topics within astronomy and astrophysics, from instrumentation to cosmology. SURP introduced students to key skills which are essential for students hoping to pursue graduate studies in any scientific field. Variable stars proved to be an excellent topic for a research project. For beginners to independent research, it introduces key concepts in research such as critical thinking and problem solving, while illuminating previously learned topics in stellar physics.
The focus of this summer project was to compare observations with structural and evolutionary models, including modelling the random walk behavior exhibited in the O-C diagrams of most Mira stars. We found that the random walk could be modelled by using random fluctuations of the period. This explanation agreed well with observations. The process of collecting and analyzing light curves from variable stars and asteroids is almost identical. In a collaboration was created to develop a simple fundamental way to study both asteroids and variable stars using methods that would allow the process to be repeated by middle school and high school students.
It was discovered that the only available software program which could be easily installed on lab computers was MPO Canopus.