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In this classical view FUors are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths.

Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables , show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables.

However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability. The Carina Project. Bright Variable Stars. Dall'Ora, M. We present new BV time series data of the Carina dwarf spheroidal galaxy dSph.

Among them 75 are RR Lyrae stars , 15 are bona fide anomalous Cepheids, one might be a Galactic field RR Lyrae star , and one is located along the Carina red giant branch. This finding supports the evidence that these objects are intermediate-mass stars during central He-burning phases. We adopted three different approaches to estimate the Carina distance modulus, namely, the first-overtone blue edge method, the period-luminosity-amplitude relation, and the period-luminosity-color relation.

The data for Carina, together with data available in the literature, strongly support the conclusion that dSph's can barely be classified into the classical Oosterhoff dichotomy. The mean period of RRab's in Carina resembles that found for Oosterhoff type II clusters, whereas the ratio between first-overtone RRc pulsators and the total number of RR Lyrae stars is quite similar to that found in Oosterhoff type I clusters.

Radio emission of cataclysmic variable stars. Most of these objects were in optical high stage, but none were detected beyond flux limits between 0. Now, it has evolved into an International Organization with members and observers from both the professional and non-professional astronomical community, contributing photometry to a public photometric database of about 22, variable objects, and using it for research projects.

As such, the AAVSO's main claim to fame is that it successfully engages backyard Astronomers, educators, students and professional astronomers in astronomical research. I will present the main aspects of the association and how it has evolved with time to become a premium resource for variable star researchers. I will also discuss the various means that the AAVSO is using to support cutting-edge variable star science , and how it engages its members in projects building a stronger international astronomical community.

We work in four observing projects: B. Dwarf spheroidal galaxies show very diverse star formation histories. For the Galactic dwarf spheroidal galaxies, a correlation exists between Galactocentric distance and the prominence of intermediate-age 2 - 10 Gyr populations. To test whether this correlation exists for the M31 dwarf spheroidal galaxies, we observed the Cassiopeia And VII dwarf galaxy, which is one of the most distant M31 dwarf spheroidal galaxies.

From the RR Lyrae stars we can obtain an independent distance and metallicity estimate for the dwarf galaxy. These results will be compared to those found for the other M31 dwarf spheroidal galaxies. Outbursts and Disk Variability in Be Stars. Labadie-Bartz, Jonathan; Chojnowski, S. Drew; Whelan, David G. In order to study the growth and evolution of circumstellar disks around classical Be stars , we analyze optical time-series photometry from the KELT survey with simultaneous infrared and visible spectroscopy from the Apache Point Observatory Galactic Evolution Experiment survey and Be Star Spectra database for a sample of Galactic classical Be stars.

The systems studied here show variability including transitions from a diskless to a disk-possessing state and vice versa , and persistent disks that vary in strength, being replenished at either regularly or irregularly occurring intervals. We study how both the photometry and spectroscopy change together during active episodes of disk growth or dissipation, revealing details about the evolution of the circumstellar environment.

We demonstrate that photometric activity is linked to changes in the inner disk, and show that, at least in some cases, the disk growth process is asymmetrical. Observational evidence of Be star disks both growing and clearing from the inside out is presented. The duration of disk buildup and dissipation phases are measured for 70 outbursts, and we find that the average outburst takes about twice as long to dissipate as it does to build up in optical photometry. Our analysis hints that dissipation of the inner disk occurs relatively slowly for late-type Be stars.

Abstract only Open source PYTHON packages that are useful for data reduction, photometry, and other tasks relevant to variable star astronomy have been developed over the last three to four years as part of the Astropy project. Using this software, it is relatively straightforward to reduce images, automatically detect sources, and match them to catalogs. Over the last year browser-based tools for performing some of those tasks have been developed that minimize or eliminate the need to write any of your own code.

After providing an overview of the current state of the software, an application that calculates transformation coefficients on a frame-by-frame basis by matching stars in an image to the APASS catalog will be described. NSVS fields were searched for candidates with both a sufficient number of observations to allow valid analysis and also with a significantly higher magnitude scatter than normal for stars of their magnitude.

Variability survey of brightest stars in selected OB associations. The stellar evolution theory of massive stars remains uncalibrated with high-precision photometric observational data mainly due to a small number of luminous stars that are monitored from space. Automated all-sky surveys have revealed numerous variable stars but most of the luminous stars are often overexposed. Targeted campaigns can improve the time base of photometric data for those objects. Aims: The aim of this investigation is to study the variability of luminous stars at different timescales in young open clusters and OB associations.

Methods: We monitored 22 open clusters and associations from to using a 0. Variable stars were detected by comparing the overall light-curve scatter with measurement uncertainties. Variability was analysed by the light curve feature extraction tool FATS. Periods of pulsating stars were determined using the discrete Fourier transform code SigSpec. metadata updates

We then classified the variable stars based on their pulsation periods and available spectral information. Results: We obtained light curves for more than 20 sources of which were found to be variable. Variable star catalogue Tables A. As an active observer, he made some 91, visual estimates of a number of different variable stars. Through this office, and his connections with other organisations around the world, he encouraged others to pursue the observation of variable stars.

Not merely content to accumulate observational data, de Roy also analysed the data and published numerous papers. Galactic Cepheid variable stars have been used for over a century as standard candles and as the first rung of the cosmic distance ladder, integral to the calculation of the Hubble constant. However, it is challenging to observe Cepheids within the Milky Way Galaxy because of extinction, and there are still uncertainties in the Cepheid period-luminosity relation or Leavitt Law that affect these important distance calculations.

The resulting abundance data will allow us to constrain the effect of metallicity on the Leavitt Law and thus allow for more accurate Cepheid distance measurements for the determination of the Hubble constant. IUE observations of variability in winds from hot stars. Observations of variability in stellar winds or envelopes provide an important probe of their dynamics.

In the course of analysis, instrumental and data handling effects were found to introduce spurious variability in many of the spectra. With these contraints, preliminary results of multiple observations of two OB stars , one Wolf-Rayet star , and a Be star are discussed. VStar: Variable star data visualization and analysis tool. VStar is a multi-platform, easy-to-use variable star data visualization and analysis tool.

VStar displays light curves and phase plots, can produce a mean curve, and analyzes time-frequency with Weighted Wavelet Z-Transform. It offers tools for period analysis, filtering, and other functions. Variable stars in the Pegasus dwarf galaxy DDO Observations obtained over a period of five years of the resolved stars in the Pegasus dwarf irregular galaxy DDO have been searched for variable stars.

Thirty-one variables were found, and periods established for Two of these variable stars are clearly eclipsing variables , seven are very likely Cepheid variables , and the remaining three are probable Cepheids. This places Pegasus very near the zero-velocity surface of the Local Group. Work aimed at compiling detailed catalogs of variable stars in the Galaxy, which has been carried out continuously by Moscow variable-star researchers since on behalf of the International Astronomical Union, has entered the stage of the publication of the 5th, completely electronic edition of the General Catalogue of Variable Stars GCVS.

This paper describes the requirements for the contents of the 5th edition and the current state of the catalog in its new version, GCVS 5. The complete revision of information for variable stars in the constellation Carina and the compilation of the 81st Name-list of Variable Stars are considered as examples of work on the 5th edition. The GCVS 5. We recommend the present paper as a unified reference to the 5th edition of the GCVS. Photometric search for variable stars in the young open cluster Berkeley We present the time series photometry of stars located in the extremely young open cluster Berkeley Using the 1.

The ages and masses of the pre-main-sequence stars have been derived from the colour-magnitude diagram by fitting theoretical models to the observed data points. The ages of the majority of the probable pre-main-sequence variable candidates range from 1 to 5 Myr. The present statistics reveal that about 90 per cent T Tauri stars have period stars are found to have a larger amplitude than the weak-line T Tauri stars.

There is an indication that the amplitude decreases with an increase in mass, which could be due to the dispersal of the discs of relatively massive stars. A short history of variable-star catalogs is presented. After the second World War, the International Astronomical Union asked astronomers of the Soviet Union to become responsible for variable-star catalogs. We review recent trends in the field of variable-star catalogs, discuss problems and new prospects related to modern large-scale automatic photometric sky surveys, outline the subject of discussions on the future of the variable-star catalogs in the profile commissions of the IAU, and call for suggestions from the astronomical community.

For the semi-regular variable star V1, we newly determined a period of The light-curve solution of the eclipsing binary V10 indicates that the system is probably a detached system. The pulsation properties of nine SX Phe stars were examined by applying multiple frequency analysis to their light curves.

We derived a new Period-Luminosity P-L relation, stars showing the fundamental mode. This paper is the first contribution in a series assessing the detections and properties of variable stars in six southern globular clusters with the KMTNet system. Variable Stars in the Field of V Aql. Wide field instruments can be used to acquire light curves of tens or even hundreds of variable stars per night, which increases the probability of new discoveries of interesting variable stars and generally increases the efficiency of observations.

At the same time, wide field instruments produce a large amount of data, which must be processed using advanced software. The traditional approach, typically used by amateur astronomers, requires an unacceptable amount of time needed to process each data set. New functionality, built into SIPS software package, can shorten the time needed to obtain light curves by several orders of magnitude. It can be used to visualize observations from many nights, to find variable star periods, evaluate types of variability , etc.

This work provides an overview of tools used to process data from the large field of view around the variable star V Aql. The Helium-burning Variable Stars. Coppola, G. We present new optical BVI time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dwarf spheroidal galaxies and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties.

This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We identified four peculiar variables. Walker and in part with the WFI available at the 2.

Construction of the Database for Pulsating Variable Stars. A database for pulsating variable stars is constructed to favor the study of variable stars in China. A web page is provided for searching the photometric data and light curves in the database through the right ascension and declination of an object.

Because of the flexibility of this database, more up-to-date data of variable stars can be incorporated into the database conveniently. Discovering new variable stars at Key Stage 3. It was aimed at students in Key Stage 3 of their education, allowing them to be involved in real astronomical research at an early stage of their education, the chance to become the official discoverer of a new variable star , and to be listed in the International Variable Star Index database The International Variable Star Index, Version 1.

Future plans are discussed. Observations of the resolved stars in dwarf galaxy GR 8, obtained over the period February to March, are presented. Thirty-four separate epochs were searched for variable stars , and a total of six were found, of which one has Cepheid characteristics. This corresponds to a distance of 2. The other five variable stars are very red, and possibly have long periods of order days or more. Trajectories of Cepheid variable stars in the Galactic nuclear bulge. The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc.

There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars , 10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk.

In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus.

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Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars , 25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars. Templeton, Matthew R. The American Association of Variable Star Observers AAVSO holds the largest single online database of variable star data in the world, collected from thousands of amateur and professional observers during the past century.

One of our core missions is to preserve and distribute these data to the research community in service to the science of variable star astronomy. Our services to the research community include: monitoring for and announcement of major astronomical events like novae and supernovae; organization and management of observing campaigns; support for satellite and other TOO observing programs by the professional community; creation of comparison star sequences and generation of charts for the observer community; and observational and other support for the amateur, professional, and educator communities in all things related to variable stars.

As we begin a new century of variable star astronomy we invite you to take advantage of the services the AAVSO can provide, and to become a part of our organization yourselves. In this poster, we highlight some of the most important services the AAVSO can provide to the professional research community, as well as suggest ways in which your research may be enhanced with support from the AAVSO. Machine learning search for variable stars. Photometric variability detection is often considered as a hypothesis testing problem: an object is variable if the null hypothesis that its brightness is constant can be ruled out given the measurements and their uncertainties.

The practical applicability of this approach is limited by uncorrected systematic errors. We propose a new variability detection technique sensitive to a wide range of variability types while being robust to outliers and underestimated measurement uncertainties. We consider variability detection as a classification problem that can be approached with machine learning.

Among candidates selected in the test set, are real variables , while 13 low-amplitude variables are new discoveries. The machine learning classifiers considered are found to be more efficient select more variables and fewer false candidates compared to traditional techniques using individual variability indices or their linear combination. Issued in honor of the fiftieth anniversary of the founding of Vassar College, the work was meant to fill a void in the literature, namely as both an introduction to the topic of variable stars as well as a manual explaining how they should be observed and the resulting data analyzed.

The book covers the relevant history of and background on types of variable stars , star charts, catalogs, and the magnitude scale, then describes observing techniques, including visual, photographic, and photoelectric photometry. The work finishes with a discussion of light curves and patterns of variability , with a special emphasis on eclipsing binaries and long period variables. One of the earliest modern variable star catalogs was constructed by Henrietta Swan Leavitt during her tenure at the Harvard College Observatory HCO in the early s.

The construction and analysis of this catalog allowed her to subsequently discover the Cepheid period-luminosity relationship, now known as the Leavitt Law. The MC variable star catalogs were updated and expanded by Cecilia Payne-Gaposchkin in and Although newer studies of the MC variables have been performed since then, the new information has not always been correlated with the old due to a lack of modern descriptors of the stars listed in the Harvard MC catalogs.

We will discuss the history of MC variable star catalogs, especially those compiled using the HCO plates, as well as our modernized version of the Leavitt and Payne-Gaposchkin catalogs. Our modern catalog can be used in conjunction with the archival plates primarily via the Digital Access to a Sky Century Harvard scanning project to study the secular behavior of the MC variable stars over the past century.

Rodriguez, E. Lopez Gonzalez, M. Space Science in Action: Stars [Videotape]. This videotape recording shows students the many ways scientists look at the stars and how they can use what they see to answer questions such as What are stars made of? Students learn about the life span of stars and the various stages they pass through from protostar to main sequence star to…. Circumstellar disks are common among many stars , at most spectral types, and at different stages of their lifetimes.

Among the near-main-sequence classical Be stars , there is growing evidence that these disks form, dissipate, and reform on timescales that differ from star to star. Our goal is to develop a statistically significant sample of variable circumstellar disk systems over multiple timescales. With a robust multi-epoch study we can determine the relative fraction of Be stars that exhibit disk-loss or disk-renewal phases, and investigate the range of timescales over which these events occur.

A larger sample will improve our understanding of the prevalence and nature of the disk variability , and may provide insight about underlying physical mechanisms. We give a simple criterion of the existence of a smooth extension of a star product and apply it to these examples. 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. analysis

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. 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.

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. 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. 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.

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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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  5. 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'.

    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.

    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.

    However, after six months it was determined that MPO Canopus was not an acceptable option because of the steep learning curve, lack of documentation and technical support. Therefore, the project decided that the best option was to design our own python based software. Using python and python libraries we developed code that can be used for photometry and can be easily changed to the user's needs. We accomplished this by meeting with our mentor astronomer, Tyler Linder, and in the beginning wrote two different programs, one for asteroids and one for variable stars.

    In the end, though, we chose to combine codes so that the program would be capable of performing photometry for both moving and static objects. The software performs differential photometry by comparing the magnitude of known reference stars to the object being studied. For asteroids, the image timestamps are used to obtain ephemeris of the asteroid from JPL Horizons automatically.

    Pritzl, Barton J. Technical Monitor. We have undertaken a search for variable stars in the metal-rich globular cluster NGC using time-series BV photometry. Twenty-eight new variables were found in this survey, increasing the total number of variables found near NGC to approx. A significant number of the variables are RR Lyrae approx.

    The periods of the fundamental mode RR Lyrae are shown to be unusually long compared to metal-rich field stars. The existence of these long period RRab stars suggests that the horizontal branch of NGC is unusually bright. Four candidate Population II Cepheids were also found. The mean V magnitude of the RR Lyrae is found to be We discuss the difficulty in determining the Oosterhoff classification of NGC and NGC due to the unusual nature of their RR Lyrae, and address evolutionary constraints on a recent suggestion that they are of Oosterhoff type II.

    Luminous blue variables and the fates of very massive stars. Luminous blue variables LBVs had long been considered massive stars in transition to the Wolf-Rayet WR phase, so their identification as progenitors of some peculiar supernovae SNe was surprising. More recently, environment statistics of LBVs show that most of them cannot be in transition to the WR phase after all, because LBVs are more isolated than allowed in this scenario. This article is part of the themed issue 'Bridging the gap: from massive stars to supernovae'.

    High-amplitude variability in young stellar objects YSOs is usually associated with episodic accretion events. It has not been observed so far in massive YSOs. A total of 11 of these 13 VYSOs are located in the midst of infrared dark clouds. The light curves of these objects sampled between and display rising, declining, or quasi-periodic behavior but no clear periodicity. Light-curve analysis using the Plavchan method shows that the most prominent phased signals have periods of a few hundred days.

    The nature and timescale of variations found in 6. We argue that the origin of the observed variability is episodic accretion. We suggest that the timescale of a few hundred days may represent the frequency at which a spiraling disk feeds dense gas to the young massive star. The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena.

    Since the most metal-poor Galactic stars are relics from the high-redshift Universe, they probe the chemical and dynamical conditions as the Milky Way began to form, the origin and evolution of the elements, and the physics of nucleosynthesis. They also provide constraints on the nature of the first stars , their associated supernovae and initial mass function, and early star and galaxy formation. I will present exemplary metal-poor stars with which these different topics can be addressed. Their stellar chemical signatures support the concept that small systems, analogous to the surviving dwarf galaxies, were the building blocks of the Milky Way's low-metallicity halo.

    This opens a new window for studying galaxy formation through stellar chemistry. Radio variability and structure of T Tauri stars. The position of the radio peak of DG Tau has shown apparent motion between and along the flow axis from this star , while its morphology has varied from point-like to bipolar. These changes and the spectral index of 0.

    Magnetic and pulsational variability of Przybylski's star HD Since its discovery more than half a century ago Przybylski's star HD continues to excite the astronomical community by the unusual nature of its spectrum, exhibiting exotic element abundances. This star was also the first magnetic chemically peculiar A-type star for which the presence of rapid oscillations was established.

    Our analysis of newly acquired and historic longitudinal magnetic field measurements indicates that Przybylski's star is also unusual with respect to its extremely slow rotation. Additionally, based on our own spectropolarimetric material obtained with HARPSpol, we discuss the impact of the anomalous structure of its atmosphere, in particular of the non-uniform horizontal and vertical distributions of chemical elements on the magnetic field measurements and the pulsational variability. Anomalies related to the vertical abundance stratification of Pr and Nd are for the first time used to establish the presence of a radial magnetic field gradient.

    The variable star population in the globular cluster NGC Individual absolute magnitudes, radii and masses are also reported for RR Lyrae stars. The inter-mode or "either-or" region in the instability strip is shared by the RRab and RRc stars. Automated classification of periodic variable stars detected by the wide-field infrared survey explorer. We describe a methodology to classify periodic variable stars identified using photometric time-series measurements constructed from the Wide-field Infrared Survey Explorer WISE full-mission single-exposure Source Databases.

    This will assist in the future construction of a WISE Variable Source Database that assigns variables to specific science classes as constrained by the WISE observing cadence with statistically meaningful classification probabilities. Consistent with previous classification studies of variable stars in general, the RF machine-learned classifier is superior to other methods in terms of accuracy, robustness against outliers, and relative immunity to features that carry little or redundant class information.

    These accuracies are achieved at purity or reliability levels of Luminous Blue Variable LBV stars represent an extremely rare class of very luminous and massive stars. Only about a dozen confirmed Galactic LBV stars are known to date, which precludes us from determining a solid evolutionary connection between LBV and other intermediate e.

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    The known LBV stars each have their own unique properties, so new discoveries add insight into the properties and evolutionary status of LBVs and massive stars ; even one new discovery of objects of this type could provide break-through results in the understanding of the intermediate stages of massive star evolution. We have culled a prime sample of possible LBV candidates from the Spitzer 24 micron archival data. All have circumstellar nebulae, rings, and shells typical of LBVs and related stars surrounding reddened central stars.

    Spectroscopic followup of about two dozen optically visible central stars associated with the shells from this sample showed that they are either candidate LBVs, late WN-type Wolf-Rayet stars or blue supergiants. We propose infrared spectroscopic observations of the central stars for a large fraction 23 stars of our northern sample to determine their nature and discover additional LBV candidates.

    These stars have no plausible optical counterparts, so infrared spectra are needed. This program requires two nights of Hale time using TripleSpec. Variable rotational line broadening in the Be star Achernar. Aims: The main theoretical problem for the formation of a Keplerian disk around Be stars is how angular momentum is supplied from the star to the disk, even more so since Be stars probably rotate somewhat subcritically.

    The nearby Be star Achernar is presently building a new disk and offers an excellent opportunity to observe this process from relatively close-up. The variable strength of the non-radial pulsation is confirmed, but does not affect the other results. IDs: H, C, D, D, and the technical program IDs A and Cataclymic variables CVs are semi-detached binary systems in which a main sequence late-type star the secondary fills its Roche lobe and transfers matter to a white dwarf the primary through the inner Lagragian point L[1].

    However, up to now no well-studied CVs shows evidence of period decrease. The fast spinning secondaries of CVs, covering a range of masses and rotation periods, are an important laboratory to understanding magnetic activities cycles in late type stars. Both V Sgr and V Oph show modulation periods of 22 yr and 7 yr respectively.

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    A discussion of the distinct magnetic activity properties of short and long orbital period P[orb] 3 hr, respectively systems in the framework of the CV evolution scenarios is presented. Kinne, Richard C. Effective distribution of data is a core element of effective astronomy today. Astronomer, educator, and science historian Dorrit Hoffleit was widely respected by the amateur and professional astronomical community as a mentor and an ardent supporter of independent research.

    Her more than catalogues, books, articles, book reviews, and news columns cover myriad aspects of astronomy, from variable stars and stellar properties to meteor showers, quasars, and rocketry. She also made important contributions to the history of astronomy. Hoffleit worked at the Harvard College Observatory from , where she discovered over variable stars. At the same time, she was offered a position as director of the Maria Mitchell Observatory on Nantucket Island in Massachusetts. Hoffleit split her dual positions into six-month stints and remained director at the Mitchell Observatory for 21 years, developing a summer research program that engaged more than undergraduate students all but three of them women in variable star research.

    Up until shortly before her death, she continued to work tirelessly on selected projects, and she was in high demand as a collaborator with colleagues at Yale and elsewhere. She served on the organization's council for 23 years and as its president from In , the AAVS0 published her autobiography, Misfortunes as Blessings in Disguise, in which Hoffleit explains how she always felt blessed by the opportunities in her life, even those which initially seemed misfortunes, and above all else valued creativity, flexibility, collegiality, and intellectual freedom in her professional life.

    Observations of the sun, an ultraviolet variable star. The uncertainty as to whether or not the sun is a variable star in that region of the ultraviolet which is absorbed in the mesosphere and stratosphere led to an experiment with acronym MUSE, Monitor of Ultraviolet Solar Energy. The experiment was first flown on an Aerobee rocket in August and subsequently on Nimbus 3 and 4 in April and April respectively. The basic philosophy behind the design of the experiment was to provide an instrument which would not require a solar pointing mechanism and at the same time would be capable of high radiometric accuracy for long periods in space.

    John Goodricke and Edward Pigott, working in York, England, between and , determined the periods of variation of eclipsing binaries such as Algol and Beta Lyrae and speculated that the eclipses of Algol might be caused by a "dark body," perhaps even a planet. They also determined the periods of variation of the first two known Cepheid variables , the stars whose period-luminosity relation today enables astronomers to determine distances to distant galaxies. Goodricke holds special interest because he was completely deaf and because he died at the age of The lives and work of these two astronomers are described.

    We analyze 10 UV time series for five stars that fulfill specific sampling and spectral criteria to constrain the origin of large-scale wind structure in O stars. We argue that excited state lines must arise close to the stellar surface and are an excellent diagnostic complement to resonance lines which, due to radiative transfer effects, rarely show variability at low velocity.

    These spliced time series reveal that nearly all of the features observed in the time series originate at or very near the stellar surface. Furthermore, we positively identify the observational signature of equatorial corotating interaction regions in two of the five stars and possibly two others. In addition, we see no evidence of features originating further out in the wind. K2 Variable Catalogue: Variable stars and eclipsing binaries in K2 campaigns 1 and 0. Armstrong, D.

    Aims: We have created a catalogue of variable stars found from a search of the publicly available K2 mission data from Campaigns 1 and 0. This catalogue provides the identifiers of variable stars , including candidate eclipsing binaries with periods up to 60 d and periodic or quasi-periodic objects, with periods up to 20 d for Campaign 1 and 15 d for Campaign 0. Methods: Lightcurves are extracted and detrended from the available data.

    These are searched using a combination of algorithmic and human classification, leading to a classifier for each object as an eclipsing binary, sinusoidal periodic, quasi periodic, or aperiodic variable. The source of the variability is not identified, but could arise in the non-eclipsing binary cases from pulsation or stellar activity. Each object is cross-matched against variable star related guest observer proposals to the K2 mission, which specifies the variable type in some cases. The detrended lightcurves are also compared to lightcurves currently publicly available.

    Results: The resulting catalogue gives the ID, type, period, semi-amplitude, and range of the variation seen. We also make available the detrended lightcurves for each object. VX Her is a pulsating variable star with a period of. It is believed to be part of an eclipsing binary system Fitch et al. This hypothesis originated from Fitch seeing VX Her's minimum point on its light curve reaching a 0.

    If VX Her were indeed a binary system, I would expect to see similar results with a fainter minimum and a broader, more horizontal dip. Having reduced and analyzed images from the Southeastern Association for Research in Astronomy Observatory in Chile and Kitt Peak, as well as images from a 0. Using photometry, I found no differing features in its light curve to suggest that it is indeed a binary system. However, more observations are needed in case VX Her is a wide binary. Velocity structure in long period variable star atmospheres. A regression analysis of the dependence of absorption line velocities on wavelength, line strength, excitation potential, and ionization potential is presented.

    The method determines the region of formation of the absorption lines for a given data and wavelength region. It is concluded that the scatter which is frequently found in velocity measurements of absorption lines in long period variables is probably the result of a shock of moderate amplitude located in or near the reversing layer and that the frequently observed correlation of velocity with excitation and ionization are a result of the velocity gradients produced by this shock in the atmosphere.

    A simple interpretation of the signs of the coefficients of the regression analysis is presented in terms of preshock, post shock, or across the shock, together with criteria for evaluating the validity of the fit. The amplitude of the reversing layer shock is estimated from an analysis of a series of plates for four long period variable stars along with the most probable stellar velocity for these stars. Wozniak, P. We evaluate several Machine Learning algorithms as potential tools for automated classification of variable stars.

    This includes some degeneracies, irreducible with the information at hand. Supervised methods naturally outperform unsupervised methods, in terms of final error rate, but unsupervised methods offer many advantages for large sets of unlabeled data. Therefore, both types of methods should be considered as promising tools for mining vast variability surveys.

    This sample size is already stretching the time capabilities of human analysts. The optical variability of stars in the KP catalog is studied. The main attractions are New South Wales police photos of crime scenes and murder victims. They're all in black and white, and a lot were taken in the s or earlier.

    Sydney noir: the settings are dark spaces in the urban jungle. No names, no details. There's a woman dead on her bed, a movie magazine on the chair beside her. There's a woman dead on a floor, beneath a sewing machine; her hat is on the bed, and so is her blood. A bit more information appears alongside the photo of a man found dead in a vacant lot. He was shot three times in the head at close range at dawn on September 30, The museum's catalogue cheerfully states, "We offer a range of stimulating and enjoyable education programmes for primary and secondary students.

    Bloody hell. Still, death is a part of life, and there is an agreeable openness about the museum's chamber of horrors. Blithe indifference is key to the Australian character. You'd never get away with this sort of carry-on in uptight, pent-up New Zealand, with its codes of conduct, its cultural sensitivities. To visit the museum as a Kiwi is to experience the small dark thrill of social transgression. Look, a photo of a male corpse lying on top of a female corpse, a rectangle of blood beneath her head!

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    Look, a photo of an Aboriginal man with a chain around his neck The room dedicated to car crashes is like an early, still-life version of David Cronenberg's film, Crash. It has a similar feel about it, the way it makes a kind of fetish out of vehicular death. There's an eroticism to one photo, in particular, a black-and-white of a white Falcon, split open against a gum tree on Burragorang Rd, Oakdale, in Blood on the smashed bodywork, dark shadows in the Australian sunlight. There's a room dedicated to famous murders, such as the case of the Pyjama Girl, from , when a woman's body was found in a culvert.

    It was partially burned. It was wrapped in a towel and hessian, and the woman had been wearing yellow crepe Chinese pyjamas. The murder of schoolboy Graeme Thorne records the killer's confession. He abducted the boy for ransom. His skull was fractured. He was 8 years old. His killer was caught. The museum is a testament to police efficiency.

    It doesn't indulge in police failure, police incompetence, police idiocy. One room has a stuffed exhibit of Tess the police dog. It could climb a vertical ladder!